Patent GB-775717-A (GB)
Title: Improvements in or relating to method and apparatus for slitting tire treads
IPC: B29D30/68
Filed: 1955-04-25
Abstract: 775,717. Slitting tyre treads. GOODRICH CO., B. F. April 25, 1955 [April 30, 1954], No. 11858/55. Class 31 (1). A method of transversely slitting tyre treads comprises rapidly reciprocating a knife substantially radially into and out of the tyre tread while the latter is slowly and continuously rotated. In the apparatus shown, a tyre T is mounted on mechanism M including a hollow shaft 11 which is rotated by means R including an electric motor 31. The tyre is adapted to be inflated by air under pressure supplied through connected tubes 14, 15, the tube 14 extending through the hollow shaft 11. The tyre may have an inflatable inner tube. The slits are produced in the tyre during its rotation by means of a reciprocating knife assembly K, including an electrically-heated knife 55, which is advanced to and retracted from operative relationship with the tyre by a knife-positioning assembly A actuated by a control cam and switch assembly C, Fig. 1. The latter comprises discs 23, 24, 25 which form a unitary assembly supported upon the shaft 11 and mounted between friction members 27, Fig. 1, rotatable with the shaft 11 and pressed towards each other by means of a spring 28 and adjustable nut 29. The discs 23, 24 have cam surfaces with which cooperate switch actuators 119, 117, Fig. 4, respectively, and the disc 25 is provided with a notch to receive a retractable latch 112. The knife 55 and its reciprocating assembly K together with the knife-positioning assembly A are mounted on a plate 40, Fig. 3, slidably supported on a frame 10 for adjustment radially of the tyre T by means of a screw and nut 42, 43. The reciprocating portion of the knife assembly is mounted upon a carriage 48, Fig. 3, slidable on the upper surface of the plate 40. The carriage 48 has a bore 51 in which is slidable a cross head 52 which is reciprocable by means of mechanism, including a connecting rod 62, eccentric 64, and a shaft 66 rotatable by an electric motor 69. The knife 55 is clamped between a removable jaw 54 and a knife holder 53 clamped to the forward portion of the crosshead 52. The cutting edge of the knife is continuous, as shown, or discontinuous. The forward faces 56 of the knifeholder 53 and jaw 54 are co-planar so as to be adapted to flatten and stretch the tyre during the slitting operation. The knife-positioning assembly A comprises a toggle linkage 74 the ends of which are, respectively, pivoted to the plate 40 and the carriage 48. The toggle is opened and closed by operation of a piston 78 movable within a pivotally-mounted cylinder 79 to the ends of which air under pressure is adapted to be supplied under the control of a solenoid-operated valve 84. In operation, the motor 31 is first energized to slowly rotate the tyre and air under pressure is then supplied to the connected pipes 14, 15 to inflate the tyre. When the air pressure in the tyre has reached a predetermined value, a switch 102, Fig. 4, is operated to energize the motor 69 so as to rapidly reciprocate the knife assembly K including the knife 55. After a predetermined interval of time, a circuit is completed to retract the latch pin 112 from the co-operating notch in the disc 25 on the shaft 11. The discs 23, 24, 25 are now clutched to the shaft 11 for rotation therewith. After a short interval of time, the latch pin 112 is caused to ride upon the periphery of the disc 25. Rotation of the cam discs 23, 24 causes the switch actuators 117, 119 to move from the recesses in the cam discs and ride upon the raised portions of the discs thereby completing circuits to effect actuation of the valve 84 so that air under pressure is supplied to the upper end of the cylinder 79 to straighten the toggle linkage 74 and move the knife assembly K into operative position adjacent the rotating tyre. The knife continues to rapidly reciprocate while the tyre rotates thereby effecting slitting of the tread until one complete revolution of the tyre has been effected. When that has been achieved, the switch actuator 117 again enters the recess in the cam disc 24 so that the motors 31, 69 are de-energized and the valve 84 returns to its initial position. Also, the air within the tyre is exhausted therefrom. The latch 112 reenters the notch in the disc 25, thereby stopping further rotation of the cam discs 23, 24.