Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1998-12-07
2001-08-14
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S255000, C264S275000, C264S296000, C219S535000, C219S544000
Reexamination Certificate
active
06274073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to a process for the production of a pipe fitting, at least certain areas of which consist of thermally weldable material (weld material), which fitting is designed for attachment to, or for the repair of, conduits which also consist of thermally weldable material, wherein several windings of at least one electrical heating wire are first laid in the desired welding area of the future contact surface between the pipe fitting and the conduit, wherein contacts are attached, if desired, to the two ends of the heating wire laid in windings, to which contacts an electrical power source is connected during the later welding of the pipe fitting, and then the position of the windings of the heating wire and possibly the position of the contacts are fixed by welding material which is applied in the injection-molding process. Pipe fittings are used for various purposes to be mounted on a previously installed conduit for media such as gas or water, possibly while the conduit is under the pressure of the medium. Appropriate pipe fittings are also used for repair purposes or to connect sections of pipe. At least certain areas of the pipe fitting and of the conduit consist of thermoplastic resin. In these cases, the pipe fitting has a welding area at its contact surface with the conduit, where several windings of at least one electric heating wire are laid. Contacts which serve to connect the wire to a source of electric power when the pipe fitting is welded on at a later time are usually attached to the ends of the heating wire.
2. Description of the Related Art
In the known process, windings of a heating wire of the type in question can be laid directly in the injection mold used to produce the pipe fitting; this wire is thus integrated into the welding material of the pipe fitting during the injection-molding process (CH 528,697 C). The heating wire is surrounded by a plastic jacket, which hinders the flow of heat to the contact surface between the pipe fitting and the conduit. The windings of the heating wire can be laid in the mold as a monofilar or bifilar spiral or as a meander.
It is also known that a plate-shaped intermediate product can be produced out of the heating wire. This is done by winding the heating wire into a bifilar spiral and by connecting these spiral windings to each other by plastic webs (DE 3,810,845 A1). Finally, it is also known that the heating wire can first be brought into the form of a helix, and that the helix can then be embedded in a star-shaped intermediate product of thermoplastic material (DE 7,121,715 U). When the pipe fitting is injection-molded, this star-shaped intermediate product is then integrated into the area of the contact surface with the conduit. The current flowing through the helix leads to maximum heating in the interior of the helix, however, and this beat is therefore unavailable for the welding process with the conduit. The heat which reaches the contact surface is inadequate. In these known pipe fittings, the strength of the weld to the conduit is unreliable. To achieve satisfactory welding results, it is necessary to use a relatively large amount of electrical energy, which is uneconomical.
SUMMARY OF THE INVENTION
The invention is based on the task of providing an economical process for producing pipe fittings of the aforementioned kind, the end products of which can be welded quickly and reliably to conduits. This is achieved according to the invention in that the heating wire, or at least certain sections thereof, is formed into a flat, wavy shape, as a result of which a wavy heating strand is produced as a first step; in that only then are the windings of the wavy heating strand laid in the future welding area of the pipe fitting; wherein, after the injection-molding of the pipe fitting and the solidification of the welding material, one of the broad sides of the wavy shape extends along the contact surface.
The process according to the invention proceeds in two stages. First, the heating wire is brought into the form of a flat, wavy line, as a result of which a special intermediate product is obtained, which is to be referred to below in brief as the “heating strand”. The special feature of this heating strand is therefore to be found in its wavy shape, which can also be described as a sine wave. Then, in the second stage of the process, windings of this wavy heating strand are laid in the injection mold in such a way that one of the broad sides of its wavy shape lies directly at the contact surface with the pipe fitting. The wavy shape and its position at the surface ensure the rapid, intense heating of the contact surface even when only a moderate amount of current flows through the strand. The softening and coalescence of the material of the pipe fitting and the conduit lead to a reliable weld after solidification.
Additional measures and advantages of the invention can be derived from the subclaims, from the following description, and from the drawings. The invention is intended to cover all of the novel features and combinations of features which can be derived from them, even if these are not explicitly stated in the claims. The invention is illustrated in the form of an exemplary embodiment in the drawings:
REFERENCES:
patent: 3907625 (1975-09-01), Vogelsanger
patent: 3943334 (1976-03-01), Sturm
patent: 3954541 (1976-05-01), Landgraf
patent: 4455482 (1984-06-01), Grandclement
patent: 4894521 (1990-01-01), Evans
patent: 4903397 (1990-02-01), Freidel
patent: 5107098 (1992-04-01), D'Auria
patent: 5229581 (1993-07-01), D'Auria
patent: 195 03 888 A1 (1995-08-01), None
patent: 0119061 (1984-09-01), None
Friedrich Kueffner
Manibs Spezialarmaturen GmbH & Co. KG
Ortiz Angela
LandOfFree
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