JPH0148220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention belongs to the technical field of a degreasing material for ceramic molded bodies, a method for producing the same, and a method for using the same.

[Prior art]

For example, ceramic auto parts (hereinafter referred to as
Injection molding is used to mass produce ceramic parts (simply referred to as ceramic parts). That is,
Ceramic parts are formed into a product by injection molding (this intermediate product is hereinafter referred to as a ceramic molded body), degreased, and then fired.

The silicon nitrite powder that makes up the ceramic parts is constantly mixed with liquid resin during injection molding to give it fluidity (of course, once injection molding is complete, the resin hardens). liquidity will disappear). For this reason, resin is contained in the ceramic molded body made by injection molding. In this case, if the ceramic molded body is fired while containing this resin, the ceramic molded body will crack. Therefore, the above-mentioned degreasing refers to the operation of removing the resin from the ceramic molded body before firing the ceramic molded body.

Incidentally, such degreasing is performed by a degreasing device 11 as shown in FIG. In FIG. 2, 1 is a furnace whose interior is heated by an electric heater (not shown), and 2 is a degreasing can placed in the furnace 1. Degreasing can 2
A large number of crucibles 3 are arranged inside. The crucible 3 is filled with granular degreasing material 4. A ceramic molded body 5 is embedded in the degreasing material 4. An inert gas (for example, nitrogen gas) 6 is flowed into the degreasing can 2 during the degreasing operation. Note that in the figure, arrows indicate the flow of the inert gas 6.

The reason why degreasing is performed in the degreasing device 11 shown in FIG. 2 is as follows.

That is, the degreasing can 2 is heated by an electric heater (not shown).
By increasing the temperature of the ceramic molded body 5
The resin used during injection molding (e.g., adhesive polypropylene, Evaflex, paraffin, anthracene, etc.) oozes out in liquid form. When such liquid resin oozes out onto the surface of the ceramic molded body 5, the degreasing material 4 is removed one after another.
be absorbed by. Therefore, more and more of it oozes out from inside the ceramic molded body 5. On the other hand, since the temperature of the degreasing material 4 is high, the liquid resin adsorbed by the degreasing material 4 is thermally decomposed into a gas and carried away by the inert gas 6. In this way, the ceramic molded body 5 is degreased.

Note that when the degreasing is completed, each crucible 3 is taken out of the furnace 1. Then, the degreasing material 4 and the ceramic molded body 5 are placed in a container (not shown). From such a container, a ceramic molded body 5
only is taken out. The remaining degreasing material 4 is collected and used again to degrease the next ceramic molded body 5.

The degreasing material 4 used in FIG. 2 is granular particles with a diameter of about 10 to 50 μ. Each particle is made of silicon nitrite powder hardened with polyvinyl alcohol. The size of the silicon nitrite powder itself in each particle is approximately 0.8μ.

In addition, in Fig. 2, the temperature inside the furnace 1 rises at a rate of 4 degrees Celsius per hour, and the temperature rises relatively slowly.
The temperature is raised to about 450 degrees. The reason why the temperature is raised at such a slow rate is that if the temperature is raised rapidly, the ceramic molded body 5 may crack without being degreased. In this regard, the reason why the ceramic molded body 5 is buried in the degreasing agent 4 is that in addition to the role of the degreasing agent 4 in absorbing the resin exuding from the ceramic molded body 5, as described above, This is because it also plays a role in mitigating sudden changes in temperature.

[Problems with conventional technology]

In the conventional device as shown in FIG. 2, during repeated use of the degreasing material 4, the polyvinyl alcohol that solidifies the silicon nitrite powder deteriorates due to heat. Therefore, the force that solidifies the silicon nitrite powder becomes weaker.
Therefore, the silicon nitrite particles constituting each particle of the degreasing material 4 break apart, and the degreasing material 4 becomes very fine particles. Needless to say, these particles are silicon nitrite particles themselves. Because of this property, the following problems occurred in the device shown in FIG.

As a result of the degreasing material 4 becoming very fine particles, the ventilation of the inert gas becomes poor, and the gas generated by the decomposition of the resin becomes difficult to be discharged. For this reason,
Degreasing function decreases.

As a result of the degreasing material 4 being decomposed into individual silicon nitrite particles, the resin adsorption performance of the degreasing material 4 is reduced. Therefore, the degreasing function of the degreasing material 4 is reduced.

Because of the above, the number of times that the degreasing material 4 can be reused is small (usually about three times is the limit).

Moreover, as a result of the degreasing material 4 becoming extremely fine, the fluidity of the degreasing material 4 as particles is lost. Therefore, when trying to fill the crucible 3 with the degreasing material 4 together with the ceramic molded body 5, cavities are likely to be formed in the crucible 3. Therefore, the degreasing material 4
filling workability is reduced.

Furthermore, when the ceramic molded body 5 is taken out after completion of degreasing, fine degreasing material 4 adheres to the surface of the ceramic molded body 5. It takes a lot of effort to remove these fine particles (silicon nitrite particles themselves).

As mentioned above, the conventional degreasing material 4 itself is relatively fine granular (with a diameter of 10μ to 50μ).
It is noteworthy that the following problems occurred even though the polyvinyl alcohol had not deteriorated.

Since the air permeability of the degreasing material 4 is not good, the degreasing material 4
has low degreasing ability.

When attempting to fill the degreasing material 4, cavities are likely to be formed. Therefore, the workability of filling the degreasing material 4 is not good.

For example, for the above reason, as mentioned above, conventionally,
The temperature increase rate of the furnace 1 was set at 4° C. per hour, and it was not possible to increase the temperature any higher. Therefore, productivity was not good. Furthermore, as shown in FIG. 2, the degreasing material 4 is placed separately in the crucible 3, but this is because the conventional degreasing material 4 has the above-mentioned tendency. This is because it was difficult to fill the degreasing material 4 into the container.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems described in the section of the problems of the prior art.

[Structure of the invention]

According to the present invention, this object is achieved by a degreasing material for ceramic molded bodies, a method for producing the same, and a method for using the same, which have the following configurations.

That is, the degreasing material for the ceramic molded body according to the present invention is a pellet-shaped degreasing material, and each pellet is a sintered product composed of at least silicon nitrite powder and alumina powder. For each pellet, the alumina content ranges from 10% to 90% by weight, and the silicon nitrite content ranges from 90% to 90% by weight, almost inversely proportional to the alumina content.
It is characterized by a range of up to 10%.

Further, the method for producing a degreasing material for ceramic molded bodies according to the present invention includes a first step of mixing silicon nitrite powder and activated alumina powder, and a step of mixing the mixture with a large number of powders while adding water to the mixture. A second step of granulating into pellets, a third step of completely dehydrating the pellets, and a third step of calcining the completely dehydrated pellets in an inert gas at a temperature of about 1200 degrees Celsius to about 1400 degrees Celsius. It is characterized by consisting of 4 steps.

Furthermore, the method for using the degreasing material for ceramic molded bodies according to the present invention is such that each pellet is a sintered product composed of at least silicon nitrite powder and alumina powder, Regarding the pellets, the alumina content ranges from 10% to 90% by weight, and the silicon nitrite content ranges from 90% to 10% by weight, almost inversely proportional to the alumina content. A large number of pellet-shaped degreasing materials are collected, a ceramic molded body is buried therein, and the ceramic molded body is heated in an inert gas stream at a heating rate of more than 4 degrees Celsius per hour. It is characterized by removing organic matter from the molded body.

〔Example〕

Next, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a longitudinal sectional view of a degreasing apparatus for ceramic molded bodies according to an embodiment of the present invention.

In FIG. 1, 1 is a furnace whose inside is heated by an electric heater (not shown);
is a degreasing can placed in such a furnace 1.
During the degreasing process, the inside of the degreasing can 2 can be gradually heated by an electric heater (not shown).
The inside of the degreasing can 2 is divided into four rooms 1 by partition walls 12.
It is divided into 3, 14, 15, and 16 sections. Bulkhead 1
2 is provided with a large number of punch holes 17. Several ceramic molded bodies 5 are placed on each partition wall 12. four rooms 13, 14,
15 and 16 are all filled with pellet-like degreasing material 4. Therefore, the ceramic molded body 5 is buried in the degreasing material 4. During the degreasing process, an inert gas (for example, nitrogen gas) is supplied into the degreasing can 2 by an inert gas ventilation device (not shown).
6 is washed away. Note that in the figure, arrows indicate the flow of the inert gas 6. 20 and 21 are an inert gas inlet and an inert gas outlet, respectively.

In the degreasing apparatus 11 shown in FIG. 1, degreasing is carried out by heating to about 450 degrees Celsius at a temperature increase rate of 8 degrees Celsius per hour while flowing an inert gas. When the degreasing is completed, the degreasing material 4 and the ceramic molded body 5 are poured from the degreasing can 2 into a container (not shown). Only the ceramic molded body 5 is removed from such a container. The remaining degreasing material 4 is collected and used again to degrease the next ceramic molded body 5.

Each pellet of the pellet-like degreasing material 4 filled in the degreasing can 2 has a size of 12 mesh diameters (about 1 mm to 2 mm in diameter). Further, each pellet is made of a sintered material composed of at least silicon nitrite powder and alumina powder. The content of alumina in each pellet is 10% by weight.
% to 90%, and the content of silicon nitrite is adjusted to be approximately inversely proportional to the content of alumina, and the weight percentage is in the range of 90% to 10%. In the case of this example, the content of alumina is 40% by weight, and the content of silicon nitrite is 59% by weight. The remaining 1% is said to be yttrium oxide.

The pellet-shaped degreasing material 4 is manufactured through the following steps.

(a) The first step is to add ρ alumina powder and yttrium oxide powder to silicon nitrite powder and mix for about 30 minutes in a V-type mixer. Note that this mixing ratio is as described above.

(b) A second step of granulating the above mixture into pellets using a dish-type granulator while spraying water. At this time, the dish-type granulator is adjusted so that the pellet size is approximately 12 mesh diameter (approximately 1 mm to 2 mm in diameter).

(c) A step of completely hydrating the pellets produced in the above step in steam at about 150 degrees Celsius for about 15 hours. This step gives the pellets even more strength. Note that this step does not have to be done, so here we will focus on the third step in particular.
(If this step is called the third step, the following step must be called the fourth step, and this corresponds to the step number in claim 2.) due to confusion in the relationship).

(d) The third step is to completely dehydrate the pellets in a drying oven at approximately 150 degrees Celsius.

(e) Completely dehydrated pellets are heated in an inert gas (e.g. nitrogen gas) from about 1,200 degrees Celsius to about 1,200 degrees Celsius.
The fourth step is firing at a temperature in the range of 1400 degrees.

The reason why alumina is mixed into the silicon nitrite powder in this example is as follows.

That is, the firing temperature of silicon nitrite is high (usually about 1800 degrees Celsius), whereas the firing temperature of alumina is relatively low (usually about 1300 degrees Celsius).
Therefore, the firing temperature can be low when firing the pellets in the fourth step. Note that in the fired pellets, the silicon nitrite powder is held in the alumina powder.

Furthermore, as mentioned above, the content of alumina ranges from 10% to 90% by weight, and the content of silicon nitrite is approximately inversely proportional to the alumina content, ranging from 90% to 90% by weight. The reason why the range is limited to 10% is because the following three facts have become clear through experiments conducted by the applicant.

(A) If the alumina content is less than 10% by weight, granulation will be difficult even if you try to granulate it with a dish granulator. Further, even if granulation is possible, the resulting pellets have low strength and easily fall apart.

(b) When the content of silicon nitrite becomes less than 10% by weight, the ability of the resulting pellets to adsorb resin becomes weak to the extent that it is not practically satisfactory.

(c) If the content of alumina and the content of silicon nitrite are within the above range, both the power of alumina to hold silicon nitrite powder and the power of silicon nitrite to adsorb resin will be practically satisfactory. is obtained.

In addition, ρ alumina is used as alumina because ρ alumina has the highest activity, that is,
This is because it has the strongest ability to absorb water and therefore has the strongest ability to solidify into pellets. Note that such ρ alumina is converted to α alumina after firing. Although ρ alumina is used in this example, other activated aluminas other than ρ alumina may be used. This is because activated alumina other than ρ alumina (such as γ alumina) is
This is because it has similar activity, although not as much as alumina.

Furthermore, in this example, the firing is performed in an inert gas (see the fourth step) because silicon nitrite decomposes into simple silicon if fired in the atmosphere.

Further, in this example, yttrium oxide is mixed because, like alumina, yttrium oxide has the property of acting as a binder for silicon nitrite powder.

Note that in the first step, a device other than the V-type mixing machine may be used to mix the silicon nitrite powder, the ρ alumina powder, and the yttrium oxide powder. In the second step, the pellets may not be made using a dish granulator, but other machines may be used. Further, a substance other than water vapor may be used for the complete hydration reaction.

As mentioned above, in this example, the degreaser 4
Pellets made of silicon nitrite powder and alumina powder (and yttrium oxide powder) are used as the material. That is, alumina (and yttrium oxide) is used as a binder for silicon nitrite particles, and polyvinyl alcohol is not used as in the conventional method. Moreover, such pellets are fired at a temperature of about 1200 degrees Celsius to about 1400 degrees Celsius. Therefore, it does not deteriorate at the temperature used during degreasing (as mentioned above, up to 450 degrees Celsius). In addition, since it has already been fired, it is inevitable that
It also has great mechanical strength. Therefore, no matter how many times the degreasing process is repeated, the pellets will not return to separate silicon nitrite powder. Thus,
The problems described in the section on problems of the prior art do not occur.

Further, the degreasing material 4 of this embodiment is a pellet having a size of about 12 mesh anda, as described above, and is not a granule as in the conventional case. For this reason, (a) it has excellent breathability when filled.

(b) Also, cavities are not formed when filling. Therefore, the workability during filling is excellent.

Therefore, as an advantage brought about by the above (a), in the degreasing device 11 according to this embodiment, the resin exuding from the ceramic molded body 5 is quickly removed by the inert gas. In other words, the degreasing speed becomes faster than before. In this way, it becomes possible to increase the temperature increase rate of the degreasing can 2 higher than before (as mentioned above, the temperature increase rate was conventionally limited to 4°C/Hr,
In this example, 8°C/Hr is also possible).

Further, as an advantage brought about by the above (b), in the degreasing device 11 according to the present embodiment, there is no need to separately fill the crucible 3 with the degreasing material 4 as in the conventional case. Therefore, since the crucible 3 is not required, the cost is reduced accordingly. Naturally, workability and productivity also improve.

〔Effect of the invention〕

As can be seen from the description of the above embodiments, the present invention
It has the following effects.

Since the degreasing material does not deteriorate, the degreasing function does not deteriorate.

Since the degreasing material has high mechanical strength and does not become fine, the degreasing function does not deteriorate.

Because of the above, the number of times the degreasing material can be reused is significantly increased (according to experiments conducted by the present applicant, it has been confirmed that it can be reused up to 30 times).

Since the degreasing material of the present invention is composed of pellets of appropriate size, it has excellent air permeability when filled. Therefore, it has better degreasing ability than conventional products. As a result, it becomes possible to increase the temperature increase rate more than before, and therefore productivity improves.

Since the degreasing material of the present invention is composed of pellets of appropriate size, no cavities are formed when it is filled.
Therefore, the workability during filling is excellent. Therefore, a conventional crucible is not required. Therefore,
It is possible to reduce costs accordingly.
Naturally, workability and productivity are also improved.

Furthermore, the degreasing material does not adhere to the surface of the ceramic molded body when the ceramic molded body is taken out after completion of degreasing. Therefore, there is no need to remove the adhered degreasing material as in the conventional case.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a degreasing device according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a conventional degreasing device. 1... Furnace, 2... Degreasing can, 4... Degreasing material, 5...
...ceramic molded body, 6...inert gas, 11...
...Degreasing equipment for ceramic molded bodies.

Claims (1)

[Scope of Claims] 1 A pellet-shaped degreasing material, each pellet being a sintered product composed of at least silicon nitrite powder and alumina powder, and each pellet containing alumina. The amount ranges from 10% to 90% by weight, and the content of silicon nitrite is approximately inversely proportional to the content of alumina, and ranges from 90% to 10% by weight. A degreasing agent for ceramic molded bodies. 2. A first step of mixing silicon nitrite powder and activated alumina powder, a second step of granulating the mixture into a number of pellets while adding water to the mixture, and a second step of completely dewatering the pellets. 3, and a fourth step of firing the completely dehydrated pellets in an inert gas at a temperature of about 1200 degrees Celsius to about 1400 degrees Celsius. Production method. 3. Each pellet is a sintered product composed of at least silicon nitrite powder and alumina powder, and the alumina content of each pellet ranges from 10% to 90% by weight. The silicon nitrite content is approximately inversely proportional to the alumina content, and the weight ratio ranges from 90% to 10%. A degreasing material for a ceramic molded body, characterized in that organic matter in the ceramic molded body is removed by burying the ceramic molded body in a stream of inert gas and raising the temperature at a temperature increase rate of more than 4° C. per hour. How to use.