JPH10324902A - Method for degreasing compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly and sufficiently degrease in a short degreasing time by executing the degrease in a low temp. range at a first process and the degrease in a further higher temp. range at a second process and mutually changing over the degreasing atmosphere at the first process from the reduced pressure state to higher pressure state than the former state. SOLUTION: At the first process, the temp. in a furnace is raised by operating a heater for a prescribed time (a first pattern) and successively, the temp. in the furnace is kept at the constant for a prescribed time by stopping or reducing the output of the heater (a second pattern) and after this, these operations are repeated. In this result, the temp. in the furnace is raised step by step. Then, related to the pressure in the atmosphere, in the first pattern, a second pressure is set, and in the second pattern, a first pressure, desirably <50 Torr is set. The second pressure is made slightly higher than the first pressure and the difference between these pressures is desirable to be >35 Torr. Further, as the degreasing gas, the inert gas of nitrogen, argon, etc., is suitable from a viepoint of preventing the change in quality of the compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for degreasing a molded article to be subjected to sintering, particularly to an injection molded article.

[0002]

2. Description of the Related Art When a metal product is manufactured by sintering a metal powder compact, a metal powder and an organic binder are mixed and kneaded. Powder injection molding (MIM: Metal Injectio)
n Molding) method is known.

[0003] The molded article manufactured by the MIM method is as follows.
Before being subjected to sintering, a degreasing treatment (a binder removal treatment) is performed.

Conventional degreasing methods include vacuum (reduced pressure) degreasing in a heating furnace, degreasing in an inert gas, solvent extraction, photochemical decomposition, and thermal decomposition. Each of these degreasing methods has advantages and disadvantages, and is appropriately selected according to the purpose.

[0005] Among these degreasing methods, vacuum degreasing and degreasing in an inert gas have the advantage that the degreasing efficiency is relatively high as compared with other methods.

However, in vacuum degreasing, the total degreasing time is 45
長 く 100 hours, which is extremely long. Therefore, there is a drawback that the productivity is low and the production cost is high. On the other hand, in the degreasing in an inert gas, the discharge property of the organic binder from the molded article is poor (unevenness). ), There is a disadvantage that defects such as swelling, deformation, and cracks are likely to occur in the molded article.

In vacuum degreasing, since the atmosphere is under vacuum or under reduced pressure (10 torr or less), the thermal conductivity to the compact is low, and the temperature inside the furnace is raised in order to make the temperature of the compact follow the furnace temperature. Having to set the speed slow is the main reason for prolonging the degreasing time.

In vacuum degreasing, if the degreasing time is forcibly shortened, the temperature distribution in the furnace and in the molded body becomes uneven due to the low thermal conductivity, thereby causing cracks and swelling, and further degreasing. Unevenness occurs, making it difficult to obtain a uniform and good quality degreased body (degreased molded body). Therefore, in order to ensure the required quality, a sufficiently long degreasing time must be secured.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for degreasing a form capable of uniformly and satisfactorily degreasing in a short degreasing time.

[0010]

This and other objects are achieved by the present invention which is defined below as (1) to (16).

(1) A method for degreasing a molded article obtained by heating a molded article obtained by molding a composition containing a raw material powder and a binder in a furnace to perform a degreasing treatment, wherein the degreasing is performed in a low temperature range. First
And a second step of performing degreasing in a higher temperature range than the first step. In the first step, the degreasing atmosphere is reduced to a first pressure in a reduced pressure state, and the first pressure is reduced. A method for degreasing a molded article, wherein the method is alternately switched to a higher second pressure.

(2) The method for degreasing a molded article according to (1), wherein the pattern of the heating temperature in the first step has a tendency to increase with time as a whole.

(3) As the heating temperature pattern in the first step, a first pattern in which the temperature rises with time and a second pattern in which the temperature rise is stopped or reduced are alternately performed at least once. The method for degreasing a molded article according to the above (1) or (2).

(4) The first step in the first step
The method for degreasing a molded article according to the above (2) or (3), wherein the switching between the pressure of (2) and the second pressure is performed according to a rising pattern of the heating temperature.

(5) As the heating temperature pattern in the first step, the first pattern in which the temperature rises with time and the second pattern in which the temperature rise is stopped or reduced are alternately performed at least once. The method for degreasing a molded article according to (1) or (2), wherein the second pressure is set in the first pattern, and the first pressure is set in the second pattern.

(6) The method according to any one of the above (1) to (5), wherein the difference between the first pressure and the second pressure is 35 torr or more.

(7) The method of any of (1) to (6) above, wherein the first pressure is 50 torr or less.

(8) The method according to any one of (1) to (7), wherein the switching from the first pressure to the second pressure is performed twice or more.

(9) The degreasing atmosphere in the first step is a degreasing gas obtained by mixing at least one selected from an inert gas, air, carbon dioxide gas, hydrogen gas, and ammonia decomposition gas. The method for degreasing a molded article according to any one of 1) to (8).

(10) The method for degreasing a molded article according to any one of the above (1) to (9), wherein the first step and the second step are continuously performed.

(11) The above (1) to (10) wherein the same type of degreasing gas is used in the first step and the second step.
The method for degreasing a molded article according to any one of the above.

(12) The method for degreasing a molded article according to any one of (1) to (11), wherein degreasing is performed while stirring the inside of the furnace in at least one of the first step and the second step. .

(13) The method according to any one of the above (1) to (12), wherein the treatment time in the first step is 2 to 25 hours.

(14) The method for degreasing a molded article according to any one of (1) to (13), further comprising a third step of cooling the molded article after the second step.

(15) The method for degreasing a molded article according to any one of the above (1) to (14), wherein the molded article is a molded article obtained by injection molding.

(16) The raw material powder is a metal powder,
The method for degreasing a compact according to any one of the above (1) to (15), wherein the content of the metal powder in the compact is 70 to 95 wt%.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for degreasing a molded article of the present invention will be described in detail.

[1] Manufacture of a molded body A molded body to be subjected to degreasing is formed by using a metal, a nonmetal or a raw material powder obtained by mixing them, for example, by compression molding (compacting), extrusion molding, injection molding or the like. However, it is particularly preferable to use a metal powder injection molding method (MIM method).

This metal powder injection molding method has an advantage that a metal sintered product having a complicated and fine shape can be manufactured with high dimensional accuracy. Therefore, the effect is effectively exerted in applying the present invention. ,preferable. Hereinafter, the steps will be sequentially described.

First, a metal powder as a raw material powder and a binder (organic binder) are prepared, and these are kneaded by a kneader to obtain a kneaded product (compound).

The metal of the metal powder is not particularly restricted but includes, for example, all metal elements such as iron, nickel, cobalt, copper, aluminum, tungsten, titanium, molybdenum, vanadium and alloys thereof. Further, two or more kinds of metal powders having different compositions can be mixed and used (mixed powder).

The method for producing the metal powder is not particularly limited, and those produced by, for example, an atomizing method, a reducing method, a carbonyl method, or a pulverizing method can be used.

The average particle size of such a metal powder is not particularly limited, but is usually preferably about 0.2 to 200 μm, more preferably about 1 to 50 μm.

On the other hand, examples of the binder include polyolefins such as polyethylene, polypropylene and ethylene-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, and polyvinyl chloride. , Polyvinylidene chloride, polyamide, polyester, polyether,
Various resins such as polyvinyl alcohol or copolymers thereof, various waxes, paraffins, higher fatty acids (eg, stearic acid), higher alcohols, higher fatty acid esters, higher fatty acid amides, and the like. Alternatively, two or more kinds can be used as a mixture.

Further, a plasticizer may be further added. Examples of the plasticizer include phthalic acid esters (eg, DOP, DEP, DBP), adipic acid esters, trimellitic acid esters, sebacic acid esters, and the like. One or more of these may be mixed. Can be used.

The content of the metal powder in the compact before degreasing is as follows:
It is preferably about 70 to 95% by weight, and 80 to 92% by weight.
% Is more preferable. If it is less than 70% by weight, the shrinkage when the molded body is fired increases, the dimensional accuracy decreases, and the porosity and the content of C in the sintered body tend to increase. On the other hand, if it exceeds 95% by weight, the content of the binder is relatively reduced, so that the fluidity during molding becomes poor, and injection molding becomes impossible or difficult, or the composition of the molded product becomes non-uniform. The preferred content of the metal powder is the same when other molding methods are employed.

At the time of the kneading, various additives such as a lubricant, an antioxidant, a degreasing accelerator and a surfactant are added as required in addition to the metal powder, the binder and the plasticizer. be able to.

The kneading conditions vary depending on various conditions such as the particle size of the metal powder to be used, the composition of the binder and the additives, and the amount of the additives. For example, the kneading temperature: room temperature to 200
C., kneading time: about 20 to 210 minutes. The kneaded material is formed into pellets (small blocks) as necessary. The particle size of the pellet is, for example, about 3 to 10 mm.

Next, the kneaded product obtained above or the pellets granulated from the kneaded product is injection-molded by an injection molding machine to produce a molded product having a desired shape. In this case, it is possible to easily produce a molded body having a complicated and fine shape by selecting a molding die.

The molding conditions for the injection molding vary depending on various conditions such as the particle size of the metal powder to be used, the composition of the binder, and the amount of the binder. For example, the material temperature is preferably about 80 to 200 ° C. , The injection pressure is preferably 20
It is about 150 kgf / cm ² .

Although the MIM method using a metal powder as the raw material powder has been described above, in the present invention, the raw material powder may be, for example, a powder of a metal compound such as various ceramics and cermets. Further, a mixture of these and the metal powder may be used.

[2] Degreasing of the molded body The molded body obtained in the above step [1] is subjected to a degreasing treatment (a binder removal treatment).

First, an example of the configuration of a furnace used for the degreasing process will be described with reference to FIG. The furnace 1 has a processing space 2 in which a substantially sealed state can be maintained. In the processing space 2, a mounting table 3 on which the molded body 10 is mounted is installed.

The furnace 1 is provided with a heater 4 for heating the inside of the processing space 2 and a stirring device 5 for stirring the atmosphere in the processing space 2. The stirring device 5 includes a motor 51
And a stirring blade 52 rotated by the motor 51. The stirring blade 52 is located in the processing space 2.

The operation of the heater 4 is controlled by control means 8 such as a microcomputer, and the temperature in the processing space 2 is controlled, particularly the temperature rising pattern.

The furnace 1 is provided with a degreasing gas supply system 6 for supplying a degreasing gas (carrier gas) to the processing space 2 and a degreasing gas exhaust system 7 for discharging the degreasing gas in the processing space 2. I have.

The degreasing gas supply system 6 is provided with pipes 61, 62, 63 for supplying three different types of degreasing gas A, B, C, respectively.
A selection valve 64 installed at a downstream end of the pipes 61, 62, 63, a pipe 65 connecting the selection valve 64 to the inside of the processing space 2, and a flow control valve installed in the middle of the pipe 65. 66.

The selection valve 64 includes a pipe 61,
62, 63, and any one or more of
It is a valve that selects the connection with Degreasing gas A, B, C
One kind alone or as a mixture of two or more kinds in a predetermined combination can be supplied.

The flow rate adjusting valve 66 is a valve for adjusting the flow rate of the degreasing gas flowing through the pipe 65.

Selection valve 64 and flow control valve 66
Are respectively constituted by electromagnetic valves, and the operation of these valves, that is, the selection by the selection valve 64 and the opening of the flow control valve 66 are controlled by the control means 8.

The degreasing gas exhaust system 7 includes a pipe 71 communicating with the processing space 2, a vacuum pump 72 provided in the middle of the pipe 71, and a valve 73 provided in the middle of the pipe 71. , A pipe 74 branched from the pipe 71, and a valve 75 installed in the pipe 74. The valves 73 and 75 are constituted by electromagnetic valves. The operations of the vacuum pump 72 and the valves 73 and 75 are controlled by the control unit 8 respectively.

The degreasing treatment using such a furnace 1 is performed by performing a first step and a second step described below. Further, it is preferable to further perform the third step.

0. Prior Step Prior to a first step described later, a preceding step can be performed as necessary.

The compact 10 obtained in the above step [1] is placed on the placing table 3 of the furnace 1 in a predetermined arrangement. Then, the furnace 1 is closed and, for example, the degreasing gas supply system 6 is used. Processing space 2
A predetermined degreasing gas (for example, nitrogen gas, argon gas, air) selected by the selection valve 64 is supplied and filled therein.

After the supply of the degreasing gas into the furnace is stopped, the heater 4 is operated to raise the furnace temperature to, for example, about 50 to 70 ° C., and the degreasing gas exhaust system 7 is operated to exhaust gas. The pressure in the processing space 2 is reduced to a predetermined pressure. This pressure is preferably at or near a second pressure described below.

1. First step The heater 4 is operated intermittently, and the whole compact 1
A heating temperature of 0 (furnace temperature) has a tendency to increase. That is, as shown in FIG. 2, the heater 4 is operated for a predetermined time (for example, 1 to 60 minutes), the furnace temperature is increased with time (= first pattern), and then the output of the heater 4 is stopped. Alternatively, the temperature inside the furnace is kept constant for a predetermined time (for example, 1 to 120 minutes) by decreasing the temperature (= second pattern), and thereafter, the first pattern and the second pattern are alternately repeated. Thereby, the furnace temperature gradually increases.
In the second pattern, as shown in FIG. 7, the rate of temperature rise may be lower than that of the first pattern.

The first pattern and the second pattern may be alternately performed at least once, but may be repeated two or more times as shown in FIGS.

One time of the first pattern is 1 to 60
Minutes, and more preferably about 5 to 30 minutes. One time of the second pattern is preferably about 1 to 120 minutes, more preferably about 10 to 60 minutes.

On the other hand, as shown in FIGS. 2 to 5, the pressure of the atmosphere in the processing space 2 of the furnace 1 is changed in conjunction with the change in the temperature rise pattern in the furnace.

That is, the valve 73 is opened, the flow control valve 66 and the valve 75 are closed, and the vacuum pump 72 is operated to evacuate the processing space 2 so that the pressure in the processing space 2 becomes the first pressure of a relatively low pressure (reduced pressure). Upon reaching, the valve 73 is closed and this pressure is maintained for a predetermined time. Further, in this state, the flow control valve 66 is opened at a predetermined opening degree, the degreasing gas selected by the selection valve 64 is supplied to the processing space 2 by a predetermined amount, and the pressure in the processing space 2 is increased to the second pressure. Then, the flow control valve 66 is closed.

When the temperature pattern is the first pattern, the second pressure is set by the above method, and when the temperature pattern is the second pattern, the first pressure is set by the above method. Thus, the degreasing gas supply system 6 and the degreasing gas exhaust system 7
Are operated alternately to change the furnace pressure so as to follow the change in the temperature pattern.

The adjustment of the furnace pressure is not limited to the above-described method. For example, while the degreasing gas exhaust system 7 is continuously operated, the gas supply amount in the degreasing gas supply system 6 is controlled to perform the first method. For setting the pressure of the gas and the second pressure, the degreasing gas supply system 6
A method in which the first pressure and the second pressure are set by controlling the gas exhaust amount in the degreasing gas exhaust system 7 in a state in which is continuously operated, or a method in which these are appropriately combined. .

Further, in the present invention, as shown in FIGS. 6 and 7, the pressure of the atmosphere in the processing space 2 of the furnace 1 is changed to the first pressure without interlocking with the change in the rise pattern of the furnace temperature. The switching to the second pressure may be alternately performed.

In the above configuration, the first pressure is preferably 50 torr or less, more preferably 15 torr or less, and even more preferably 10 torr or less.

Then, the second pressure is 30 to 2000 to
It is preferably about rr, more preferably 75 to 1200 torr or less.

The difference between the second pressure and the first pressure is 3
It is preferably at least 5 torr.

Examples of the degreasing gas include an inert gas such as nitrogen gas and argon gas, air, carbon dioxide gas, hydrogen gas and ammonia decomposition gas, and one or more of these are mixed. Can be used. An inert gas such as a nitrogen gas or an argon gas is preferable for preventing deterioration of the molded body 10, and air is preferable for reducing the manufacturing cost.

The upper limit of the furnace temperature (heating temperature) in the first step is not particularly limited, but is preferably 35.
The temperature can be about 0 ° C., more preferably about 300 ° C.

With the above-described structure, the molded body can be uniformly and satisfactorily degreased in a shorter degreasing time, and the occurrence of defects such as swelling, deformation, and cracks can be prevented. That is, in the first pattern, since the second pressure is relatively high, the heat transfer to the molded body 10 is quick and uniform, which contributes to prevention of the occurrence of the defect. In the second pattern, since the first pressure is set to a relatively low first pressure, the binder component contained in the molded body is discharged (volatilized).
Is promoted, which contributes to the promotion of the degreasing time. Further, a more excellent effect is exerted by a synergistic effect obtained by alternately performing the two patterns.

Further, by operating the degreasing gas supply system 6 even under reduced pressure and controlling the pressure in the furnace as described above while flowing a small amount of gas, the decomposed gas generated from the molded product can be efficiently removed from the furnace. Can be discharged.

In the first step, the stirrer 5
Is preferably operated to perform degreasing while stirring the inside of the processing space 2. Thereby, the composition (concentration) and temperature distribution of the degreasing gas in the processing space 2 become uniform, and the molded body 10
Degreasing is performed more uniformly and efficiently, and the above-described effects are more remarkably exhibited.

The processing time in the first step is not particularly limited, but is usually preferably about 2 to 25 hours, more preferably about 4 to 20 hours. If it is less than 2 hours, the degreasing may be insufficient depending on other conditions, and if it is more than 25 hours, the entire degreasing time will be long.

2. Second Step After the first step (preferably, continuously to the first step), a second step is performed. In the second step, while the heater 4 is operating, the degreasing gas supply system 6 is operated to supply the degreasing gas selected by the selection valve 64 into the processing space 2, and the valve 73 is closed and the valve 75 is closed. Is opened, and the same amount of degreasing gas as the above-mentioned supply amount is discharged out of the furnace through the pipes 71 and 74.

In this case, the opening of the flow control valve 66 is set to be relatively large, and the supply amount (flow rate) of the degreasing gas into the processing space 2 is sufficiently ensured. Specifically, when the capacity of the processing space 2 of the furnace 1 is 2 to 8 m ³ ,
It is preferably about 80 to 450 liters / minute, more preferably about 130 to 380 liters / minute. This preferred supply rate increases or decreases according to the capacity of the furnace 1.

The type and composition of the degreasing gas in the second step may be the same as or different from the degreasing gas used in the first step, but the same type, that is, the same composition or the same main component of the gas is common. Are preferred.

The furnace temperature (processing temperature) in the second step is set to a higher temperature range than that in the second step, and the maximum temperature is preferably about 750 ° C., more preferably 6 ° C.
It can be about 00 ° C. In this case, FIGS.
As shown in (2), it is preferable that the temperature in the furnace in the second step is increased with time, and then maintained in a high temperature state (maximum temperature) for a certain period of time.

Also in the second step, it is preferable to operate the stirrer 5 in the same manner as described above to stir the inside of the processing space 2. Thereby, the composition (concentration) and temperature distribution of the degreased gas in the processing space 2 are kept uniform, and the compact 10
Is uniformly and efficiently degreased.

The treatment time in the second step is not particularly limited, but is usually preferably about 2 to 18 hours, and is preferably 3 to 1 hour.
About 5 hours is more preferable. If the time is less than 2 hours, the degreasing may be insufficient depending on other conditions.
If the time is exceeded, the entire degreasing time becomes longer.

In the degreasing treatment in the second step, a degreasing gas composed of air, an inert gas (non-oxidizing gas), or the like flows into the furnace. Temperature distribution becomes stable. Therefore, the molded body is
The degreasing is performed uniformly and efficiently, and the temperature rise rate in the furnace is greatly increased, and the degreasing time is greatly reduced.

Further, the consumption of the degreasing gas is reduced by shortening the degreasing time. In particular, the reduction in consumption of expensive degreasing gas such as argon gas is advantageous for reducing manufacturing costs.

Unlike the above, the degreasing gas supply system 6 is actuated to supply and fill a predetermined degreasing gas into the processing space 2, and in this state, the pressure in the processing space 2 is reduced without exhausting. Degreasing may be performed in a temperature pattern as shown in FIGS. In this case, the consumption of the degreasing gas is further reduced, and the advantage is great.

3. Third Step After the second step, a third step is performed. In the third step, the operation of the heater 4 is stopped or the power is reduced to lower the furnace temperature, and the compact 10 is cooled to, for example, room temperature.

At this time, it is preferable to set a small opening degree of the flow control valve 66 to supply a small amount of the degreasing gas into the processing space 2. The supply amount of the degreasing gas in the third step is 0.05 to less than the supply amount of the degreasing gas in the second step.
It is preferably about 0.7 times, and more preferably about 0.1 to 0.5 times.

Specifically, the supply amount of the degreasing gas is preferably about 4 to 310 L / min, more preferably about 15 to 170 L / min, based on the capacity of the furnace 1 as described above. it can.

The degreasing gas in the third step is preferably the same type as the degreasing gas used in the second step.

[3] Sintering of the compact The degreased body obtained as described above is fired and sintered in, for example, a sintering furnace (not shown) to be a metal sintered body. The sintering conditions are not particularly limited.
The heating is performed at about 0 ° C. for about 15 to 30 hours.

The sintering atmosphere is, for example, 5 × 10 ^-2.
Under reduced pressure (vacuum) of not more than torr (particularly 1 × 10 ⁻² to 1 × 10 ⁻⁶ torr), or an inert gas such as nitrogen gas or argon gas.

In the present invention, the first step and the second step
There is a difference in the supply amount (total consumption amount) of the degreasing gas between the above steps.

That is, in the first step, since the heating temperature is relatively low, the decomposition of the organic component such as the binder in the molded body is gradually progressing, and therefore, the decomposition of the first pattern is difficult. The supply amount of the degreasing gas may be small, and as a result, the heat loss can be suppressed and the consumption amount of the degreasing gas can be reduced.

On the other hand, in the second step, since the heating temperature is higher than that in the first step, the decomposition of the organic components such as the binder in the molded product is remarkably caused, and the supply amount of the degreasing gas is increased. In addition to promoting the decomposition of the organic components, the gas generated by the decomposition is quickly discharged out of the furnace together with the degreasing gas. As a result, the molded body is degreased at a high speed, and the residual amount (residual carbon) of organic components in the degreased molded body (defatted body) is reduced as compared with the conventional method, and the variation is also reduced. Thus, a high-quality and homogeneous degreased body (that is, a sintered product) can be produced in a short time and at low cost.

In the third step, the cooling efficiency can be improved by flowing the degreasing gas into the furnace, and the decomposition gas remaining in the furnace is prevented from re-adhering to the degreased body. can do. Further, since the supply amount is relatively small, the consumption amount of the degreasing gas does not increase.

[0092]

Next, specific examples of the method for producing a sintered body according to the present invention will be described.

Example 1 A binder composed of 87 wt% of stainless steel (SUS36L) powder having an average particle diameter of 10 μm, 6 wt% of polypropylene (thermoplastic resin) and 5 wt% of wax, and dibutyl phthalate (plasticizer) ):
2 wt%, and these were kneaded in a kneader at 115 ° C. for 2 hours.

Next, the kneaded product was pulverized and classified to obtain pellets having an average particle diameter of 3 mm. The pellets were subjected to metal powder injection molding using an injection molding machine to obtain a ring-shaped compact (100
Was manufactured. The molding conditions during injection molding were a mold temperature of 150 ° C. and an injection pressure of 50 kgf / cm ² .

Next, the obtained molded body was subjected to a degreasing treatment using a furnace (capacity: 4 m ³ ) having the structure shown in FIG. 1 according to the temperature and pressure change patterns shown in the graph of FIG. (See Table 1 for the weight of a single molded article.)

The degreasing treatment includes a pre-process and first, second and third steps. In the first, second and third steps, nitrogen gas was used as a degreasing gas, respectively. Second
In the step, the degreasing gas is introduced into the furnace at a pressure of 380-10.
It was distributed at a rate of 00 torr and a supply of 150 to 300 l / min.

In all the steps, the stirrer was operated to stir the inside of the furnace.

Example 2 A molded body was manufactured in the same manner as in Example 1, and the molded body was subjected to a degreasing treatment with the furnace temperature and pressure change patterns as shown in FIG. The same as in Example 1.

Example 3 A molded product was produced in the same manner as in Example 1, and the molded product was subjected to a degreasing treatment with the furnace temperature and pressure change patterns as shown in FIG. The same as in Example 1.

Example 4 A molded product was produced in the same manner as in Example 1, and the molded product was subjected to a degreasing treatment with the furnace temperature and pressure change patterns as shown in FIG. The same as in Example 1.

(Example 5) A molded body was manufactured in the same manner as in Example 1, and the molded body was subjected to a degreasing treatment by changing the temperature and pressure patterns in the furnace as shown in FIG. The same as in Example 1. Note that the pre-process was not performed.

(Example 6) A molded product similar to that of Example 1 was manufactured, and the molded product was subjected to a degreasing treatment with the change pattern of the furnace temperature and pressure as shown in FIG.
Same as Example 1. Note that the pre-process was not performed.

(Comparative Example 1) A molded body similar to that of Example 1 was manufactured, and the molded body was subjected to a degreasing treatment according to a temperature change pattern shown in a graph of FIG. 8, and a furnace was stirred in each step. Except that there was no, it was the same as Example 1. Note that the pre-process was not performed, and in the first process, the inside of the furnace was maintained at a constant reduced pressure (about 0.01 torr).

(Comparative Example 2) A molded article similar to that of Example 1 was manufactured, and the molded article was subjected to a degreasing treatment according to the temperature change pattern shown in the graph of FIG. 9 and the furnace was stirred in each step. Except that there was no, it was the same as Example 1. In the first step, a nitrogen gas (pressure 760 torr) was passed through the furnace under the same conditions as in the second step.

(Examples 7 to 12) For each of Examples 1 to 6, the degreased gas used in each step was mixed with a three-component gas mixture of argon gas, CO ₂ gas, and nitrogen gas (mixing ratio = 1: 1). Except having changed to 1: 1), it was the same as corresponding Examples 1-6, respectively.

Examples 13 to 18 correspond to Examples 1 to 6, respectively, except that the degreasing gas used in the previous step and the first step was changed to air. The same as above.

With respect to each of the degreased bodies obtained in Examples 1 to 18 and Comparative Examples 1 and 2, the incidence of defects (swelling, deformation, cracking) was examined. The results are shown in Tables 1 to 3 below. In addition, the total time (total) required for this degreasing treatment and the first
Tables 1 to 3 also show the time required for the step.

[0108]

[Table 1]

[0109]

[Table 2]

[0110]

[Table 3]

As shown in Tables 1 to 3, Examples 1 to 3 were used.
In No. 18, the degreasing time was short, the appearance of the degreased body was good, and almost no defects were generated.

On the other hand, Comparative Example 1 has no defect but has a long degreasing time, and Comparative Example 2 has a short degreasing time but a high defect generation rate in the degreased body.

[0113]

As described above, according to the method for degreasing a molded article of the present invention, the degreasing time can be greatly reduced, and a defatted article of good quality without defects can be obtained. .

As a result, the productivity is improved, the consumption of the degreasing gas and the energy consumption for the degreasing can be reduced, and the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration example of a furnace used in the present invention.

FIG. 2 is a graph showing an example of changes over time in furnace temperature and pressure in the degreasing process according to the present invention.

FIG. 3 is a graph showing an example of a change over time in a furnace temperature and a pressure in a degreasing process according to the present invention.

FIG. 4 is a graph showing an example of a change over time in a furnace temperature and a pressure in a degreasing process according to the present invention.

FIG. 5 is a graph showing an example of a change over time in a furnace temperature and a pressure in a degreasing process according to the present invention.

FIG. 6 is a graph showing an example of a change over time in a furnace temperature and a pressure in a degreasing process according to the present invention.

FIG. 7 is a graph showing an example of changes over time in furnace temperature and pressure during degreasing according to the present invention.

FIG. 8 is a graph showing a change over time in a furnace temperature in a degreasing process of a comparative example.

FIG. 9 is a graph showing a change over time in a furnace temperature in a degreasing process of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace 2 Processing space 3 Mounting table 4 Heater 5 Stirrer 51 Motor 52 Stirring blade 6 Degreasing gas supply system 61-63 Pipe line 64 Selection valve 65 Pipe line 66 Flow control valve 7 Degreasing gas exhaust system 71 Pipe line 72 Vacuum pump 73 valve 74 conduit 75 valve 8 control means 10 molded body

Claims (16)

[Claims] 1. A method for degreasing a molded body obtained by heating a molded body obtained by molding a composition containing a raw material powder and a binder in a furnace to perform a degreasing treatment, wherein the degreasing is performed in a low temperature range. A first step and a second step of performing degreasing in a higher temperature range than the first step. In the first step, the degreasing atmosphere is reduced to a first pressure in a reduced pressure state, A method for degreasing a molded body, wherein the method is alternately switched to a second pressure higher than a pressure. 2. The degreasing method according to claim 1, wherein the heating temperature pattern in the first step has a tendency to increase with time as a whole. 3. The heating temperature pattern in the first step is a pattern in which a first pattern in which the temperature rises with time and a second pattern in which the temperature rise is stopped or reduced are alternately performed at least once. The method for degreasing a molded article according to claim 1 or 2, wherein 4. The method according to claim 2, wherein the switching between the first pressure and the second pressure in the first step is performed in accordance with a heating temperature rising pattern. . 5. The pattern of the heating temperature in the first step is a pattern in which a first pattern in which the temperature rises with time and a second pattern in which the temperature rise is stopped or reduced are alternately performed at least once. And the second pressure and the second pressure in the case of the first pattern.
The method according to claim 1, wherein the first pressure is set at the time of the pattern. 6. The method according to claim 1, wherein a difference between the first pressure and the second pressure is 35 torr or more. 7. The method according to claim 1, wherein the first pressure is not more than 50 torr. 8. The method according to claim 1, wherein the switching from the first pressure to the second pressure is performed twice or more. 9. The degreasing atmosphere in the first step is a degreasing gas obtained by mixing at least one selected from an inert gas, air, carbon dioxide gas, hydrogen gas, and ammonia decomposition gas. 9. The method for degreasing a molded article according to any one of items 8 to 8. 10. The method according to claim 1, wherein the first step and the second step are continuously performed. 11. The method according to claim 1, wherein the same type of degreasing gas is used in the first step and the second step. 12. The method according to claim 1, wherein the degreasing is performed while stirring the inside of the furnace in at least one of the first step and the second step. 13. The processing time in the first step is 2 hours.
The method for degreasing a molded article according to any one of claims 1 to 12, wherein the treatment is performed for about 25 hours. 14. The method according to claim 1, further comprising a third step of cooling the molded body after the second step. 15. The method for degreasing a molded article according to claim 1, wherein the molded article is a molded article obtained by injection molding. 16. The method according to claim 1, wherein the raw material powder is a metal powder, and the content of the metal powder in the molded body is 70 to 95 wt%.