US1895364A - Method for salvaging and resintering cemented carbides - Google Patents

Description

Patented Jan. 24, 1933 STATES tries STANLEY 1P. BILLINGS, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK METHOD FOR SALVAGING AND RESINTERING CEMENTED CARBIDES No Drawing.

The present invention relates to cemented carbides of the character disclosed in Schroter Reissue Patent No. 17 ,62& and more particularly to a method for salvaging cemented carbide tool bits which have been broken or otherwise injured so that their usefulness is im aired or destroyed.

(gemented carbides are largely employed 1n the form of tools such as turning tools, cut-. ting, forming,. bending dies, etc., which are generally copper brazed to supporting steel shanks; These tools are usually subject to very severe operating conditions and since they are quite brittle they sometimes crack or break. Under such circumstances it has heretofore been customary to scrap the tools. Since cemented carbide is used extensively and is costly the loss from scrap material constitutes an important item.

I have found that scrap of this material may be salvaged by resintering the broken pieces under pressure. The scrap material may be broken. either into larger or small pieces and then pressed in a refractory mold. It is not necessary to break up the cemented carbide material into a fine powder or even into very small pieces since large pieces may be resintered under pressure with satisfactory results.

Ordinarily, cemented tungsten carbide contains about 3 to of a binder or cementing material, for example cobalt. The hardness of such material may vary from about 85-89 on the RockwellA scale. \Vhen different grades of cemented tungsten carbide containing varying amounts of cementing material are resintered under pressure the hardness of the resintered material is usually increased to about 91 or 93 on the Rockwell A scale.

The material produced from the broken pieces of cemented carbide is tough and may be pressed into relatively intricate shapes so that prelim nary grinding 1s unnecessary.

In carrying out my invention I employ a bon plungers as disclosed in Gilson Patent No. 1,756,857. Broken pieces of cemented carbide are placed in the mold between the plungers and a relatively small pressure applied thereto while the cemented carbide is having oppositely disposed car-' Application filed October 2, 1931. Serial No. 566,592.

heated up to its sintering temperature. The latter temperature is above 1000 C. and usually from about 1350 to 1425 C. I have found that either no pressure or up to about 200 pounds per square inch is sufficient. Heat may be applied to the pressed material either through the plunger-s or if desired at right angles to the direction of pressure as disclosed Gilson Patent No. 1,671,953. A transformer supplying 10,000 amperes at about 10 volts will furnish a current sufficient to heat the pressed material in small sections to its sintering temperature in 5 or 6. minutes.

Large sections require more current or more time. When the above temperature is reached I prefer to increase the pressure to about2000 pounds per square inch and to maintain the latter pressure from about 2 to 4 minutes depending upon the size of the part to-be fabricated.

If the cemented carbide which is being salvaged consists of tungsten carbide and cobalt, I may add a small quantity of powdered material consisting largely of tungsten carbide but containing an appreciable amount, for example from about 3 to 2.0% cobalt. The addition of such powdered material is not essential however and may be omitted if desired.

Before pressing and resintering the cemented carbide I prefer to remove all foreign material such as scale, grease, oil and the like. The size of the particles which are to be resintered appears to be immaterial. They may be of any size which will clear the mold opening. Large pieces weighing one. pound or more may be pressed and sintered as easily as small pieces weighing one-half gramor less. The heated material in fractured form becomes plastic at its sintering temperature. This assists in forming relatively long pieces of material into any desiredshapc so that preliminary grinding is unnecessary.

Ordinarily. long pieces of cemented carbide cannot be fabricated from powdered materials as the powdered material binds against the side of the mold and the pressure is therefore not distributed evenly throughout the entire body of powdered material. This is not the case however when pieces of and the sections joined or welded together by my resintering method.

Furthermore, cemented carbide parts that have become worn or broken in use may be restored to original shape and dimension by the resintering method. F or example, a

worn out sand blast nozzle may be restored by placing it in arefractory mold which has dimension and shape of the original nozzle and by adding a portion of powdered or fractured material equal to the Wear loss, the nozzle'may be restored to original dimension and shape. In case it is desired to change the shape or dimension of sintered cemented carbide parts this may be done by the resintering method i. e. a cube may be changed to a sphere or vice versa, or sections made for a specific use may be changed to an entirely different form. During the resintering operation holes or pro1ections of any desired shape including external and internal, straight and tapered screw threads, and definite forms such as cutter teeth and the like may be cast from the broken carbide materials.

By the expression large pieces as employed in the claims, I mean to exclude powdered or finely divided materials. For example, as indicated above large pieces weigh ing one-half gram as well as pieces weighing one pound or more may be formed or welded together into a single finished product.

What I claimas new and desire to secure by Letters Patent of the United States, is:

v 1. The method of salvaging a sintered hard metal composition consisting mainly of a refractory carbide which comprises heating large pieces of said composition in a mold at a temperature above 1000 C. while pressure is simultaneously applied thereto.,

2. The method of salvaging cemented carbide material which comprises placing said. material in a mold, adding to said mold a powdered mixture having approximately the same composition as the material in said mold and applying pressure to the material in the mold while it is heated to a temperature above 1000 C.

3. The method of salvaging a worn or broken cemented carbide structure which placing said material in a mold having substantially the same dimensions and shape as the original cemented carbide material, addneeaeea ing to said mold a portion of material having substantially the same composition as said cemented carbide material, and applying pressure to the material in said mold, while itis heated to a temperature above 1000 C,

,5. The method of salvaging cemented carbide material which comprises placing large pieces of said material in a mold, applying a relatively low pressure to said material while it is heated to its sintering temperature and then applyinga higher pressure and maintaining said pressure for several minutes.

6. The method of salvaging cemented carbide which comprises cleaning large pieces of cemented carbide, placing the piece'sin a mold, applying a relatively low pressure thereto while the material is heated up to a temperature of about 1400 C. and then applying higher pressure and maintaining said pressure for several minutes. I In witness whereof, I have hereunto set my hand.

STANLEY P. BILLINGS,

Images