Method and apparatus for producing a welded joint in thermoplastic strap with differential pressure

• US 5,348,781 A
• Filed: 10/08/1993
• Issued: 09/20/1994
• Est. Priority Date: 10/30/1992
• Status: Expired due to Fees

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Signode Corporation (Illinois Tool Works Inc.)
• Inventors: Koblella, Robert J.
• Primary Examiner(s): Thomas, Alexander S.
• Application Number:
  US08/131,941
• Time in Patent Office: 347 Days
• Field of Search: 428/57, 428/220, 156/73.5, 156/73.4
• US Class Current: 428/57
• CPC Class Codes: B29C 65/0636 Orbital
• CPC Class Codes: B29C 66/01 General aspects dealing with the joint area or with the area to be joined B29C65/76, B29C65/82 take precedence
• CPC Class Codes: B29C 66/1122 Single lap to lap joints, i.e. overlap joints B29C66/45, B29C66/472, B29C66/52272 take precedence
• CPC Class Codes: B29C 66/4322 by joining a single sheet to itself B29C66/4332 takes precedence
• CPC Class Codes: B29C 66/4324 for making closed loops, e.g. belts
• CPC Class Codes: B29C 66/49 Internally supporting the, e.g. tubular, article during joining B29C66/63 takes precedence
• CPC Class Codes: B29C 66/71 characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/73712 mono-axially
• CPC Class Codes: B29C 66/81433 being toothed, i.e. comprising several teeth or pins comprising a single tooth B29C66/81429, or being patterned
• CPC Class Codes: B29C 66/8161 said pressing elements being supported or backed-up by springs or by resilient material
• CPC Class Codes: B29C 66/8227 using springs
• CPC Class Codes: B29C 66/8322 Joining or pressing tools reciprocating along one axis
• CPC Class Codes: B29C 66/91 by measuring or controlling the temperature, the heat or the thermal flux
• CPC Class Codes: B29C 66/9241 by controlling or regulating the pressure, the force or the mechanical power
• CPC Class Codes: B29C 66/9261 by controlling or regulating the displacement of the joining tools
• CPC Class Codes: B29C 66/949 characterised by specific time values or ranges
• CPC Class Codes: B29K 2067/00 Use of polyesters or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2067/003 PET, i.e. poylethylene terephthalate
• CPC Class Codes: B65B 13/322 Friction welding
• CPC Class Codes: Y10T 156/1028 by bending, drawing or stretch forming sheet to assume shape of configured lamina while in contact therewith
• CPC Class Codes: Y10T 428/19 : Sheets or webs edge spliced or joined

Abstract

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 tile 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 subsequently 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.

Claims

1. A welded joint defined between two lengths of thermoplastic strap, comprising:

said two lengths of thermoplastic strap being disposed in a face-to-face overlapping relationship with respect to each other at a location at which said welded joint is to be defined;

at least part of the thickness of each one of said two strap lengths being resolidified from a fused state during which said two lengths of said strap disposed at said location at which said welded joint is to be defined were subjected to above-ambient pressure;

said resolidified thickness part of one of said two strap lengths being merged with the resolidified thickness part of the other one of said two strap lengths so as to define a continuous resolidified region; and

said resolidified region including a peripheral region, and an adjacent central region having a substantially disc-like configuration, wherein said above-ambient pressure was maintained, during said fused state, for a longer period of time within said central region than within said peripheral region.

2. The joint in accordance with claim 1 in which said strap is polyester and said peripheral resolidified region includes a plurality of closed cavities.

3. The joint as set forth in claim 2, wherein:

said central region is substantially free of said cavities.

4. The joint as set forth in claim 1, wherein:

said strap is fabricated from polyethylene terephthalate.

5. The joint as set forth in claim 1, wherein:

the thickness of each one of said lengths of strap is approximately 0.5 mm;

the width of each one of said lengths of strap is approximately 11 mm;

the length of said welded joint, along the length of said strap, is approximately 17 mm; and

the thickness of said welded joint comprising said resolidified region is approximately 0.1 mm.

6. A welded joint defined between two lengths of thermoplastic strap, comprising:

said two lengths of thermoplastic strap being disposed in a face-to-face overlapping relationship with respect to each other at a location at which said welded joint is to be defined;

at least part of the thickness of each one of said two strap lengths being resolidified from a fused state;

said resolidified thickness part of one of said two strap lengths being merged with the resolidified thickness part of the other one of said two strap lengths so as to define a continuous resolidified region; and

said overlapping lengths of said strap disposed in said fused state and at said location at which said welded joint is to be defined comprising a central weld region, having a substantially circular configuration, and an adjacent peripheral weld region, which substantially annularly surrounds said central weld region, wherein said central and peripheral weld regions are subjected to above-ambient pressure, and wherein further, said above-ambient pressure is firstly released within said peripheral weld region and subsequently released within said central weld region.

7. The joint as set forth in claim 6, wherein:

said strap is fabricated from polyester.

8. The joint as set forth in claim 7, wherein:

said strap comprises polyethylene terephthalate.

9. The joint as set forth in claim 6, wherein:

said peripheral weld region comprises a plurality of closed cavities; and

said central weld region is substantially free of cavities.

10. The joint as set forth in claim 6, wherein:

the thickness of each one of said lengths of strap is approximately 0.5 mm;

the width of each one of said lengths of strap is approximately 11 mm;

the length of said welded joint, along the length of said strap, is approximately 17 mm; and

the thickness of said welded joint comprising said resolidified region is approximately 0.1 mm.

11. A welded joint defined between two lengths of thermoplastic strap, comprising:

two lengths of thermoplastic strap disposed in a face-to-face, overlapping relationship with respect to each other at a location at which a welded joint is to be defined;

at least part of the thickness of each one of said two strap lengths being resolidified from a fused state wherein said two lengths of said strap disposed at said location at which said welded joint is to be defined are subjected to above-ambient pressure;

said resolidified thickness part of one of said two strap lengths being merged with said resolidified thickness part of the other one of said two strap lengths so as to define a continuous resolidified weld region which defines said welded joint; and

said continuous resolidified weld region which defines said welded joint comprises a central weld region at which said above-ambient pressure was maintained for a first predetermined period of time, and a peripheral weld region which substantially surrounds said central weld region and at which said above-ambient pressure was maintained for a second predetermined period of time which was shorter than said first predetermined period of time during which said above-ambient pressure was still maintained upon said central weld region.

12. A welded joint as set forth in claim 11, wherein:

said central weld region is substantially free of cavities.

13. A welded joint as set forth in claim 11, wherein:

said peripheral weld region comprises a plurality of closed cavities.

14. A welded joint as set forth in claim 11, wherein:

said strap is fabricated from polyester.

15. A welded joint as set forth in claim 11, wherein:

said strap is fabricated from polyethylene terephthalate.

16. A welded joint as set forth in claim 11 wherein:

the thickness of each one of said lengths of strap is approximately 0.5 mm;

the width of each one of said lengths of strap is approximately 11 mm;

the length of said welded joint, along the length of said strap, is approximately 17 mm; and

the thickness of said welded joint comprising said resolidified region is approximately 0.1 mm.

17. A welded joint defined between two lengths of thermoplastic strap, comprising:

said two lengths of thermoplastic strap being disposed in a face-to-face overlapping relationship with respect to each other at a location at which said welded joint is to be defined;

at least part of the thickness of each one of said two strap lengths being resolidified from a fused state during which said two lengths of said strap disposed at said location at which said welded joint is to be defined were subjected to above-ambient pressure;

said resolidified thickness part of one of said two strap lengths being merged with the resolidified thickness part of the other one of said two strap lengths so as to define a continuous resolidified region; and

said resolidified region including a peripheral region and an adjacent central region, wherein said peripheral region substantially surrounds said central region, and wherein further, said above-ambient pressure was maintained, during said fused state, for a longer period of time within said central region than within said peripheral region.

18. The joint as set forth in claim 17, wherein:

said central region is substantially free of cavities; and

said peripheral region comprises a plurality of closed cavities.

19. The joint as set forth in claim 17, wherein:

said strap is fabricated from polyester.

20. The joint as set forth in claim 17, wherein:

said strap is fabricated from polyethylene terephthalate.