Patent GB-707092-A (GB)
Title: Methods of manufacturing bolts and the like
IPC: B21K1/44
Filed: 1951-09-24
Abstract: 707,092. Forging bolts. SCHWARZ, J. Sept. 24, 1951 [Sept. 27, 1950], No. 22334/51. Classes 83 (2). and 83 (4) A method of making bolts and the like by cold working is characterized in that the work is consolidated over the entire length of the bolt shank by cold hammering by means of forming hammers acting transversely in relation to the axis of the bolt. A cold rolled or cold drawn steel pin 2 is cold hammered from the diameter 3 to form a shank of diameter 4 and chamfers 5 and 6. The end 31 of the bolt is chamfered by cold deformation and a thread 7 is rolled so that it cuts into the chamfer 6. The shank is about 1 per cent to 5 per cent smaller than the core diameter of the thread 7. A short serration 8 is rolled or hammered adjacent one end of the head portion 9 and an unthreaded nut 10 is pushed on to the head portion 8, 9 and pressed on by hammering, pressing or rolling. Instead of serrations, knurling, grooves, threads or the like, may be provided and a securing pin may be passed transversely through the nut and head portion. In an embodiment axial holes 12 and 13, Fig. 3, are bored in a blank 11 having an external diameter larger than the final bolt head diameter. A hexagonal mandrel is introduced into the hole 13 and a hexagonal hole 14 is formed in the blank by external rolling or hammering. The shank 15 is formed by cold hammering after inserting a mandrel in the bore 12. The surface on which the thread 18 is to be formed is ground to remove the hardened skin after which the thread is cold rolled whereby the same consolidation is obtained as in the shank 15. A transverse slot 17 may be provided in the head 16 for a screw-driver. In another embodiment a bolt is produced from a metal tube by forming the head 20, Fig. 6, with an external hexagon by hammering and the shank by cold hammering on a mandrel. A filling member 22 or 23 may be rolled, hammered or screwed into the head or the bolt end respectively so that the bolt is fluid tight and may be used as a lubricating pin. In a further embodiment a headless boltpin 47, Fig. 7, hardened over its entire length by cold hammering is placed in a die 34 in a carrier 32 which may be a rotatable disc or a chain conveyer. Punches 41, 42 and 43 are mounted in a vertically reciprocating carrier 40 which also carries a high frequency heating coil 44. The punches 41 and 42 have conical formers 48, 49 and central cones 50, 51. The punch 43 comprises a former 52 for imparting the final shape to the bolt head and a spring-loaded plunger 53 which is limited in its vertical displacement by a pin 57 engaging in a groove 58 in the plunger. Instead of the spring 55 a fixed pin may strike the plunger as the carrier 40 ascends in order to eject the bolt. A fixed electromagnet 59, 60 may be provided for extracting the bolts from the punch formers in which case the dies 34 must be non-magnetic. During the upsetting the lower end of the pin 47 is chamfered by being pressed on to chamfers 37 in the dies 34. The headed pins are ejected by a push member 61 unless a chain conveyer is used when the headed pins automatically fall at the point of reversal of the chain due to gravity. The dies may also be arranged around the periphery of a disc rotating about a horizontal axis, so that the pins automatically fall out after being headed. The heating may be effected by indirect electric resistance heating, inductive heating, supersonic heating or gas heating. An annular bead 39 on the collar 38 of the dies prevents a sharp bend at the junction of the bolt shank and the head. In another embodiment a round pin is hammered or rolled at both ends to form reduced portions 123, Fig. 14, and fillets 124. The central portion 125 is cut at the centre 126 by cutting rolls or abrasive discs and the pin halves are then placed in dies and the bolt heads formed by cold punching or hammering and the threads by cold rolling. Instead of the round pin a hollow cylindrical externally hexagonal pin may be used in which case the cold forming of the shank portion is carried out on a mandrel which is withdrawn before the last cold deformations.