JPS63297275A - Method for degreasing - Google Patents

Abstract

PURPOSE:To save quantities of supply electric power and an inert gas, by carrying out degreasing of a compact containing ceramics powder and a resin component in the initial and final periods in air in a degreasing furnace and simultaneously performing degreasing in the middle period in an inert gas atmosphere. CONSTITUTION:A compact containing ceramics powder and a resin component is heated in air in a degreasing furnace to heat the compact to the first temperature below a temperature at which the above-mentioned resin component melts. The aforementioned compact is then heated from the above-mentioned first temperature to the second temperature in an inert gas atmosphere and degreased so that the aforementioned binder may not flame up in air. After this step, the inert gas in the above-mentioned furnace is replaced with air while keeping the aforementioned compact at the above-mentioned second temperature.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) This invention relates to the degreasing of powder moldings containing a molding aid, and particularly to powder moldings containing a large amount of the molding aid. This invention relates to a method for degreasing powder molded articles suitable for degreasing objects.

(Prior art) Generally, fine ceramic products are produced by putting raw material powder prepared by adding molding aids and sintering aids into a mold, molding it, degreasing it, and then sintering it in a firing process. will be developed. Conventionally, there are various methods for the above-mentioned molding, such as press molding using a dry press, isostatic pressing, mud-breaking molding, and solid molding, but these molding methods are not suitable for mass production. Therefore, as a method for efficiently molding 7-in-se-2 mixes, a method of molding by injection molding is being developed and being developed.

However, in order to mold fine ceramics by injection molding, it is necessary to impart suitable fluidity to the powder, and it is necessary to add a larger amount of molding aid than in conventional molding methods. The amount added is based on the powder type, particle size distribution,
Average grain size 4 degrees, specific surface area.

Although it varies depending on the type of molding aid, etc., 1
It ranges from 8 to 3 Qwt%. Usually, the added forming aid evaporates due to heating in the degreasing process.

However, in the conventional degreasing process, an inert gas such as nitrogen is supplied at a constant flow rate throughout the degreasing process.In other words, at the point when the temperature in the degreasing furnace starts to rise Inert gas was continuously supplied from 1 to 2 until the ascent was stopped and cooling was completed.

However, in this method of supplying inert gas during the entire degreasing process, the amount of gas used is large (and the cost required for degreasing increases.1) In an inert gas atmosphere, the maximum heating temperature cannot be increased. It is necessary to set the temperature higher, and the power consumption increases due to the heat diffusion caused by the inflow and outflow of inert gas, which together with the gas consumption increases, increases the degreasing cost.Furthermore, In an inert gas atmosphere, a trace amount of carbon components remains as a residue, and this residual liquid may cause deterioration in the strength of the ceramic product after sintering.

(Problems to be Solved by the Invention) The present invention has been made in consideration of the above circumstances, and is a degreasing method that reduces power consumption, reduces degreasing costs, and contributes to quality improvement. and its apparatus.

[Structure of the invention]

(Means and effects for solving the problem) Degreasing in a degreasing furnace is performed in an oxidizing atmosphere at the beginning and end of degreasing, and in an inert gas atmosphere during the intermediate stage of degreasing. This also makes it possible to reduce the amount of inert gas supplied.

(Example) Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a degreasing apparatus used in the degreasing method of this embodiment. This device consists of a furnace body (1) made of, for example, a refractory material, a heater (2) installed on the entire inner wall of this body (1), and a power supply for this heater (2). A power supply (3) for supplying power to the furnace body (1), an opening/closing door (5) for taking in and out the fine ceramic powder moldings (4)... to the furnace body (1), and a door (5) installed in the furnace body (1) Powder molded product (
4) A mounting table (6
), and a gas supply pipe (7) whose one end opens inside the furnace body (1) and whose other end is provided outside through the furnace body (1)
), a solenoid valve (8) whose outer end of the gas supply pipe (7) is connected to the gas outflow side, and a nitrogen (Nt) gas source (9) connected to the gas inflow side of this solenoid valve (8). ), an air intake port also connected to the gas inflow side of the solenoid valve (8), and an N
A flowmeter αυ is installed between the gas source (9) and the solenoid valve (8) to measure the flow rate of the gas and output an electric signal 8F indicating the flow rate, and a A temperature sensor a2 that detects and outputs an electric signal ST indicating the furnace temperature, and a control section that inputs the electric signals 8T and 8F and controls the solenoid valve (8) and power source (3) according to a predetermined program to be described later. C13, the exhaust duct α-hiro provided at the top of the furnace body (1), and this exhaust duct) (organic gas emitted from the powder molded product (4)... connected to the outer end of 141 and degreased) The powder molded product (4)... is made by adding 2Qwt% of wax-based binder as a molding aid to silicon nitride (si, N,). The mounting table (6) has a structure in which the powder molded products (4) can be stored in multiple stages.

Next, a degreasing method of the present invention using the degreasing apparatus having the above configuration will be described.

First, open the opening/closing door (5) and place the powder moldings (4) formed by injection molding on the mounting table (6) provided in the furnace body (1) in multiple stages so as not to touch each other. Store it like this.

Next, close the opening/closing Jif (5) and close the powder molding (4).
... is sealed in the furnace body (1), and then a signal Sv is applied from the control unit (13) to the solenoid valve (8) to cause air to flow into the furnace body (1) from the air intake port. Next, the control unit αJ applies a temperature control signal SC to the power supply (3) based on the electric signal 8T from the temperature sensor α3 so that the temperature inside the furnace becomes as follows (see Fig. 2). That is, first, the temperature is raised from room temperature to 100°C at a rate of 4°C/hour.In other words, from room temperature to 140°C, degreasing is performed in an air atmosphere.Then, the furnace temperature is raised to 100°C at a rate of 4°C/hour. When the temperature reaches 140°C, which is lower than the melting temperature of the reactor, the solenoid valve (8) is switched and nitrogen and gas are supplied from the gas source (9) into the furnace body (1) at a rate of 780 m''/trial.

Then, the temperature was raised from 140°C to 200°C at a rate of 1°C/hour, then from 200°C to 300°C at a rate of 2°C/hour, and then from 300°C to 400°C for 5
Raise the temperature at a rate of °C/hour. That is, in a temperature range where the resin component in the organic binder is thermally oxidized, the inside of the furnace is replaced with an inert gas atmosphere. At this time, about 95% of the organic binder
0 and 10 are removed as organic gases and discharged from exhaust ducts 0 to combustion burner α9, becoming harmless gases. When the temperature in the furnace body (1) reaches 400°C, at which the organic binder does not ignite, the temperature rise in the furnace is stopped and the temperature rises to 400°C.
Switch the solenoid valve (8) again while maintaining the temperature at 0°C. As a result, air is allowed to flow into the furnace body (1) through the air intake port αQ, and the atmosphere inside the furnace is gradually replaced with air by natural diffusion, thereby performing in-air degreasing for about 6 hours. By this in-air degreasing at 400° C., the organic binder in the powder molded product (4) undergoes an oxidation reaction and is diffused and removed, so that it does not remain as a carbon-containing residue. Also, heater (2)...
As shown in Table 1, compared to the case where the furnace temperature is raised to 500° C. in an N1 gas atmosphere throughout the degreasing process, as shown in Table 1, N.

Gas supply amount is 37%, and power supply amount to heater (2)... is 6! ! +Reduce.

Table 1 Furthermore, as mentioned above, since almost no carbon residue remains in the powder molded product (4)... as shown in Table 2, it can be heated up to 500°C in a N or gas atmosphere. Compared to the conventional method of degreasing by raising the temperature, the three-point bending strength and density measured on test pieces cut from the sintered body are slightly improved.

Table 2 Thus, when the degreasing in the air is completed, the heater (2)
Stop power supply to ... and allow the furnace to cool to room temperature in an air atmosphere.

Note that the temperature increase rate in the above examples is for ceramics,
It may be changed as appropriate depending on the type and amount of the binder. Furthermore, helium (He) gas or argon (Ar) gas may be used instead of Nt gas. Furthermore, in the above embodiment, the exchange between N, gas and air is performed using a solenoid valve (
8), but using separate supply pipes,
This may be done by opening and closing the opening/closing door.

〔Effect of the invention〕

In the degreasing method of the present invention, the initial stage of raising the temperature for degreasing and the final stage of raising the temperature for degreasing are performed in air, and the intermediate stage is degreased in an inert gas atmosphere, so the maximum degreasing temperature is compared. The temperature can be set to a low temperature, and the amount of power supplied for heating up and the amount of gas used to create an inert gas atmosphere can be saved, improving economic efficiency and lowering production costs. Furthermore, this atmospheric degreasing prevents any carbon-containing residue from remaining in the powder compact after degreasing, so the mechanical properties after sintering are consistent with those of the powder degreased in an inert gas atmosphere. This is somewhat improved compared to molded products.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a degreasing apparatus used in a degreasing method according to an embodiment of the present invention, and FIG. 2 is a graph for explaining the same degreasing method. (1): Furnace body, (4): Powder molded product. (9): N! gas source. Agent Patent Attorney Noriyuki Chika Yudo Mitsuyuki Matsuyama

Claims (1)

[Claims] A molded body made of ceramic powder and an organic binder containing a resin component is heated in the air in a degreasing furnace from room temperature to below the temperature at which the resin in the organic binder melts and in the vicinity of the first
a first step in which the temperature is raised to a temperature, and a second step in which the organic binder in the molded body is reduced from the first temperature in an inert gas atmosphere to an extent that the organic binder in the molded body does not ignite in the air after this first step. A second step of raising the temperature to a temperature and degreasing the molded body, and after this second step, gradually replacing the inert gas in the degreasing furnace with air while holding the molded body at a temperature near the second temperature. A degreasing method characterized by comprising a third step of.