Patent GB-557419-A (GB)
Title: Improvement in process and apparatus for forming seams in sheets and films of thermoplastic materials
IPC: B29C65/18
Filed: 1942-05-15
Abstract: 557,419. Seaming non-metallic sheet material. NATIONAL CARBON CO., Inc. May 15, 1942, No. 6591. Convention date, June 20, 1941. [Class 42. (i)] Sheets and films of thermoplastic material are seamed by continuously feeding successive overlapping portions of two surfaces of the material through a heat-sealing zone while supplying a small amount of a: volatile organic softening agent for the material at a predetermined rate between the surfaces and at a point or points thereof immediately adjacent the heatsealing zone; a low pressure is applied to the overlapping portions of the two surfaces at the heat-sealing zone and, during application of the pressure, heat is supplied to at least one of the surfaces of the seam to produce a difference of temperature between the surfaces of the seam, the seamed films being then withdrawn from the heat-sealing zone. As shown films 166, 168, Fig. 4, which are to be seamed, are carried over a table 13 by conveyer belts 91, 92, Fig. 1, between sealing rolls 37, 39 driven from a motor 41, the roll 37 being journalled in a carriage 17 slidable in a member 11 and connected by a cable 19 to a drum 25 rotatably mounted on the member 11 and carrying a counter-weighted arm 29 pivotally connected to the core 31 of a solenoid S. Each sealing roll consists of a sleeve 100, Fig. 3, of insulating material secured upon a shaft 85, with metal connector rings 101, 101' at its ends spaced by a heater ring 103 and insulating rings 105, the outer peripheral surface of the ring 103 being grooved to accommodate a resistance element having its ends connected to the rings 101, 101' and the resistance element being covered by a sealing ring 109 of refractory material or of metal which is secured to the ring 103 ; current for heating the rolls is conducted to the resistance elements by carbon brushes engaging the rings 101, 101' and connected to a low voltage heating transformer, the primary coil thereof being connected to the main circuit 43 and the secondary coil which is connected to the brushes, being provided with two tappings which are adjustable to vary the current flowing to the resistance elements and are connected to breaker points, an electromagnet and switch for the motor 41 so that when the switch is closed to start the motor, the electromagnet is energized to break contact at one breaker point and close it at the other, the entire secondary current from the transformer then flowing to the rolls and maintaining the desired high temperature required for the sealing operation. At the same time, closing of the switch energizes the solenoid S thereby raising me lever 29 and causing the predetermined pressure to be exerted between the sealing rolls ; the motor switch is opened on completion of the sealing operation with de-energizing of the solenoid S, raising of the member 17 by the counterweight 33 and separation of the sealing rolls, and de-energizing of the electromagnet with reduction of current flowing through the resistance elements to a selected value. The solvent is fed to the heat-sealing zone from a reservoir to a conduit 139 having a header 140 provided with one or more fine tubes 141 having fine passages therethrough; the conduit is provided with a regulating valve and a stop valve controlled by a solenoid connected to a microswitch 149 so that when there is no film between the sealing rolls, the current through the solenoid is broken at the switch 149 and the stop valve is closed. The sheet 168 is guided by a curved channel plate 164 secured to and co-operating with a flat plate 162 secured to the margin of a plate 160 on the table 13 and the tubes 141 are disposed closely adjacent the sealing rolls and between the latter and the margins of the plates 162, 164 ; various guides may be provided to form a wide variety of seams, some of which may have cords inserted therein. Specifications 406,338, 437,773 and 557,258, [all in Group IV], are referred to.