| 摘要 |
679,283. Seaming thermoplastic sheets. COMMUNICATIONS PATENTS, Ltd. May 26, 1950 [May 27, 1949], No. 13333/50. Class 42 (i). [Also in Group XI] Thermoplastic strip or sheet material is welded by subjecting it to pressure and heat applied between metal ribbons 12, 17, both heated by passage of current for a short period determined by an adjustable timing means, the ribbons being allowed to cool before removal of the thermoplastic. The two metal strips 12, 17 have a thickness of 0.01-0.5 mm. and may be maintained at a temperature just below the softening temperature of the plastic, being heated to welding temperature for a period controlled by the discharge of one or more capacitors. The strips 12, 17 of nickel chromium iron alloy are mounted on bars 5, 6 from which they are insulated by layers of silicone rubber. A.C. is supplied from a transformer 33 to the ends of the strips which pass over rollers 18 on the bars 5, 6 to clamps 14 and may be held taut by springs. The bar 5 is fixed to a casing 4 containing the electric gear and the bar 6 is on arms 7 hinged to the rear of the casing 4. The bar 6 is moved down against a spring to the lower bar 5 by a solenoid 10 to clamp the plastic on operation of a foot- or hand-operated switch 30. D.C. is supplied at 24 and when the switch 30 is off, relays A-C are released and an indicator lamp 31 is lit. When switch 30 is operated, relay A lights indicator lamp 32 and operates through contacts Al, relay B, which energizes the solenoid 10 to operate the clamp. Relay B also actuates through contacts B<SP>1</SP>, relay C which energizes through contact C3 the transformer 33 to pass current through the heating strips 12, 17. Relay C through contacts Cl disconnects relay A from the D.C. supply, so that relay A is energized only by the capacitor 26, and when this is discharged relay A terminates the heating of the strips by operating contacts A4. Release of relay A leaves relay B operated by the charge of capacitor 27 and when this is discharged relay B is released and the solenoid 10 is de-energized, whereupon the bars 5, 6 open under action of the spring. Capacitors 26, 27 are associated with potentiometers 28, 29 to adjust the timing, the latter being adjusted by control knobs 22, 23. Other timing means, e.g. clockwork or electronic valves may be used. Personal operation may be replaced by automatic means for feeding the plastic to and from the apparatus. A small current may be passed constantly through the strips 12, 17 by by-passing contacts A4, C3 of the primary of the transformer 33. |
