Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Post sintering operation
Patent
1987-12-21
1989-08-08
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Post sintering operation
419 8, 419 49, B22F 704
Patent
active
048551031
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of manufacturing metal products from a powder which is received in a mould cavity formed by a gas-tight casing and is isostatically hot pressed in the casing to form a monolithic body.
In the manufacture of blade rings and hubs having blade rims for compressors or turbines by applying the isostatic hot pressing technique it has already been proposed to insert prefabricated blades through apertures which are matched to the cross section of the blades, in a wall of a casing wherein the ring or hub is to be produced by isostatic hot pressing of a metal powder. It is then necessary to make a gas-tight connection between the blades and the wall, which necessitates accurate welding at that side of the wall which faces the mould cavity. This working operation is expensive and time-consuming and cannot be repeated also at the other side of the wall, because there would then be produced at said side an irregularity in the flow passage, which generates turbulence which cannot be accepted. Accordingly, there will be a gap around the blade at said one side, and in some cases this gap cannot be accepted due to a marked fracture indication with associated reduction of the fatigue strength of the finished product.
The purpose of the invention is to overcome these drawbacks of the prior art method of manufacturing blade rings and hubs having blade rims, and at the same time facilitate adjustment of the detail design of the product while satisfying strict strength requirements. Thus, the invention has been developed primarily for the manufacture of monolithic bodies by isostatic hot pressing with prefabricated elements inserted therein, e.g. for the manufacture of blade rings and hubs having blade rims for compressors or turbines, said blades forming the prefabricated elements. However, the invention is not limited to the manufacture of these specific products; it is much broader than that.
The fact is that in isostatic hot pressing there is used at present occasionally cores of steel or other metal. As far as these cores cannot be withdrawn from the finished product, they are removed by etching. The drawback of such cores is that they are not shape-permanent at the high pressures and temperatures involved in isostatic hot pressing.
Cores of ceramic material are also used, however, and these cores contrary to the metal cores are shape-permanent but can be removed only by withdrawal, which restricts the use thereof.
In the specific case of attaching blades or other prefabricated elements the core also serves as a holder for maintaining these prefabricated elements in a fixed position by said elements being partly received by the core.
The material of the fixing body preferred at present, which is then blasted away, is hexagonal boron nitride, because the graphite tends to diffuse into the metal--at least so far no method or means has been invented in order to prevent this at the high temperatures involved--and consequently may cause a modification of the properties of the metal, which is not desired and cannot always be accepted. Although it has not been found by tests so far if there are other materials which are as good as hexagonal boron nitride for the related purpose or even better, it cannot be excluded that there is another similar ceramic material. In this connection a similar material means that the material can be easily machined, is shape-permanent at the high temperatures and pressures involved in isostatic hot pressing, and can be removed by blasting after the isostatic hot pressing.
In order to explain the invention embodiments thereof will be described in more detail below applied to the manufacture of blade rings and hubs having blade rims, reference being made to the accompanying drawings in which
FIG. 1 is an axial sectional view of a casing for isostatic hot pressing arranged for the manufacture of blade rings having a blade rim between the rings,
FIG. 2 is a perspective view of the fixing body in the embodiment of FIG. 1 having the blades attached thereto, and
FIG. 3 is
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ASEA Tidning, 1981.
Asea Stal AB
Jorgensen Eric
Lechert Jr. Stephen J.
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