CN105665722B - The twin-jet nozzle that freely lands mixes powder aerosolization water cooling and coagulates Metal Substrate aluminium oxide magnetic abrasive preparation method soon - Google Patents

Abstract

The preparation method of free-fall double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive is characterized in that: the hard abrasive of the magnetic abrasive is made of alumina powder, and the metal-based materials are four elements: iron, silicon, aluminum and copper Composed of alloys; the nozzle adopts upper and lower double-layer free-fall nozzles, the upper free-fall nozzle is a low-pressure powder mixing jet nozzle, and the lower free-fall nozzle is a high-pressure air flow nozzle; the cooling method is water cooling, by adjusting the water level of the cooling water in the atomization water cooling chamber , control the cooling rate of the metal droplets containing alumina abrasives, thereby forming a magnetic abrasive in which the alumina abrasives are distributed on the surface of the magnetic abrasive metal matrix; the powder feeding and mixing adopts a screw feeding mixer to realize the precise control of the flow of alumina abrasives . The metal-based alumina magnetic abrasive prepared by the invention has firm combination of alumina and a metal matrix, high magnetic grinding performance, program-controlled production process, stable product performance, and is suitable for large-scale production.

Description

Free-fall dual-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive Preparation

technical field

The invention provides a method for preparing a free-fall double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive, which belongs to the technical field of composite material preparation.

Background technique

From the perspective of material science, magnetic abrasive is a composite material, that is, an iron-based reinforced composite material, which is mainly composed of a ferromagnetic phase and an abrasive grain phase. The ferromagnetic phase requires good magnetic permeability and electrical conductivity, and the commonly used materials are pure iron powder or iron-based alloy powder. Abrasive phase is a kind of granular substance with high hardness, strength and stability, which has the functions of grinding, grinding and polishing. The commonly used materials are corundum, alumina, silicon nitride, silicon carbide, etc. The chemical composition, ratio and structure of the magnetic abrasive are the key factors determining the performance of the magnetic abrasive, which requires a close combination between the ferromagnetic phase and the abrasive grain phase, and an appropriate particle size, as well as a suitable Preparation.

There are many methods for preparing magnetic abrasives in the prior art, which can be roughly divided into three categories: mechanical mixing method, composite material method, and reaction casting method.

The mechanical mixing method is a method in which ferromagnetic powder, abrasive powder and grinding liquid are uniformly mixed at room temperature in a certain proportion, and the grinding process is carried out directly. It is usually made by mixing ferromagnetic powder of a certain particle size with abrasive powder such as Al2O3, SiC, Cr2O3, TiC, etc., and then adding binders such as oleic acid, polyethylene glycol, silica gel, etc. This method can produce a variety of magnetic abrasives, the preparation process is simple, and the cost is low. However, during the grinding period, the abrasive particles and the magnetic powder are relatively easy to separate and scatter, and the grinding efficiency is low, which limits the scope of application.

From the perspective of materials science, magnetic abrasive is a kind of composite material powder, that is, iron-based particle-reinforced composite material powder. It is a multi-phase material made of two or more materials through a certain composite process, and its performance is obviously better than that of the raw material in certain aspects. With the development of composite materials, the preparation technology of magnetic abrasives has also been developed accordingly. There are many kinds of preparation processes, mainly including sintering method, bonding method, composite coating method and so on.

The sintering method is currently the most commonly used method for the preparation of magnetic abrasives. In Japan, this method has been successfully applied in industrial production. According to the specific sintering conditions, it is divided into atmospheric pressure sintering, hot pressing sintering, laser sintering, microwave sintering and so on. The processing performance and service life of magnetic abrasives largely depend on the bonding strength of the abrasive grain phase and the ferromagnetic phase. The magnetic abrasive prepared by sintering method has a considerable part of the abrasive phase separated from the ferromagnetic phase during the mechanical crushing and sieving process, resulting in a decrease in the bonding strength and durability of the ferromagnetic phase and abrasive grains.

The bonding method is divided into inorganic bonding and organic bonding according to the different binders selected. It is to bond a certain proportion of uniformly mixed ferromagnetic powder and abrasive powder with a binder, then solidify, and then mechanically pulverize , screening, and make magnetic abrasive powders of different particle sizes. The magnetic abrasive prepared by the bonding method does not need to be pressed into blocks in advance, and does not need equipment such as an electric furnace containing an inert gas, a laser machine, etc. Therefore, the method is simple in process, easy to implement, and low in cost. However, the structure is loose, the bonding is poor, the density is low, the thermal stability is poor, the abrasive grain phase is easy to fall off, and the service life is short. And when the temperature is high, the bonded magnetic abrasive makes the processed surface dark black, and the original processed surface is easily polluted and damaged.

The composite coating method uses the method of composite electroplating or composite electroless plating to uniformly mix certain abrasive particles into the metal coating, and the special coating formed is the composite coating. Applying the composite coating process to the preparation technology of magnetic abrasives, after years of development, the composite coating method has been successfully applied in many scientific and technological fields, but the production cost is high, mass production is difficult to achieve, and improper treatment of the plating solution will also cause environmental pollution.

The principle of the reaction casting method is to synthesize one or several high-strength ceramic reinforcement phases in situ in the body through the chemical reaction between elements and elements or elements and compounds under certain conditions. After alloying, it is melted by heating and blown into powder under high pressure. The current problem of the reaction casting method is that the content of ceramic hard abrasive in the magnetic abrasive is low and the grain size of the hard abrasive is difficult to control.

The plasma spraying method is to pre-mix the iron-based powder and hard abrasive particles in a certain proportion and place them in the raw material powder supply chamber of the plasma spraying equipment. In the vacuum chamber of the plasma spray device, a high-frequency discharge voltage is applied between the two electrodes, and the plasma spray flame is generated by the plasma generator. The mixed raw material powder is continuously sprayed into the plasma flame at the same time. The temperature of the plasma flame can reach a high temperature of 5000~10000 °C, and the raw material powder is continuously melted into micro-droplets, and then cooled and solidified into spherical magnetic abrasive particles. Although this method solves the problem of poor compatibility between the iron-based phase and the abrasive phase, the magnetic abrasive prepared by this method is subjected to the high temperature of the plasma flame, and the sharp cutting edge of the abrasive grain phase is passivated, resulting in a significant reduction in grinding efficiency. , and its grinding ability is even inferior to magnetic abrasives prepared by other simple methods.

At present, the main problems of magnetic grinding and finishing are the low service life of magnetic abrasives, poor metal cutting ability, difficult preparation and high cost. The backwardness of the research on magnetic abrasive preparation technology has become a bottleneck problem restricting the further popularization and application of magnetic particle grinding and finishing technology (such as free-form surface grinding and finishing). For this reason, the inventors invented the "preparation method of gas atomization fast setting magnetic abrasive" (ZL201010206408.6), "gas atomization fast setting magnetic abrasive preparation equipment" (ZL201110156753.8), "gas atomization fast setting method preparation Structural and Morphological Control Method of Magnetic Abrasives" (ZL201110156741.5), and achieved good results in practice, but there are still some key technical problems that affect the quality of magnetic abrasive preparation, such as:

(1) Jet nozzle problem: due to the use of a single nozzle, the jet velocity of the gas-solid two-phase flow is high, resulting in rapid erosion and wear of the jet nozzle, and it fails in a very short time, and the preparation function of the magnetic abrasive is lost; at the same time, it is also due to the A single nozzle is used, and the hard abrasive and high-pressure gas are used as the atomizing medium. If the jet velocity of the gas-solid two-phase flow is low, the atomization effect will be poor and the magnetic abrasive particles will be coarse. However, if the jet velocity of the gas-solid two-phase flow is high, although the magnetic Although the particle size of the abrasive is reduced, the hard abrasive will splash out again after entering the molten metal, resulting in a sharp decrease in the hard abrasive contained in the magnetic abrasive metal matrix, and the grinding performance of the magnetic abrasive is significantly reduced.

(2) Erosion and wear of the molten metal guide tube: the tightly coupled atomization method is adopted. Before the molten metal flow is atomized, the gas-solid two-phase flow is first sprayed onto the lower end of the molten metal guide tube, causing The lower end of the molten metal diversion pipe produces severe erosion and wear in a short period of time, and causes the danger of back spraying of molten metal and high-pressure gas along the molten metal diversion pipe.

(3) Condensation rate control of liquid magnetic abrasive droplets: Since the problem of accurate control of condensation rate of molten magnetic abrasive droplets has not been solved, the prepared magnetic abrasives have been unstable in depth distribution of hard abrasives in the metal matrix. Affect the grinding ability of magnetic abrasives, and the scrap rate is high.

(4) The content control of hard abrasives in magnetic abrasives: due to the difficulty of accurately controlling the flow rate of hard abrasives in gas-solid two-phase flow in the pneumatic powder mixing device, the content of hard abrasives in magnetic abrasives is unstable and the magnetic abrasives Performance is unstable.

(5) The problem of erosion and wear of the molten metal guide tube: using the tightly coupled atomization method, before atomizing the molten metal flow, the gas-solid two-phase flow is first sprayed onto the lower end of the molten metal guide tube, causing The lower end of the molten metal diversion pipe produces severe erosion and wear in a short period of time, and causes the danger of back spraying of molten metal and high-pressure gas along the molten metal diversion pipe.

Contents of the invention

The object of the present invention is to provide a magnetic abrasive preparation method which can overcome the above defects, has simple manufacturing process, ideal bonding strength and grinding efficiency of the prepared magnetic abrasive, and is conducive to realizing mass production. Its technical solution is:

A method for preparing a free-fall double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive, characterized in that: the hard abrasive of the magnetic abrasive is made of alumina powder, and the metal-based material is iron, silicon, aluminum, copper four The alloy composed of two elements; the nozzle adopts upper and lower double-layer free-fall nozzles, and the upper free-fall nozzle is a low-pressure powder-mixing jet nozzle, which sprays out a low-pressure inert gas mixed-powder jet containing alumina abrasives, which is used to break through the metal in the downstream process. The surface tension of the liquid flow injects alumina abrasives into the metal liquid flow, but does not atomize the metal liquid flow; the lower free-fall nozzle is a high-pressure air flow nozzle, which ejects a high-speed inert air flow, which is used to The metal liquid flow of the abrasive is atomized to make it atomized into metal droplets mixed with alumina abrasive; the cooling method is water cooling: by adjusting the water level of the cooling water in the atomization water cooling chamber, the metal liquid containing alumina abrasive is controlled The flight distance of the droplets in the atomized water-cooling chamber, and then control the cooling rate of the metal droplets containing alumina abrasives, thereby forming a magnetic abrasive in which the alumina abrasives are distributed on the surface of the magnetic abrasive metal matrix; the mixing powder adopts spiral mixing The powder device realizes the precise and convenient control of the flow rate of alumina abrasive in the low-pressure inert gas mixed powder jet, which makes the content of alumina abrasive in the magnetic abrasive stable.

In order to achieve the purpose of the invention, the preparation method of the free-fall double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive, the preparation of the metal-based alumina magnetic abrasive comprises the following steps:

1) Fill the aluminum oxide abrasive tank (26) with a set amount of alumina abrasive and tighten the aluminum oxide abrasive tank cover (25);

2) Metal-based materials iron, silicon, aluminum, and copper are added to the electric furnace according to the specified ratio, heated to the molten state and reached the specified superheat;

3) Open the cold water valve (6) and adjust the water level of the cooling water (37) in the atomizing water cooling chamber (36) to a specified height;

4) Turn on the blower (12) and suck the gas in the atomized water-cooling chamber (36);

5) Open the air valve 1 (16) connected between the high-pressure nitrogen cylinder 1 (13) and the high-pressure air flow nozzle (34) and adjust to the specified air flow pressure, and fill the atomizing water cooling chamber (36) with nitrogen, so that the The metal gas atomization carried out is completely placed in a nitrogen atmosphere;

6) Open the air valve 2 (15) connected between the high-pressure nitrogen cylinder 2 (14) and the low-pressure powder mixing jet nozzle (33) and adjust to the specified air flow pressure;

7) Start the screw conveying device (24) and control the powder feeding speed according to the process requirements;

8) Pour the molten metal in the electric furnace (30) evenly into the heat preservation crucible (31), and keep the specified liquid level until the molten metal in the electric furnace (30) is exhausted;

9) After all the molten metal in the heat preservation crucible (31) has flowed out, close the screw conveying device (24), air valve 1 (16), air valve 2 (15), and blower (12) in order;

10) Close the gate valve (5) to close the atomization water cooling chamber (36) and the magnetic abrasive tank (39), open the drain valve (1) to allow the water in the magnetic abrasive tank (39) to flow out, and open the pressure filter air valve ( 4) Make the high-pressure gas enter the inner cavity of the magnetic abrasive tank (39), the filter screen (2) blocks the magnetic abrasive in the upper cavity of the magnetic abrasive tank (39), and the water in it is forced out;

11) Remove the magnetic abrasive pot (39), take out the magnetic abrasive in it, vacuum dry, sieve and package, so as to obtain magnetic abrasives of different particle sizes.

Compared with the prior art, the present invention has the following advantages:

1. Due to the use of high and low pressure double-layer free-fall nozzles, the function of the upper free-fall nozzle is to break through the surface tension of the metal liquid flow in the downstream process and inject alumina abrasive into the metal liquid flow, but not to atomize the metal liquid flow. The function of the upper free-falling nozzle is to atomize the metal liquid flow mixed with alumina abrasive, so that it is atomized into metal droplets mixed with alumina abrasive. The atomization is effectively separated, avoiding the splashing and waste of alumina abrasive caused by single nozzle atomization, and the problems of uneven magnetic abrasive particle size and uneven alumina abrasive content, ensuring the uniformity of magnetic abrasive particle size and magnetic abrasive alumina abrasive content and controllability.

2. Since the upper free-falling nozzle does not atomize the metal liquid flow, the air pressure of the sprayed aluminum oxide abrasive is low, which effectively solves the problem of erosion and wear of the nozzle containing aluminum oxide abrasive.

3. Due to the use of free-fall nozzles, the metal liquid guide pipe is located above the two nozzles, and the airflow ejected from the two nozzles does not directly act on the lower end of the metal guide pipe, which avoids the tight coupling nozzle containing hard The high-speed air flow of the abrasive material severely erodes and wears the metal guide tube, and at the same time avoids the problem of backflow and upspray of the metal liquid caused by the erosion and wear of the metal liquid flow guide.

4. Adding metal copper to the metal-based material effectively improves the bonding strength between the metal-based material and the alumina abrasive particles in the magnetic abrasive.

5. The cooling method of water-cooling and quick-condensation is adopted, which solves the problem of dissociation of alumina abrasive particles from the metal matrix and the control of depth distribution in the magnetic abrasive, and can control the distribution of alumina abrasive in the superficial layer of the magnetic abrasive, making the preparation The magnetic abrasive material has high magnetic permeability and strong grinding ability. At the same time, it greatly reduces the flying distance of the powder-mixed metal droplets, reduces the overall height of the free-fall atomizing water cooling chamber and equipment, and reduces the cost.

6. The screw feeding and mixing device is used to solve the problem that the powder feeding and mixing device is difficult to accurately control the flow rate of hard abrasives in the gas-solid two-phase flow, so that the content of hard abrasives in the magnetic abrasive is stable.

7. The rapid cooling method of water cooling and quick solidification and the addition of silicon, aluminum, and copper in the metal-based material increase the bonding strength between the metal-based material and the alumina abrasive.

8. The process of preparing magnetic abrasives in the present invention can be automated, with stable and reliable performance, and is suitable for large-scale production of high-performance metal-based alumina magnetic abrasives.

Description of drawings

Fig. 1 is a schematic diagram of the free-fall double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive preparation equipment adopted in the present invention, wherein: 1-water release valve, 2-filter screen, 3-magnetic abrasive material, 4-press filter Air valve, 5-gate valve, 6-cold water valve, 7-water seal tank, 8-water seal water, 9-water inlet valve, 10-inlet valve, 11-intake pipe, 12-drain pipe, 13-high pressure Nitrogen cylinder 1, 14-high pressure nitrogen cylinder 2, 15-air valve 2, 16-air valve 1, 17-screw powder mixer, 18-air pipe 3, 19-air pipe 1, 20-air pressure gauge 1, 21-air pressure Table 2, 22-air pipe 2, 23-air pipe 4, 24-screw conveying device, 25-alumina abrasive tank cover, 26-alumina abrasive tank, 27-hard abrasive, 28-powder mixing air pipe, 29-molten metal , 30-electric furnace, 31-insulation crucible, 32-metal liquid guide tube, 33-low-pressure powder mixing jet nozzle, 34-high-pressure air nozzle, 35-water level gauge, 36-atomizing water cooling chamber, 37-cooling water, 38 - shell of atomizing water cooling chamber, 39 - magnetic abrasive tank, 40 - filtered water, 41 - double nozzle atomizing water cooling device, 42 - exhaust dust removal device, 43 - blower, 44 - gas station.

Detailed ways

Example 1

The preparation of metal-based alumina magnetic abrasive comprises the following steps:

1) Fill the aluminum oxide abrasive tank (26) with a set amount of alumina abrasive and tighten the aluminum oxide abrasive tank cover (25);

2) The metal-based material is iron:silicon:aluminum:copper=83%:9%:6%:2% by weight, put into an electric furnace and heated to a molten state and reach the specified superheat;

3) Open the cold water valve (6) and adjust the water level of the cooling water (37) in the atomizing water cooling chamber (36) to a specified height;

4) Turn on the blower (12) and suck the gas in the atomized water-cooling chamber (36);

5) Open the air valve 1 (16) connected between the high-pressure nitrogen cylinder 1 (13) and the high-pressure air flow nozzle (34) and adjust to the specified air flow pressure, and fill the atomizing water cooling chamber (36) with nitrogen, so that the The metal gas atomization carried out is completely placed in a nitrogen atmosphere;

6) Open the air valve 2 (15) connected between the high-pressure nitrogen cylinder 2 (14) and the low-pressure powder mixing jet nozzle (33) and adjust to the specified air flow pressure;

7) Start the screw conveying device (24) and control the powder feeding speed according to the process requirements;

8) Pour the molten metal in the electric furnace (30) evenly into the heat preservation crucible (31), and keep the specified liquid level until the molten metal in the electric furnace (30) is exhausted;

9) After all the molten metal in the heat preservation crucible (31) has flowed out, close the screw conveying device (24), air valve 1 (16), air valve 2 (15), and blower (12) in sequence;

10) Close the gate valve (5) to close the atomization water cooling chamber (36) and the magnetic abrasive tank (39), open the drain valve (1) to allow the water in the magnetic abrasive tank (39) to flow out, and open the pressure filter air valve ( 4) Make the high-pressure gas enter the inner cavity of the magnetic abrasive tank (39), the filter screen (2) blocks the magnetic abrasive in the upper cavity of the magnetic abrasive tank (39), and the water in it is forced out;

11) Remove the magnetic abrasive pot (39), take out the magnetic abrasive in it, vacuum dry, sieve and package, so as to obtain magnetic abrasives of different particle sizes.

Claims (2)

1. The preparation method of free-fall double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive is characterized in that: the hard abrasive of the magnetic abrasive is made of alumina powder, and the metal base material is iron, silicon, aluminum, copper four The alloy composed of two elements; the nozzle adopts upper and lower double-layer free-fall nozzles, and the upper free-fall nozzle is a low-pressure powder-mixing jet nozzle, which sprays out a low-pressure inert gas mixed-powder jet containing alumina abrasives, which is used to break through the metal in the downstream process. The surface tension of the liquid flow injects alumina abrasives into the metal liquid flow, but does not atomize the metal liquid flow; the lower free-fall nozzle is a high-pressure air flow nozzle, which ejects a high-speed inert air flow, which is used to The metal liquid flow of the abrasive is atomized to make it atomized into metal droplets mixed with alumina abrasive; the cooling method is water cooling: by adjusting the water level of the cooling water in the atomization water cooling chamber, the metal liquid containing alumina abrasive is controlled The flight distance of the droplets in the atomized water cooling chamber, and then control the cooling speed of the metal droplets containing alumina abrasives, thereby forming a magnetic abrasive in which the alumina abrasives are distributed on the surface of the magnetic abrasive metal matrix; the mixing powder is mixed by a screw The device makes the content of alumina abrasive in the magnetic abrasive stable. 2. The method for preparing the free-falling double-nozzle mixed powder gas atomization water-cooled fast-setting metal-based alumina magnetic abrasive according to claim 1, wherein the preparation steps of the metal-based alumina magnetic abrasive are as follows: 1) Fill the aluminum oxide abrasive tank (26) with a set amount of alumina abrasive and tighten the aluminum oxide abrasive tank cover (25); 2) Metal-based materials iron, silicon, aluminum, and copper are added to the electric furnace according to the specified ratio, heated to the molten state and reached the specified superheat; 3) Open the cold water valve (6) and adjust the water level of the cooling water (37) in the atomizing water cooling chamber (36) to a specified height; 4) Turn on the blower (12) and suck the gas in the atomized water-cooling chamber (36); 5) Open the air valve 1 (16) connected between the high-pressure nitrogen cylinder 1 (13) and the high-pressure air flow nozzle (34) and adjust to the specified air flow pressure, and fill the atomizing water cooling chamber (36) with nitrogen, so that the The metal gas atomization carried out is completely placed in a nitrogen atmosphere; 6) Open the air valve 2 (15) connected between the high-pressure nitrogen cylinder 2 (14) and the low-pressure powder mixing jet nozzle (33) and adjust to the specified air flow pressure; 7) Start the screw conveying device (24) and control the powder feeding speed according to the process requirements; 8) Pour the molten metal in the electric furnace (30) evenly into the heat preservation crucible (31), and keep the specified liquid level until the molten metal in the electric furnace (30) is exhausted; 9) After all the molten metal in the heat preservation crucible (31) has flowed out, close the screw conveying device (24), air valve 1 (16), air valve 2 (15), and blower (12) in sequence; 10) Close the gate valve (5) to close the atomization water cooling chamber (36) and the magnetic abrasive tank (39), open the drain valve (1) to allow the water in the magnetic abrasive tank (39) to flow out, and open the pressure filter air valve ( 4) Make the high-pressure gas enter the inner cavity of the magnetic abrasive tank (39), the filter screen (2) blocks the magnetic abrasive in the upper cavity of the magnetic abrasive tank (39), and the water in it is forced out; 11) Remove the magnetic abrasive tank (39), take out the magnetic abrasive in it, vacuum dry, sieve and pack, so as to obtain magnetic abrasives of different particle sizes; 12) In the above process, control the temperature of the molten metal, the powder feeding speed of the screw conveying device (24), the injection pressure of the low-pressure powder mixing jet nozzle (33) and the high-pressure air nozzle (34), and the cooling water (37) according to the process requirements. ) in the water level in the atomizing water-cooling chamber (36), high-quality magnetic abrasives can be produced.