Patent GB-709246-A (GB)
Title: Improvements in processes and apparatus for making piston rings
IPC: B24B19/11
Filed: 1952-03-31
Abstract: 709,246. Making piston rings. GENERAL MOTORS CORPORATION. March 31, 1952 [April 10, 1951 ; May 3, 1951], No. 8100/52. Class 83 (2). [Also in Group XXIII] A machine for forming a piston ring comprises a device having a plurality of elements adapted to be spaced around the outer periphery of the ring for constricting and holding it in circular form, and a grinding device for reducing the outer peripheral surface of the ring to circular form. To form the rings, round steel wire is rolled to a rectangular section and wound in the form of a helix, each coil of which is cut. The rings 1, Fig. 2, thus produced are clamped on an oval mandrel 5 by clamp bars 13 and a clamping plate 15 with an annular flange 19, after which they are heat treated in an electric furnace 21 so that they retain their clamped shape. The flat faces of each ring are then ground between two flat rotating grinding wheels before it is constricted to circular form by means of a ring of tapered rollers 67. Fig. 8, and a clamping flange 81 which is displaced axially between the rollers by a bolt 88 to drive the ring along the tapered portions of the rollers and on to a circular portion 69. The ring is now rotated in contact with a grinding wheel 95 by an electric motor 37 which through a reduction gear drives a shaft 51 carrying a gear 55 meshing with pinions 77 secured to the roller shafts. Pilot pins 91 maintain the flange in alignment with the rollers. In a modification, the grinding wheel rotates about an axis parallel with the shaft 51 and the outer peripheral surface of the ring engages arcuate guide portions at each side of its area of contact with the wheel. A quick release mechanism is provided for the flange 81 in the form of a plate 89 which has a slot 90 to enable it to be slipped out of engagement with the bolt 88. In a further modification, the rollers are cylindrical with an annular recess into which the ring is inserted by first bending its ends into overlapping relation, no clamping flange being necessary. The rings may be automatically fed to the grinding wheel by the apparatus shown in Figs. 13 and 15 in which a stack of rings is intermittently fed past a grinding wheel 371 by a plunger 325 reciprocated by fluid pressure. The stroke of the plunger is controlled by adjustable stops 324 and a fresh ring is fed through a shoot 299 to the stack on each movement of the plunger. The rings are contacted prior to engagement with the grinding wheel and allowed to expand after engagement by tapered bores 283 while rollers 327 rotate the rings during the period of engagement. The rollers are rotated by a chain drive 351, reduction gear 357 and belt drive 353 from an electric motor 369. The rings leave the apparatus by way of a delivery shoot 304. Stationary ring guiding means are provided at each side of the area of contact between the rings and the grinding wheel. The outer peripheral surfaces of the rings may also be ground by assembling them with the aid of a cylindrical jig on a mandrel which is then inserted axially into abrading relation with a number of honing stones arranged in a circle and secured in a hollow oscillatable and variable stroke head. The rings are allowed to expand into engagement with the stones by temporarily loosening the clamping means. The operation may be terminated with the rings loose on the mandrel. The interior of the rings is bored to a true cylindrical surface while they are held compressed in a cylindrical sleeve. After boring they are mounted on an arbor and oil grooves and chamfered surfaces are cut by forming tools after which the external surface is finish ground. The gaps in the ends of the rings are next milled off while the ring is supported in a hinged two part cylindrical fixture. The rings are finished by electroplating and further grinding.