| 摘要 |
Apparatus for welding thermoplastic sheet between a pair of pinch bars is made so that the mobile bar is raised and lowered by a lever operated by a transverse rod of adjustable length and riding the perimeter of a cam wheel. The motion of a travelling knife moving alongside the welding bars is controlled by an electrical circuit common with others for controlling the power to the welding bars in response to a local temperature sensor and for controlling the dwell period during which the welding bars are maintained in contact with the thermoplastic sheet. Appts. is suitable for various thickness of film, by appropriate adjustment of the lever bias, for film thickness, and weld cycle timers for heat transfer and weld temps. The cam lever motion causes the jaw to be moving slowly when coming into contact with the film, without wasting time during other parts of the jaw movement. The control circuit prevents the jaws from overheating, adjusting the heater power as necessary to cope with any welding cycle variations, e.g. occasional extended intervals between successive welds. Pref. the power is interrupted by a relay responding to a resistance circuit having a negative temp. coefficient. |
