Patent GB-530904-A (GB)
Title: Improvements in or relating to composite machine elements and processes of making the same
IPC: F16D69/02
Filed: 1939-07-05
Abstract: 530,904. Forming coherent masses from powdered metal. STEVENS, A. H. (Wellman Co., S. K.). July 5, 1939, No. 19579. [Class 82 (i)] [Also in Groups XXII and V] Welding. In making composite machine elements such as friction clutches, brakes or bearings, a porous facing member of compressed powdered material consisting predominantly of a high melting point metal comprising copper, iron, or mixture thereof is held in contact with a ferrous backing member and the parts heated to effect a direct weld between them without fusing the high melting point metal, while preventing oxidation or corrosion of the backing by gases sorbed in the facing member. The weld is stated to be stronger in shear parallel to the surfaces than the facing member. For clutch and brake discs the porous material may consist of 73 per cent. copper, 14 per cent. lead, 7 per cent. tin, and 6 per cent. graphite. For friction clutches it may consist of 70.9 per cent. copper, 10.9 per cent. lead, 6.3 per cent. tin, 7.4 per cent. graphite and 4.5 per cent. air floated silica, or 62 per copper, 8 per cent. iron, 12 per cent. lead, 7 per cent. tin, 7 per cent. graphite and 4 per cent. silica and for bearings it may consist of 79 per cent. copper, 9 per cent. lead, 2 per cent. nickel and 10 per cent. graphite. The copper may be electrolytic, reduced or mechanically powdered and the iron may be obtained by reduction of magnetic iron oxide, in order to obtain a coherent ring-shaped mass, the powder may be pressed in a die by a steel pressure plate at pressure about 22,000 lb. per sq. inch and the ring is then entered preferably in a reducing atmosphere of carbon monoxide or hydrogen at a temperature from 1250‹F. to 1450‹F. or higher for about 30 minutes. The ring is then straightened and cleaned by sandpapering &c. In making a clutch disc 1 to be subsequently riveted to hub 2, the packing disc 1a of sheet steel is cleaned by dipping in hot caustic and then in acid and rinsing, drying and polishing and is then assembled with the facing rings 1b and placed in a furnace containing a reducing atmosphere and pressed together and heated to welding temperature, e.g. 1350‹F. - 1500‹F. without fusing the predominant metal of the facing. This joint should show a distinct line of demarcation between the members. A number of articles may be produced' simultaneously by piling the assemblies one upon another in the furnace, the facing rings being separated by powdered graphite or sheets of mica. Sintering and welding may be effected in different operations or successively in the same heating operation. In order to prevent moisture absorbed in the pores of the facing from corroding the backing, the facing may be made from dry pure materials and kept in a reducing atmosphere until required. The welding may be effected in an air conditioned room with a relative humidity below 40 per cent. Alternatively the facing after fabrication may be heated in a vacuum or reducing atmosphere up to 750‹F. to expel the moisture. In another form the backing may be provided with an electrolytic deposit of copper nickel or silver. In a process in which the sintering of the compressed powder and welding to the backing are effected in the same heating operation, the gases are driven out by a current of dry hydrogen. In this form a pile of parts la, 1b, Fig. 13,. each set of which is separated from adjacent sets by a spacer comprising a metal disc h<SP>1</SP> coated on each side with compressed powdered metal facings h<SP>2</SP>, h<SP>3</SP> surmounted by graphite h<SP>4</SP>, is placed on a base d', Fig. ill, resting on a cored out casting a<SP>6</SP> on the heat insulating lining a<SP>8</SP> of a steel pan a<SP>2</SP> which forms the base of a furnace, and is welded to channels a<SP>1</SP>. The base d' forms the bottom of a chamber d, the top of which consists of a sheet metal diaphragm d<SP>3</SP>. This chamber has a protective air seal in the form of an inverted cover e. the lower end of which is embedded in loose circulating material a<SP>15</SP>. A block d<SP>5</SP> is inserted between the cover and diaphragm. The furnace cover b which consists of a sheet metal casing with a flange b<SP>6</SP> embedded in the material a<SP>15</SP>, and enclosing insulating material and a resistance heater b<SP>8</SP>, is slidable on rods a<SP>13</SP> carried by channels a<SP>1</SP>. The cover b carries steel channels c<SP>6</SP>, an air pressure device consisting of a flexible chamber c<SP>1</SP> formed of circular plates connected by flexible wall c<SP>3</SP> of rubber and canvas, and a top plate c' welded to channels c<SP>8</SP>. The furnace cover may be raised for charging purposes by a hoist engaging on an apertured plate c<SP>9</SP> connected to the channels c'. A current of dry reducing gas such as hydrogen is passed through the chamber d from a tube d<SP>6</SP> to an outlet tube d<SP>7</SP> and natural gas is supplied to the inside of the cover e through a pipe a<SP>10</SP> and the. cored out casting a<SP>6</SP> in order to prevent entrance of air. Thermo couples f<SP>1</SP>, f<SP>2</SP> are connected by conductors passing out through conduit a<SP>12</SP>. After charging and replacing the diaphragm d<SP>3</SP>, air seal cover e, and the furnace cover b. which is still maintained by the hoist, heating is effected by natural gas supplied by pipe a<SP>10</SP> and dry reducing gas such as hydrogen through pipe d<SP>6</SP> to absorb and remove gas expelled from the pores of the facing. The gas is ignited at a" in the pipe a<SP>10</SP> to indicate that such gas is being supplied to the chamber e when the temperature reaches 1200‹F. to 1300‹F. the compressed powder is sintered and when it reaches welding temperature, e.g. 1350‹F. to 1500‹F. the hoist is eased off and the nuts a<SP>14</SP> applied and air chamber c' inflated to give welding pressure through the diaphragm d<SP>3</SP>. In the form in which the backing is coated with copper &c. a similar furnace is used but the chamber d and supply of hydrogen are omitted, charcoal being placed on the coating a<SP>6</SP> to provide an atmosphere of carbon monoxide. Instead of applying the facing direct to the clutch disc, a compound facing is made as above which may be riveted to the clutch disc. The parts in this case may be assembled before the powder is compressed. In a modification of this form perforation may be made in the facings and the backing rings spot-welded to the disc. In a further form, Fig. 10, the disc 11 is placed between blocks 15, 16 supported on a soft rubber ring 17 and the powder compressed in a die on the perforated edge of the disc by an annular plunger 18. The block 16 may be forced down positively at half the speed of the plunger 18. The artictle is then sintered and welded as previously described. The disc 11 may in this case be in the form of a strong woven screen or other foraminous form. Specification 530,953, [Group XII], is referred to.