US3259324A - Methods of breaking up sintered compacted metal bodies - Google Patents

Description

United States Patent 3,259,324 METHODS OF BREAKING UP SINTERED COMPACTED METAL BODIES Dennis Ball, Little Chalfont, and Peter Ayers, High Wycombe, England, assignors to The British Aluminium Company Limited, London, England, a company of Great Britain No Drawing. Filed July 1, 1963, Ser. No. 292,102 Claims priority, application Great Britain, July 3, 1962, 25,472/ 62 1 Claim. (Cl. 241-17) This invention relates to improvements in methods of breaking up sintered compacted metal bodies and is particularly, but not exclusively, concerned with refractory hard metal bodies within which term is included sintered compacted bodies consisting essentially of at least one of the materials in the group consisting of the silicides, .borides and carbides of the transition elements in Groups IV, V and VI of the Periodic system. The term consisting essentially is used herein to denote that the body contains at least 90% by weight of one of the compounds or .a mixture of two or more of the compounds in the group specified.

There are many applications where it is desired to break up a sintered compacted metal body so as to reduce it to a size suitable for it to be pulverised by conventional crushing and grinding processes.

The applicants have previously proposed the use in electrolytic cells for the production of aluminium of cathodic current-conducting elements consisting essentially of a sintered compacted mass of at least one of the materials in the group consisting of the carbides and borides of titanium, zirconium, tantalum and niobium. Such elements are required to extend into the cell from the floor or side-w alls thereof or to depend through the top of the cell from current-conducting supports or busbars. Such elements may suffer some emosion during use, or be accidentally fractured, either during the life of the cell or during the dismantling of the cell or the end of its useful life and it is highly desirable on the grounds of economy to reclaim the material of which the element is composed for refabrication. The sintered compacted elements are, however, very hard and it is desirable to break them up into relatively small pieces to facilitate subsequent crushing and grinding processes whilst maintaining the impurity pick-up at a minimum.

We have described in our co-pending United States application No. 292,101 of even date herewith and now Patent No. 3,203,470 a method of rapidly cooling a solid body which comprises exposing the body to a bed of particles fluidised by a cooling liquid. This method of rapidly cooling a solid body is particularly suitable for the purpose of thermally shocking a sintered compacted body to cause fracture thereof and facilitate the breaking up of the body.

The present invention, broadly stated, provides a method of breaking up a sintered compacted metal body which comprises exposing the body at an elevated temperature to a bed of particles fluidised by a cooling liquid.

The fluidised particles help to break up the film of vapour which normally forms round a body whose temperature is above the boiling point of the liquid in which it is immersed, and thus the rate at which heat is transferred between the hot body and the liquid is considerably increased. This leads to a more rapid cooling of the outside of the body and hence to higher temperature gradients and higher stresses within the body which in turn cause fracture of the material. In many cases, the thermal shocking of the body will only produce cracks thereon so that the breaking up process then has to be completed by subjecting the body to impact.

3,259,324 Patented July 5, 1966 ice The cycle of thermal shocking and impact may be repeated as many times as is required until the body has been broken down in pieces of the required size, but it has been found that one cycle is frequently adequate for the purpose.

After the body has been broken up and finally crushed and ground to particles of the required small size, the resultant powder is ready for refabrication. It is normally advantageous to incorporate some new powder with the reclaimed material.

More particularly stated, the invention provides a method of breaking up a sintered compacted body con sisting essentially of at least one of the materials in the group consisting of the silicides, carbides and borides of the transition elements in Groups IV, V and VI of the Periodic System which comprises heating the body to an elevated temperature, thermally shocking the body by immersion in a bed of particles fluidised by a cooling liquid and subjecting the thermally shocked body to impact.

The invention also extends to the pulverising for refabrication sintered compacted bodies consisting essentially of at least one of the compounds in the group consisting of the silicides, carbides and borides of the transition elements in Groups IV, V and VI of the Periodic system which comprises heating to an elevated temperature a previously sintered compacted body consisting essentially of at least one of the materials in the group specified, thermally shocking the body by immersion in a bed of particles fluidised by a cooling liquid, subjecting the thermally shocked body to impact, repeating at least once on the resultant pieces the cycle of thermal shock and impact, and pulverising the product of the thermal shock and impact cycles to a size suitable for further sintering and compacting operations.

The invention further extends to the manufacture of a sintered compacted body consisting essentially of at least one of the materials in the group specified which com prises sintering and compacting a pulverulent mass at least a part of which consists of the pulverised product produced by the immediately preceding paragraph.

The invention still further extends to a sintered compacted body produced by the method according to the immediately preceding paragraph.

The invention is of particular but not exclusive, application in the reclamation of material from sintered compacted bodies consisting essentially of at least one of the compounds in the group consisting of the carbides and borides of titanium, zirconium, tantalum and niobium.

The following is an example of the method according to the invention.

A cylindrical body consisting essentially of sintered compacted mixture of 70% titanium diboride 30% titanium carbide which body was 3 inches in diameter and 12 inches long, was recovered from an aluminum reduction cell for refabrication. The body was uniformly heated in an electric muflle furnace to a temperature of about 800 C. and was then plunged into a bed of 1 mm. diameter particles of lead shot fluidised by water flowing vertically upwards through the bed at a rate of 100 gallons/min./ft. After the quenching operation, which proceeded quietly and without splashing, the body was removed after about a minute and broken into approximately 1 in. pieces by gently tapping it with a hammer. These pieces were reheated and quenched again in the same fluidised bed and the resultant pieces were of a size suitable for comminution in a jaw crusher and finally in a ball mill. The material when so comminuted was ready for reflrabrication. A new solid sintered compacted body was then fiabri'cate-d from a powder incorporating by weight of the reclaimed material.

The body to be broken up should be thermally shocked by exposing it to a temperature difierence of at least 575 C. Thus, for example, a sintered compacted titanium diboride bar has been successfully broken up by heating it to a temperature of 600 C. and immersing it in a bed of particles fluidised by water at ambient temperature. The particles of the bed preferably are of a size in the range of from 0.5 to 5 mm. and the cooling liquid is supplied at a rate selected in relation to the mass of the particles to be suflicient to maintain the particles fluidised. The cooling liquid is supplied under pressure to a plenum chamber and passes through a porous wall of the plenum chamber on which the particles are supported, the porous wall, in effect, providing a porous floor to the chamber in which the bed is contained.

We claim:

A method of pulverising for refabrication a sintered compacted body consisting essentially of at least one of the compounds in the group consisting of the silicides, carbides and borides of the transition elements in Groups IV, V and VI of the Periodic System which comprises heating to an elevated temperature of at least 600 C. a previously sintered compacted body consisting essentially of at least one of the materials in the groups specifled, thermally shocking the body by immersion in a bed of particles fluidised by a cooling liquid at a temperature of at least 575 C. below said elevated temperature, subjecting the thermally shocked body to impact, repeating at least once on the resultant pieces the cycle of thermal shock and impact, and pulverising the product of the thermal shock and impact cycles to a size suitable for further sintering and compacting operations.

References Cited by the Examiner ROBERT C. RIORDON, Primary Examiner.

WILLIAM W. DYER, 1a., Examiner.

D. MAXSON, H. F. PEPPER, Assistant Examiners.