CN1061293C - Electrothermal welding method - Google Patents

Abstract

There is provided a method of joining pipes by joining a first pipe of plastics material to a second pipe of a material which does not bond well to the plastics material, the method comprising providing an electrofusion sleeve of plastics material which bonds well to the first pipe, the sleeve having a first electrical heating coil on an inner surface at one end for receiving the first pipe and a second electrical heating coil on an inner surface at the other end for receiving the second pipe. The sleeve includes a bonding material at the other end thereof which, when heat activated, produces a good bond between the material of the sleeve and the material of the second tube. After the two pipes are inserted into the two ends of the sleeve, current is applied to the two coils to cause the first end of the sleeve to be bonded to the first pipe by means of electro-thermal welding and the second end of the sleeve to be bonded to the second pipe by means of electro-thermal welding and by means of a bonding material.

Description

Electrothermal welding method

This invention relates to methods and apparatus for joining two or more pipes together by electrothermofusion.

Electrothermofusion is a known technique, for example in French patent 2,516,439, which joins two pipes together by means of a sleeve in which an electric heating coil is housed, and the two pipes being joined After the tubes are inserted into the ends of the sleeve, electricity is applied to the coil to fuse the outer surfaces of the two tubes to the sleeve. This technique is widely used to join pipes made of the same plastic material, or pipes made of different plastic materials that bond well to each other by means of heat. In this case, the electrothermal fusion sleeve can be made of the same material as the plastic pipe, or a material that can bond well to both plastic pipes by means of electrothermal fusion.

However, in some applications it is necessary to join pipes of one plastic material which does not bond well to pipes of another plastic material or metal. For example, polyolefins such as polyethylene, polypropylene, and polybutene are difficult to bond to other materials such as nylon (polyamide) and polyvinyl chloride, so electrothermal welding has not been widely used in these occasions . As a result, for pipes of polyethylene or other materials that do not bond well to other plastics or metals, mechanical couplings are often used.

It is an object of the present invention to provide an electrothermal welding method and apparatus which can join pipes made of plastic materials which normally do not bond well to other plastic or metal pipes.

One aspect of the present invention provides a method of joining a first pipe of a plastic material to a second pipe of a material that does not bond well to the plastic material, the method comprising : provide an electrothermal fusion sleeve (2) made of plastic material that can be well bonded to the plastic material of the first pipe (P ₁ ), the inner surface of the electrothermal fusion sleeve at one end A first electric heating coil (6) is installed on it to receive the first pipe, and a second electric heating coil (7) is installed on the inner surface of the other end of the casing to receive the second pipe; The first pipe (P ₁ ) is inserted into the first end of the electrothermal fusion sleeve (2), and the second pipe (P ₂ ) is inserted into the other end of the electrothermal fusion sleeve; and to the first (6) and The second (7) electric heating coil is fed with current, so that the first end of the sleeve (2) is bonded to the first pipe (P ₁ ) by means of electrothermal welding, and the second end of the sleeve (2) is The ends are bonded to the second pipe (P ₂ ) by means of electrothermal welding. It is characterized in that, before inserting the second pipe (P ₂ ) into the second end of the electrothermal fusion sleeve (2), an adhesive material (7a, 17b) is added to the second end of the sleeve, using it In direct contact with the plastic material of the sleeve (2) and with the material of the second pipe ( _P2 ) when the other end of the sleeve receives the second pipe, the bonding material (7a, 17b) Activation by energized heat produces a good bond between the material of the sleeve (2) and the material of the second pipe ( _P2 ).

In a preferred embodiment, it is further characterized in that the bonding material is in the form of a cladding, preferably a coating, on the wire of the second electric heating coil; and in a second embodiment, the bonding The material is in the form of a preformed film covering the second electric heating coil for contacting the second sleeve when the second tube is inserted into the second end of the sleeve.

Examples of preferred materials that can be used to make the two tubes are polyolefins, preferably polyethylene, as the plastic material for the first tube and nylon (polyamide) as the material for the second tube. In such applications, the electrothermal fusion sleeve can also be made of polyethylene. However, the invention can also be used with plastic tubes of other materials that do not bond well to each other, for example, polypropylene for the first tube material and/or another polar material for the second tube s material.

The thermoplastic bonding material is preferably a polyolefin-based copolymer containing active polar groups. When thermal energy is applied to this copolymer, free radicals will be generated, and then the free radicals will react with any contact with it. Polar groups or polar materials form a bond. One such material is a copolymer of PE (polyethylene) and maleic anhydride, Maleic anhydride is derived by dehydration of maleic acid. The other is a copolymer of EVA and maleic anhydride. Commercial formulations of these materials are known.

The present invention also provides an apparatus for joining a plastic pipe to another plastic pipe or metal pipe which does not bond well by electrothermal welding.

Additional features and advantages of the invention will be apparent from the description below.

The invention will be described below, by way of example only, with reference to the accompanying drawings. Attached are:

Figure 1 is a longitudinal half-sectional view illustrating an electrothermal fusion sleeve made according to the present invention;

Fig. 2 is a partial enlarged view illustrating the structure of the first electric heating coil at one end of the electrothermal fusion sleeve in Fig. 1;

Fig. 3 is a partially enlarged view illustrating the structure of the second electric heating coil at the second end of the electrothermal fusion sleeve; and

FIG. 4 is a diagram illustrating a modification of the structure of the second electric heating coil in FIG. 3. FIG.

The electrothermal fusion fitting shown in Fig. 1 includes: a thermoplastic electrothermal fusion sleeve 2, which has a tube tube 3 for receiving the first plastic pipe _P1 at one end and a tube tube for receiving the second tube P2 _at the other end 4. This second pipe is to be connected to the first pipe by electrothermofusion. The two tubes 3, 4 are preferably separated by an annular shoulder 5 (or other protrusion) so as to limit the depth at which the two tubes can be inserted into the two tubes respectively, and to keep the two tubes coaxial with each other in a straight line At the same time, the electrothermal fusion sleeve is coaxial with it and in a straight line.

The electrothermal fusion sleeve 2 includes a first electric heating coil 6 on the inner surface of one end for receiving the pipe P ₁ inserted into the barrel 3, and a second electric heating coil 7 ( Preferably a section of the coil 6 ) for receiving the pipe P ₂ inserted into the tube 4 . The bushing 2 also includes terminals 8, 9 for connecting current to the coils 6, 7 to melt the inner surface of the bushing and the outer surface of the received plastic pipe, thereby bonding them on the Together.

The structure and state of the electrothermal welding fittings described above are familiar to everyone for the connection of pipes made of the same plastic material or pipes of different materials that are easily bonded together by electrothermal welding. However, this technique is not commonly used to join two plastic pipes that are not easily bonded together by electrothermal welding, for example, polyolefin (such as polyethylene) pipes and another material that is not easily bonded to polyethylene is nylon. (polyamide) or other polar material or metal pipe connection. The electrothermowelding fitting shown in Figure 1, and in particular the configuration further depicted in Figures 2-4, is designed to bond, for example, polyethylene pipe to another material such as polar plastic or metal that does not normally bond to polyethylene. It is possible to bond the pipes together.

In the following embodiment, we assume that the pipe _P1 received in the tube 3 is a polyethylene tube, and the tube _P2 received in the tube 4 is a tube made of other plastic materials such as nylon (polyamide) , this material usually cannot be bonded directly to _P1 pipe.

In this embodiment, the electrothermal fusion sleeve 2 is also made of polyethylene. The coating of the electric heating wire of the coil 6, designated 6a in FIG. 2, is also polyethylene. Therefore, when current is applied to the coil 6, its polyethylene coating 6a is melted in the welding zone _Z1 , and similarly, the adjoining surfaces of the pipes in the casing 2 and the tube 3 are also melted. It melts in this area and produces an integral bond between the sleeve 2 , the wire coating 6 a and the polyethylene of the plastic pipe P ₂ incorporated into the tube 3 . Zones _Z2 and _Z3 at both _ends of the welding zone Z1 are relatively cool areas, where welding usually does not occur.

马来酐是用马来酸脱水衍生出来的。另一种是EVA(乙烯-乙酸乙烯共聚物)与马来酐的共聚物。However, since the pipe P ₂ is made of a material that does not normally bond to polyethylene (polyamide in this embodiment), the other end of the sleeve 2 that wraps around the tube 4 to receive the pipe P ₂ The structure of the coil 7 is not exactly the same as that of the coil 6. As shown in Figure 3, the metal wire of the coil 7 is covered with an outer layer 7a, preferably a coating of bonding material, which, after being activated by the current in the coil 7, can bond the polyethylene of the casing 2 to the pipe P. ₂ polyamides form a good bonding link. Particularly good results are obtained when the outer coating is a polyolefin-based copolymer containing reactive polar groups which, when thermal energy is applied, generate free radicals which then Forms a bond with any polar group or polar material that comes into contact with it. One such material is a copolymer of PE (polyethylene) and maleic anhydride,

Maleic anhydride is derived by dehydration of maleic acid. The other is a copolymer of EVA (ethylene-vinyl acetate copolymer) and maleic anhydride.

When current is applied to the coil 7, its outer coating 7a is activated, creating a strong bond between the polyethylene of the sleeve 2 and the polyamide of the pipe _P2 , its position is to bury the coil 7 The welding zone is equivalent to the welding zone Z ₁ where one end of the casing receiving pipe P ₁ embeds the coil 6 .

This technology also better ensures that the coating 7a is firmly bonded to the coil metal wire 7, thereby reducing or eliminating the possibility of leakage passages between the coating and the metal wire, which is a problem when used for gaseous fuels. particularly dangerous.

FIG. 4 shows a variant in which the bonding material enabling a strong bond between the polyethylene on the fitting and the material of the plastic pipe P ₂ (for example polyamide) is prefabricated to cover the coil 7. In the form of a film, the pipe P ₂ comes into contact with the pipe when it is inserted into the cartridge 4 .

Therefore, as shown in the partial view of Figure 4, the electrothermal fusion sleeve 12 is also made of polyethylene as mentioned above, but the metal wire of the coil 17 at the end of the sleeve without the tube 4 to insert the pipe _P2 , Polyethylene is also used as a coating (instead of an adhesive material) which is a prefabricated film 17b covering the entire coil 17 section. A film 17b of adhesive material is therefore used here as a bonding surface between the polyethylene coating 17a and the plastic of the pipe _P2 . When passing electric current to coil 17, polyethylene coating 17a just melts, thereby integrally bonded on the polyethylene of sleeve pipe 12; A good bonded connection is produced between the layer 17a and the adjacent surface of the polyamide plastic pipe _P2 .

It goes without saying that the casing 12 receives the casing structure and the coil structure at the other end of the plastic pipe _P1 , and if _P1 is not a polyethylene pipe, it will also be the same as the above-mentioned variant in FIG. 4 .

A good bond between the coil and the tube, as described above with respect to Figures 3 and 4, also substantially reduces the possibility of creating a leak path between the coil and the tube which would be detrimental to the delivery of pressurized gas. Plastic pipes for fuel are especially dangerous.

Although the present invention has been described in terms of two preferred embodiments, it should be understood that these are examples only and that many other variations, modifications and applications of the present invention are possible.

Claims (10)

1. one kind first pipe (P of plastic materials ₁) with can not be with second pipe (P of the material of the fine bonding of this plastic materials ₂) method that couples together, this method comprises:

An electric heat welding sleeve pipe (2) of making of plastic materials is provided, and this plastic materials is finely to be bonded to first pipe (P ₁) plastic materials on, the electric heat welding sleeve pipe is equipped with the first electric heating coil (6) on the internal surface of first end, in order to admitting first pipe, and the second electric heating coil (7) is housed on the internal surface of sleeve pipe second end, in order to admit second pipe;

With first pipe (P ₁) insert first end of electric heat welding sleeve pipe (2), and with second pipe (P ₂) insert second end of electric heat welding sleeve pipe; And

Feed electric current to first (6) and second (7) the electric heating coil, so that first end of sleeve pipe (2) is bonded to first pipe (P by means of electric heat welding ₁) on, and make second end of sleeve pipe (2) be bonded to second pipe (P by means of electric heat welding ₂) on, it is characterized in that: second pipe (P ₂) insert that second end at sleeve pipe (2) added a kind of binding material (7a, 17b) before second end of electric heat welding sleeve pipe (2), so that it directly contacts with the plastic materials of sleeve pipe, and receive second pipe (P in sleeve pipe second termination ₂) time contacts with the material of this second pipe, this binding material (7a, 17b) can be at material and second pipe (P of sleeve pipe (2) when the hot activation that is energized ₂) material between produce good bonding.

2. the process of claim 1 wherein said second pipe (P ₂) also be that plastic materials is made.

3. the process of claim 1 wherein that said binding material (7a) is to occur with the form of the covering on second electric heating coil (7) wire.

4. the method for claim 3, wherein said binding material (7a) are to be coated on the wire of the second electric heating coil (7).

5. the method for claim 2, wherein said binding material is the prefabricated membrane (17b) that covers on the second electric heating coil (7), as second pipe (P ₂) when inserting second end of sleeve pipe (2), this film contacts with second pipe.

6. the process of claim 1 wherein that said first plastic materials is a polyolefin.

7. the method for claim 6, wherein said first plastic materials is a polyethylene.

8. the method for claim 6, wherein said binding material (7a, 17b) is that what to contain active polar group is the copolymer of basis with the polyolefin, this copolymer will produce free radicals after being applied in heat energy, the free radicals energy forms bonding with the polyolefinic polar group that contacts with binding material and links.

9. the method for claim 8, wherein said binding material (7a, 17b) is the polyethylene and ethylene copolymers that contains the maleic anhydride active component.

10. the process of claim 1 wherein and all are the manufactured materials of electric heat welding sleeve pipe (2) and the coating material of electric heating coil (6) wire and first pipe (P ₁) identical plastic materials.

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