JPH03218984A - How to remove binder - 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 [Industrial Application Field] The present invention relates to a process for removing a thermoplastic binder from a press-molded powder body containing a thermoplastic binder to impart press-formability. This invention relates to a binder method.

0 Prior Art] In order to impart pressure moldability, for example, one or two of metal powder, ceramic powder, and cerment powder are used.
The amount of thermoplastic pine goo added to and kneaded in the powder containing seeds or more is at least 25 vol% of the kneaded material.
exceeds. An important technical issue is a de-binding method that removes this thermoplastic binder from a press-molded product while maintaining its shape without causing deformation, blistering, or cranking due to its own weight. It becomes.

In line with this intention, Japanese Patent Publication No. 61-48563 discloses a binder removal method in which an inert gas is blown in a turbulent flow onto a press-molded body. Also, special public service in 1986
Japanese Patent Publication No. 33282 proposes a binder removal method in which the atmospheric pressure of a press-molded body is maintained in a pressurized state that is equal to or higher than the vapor pressure of a thermoplastic binder.

[Problem to be solved by the invention]

The technique disclosed in the above-mentioned Japanese Patent Publication No. 61-48563 cannot prevent the bulging or cracking of the press-molded product that occurs during dehindering due to the turbulent flow of the blown gas, so it is difficult to vaporize the thermoplastic binder. Although it is expected that it will speed up the debinding process, in reality it is difficult to maintain a uniform turbulent state throughout the interior of the debinding furnace.

As a result, even if the atmospheric temperature in the debinding furnace is uniform, the debinding speed is different between the side facing the air and the back side of the press-formed body, and even within a single press-formed body. Depending on the location, the degree of binder removal may be uneven. Furthermore, when a plurality of press-formed bodies are housed in a debinding furnace, the above-mentioned tendency becomes severe and deviations occur in the progress of debinding between the press-formed bodies. Therefore, in reality, there is a problem in that it is difficult to stably obtain sound debinding properties without deformation due to its own weight and without the occurrence of blisters or cranks.

Furthermore, as in the technique disclosed in Japanese Patent Publication No. 62-33282, keeping the atmospheric pressure in a pressurized state throughout the debinding process increases the boiling point of the thermoplastic binder contained in the press-molded product. Since the difference between the melting point and the boiling point of this thermoplastic hainter becomes larger than in the case of a normal pressure atmosphere, boiling vaporization of the thermoplastic hainter in the press-molded product is suppressed, and defects such as blistering or cracking are prevented. Efficacy is predicted for prevention. However, keeping the interior of the binder removal furnace in a pressurized atmosphere from beginning to end causes an increase in the boiling point of the thermoplastic binder, as described above, which slows down the vaporization of the binder. That is, since the progress of binder removal is shifted to the high temperature side with respect to the normal pressure state, for example, debinding hardly progresses in the temperature range near the melting point of the thermoplastic binder, where deformation due to its own weight is most likely to occur. Therefore, there is a problem in that the press-molded body is inevitably deformed due to its own weight.

Furthermore, in order to complete debinding, it is necessary to raise the temperature at which debinding ends to a higher temperature by an amount corresponding to the added pressure in the atmosphere, which lengthens debinding time and increases heating energy. There is a problem in that it leads to

The present invention aims to solve these problems, and although the thermoplastic binder can be removed from a press-molded product in a short time, it does not cause deformation, blistering, or cranking due to its own weight. It is an object of the present invention to provide a method for healthy debinding that does not cause such problems.

[Means to solve the problem]

Therefore, the present invention provides a binder removal method for removing a thermoplastic binder from a powder press-molded article containing a thermoplastic binder in order to impart press-formability. (2) vaporizing a part of the thermoplastic binder by placing it in a reduced pressure atmosphere below normal pressure and heating it to a temperature below the melting point of the thermoplastic binder contained in the press-molded body; The atmospheric gas pressure of the press-molded body is set to normal pressure or higher pressure using an inert gas for the powder material, and the atmospheric temperature of the press-molded body is adjusted to the temperature of the thermoplastic binder contained in the press-molded body. (3) Lowering the atmospheric gas pressure of the press-molded product to below the gas pressure in (2) above, and reducing the atmospheric temperature so that at least the majority of the thermoplastic binder is vaporized. The gist is a debinding method that includes the step of raising the binder to a temperature at which it is removed.

[Function] In the correlated transformation of a solid, a liquid, and a gas, the influence of atmospheric pressure is less on the equilibrium temperature (boiling point) between a liquid and a gas (vaporized vapor) than on the equilibrium temperature (melting point) between a solid and a liquid.
Based on the knowledge that the value of Therefore, by controlling the atmospheric pressure and temperature of the press-molded body, the thermoplastic binder is made to behave most effectively for healthy debinding.

In step (1) described above, the press-molded body is placed in a reduced pressure atmosphere and heated at a temperature below the melting point of at least the thermoplastic binder contained in the press-molded body, so that a portion of the pine goo is heated. It vaporizes through transformation between solid and vapor.

This vaporized vapor also evaporates from the surface layer of the press-molded body.

(2) At the process stage, the atmospheric pressure is reduced by an inert gas (for example, N2 gas for Fe-based materials, air for stainless steel-based materials, etc.) for the powder material selected to make up the Kada compact. Since the pressure is restored to normal pressure or higher and the atmospheric temperature is raised, debinding proceeds while preventing blistering or cranking due to severe vaporization, and the thermoplastic binder is removed in the press-molded product. The area occupied by the area begins to become porous.

This porous formation causes the thermoplastic binder to flow out from the inside of the press-molded body to the surface layer, and is further diffused from the surface, thereby promoting binder removal.

In the step (3), the atmospheric pressure of the press-molded body is lowered to below the gas pressure in the step (2), and the atmospheric temperature is raised to a temperature sufficient for vaporizing the thermoplastic binder. The thermoplastic solder is quickly removed.

Through the steps ( ]), (2) and (3), the thermoplastic Hinter vaporizes without bumping in a short time,
The area where the thermoplastic binder has diffused becomes porous, and this porous phenomenon promotes the movement of the thermoplastic binder to the surface of the press-molded product, which is then heated to a temperature at which vaporization progresses at a sufficient rate. As a result, overall rapid debinding is achieved.

〔Effect of the invention〕

As described above, the present invention allows the thermoplastic binder to adopt the most preferable behavior at each stage of the debinding process, so that the binder can be removed in a short period of time as a whole. Sound debinding can be performed without defects such as blistering or cracking.

[Example] Next, a specific example of the method of the present invention will be described with reference to the drawings.

Average particle size 4.5! M, carbon content 0.01%, oxygen ¥0.
4500 g of 2% spherical iron powder was used as the powder material. The thermoplastic binder is a mixture of acrylic, 727 polypropylene, and paraffin wax in a ratio of 1:1:1. When each component of the thermoplastic binder is heated under normal pressure, it has been clearly observed that acrylic starts to evaporate at 270-300°C, Acuteic polypropylene at 230-260°C, and paraffin wax at 190-220°C. Ta.

The thermoplastic binder 5 is added to 4500 g of the powder material.
00g was added and kneaded in a pressure kneader at 140°C for 2 hours. The obtained kneaded material is crushed and supplied to an injection molding machine,
A press-molded body as shown in FIG. 1 was molded under the conditions of 150°C and It/cd (this press-molded body was sintered after removing the binder to become a sintered part). The pressure-formed product was placed in an upright debinding furnace as shown in Figure 1, and then left at room temperature (as shown in Figure 2).
The temperature was raised from room temperature to 280°C at a rate of 15°C/h, then raised to 400''C at a rate of 30°C/h, held at that temperature for 2 hours, and then cooled. The atmospheric pressure in the debinding furnace was varied as shown in Table 1.After debinding and debinding, each molded product was subjected to an external inspection and an internal inspection using X-rays.The results are shown in Table 1. The results were as shown in the table.

Example 1 - (Atmospheric temperature at the re-process stage, (2) process stage li!, and (3) process stage was changed from normal temperature to 100%
°C], (100-280 °C] and [280″C]
−400°C]. The atmospheric pressure was (1) 10-” torr vacuum at the process stage, (2) N2 at the process stage.
The pressure was controlled to be pressurized to 5 atmospheres by gas, and then to normal pressure by N2 gas in the step (3).

Example 2 At the same ambient temperature as in Example 1, the atmospheric pressure was (1
The pressure was controlled to be a vacuum of 10-2 torr in step (2), normal pressure using N2 gas in step (3), and continued to be at normal pressure in step (3).

Example 3 At the same ambient temperature as in Example 1, the atmospheric pressure was (1
The pressure was controlled to a vacuum of 10-2 Lorr in step (2), normal pressure using N2 gas in step (3), and a vacuum of 10-2 Lorr in step (3).

The de-soldering molded bodies according to Examples 1, 2 and 3 are as follows:
In all cases, A: No deformation due to its own weight was observed and good shape retention; B: No swelling, membrane tension, or crank formation was observed in appearance; C: Hole defects were found in the structure even when internally observed using X-rays. The results were good, with no occurrence of cranks, and sound debinding with no defects.

Comparative Example 1 - At the same ambient temperature as in Example 1, the atmospheric pressure was maintained at normal pressure using N2 gas from the beginning to the end of binder removal. The binder-free molded body deforms greatly due to its own weight,
The height was also less than half, and it remained in its original shape. In particular, it was observed that this deformation occurred relatively early in debinding when the atmosphere temperature was 150°C or less, and the results were poor.

Comparative Example 2 At the same ambient temperature as in Example 1, the atmospheric pressure was maintained at a vacuum of 10<-2 >torr from the beginning to the end of binder removal. Although the binder-free molded product showed no deformation due to its own weight and had good shape retention, several blisters and film-forming phenomena were observed on the surface, and cracks also occurred, resulting in poor results. It has been confirmed that these defects are caused by rapid gasification of the binder in the temperature range of 100 to 280°C.

Table 1 Table showing the atmospheric temperature and pressure in the debinding furnace

[Brief explanation of drawings]

FIG. 1 is a perspective view of a press-molded body in a specific example of the method of the present invention, and FIG. 2 is a graph showing an increase in ambient temperature in a specific example of the method of the present invention.

Claims (1)

[Scope of Claims] 1. A binder removal method for removing a thermoplastic binder from a pressed powder body containing a thermoplastic binder to impart pressure moldability, comprising: (1) Pressure molding. a step of vaporizing a part of the thermoplastic binder by placing the body in a reduced pressure atmosphere below normal pressure and heating it to a temperature below the melting point of the thermoplastic binder contained in the press-molded body; Using an inert gas for the selected powder material, the atmospheric gas pressure of the press-molded body is set to normal pressure or higher pressure, and the atmospheric temperature of the press-molded body is adjusted to the heat contained in the press-molded body. (3) lowering the atmospheric gas pressure of the press-molded body to below the gas pressure in (2) above, and reducing the atmospheric temperature so that at least a large part of the thermoplastic binder is vaporized. A method for removing a binder, comprising the step of increasing the temperature to a temperature at which the binder is removed. 2. The binder removal method according to claim 1, wherein the powder of the press-molded body is a mixed powder of one or more of metals, ceramics, and cermets.