METHOD AND APPARATUS FOR PRODUCING A WELDED JOINT IN THERMOPLASTIC STRAP WITH DIFFERENTIAL PRESSURE

• Main Author: KOBIELLA, ROBERT J
• Format: Patent
• Language: English; French
• Published: 25.06.1996
• Edition: 6
• Subjects: AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING; CONVEYING; HANDLING THIN OR FILAMENTARY MATERIAL; MACHINES, APPARATUS OR DEVICES FOR, OR METHODS OF, PACKAGINGARTICLES OR MATERIALS; PACKING; PERFORMING OPERATIONS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDEDFOR; SHAPING OR JOINING OF PLASTICS; STORING; TRANSPORTING; UNPACKING; WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL

A novel method and apparatus are provided for making an improved welded joint between overlapping lengths of thermoplastic strap. The welded joint includes a central region and an adjacent peripheral region. The pressure on the strap joint during formation is released first in the peripheral region and subsequently in the central region. An embodiment of the apparatus for making such a joint includes an anvil, a central strap-engaging member, a peripheral strap engaging member, and a mechanism for moving the anvil sequentially to three positions. At a first position the overlapping strap lengths are pressed between the anvil and both the central and peripheral strap-engaging members. In the second position of the anvil the peripheral strap-engaging member does not press against the strap lengths while the central strap-engaging member continues to press the strap lengths against the anvil. In the third position of the anvil the anvil and strap-engaging members are sufficiently spaced apart to release all of the pressure on the strap lengths.