Electrofusion of electrofusion joint, method of confirming state of fusion and fusion joint suitable for use in the methods

• US 5,116,082 A
• Filed: 07/21/1989
• Issued: 05/26/1992
• Est. Priority Date: 07/21/1988
• Status: Expired due to Fees

• Current Assignee: Mitsui Chemicals Incorporated (Mitsui Chemicals)
• Original Assignee: Mitsui Petrochemical Industries, Ltd.
• Inventors: Handa, Takayuki, Uda, Naotake
• Primary Examiner(s): Arola, Dave W.
• Assistant Examiner(s): Chun, Heather
• Application Number:
  US07/383,015
• Time in Patent Office: 1,040 Days
• Field of Search: 285/21, 285/93, 285/22, 156/304.1, 156/304.2, 156/304.6, 156/274.2, 219/535, 219/544
• US Class Current: 285/21.2
• CPC Class Codes: B29C 65/342 comprising at least a single wire, e.g. in the form of a winding
• CPC Class Codes: B29C 65/3468 characterised by the means for supplying heat to said heated elements which remain in the join, e.g. special electrical connectors of windings B29C65/3668 takes precedence
• CPC Class Codes: B29C 65/3476 being metallic
• 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 66/1142 Single butt to butt joints
• CPC Class Codes: B29C 66/5221 for forming coaxial connections, i.e. the tubular articles to be joined forming a zero angle relative to each other
• CPC Class Codes: B29C 66/5229 involving the use of a socket
• 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 66/91651 by controlling or regulating the heat generated by Joule heating or induction heating
• CPC Class Codes: B29C 66/91655 by controlling or regulating the current intensity
• 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: B29C 66/92651 by using stops
• CPC Class Codes: B29C 66/929 characterized by specific pressure, force, mechanical power or displacement values or ranges
• CPC Class Codes: B29C 66/94 by measuring or controlling the time
• CPC Class Codes: B29C 66/972 by extrusion of molten material
• CPC Class Codes: B29C 66/976 by the use of an indicator pin, e.g. being integral with one of the parts to be joined
• CPC Class Codes: F16L 47/03 Welded joints with an electrical resistance incorporated in the joint
• CPC Class Codes: G05D 23/27535 Details of the sensing element

Abstract

An electrofusion joint includes an electrical heating wire embedded in its inner peripheral region. The electrofusion joint can be fitted to an end of a plastic pipe. By supplying electrical current to the electrical resistance heating wire the interface between the joint and the pipe are fusion bonded. In order to allow easy determination of the completion of fusion bonding, the electrofusion joint is provided with an annular groove in the outer peripheral surface extending to a region of the joint near the electrical resistance heating wire. A pin or bar-like core member is located at and extends upwardly from the center of the groove. A stopper member is provided above the core to control the extent of projection of the pin or bar-like core such that any rise in pressure due to flow of molten resin in the groove of the joint which is transfered to the pin or bar-like core member enables confirmation that the fusion has been successfully accomplished by the observation of the limited movement of the stopping member with minimal flow of resin. Furthermore, as the stopper member is lifted by this pressure the electrical contact between the heating wire and electrical current supply is broken and further heating is terminated.

Claims

1. An electrofusion joint having an electrical heating wire embedded in the inner peripheral region thereof, said electrofusion joint being adapted to be fitted to an end of a plastic pipe and said electrical resistance heating wire being adapted to be supplied with electrical current so that the interface between said joint and said pipe may be fused to bond said joint and said pipe, said electrofusion joint comprising:

an annular groove formed in the outer peripheral surface of said joint and extending to a region near said electrical resistance heating wire;

a core member extending upwardly from said groove above the outer peripheral surface of said joint; and

a stopper member provided above said core member and capable of limiting the lift of said core member in response to pressure exerted on said core member by molten joint material formed in said groove when electrical current is supplied to said heating wire.

2. An electrofusion joint according to claim 1, wherein said stopper member has a cap-like form and is made of at least translucent material, whereby the fusion bond formed between said joint and pipe may be observed through said material, said stopper member being installed so as to cover said annular groove from the upper side of said annular groove.

3. An electrofusion joint according to claim 1, wherein said stopper member is provided to surround said annular groove, with at least part of its circumference opened.

4. An electrofusion joint according to claim 1, wherein said stopper member is detachably mounted on said fusion joint.

5. An electrofusion joint according to claim 5, wherein said stopper member is detachably inserted into a socket formed in said electrofusion joint to complete an electrical circuit with said electrical resistance heating wire, whereby projection of said core member against said stopper member following fusion bonding between said joint and said pipe causes said electrical circuit to be disconnected.