JPH06345544A - Method for dewaxing molded body - Google Patents

Abstract

PURPOSE:To shorten the time required to remove a binder from a ceramic molded body before burning without causing degreasing cracking. CONSTITUTION:A compound prepd. by kneading powdery ceramic with a binder is injection-molded and the resultant molded body is set in a degreasing furnace and subjected to primary treatment at a low heating rate of about 5 deg.C/hr until average pore diameter is made almost constant. Secondary treatment is then carried out by heating to a specific temp. at a high heating rate of about 50 deg.C/hr to perfectly degrease the molded body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degreasing method required for producing ceramics or metal sintered parts.

[0002]

2. Description of the Related Art As a method for producing parts such as ceramics, a compound obtained by kneading ceramic powder and a binder is injection-molded, the molded body obtained by injection molding is heated to remove the binder, and then the molded body is formed. A firing method is generally used.

Various degreasing methods have heretofore been proposed since the removal (degreasing) of the binder from the above-mentioned molded body is insufficient, or when the binder is rapidly removed, the molded body becomes defective. For example, Japanese Unexamined Patent Publication (Kokai) No. 52-117909 discloses the use of two kinds of resins having different decomposition rates by heating as binders, and Japanese Unexamined Patent Publication (Kokai) No. 61-117166 discloses an inert atmosphere in the middle of degreasing. It is disclosed to switch to the atmosphere.

When degreasing is not limited to the above method, degreasing conditions are determined based on thermal analysis data. An example will be described based on FIGS. 3A and 3B. Here, (a) is the thermal analysis data of the wax-based binder,
(B) shows the thermal analysis data of the resinous binder, TG shows the thermogravimetric analysis curve, DTA shows the differential thermal analysis curve, and this data was obtained with a constant temperature rise gradient. As can be seen from the differential thermal analysis curve in FIG. 3 (a), an exothermic reaction (for example, a reaction such as CO removal) occurs at 235 ° C., 303 ° C., and 406 ° C. Since it is considered that the thermal decomposition is almost completed at 303 ° C, heating is carried out up to 303 ° C at a constant temperature rising rate at which degreasing cracks do not occur, and in Fig. 3 (b), it can be seen from the differential thermal analysis curve. As described above, the exothermic reaction occurs at 225 ° C., 331 ° C. and 408 ° C., but it is considered from the thermogravimetric analysis curve that the thermal decomposition is almost completed at 408 ° C.
The heating is performed up to 08 ° C. at a constant temperature rising rate at which degreasing cracks do not occur.

[0005]

[Problems to be Solved by the Invention] Japanese Patent Application Laid-Open No. 52-1179
The conventional degreasing methods that determine the degreasing conditions based on thermal analysis data, including the methods disclosed in Japanese Patent Publication No. 09 and Japanese Patent Application Laid-Open No. 61-117166, do not cause degreasing cracks and are completely degreased. Even if this is the case, the temperature at which the binder is completely pyrolyzed is calculated from the thermal analysis data, and the temperature is raised to this temperature at a constant rate, so it takes more time than is necessary and is wasteful.

[0006]

According to the present invention, it has been found from the data obtained by taking out a molded product in the middle of degreasing from an actual degreasing furnace that all the molded products have a constant pore size during the degreasing process. , Based on this knowledge,
The gist is that the heating rate is slowed from the start of heating in the degreasing step until the average pore size of the molded body becomes substantially constant, and then the heating rate is increased after the average pore size becomes substantially constant.

[0007]

When the pore size of the molded body becomes constant, this pore size is the same as the final pore size of the degreased body, and a sufficient space is secured as a discharge passage for the gas generated by the thermal decomposition of the binder.

[0008]

【Example】

(Example 1) A compound in which a wax binder (42.5 vol%) and ceramic powder are kneaded is injection-molded to obtain a molded body having a diameter of 10 to 20 mm and a length of 150 mm.
This molded body was placed in a porous container and set in a degreasing furnace, and then the furnace was evacuated to 5 ° C / 150 ° C / hour.
A primary treatment is performed in which the temperature is raised to 150 ° C. and the temperature is maintained at 150 ° C. for 3 hours. Here, the primary treatment temperature of 150 ° C. is the temperature at which the average pore diameter of the molded body becomes a constant value from FIG. Then, the temperature is raised to 500 ° C. at 50 ° C./hour in the atmosphere, and 5
The molded product was completely degreased by performing a secondary treatment of holding it at 00 ° C. for 1 hour. The resulting degreased body was completely degreased with no cracks, and the total degreasing time was 40 hours.

(Example 2) Wax type binder (42.5
(vol%) and ceramic powder are kneaded to obtain a molded product having a diameter of 10 to 20 mm and a length of 150 mm by injection molding. This molded body was placed in a porous container and set in a degreasing furnace. Then, the furnace was evacuated and replaced with a nitrogen atmosphere, and the temperature was raised to 220 ° C. at 5 ° C./hour, and 2
A primary treatment is carried out by holding at 20 ° C. for 3 hours. Here, 220 ° C., which is the primary treatment temperature, is the temperature at which the average pore diameter of the molded body becomes a constant value from FIG. After this, in the atmosphere at 50 ℃
/ The molded article was completely degreased by performing a secondary treatment in which the temperature was raised to 500 ° C./hour and the temperature was kept at 500 ° C. for 1 hour. The resulting degreased body was completely degreased with no cracks, and the total degreasing time was 54 hours.

Whether or not the average pore diameter has become constant may be directly measured, but as can be seen from the graph showing the relationship between porosity, temperature and time in FIG. When the porosity reaches 50% of the porosity of the molded product after degreasing, the average pore diameter becomes substantially constant. Therefore, even if the average pore diameter is indirectly known by measuring the porosity with a mercury porosimeter. Good. A specific example is shown below (Example 3).

(Example 3) Wax type binder (42.5
(vol%) and ceramic powder are kneaded to obtain a molded product having a diameter of 10 to 20 mm and a length of 150 mm by injection molding. This molded body was placed in a porous container and set in a degreasing furnace, and then air was circulated in the furnace at 5 ° C /
A primary treatment is carried out by raising the temperature to 200 ° C. every hour and holding the temperature at 200 ° C. for 3 hours. Here, the primary treatment temperature is 200
From FIG. 2, the temperature is a temperature at which the porosity of the molded product during degreasing reaches half the porosity of the molded product after degreasing, that is, 20%. After this, raise the temperature to 500 ° C at 50 ° C / hour in the atmosphere,
The molded product was completely degreased by performing a secondary treatment of holding it at 500 ° C. for 1 hour. The obtained degreased body was completely degreased without cracks, and the total degreasing time was 46 hours.

Example 4 Resin binder (48.0 vol
%) And ceramic powder are kneaded to obtain a molded body having a length of 50 mm, a width of 20 mm and a thickness of 5 mm. This molded body was placed in a porous container and set in a degreasing furnace. Then, the furnace was evacuated and then replaced with a nitrogen atmosphere, and the temperature was raised to 280 ° C. at 5 ° C./hour.
A primary treatment is carried out by holding at 80 ° C. for 3 hours. Here, the primary treatment temperature of 280 ° C. is the temperature at which the average pore diameter of the molded body becomes a constant value from FIG. After this, in the atmosphere at 50 ℃
/ The molded article was completely degreased by performing a secondary treatment in which the temperature was raised to 500 ° C./hour and the temperature was kept at 500 ° C. for 1 hour. The resulting degreased body was completely degreased with no cracks, and the total degreasing time was 66 hours.

From the above Examples 1 to 4, it can be seen that the degreasing method of the present invention is effective in any of vacuum atmosphere, nitrogen atmosphere and air atmosphere. It was found that the degreasing progresses from the initial stage of degreasing by increasing the speed, and the average pore diameter stabilizes quickly.

In mass-produced products, it is inefficient to check whether or not the average pore diameter has become substantially constant, so that the average pore diameter will be substantially constant in advance for each product shape and binder type. It is preferable to specify the following heating conditions and to determine the heating rate, the primary treatment temperature, the secondary treatment temperature, etc. in accordance with these.

Further, in the examples, the molded body composed of the ceramic powder and the binder was described, but a metal powder may be used instead of the ceramic powder.

[0016]

As described above, according to the present invention,
From the start of heating in the degreasing process until the average pore size of the molded body becomes substantially constant, that is, while the degreasing cracks are likely to occur, the heating rate is slowed, and after the average pore size becomes substantially constant, that is, degreasing cracks occur. Since the heating rate is increased after the occurrence of the occurrence of the problem is reduced, the total degreasing time can be greatly shortened.

Specifically, based on thermal analysis data obtained from thermogravimetric analysis and differential thermal analysis, Examples 1 to 3
Prepare the wax-based binder used in the above and the molded product, and raise the temperature at a constant rate (5 ° C / hour) to a temperature (about 300 ° C) at which the thermal decomposition of the binder is completed in each of vacuum atmosphere, air atmosphere and nitrogen atmosphere. Then, a secondary treatment of heating at 50 ° C./hour to 500 ° C. in the atmosphere was performed, and the secondary treatment was continued for 1 hour. The total degreasing time was 70 hours in any atmosphere. Also,
Prepare the resin-based binder and the molded body used in Example 4,
Temperature at which the thermal decomposition of the binder is completed in each of the vacuum atmosphere, air atmosphere, and nitrogen atmosphere (about 400 ° C)
Primary treatment to raise the temperature at a constant rate (5 ° C./hour) to 50 ° C./hour to 500 ° C. in the atmosphere, and then to hold for 1 hour. It took 90 hours to go in the atmosphere.
On the other hand, as described above, the total degreasing time is 40 hours in Example 1, 54 hours in Example 2, 46 hours in Example 3, and 66 hours in Example 4. Therefore, the degreasing time can be significantly shortened compared to the conventional case.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average pore size of a molded product and temperature and time.

FIG. 2 is a graph showing the relationship between the porosity of a molded product and the temperature and time.

3A and 3B are graphs showing thermal analysis data of a wax-based binder and a resin-based binder.

Front page continued (72) Inventor Takeshi Yasui 1-4-1 Chuo, Wako, Saitama Prefecture

Claims (3)

[Claims] 1. A degreasing method in which a compound obtained by kneading a ceramic powder or a metal powder and a binder is molded into a predetermined shape to obtain a molded body, and then the molded body is heated to remove the binder in the molded body. A method for degreasing a molded product, wherein the heating rate is slowed until the average pore size of the molded product becomes substantially constant, and then the heating rate is increased after the average pore size becomes substantially constant. 2. A degreasing method in which a compound obtained by kneading a ceramic powder or metal powder and a binder is molded into a predetermined shape to form a molded body, and then the molded body is heated to remove the binder in the molded body. Slow the heating rate until the porosity of the molded body becomes almost constant,
A degreasing method from a molded body, characterized in that the heating rate is increased after the porosity becomes substantially constant. 3. The average pore diameter is considered to be substantially constant when the porosity of the molded body during degreasing reaches 50% of the porosity of the molded body after degreasing. The method for degreasing a molded article according to claim 2.