The present invention relates to furnaces used for the isostatic treatment of products in a gaseous atmosphere at high temperatures and high pressure. More specifically, the present invention deals with furnaces used for the pressure sintering of powdered materials, such as metal powders, ceramic powders, or mixtures thereof, to form homogeneous solid bodies.
Pressure furnaces known to the prior art such as cylindrical elongated furnaces which can treat products at 1000.degree. C. or above at pressures of 500 bar or above are normally quite complicated and expensive. In most of these furnaces the hot billet, immediately after being pressed, can be removed from the furnace in order to reduce the operational cycle time. In some furnaces which are constantly kept warm, i.e., furnaces in which the billet is inserted into the furnace when warm and wherein the warm billet is removed therefrom immediately after pressing, charging thereof can be accomplished from below, and in these furnaces the surrounding air (the oxygen of which damages the furnace) can be prevented from flowing in without the help of complicated hoods and the like. In other furnaces which are charged from above, the furnace can be allowed to cool to a temperature at which the incoming oxygen in the air does not damage the furnace. Indeed, in certain situations it is acceptable or desirable that the pressed billet be allowed to partly or completely cool under pressure such that the ultimately desired properties be obtained.
To accelerate the cooling in these furnaces, it has been proposed to arrange a passageway, controllable by a valve from the outside, between the furnace space inside the conventional insulating casing and the gap between the insulating casing and the inner wall of the pressure chamber cylinder. The heat is then carried off through the cylinder wall and by means of a coolant circulating through channels in the pressure chamber cylinder. However, opening the valve in such a passageway and thereby regulating the flow of hot pressure medium without regard to the desired cooling rate, and not recognizing the harmful effects of heating of the cylinder wall, has lead to various practical problems.
The object of the present invention is to provide a pressure furnace which is improved over prior art furnaces. The present inventive furnace, it should be noted, is applicable as the furnace described in U.S. Pat. No. 3,995,101.