JPH0820182B2 - Sintering furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintering furnace for sintering a powder molded product which is molded by adding a wax, a binder and the like.

Conventional technology Conventionally, the fields in which sintering furnaces were used were limited to special fields for manufacturing superalloys, fine ceramics, etc. It is also used in the field of manufacturing and processing industrial equipment parts, which are extremely demanding, and not only when manufacturing precision parts with complicated shapes that could not be completed by conventional machining or precision casting, economic efficiency, work environment improvement, etc. From the viewpoint of the above, there are many cases where a sintering furnace is used also when manufacturing a metal part whose processing is not so difficult. Moreover, since the manufacturing of industrial equipment parts by the sintering furnace is very suitable for mass production, it is expected that switching from machined products to powder metallurgy products will be actively carried out in the future.

In such a conventional sintering furnace, a mounting table for mounting a powder molded product, which is an injection molded product of a raw material powder to which wax or the like is added, is disposed inside a furnace shell to which a vacuum exhaust pump or the like is connected. A heater for heating the powder molded product is provided around the mounting table, while the pressurized nitrogen gas introduced from the outside of the furnace shell is internally circulated to generate powder at a high temperature. A cooling gas circulation mechanism for forcibly cooling the product is provided so that a good sintered body can be obtained. Since the sintering temperature (about 1200 ° C) is extremely high, graphite is used as the material of the mounting table. Therefore, in a series of heat treatment processes such as dewaxing and sintering, In order to prevent the so-called carburizing phenomenon, which is one of the factors that impair the quality, a carburizing inhibitor made of alumina powder or the like is laid on the contact surface on which the powder molded product is placed.

However, in the case of the above-mentioned conventional example, if the object to be heat-treated is a relatively large-sized powder sintered product, the performance as an apparatus can be fully enjoyed without any problems, but from the flow of the times. The heat treatment of small-sized powder-sintered products, for which demand is expected to increase, has the following two drawbacks. First, as a first drawback, when the cooling gas circulation mechanism is driven while the series of heat treatment steps are sequentially performed, the powder sintered product is scattered around with the carburizing inhibitor due to the wind pressure of the pressurized nitrogen gas. The second disadvantage is that although the surface temperature variation of the powder molded product must be suppressed to at least ± 3 ° C, the heat capacity of the powder sintered product and the mounting table is equivalent. Due to such a difference, the difference in surface temperature between the facing surface of the heater and the contact surface of the mounting table is far beyond this allowable range. These disadvantages mean that good heat treatment cannot be performed if the target of heat treatment is a small powder sintered product, which can be a major obstacle in converting industrial machined parts machining products to powder metallurgy products. .

The present invention was devised in view of the above circumstances, and an object thereof is to provide a sintering furnace capable of performing excellent heat treatment even with a small powder sintered product.

Means for Solving the Problems The sintering furnace according to the present invention is arranged opposite to the heater, and has a mounting table having a recessed portion for accommodating an object to be processed, and a cooling medium flow path embedded in the mounting table, A cooling gas circulation mechanism, which is provided in the furnace shell and circulates a cooling gas introduced from the outside of the furnace shell, is provided.

The object to be processed, which is accommodated in the concave portion of the mounting table, is heated by the heating heater via the mounting table in the heated state, while it is heated through the mounting table in the cooling state by the cooling medium flowing in the cooling medium distribution path. In addition to being cooled, even if cooling gas circulates inside the furnace shell due to the cooling gas circulation mechanism, it is contained in the concave portion that is slightly lower than the upper surface of the mounting table. , No direct wind pressure of the cooling gas is given.

Example An example of a sintering furnace according to the present invention will be described below with reference to the drawings. FIG. 1 is an internal configuration diagram of a sintering furnace, FIG. 2 is a perspective view of a mounting table, and FIG. 3 is a sectional view taken along the line AA of FIG.

Opening and closing doors 11 for loading and unloading the powder molded product a to be heat-treated are respectively provided on both open end surfaces of the cylindrical furnace shell 10, and inside the furnace shell 10, a cylindrical heat insulating wall 12 is provided. It is arranged. Moreover, on the back side of the opening / closing door 11, heat insulating doors 121 for closing both open end surfaces of the heat insulating wall 12 are provided. Further, a plurality of rod heaters 13 as heating heaters are fixed to the inner wall of the heat insulating wall 12, and the powder molded product a is placed inside the heat insulating wall 12 corresponding to the position where each rod heater 13 faces each other. A plurality of mounting bases 20 are arranged. On the other hand, a carrier gas introduction path 15, a vacuum exhaust path 16 and the like are connected to the wall surface of the furnace shell 10, respectively, and vapor gas generated from the powder molded article a at the time of dewaxing was supplied through the carrier gas introduction path 15. The carrier gas is transferred and recovered by a wax trap device (not shown) provided in the middle of the vacuum exhaust path 16.

By the way, since the sintering temperature (about 1200 ° C.) of the powder molded product a is very high, the main constituent parts inside the furnace shell 10 represented by the rod heater 13 and the mounting table 20 are made of graphite. If these components are exposed to the atmosphere while having a high temperature, they will oxidize and deteriorate. Therefore, from the viewpoint of shortening the cycle of the heat treatment process, one of the doors 11 is provided with a cooling gas circulation mechanism 14 for forcibly cooling the internal components of the furnace shell 10 including the powder molded product a for which the heat treatment has been completed. Equipped. The cooling gas circulation mechanism 14 includes a cooling fan 141 that circulates the pressurized oxygen gas or the like introduced into the furnace shell 10, and a heat exchanger 142 that includes an erotic fin tube arranged around the cooling fan 141.
With the heat insulating door 121 slightly opened, the pressurized nitrogen gas is forcibly circulated, and in this process, the powder molded product a stored on the mounting table 20 is also cooled. . Next, the mounting table 20 will be described in detail. As shown in FIG. 2, recesses 22 arranged in 5 rows and 5 columns are provided on the upper surface of a graphite plate, and nitrogen gas or the like is used as a cooling medium. A cooling pipe 21 (corresponding to a cooling medium distribution path) that circulates is buried. Moreover, the mounting table 20 is arranged inside the heat insulating wall 12 in the form of a plurality of shelves. Among them, the cooling pipe 21 drawn into the inside of the furnace shell 10 from the nitrogen gas supply device (not shown) provided outside the furnace shell 10 is arranged inside the mounting table 20 along the lateral arrangement of the recesses 22. Although it is not shown in the drawing,
Further, after being sequentially passed through the mounting table 20 from the lower stage to the upper stage, it is taken out again to the outside of the furnace shell 10. On the other hand, a circular cut groove 221 for laying a carburizing inhibitor made of alumina powder or the like is provided at the center of the bottom surface of the concave portion 22 having an empty space to allow the powder molded product a to be accommodated with a margin. There is.

The principle that good heat treatment can be performed even with a small powder molded product a by the sintering furnace configured as described above will be described.

First, after the powder molded product a to be heat-treated is set in the concave portion 22 in which the carburizing inhibitor is preliminarily spread, the opening / closing door 11 is opened and the operation of the sintering furnace is started. Is driven, the energization of the rod heater 13 is started, and eventually the dewaxing step and the main sintering step are sequentially advanced. Most of the heating of the powder molded product a in these steps is contained in the concave portion 22 corresponding to a position slightly lower than the upper surface of the mounting table 20, so that the heat capacity is much higher than that of the powder molded product a. Is carried out by the heat of the mounting table 20 which is large, the degree of uniform heating is increased by the degree of the degree of direct heating from the rod heater 13, and therefore the variation in the surface temperature of each surface is also required. It may be possible to keep the temperature within ± 3 ° C.

Then, when the main sintering process is completed, a nitrogen gas supply device (not shown) is driven as a quenching process to cause the nitrogen gas to flow through the cooling pipe 21. Then, the powder molded article a is cooled rapidly together with the mounting table 20, and is rapidly lowered from the sintering temperature to room temperature. Moreover, in this quenching process, even when the cooling gas circulation mechanism 14 is driven, the wind pressure of the pressurized nitrogen gas is prevented from directly contacting the powder molded product a and the carburizing inhibitor. Since it is only necessary to cool the main constituent parts inside the furnace shell 10, as a result, the powder molded product a and the carburizing inhibitor which would lead to shape deformation and quality deterioration are not blown off.

Therefore, according to the present embodiment, even if the object to be heat-treated is a small powder molded article a, good heat treatment can be performed, and the heat treatment cycle time can be shortened. It will be possible to fully enjoy the merits that it has, and it will be of great significance to greatly promote the conversion of machined products of industrial equipment parts to powder metallurgy products.

The sintering furnace according to the present invention is not limited to the above-described embodiment, and for example, not only the structure and the number of the mounting tables but also the recess for accommodating the powder molded product may be groove-shaped. Alternatively, the concave portion may be closed by another member. Further, in the cooling gas circulation mechanism, its main part may be equipped outside the furnace shell.

As described above, in the case of the sintering furnace of the present invention, the powder molded product can be cooled by the cooling medium flowing through the cooling medium distribution passage provided in the mounting table. Then, good heat treatment can be performed even for a small-sized powder molded product whose demand is expected to increase in the future. Therefore, it is of great significance in further promoting the conversion of machined products of industrial equipment parts to powder metallurgy products.

[Brief description of drawings]

1 to 3 are explanatory views of an embodiment of a sintering furnace according to the present invention. FIG. 1 is an internal configuration diagram of the sintering furnace, FIG. 2 is a perspective view of a mounting table, and FIG. The figure is A- in Figure 2.
It is sectional drawing by the A line. 10 …… Furnace shell 13 …… Rod heater 14 …… Cooling gas circulation mechanism 20 …… Mounting table 21 …… Cooling pipe 22 …… Recess

Claims (1)

[Claims] 1. A sintering furnace in which an object to be processed inserted into a furnace shell is heated by a heater to sinter, and is provided so as to face the heater and has a recess for accommodating the object to be processed. A mounting table; a cooling medium flow path provided in the mounting table; and a cooling gas circulation mechanism provided in the furnace shell and internally circulating a cooling gas introduced from the outside of the furnace shell. A sintering furnace.