JPS6328190Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a type of auxiliary tool used when densifying powder molded products by sintering, and is related to the shape of the lid of the storage box that stores the molded products in the furnace. .

When sintering a powder molded product, the molded product to be sintered is usually stored in a storage box 1 made of heat-resistant metal such as stainless steel or molybdenum, or graphite, as shown in FIG. They are stacked in multiple layers and fired in a furnace. storage box 1
As shown in Fig. 2, the inside of the is a bottom plate 4 placed on an appropriate support column 3, and the powder molded products to be sintered are arranged on the bottom plate 4, covered as necessary, and placed in an appropriate number of stages. Stack.

By the way, the temperature distribution inside the firing furnace is surprisingly uneven; when storage boxes are stacked, the middle and lower tiers are often 20 to 60°C higher than the upper tiers, and even inside the same storage box, the side walls of the box The temperature is high in the area close to , and the temperature is low in the center.

Uneven firing temperature is one of the causes of uneven product quality, and the difference between products placed in the center of the box and those placed near the side walls is different after sintering. There were differences in density and dimensions. Therefore, a means to maintain uniformity of the temperature inside the furnace is naturally required.

Among the above-mentioned problems, this invention particularly relates to the shape of the lid that maintains uniformity of temperature within the storage box.

To explain in detail with reference to the drawings, FIG. 1 shows a state in which storage boxes 1 are covered with lids 2 and stacked in three tiers,
FIG. 2 shows the inside of the storage box 1, with the bottom plate 4 placed on the support column 3. The objects to be fired are arranged on this bed plate 4 and covered with a lid 2.

FIG. 3 shows a lid according to this invention, in which the top surface 5 is flat, and the thickness of the bottom surface 6 is thinner near both sides of the storage box and thicker as it approaches the center. It swells into a circular arc.

To explain the function of the lid of the present invention, if we consider the case where the storage box is heated from both sides and heat is conducted to the molded product in the center of the storage box, the amount of heat transferred is Most of the heat is due to radiation, while the amount due to convection is small. In the case of a vacuum furnace, there is no heat transfer by convection, and radiant heat is dominant, but if there is a lid, only conduction occurs until the lid becomes red hot.

Therefore, the amount of heat transmitted to the molded product inside the storage box is due to the amount of heat conducted directly from the floor plate inside the storage box to the molded product, and the radiant heat from the lid. In order for the radiant heat from the lid to be uniformly transmitted to the molded product, it is necessary that the temperature of the lid itself be the same between both sides and the center. In order to meet this condition, the center of the lid is made thicker to increase the speed at which the amount of heat from both sides is transmitted to the center.Furthermore, when the lid is viewed as a radiant heat source, the molded body in the center is thickened on both sides. As with the molded body in the section, it is close to the heat source, which further contributes to equalizing the temperature inside the storage box.

Furthermore, considering the temperature change when the lid is left to cool after heating is complete, the conventional thin plate-shaped lid has a small heat capacity, so the temperature decreases faster when it is left to cool compared to the surrounding area.
The temperature of the object to be fired directly below it also decreases faster than in the surrounding area.

On the other hand, according to this invention, since the heat capacity of the lid at the center is larger than that at the periphery, there is an effect of equalizing the rate of temperature drop during cooling of the storage box as a whole.

Therefore, by using the lid of this invention, temperature changes within the storage box are made uniform not only during heating but also during cooling, which is effective in making the quality of the product uniform.

FIG. 4 shows another example with the same effect, in which the center bulges in a step-like shape, and FIG. 5 shows an example in which the center bulges in a trapezoidal shape.

[Brief explanation of the drawing]

Figure 1 shows three stacked storage boxes with lids. FIG. 2 shows the relationship between the support columns and floor plates inside a conventional storage box. FIG. 3 shows the lid of the present invention, which has a circular arc-shaped bulge in the center. FIG. 4 also shows the lid bulging out in a stepped manner. FIG. 5 also shows a lid bulging into a trapezoidal shape. 1 is a storage box, 2 is a lid, 3 is a support column, and 4 is a floor plate. 5 is the top surface of the lid, and 6 is a bulge on the bottom surface.

Claims (1)

[Scope of utility model registration request] A lid for a storage box for sintering powder molded products in a sintering furnace.The top surface is flat, and the thickness is thinner near both sides of the storage box and closer to the center. The lid is thick and thick.