JPS6160802A - Powder injection molding method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for injection molding metal powder and ceramic powder.

[Conventional technology]

Injection is an effective method for producing molded bodies with complex shapes using metal powders such as 2%Ni -98%Fe, 5US316, stellite, and cemented carbide, and ceramic powders such as alumina, silicon carbide, silicon nitride, and zirconia as starting materials. Molding processes are known.

These injection molding methods consist of the following four steps. That is, (11 raw material powder is mixed with an organic binder to form a thermoplastic mixture.

(2) After the mixture is softened in a heating cylinder, it is injected into a mold while being pressurized.

(3) Open the mold and take out the molded object.

(4) After removing the organic binder from the compact, it is fired to increase the density.

The key to the injection molding method, which consists of the above steps, is the binder, which determines the success or failure of the above steps. A binder is added to impart moldability to the powder, and if the moldability is poor, defects such as silver marks, weld lines, cracks, etc. will occur in the molded product.

In order to improve moldability, it is necessary to add a binder of 1a, but on the other hand, as the binder load increases, defects such as cracks, foaming, and deformation may occur in the molded product during degreasing to remove the binder. Therefore, searches have been made for binders that have characteristics that minimize binder sinkage and do not cause defects during the degreasing process.

Currently, binders generally used include low molecular weight polyethylene, polystyrene, paraffin, and microcrystalline wax with a small amount of thermoplastic resin, oil, etc. added thereto.

Mataflopyrene, vinyl alcohol, polyvinyl butyral, polyethylene glycol, methyl cellulose, hydrodipropyl methyl cellulose, carboxy methyl cellulose, polyethyl cellulose, hydroxy ethyl cellulose, etc. are also known as binders.

It is also known to incorporate small amounts of stearic acid into the binder to facilitate the h-shape of the molded article.

[Problems that the invention attempts to solve]

In the degreasing process in powder injection molding,
A method has been adopted in which the binder is decomposed and removed by evaporation by heating the molded body from room temperature to 400 to 500°C. In this case, the molded body is heated to the maximum temperature,
It is essential that the rate of generation of steam generated by decomposition of the binder during heating does not exceed the rate at which it fills the voids within the molded body and is released to the outside. Otherwise, vapor pressure will build up within the molded body, resulting in cracking, foaming, and deformation. Therefore, this process requires 70 to 100
This takes time and detracts from the inherent high productivity advantages of injection molding. This is the first and biggest problem of the powder injection molding method.Next, the second problem is that heating to 400-500℃ for a long time results in wasted thermal energy, which is low-temperature energy. This makes it difficult to economically recover it as effective thermal energy.

Further, as mentioned above, degreasing depends on thermal decomposition of the binder, but complete degreasing is difficult, and it is common for a small amount of carbon and oil to remain in the molded body. This may cause deterioration of the properties of the product after firing, which is the fifth problem.

Fourth, since the fats and oils recovered in the degreasing process are decomposition products of the binder, they cannot be reused as a binder and are usually discarded, which is one of the reasons for increasing the cost of formed products.

A water freezing injection molding method is known as a method for solving the above-mentioned problems. This method is characterized by using water as a binder, and in this method, for example, approximately 40 volume 1 ft% of water is mixed with alumina powder of 1 μm or less to give the powder plasticity at room temperature. The mixture is injected into a mold cooled to -5 to -10°C, the molded product is given strength by freezing water, and the molded product is removed by opening the mold. At this time, freezing has the effect of facilitating release from the mold.

The molded body is then dehydrated. The saturated vapor pressure of water is 25℃
Since it has a 25-H content, which is extremely high compared to conventional organic binders, most of the water can be removed by evaporation at room temperature, and natural drying is also possible. Vacuum drying is also effective in increasing the dehydration rate, and dehydration time can also be shortened by applying slight heating.

In this way, this method solves the problem that the degreasing time of the conventional injection molding method is too long.

This method does not require high-temperature heating, so it is advantageous in terms of thermal energy.Water is also cheaper than organic binders, and can be recovered and reused if necessary.

As described above, the water-refrigeration injection molding method has many advantages, but it also has the disadvantage that it uses water and is limited in the materials that can be used. That is, most of the gold M powder is easily oxidized by contact with water, and the generated oxides inhibit the sintering of the metal powder, causing problems in the strength and toughness of the molded body. Furthermore, when the particles become fine like ceramic powder, not only does the amount of moisture adsorbed increase, but also the amount of OH- ions adsorbed to active portions with particularly large binding energy rapidly increases. Therefore, OH- ions, which cannot be removed unless the particles reach the rod temperature at which they become fine, increase.

Particles containing strongly adsorbed OH-ions generally impair sintering by 15 g. Magnesia powder adsorbs fcOH-''
It is known that ions cause abnormal grain growth during the sintering process. It is also known that silica reacts with adsorbed moisture to release ammonia and convert into silica r/C. Tungsten carbide also reacts with adsorbed moisture at around 1200°C, releasing hydrogen and carbon monoxide. As mentioned above, injection molding using water cooling cannot be applied to materials that change in quality due to absorption of moisture.

This invention was made in order to solve the above-mentioned drawbacks of the injection molding method using water-cooling, and provides a powder injection molding method in which the binder does not contaminate metal and ceramic powder, and the binder can be easily removed after molding. The purpose is to provide the following.

Means for Solving Problem C] In order to solve the above problems, the present invention uses tertiary butanol (CH3)3C as a substitute for water in the water freezing injection molding method.
It is characterized by using 0H (2, Methi ka2 Proper Tool) as a binder.

As a binder for frozen injection molding, tertiary butanol has properties superior to water.
0.71/1 molecule of water at -j] d74.1
2, which is 4.1 times that of water. Therefore, unit body! % of R heat
A, number is water Ob, 56 X 10-” P mot/
.

For cAVc, 6th butanol is 1.05 x 10-
"pm"/i is about one-fifth. This is the fifth
This means that when butanol fills the spaces between particles of raw material powder, the amount of gas generated during binder removal is only one-fifth of that in the case of water. This point is extremely advantageous in reducing the debinding time by one hour.

Since the melting point of 6-butanol is 25.66°C, which is close to room temperature, it can be frozen by circulating cold water, and unlike water, special freezing equipment is not required. Also, the heat of solidification of water79.
4/c4 tc, the heat of solidification of 6-butanol is only about 4.6 times lower at 17.1 d/d, which makes tert-butanol even more advantageous from an energy consumption point of view. .

Next, the vapor pressure of 6-butanol is 45aH2 at 25°C, which is higher than 25flHy of water. This is because 6th butanol is more advantageous than water in terms of ease of debinding, and the heat of vaporization of water at 25°C is 586'/-, whereas the heat of vaporization of 5th butanol is 118'/-, which is approximately 5. Extremely small, 1/71. means that the energy required for debinding is extremely small compared to water.

A part of @5-butanol also adsorbs rfJ'VC on the powder surface after debinding at room temperature. In this case, water absorbs O)r ions! In contrast, 5-butanol is adsorbed by alkyl groups. ◇Unlike OH- ions, alkyl groups are relatively easy to de-N, and do not adversely affect the sintering of the compact. .

In addition, 6-butanol is a stable single-component substance,
There is almost no decomposition or deterioration due to evaporation, condensation, or solidification at room temperature, so it can be recovered and reused. This point is extremely economically advantageous compared to conventional organic binders such as water and [EL].

The amount of these 6-butanol binders depends largely on the particle size distribution of the applied powder. It is necessary that the binder completely fills the voids between the particles, and empirically, it is necessary to add several vol.% of the binder.

If the amount of binder is less than 60 volume, flow characteristics suitable for injection cannot be obtained, and if the amount is too large, it will not only take time to remove the binder but also cause defects. It is necessary that

Also, the heating temperature of the mixture in the heating cylinder is 26 to 4
It is necessary that the temperature is 0°C. This is because the melting point of tertiary butanol is 25.66°C, so it is necessary to maintain it above this temperature to make it molten. Also, heating it above 40°C increases the vapor pressure of 6th butanol, which reduces dissipation loss. This is because the increase becomes a problem.

Regarding cooling of the molded object in the mold, it is necessary to keep the surface of the molded object at least below the melting point and freeze it.
Keep the temperature below 5℃. However, if the cooling temperature is too low, the rate of binder removal in the subsequent step will decrease, which is not desirable. In addition, simple water cooling is not sufficient, and a special cold source is required, so the mold is cooled to at least bring the temperature of the molded object to 5 to 25 degrees.
It is necessary to adjust the temperature at ℃t14.

Although mold release of molded bodies frozen with 6-butanol is good, even better mold release is possible if, for example, stearic acid is mixed in advance as a mold release agent, as in conventional powder injection molding methods.

As described above, the gist of the present invention is to mix 30 to 55 volumes of 6-butanol with the metal powder and ceramic powder in injection molding of metal powder and ceramic powder, and to mix the mixture with JICy4 at a temperature above the melting point of the 5-butanol. Then, the mixture is injected into a cooled mold and held in the mold, and the surface temperature of the obtained molded body is lowered to below the melting point of 6th butanol to freeze the 5th butanol in the molded body. , a powder injection molding method characterized by taking out a molded body.

Examples of the present invention will be described below.

[Example] Silicon nitride with an average intergranular diameter of 0.75 μmo and Y2O2 (6 weight%) and A1103 (2 weight%) as sintering aids.
) and prepare a 40 volume mound of 1 yen butanol powder for 60% by volume of this raw material powder.

After charging the mixture into a kneader and creating a desired atmosphere, kneading is started. The inner wall of the mixing tank of the kneader is controlled at 50°C by an electric heater or a hot medium heater.
Butanol dissolves and crosstalk progresses. 12 minutes after the crosstalk started
After an hour, turn off the heater power, run cold water at 20℃ through the jacket attached to the mixing tank and blade, and cool it down for 5 minutes.
Continuing to mix lines for 0 minutes. During this time, the 6th butanol freezes and becomes a binder for the raw material powder, forming a pellet-like mixture. The pellets are taken out and charged into a hopper of a screw in-line type or plunger type injection molding machine.

The outlet temperature of the heating cylinder of the injection molding machine is set at 50°C, while cold water at 20°C is passed through the mold.

Next, a series of sequences including mold clamping, cylinder advancement, injection, holding pressure, mold opening, molded body ejection, cylinder retraction, screw retraction, and plasticization by screw rotation are performed.

The binder near the surface of the molded product solidifies and becomes hard, and the mold can be easily released from the mold. This molded body was placed in a vacuum dryer, the temperature was set at 25°C, and the maximum vacuum degree was 10” T.
orr K Evacuate. After 5 hours, stop and take out the molded body, then charge the molded body into the vacuum pressure sintering furnace, and turn the sintering furnace to 1.
After holding at 0-'' Torr/1200℃ for 3 hours to remove adsorbed substances, the temperature was 180゛0℃ and nitrogen atmosphere at 9.8K.
Hold the gAG IC for 6 hours, reduce the pressure, and let it cool.

By the above procedure, 43.8mX 14.8aomX
19.1 ms and 4! c8mX7.4awX 19.1
Molded bodies were produced using m+02 types of rectangular cavities.

As a result, no defects due to binder removal were observed not only in the thin type of 7.4 t* but also in the thick type of 14.8-t*.
In each case, uniformly shrunk sintered bodies with a theoretical density ratio of 98 cm were obtained.

The scope of application of the metal powder and ceramic material in the present invention is not limited to the silicon nitride powder of the above embodiment, but also silicon carbide,
Also included are ceramic powders such as alumina, zirconia, and titanium diboride, and metal powders such as Ni-Fe alloys, stainless steel, stellite, and cemented carbide.

〔Effect of the invention〕

As described above, the method of the present invention, which uses 6-butanol as an inder for freezing injection molding of metal powders and ceramic powders, enables debinding in a short time, and injection molding can be performed at around room temperature, so it is possible to save energy. There is no contamination of the raw material powder as in the frozen injection molding method using water,
Moreover, it is an economical injection molding method because 5th butanol can be recovered and reused.

Agent Patent attorney Kimura 3 Lawyers 1 person Draw L [-Zan (spontaneous) 't,)"Ilgo office director +': I'k
Showa J1159 +r, i0 u9 ++1, Indication of the case Patent application No. 59-179359 2, Name of the invention Method for molding powder (after amendment) 3, Supplement 11: Relationship with the case Patent Applicant name Title (412 items 1 Contents of Kouko Tube Co., Ltd. 4, Agent 7, Supplementary 11 et al. (2) Claim J is amended as shown in the attached sheet.

(3) "Injection molding method" on page 1, lines 16-17 of the specification
is corrected as "molding method".

(4) Add the following sentence between the 8th and 9th lines of page 6.

``In the normal injection molding method that uses an organic binder, the deformation characteristics of the plasticized product consisting of the binder and powder change sensitively to temperature, so a mechanism for heating and plasticizing the mixture is built into the injection molding machine. It is necessary to strictly control the temperature.On the other hand, since the deformation characteristics of plasticized materials using water as a binder are stable around room temperature, plasticization and molding can be performed separately without using an injection molding machine. It can also be done mechanically, for example, using a combination of a crosstalk machine and a die forging machine.

In this case, cross-wiring is performed at room temperature, and the plasticized material is charged into the mold of a die forging machine to perform die forging.'' (5) ``Water-cooled injection molding method'' in line 9 of page 6 of the same Corrected as "molding method".

(6) "Page 7, line 9, line 9, line 11, lines 14-15"
"injection molding" is corrected to "molding".

(7) "Freeze injection molding" on page 7, line 18, line 2 of page 8 is corrected to "freeze molding."

(8) "For cdVC" on page 8, line 7 is corrected to "j for cdVC."

(9) "Injection molding" on page 11, lines 4, 8, and 15 to 16 is corrected to "molding."

"Injection" on page 11, line 12 of the same page is corrected to "charging."

02) Add the following sentence between page 13, line 17 and line 18.

First, an example of a frozen die forging method using @3-butanol as a binder will be described.

〔Example〕

Prepare silicon nitride powder with an average particle size of 0.75 μm, sintering aid Ytos (6% by weight), and 40 g (2% by weight) of A. Furthermore, an amount equivalent to $40 volume of tertiary butanol is prepared for 60 volume % of this raw material powder.

After charging both of them into a pressurized kneader and creating a nitrogen atmosphere, crosstalk is started. The inner wall of Nigu was heated with an electric heater and maintained at 60°C. As a result, the 6th butanol dissolves and crosstalk progresses.

At the same time as kneading, pressurize* is applied to the kneaded material 1'! After 12 hours, the plasticized mixture was taken out. This was molded into a rectangular parallelepiped, placed in a forging mold cooled by running cold water at 20°C, and immediately compression-molded. , and held for about 6 minutes.The 6th butanol near the surface of the molded product is hard, so it can be easily released from the mold.The molded product is placed in a vacuum dryer, and the temperature is set at 25°C. The 6th butanol was evaporated and removed by IC evacuation at a vacuum degree of 10' Torr.

After 6 hours, the molded body was stopped and the molded body was taken out.Then, the molded body was charged into a vacuum pressurized sintering furnace.Then, the vacuum degree was 10 Torr.

After holding at 1000°C for 3 hours to remove adsorbed substances,
800℃, nitrogen atmosphere, 9.8 k17/cλGK
After holding for 3 hours, the pressure was reduced and allowed to cool. After cooling, the compact is taken out and deburred by diamond grinding.

By the above procedure, 43.8mX 14.81WIx1
Molded bodies were produced using two types of rectangular cavities: 9.1-inch and 46.8-inch x Z4-guan x 191-inch. As a result,
Not only thin VC of 7, 4, m, but also thick VC of 14.8 m.
However, no defects due to binder removal were observed, and uniformly shrunken sintered bodies with a theoretical density ratio of 98% were obtained in all cases.'' (6) Page 14, lines 6, 8, and Correct “injection molding” in line 9 to “molding”.

Scope of claims (amendment) “For forming metal powders and ceramic powders.

60 to 55 volumes of tertiary butanol are mixed with the gold W4 powder and ceramic powder, the mixture is adjusted to a temperature higher than the melting point of tertiary butanol, and then the mixture is placed in a cooled mold. The method of producing powder is characterized in that the surface temperature of the obtained molded body is lowered to below the melting point of the 6th butanol to freeze the 5th butanol in the molded body, and the molded body is taken out. Molding method. ”

Claims (1)

[Claims] (1) In injection molding of metal powder and ceramic powder, 30 to 55% by volume of tertiary butanol is mixed with the metal powder and ceramic powder, the mixture is adjusted to a temperature equal to or higher than the melting point of tertiary butanol, and then the After injecting the mixture into a cooled mold and holding the mold, the surface temperature of the obtained molded body is lowered to below the melting point of tertiary butanol to freeze the tertiary butanol in the molded body, and the molded body is taken out. A powder injection molding method characterized by: