GB678005A - Improvements in or relating to the production of tubular metal pins - Google Patents

Abstract

678,005. Making tubular pins. ELASTIC STOP NUT CORPORATION OF AMERICA. Aug. 2, 1949 [July 30, 1948], No. 20095/49. Classes 83 (ii) and 83 (iv). [Also in Group XXV] In a method of making tubular spring steel pins 12, Fig. 1, having a longitudinal gap, flat blanks 11 of length equal to that of the pin and width equal to the circumference of the pin are bent in successive stages to tubular shape. A spring steel strip 10 of width equal to the required length of pin is fed by friction rollers 31, Fig. 2, to a reciprocating cutter 36, Fig. 3, on a shearing machine 14 having an adjustable stop 53 set for cutting the strip to the required circumferential dimension of the pin. A slotted feed guide 39 for the strip is pivoted at 40 to the machine frame and yieldingly raised by a spring 41 so that the end of the strip remains engaged with the back of the cutter 36 as it returns upwards and is prevented from fouling the cut off blanks 11 which are ejected successively sideways in end-to-end elation by pins 49 on a chain 50 driven by sprocket-wheel 52 in phase with the cutter 36 and moving the blanks through a guide 54 to co-operating feeder rolls 75<SP>1</SP>, 76<SP>1</SP> on a rolling mill 15 in which the blanks are successively bent to tubular shape. The mill 15 comprises ten intergeared pairs of co-operating forming rolls driven by an electric motor 20, belt drive 64 and worm gear 66, Fig. 4, shafts 57. The rolls are driven at successively faster speeds to prevent the blanks fouling each other by interconnecting groups of two or three roll pairs through chain and sprocket drives 72, the number of teeth on the sprockets being less on each succeeding roll in a group and each group being driven from the preceding group by a driving sprocket on the shaft of the last roll of the group. The first pair of forming rolls 75a, 76a, Fig. 6, interengage to form a pass for the blank 11a in which the sides 92a of the blank only are bent, a pair of small grooves 91 and tapering sides 84 in the main groove 92 permitting the full width of the flat blank to be introduced into the rolls. Further similar roll pairs successively bend the remaining flat parts of the blank or reduce the radius of curvature until in the final stages roll pairs 75i, 76i, Fig. 14, form substantially circular passes of successively decreasing radii. The lower rolls have a ring-like mandrel 133 projecting into the formed blank without engaging the internal wall and having tapered faces 132 which engage the sides of the blank to control the width of the longitudinal gap which is successively decreased at each stage. The passes of each roll pair are adjustable by bolts 62 which move the upper rolls. Guides 77, Figs. 17 and 19, are inserted between each roll pair and comprise flat plates such as 93, 94, which are cut away at their ends, substantially to the peripheral shape of the forming rolls so that they project as far as possible into the pass in such a manner that the leading ends of the blanks are engaged after leaving the roll passes before the trailing ends leave the preceding guides. The successive upper guide plates 94 are grooved substantially to the outer shape of the blanks and carry ribs 96, 96a which also project into the roll passes to locate the blanks and in the later stages to prevent them from rotating about a longitudinal axis. The strip used may have bevelled edges so that the ends of the finished pins are tapered for ease of insertion into holes. Spring steel containing 0.92-1.0 per cent carbon such as S.A.E. 1095 is preferably used and, after formation, the pins may be heat-treated in salt baths to develop a Rockwell hardness of about 52 C.