JPS58199801A - Sintering method - Google Patents

Abstract

PURPOSE:To improve production efficiency without generating cracking and deterioration in quality in a sintered product by opening a heat insulation door half at a still relatively high temp. in a cooling stage after completion of sintering of a large sized product or a large charge product then introducing a gas into the furnace to cool the product quickly. CONSTITUTION:A heat insulation door is opened half to accelerate cooling at a temp. 3 after sintering and keeping the temp. Ts or 2 in a sintering method of a large sized product or large charge product. In succession, a gas such as N2 is introduced into the furnace at a temp. 4 to cool the product quickly as shown by a solid line. Then, the cooling can be completed in about 10hr as shown by a time T1. The large sized product is thus kept free from cracking and residual thermal stress and the deterioration in quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently sintering large items or items with a large amount of charge.

Traditionally, there have been many requests for large parts such as cemented carbide and ceramics.
In addition, it is becoming increasingly common to process a large amount of items in one sintering process. In such cases, unlike small products, uniform heating inside the furnace is particularly required during temperature rise and maintenance, resulting in a furnace with a structure with good heat insulation efficiency, but on the other hand, this means that the cooling time after sintering is extremely long. If this time is unnecessarily shortened, cracks will occur in the fired crystals in large products, thermal stress will remain, and quality will vary in products with large charges, resulting in a large number of defective products. On the other hand, due to the need to increase production efficiency, various methods and sintering furnaces have been developed to shorten this cooling time.

FIG. 1 shows sintering and cooling curves, where the vertical axis is temperature and the horizontal axis is time. 1 indicates the temperature rise curve, and Ts or 2 indicates the sintering keep. After this, in normal cases, slow cooling is performed as shown by dotted line 5, and it may take about 80 hours. One way to shorten this cooling time is to use N2 from outside the furnace during the cooling process.
By introducing a gas such as T and rotating a cooling fan installed in the furnace, T! 1-(T
I+T2) time can be shortened. For example, it can save about 10 hours. However, because this method rapidly exchanges heat with a large heat capacity, it is necessary to use expensive heat-resistant materials for the internal structure of the furnace, and substances adhering to insulation materials may react with the product and cause negative effects. Normally, the upper limit of the operating temperature of the fan is 600°C.

The present invention provides a method that can further shorten the time compared to the above methods.

Normally, the objects to be sintered in a sintering furnace are placed in a high-temperature area surrounded by insulating material, but conventionally, the insulating door made of this insulating material was used to promote cooling from the outside. However, the inventors focused on this heat insulating door, and after sintering, the heat insulating door was opened half-open at 3 in Figure 1 to promote cooling, and then at 4, a gas such as N2 was introduced. This method performs rapid cooling as shown by the solid line. As a result, cooling was completed in about 10 hours, as shown by T1. Moreover, as a result of this, there was no occurrence of cracks or residual thermal stress in large products, and there was no deterioration in quality.

By the method of the present invention, large cemented carbide such as rolls can be sintered in a cycle of 15 to 20 hours,
Production efficiency has improved significantly.

[Brief explanation of the drawing]

Claims (1)

[Claims] (1) In the sintering method for large products or large-charge products, it is recommended to leave the insulation door in the sintering furnace ajar during the relatively high temperature stage of the cooling process after sintering is completed, and then introduce gas to rapidly cool the product. Characteristic sintering method.