WO2022139186A1 - Method for preparing feedstock for powder injection molding - Google Patents

Abstract

The present invention relates to a method for preparing feedstock for powder-injection molding, the method comprising: a first step for primary mixing of powder and bonding agent mixture by means of a single or twin extruder; and a second step for secondary mixing, in a shear roll mixer, of the mixture that has passed through primary mixing.

Description

Manufacturing method of feedstock for powder injection molding

The present invention relates to a method for manufacturing a feedstock for powder injection molding, and more particularly, to a method for manufacturing a feedstock for powder injection molding with improved dispersibility by going through a second kneading step.

Powder injection molding refers to a technology for manufacturing metal products or ceramics products through injection molding by mixing powders such as metals or ceramics with a binder made of organic materials, removing the binder, and finally sintering.

This powder injection molding method is a fusion of powder metallurgy technology and plastic injection molding technology, and it is a technology that can be applied when manufacturing complex and fine tolerance parts. Also, depending on the material, it can be classified into metal injection molding (MIM) and ceramic injection molding (CIM).

Such powder injection molding (PIM) includes a step of preparing a feedstock by kneading metal or ceramic powder and a binder, injection molding the feedstock, a degreasing step of removing the binder, and a sintering step.

On the other hand, in the feedstock, metal or ceramic powder usually occupies 85 wt% or more, and the remaining amount is included as a binder. Although the composition of the binder contained in the binder and the particle size of the powder used are important, it can be said that the preparation of a feedstock in which the metal or ceramic powder and the binder are uniformly dispersed in the kneading step is the most important.

As shown in FIG. 1, the method used for feedstock production so far is first kneaded in a kneader, a ball mill, or a Bambari mixer, and pulverized in a grinder using the process of 1). Next, there is a method of manufacturing by second kneading using a single screw extruder or a twin screw extruder, and then cutting.

Alternatively, after primary kneading as described above, there is also a method of using the process of 2) in which the grinding process is omitted and the second kneading process is performed immediately using a single screw extruder or a twin screw extruder.

Alternatively, the process of 3) in which the feedstock is prepared by primary kneading and grinding only as described above may be used.

However, these methods have shortcomings in that it takes 30 minutes or 3 hours in the first kneading process, so it takes a long time to prepare the feedstock, or because it is a batch-type process, there is a lot of manpower input.

As another method, as shown in FIG. 2 , there is a method of manufacturing a feedstock by passing through a single screw extruder or a twin screw extruder and then cutting with a cutter. The method can produce feedstock in a continuous process, but in the case of a single screw extruder, the kneading function is insufficient, and in the case of a twin screw extruder, kneading is possible, but the residence time is too short, so there is a problem of insufficient kneading.

As a result, when the feedstock is manufactured in a continuous process using the conventional method, there is a problem in that the dispersion between the powder and the binder is not uniform. Therefore, there is a high possibility of defects occurring in injection, degreasing, and sintering processes, which are processes after feedstock manufacturing.

As a patent related to such a method for manufacturing a feedstock, for example, in Korean Patent Registration No. 10-0660653, a step of preparing a nano-sized Fe-Ni alloy metal powder having a Ni content of 2 wt% to 80 wt%, a soluble organic binder A feedstock for molding nano-sized metal powder comprising mixing 2 wt% to 50 wt% of a binder solution including a solvent and a metal powder, and wet milling the mixture so that aggregates of the metal powder are uniformly formed method is presented.

In the above patent, since the feedstock for molding of nano-sized metal powder can maintain a uniform microstructure inside the molded body, a fully densified thread-like nano-structured product can be manufactured without deformation such as distortion or cracking even after sintering. For simplification and cost reduction, the mixing step and wet milling step are not exposed to external air, and are characterized in that they are carried out in an inert gas or protective gas atmosphere.

In addition, in Korea Patent No. 10-0707855, 1) a small amount of alkali metal ions are contained in a container containing either water or an organic solvent, and at the same time, two or more metal electrodes are spaced apart in the container and time passes A first step of producing metal microparticles with a size of 100 nm or less by applying an electric current whose size and direction change periodically according to the , powder injection molding comprising a third step of dissolving the added organic binder and uniformly mixing it with the fine particles, and a fourth step of pulverizing the organic binder and fine particle mixture in the container after removing the water or organic solvent inside the container A method for manufacturing a metal microparticle feedstock is presented.

It is an object of the present invention to provide a method for manufacturing a feedstock for powder injection molding in which a binder and a powder constituting a feedstock serving as a source of powder injection molding can be effectively kneaded.

The method for producing a feedstock for powder injection molding according to an embodiment of the present invention includes a first step of first kneading a mixture of powder and a binder through a single screw or twin screw extruder, and a shear roll mixer ( and a second step of secondary kneading in a shear roll mixer).

The single screw extruder may have a screw diameter of 20 mm to 70 mm, and a length/diameter (L/D) of 30 to 40.

The twin screw extruder may rotate the screw in the same direction or in the opposite direction.

The twin screw extruder may have a screw diameter of 20 mm to 70 mm, and a length/diameter (L/D) of 30 to 40.

The shear roll mixer has two rollers rotating in different directions, and the roller diameter may be 80 mm to 350 mm.

The distance between the two rollers of the shear roll mixer may be 20 mm to 60 mm.

A single screw extruder, a twin screw extruder, and a shear roll mixer have a knife attached to the end thereof, and the mixture passing therethrough can be cut into pellets.

According to the manufacturing method of the present invention, the process of kneading the powder and the binder can be continuously performed, so that the feedstock manufacturing time can be reduced. In addition, it is possible to prepare a uniformly dispersed feedstock compared to a feedstock manufactured by a conventional process, thereby having the effect of preventing the possibility of defects in the accompanying injection, degreasing, and sintering processes in advance.

1 and 2 are flowcharts illustrating a process for manufacturing a feedstock according to a conventional method.

3 is a flowchart illustrating a process for manufacturing a feedstock according to an embodiment of the present invention.

The present invention relates to a method of manufacturing a feedstock for powder injection molding, which will be described in detail below with reference to FIG. 3 .

The method for producing a feedstock for powder injection molding according to the present invention includes a first step of first kneading a mixture of powder and a binder through a single screw or twin screw extruder, and a shear roll mixer for the first kneaded mixture Including a second step of secondary kneading in.

That is, in the first step, the powder and binder are kneaded with a single screw or twin screw extruder, and then the feedstock that is not uniformly dispersed is produced uniformly dispersed feedstock in the second step using a shear roll mixer capable of continuous processing. will be.

In the present invention, 'powder injection molding' means used for injection molding of powders such as metal or ceramic.

For example, the powder may be a metal or ceramic powder.

The metal powder may be, for example, a powder of stainless steel, aluminum, iron, in particular iron carbonyl powder, chromium, cobalt, copper, nickel, silicon, titanium and tungsten. In addition, the metal powder may be a powdered metal alloy, for example, high-alloy steel or low-alloy steel and metal alloy based on aluminum, iron, titanium, copper, nickel, tungsten or cobalt. These include powders of already finished alloys, for example superalloys such as IN713C, GMR 235 and IN 100, and alloys known from magnet technology using the main constituents Nd-Fe-B and Sm-Co, and individual alloy constituents. It may contain both powder mixtures of Furthermore, the metal powder may be a metal carbonyl powder, a metal oxide, a metal carbide, and also a metal nitride.

The ceramic powder may be, for example, an oxide ceramic powder such as Al ₂ O ₃ , ZrO ₂ , or Y ₂ O ₃ ; non-oxide ceramic powders such as SiC, or Si ₃ N ₄ ; further complex oxide powders such as NiZnFe ₂ O ₄ ; or an inorganic color pigment such as CoAl ₂ O ₄ .

For example, the average particle size of the powder may be 1 μm to 20 μm.

For example, the binder may include one or more organic materials commonly used in feedstock for powder injection molding. For example, the binder may include polyolefin (such as polyethylene or polypropylene), polyoxymethylene, polyvinyl alcohol, stearic acid, waxes, and the like.

For example, the binder may include 10% to 50% by weight of the high-viscosity polyoxymethylene polymer and 50% to 90% by weight of the low-viscosity polyoxymethylene polymer.

When the content of the high-viscosity polyoxymethylene polymer is less than 10% by weight, it is impossible to control the rate of decomposition in the acid in gaseous state, which may result in poor degreasing. If it exceeds 50% by weight, the viscosity increases and injection molding may be difficult. .

The high-viscosity polyoxymethylene polymer has a melt flow index of 1 g/10 min to 10 g/10 min when measured at a temperature of 190 ° C and a load of 2.16 kg in accordance with ASTM D1238, and the low-viscosity polyoxymethylene polymer is in accordance with ASTM D1238 Therefore, the melt flow index may be 40 g/10min to 300 g/10min when measured with a load of 2.16 kg at a temperature of 190 °C.

If the melt flow index of the high-viscosity polyoxymethylene polymer is less than 1 g/10 min, the injection speed should be basically increased when injecting small and complex shapes. It can be difficult to do. Therefore, injection failure may occur, and the kneading with the powder is not uniform, and the product may collapse in the degreasing and sintering process.

In addition, if the melt flow index of the high-viscosity polyoxymethylene polymer exceeds 10 g/10 min, the polymer that can serve as a desired support during degreasing may be decomposed and the product may collapse in the degreasing and sintering process.

If the melt flow index of the low-viscosity polyoxymethylene polymer is less than 40 g/10min, the overall viscosity of the composition obtained by kneading the high-viscosity and low-viscosity polyoxymethylene is lowered, so a high injection pressure is required. There may be difficulties. In addition, when the melt flow index exceeds 300 g/10min, it is a low molecular weight polymer, so it may be easy to establish injection process conditions, but the product may collapse due to rapid decomposition during degreasing.

The high-viscosity and low-viscosity polyoxymethylene polymers are oxymethylene homopolymers containing oxymethylene-(OCH ₂ )n- groups as repeating units and capped at both ends by ester or ether groups, or in a polymer chain composed of oxymethylene monomer units. It may be an oxymethylene-based copolymer or terpolymer in which oxyalkylene units having 2 to 10 carbon atoms are randomly inserted and both ends of the polymer are blocked by ester or ether groups.

As an example, the feedstock for powder injection molding may contain 20 to 80% by volume of the binder, and 20 to 80% by volume of the powder, based on the total volume.

For example, the feedstock for powder injection molding may further include an additive selected from the group consisting of a lubricant and a dispersant.

The lubricant is distributed so that the powdery inorganic material is uniformly and evenly spaced in the metal powder injection molding binder to improve dimensional stability after sintering, and includes stearic acid, ethylene oxide, diethanolamine, glycerin, Sorbitol (Sorbitol), or behenic acid (Behenic Acid) and the like can be exemplified.

As the dispersant, a dispersing agent commonly used may be used, and stearic acid, Zinc-Stearate, Calcium-Stearate, and the like may be exemplified.

The feedstock for powder injection molding may contain less than 3% by volume of a lubricant and a dispersant, respectively, based on the total volume.

In the first step, a feedstock in the form of primary pellets is prepared by first kneading a mixture of powder and binder using a single screw or twin screw extruder.

The extruder is a device that heats and fluidizes powder and binder in a barrel to form primary pellets through continuous extrusion. As an example, an extruder may include a feeder, a screw carrying the raw material, a barrel surrounding the screw, and a die as an outlet.

The extruder may be divided into a single screw extruder and a twin screw extruder according to the number of screws.

When a single screw extruder is used, the screw diameter may be 20 mm to 70 mm, and the length/diameter (L/D) may be 30 to 40 mm.

If the screw diameter of the single screw extruder is smaller than 20 mm, the mixture of powder and binder entering between the diameters may be too small, which may decrease productivity, and if the screw diameter of the single screw extruder exceeds 70 mm, mass production may be possible. .

In addition, when the length/diameter (L/D) of the uniaxial compressor is 30 to 40, the product can be efficiently produced.

In the case of using a twin-screw compressor in the first step, it is possible to rotate the screw in the same direction or in the opposite direction.

When a twin screw extruder is used, the screw diameter may be 20 mm to 70 mm, and the length/diameter (L/D) may be 30 to 40 mm.

If the screw diameter of the twin-screw extruder is smaller than 20 mm, the mixture of powder and binder that enters between the diameters may be too small, which may decrease productivity, and if the screw diameter of the twin-screw extruder exceeds 70 mm, mass production may be possible .

In addition, when the length/diameter (L/D) of the uniaxial compressor is 30 to 40, the product can be efficiently produced.

Both the single-screw compressor and the twin-screw compressor have rotary knives attached to their ends, so that the mixture that has passed through the compressor is cut into pellets and can be manufactured as a feedstock.

In addition, the primary kneading conditions may control the kneading temperature, screw rotation speed, kneading time, etc. according to the type or additive of the binder used.

In the second step, the first kneaded mixture is second kneaded in a shear roll mixer.

The shear roll mixer includes two rollers rotating in opposite directions, and for example, by rotating the two rollers at different rotational speeds, in the gap between the two rollers according to the roller running direction A shear force may be applied to the mixture.

The diameter of the rollers of the shear roll mixer may be 80 mm to 350 mm. If the roller diameter of the shear roll mixer is less than 80 mm, the mixture of powder and binder between the two rollers may be too small, which may decrease productivity. .

The distance between the two rollers of the shear roll mixer may be 20 mm to 60 mm. If the gap between the two rollers of the shear roll mixer is less than 20 mm, the amount of feed stock fed may decrease, and productivity may decrease. If it is exceeded, the amount of feedstock to be fed increases as well as shear force received by the feedstock is lowered, so dispersion may not be effective.

In addition, since a knife is provided at the end of the shear roll mixer, it can be automatically cut into pellets without the need for a separate cutting facility.

As described in detail, the present invention can reduce the feedstock manufacturing time by continuously performing the process of kneading the powder and the binder in one process, and prepare a uniformly dispersed feedstock compared to the feedstock manufactured in the conventional process This can prevent the possibility of defects occurring in the accompanying injection, degreasing, and sintering processes in advance.

Hereinafter, the present invention will be described with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

[Preparation Example 1: Preparation of feedstock for powder injection molding]

Prepare 60 vol % of STS316L metal powder and 40 vol % of a binder containing high-viscosity and low-viscosity polyoxymethylene and other dispersants.

(Example 1)

The prepared metal powder and binder are first kneaded with a single screw extruder, and then kneaded with a shear roll mixer secondarily.

(Example 2)

The prepared metal powder and binder are first kneaded with a twin-screw extruder, and then kneaded second with a shear roll mixer.

(Comparative Example 1)

The prepared metal powder and binder are first kneaded with a kneader and then pulverized.

(Comparative Example 2)

The prepared metal powder and binder are first kneaded with a kneader, then pulverized, and then kneaded secondarily with a single screw extruder.

(Comparative Example 3)

The prepared metal powder and binder are first kneaded with a kneader, then pulverized, and then kneaded secondarily with a twin screw extruder.

(Comparative Example 4)

The prepared metal powder and binder are first kneaded with a twin-screw extruder.

(Comparative Example 5)

The prepared metal powder and binder are first kneaded with a Bambari mixer, then pulverized, and then kneaded secondarily with a single screw extruder.

(Comparative Example 6)

The prepared metal powder and binder are first kneaded with a Bambari mixer and then pulverized.

[Experimental Example: Measurement of Physical Properties of Feedstock for Injection Molding of Manufactured Powder]

Using an electric injection machine having a clamping force of 50 Ton, 10 feedstocks prepared in Examples and Comparative Examples are injected into dumbbell-shaped dog bone specimens, respectively. At this time, the injection temperature is 195 °C.

Table 1 shows the results of measuring the flexural strength of the prepared specimens, and the standard deviation and bondability of the flexural strength.

Flexural strength is a three-point flexural strength measurement using Instron equipment, and the section where actual physical properties are measured is cylindrical with a radius of 2.25 mm, the length of the specimen support span is 64 mm, and the test speed is 2.00 mm/ is min.

If the standard deviation of the flexural strength is less than 0.750 MPa, it is judged to be suitable.

	Example 1	Example 2	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5	Comparative Example 6
Flexural strength (average, MPa)	22.439	22.709	21.701	21.785	21.905	21.724	22.001	22.015
standard deviation (MPa)	0.704	0.690	0.882	0.821	0.801	0.874	0.784	0.795
compatibility	O	O	X	X	X	X	X	X

Referring to Table 1, the feedstocks prepared in Examples 1 and 2 have excellent flexural strength compared to the feedstocks prepared in Comparative Examples 1 to 6, and the standard deviation of the flexural strength is less than 0.750 MPa. You can see this excellence.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also presented. It belongs to the scope of the right of the invention.

The present invention relates to a method of manufacturing a feedstock for powder injection molding, and since the process of kneading the powder and the binder can be continuously performed, the effect of reducing the feedstock manufacturing time can be obtained. In addition, it is possible to prepare a uniformly dispersed feedstock compared to a feedstock manufactured by a conventional process, thereby having the effect of preventing the possibility of defects in the accompanying injection, degreasing, and sintering processes in advance.

Claims (7)

1. A first step of first kneading the mixture of powder and binder through a single screw or twin screw extruder, and

   A second step of second kneading the first kneaded mixture in a shear roll mixer

   A method of producing a feedstock for powder injection molding comprising a.
2. The method of claim 1,

   The single screw extruder has a screw diameter of 20 mm to 70 mm, and a length/diameter (L/D) of 30 to 40. A method of manufacturing a feedstock for powder injection molding.
3. The method of claim 1,

   The twin screw extruder is a method of manufacturing a feedstock for powder injection molding in which the rotation method of the screw is in the same direction or in the opposite direction.
4. The method of claim 1,

   The twin screw extruder has a screw diameter of 20 mm to 70 mm, and a length/diameter (L/D) of 30 to 40. A method of manufacturing a feedstock for powder injection molding.
5. The method of claim 1,

   The shear roll mixer is a method of producing a feedstock for powder injection molding in which two rollers rotate in opposite directions, and the roller diameter is 80 mm to 350 mm.
6. 6. The method of claim 5,

   The distance between the two rollers of the shear roll mixer is 20 mm to 60 mm. A method of manufacturing a feedstock for powder injection molding.
7. The method of claim 1,

   The single screw extruder, twin screw extruder, and shear roll mixer is a method for producing a feedstock for powder injection molding, wherein a knife is attached to an end thereof, and the mixture passing therethrough is cut into pellets.

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