JPS6343550B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a molded article having a cavity, such as a drill bit.

A method of manufacturing a molded body having such a cavity is disclosed in Japanese Patent Application Laid-Open No. 53-47307.

This conventional method involves scattering hard metal powder on the inner surface of a rubber mold as necessary, then placing a core mold made of solid paraffin to form a cavity while filling the mold with metal powder, then closing the mold and letting it cool. The metal powder layer is solidified by isostatic pressing, then removed from the mold and heated in a de-aging furnace to eliminate the core mold, and then hot isostatic sintered to form a hollow object.

In this method, the inner surface of the cavity is formed of a layer of sintered metal powder, which is easily chipped, and requires an extra step of heating and extinguishing the core mold formed from solid paraffin to form the cavity. Furthermore, by scattering hard metal powder before filling the mold with metal powder, the hard metal powder is exposed on the outer surface of the object, but the bonding strength between this hard metal powder and sintered metal powder is low; Hard metal powder easily falls off.

In order to solve the above-mentioned problems, the present invention provides a method for producing a molded body having a cavity by providing an appropriate powder layer 4 on the outer surface of a core member 3 having a cavity on the inner surface by cold isostatic pressing, and then After sintering, a wear-resistant layer is attached to the outer surface by thermal spraying, followed by hot isostatic pressing.

A powder suitable for use in the method of the invention is preferably a nickel alloy steel powder containing 3.5% nickel.

To carry out the method of the invention, after introducing and distributing the powder material into a rubber mold, a core member made of steel, generally suitable for bearings, is placed into the powder and the powder is then compressed; The core member is first placed in the mold, after which the powder material is introduced and compacted. The mold is closed and cold isostatic pressing is then carried out until a compact having a density of approximately 90% is obtained. This pressed body is removed from the mold and then sintered in a furnace. After cooling, the sintered body is coated with a wear-resistant layer by thermal spraying, such as plasma spraying, and the structure thus obtained is hot isostatically pressed. In hot isostatic pressing, a deep-drawn container with a thin wall thickness, for example, a container made of low carbon steel with a wall thickness of about 0.5 mm, is filled with ceramic powder, and the entire sintered body is inserted into the container. The container is then heated and placed under pressure from all around. After hot isostatic pressing, the object can be easily separated from the surrounding ceramic mass and cleaned by sandblasting. This method produces parts with precise dimensions comparable to forged parts.

When producing rock drilling drill bits using this method, after sintering, only the parts of the bit that come into direct contact with the rock, rather than the entire surface of the cutting teeth, are coated with a wear-resistant layer by thermal spraying. After selective application of the wear layer, the entire preformed drill bit is hot isostatically pressed as described above.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

A drill bit 1 shown in FIG. 1 has a hollow core member 3 made of bearing steel, and a raceway 2 for rolling elements (not shown) is provided on the inner surface of the core member 3. A powder layer 4 is placed on this core member 3 in a rubber mold.
and cold isostatic pressing of this bonded product. This operation is preferably carried out at room temperature and about 6000 atmospheres. Next, the drill bit preformed by cold isostatic pressing is removed from the mold and sintered in a sintering furnace at a temperature of about 1200°C at 1 atm under hydrogen reduction for about 1 hour. Pressure molding material is approximately 90
% density. A wear-resistant layer 5 is then applied on layer 4 by plasma spraying, and the object thus obtained is inserted into a container and heated for at least 2 hours, for example under about 1600 atmospheres and at a temperature of about 1100°C. Equal pressure molding. By this operation, layers 4 and 5 become 99
% density, and a strong bond occurs between both layers.

The mechanical properties of the drill bit formed as described above by the method of the invention are significantly improved in the bond between layers 4 and 5 and between layer 4 and core member 3. This method results in molded bodies with a very high degree of wear resistance and resistance to chipping of cutting teeth in combination with core parts that have other functional uses, such as bearings, for example.

It can be seen that the original core member 3, after this mechanical manipulation and heat treatment, assumes the shape shown in FIG. 1, provided with the tracks 2 of the rolling elements.

Furthermore, from FIG. 2 it can be seen that the wear-resistant layer 5 is not provided on the entire surface of the cutting teeth of the drill bit, but only on those areas that come into direct contact with the rock during operation.

The invention thus provides essentially three parts: a significantly improved cutting part 5, a support part 4,
A molded body, such as a drill bit, is obtained which consists of a core part or bearing part 3, these three parts being connected in an economically and technically advantageous manner so that the drill bit meets the desired requirements. Further, since the cavity is formed by the inner surface of the core member, there is no need for a step of eliminating the core mold of solid paraffin for forming the cavity.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a drill bit manufactured according to the present invention, and FIG. 2 is a perspective view of a portion thereof. In the figure, 3 indicates a core member, 4 indicates a powder layer, and 5 indicates a wear-resistant layer.

Claims (1)

[Claims] 1. A suitable powder layer 4 is provided on the outer surface of the core member 3 having a cavity on the inner surface by cold isostatic pressing, and after this is sintered, a wear-resistant layer is thermally sprayed on the outer surface. 1. A method for producing a molded body having a cavity, characterized in that the molded body is adhered by a method and then subjected to hot isostatic pressing. 2. In the method described in claim 1,
A method for manufacturing a molded body having a cavity in which the powder of the powder layer 4 is alloy steel powder containing nickel. 3. In the method described in claim 2,
A method for manufacturing a compact having a cavity in which the alloy steel powder contains 3.5% nickel. 4. In the method according to any one of claims 1 to 3, after sintering the powder layer,
A method for manufacturing a molded article having a cavity in which a wear-resistant layer 5 is provided only on the surface that is directly subjected to abrasion during use. 5. A method for manufacturing a molded body having a cavity in which the core member 3 is made of bearing steel, in the method according to any one of claims 1 to 4.