Patent GB-637603-A (GB)
Title: Improvements relating to machines for welding thermoplastic materials
IPC: H05B6/62
Filed: 1947-11-26
Abstract: 637,603. Seaming non-metallic sheet material. FERRANTI, Ltd., and CAPPER, J. F. Nov. 26, 1947, No. 31254. [Class 42 (i)] [Also in Groups XI and XXXVIII] In a machine for seam-welding thermoplastic sheet material by the simultaneous application of pressure and high-frequency electric heating, a pair of opposing electrodes are caused to grip, advance and release a portion of the seam and then return to the " engage " position to repeat the steps with another portion of the seam, each portion being subjected to a high-frequency field for part only of the engagement period of time during which it is gripped by the electrodes. As shown, the seam to be welded is gripped, under pressure of spring 21, between electrodes 10, 11 mounted on arms 18, 13 fixed to rock-shafts 19, 14. Rotation of a cam 55 by motor 62 acts, through lever 54 and roller 56 to rock a lever 51 fixed to shaft 14 and, through pin-and-slot connection 52, 53, a lever 50 fixed to shaft 19; electrode arms 18, 13 are thereby also rocked causing the electrodes to advance the seam to a " release " position. At this position, rotation of a cam 34 acts through lever 33 and link 32 to rock a shaft 27 carrying the bearing arms 25, 26 of shaft 19 which is thus lifted to raise upper electrode 10 out of engagement with the seam; simultaneously, the movement of arm 25 moves a stud 45 away from an arm 44, allowing a pressure foot 38 on an arm 39 to descend under the action of a spring 72 to hold the work against a work surface 36. While the work is thus held, continued rotation of cam 55 causes the electrode arms to swing back beyond the vertical to an " engage " position where further movement of cam 34 causes shaft 19 to drop again so that the electrodes once more grip the work and the pressure foot 38 is raised by the engagement of stud 45 with arm 44. The feeding movement of the electrodes then recommences and the cycle of operations is repeated. The length of the forward movement, and hence the spacing of successive welded areas, can be varied by adjusting the position of roller 56 by rotation of a spindle 58, to which a pointer 74 is attached; the machine may thus produce a continuous seam weld or a series of spot welds. The pressure of the upper electrode and the pressure foot can be controlled by means of set-screws 75, 77. To insert the seam between the electrodes, upper electrode 10 and pressure foot 38 are lifted by means of a handle 49 acting through a lever 48 on studs 22, 47. A pulse or pulses of high-frequency energy is applied during each feeding movement by means of a switch 69 operated by a cam 70; operation of switch 69 causes a trigger pulse to be applied by a trigger-pulse generator 68 to a multivibrator 67 which applies a single pulse of the desired duration to a high-frequency generator 63. A high-frequency pulse of the same duration is thereby applied through lead 64 to the lower electrode 11, upper electrode 10 being earthed. The length of the pulse or series of pulses applied during each feed movement is arranged to be less than the engagement period of the electrodes corresponding to the most rapid operation of the machine. The machine may be arranged to give to the electrodes a faster return movement than forward movement, and may be driven by treadle instead of by electric motor. Specification 604,018 is referred to.