Joining bodies of thermoplastic material

• US 5,888,331 A
• Filed: 12/27/1996
• Issued: 03/30/1999
• Est. Priority Date: 04/01/1993
• Status: Expired due to Fees

• Current Assignee: BG plc (Shell Plc)
• Original Assignee: BG plc (Shell Plc)
• Inventors: Greig, John Martyn
• Primary Examiner(s): Ball, Michael W.
• Assistant Examiner(s): YAO, SAMCHUAN CUA
• Application Number:
  US08/777,402
• Time in Patent Office: 823 Days
• Field of Search: 156/156, 156/272.2, 156/187, 156/188, 156/309.9, 156/432
• US Class Current: 156/187
• CPC Class Codes: B29C 2035/0822 using IR radiation
• CPC Class Codes: B29C 63/0069 of tubular articles
• CPC Class Codes: B29C 63/10 around tubular articles
• CPC Class Codes: B29C 63/14 around tubular articles
• CPC Class Codes: B29C 65/00 Joining or sealing of preformed parts , e.g. welding of plastics materials; Apparatus therefor general aspects of processes or apparatus for joining preformed parts B29C66/00; using porous material formed by internal pressure generated therein for joining preformed parts B29C44/1228, B29C44/326
• CPC Class Codes: B29C 65/028 making use of inherent heat, i.e. the heat for the joining comes from the moulding process of one of the parts to be joined
• CPC Class Codes: B29C 65/1416 Near-infrared radiation [NIR]
• CPC Class Codes: B29C 65/1425 Microwave radiation
• CPC Class Codes: B29C 65/1435 at least passing through one of the parts to be joined, i.e. transmission welding
• CPC Class Codes: B29C 65/1477 making use of an absorber or impact modifier B29C65/1677 takes precedence
• CPC Class Codes: B29C 65/1483 coated on the article
• CPC Class Codes: B29C 65/16 Laser beams
• CPC Class Codes: B29C 65/1616 Near infrared radiation [NIR], e.g. by YAG lasers
• CPC Class Codes: B29C 66/0242 Heating, or preheating, e.g. drying B29C66/3464 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 66/7212 characterised by the composition of the fibres
• CPC Class Codes: B29C 66/72141 Fibres of continuous length
• CPC Class Codes: B29C 66/73921 characterised by the materials of both parts being thermoplastics
• CPC Class Codes: B29C 66/91411 of the parts to be joined, e.g. the joining process taking the temperature of the parts to be joined into account
• CPC Class Codes: B29C 66/919 characterised by specific temperature, heat or thermal flux values or ranges specific electrical resistance values B29C66/81262
• CPC Class Codes: B29K 2023/06 : PE, i.e. polyethylene
• CPC Class Codes: B29K 2077/10 : Aromatic polyamides [polyaramides] or derivatives thereof
• CPC Class Codes: B29K 2277/10 : Aromatic polyamides [Polyaramides] or derivatives thereof
• CPC Class Codes: B29L 2007/007 : Narrow strips, e.g. ribbons, tapes, bands belts B29L2029/00; tapes as carrier of sound or information B29L2017/008
• CPC Class Codes: B29L 2009/00 : Layered products
• CPC Class Codes: B29L 2023/22 : Tubes or pipes, i.e. rigid bent tubes not for use as pipe couplings B29L2023/004

Abstract

A pipe of polyethylene is reinforced by two layers of polyethylene tape wound around the pipe in opposite directions under tension. The pipe contains carbon black and the layers are unpigmented and free from fillers and are transparent to infra-red radiation to which the first major surface is exposed. The radiation is in the near infra-red region and has a substantial part of the radiant energy of a wavelength of less than 2.5 micrometers. Very little radiation is absorbed by the layers but a very high absorption occurs in the outer surface of the pipe. This causes the interface between the second major surface of the layer and the first major surface of the pipe and between the second major surface of the layer and the first major surface of the layer to reach temperatures at which fusion welding in the layers welds them together and welds the layer and the pipe together.

Claims

1. A method of fusion welding of a first and second layers of thermoplastic material to a thermoplastic pipe, said thermoplastic pipe having major internal and external surfaces separated by the thickness of the pipe, which comprises:

winding a first layer of thermoplastic material on a thermoplastic pipe under tension sufficient to urge said first layer under pressure against said pipe, said first layer having major internal and external surfaces separated by the thickness of the first layer, said first layer being superimposed on the pipe such that the internal surface of the first layer is pressed against the external surface of said pipe, an absorber of near infra-red radiation being at or adjacent the external surface of said pipe;

winding a second layer of thermoplastic material on said first layer under tension sufficient to urge said second layer against said first layer, said second layer having major internal and external surfaces separated by the thickness of the second layer, said second layer being superimposed on said first layer such that the internal surface of said second layer is pressed against the external surface of said first layer, and second layer being wound on said first layer in a winding direction which is opposite to the direction that said first layer is wound on said pipe, whereby said adjacent surfaces of said pipe and first layer and the adjacent surfaces of the first and second layers are pressed together due to the tension in said first and second layers; and

subjecting the external surface of said second layer to radiation in the near infra-red region having a wavelength chosen so that the first and second layers are substantially transparent to said radiation and so that the radiation is absorbed by said radiation absorber, said radiation being sufficient to cause the adjacent surfaces of said pipe and first layer and the adjacent surfaces of said first and second layers to reach a temperature at which they are joined by fusion welding while under pressure due to the tension in said first and second layers, said pressure being sufficient to cause the first layer to be fusion welded to the pipe and to cause the second layer to be fusion welded to the first layer without causing damage to the pipe due to excessive heat.

2. A method according to claim 1 wherein each of said first and second layers comprises tape carrying a number of reinforcing fibres extending lengthwise of the tape and being evenly spaced across the tape, each of said tapes being progressively wound at an angle to the length of the pipe.

3. A method according to claim 1 in which at least one of the first and second layers contains an absorber to adjust the transparency to said radiation of said at least one of the layers.

4. A method according claim 1 wherein said pipe and said first and second layers are composed of polyethylene, said absorber comprises carbon black, and wherein a substantial part of said radiation has a wavelength less than 2.5 micrometers.

5. A pipe made by a method according to claim 1.

6. A method of fusion welding at least one layer of thermoplastic material to a thermoplastic pipe, said pipe having major internal and external surfaces separated by the thickness of the pipe, comprising:

positioning at least one thermoplastic tape axially on said pipe, said at least one tape having major internal and external surfaces separated by the thickness of said tape, the internal surface of said tape being in contact with the external surface of said pipe, an absorber of near infra-red radiation being at or adjacent the external surface of said pipe;

subjecting the external surface of said tape to radiation in the near infra-red region having a wavelength chosen so that said tape is transparent to said radiation and so that the radiation is absorbed by said absorber, said radiation being sufficient to cause the external surface of said pipe and the internal surface of said tape to reach a fusion welding temperature which enables the tape and pipe to be fusion welded; and

pressing the tape against the pipe while the internal surface of the tape and the external surface of the pipe are at said fusion welding temperature to fusion weld said tape to said pipe without resulting in damage to the pipe due to excessive heat.

7. A method according to claim 6 in which said tape carries a number of reinforcing fibres extending lengthwise of the tape and being evenly spaced across the tape.

8. A pipe made by a method according to claim 6.