WO2002016110A1

WO2002016110A1 - Method for momentarily heating the surface of a mold and system thereof

Info

Publication number: WO2002016110A1
Application number: PCT/KR2001/001160
Authority: WO
Inventors: Sook-Jia Yim
Original assignee: Yim Sook Jia
Priority date: 2000-08-24
Filing date: 2001-07-06
Publication date: 2002-02-28
Also published as: CA2423984A1; AU2001269576A1; AR029727A1

Abstract

Disclosed herein is a system for momentarily heating the surface of a mold and system thereof. The system comprises a casting material feeder, upper and lower molds, an injection molding control, an air and gaseous fuel mixture and supply unit, an interface and a control panel. The casting material feeder serves to supply molten casting material. The upper and lower molds serve to form a predetermined shaped cast. The injection molding control serves to control the upper mold and the lower mold. The air and gaseous fuel mixture and supply unit serves to supply compressed air and gaseous fuel simultaneously or selectively. The gaseous fuel mixture and supply control serves to control the operation of the air and gaseous fuel mixture and supply unit. The interface serves to interface the injection molding control and the gaseous fuel mixture and supply control. The control panel serves to visually display the control, condition and operation of the components of the system.

Description

METHOD FOR MOMENTARILY HEATING THE SURFACE OF A MOLD AND

SYSTEM THEREOF

BACKGROUND OF THE INVENTION

Field ofthe Invention

The present invention relates generally to methods for momentarily heating the surface of a mold and system thereof, and particularly to a method for momentarily heating the surface of a mold and system thereof, which is capable of momentarily heating the surface of the mold prior to injection molding and cooling a molded product immediately after the molding, thereby improving the quality of products in appearance, preserving the physical and thermal properties of resin in the products, and increasing the productivity of a manufacturing process of the products for the reduction of the manufacturing cost ofthe products.

Description ofthe Prior Art

In a technical field where resin (such as synthetic resin, plastics or the like) products are manufactured, various attempts have been made to momentarily heat a mold to the same temperature as that of resin while the cavity ofthe mold is being filled with the resin, and to rapidly cool the mold after the cavity ofthe mold is filled with the resin. The object of these attempts is to increase the quality of products in appearance, to improve the strength and themial properties of the products and to increase the productivity of the manufacturing process ofthe products for the reduction ofthe manufacturing costs ofthe products. German Pat. Appln. No. 297 08 721.5 and PCT Appln. No. WO 98/51460 disclose a mold capable of being temporarily heated by the flame of gaseous fuel and synthetic resin foraung method thereof. According to the above described patents, a synthetic resin injecting mold process is automated and the molded products of synthetic resm may be manufactured continuously. . ^{■ ■ > ' •} However, according to the above-described patents, since a molded product cannot be cooled immediately after the forming ofthe product, the quality ofthe molded product is reduced in appearance, the strength and thermal properties of the injection- molded product are deteriorated and the productivity ofthe molding process is reduced.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object ofthe present invention is to provide a method for momentarily heating the surface of a mold, which allows the mold to be filled with molten resin for injection molding after the preheating ofthe mold to a predeteπnined temperature and allows an injection-molded product to be cooled upon the completion of the injection molding, thereby increasing the quality of the injection-molded product in appearance and improving the strength and thermal properties of the injection-molded product. Another object of the present invention is to provide a system for momentarily heating the surface of a mold, which comprises upper and lower molds for forming resin and performing the heating ofthe upper and lower molds, a supply unit for supplying air and gaseous fuel, a safety unit for preventing the danger of gas explosion, and a control unit for controlling the operation ofthe above components. A further object ofthe present invention is to provide a method for momentarily heating the surface of a mold and system thereof, in which one or more cores are disposed between its upper and lower molds, the cores are momentarily heated using gaseous fuel or an induction heater, and heating and cooling are performed in the process of injection molding, thereby improving the quality of an injection-molded product. Heating of the mold surface may also be performed by laser, microwave, radiant, resistive, impingement (i.e., high velocity gas), piezoelectric or any other suitable heating technique that can heat the mold surface quickly. Another method of heating the mold surface is alternating or staged or pulsed between upper and lower molds or external and internal molds.

In order to accomplish the above objective, the present invention provides a method for momentarily heating a surface of a mold, comprising the steps of: opening upper and lower molds ofthe mold, and supplying gaseous fuel; injecting and igniting the gaseous fuel from the lower mold after allowing the upper and lower molds to come close to each other at a predetermined distance; heating the upper mold for a predetermined time period; filling a forming space between the upper and lower molds with molten material through the upper mold immediately after stopping heating and closing the upper and lower molds; cooling a molded product in the closed mold, further cooling a molded product by injecting compressed gas to the molded product after allowing the upper and lower molds to be opened at a predetermined distance; and ejecting the molded product from the upper and lower molds after allowing the upper and lower molds to be completely opened. In addition to cooling by compressed gas, the molded product may be cooled directly or indirectly in the mold by cooling channels in the mold, condensing of a vapor, water spray, or other suitable means of removing heat quickly.

In addition, the present invention provides a system for momentarily heating the surface of a mold, comprising: a casting material feeder for supplying molten casting material; upper and lower molds for fonning a predetermined shaped cast; an injection molding control for controlling the upper mold and the lower mold; an air and gaseous fuel mixture and supply unit for supplying compressed air and gaseous fuel simultaneously or selectively; a gaseous fuel mixture and supply control for controlling the operation ofthe air and gaseous fuel mixture and supply-unit; an- interface for interfacing the injection molding confrol and the- gaseous fuel mixture and supply confrol; andi a control panel for visually displaying the confrol, condition and operation of the components ofthe system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objectives,, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic diagram showing a system for momentarily heating the surface of a mold using. the flame of gaseous fuel in accordance with the present invention;

Fig. 2 is a diagram showing piping for supplying air and gaseous fuel to the main body ofthe system in detail;

Figs. 3 a to 3 f are process charts showing the method for temporarily heating the surface of a mold using the flame of gaseous fuel in accordance with an embodiment of the present invention;

Figs. 4a to 4d are process charts showing the method for temporarily heating the surface of a mold using the flame of gaseous fuel in accordance with another embodiment ofthe present invention; Figs. 5a to 5d are process charts showing the method for temporarily heating the surface of a mold using the flame of gaseous fuel in accordance with a fuither embodiment ofthe present invention;

Fig. 6 is a block, diagram, illustrating the confrol panel of the system for ^' momentarily heating thfe^'sui ace of a riiόld;^{1 "}■

Fig: 7 is ^"'schematic diagram showing a system for momentarily 'heating . the surface of a mold using an induction heater in accordance with the present invention; Fig. 8 is a flowchart showing the operation ofthe system for momentarily heating the surface of a mold using the induction heater;

Fig. 9 is a schematic diagram showing a water-cooled system for momentarily heating and cooling the surface of a mold in accordance with an embodiment of the present invention;

Fig. 10 is a schematic diagram showing a system for momentarily heating and cooling the surface of a mold in accordance with an embodiment ofthe present invention;

Fig. 11 is a schematic diagram showing a system for momentarily heating and cooling the surface of a mold in accordance with an embodiment of the present invention; and

Fig. 12 is a detailed view ofthe core shown in Fig. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

Fig. 1 is a schematic diagram showing a system for momentarily heating the surface of a mold using the flame of gaseous fuel in accordance with the present invention. Fig. 2 is a diagram showing piping for supplying air and gaseous fuel to the main body of the system in detail.

Reference numeral 10 designates a casting material feeder for supplying molten casting material. The casting material feeder 10 supplies injectable material, _.such as synthetic resin or metal,"

An upper mold 20 is fixed to the lower end ofthe casting material feeder 10 under the casting material feeder 10. The upper mold 20 has a casting material supply hole 22 for supplying casting material from the casting material feeder 10 to the upper mold 20, a cavity 24 for forming the casting material into a predetemώied-shaped cast. The upper mold 20 is provided with a limit switch 83 for sensing the position ofthe upper mold 20.

A lower mold 30 is disposed under the upper mold 20. The lower mold 30 comprises a mold portion 32 for insertion into the cavity 24 ofthe upper mold 20 to form the casting material into a predetermined-shaped cast, a lower mold supply conduit 31 formed in the lower mold 30 to supply mixed gaseous fuel and compressed air, a plurality of discharge holes 34 for heating and cooling the upper mold 20 using the mixed gaseous fuel and the compressed air supplied through the lower mold supply conduit 31, an ignition unit 40 for igniting gaseous fuel injected by an igniter 41 using high voltage current generated by a high voltage generator 44 and sensing gaseous fuel flame by means of a flame sensor 42, a limit switch 84 for sensing the position ofthe lower mold 30, an air and gaseous fuel mixture and supply unit 90 for supplying air or mixed gaseous fuel supplied through an air and mixed gaseous fuel supply conduit 86, and an elevating cylinder 80 including an elevating shaft 82 for selectively lifting or lowering the lower mold 30 by the control of an injection molding confrol 50. The discharge holes 34 are constructed in the form of slits, respectively having widths of 0.01 to 0.1 mm, and are distributed on the surface ofthe lower mold 30 in accordance with the shape ofthe cast. Although not depicted in the drawing, conduits for supplying air and gaseous fuel and a coolant supply conduit for supplying coolant are provided in the lower mold 30.

The upper and lower molds 20 and 30 are separately formed. The upper mold 20 and/or the lower mold 30 may be provided with additional parts necessary for injection ^• molding, including cooling channels:

The injection molding control 50 controls the upper and lower molds 20 and 30. In detail, the injection molding control 50 controls the mechanical operation for an injection molding process.

The air and gaseous fuel rriixture and supply unit 90 serves to supply compressed air and gaseous fuel simultaneously or selectively, and comprises a variety of pipelines for supplying air and/or gaseous fuel and a variety of valves and gauges for controlling the flow of air and/or gaseous fuel. The air and gaseous fuel mixture and supply unit 90 is divided into an air and gaseous fuel supply line 91 for ignition and an air and gaseous fuel supply line 110 for heating. A compressed air supply line 130 for supplying compressed air and a gaseous fuel supply line 140 for supplying gaseous fuel are respectively connected to the air and gaseous fuel mixture and supply unit 90. A compressed air supply source 136 for supplying compressed air and a gaseous fuel supply source 146 for supplying gaseous fuel are respectively connected to the compressed air supply line 130 and the gaseous fuel supply line 140. The air and gaseous fuel supply line 91 for ignition includes an air and gaseous fuel mixture element 92 for ignition, an air supply line for ignition and a gaseous fuel supply line for ignition. The air supply line for ignition includes a first pneumatic pressure gauge 93 for measuring the pressure of supplied air, a first needle valve 94 for preventing compressed air from flowing backward, and a first solenoid valve 95 for interrupting the supply of compressed air and a first manual valve 96 for regulating the amount of supplied compressed air. The gaseous fuel supply line for ignition includes a first fluidic pressure gauge 101 for measuring the pressure of supplied gaseous fuel, a second needle valve 102 for preventing gaseous fuel from flowing backward, and a second solenoid valve 103 for inteπupting the supply of gaseous fuel and. a second manual valve 104 for regulating the amount of supplied gaseous fuel. The air and gaseous fuel mixture element 92 for ignition serves to mix air and gaseous fuel supplied through the air and gaseous fuel supply lines for ignition.

The air and gaseous fuel supply line 110 for heating includes an air and gaseous fuel mixture element 111 for heating, an air supply line for heating, and a gaseous fuel supply line for heating. The air supply line for heating includes a second pneumatic pressure gauge 112 for measuring the pressure of supplied air, a third needle valve 113 for preventing compressed air from flowing backward, and a third solenoid valve 114 for interrupting the supply of compressed air and a first pressure switch 115 for sensing the pressure of supplied compressed air and interrupting the supply of compressed air when the pressure of the supplied compressed air is not equal to a predeterrnined value. The gaseous fuel supply line for heating includes a second fluidic pressure gauge 120 for measuring the pressure of supplied gaseous fuel, a fourth needle valve 121 for preventing gaseous fuel from flowing backward, and a fourth solenoid valve 122 for interrupting the supply of gaseous fuel and a second pressure switch 123 for sensing the pressure of supplied compressed air and interrupting the supply of gaseous fuel when the pressure of the supplied gaseous fuel is not equal to a predetermined value. The air and gaseous fuel mixture element 111 for heating serves to mix air and gaseous fuel supplied through the air and gaseous fuel supply lines for heating.

The compressed air supply line 130 is connected to both air supply line for ignition of the air and gaseous fuel supply line 91 for ignition and the air supply line for heating of the air and gaseous fuel supply line 110 for heating, while the gaseous fuel supply line 140 is connected to both gaseous fuel supply line for ignition of the air and gaseous fuel supply line 91 for ignition and the gaseous fuel supply line for heating ofthe air and gaseous fuel supply line 110 for heating. The compressed air supply line 130 serves to supply compressed air generated in and supplied from a compressed air supply 136, and the gaseous fuel line 140 serves to supply gaseous fuel supplied from the gaseous fuel supply source 146.

The compressed air supply line 130 comprises a first flux regulator 131. for manually regulating the amount of compressed air, a first filter 132 for filtering impurities included in compressed air, a fifth solenoid valve 133 for interrupting the supply of compressed air, a third pneumatic pressure gauge 134 for sensing the pressure of supplied compressed air and a fifth manual valve 135 for regulating the amount of supplied compressed air. The fuel gas supply line 140 comprises a second flux regulator 141 for manually regulating the amount of gaseous fuel, a second filter 142 for filtering impurities included in gaseous fuel, a sixth solenoid valve 143 for interrupting the supply of gaseous fuel, a fourth pneumatic pressure gauge 144 for sensing the pressure of supplied gaseous fuel and a sixth manual valve 145 for regulating the amount of supplied gaseous fuel.

A gaseous fuel mixture and supply control 70 serves to confrol the operation of the air and gaseous fuel mixture and supply unit 90. The gaseous fuel mixture and supply control 70 is connected to the injection molding control 50 through an interface 60, and receives signals from and transmits signals to the injection molding control 50. The gaseous fuel mixture and supply confrol 70 includes a microprocessor.

In addition, there may be included a safety unit that serves to automatically interrupt the supply of air and gaseous fuel when flames are not sensed by the flame sensor 42 in a predetermined time period after ignition is performed by the igniter 41 of the ignition unit 40, gas of a predeteπnined degree of density is detected by a gas detector (not shown) disposed near the upper and lower molds 20 and 30, or the pressures of air and gaseous fuel inputted from a first pressure switch 115 and a second pressure switch 123 are higher than a predetermined pressure. The heating system of the present invention includes a control panel for controlling the components ofthe system and mputting the operational conditions ofthe components. The confrol panel is illustrated as a block diagram in Fig.6.

The confrol panel includes a key input unit 151, a sensing unit 152, a Central Processing Unit (CPU) 153, an alarm 154, a display 155 and an instrument panel 156. The key input unit 151 has a plurality of keys, and serves to input various operational conditions for injection molding.

The sensing unit 152 serves to sense the various states of the system, convert a sensing signal to an electric signal and output the electric signal. The states include the elevation ofthe dies, the pressures and amounts of air and gaseous fuel, the leakage of gas and the like.

The CPU 153 serves to perform determination on the basis on an input signal and to output a control signal. The CPU 153 can be included in the injection molding control 50 and the gaseous fuel mixture and supply confrol 70.

The alarm 154 serves to warn of system eπor and danger situations. The alarm 154 may be activated when gas leaks or pressure variations outside predetermined limits occur.

The display 155 serves to indicate the information ofthe operation ofthe system. A user can monitor the operation ofthe system using the display 155.

The instrument panel 156 serves to indicate the operation of various components ofthe system. The instrument panel 156 may indicate the pressures of air and gaseous fuel and the state of safety.

Hereinafter, a method for momentarily heating the surface of a mold using the flame of gaseous fuel is described with reference to Figs. 3a to 3f.

In STEP SI 00, the upper mold 20 and the lower mold 30 are opened at a predetermined distance and the supply of gaseous fuel is prepared. . h STEP S 101, the upper mold 20 comes close to the lower mold 30 and gaseous fuel is injected and ignited. In more detail, compressed air and gaseous fuel are supplied from the compressed air supply source 136 and the gaseous fuel supply source 146 through the compressed air supply line 130 and the gaseous fuel supply line 140, enter the air and gaseous fuel supply line 91 for ignition and are mixed together while passing through the air and gaseous fuel mixture element 92, and the mixed air and gaseous fuel passes through the supply conduit 31 of the lower mold 30, is injected through the discharge holes 34 ofthe mold portion 32 and is ignited in the igniter 41 of the ignition unit 40 using high voltage current generated in the high voltage generator 44. If flame is not sensed by the flame sensor 42 after the ignition is performed, the supply of air and gaseous fuel is interrupted by the operation ofthe solenoid valves 95 and 103.

After the air and gaseous fuel supplied through and mixed in the air and gaseous fuel supply line 91 for ignition are normally injected, compressed air and gaseous fuel are supplied tiirough and mixed in the air and gaseous fuel supply line 110 and are injected tiirough the lower mold 30. At this time, the supply ofthe compressed air and gaseous fuel being supplied through the air and gaseous fuel supply line 91 for ignition is interrupted and is not supplied to the lower mold 30 anymore. . .

In STEP SI 02, the cavity 24 of the upper mold 20, which comes close to the lower mold 30 at a predeterrnined distance (for example, 1 to 40 cm), is heated by the gaseous fuel supplied through the air and gaseous fuel line 110 for heating and ignition, for a predeterrnined time (for example, about 1 to 60 seconds).

In STEP S103, after the supply of air and gaseous fuel is interrupted and flame is extinguished by the interruption ofthe supply of the air and gaseous fuel, the elevating shaft 82 is elevated by the operation of the elevating cylinder 80 and, accordingly, the lower mold 30 is closed by the upper mold 20. As soon as the lower mold 30 is closed by the upper mold 20, molten casting material is supplied through the casting material supply hole 22 of he upper mold 20 from the casting material feeder 10.

After the injection ofthe casting material is completed and the cast part cools from

5 to 300 seconds, STEP S104 is performed. In STEP S104, after the upper and lower molds 20 and 30 are opened at a predetermined distance (for example, in a range of 1 to

400 mm), compressed air is injected toward a formed cast (will be described) through the air and gaseous fuel supply line 110, the supply conduit 31 and the discharge holes 34, and cools the formed cast. At this time, the cooling ofthe formed cast is performed for, for example, 5to 30 seconds. Additionally, in STEP SI 05, after the upper and lower molds 20 and 30 are completely opened, a formed cast 146 is ejected. With this, the entire injection molding process is completed.

A method for momentarily heating the surface of a mold using the flame of gaseous fuel in accordance with a second embodiment of the present invention is described with reference to Figs. 4a to 4d. In this case, a core 35 is disposed between the upper and lower molds 20 and 30 as an auxiliary mold for the injection molding ofthe cast

146.

This system, which can be applied to this method, further comprises one core 35 disposed between the upper and lower molds 20 and 30, a upper mold supply conduit 21 for supplying mixed gaseous fuel and compressed air, said upper mold supply conduit 21 being formed in the upper mold 20, a plurality of upper mold discharge holes 23 for heating and cooling the core using the mixed gaseous fuel and the compressed air supplied through the upper mold supply conduit 21, a lower mold supply conduit 31 for supplying mixed gaseous fuel and compressed air, said lower mold supply conduit 31 being formed in the lower mold 30, a plurality of lower mold discharge holes 34 for heating and cooling the core 35 using the mixed gaseous fuel and the compressed air supplied through the lower mold supply conduit 31, and an air and mixed gaseous fuel supply conduit 86 for connecting the air and gaseous fuel rnixture and supply unit 90 respectively to the upper mold supply conduit 21 and the lower mold supply conduit 31. The core 35is formed to come into tight contact with the upper and lower molds

20 and 30 when the upper and lower molds 20 and 30 are closed, so that injection pressure is completely transmitted to the upper and lower molds, thus preventing the core and upper and lower molds from being damaged by high injection pressure.

The core 35 has a thickness ranging from 0.1 to 15 mm and is formed to correspond to the shape ofthe cast. The discharge holes 23 and 34 are constructed in the form of slits, respectively have widths of 0.01 to 5 mm and are distributed on the surface ofthe lower mold 30 to correspond to the shape ofthe cast.

The method for momentarily heating the surface of a mold in accordance with the second embodiment is different from the method for momentarily heating the surface of a mold in accordance with the first embodiment, in that the core 35 is disposed between the upper and lower molds 20 and 30, a supply line is connected to the upper mold 20 to supply mixed compressed air and gaseous fuel, and an ignition unit (not shown) identical to the ignition unit 40 (including the igniter 41, the flame sensor 42 and the high voltage generator 44) mounted to the lower mold 30 is preferably mounted to the upper mold 20. Additionally, the core 35 is provided with support means for elevating and supporting the core 35. h STEP S200, the upper mold 20, the core 35 and the lower mold 30 are opened at predeteπnined distances and the supply of gaseous fuel is prepared. Thereafter, the upper mold 20, the core 35 and the lower mold 30 come close to ope another at ^• predeterrnined distances- and gaseous fuel is injected' to the core 35 from the upper and/or lower molds 20 and/or 30 and ignited. In more detail, compressed air and gaseous fuel are supplied from the compressed air supply source 136 and the gaseous fuel supply source 146 through the compressed air supply line 130 and the gaseous fuel supply line 140, enters the air and gaseous fuel supply line 91 for ignition and are mixed together while passing through the air and gaseous fuel mixture element 92, and the mixed air and gaseous fuel passes through the supply conduits 21 and 31 ofthe upper and lower molds 20 and 30, is injected through the discharge holes 23 and 34 and is ignited in the igniter 41 ofthe ignition unit 40 using high voltage current generated by the high voltage generator 44. If a flame is not sensed by the flame sensor 42 after the ignition is performed, the supply of air and gaseous fuel is interrupted by the operation ofthe solenoid valves 95 and 103.

After the air and gaseous fuel supplied through and mixed in the air and gaseous fuel supply line 91 for ignition are normally injected, compressed air and gaseous fuel are supplied through and mixed in the air and gaseous fuel supply line 110 and are injected through the upper and lower molds 20 and 30. At this time, the supply ofthe compressed air and gaseous fuel being supplied through the air and gaseous fuel supply line 91 for ignition is interrupted and is not supplied to the upper and lower molds 20 and 30 anymore. Accordingly, the cavities 24 and 38 defined by the upper and lower molds 20 and 30 and the core 35, which come close to one another at predetermined distances (for example, the distances between the upper mold 20 and the core 35 and between the core 35 and the lower mold 30 are in a range of 1 to 40 cm), are heated by the gaseous fuel supplied through the air and gaseous fuel line 110 for heating and ignition, for a predeterrnined time period (for example, about 1 to 60 seconds). In STEP S201, after the supply of air and gaseous fuel supplied from the air and gaseous fuel supply line 110 is interrupted and the flame is extinguished by the interruption ofthe supply ofthe air and gaseous fuel, the elevating shaft 82 is elevated by the operation ofthe elevating cylinder 80 and, accordingly, the core 35 and the lower mold 30 are closed by the upper mold 20. As soon as the core 35 and the lower mold 30 are closed by the upper mold 20, molten casting material is supplied through the casting material supply hole 22 ofthe upper mold 20 and the casting material supply hole 36 of the core 35 from the casting material feeder 10.

After the injection ofthe casting material is completed and the formed cast 146 has cooled for 5 to 300 seconds, STEP S202 is performed. In STEP S202, after the upper and lower molds 20 and 30 are opened away from the core 35 at predetermined distances (for example, in a range of 1 to 400 mm), compressed air is injected to the core 35 and the formed cast 146 through the air and gaseous fuel supply line 110, the supply conduits 21 and 31 and discharge holes 23 and 34 and cools the core 35 and the formed cast 146. At this time, the cooling of the formed cast 146 is performed for, for example, 5 to 30 seconds.

Additionally, in STEP S203, after the upper and lower molds 20 and 30 and the core 35 are completely opened, the formed cast 146 is ejected. With this, the entire injection molding process is completed.

A method for momentarily heating the surface of a mold using the flame of gaseous fuel in accordance with a third embodiment ofthe present invention is described with reference to Figs. 5a to 5d. In this case, a plurality of cores are disposed between the upper and lower molds 20 and 30 as auxiliary molds for the injection molding ofthe cast 146.

The cores consist of a first core 35 in contact with the upper mold 20 and a second core 37 in contact with the lower mold 30, a casting material supply hole 36 is formed_, in the first core 35 to coπespond to the casting material supply hole 22 in the upper mold 20, and a forming space 39 is formed between the first and second cores 35 and 37 to form casting material supplied through the casting material supply hole 36 ofthe first core 35.

The method for momentarily heating the surface of a mold in accordance with the second embodiment is different from the method for momentarily heating the surface of a mold in accordance with the first embodiment, in that a plurality of cores, for example, a first core 35 and a second core 37, are disposed between the upper and lower molds 20 and 30, a supply line is connected to the upper mold 20 to supply mixed compressed air and gaseous fuel, and an ignition unit (not shown) identical to the ignition unit 40 (including the igniter 41 , the flame sensor 42 and the high voltage generator 44) mounted to the lower mold 30 is preferably mounted to the upper mold 20. Additionally, the first and second cores 35 and 37 are provided with support means for elevating and supporting the cores 35 and 37.

In STEP S300, the upper mold 20, the first and second cores 35 and 37 and the lower mold 30 are opened at predeterrnined distances and the supply of gaseous fuel is prepared. Thereafter, the upper mold 20, the first and second cores 35 and 37 and the lower mold 30 come close to one another at predeterrnined distances and gaseous fuel is injected to the first and second cores 35 and 37 from the upper and lower molds 20 and 30 and is ignited. In more detail, compressed air and gaseous fuel are supplied from tiie compressed air supply source 136 and the gaseous fuel supply source 146 through the compressed air supply line 130 and the gaseous fuel supply line 140, enter the air and gaseous fuel supply line 91 for ignition and are mixed together while passing through the air and gaseous fuel mixture element 92, and the mixed air and gaseous fuel passes through the upper and lower molds 20 and 30, is injected through the discharge holes 23 and 34 and is- ignited in the igniter 41 of the ignition unit 40 using high voltage current generated by the high voltage generator 44.

If a flame is not sensed by the flame sensor 42 after the ignition is performed, the supply of air and gaseous fuel is interrupted by the operation ofthe solenoid valves 95 and 103. After the air and gaseous fuel supplied through and mixed in the air and gaseous fuel supply line 91 for ignition are normally injected, compressed air and gaseous fuel are supplied through and mixed in the air and gaseous fuel supply line 110 and are injected through the supply conduits 21 and 31 ofthe upper and lower molds 20 and 30. At this time, the supply ofthe compressed air and gaseous fuel being supplied through the air and gaseous fuel supply line 91 for ignition is interrupted and is not supplied to the upper and lower molds 20 and 30 anymore. Accordingly, the cavities 24 and 38 defined by the upper and lower molds 20 and 30 and the first and second cores 35 and 37, which come close to one another at predeterrnined distances (for example, the distances between the upper mold 20 and the first core 35, between the first core 35 and the second core 37 and between the second core 37 and the lower mold 30 are in a range of 1 to 40 cm), are heated by the gaseous fuel supplied through and injected from the air and gaseous fuel line 110 for heating and ignition, for a predetermined time period (for example, about 1 to 60 seconds).

In STEP S301, after the supply of air and gaseous fuel supplied from the air and gaseous fuel supply line 110 is interrupted and the flame is extinguished by the interruption ofthe supply ofthe air and gaseous fuel, the elevating shaft 82 is elevated by the operation ofthe elevating cylinder 80 and, accordingly, the first and second cores 35 and 37 and the lower mold 30 are closed by the upper mold 20. As soon as the first and second cores 35 and 37 and the lower-mold 30 are closed by the upper mold 20, molten casting material is supplied through the casting material supply hole 22- ofthe upper mold 20 and the casting material supply hole 36 of the first core 35 from the casting material feeder 10.

After the injection ofthe casting material is completed and the formed cast cools for 5 to 300 seconds, STEP S302 is performed. In STEP S302, after tiie upper and lower molds 20 and 30 are opened away from the first and second cores 35 and 37 at predetermined distances (for example, in a range of 1 to 400 mm), compressed air is injected toward the first and second cores 35 and 37 and the formed cast 146 through the air and gaseous fuel supply line 110, the supply conduits 21 and 31 and the discharge holes 23 and 34 and cools the first and second cores 35 and 37 and the formed cast 146. At this time, the cooling of the formed cast 146 is performed for, for example, 5 to 30 seconds.

Additionally, in STEP S303, after cooling is performed for a certain time period, gaseous fuel is injected from the upper and lower molds 20 and 30, is ignited and heats the first and second cores 35 and 37. While the first and second cores 35 and 37 are heated, the first and second cores 35 and 37 are separated and the cast 146 is ejected. With this, all the injection mold process is completed.

As described above, in Figs. 3a to 3f, there is depicted the first embodiment in which no core exists between the upper and lower molds 20 and 30. In Figs. 4a to 4d, there is depicted the second embodiment in which a single core 35 is disposed between the upper and lower molds 20 and 30. In Figs. 5a to 5d, there is depicted the third embodiment in which a plurality of cores 35 and 37 are disposed between the upper and lower mold cores 20 and 30. Ofthe embodiments, it is preferable that a plurality of cores 35 and 37 are disposed between the upper and lower mold cores 20 and 30.

The cores respectively have thicknesses of 0.1 to 15 mm and are formed to coπespond to the shape of the cast. The discharge holes are constructed in the form of slits, respectively have widths of 0.01 to 5 mm and are distributed on the surface of ti e lower mold to coπespond to the shape ofthe cast.

The ignition unit 40 may utilize high voltage current or an electronic spark for igniting mixed air and gaseous fuel, and preferably prepares for the failure of ignition and an accidental fire after ignition. Such an ignition unit 40 may be directly mounted on an injection molding apparatus or separated from the injection molding apparatus. The ignition unit 40 is preferably disposed in the mold and attached to the mold. In the ignition unit 40, the length of flames may be adjusted to be relatively long or relatively short using combustion gas such as gaseous fuel mixed with oxygen or compressed air. In the air and gaseous fuel mixture and supply unit 90, the gaseous fuel must be mixed with the oxygen or compressed air for burning the gaseous fuel prior to the supply ofthe gaseous fuel and the oxygen or compressed air so as to completely bum the gaseous fuel in a forming space defined between two molds. Since the danger of explosion occurs when the gaseous fuel is kept in a state where the gaseous fuel is mixed with the oxygen or air, the gaseous fuel is mixed with the oxygen or air in the gaseous fuel mixture and supply element 92 for ignition and the gaseous fuel mixture and supply element 111 for heating in the process of supplying the gaseous fuel and the oxygen or air. The gaseous fuel and the oxygen or ah" are supplied to and mixed in the elements 92 and 111, and immediately the mixed gaseous fuel and the oxygen or air is supplied to the interior of the lower mold 30. In order to regulate the amount ofthe gaseous fuel and the amount of the oxygen or air, 16110

the manual valves 96, 104, 135 and 145 and the flux regulators 131 and 141 are employed. One selects between the oxygen and the air, depending upon the material of the molded products. That is, the oxygen is employed for manufacturing relatively precise injection molding products of synthetic resin, while the compressed air is employed for manufacturing relatively rough injection molding products. While the oxygen or compressed air is supplied, impurities, such as humidity and dust, must be filtered off through the first filter 132. In the case of the gaseous fuel, various impurities must be filtered off through the second filter 142 and thereafter be supplied to the lower mold 30.

In the safety unit ofthe present invention, when it is sensed that the pressure ofthe gaseous fuel or the oxygen or air supplied through the pneumatic pressure gauge 93 or 112, the fluidic pressure gauge 101 or 120 or the pressure switch 134 or 144 is greater or less than a predetermined pressure, the related supply line 91, 110, 130 or 140 is stopped up by the solenoid valve 95, 103, 114, 122, 133 or 143, thereby preventing danger due to abnormal pressure. If the gas detector is mounted to the lower portion o the system ofthe present invention or on the ceiling of a room where the system ofthe present invention is installed, the supply ofthe gaseous fuel and oxygen or compressed air is interrupted when the leakage of gas is detected. Additionally, when the flame sensor 42 ofthe ignition unit 40 senses the failure of ignition and an accidental fire, the supply ofthe gaseous fuel and oxygen or compressed air is interrupted. The safety unit and the gaseous fuel mixture and supply control 70 for controlling the air and gaseous fuel mixture and supply unit 90 allows their operating time period, position and numerical value to be set and controlled by means ofthe confrol panel 150.

Ail theπnoplastic polymers can be injection molded according to the present invention. Suitable polymers for use in the present invention include those from group consisting of alkylene aromatic polymers such as polystyrene; rubber-modified alkylene aromatic polymers or copolymers, more commonly known as high impact polystyrene (HIPS) or ABS, alkylene aromatic copolymers such as styrene/acrylonitrile or styrene/butadiene; hydrogenated alkylene aromatic polymers and copolymers such as hydrogenated polystyrene and hydrogenated styrene/butadiene copolymers; alpha-olefin homopolymers such as low density polyethylene, high density polyethylene and polypropylene; linear low density polyethylene (an ethylene/octene-1 copolymer) and other copolymers of ethylene with a copolymerizable, mono-ethylenically unsaturated monomer such as an alpha-olefin having from 3 to 20 carbon atoms; copolymers of propylene with a copolymerizable, mono-ethylenically unsaturated monomer such as an alpha-olefin having from 4 to 20 carbon atoms, copolymers of ethylene with a vinyl aromatic monomer, such as ethylene/styrene interpolymers; ethylene/propylene copolymers; copolymers of ethylene with an alkane such as an ethylene/hexane copolymer; thermoplastic polyurethanes (TPU's); and blends or rnixtures thereof, especially blends of polystyrene and an ethylene/styrene interpolymer

Other suitable polymers include polyvinyl chloride, polycarbonates, polyamides, polyimides, polyesters such as polyethylene terephthalate, polyester copolymers such as polyethylene terephthalate-glycol (PETG), phenol-formaldehyde resins, thermoplastic polyurethanes (TPUs), biodegradable polysaccharides such as starch, and polylactic acid

polymers and copolymers.

Certain blends and alloys of these polymers can also be injection molded in accordance with the teachings ofthe present invention.

The polymers listed above, together with alloys and blends made therefrom, can optionally contain mold release agents, fillers (such as glass fibers, stainless steel fibers, nickel-coated graphite fibers,carbon fibers, nanocomposite clay particles, metallic particles, talc, and the like), pigments, colorants, flame retardants, antioxidants and other additives.

The present invention can also be employed effectively with generally well known fabrication techniques, which can be used alone or in combination, such as foam molding, blow molding, thermoforming, extrusion, SCORIM, gas-assisted injection molding, co-injection, in-mold lamination, and like.

In connection with foam molding and related processes involving expanded thermoplastic or thermoset polymers disclosed herein, certain chemical blowing agents

(such azodicarbonamide, sodium bicarbonate, and the like) and/or physical blowing agents ( such as CO ,N₂, steam, and like.) can also be used.

In addition to thermoplastics, this process is considered suitable for thermosetting resin materials formed by molding techniques generally refeπed to as reaction injection molding (RIM) or resin transfer molding (RTM). Examples of thermosetting resin materials include epoxies, urethanes, acrylates, and vinyl esters. Rapid heating of the mold is desirable for rapid polymerization of thermosets.

The large heat of polymerization encountered with materials such as epoxies can be effectively managed by rapidly heating the mold selectively, thereby allowing for a large thermal mass to absorb the heat of polymerization.

The teachings ofthe present invention can also be used with a group of high density foams having microcellular closed cell structures disclosed in U.S. Patent 4,473, 665,

5,674,916 and 5,869,544 teachings of which are incorporated herein by reference.

The operable mold surface temperature ranges from the applicable melting point (m.p.) or glass transition temperature (Tg), as the case may be, depending, on the polymeric material being processed, to 300 °C above the relevant m.p. or Tg, preferably 200 °C, more preferably 150 °C, most preferably 100 °C.

EXAMPLE

Wheel caps for automobiles were injection-molded of polycarbonate/ABS alloy resin. The method for momentarily heating the surface of a mold using the flame of gaseous fuel and system thereof in accordance with the present invention was applied to the manufacture ofthe wheel caps. The molding pressure ofthe system was 405 tons. No resin weld line and no flow mark appeared on the exterior of the molded products. Additionally, pinholes that inevitably appear on the general products of polycarbonate/ABS alloy resin did not appear on the products of this example. Furtheπnore, the brilliance, impact strength and thermal deformation temperature of the products manufactured by the method and system were improved as described in table 1 in comparison with the products made by the conventional method and system.

TABLE 1

Product made by the Product made by the method conventional method and and system ofthe present system invention

Brilliance (the angle of reflection: 60°) 75 100

Impact strength (1/8", notched ASTMD-256)

52 62

(Kg-cm/cm)

Thermal deformation temperature (1/8",

123 141

1.80N/mm² ASTM D-648)

(°C)

As can be seen from the above example, since products of polycarbonate/ABS alloy resin having no defect in appearance can be manufactured in accordance with the present invention, wheel caps of superior quality can be manufactured without coating, thereby reducing its manufacturing cost and improving its quality.

Additionally, in accordance with the present invention, the strength and thermal properties of the products can be improved, and the resin of high strength can be freely formed regardless of its fluidity.

Meanwhile, in accordance with a feature of the present invention, the upper and lower molds 20 and 30 may be heated by an induction heater that generates high temperature heat using electricity instead of gaseous fuel. When the molds 20 and 30 are heated using gaseous fuel, heat is directly applied to the molds 20 and 30; whereas when the molds 20 and 30 are heated using an induction heater, electricity flows into the molds 20 and 30 by the action of induction and heat is generated in the molds 20 and 30 by the resistance of the molds 20 and 30. When the induction heater is employed to heat the molds 20 and 30, the constructions concerning the supply of gaseous fuel are not necessary. However, the constructions concerning the supply of compressed air for cooling the molds 20 and 30 are preferably provided. ,.

That is, in the method and system ofthe present invention, the upper and lower molds 20 and 30 can be momentarily heated by heating means such as the induction heater.

Fig. 7 is a schematic diagram showing a system for momentarily heating the surface of a mold that employs an induction heater and two cores. This system for momentarily heating the surface of a mold comprises a casting material feeder 10 for supplying molten casting material, upper and lower molds 20 and 30 for forming a predetermined shaped cast, an injection molding control 50 for controlling the upper and lower molds 20 and 30, a compressed air supply line 130 for supplying compressed air, one or more cores 35 and 37 disposed between the upper and lower molds 20 and 30, a voltage generator 73 for generating voltage of a predetermined level, induction heaters 74 and 75 for heating the cores 35 and 37 using cunent applied from the voltage generator 73, the induction heaters 74 and 75 being mounted on the inner portion ofthe upper mold 20 and the upper portion of the lower mold 30, a controller 72 for controlling the compressed air supply line 130 and the voltage generator 73, an interface 60 for interfacing the injection molding confrol 50 and the controller 72, and a control panel 150 for visually displaying the confrol, condition and operation of the components of the system.

The system further comprises a plurality of supply conduits 21 and 31 and a plurality of discharge holes 23 and 34 in the upper and lower molds 20 and 30. The supply conduits 21 and 31 are respectively connected to a compressed air supply conduit 87 for supplying compressed air provided by the compressed air supply line 130. The cores 35 and 37 respectively have thicknesses of 0.1 to 15 mm and are formed to correspond to the shape ofthe cast. The discharge holes 23 and 34 are constructed in the

5 form of slits, respectively have widths of 0.01 to 5 mm and are distributed on the surfaces ofthe molds 20 and 30 to coπespond to the shape ofthe cast.

When the induction heaters 74 and 75 are employed as heating means, the lower and upper molds 20 and 30 are momentarily heated using cunent generated by the voltage generator 73 and are cooled by the molds 20 and 30 and/or by means of compressed air of

10 high pressure after injection molding, thereby producing injection- molded products.

Fig. 8 is a flowchart showing the operation ofthe system for momentarily heating the surface of a mold that employs the induction heaters 74 and 75 and the two cores 35 and 37. First of all, in STEP S400, the upper and lower molds 20 and 30 are momentarily heated by the induction heaters 74 and 75 using current generated by the voltage generator

15 73 after the upper and lower molds 20 and 30 are caused to come close to each other at a predetermined distance. In STEP S401, molten casting material is injected from the casting material feeder 10 and is molded after the heated lower mold 30 is raised to and engaged with ti e upper mold 20 and the formed cast cools for 5 to 300 seconds. In STEP S402, compressed air is supplied from a compressed air supply line 130 to the cores 35

20 and 37 through a compressed air supply line 87, the supply conduits 21 and 31 and the discharge holes 23 and 24, and cools the molded product. In STEP S403, the molded product is ejected after the molded product is cooled sufficiently.

A user can select one of the two heating fashions, that is, one heating fashion using gaseous fuel and the other heating fashion using an induction heater, depending

25 upon the type or features ofthe products to be injection-molded. hi the meantime, when the induction heaters 74 and 75 are employed, the injection molding control 50 and interface 60 for controlling the components ofthe system and a controller 72 for transmitting and receiving confrol signals are included in the system. The controller 72 includes a control program. Fig. 9 is. a schematic diagram showing a water-cooled system for momentarily heating and cooling the heated surface of a mold.

That is, although in the previous embodiments a mold is heated by the air and gaseous fuel mixture and supply unit 90 using an air and gaseous fuel mixture and cooled using compressed air, there is shown the water-cooled system that cools a heated mold by injecting cooling water to the heated mold.

To this end, cooling water passages 204 and 206 are aπanged through upper and lower molds 20 and 30, a cooling water supply conduit 203 is connected to the cooling water passages 204 and 206, an electronic valve 200 is positioned on the cooling water supply conduit 203 to selectively open or close the cooling water supply conduit 203, and a motor pump 202 is positioned on the cooling water supply conduit 203 to supply cooling water through the cooling water supply conduit 203.

In such a system, although the surface ofthe mold is heated in the same manner as that shown in Fig. 5, the heated surface ofthe mold is cooled using cooling water instead of compressed air. Molds and cores are heated using air and gaseous fuel mixture supplied by tiie air and gaseous fuel mixture and supply unit 90. After the molds and the cores have been heated, the upper and lower molds 20 and 30 and the first and second cores 35 and 37 are closed and molten material is injected into the mold. Thereafter, the upper and lower molds 20 and 30 are allowed to be opened away from the first and second cores 35 and 37 at predetermined distances (for example, 1 to 400mm). When the upper and lower molds 20 and 30 have been opened, the electronic valve 200 is opened and the motor 202 is operated by the control ofthe controller 72. Consequently, cooling water is supplied to the upper and lower molds 20 and 30 through the cooling water supply conduit 203, so the cooling water is injected to the first and second cores 35 and 37 through the supply holes 205 and 207 of the cooling water passages 204 and 206 and cools ti e first and second cores 35 and-37: In this case, a time period for cooling a molded product 146 is, for example, in the range of 5 to 300 seconds. The system of this embodiment may be applied to a case where cooling faster than cooling using compressed air is required.

Fig. 10 shows a system for momentary heating the surface of a mold, in which the surface of the mold is cooled using cooling water in tiie same manner as that of the embodiment shown in Fig. 9, while the surface ofthe mold is heated by a variable electric resistance heater.

A variable electric resistance heater 210 is positioned between the upper mold 20 and tiie first core 35, and generates heat by its own electric resistance using a voltage supplied from a voltage generator 73. hi the system shown in Fig. 10, an upper mold 20 and a first core 35 are heated by the electric resistance heater 210 for a predeterrnined time period, for example, about 1 to 300 seconds.

After the upper mold 20 and the first core 35 are heated, the upper and lower molds 20 and 30 and the first and second cores 35 and 37 are closed and molten material is injected into the mold. Thereafter, the upper and lower molds 20 and 30 are allowed to be opened away from the first and second cores 35 and 37 at predetermined distances (for example, 1 to 400mm). Additionally, it is desirable to keep a predeteπnined distance between tiie upper mold 20 and the electric resistance heater 210, for example, in the range of0.1 to 30mm. At this time, when the upper and lower molds 20 and 30 have been opened, the electronic valve 200 is opened and the motor 202 is operated by the control of the controller 72. Consequently, cooling water is supplied to the upper and lower molds 20 and 30 through the cooling water supply conduit 203, so the cooling water is sprayed oh the first and second cores 35 and 37 through the supply holes 205 and 207 "of cooling water passages 204 and 206 and cools the first and second cores 35 and 37. In this case, a time period for cooling a molded product 146 is, for example, in the range of 5 to 300 seconds.

In the system for momentarily heating the surface of a mold shown in Fig. 10, the molds and the cores are heated by the variable electric resistance heater 210 instead of air and fuel gaseous mixture and the surface ofthe molds and the cores are cooled by cooling water. The system of this embodiment may be applied to a case where cooling faster than cooling using compressed air is required. While cooling water is sprayed, a voltage is not supplied to the electric resistance heater 210. The variable electric resistance heater 210 can be inserted not only between the upper mold 20 and the first core 35 but also between the lower mold 30 and the second core 37. Additionally, the variable electric resistance heater 210 can be inserted between the upper mold 20 and the first core 35 and/or between the second mold 30 and the second core 37. The variable electric resistance heater 210 is preferably made of silicon line material having superior resistance.

In an embodiment shown in Fig. 11, the molds and the cores are cooled in the same water-cooled manner as that for the embodiments shown in Figs. 9 and 10, while the molds aid the cores are heated by a coating type electric resistance heater.

The system for momentarily heating the surface of a mold is similar in construction to the system shown in Fig. 10, but the surface is coated with a coating type electiic resistance heater 220 is foπned on the upper surface of the first core 35. The coating type electiic resistance heater 220 generates heat by its own electiic resistance using a certain voltage supplied from a voltage generator 73.

As shown in Fig. 12, the coat of the electric resistance heater 220 is fonned by coating the upper surface ofthe core 35 primarily with a first su ting layer 221 , coating the first insulating layer 221 with an electric resistance layer 222 and coating the electiic resistance layer 222 secondarily with a second insulating layer 223. The first insulating layer 221. is to insulate the electric resistance layer.222 from the core, 35, and the second insulating layer 222 is to insulate the electric resistance layer 222 from the upper mold 20. The electiic resistance layer 222 and a plurality of insulating layers 221 and 223 are stacked together with one on top of another, so the amount of heat applied to the layers can be controlled.

The insulating layers 221 and 223 and the electric resistance layer 222 each have a thickness ranging from 0.01 to 10mm. The insulating layers 221 and 223 are preferably formed of MgO + Teflon having insulation and heat-resistance characteristics, while the electiic resistant layer 222 is preferably formed of conductive metal or thermopolymer line material having superior electric resistance.

In the system shown in Fig. 11, the first core 35 is heated by the electiic resistance heater 220 for a predeteπnined time period (for example, about 1 to 300 seconds). At this time, when the upper and lower molds 20 and 30 have been opened, an electronic valve 200 is opened and a motor 202 is operated by tiie confrol of a controller 72. Consequently, cooling water is supplied to the upper and lower molds 20 and 30 through a cooling water supply conduit 203, so the cooling water is sprayed on the first and second cores 35 and 37 through the supply holes 205 and 207 of cooling water passages 204 and 206 and cools the first and second cores 35 and 37. In this case, a time period for cooling a molded product 146 is, for example, in the range of 5 to 300 seconds.

In tiie system for momentary heating the surface of a mold shown in Fig. 11, the molds and the cores are heated by the coating type electric resistance heater 210 instead of an air and fuel gaseous mixture, and are cooled using cooling water. The system of this embodiment may be applied to a case where cooling faster than cooling using compressed air is required. While cooling water is sprayed, a voltage is not supplied from a voltage generator 73 to the coating type electric resistance heater 220.

The coating type, electric resistance heater 220 may be formed on- the -upper surface ofthe first core 35 or the lower surface ofthe second core 37. In accordance with products, the coating type electric resistance heater 220 may be formed on tiie upper surface of the first core 35 and/or the lower surface of the second core 37, and may heat the cores.

The method and system of the present invention is not limited to the injection molding of synthetic resin products, but the method and system can be applied to reactive injection molding, metallic cast forming and ceramic forming and the like.

As described above, the present invention provides a method for momentarily heating the surface of a mold and system thereof, which is capable of improving the quality of products in appearance, preserving the physical and thermal properties of resin in the products, increasing the productivity ofthe manufacturing process ofthe products and reducing the manufacturing cost ofthe products.

Although the prefeπed embodiments ofthe present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit ofthe invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A method for momentarily heating a surface of a mold, comprising the steps of: opening upper and lower molds ofthe mold, and supplying gaseous fuel; injecting and igniting the gaseous fuel from the lower mold after allowing the upper and lower molds to come close to each other at a predetermined distance; heating the upper mold for a predeteπnined time period; filling a foπning space between the upper and lower molds with molten material through, the upper mold immediately after stopping heating- and -closing the upper and lower molds and allowing ti e formed cast to cool for a predeteπnined time period; cooling a molded product by injecting compressed air to the molded product after allowing the upper and lower molds to be opened at a predeteirained distance; and ejecting the molded product from the upper and lower molds after allowing the upper and lower molds to be completely opened.

2. The method according to claim 1, wherein said predeterrnined time period for which the upper mold is heated is in a range of 1 to 60 seconds, said predeteπnined distance between the upper and lower molds, while the upper mold is heated, is in a range of 1 to 40 cm, said predetennined time period for which the molded product is cooled in the closed mold is in a range of 5 to 300 seconds, said predeterrnined time period for which the molded product is cooled with compressed air is in the range of 5 to 30 seconds, and said predetennined distance between the upper and lower molds, while the upper mold is cooled, is in a range of 1 to 400 mm.

3. A method for momentarily heating a surface of a mold, comprising the steps of: opening upper and lower molds and a core of the mold, and supplying gaseous fuel; injecting and igniting the gaseous fuel from tiie upper and lower molds after allowing the upper and lower molds to come close to each other at a predetermined distance; heating the core for a predetermined time period; filling a forming space between the upper and lower molds with molten material through the upper mold immediately after stopping heating and closing the upper and lower molds and the core and allowing the .molded product to cool for a-predeteπnined time period; cooling the core and a molded product for a predetermined time period by injecting compressed air to the core and the molded productafter allowing the upper and lower molds to be opened away from the core at predeterrnined distances; and ejecting the molded product from the upper and lower molds after allowing the upper and lower molds and the core to be completely opened.

4. The method according to claim 3, wherein said predetermined time period for which the core is heated is in a range of 1 to 60 seconds, said predetermined distances between the upper mold and the core and between tiie core and the lower mold while the core is heated is in a range of 1 to 40cm, said predeterrnined time period for which the molded product cools in the closed mold is in the range of 5 to 300 seconds, said predetermined time period for which the core and the molded product are cooled by compressed air are in a range of 5 to 30 seconds, and said predetermined distances between the upper mold and the core and between the core and tiie lower mold while the core and the molded product are cooled are in a range of 1 to 400 mm.

5. A method for momentarily heating a surface of a mold, comprising the steps of: opening upper and lower molds and first and second cores of the mold, and supplying gaseous fuel; injecting and igniting the gaseous fuel from tiie upper and lower molds after allowing the upper and lower molds to come close to each other at a predetemfrned distance; heating the core for a predetermined time period; filling a forming space between tiie upper-and lower molds -with molten material through the upper mold, immediately after stopping heating and closing the upper and lower molds and the core and allow the molded product to cool for a predetermined time period; cooling the core and a molded product for a predeteπnined time period by injecting compressed air to ti e core and tiie molded product after allowing the upper and lower molds to be opened away from the core at predeterrnined distances; and ejecting the molded product from the upper and lower molds after allowing the upper and lower molds and the core to be completely opened.

6. The method according to claim 5, wherein said predeterrnined time period for which the core is heated is in a range of 1 to 60 seconds, said predeteπnined distances between the upper and tiie core and between the core and the lower mold while the core is heated is in a range of 1 to 40 cm, said predeterrnined time period for which the core and the molded product are cooled in the closed mold is in a range of 5 to 300 seconds, said predeteπnined time period for which the core and the molded product are cooled by

■ compressed gas is in the range of 5 to 30 second, and said predetermined distances between the upper mold and the core and between the core and the lower mold while the core and tiie molded product are cooled by compressed air are in a range of 1 to 400 mm.

7. A method for momentarily heating ti e surface of a mold, comprising the steps of: momentarily heating upper and lower molds by an induction heater using cunent generated by a voltage generator after causing the upper and lower molds to come close to each other; injecting, molten casting material from a casting material feeder- and molding it- after raising the heated lower mold to and engaging ti e heated lower mold with the upper mold a d allowing the molded product to cool in the close mold; supplying compressed air from a compressed air supply line to tiie upper aid lower molds through a compressed air supply line to cool a molded product; and ejecting the molded product after cooling the molded product sufficiently.

8. A method for momentarily heating a surface of a mold, comprising the steps of: opening upper and lower molds and first and second cores of the mold, and supplying gaseous fuel; injecting and igniting the gaseous fuel from the upper and lower molds after blowing the upper and lower molds to come close to each other at a predetermined distance; heating ti e core for a predetermined time period; filling a forming space between the upper and lower molds with molten material through the upper mold, immediately after stopping heating, closing the upper and lower molds and the core and allowing the molded product to cool for a predeterrnined time period; cooling the core aid a molded product for a predetermined time period by spraying cooling water on the core and the molded product after allowing the upper aid lower molds to be opened away from the core at predetermined distances; and ejecting the molded product from the upper and lower molds after allowing the upper aid lower molds and the core to be completely opened.

9. The method according to claim 8, wherein said predeterrnined time period for which ti e core is heated is in a range of 1 -to 60 seconds,- said predetermined distances between the upper mold and the first core, between tiie first and second cores and between ti e second core and the lower mold while the core is heated ae in a range of 1 to 40 cm, said predetermined time period for which the core and tiie molded product ae cooled in the closed mold is in a range of 5 to 300 seconds, said predetermined time period for which the core and tiie molded product ae cooled by cooling water is in the range of 5 to 30 seconds and said predeteirnined distances between the upper mold aid the first core and between the second core and the lower mold while the core and the molded product ae cooled by the cooling water ae in a range of 1 to 400 mm.

10. A method for momentarily heating the surface of a mold, comprising the steps of: momentarily heating upper and lower molds by a variable electric resistance heater using current generated by a voltage generator after causing the upper aid lower molds to come close to each other; injecting molten casting material from a casting material feeder and molding it after raising the heated lower mold to and engaging the heated lower mold with t e upper mold and allowing tiie molded product to cool in the close mold; supplying compressed air from a compressed air supply line to the upper and lower molds through a compressed air supply line to cool a molded product; and ejecting the molded product after cooling the molded product sufficiently.

_f 11. The method according to claim 10, wherein said predetermined time period for which the upper mold and the core ae heated is in a range of 1 to 60 seconds, said predetennined distances between the upper mold and the first core, between the first and second cores and between the second core and the lower mold while the core is-heated ae • in a range of 1 to 40 cm, said predetermined distance between the mold and the voltage generator is in a range of 0.1 to 30 mm, said predetermined time period for which the core and the molded product ae cooled by the cooling water is in a range of 5 to 300 seconds, aid sad predeterrnined distances between the upper mold and the first core and between the second core and tiie lower mold while the core and the molded product ae cooled by the cooling water ae in a range of 1 to 400 mm.

12. A method for momentarily heating the surface of a mold, comprising the steps of: momentarily heating upper and lower molds by a coating type electric resistance heater using current generated by a voltage generator after causing the upper and lower molds to come close to each other; injecting molten casting material from a casting material feeder and molding it after raising the heated lower mold to and engaging the heated lower mold with the upper mold and allowing ti e molded product to cool in the close mold; supplying compressed air from a compressed air supply line to the upper and lower molds through a compressed air supply line to cool a molded product; and ejecting the molded product after cooling the molded product sufficiently.

13. The method according to claim 12, wherein said predetennined time period for which ti e upper mold and the core ae heated is in a range of 1 to 60 seconds, said predetennined distaices between the upper mold aid the first core, between the first aid second cores and between the second core and the lower mold while the core is heated ae in a range of 1 to 40 cm, said predetermined time period for which the core and tiie molded product ae cooled by .the cooling water is in a range of 5 to 300 seconds, and said predetermined distances between the upper mold and the first core and between the second core aid the lower mold while the core and the molded product ae cooled by the cooling water are in a ra ge of 1 to 400 mm.

14. A product fabricated by the method according to any of claims 1 to 12.

15. A system for momentarily heating the surface of a mold, comprising: a casting material feeder for supplying molten casting material; upper and lower molds for forming a predetermined shaped cast; an injection molding control for controlling the upper mold and the lower mold; an air and gaseous fuel mixture aid supply unit for supplying compressed air and gaseous fuel simultaneously or selectively; a gaseous fuel mixture and supply control for controlling the operation ofthe air aid gaseous fuel mixture and supply unit; ai interface for interfacing the injection molding control and the gaseous fuel mixture aid supply control; aid a control panel for visually displaying the control, condition and operation of ti e components ofthe system.

16. The system according to claim 15, wherein said upper mold has a casting material supply hole for supplying casting material from the casting material feeder to the upper mold aid a cavity for forming the casting material into a predetermined-shaped cast, a d is provided with a limit switch for sensing the position of the upper mold.

Λ 7..The. system according to claim 15, wherein said lower mold comprises, a mold portion for insertion into the cavity ofthe upper mold to fonn the casting material into a predetermiiied-shaped cast, a lower mold supply conduit for supplying mixed gaseous fuel and compressed air, said lower mold supply conduit being foπned in ti e lower mold, a plurality of lower mold dischage holes for heating and cooling the upper mold using the mixed gaseous fuel and the compressed air supplied through the lower mold supply conduit, ai ignition unit for igniting gaseous fuel injected by an igniter using high voltage cunent generated by a high voltage generator and sensing gaseous fuel flame by meats of a flame sensor, a limit switch for sensing the position ofthe lower mold, ai air and gaseous fuel mixture and supply unit for supplying air or mixed gaseous fuel supplied through a gaseous fuel supply conduit, and an elevating cylinder including an elevating shaft for selectively lifting or lowering the lower mold by the control of an injection molding control.

18. The system according to claim 17, wherein said dischage holes ae constructed in the form of slits on the mold, respectively have widths of 0.01 to 0.1 mm. a d ae distributed on the surface ofthe lower mold to coπespond to the shape ofthe cast.

19. The system according to claim 17, further comprising a safety unit, said safety unit automatically inteπupting the supply of air and gaseous fuel when a flame is not sensed by tiie flame sensor in a predeteπnined time period after ignition is performed by the igniter of the ignition unit, gas of a predeterrnined degree of density is detected by a .gas detector disposed nea the upper aid lower-molds, or the pressure of air and gaseous fuel inputted from a first pressure switch aid a second pressure switch ae higher than a predeteπnined pressure.

20. The system according to claim 15, wherein said air and gaseous fuel mixture and supply unit comprises: an air and gaseous fuel supply line for ignition including an air and gaseous fuel mixture element for ignition, an air supply line for ignition and a gaseous fuel supply line for ignition, said afr supply line for ignition including, a first pneumatic pressure gauge for measuring the pressure of supplied air, a first needle valve for preventing compressed air from flowing backward. and a first solenoid valve for inteπupting the supply of compressed air and a first manual valve for regulating the anount of supplied compressed air, said gaseous fuel supply line for ignition including, a first fluidic pressure gauge for measuring the pressure of supplied gaseous fuel, a second needle valve for preventing gaseous fuel from flowing backwad. and a second solenoid valve for interrupting the supply of gaseous fuel and a second manual valve for regulating the amount of supplied gaseous fuel; ai air and gaseous fuel supply line for heating including an afr and gaseous fuel mixture element for heating, an air supply line for heating and a gaseous fuel supply line for heating, said air supply line for heating including, a second pneumatic pressure gauge for measuring the pressure of supplied air, a third needle valve for preventing compressed afr from flowing backward, and ^• a third solenoid valve for inteπupting the supply of compressed air aid a first pressure switch for sensing the pressure of supplied compressed air and inteπupting the supply of compressed air when the pressure of the supplied compressed air is not equal to a predeterrnined value, said gaseous fuel supply line for heating includes, a second fluidic pressure gauge for measuring the pressure of supplied gaseous fuel, a fourth needle valve for preventing gaseous fuel from flowing backwad, and a fourth solenoid valve for interrupting the supply of gaseous fuel and a second pressure switch for sensing the pressure of supplied compressed air and interrupting the supply of gaseous fuel when the pressure ofthe supplied gaseous fuel is not equal to a predetermined value; a compressed air supply line connected to the air and gaseous fuel supply line for both ignition aid heating, said compressed air supply line including, a first flux regulator for manually regulating the amount of compressed air, a first filter for filtering impurities included in compressed air, a fifth solenoid valve for teπupting the supply of compressed air, a third pneumatic pressure gauge-. for sensing. the pressure of supplied compressed air, and a fifth manual valve for regulating the amount of supplied compressed air; a gaseous fuel supply line connected to both the gaseous fuel supply line for ignition ofthe air aid gaseous fuel and the gaseous fuel supply line for heating ofthe air aid gaseous fuel, said fuel gas supply line including, a second flux regulator for maiually regulating the amount of gaseous fuel, a second filter for filtering impurities included in gaseous fuel, a sixth solenoid valve for interrupting the supply of gaseous fuel, a fourth pneumatic pressure gauge for sensing the pressure of supplied gaseous fuel, and a sixth manual valve for regulating the amount of supplied gaseous fuel; a compressed air supply source for supplying compressed afr, said compressed air supply source being connected to the compressed air supply line; and a gaseous fuel supply source for supplying gaseous fuel, said gaseous fuel supply source being connected to the gaseous fuel supply line.

21. The system according to claim 15, wherein said control paiel comprises, a key input unit for inputting vaious operational conditions for injection molding, a sensing unit for sensing the vaious states of the system, converting a sensing signal to an electiic signal and outputting the electric signal, a central processing unit for performing determination on the basis of ai input signal and outputting a control signal, an alaπn for waning of tiie eπor ofthe system and the danger of safety, a display for indicating the information ofthe operation of the.system,.and . ai instrument paiel for indicating the operation of various components of the system.

22. The system according to claim 15, further comprising, one or more cores disposed between the upper and lower molds, a upper mold supply conduit for supplying mixed gaseous fuel aid compressed air, said upper mold supply conduit being formed in the upper mold, a plurality of upper mold dischage holes for heating and cooling the cores using the mixed gaseous fuel and the compressed air supplied through the upper mold supply conduit, a lower mold supply conduit for supplying mixed gaseous fuel and compressed air, said lower mold supply conduit being formed in the lower mold, a plurality of lower mold dischage holes for heating and cooling the cores using the mixed gaseous fuel and the compressed afr supplied tiπough the lower mold supply conduit, aid a gaseous fuel supply conduit for connecting the air and gaseous fuel mixture and supply unit respectively to the upper mold supply conduit and the lower mold supply conduit.

23. The system according to claim 22, wherein said cores respectively have thicknesses of 0.1 to 15 mm and ae respectively formed in accordance with the shape of tiie cast, and said discharge holes ae constructed in the foπn of slits, respectively, have widths of 0.01 to 5 mm and ae distributed on the surface ofthe mold in accordance with the shape ofthe cast.

24. The system according to claim 22, wherein said cores consist of a first core in contact with the upper mold aid a second core in contact with the lower mold, a first casting material supply hole is formed in the first core to coπespond to a second casting material supply hole in the upper mold, and a foπning space is formed between the first and second cores to form casting material supplied through the first casting material supply hole ofthe first core.

25. A system for momentarily heating the surface of a mold, comprising: a casting material feeder for supplying molten casting material; upper and lower molds for forming a predetermined shaped cast; an injection molding control for confrolling the upper and lower molds; a compressed air supply line for supplying compressed air; one or more cores disposed between the upper and lower molds; a voltage generator for generating voltage of a predeteπnined level; induction heaters for heating the cores using cunent applied from the voltage generator, said induction heaters being mounted on the inner portion of the upper mold and tiie upper portion ofthe lower mold; a controller for controlling the compressed air supply line and the voltage generator; ai interface for interfacing the injection molding control and the controller; and a control paiel for visually displaying the control, condition and operation ofthe _^ components ofthe system.

26. The system according to claim 25, further comprising a plurality of supply conduits and a plurality of dischage holes in the upper and lower molds,- herein sad supply conduits ae respectively connected to a compressed air supply conduit for supplying compressed air provided by the compressed air supply line.

27. The system according to claim 26, wherein said cores respectively have thicknesses of 0.1 to 15 mm and ae formed to coπespond to the shape ofthe cast, aid said dischage holes ae constructed in the form of slits, respectively having widths of 0.01 to 5 mm and ae distributed on the surfaces of tiie molds to coπespond to the shape ofthe cast.

28. A product fabricated by the system according to any of claims 15 to 27.