HK1007466B - Injection molding apparatus having heated nozzle manifolds in a common plane interconnected through connector manifolds - Google Patents

Description

Injection molding apparatus with hot nozzle manifolds co-planar interconnected by connecting manifolds

The present invention relates generally to injection molding and, more particularly, to a pair of heated connecting manifolds that extend between a heated center manifold and four or more heated nozzle manifolds that are all mounted in a common plane in a cold mold in such a way as to eliminate or compensate for the effects of manifold expansion and contraction.

It is well known in the injection molding art to simultaneously fill a plurality of cavities with a plurality of separate nozzles extending from a single heated nozzle manifold. The melt channel branches at the nozzle manifold, each branch subtending a melt bore through each nozzle. These manifolds are held in place in a cold mold, and expansion and contraction of the heated nozzle manifold causes the nozzle manifold to slide across the back end of the nozzle. It is important that each branch of the melt channel be aligned exactly in line with the melt bore through the nozzle, particularly in view of the high temperature and pressure conditions of the injection molding system. Thus, the amount of movement at each nozzle location must be pre-calculated and when the operating temperature is reached, the precisely sized branch of the melt channel is slid into direct alignment with the melt bore of the nozzle. While this conventional technique is acceptable for smaller injection molding systems, it is difficult to provide the larger sliding distances required for larger casting systems.

Furthermore, there is an increasing demand for injection molding systems having many cavities. As seen in Gellert, U.S. patent No. 4,761,343 issued on 8/2 1988, a number of support nozzle manifolds are interconnected by a bridge manifold to increase the number of cavities. The sliding of the bridge manifold across the top of the support manifold provides for increased expansion and contraction. However, this bridging structure has the disadvantage that the branch manifolds and the bridging manifolds must extend in two different planes, which is unacceptable in certain applications, such as in the casting of a deckbox requiring a minimum mould height. This configuration also has the disadvantage that the branches bridging the melt channels in the manifold still must be slid into alignment with the melt channels in the support manifold. As a result, although conditions are provided for accommodating thermal expansion, there is no practical compensation for thermal expansion in the sense that dimensional changes caused by thermal expansion are absorbed.

In united states patent number 4,219,323 to Bright et al, published 26/8 1980, a connecting link is shown connecting two heated nozzle manifolds. Despite the advantages that the nozzle manifolds and the connector link both extend in the same plane and that the connector link absorbs thermal expansion, there are disadvantages that only two nozzle manifolds can be connected to each other and that the use of a sleeve inside the connector link is required to cover the expansion slot to prevent melt leakage under high temperature and high pressure operating conditions.

It is therefore an object of the present invention to at least partially overcome the disadvantages of the prior art by providing an injection molding apparatus with a heated connecting manifold extending in the same plane as a heated center manifold and at least four heated nozzle manifolds and between the center manifold and the nozzle manifolds to compensate for thermal expansion and contraction.

To achieve this object, in one aspect, the present invention provides an injection molding apparatus having a heated central manifold and a plurality of heated nozzle manifolds mounted on a mold, the central manifold having melt passages for conveying melt from a central inlet of the central manifold through the nozzle manifolds to a plurality of heated nozzles extending from each nozzle manifold, each nozzle being seated on the mold with a melt bore extending in line with a gate leading to a cavity, wherein the central manifold is centered relative to the mold, a pair of connecting means extending in opposite directions from the central manifold to define a central axis, at least one pair of heated nozzle manifolds being mounted on opposite sides of each connecting means so that each nozzle manifold is offset from the central axis associated with the central manifold, the nozzle manifolds and the connecting means extending in a common plane, the method is characterized in that: each connecting device, or each nozzle manifold, is free to move longitudinally relative to the mold, the melt channel extending outwardly from the central manifold to each connecting device, then diverge at each connection device and extend sideways to each nozzle manifold, then diverge at each nozzle manifold, and extending to a melt bore through each nozzle extending from each nozzle manifold, each connecting device slidably connected back to the center manifold and slidably connected laterally to adjacent nozzle manifolds, thereby partially compensating for thermal expansion and contraction of the coupling device and heated manifold relative to the cooled mold, each nozzle manifold being fabricated and mounted, such that when the manifold and the connection device are heated to operating temperatures, thermal expansion of the interior of the central manifold, the connection device, and the nozzle manifold slides the branches of the melt channel into direct alignment with the melt bores through the nozzles.

Preferably, each connection means comprises a heated connection manifold.

Preferably, each connector manifold has an elongated connector sleeve extending rearwardly to the central manifold through which the melt channel passes for slidable connection with the central manifold, and each connector manifold has another elongated connector sleeve extending outwardly from opposite sides of the central manifold through which the melt channel passes to each nozzle manifold for slidable connection with each nozzle manifold.

Preferably, each coupling sleeve has at least one non-threaded cylindrical portion extending from one end, and a melt bore centrally extending therethrough from one end to the other, at least one unthreaded portion of each of said one coupling sleeves, an unthreaded cylindrical aperture received in one of the center manifold and said each coupling manifold in alignment with the melt passage, at least one unthreaded portion of each of said other coupling sleeves, an unthreaded cylindrical aperture received in one of the coupling manifold and said each nozzle manifold in alignment with the melt bore, the unthreaded portion of the coupling sleeve being fitted into said unthreaded cylindrical aperture to allow the unthreaded portion of the coupling sleeve to slide sufficiently in said unthreaded cylindrical aperture without allowing pressurized melt flowing through the melt passage to leak.

Preferably, each coupling sleeve has a threaded cylindrical portion extending from one end, a non-threaded cylindrical portion extending from the other end, and a melt bore concentrically passing from said one end to said other end, the threaded portion of each of said one coupling sleeve being removably threaded into a threaded cylindrical bore hole of the linearly aligned melt bore on one of the central manifold and said each coupling manifold, the non-threaded portion of each of said one coupling sleeve being received in a non-threaded cylindrical bore hole of the linearly aligned melt channel on the other of the central manifold and said each coupling manifold, the threaded portion of each of said other coupling sleeve being removably threaded into a threaded cylindrical bore hole of the linearly aligned melt channel on one of the coupling manifold and said each nozzle manifold, the unthreaded portion of each of said other adapter sleeves is received in the adapter manifold and the unthreaded portion of each of said adapter sleeves, is received in an unthreaded cylindrical bore of the linearly aligned melt channel on the other of the adapter manifold and said each nozzle manifold, and the unthreaded portion of the adapter sleeve fits into said unthreaded cylindrical bore, allowing the unthreaded portion of the adapter sleeve to slide sufficiently in said unthreaded cylindrical bore without allowing pressurized melt flowing through the melt channel to leak.

Preferably, the unthreaded cylindrical portion of each adapter sleeve has a predetermined outside diameter and each unthreaded bore of the linearly aligned melt channel has a predetermined inside diameter, the predetermined outside diameter being less than the predetermined inside diameter just enough to enable the unthreaded cylindrical portion of the adapter sleeve to fit into the unthreaded cylindrical bore.

Preferably, the predetermined outer diameter dimension is sufficiently close to the predetermined inner diameter to form a sealed joint to prevent excess molten plastic from escaping therebetween.

Preferably, the non-threaded cylindrical portion of the connecting sleeve is made of a material having a greater coefficient of expansion than the material surrounding the second cylindrical bore.

Preferably, a pair of heated nozzle manifolds are mounted on opposite sides of each connecting manifold, and the positioning means is a positioning ring located between the mold and each nozzle manifold for positioning each nozzle manifold relative to the mold.

Preferably, each locating ring is aligned linearly with the center of the corresponding nozzle manifold.

Preferably, the positioning means includes a positioning ring seated between the mold and each of the connecting manifolds for positioning each of the connecting manifolds relative to the mold, the positioning means further including a slidable positioning device extending between the mold and each of the nozzle manifolds, each of the other connecting sleeves positioning a respective one of the nozzle manifolds relative to the connecting manifold in a first direction along the central axis and permitting movement in a second direction substantially perpendicular to the first direction to compensate for thermal expansion and contraction of the one nozzle manifold and the connecting manifold, the slidable positioning device positioning the each nozzle manifold relative to the mold in the second direction and permitting movement of the each nozzle manifold relative to the mold in the first direction, whereby the connecting sleeves and the slidable positioning device permit sufficient movement in both the first and second directions, to accommodate thermal expansion and contraction of the heated manifold relative to the cooled mold.

Preferably, each retaining ring is aligned linearly with the center of the corresponding connection manifold.

Preferably, a pair of heated nozzle manifolds are provided on opposite sides of each connecting manifold.

Preferably, two pairs of heated nozzle manifolds are provided on opposite sides of each connecting manifold.

Preferably, each locating means has an elongate locating element extending in the first direction, the locating element being slidable relative to at least one of the mould and said each nozzle manifold.

Preferably, the positioning element extends in line with the centre of each of said nozzle manifolds.

Preferably, the positioning element is a positioning pin.

In another aspect, the present invention provides a plurality of mold manifold systems comprising a central manifold, a pair of connecting manifolds connected to the central manifold by connecting sleeves, and a pair of nozzle manifolds connected to the connecting manifolds by connecting sleeves, wherein the nozzle manifolds comprise at least two injection nozzles and the connecting sleeves are fixedly connected to the connecting manifolds by a fastening portion so that they move with the connecting manifolds due to thermal expansion of the connecting manifolds to further seal melt channels between the connecting manifolds and the central manifold and between the connecting manifolds and the nozzle manifolds.

Further objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings.

FIG. 1 is a partial plan view of an injection molding system having four heated nozzle manifolds coupled to a central manifold in a partially assembled mold according to one embodiment of the present invention.

Fig. 2 is a sectional view taken along line 2-2 in fig. 1.

Fig. 3 is a cross-sectional view taken along line 3-3 of fig. 1.

FIG. 4 is an isometric view of a melt coupling sleeve.

Fig. 5 is a plan view showing a pair of connecting manifolds connecting eight heated nozzle manifolds to a central manifold in a partially assembled mold, in accordance with another embodiment of the present invention.

Fig. 6 is a cross-sectional view taken along line 6-6 of fig. 5.

Fig. 7 is a cross-sectional view taken along line 7-7 in fig. 5.

Fig. 8 is an isometric view showing the nozzle manifold with alignment pins and cam, which is visible in place in fig. 7, received in a groove in the mold.

Referring first to fig. 1, 2 and 3, four heated nozzle manifolds 10 are shown connected to a heated central manifold 12 by a pair of heated connecting manifolds 14, according to one embodiment of the present invention, which compensate for thermal expansion and contraction in the manifolds. The manifolds can all be mounted in the mold 16 on a common plane 18. Although the mold 16 generally has a large number of plates and inserts depending on the application, for ease of illustration only the manifold retaining plate 20 and the backing plate 22 are shown here, secured together by screws 24. In other embodiments, hydraulic plates with valve elements and actuators may be employed to provide a valve control system rather than a gate control system.

As shown in FIG. 1, the connector manifold 14 is connected to each end 26 of the central manifold 12 by elongated connector sleeves 30 that extend rearwardly. The central axis 32 extends in a first direction through the central manifold 12, the connecting sleeve 30, and the connecting manifold 14.

Referring again to fig. 4, each coupling sleeve 30 has a threaded cylindrical portion 34 extending from one end 36 and an unthreaded cylindrical portion 38 extending from the other end 40. The adapter sleeve 30 also has a central bore 42 and a hexagonal flange 44 which allows the adapter sleeve to be easily secured in place and removed. In this embodiment, the adapter sleeve 30 is threaded with the threaded portion 34 into a threaded bore 46 on the adapter manifold 14, and the unthreaded portion 38 is slidably received in a mating unthreaded cylindrical bore 48 on the central manifold 12, as shown in FIG. 1. In other embodiments, the orientation may be reversed, or both ends of the connecting sleeve 30 may be unthreaded portions 38, in which case the ports 46 on the connecting manifold 14 would also be unthreaded.

The unthreaded portion 38 of the adapter sleeve 30 is configured to fit tightly enough into the unthreaded bore 48 of the center manifold 12 to prevent melt leakage, but yet slide sufficiently within the bore 48 to accommodate thermal expansion and contraction. In the preferred embodiment, the manifolds 10, 12, 14 are formed of a material having a relatively low coefficient of expansion, such as steel, and the connecting sleeve 30 is formed of a material having a relatively high coefficient of expansion, such as beryllium copper. In this way, the coupling sleeves 30 are easy to install and expand to a tight fit when they are heated to operating temperatures and exposed to high pressures. In other implementations, these components may all be made of the same material and pre-loaded.

On opposite sides of each connecting manifold 14, a pair of nozzle manifolds 10 are mounted. Each nozzle manifold 10 is connected to a connecting manifold 14 by an elongated connecting sleeve 50 extending laterally from each connecting manifold 14. These laterally extending coupling sleeves 50 are substantially identical to the rearwardly extending coupling sleeves 30 described above and shown in FIG. 4. Specifically, each laterally extending connecting sleeve 50 has a threaded portion 52 received in a threaded aperture 54 on connecting manifold 14 and a threaded portion 56 received in an unthreaded aperture 58 on nozzle manifold 10. As described above, the unthreaded portion 56 of each coupling sleeve 50 is configured to fit snugly enough within the unthreaded bore 58 of nozzle manifold 10 to prevent melt leakage, but yet slide sufficiently within bore 58 to accommodate thermal expansion and contraction. Of course, in other embodiments, their orientation may be reversed, i.e., their unthreaded portions 56 received on the connection manifold.

As shown in fig. 2, the central manifold 12 is heated using integral electrical heating elements 60, each connecting manifold 14 is heated using integral electrical heating elements 61, and the mold 16 is cooled using cooling water pumped through cooling pipes 62. The heated central manifold 12 is positioned with a central positioning ring 64 located between it and the manifold mounting plate 20. A void 66 is left between the heated central manifold 12 and the cooled mold 16 and between the heated connecting manifold 14 and the cooled mold 16 to thermally isolate the manifolds from the surrounding cooled mold 16.

The central manifold 12 also has a central manifold extension or inlet sleeve 68, with the inlet sleeve 68 extending from the rear through the back plate 22 to a central inlet 70. Melt channels 72 extend from the central inlet 70, diverge at the central manifold 12, and extend in opposite directions from the central manifold 12, through the central bore 42 of the connecting sleeve 30, and into the connecting manifold 14. The melt channel again branches at the connecting manifolds 14 and extends in opposite directions from each connecting manifold 14, through the central bore 74 of each connecting sleeve 50, and into each nozzle manifold 10.

Each nozzle manifold 10, also heated by an integral electrical heating element 76, has a plurality of heated nozzles 78 extending therefrom. Although nozzle manifolds 10 and the melt channels passing therethrough may have a variety of different configurations, shown here is melt channel 72 that branches at each nozzle manifold 10 and extends to eight separate heated nozzles 78. As best seen in fig. 3, the melt channel 72 passes continuously through a central melt bore 80 through each nozzle 78 to a gate 82 opposite a cavity 84. The arrangement of the various manifolds and connecting sleeves, and the configuration of the melt channels 72 passing through them, ensures that the length experienced by each gate 82 through which the melt flows into the system is exactly the same.

Each nozzle 78 is positioned with its central melt bore 80 in-line with the gate 82 by an annular positioning sleeve 86 seated on a circular seat 88 in the manifold retainer plate 20. The front surface 90 of each nozzle manifold 10 abuts the rear end 92 of the nozzle 78 and is held in place by screws 94 threaded into the manifold retaining plate 20. In this position, there is an isolation space 96 between each heated nozzle manifold 10 and the surrounding cooled mold 16. Each nozzle manifold 10 is centrally located by a locating ring 98 that sits between it and the manifold retaining plate 20. The screws 94 holding each nozzle manifold 10 in place pass through holes 100 in the nozzle manifold 10, the holes 100 being sufficiently larger than the screws 94 to accommodate movement of the nozzle manifold 10 away from the center 102 of the nozzle manifold 10 at each particular nozzle 78 due to thermal expansion and contraction.

In use, after assembly as shown, cooling water is pumped through the cooling conduit 62 to cool the mold 16 and, in addition, power is applied to the heating elements 60, 61, 76 to heat the manifolds 10, 12, 14 and connecting sleeves 30, 50 to operating temperatures. This of course causes expansion of the manifolds 10, 12, 14 and connecting sleeves 30, 50 relative to the surrounding cold mold 16. Each nozzle manifold 10 of the central manifold 12 is centered and positioned by a retaining ring 64, 98, and the distance change between them due to thermal expansion is absorbed or compensated by the connecting sleeves 30, 50. The unthreaded portion 38 of each coupling sleeve 30, which slides in the unthreaded bore 48 on the central manifold 12, absorbs thermal expansion in a first direction along the central axis 32. The unthreaded portion 56 of each coupling sleeve 50 slides in an unthreaded aperture 58 on the corresponding nozzle manifold 10, absorbing thermal expansion in a second direction perpendicular to the first direction. As noted previously, the relative orientation of the threaded and unthreaded portions may vary between manifolds.

Of course, nozzles 78 are each centrally located so that the amount of thermal expansion between the center 102 of each nozzle manifold 10 and each nozzle 78 is still precalculated, and nozzle manifolds 10 are manufactured such that when operating temperatures are reached, the respective branches of the sized melt channel 72 slide into direct alignment with the melt bores 80 of the corresponding one of the nozzles 78. However, the farthest nozzle 78 is much less distant from center 102 of nozzle manifold 10 than farthest nozzle 78 is from center 104 of center manifold 12. In other words, the use of coupling manifold 14 and coupling sleeves 30, 50 reduces the amount of expansion and contraction that must be controlled in conventional methods, i.e., limited to the distance between each nozzle 78 and the center 102 of nozzle manifold 10. Although heated connecting manifolds 14 with connecting sleeves 30, 50 are shown, in other embodiments, a similar slidable T-shaped connection between central manifold 12 and each pair of nozzle manifolds 10 may be used in place of them.

After the manifolds 10, 12, 14 have been expanded into position with each branch of the melt channel 72 aligned linearly with the melt bore 80 of a corresponding one of the nozzles 78, pressurized melt is added to the central inlet 70 of the melt channel 72 from a molding machine (not shown) according to a predetermined cycle. The melt flows through melt channels 72 in manifolds 10, 12, 14, is aligned with a central melt bore 80 in each nozzle 78, and then through gates 82 into cavities 84 in mold 16. After the cavity 84 is filled, suitably filled and the cooling cycle is complete, the injection pressure is released and the melt delivery system is depressurized to avoid beading at the gate 82. The mold 16 is then opened and the cast product is ejected. After injection, the mold 16 is closed and the cycle is repeated for a period of time depending on the size of the wall section of the cast part and the type of molding material.

Referring now to fig. 5-8, shown therein is an injection molding system according to another embodiment of the present invention. Since many of the elements are identical to those described above, the same reference numerals have been used previously to describe and illustrate the same elements of the two embodiments.

As seen in fig. 5, two connecting manifolds 14 are slidably connected to the central manifold 12, again by connecting sleeves 30 extending in a first direction, but here the connecting manifolds 14 are much longer and each connecting manifold 14 extends between multiple pairs (more than a single pair) of nozzle manifolds 10. Although the nozzle manifolds 10 are still slidably connected to the connection manifolds 14 by the connection sleeves 50 extending in the second direction, as seen in fig. 6, each connection manifold 14 is centered by a retaining ring 106 seated between it and the manifold retainer plate 20. Each nozzle manifold 10, although partially positioned by a connecting sleeve 50 extending from the connecting manifold 14, is also positioned by an elongated locating pin 108. As seen in fig. 1-5, locating pins 108 extend from holes 110 in nozzle manifold 10 into holes 112 in cam 114, which cam 114 is received in a groove 116 in manifold retainer plate 20. As seen in fig. 1, locating pins 108 extend in a first direction parallel to central axis 32 and, in this embodiment, are aligned in a straight line with center 102 of nozzle manifold 10.

Thus, when the manifolds 10, 12, 14 are heated to the operating temperature, the unthreaded portion 38 of each coupling sleeve 30 slides within the unthreaded bore 118 of one of the coupling manifolds 14 to absorb thermal expansion between the fixed center 104 of the central manifold 12 and the fixed center 120 of the coupling manifold 14 in the first direction along the central axis 32. Although the effect of thermal expansion over this distance between the fixed center 104 of the central manifold 12 and the fixed center 120 of the connecting manifold 14 is thus absorbed, the effect of thermal expansion between the fixed center 120 of the connecting manifold 14 and each manifold 78 must still be taken into account. As described above, the holes 100 are made sufficiently larger than the screws 94 passing through them to allow each nozzle manifold 10 to slide across the rear end 92 of a nozzle 78 secured in place. The amount of movement at each nozzle 78 is precalculated, and the nozzle manifold 10 does so: when the operating temperature is reached, each branch of the sized melt channel 72 slides into direct alignment with the melt bore 80 in the nozzle 78. Locating pins 108 allow each nozzle manifold 10 to move in a first direction parallel to central axis 32, but prevent it from moving in a second direction perpendicular to the first direction. The amount of movement of the melt channel 72 in communication with the melt bore 80 on each nozzle 78 in the first direction is a combination of the expansion of the connecting manifold 14 from its center 120 to the connecting sleeve 50 and the expansion of the nozzle manifold 10 extending therefrom. The amount of movement in the first direction is therefore dependent upon the distance in the first direction between each particular nozzle 78 and the positioning ring at the center 120 of the connecting manifold 14.

As they are heated, the connecting manifold 14 and nozzle manifold 10 also expand relative to each other in a second direction. However, the unthreaded portion 56 of connecting sleeve 50 extending to each nozzle manifold 10 slides within unthreaded bore 58 on nozzle manifold 10, absorbing or compensating for the relative expansion of connecting manifold 14 and nozzle manifold 10 in the second direction. Accordingly, coupling sleeve 50 absorbs relative movement of manifolds 10, 14 in the second direction due to thermal expansion, and therefore, locating pins 108 can be used to locate each nozzle manifold 10 in the second direction, but allow it to slide in the first direction. As a result, the amount of movement of the melt channel 72 in the second direction relative to the melt bore 80 on each nozzle 78 depends on the distance that the nozzle 78 is offset from the locating pin 108.

Thus, the combination of coupling sleeve 50 and locating pin 108 allows each nozzle manifold 10 to move sufficiently in both the first and second directions to accommodate thermal expansion of the heated manifolds 12, 14 relative to the cold mold 16. Of course, if the heating elements 60, 61, 76 are turned off for disassembly or repair, this movement of the manifolds 10, 12, 14 is reversed. Although locating pins 108 and cams 114 are shown, in other embodiments, other locating means may be used to locate nozzle manifold 10 in the second direction, but allow them to slide freely in the first direction.

Although the injection molding apparatus has been described with respect to the embodiments, it will be apparent that various other modifications are possible without departing from the scope of the invention, which is understood by those skilled in the art and defined by the claims set out below. For example, in a layered casting system, the central manifold 12 may be a melt delivery manifold without the inlet sleeve 70.

Claims (18)

1. In an injection molding apparatus having a heated central manifold (12) and a plurality of heated nozzle manifolds (10) mounted to a mold (16), the central manifold (12) having melt channels (72) for conveying melt from a central inlet (70) of the central manifold (12) through the nozzle manifolds (10) to a plurality of heated nozzles (78) extending from each nozzle manifold (10), each nozzle being seated on the mold (16) with a melt bore (80) extending in alignment with a gate (82), the gate (82) being directed to a cavity, wherein the central manifold (12) is centered with respect to the mold (16), a pair of connecting means extending from the central manifold (12) in opposite directions to define a central axis, at least one pair of heated nozzle manifolds (10) being mounted on opposite sides of each connecting means, so that each nozzle manifold (10) is offset from the central axis associated with the central manifold (10), the nozzle manifolds (10) and the connecting means both extend in a common plane (18), the positioning means positioning at least one of each connecting means or each nozzle manifold with respect to the mould,

the method is characterized in that:

each connecting device (14) or each nozzle manifold (10) being free to move longitudinally relative to the mold (16), a melt channel (72) extending outwardly from the central manifold (12) to each connecting device, then diverging at each connecting device and extending laterally to each nozzle manifold (10), then diverging at each nozzle manifold (10) and extending to a melt bore (80) through each nozzle (78) extending from each nozzle manifold (10), each connecting device (14) being slidably connected rearwardly to the central manifold and slidably connected laterally to adjacent nozzle manifolds, thereby partially compensating for thermal contraction of the connecting device (14) and heated manifold relative to the cooled mold, each nozzle manifold (10) being constructed and arranged such that when the manifold and connecting device (14) are heated to an operating temperature, thermal expansion of the interior of the central manifold (12), the connecting device (14) and the nozzle manifold (10) slides the branches of the melt channel (72) into direct alignment with the melt bore (80) through the nozzle (78).

2. Injection molding apparatus as claimed in claim 1, wherein each connecting device (14) comprises a heated connecting manifold.

3. Injection molding apparatus as claimed in claim 2, wherein each connecting manifold (14) has an elongated connecting sleeve (30) extending rearwardly to the central manifold (12) through which the melt channel (72) passes for slidable connection with the central manifold (12), each connecting manifold (14) further having another elongated connecting sleeve (50) extending outwardly from opposite sides of the central manifold (12) through which the melt channel (72) passes to each nozzle manifold (10) for slidable connection with each nozzle manifold (10).

4. An injection molding apparatus as claimed in claim 3, wherein each coupling sleeve (30, 50) has at least one unthreaded cylindrical portion (38) extending from one end and having a melt bore (42) centrally extending therethrough from said one end to the other end, at least one unthreaded portion (38) of each of said one coupling sleeves (30), an unthreaded cylindrical opening (48) of a linearly aligned melt channel (72) received in one of the central manifold (12) and said each coupling manifold (14), at least one unthreaded portion (56) of each of said other coupling sleeves (50), an unthreaded cylindrical opening (58) of a linearly aligned melt bore (72) received in one of the coupling manifold (14) and said each nozzle manifold (10), the unthreaded portion (56) of the coupling sleeve (50) being fitted into said unthreaded cylindrical opening A port (58) allowing the unthreaded portion (56) of the connecting sleeve (50) to slide sufficiently within the unthreaded cylindrical bore (58) without allowing leakage of pressurized melt flowing through the melt channel (72).

5. An injection molding apparatus as claimed in claim 3, wherein each coupling sleeve (30, 50) has a threaded cylindrical portion (34, 52) extending from one end, a non-threaded cylindrical portion (38, 56) extending from the other end, and a melt bore (42) passing centrally from said one end to said other end, the threaded portion (34) of each of said one coupling sleeve (30) being removably threaded into a threaded cylindrical opening (46) of a linearly aligned melt bore (72) in one of the central manifold (12) and said each coupling manifold (14), the non-threaded portion (38) of each of said one coupling sleeve (30) being received in a non-threaded cylindrical opening (48) of a linearly aligned melt channel (72) in the other of the central manifold (12) and said each coupling manifold (14), a threaded portion (52) of each of said other connecting sleeves (50) removably threaded into a threaded cylindrical bore (54) of a linearly aligned melt channel (72) on one of the connecting manifold (14) and said each nozzle manifold (10), a non-threaded portion (56) of each of said other connecting sleeves (50) received in a non-threaded cylindrical bore (58) of a linearly aligned melt channel (72) on the other of the connecting manifold (14) and said each connecting sleeve (50), the non-threaded portion (56) of the connecting sleeve (50) fitted into said non-threaded cylindrical bore (58) allowing the non-threaded portion (56) of the connecting sleeve (50) to slide substantially in said non-threaded cylindrical bore (58), without allowing leakage of pressurized melt flowing through the melt channel (72).

6. The injection molding apparatus as claimed in claim 5, wherein said unthreaded cylindrical portion (38, 56) of each coupling sleeve (30, 50) has a predetermined outside diameter, and each unthreaded bore (48, 58) of the linearly aligned melt channel (72) has a predetermined inside diameter, said predetermined outside diameter being smaller than said predetermined inside diameter just enough to enable said unthreaded cylindrical portion (38, 56) of the coupling sleeve (30, 50) to fit into said unthreaded cylindrical bore (48, 58).

7. An injection molding apparatus as claimed in claim 6, wherein said predetermined outer diameter dimension is sufficiently close to said predetermined inner diameter to form a sealed engagement to prevent excess molten plastic from escaping therebetween.

8. Injection molding device according to claim 7, wherein the unthreaded cylindrical portion (38, 56) of the connecting sleeve (30, 50) is made of a material having a higher coefficient of expansion than the material surrounding the second cylindrical opening.

9. An injection molding apparatus as claimed in claim 3, wherein a pair of heated nozzle manifolds (10) are mounted on opposite sides of each connecting manifold (14), and the positioning means is a positioning ring (98) located between the mold (16) and each nozzle manifold (10) for positioning each nozzle manifold (10) relative to the mold (16).

10. Injection molding apparatus as claimed in claim 9, wherein each retaining ring (98) is aligned linearly with the center of the corresponding nozzle manifold (10).

11. An injection molding apparatus as claimed in claim 3, wherein the positioning means includes a positioning ring (106) located between the mold (16) and each of the connecting manifolds (14) for positioning each of the connecting manifolds (14) relative to the mold (16), the positioning means further including a slidable positioning device extending between the mold (16) and each of the nozzle manifolds (10), each of the other connecting sleeves (50) positioning a corresponding one of the nozzle manifolds (10) relative to the connecting manifold (14) in a first direction along the central axis (32) and allowing movement in a second direction substantially perpendicular to the first direction to compensate for thermal expansion and contraction of the one of the nozzle manifolds (10) and the connecting manifold (14), the slidable positioning device positioning each of the nozzle manifolds (10) relative to the mold (16) in the second direction, while allowing movement of each nozzle manifold (10) relative to the mold (10) in a first direction, the connecting sleeve (50) and the slidable positioning device, therefore, allow sufficient movement in both the first and second directions to accommodate thermal expansion and contraction of the heated manifold (10) relative to the cooled mold (16).

12. Injection molding apparatus as claimed in claim 11, wherein each positioning ring (106) is aligned linearly with the center of the corresponding connecting manifold (14).

13. Injection molding apparatus as claimed in claim 12, wherein a pair of heated nozzle manifolds (10) are provided on opposite sides of each connecting manifold (14).

14. Injection molding apparatus as claimed in claim 12, wherein two pairs of heated nozzle manifolds (10) are provided on opposite sides of each connecting manifold (14).

15. Injection molding apparatus as claimed in claim 11, wherein each positioning device has an elongated positioning element extending in the first direction, the positioning element being slidable relative to at least one of the mold (16) and said each nozzle manifold (10).

16. Injection molding apparatus as claimed in claim 15, wherein the positioning element extends in line with the center of each nozzle manifold (10).

17. Injection molding apparatus as claimed in claim 16, wherein the positioning element is a positioning pin (108).

18. A multi-manifold molding system for an injection molding apparatus as claimed in claim 1, comprising a central manifold (12), a pair of connecting manifolds (14) connected to said central manifold (12) by connecting sleeves (30), and a pair of nozzle manifolds (10) connected to said connecting manifolds (14) by connecting sleeves (50), wherein:

the nozzle manifold (10) includes at least two injection nozzles and the connecting sleeve is fixedly connected to the connecting manifold (14) by a fastening portion so that due to thermal expansion of the connecting manifold (14) they move with the connecting manifold (14) to further seal melt channels between the connecting manifold (14) and the central manifold (12) and between the connecting manifold (14) and the nozzle manifold (10), wherein branches of a melt channel (72) of the nozzle manifold (10) slide into direct linear alignment with melt bores (80) through the nozzles.