JPH08224783A - Electric heating mat - Google Patents

Abstract

PURPOSE: To provide an electric heating mat which is fused to be bonded strongly with a molten resin injected into a cavity. CONSTITUTION: A through hole 11 is formed in a synthetic resin sheet 1, a spiral groove 12 is formed around the hole 11 on the surface of the sheet 1, and a heating wire is set along the groove 12. A hotmelt type adhesive (b) is applied on the surface of the sheet 1 surrounding the hole 11. Since the sheet 11 and an injected resin are fused to be bonded surely and strongly to prevent a fluid in a pipe from bleeding and leaking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electric fusion welding in which a branch pipe integrally projects from the upper surface of a saddle curved in a substantially semi-circular shape, and heating wires are spirally embedded at a predetermined interval on the back surface of the saddle. The present invention relates to an electric heating mat used when injection molding a branch pipe joint.

[0002]

2. Description of the Related Art Generally, an electric heating mat of this type is constructed by fitting a heating wire along a spiral groove formed on the surface of a synthetic resin sheet. When molding a worn branch pipe joint, the molten resin was injected into the cavity after setting the electric heating mat in the mold.

[0003]

However, since the synthetic resin sheet set in the mold at the time of this injection molding and the molten resin injected in the cavity are not well compatible with each other, they are not completely fusion-bonded to each other. Sometimes. When performing piping work using a branch pipe joint for electric fusion with such defects, extremely fine cracks may occur at the boundary between the synthetic resin sheet and the molten resin, and especially the saddle and the branch pipe. When a crack is generated at the joint, the fluid in the pipe may be exuded or leak through the gap formed between the spiral groove and the heating wire, starting from the crack.

The present invention has been made to solve the above problems and provides an electric heating mat which is firmly fusion-bonded to a molten resin injected into a cavity.

[0005]

The electric heating mat of the present invention comprises:
A through hole is provided in a synthetic resin sheet, a spiral groove is provided on the surface of the sheet around the through hole, and a heating wire is fitted along the spiral groove. A hot-melt type adhesive is applied to the surface of the sheet that surrounds the sheet.

[0006]

Since a hot-melt type adhesive is applied to the surface of the sheet surrounding the through hole, when the sheet is set in the mold and the molten resin is injected into the cavity,
The hot-melt type adhesive is melted, and the synthetic resin sheet and the molten resin are integrally bonded via the adhesive.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a plan view of an electric heating mat showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line XX of FIG. 1, FIG. 3 is a sectional view showing a state in which the electric heating mat is set in a mold, and FIG. YY in Figure 3
FIG. 5 is a sectional view of a branch pipe joint for electric fusion welding obtained by the present invention. In the figure, 1 is a thin sheet made of synthetic resin such as polyethylene, polypropylene, polybutene, 2 is a heating wire, 3 is a terminal pin, and 1a is an electric mat.

The synthetic resin sheet 1 is made of a thin sheet of polyethylene, polypropylene, polybutene or the like, and a through hole 11 is provided at substantially the center thereof.
A spiral groove 12 is provided on the surface of the sheet 1 around the through hole 11. A heating wire 2 such as a nichrome wire is fitted along the spiral groove 12 in the electric heating mat 1a, and terminal pins 3 are attached to both ends of the heating wire 2 drawn from the inner peripheral edge and the outer peripheral edge of the groove 12. It is connected.

The pitch P of the spiral groove 12 is determined by the heating wire 2
It can be appropriately set according to the wire diameter of For example,
When the heating wire 2 having a wire diameter of 0.3 to 1.5 mm is used, the pitch P of the groove 12 is appropriately set within the range of 0.6 to 5.0 mm, and the width and depth of the groove 12 are set to the electric value. It may be formed to have a diameter substantially equal to or slightly larger than the wire diameter of the heating wire 2. When the heating wire 2 is fitted along the spiral groove 12 and then the opening of the groove 12 is melted and partially closed by a heater or the like, the heating wire 2 escapes from the groove 12. Thus, it is possible to effectively prevent the heating wires 2 from short-circuiting.

The sheet 1 is surrounded by the through hole 11.
An annular groove 13 is provided on the surface of the, and the annular groove 13 is filled with a hot melt type adhesive b. As the adhesive agent b, an adhesive agent having tackiness at room temperature or a hot-melt adhesive agent having no tackiness can be used, but an adhesive agent having no tackiness is preferable from the viewpoint of workability. For example, a hot-melt type adhesive obtained by mixing an ethylene vinyl acetate copolymer resin with a tackifier, a softening agent, etc. can be used,
Viscoelastic deformation easily occurs at the temperature of C, 60 ~ 130 ° C
Those having a melt viscosity of 700,000 cps or less at the above temperature can be preferably used. It should be noted that the adhesive b may be applied to the surface of the sheet 1 surrounding the through hole 11 without filling the annular groove 13, and if necessary, the adhesive b may also continuously make one round on the outer peripheral side of the spiral groove 12. A hot melt type adhesive may be applied to.

When the branch pipe joint for electric fusion is injection-molded using this electric heating mat 1a, the electric heating mat 1a is placed on the lower mold 5 having a substantially semi-arcuate curved surface. Therefore,
The lower die 5 was covered with the upper die 6, and the terminal holding plugs 4 were attached to the terminal pins 3 connected to both ends of the heating wire 2, and the respective terminal holding plugs 4 and 4 were provided on the upper die 6. Fit into the holding hole 61. As shown in FIG. 4, the upper mold 6 has a half-split structure composed of split molds 6a and 6b.
The terminal holding plug 4 is sandwiched and fixed in the holding holes 61 provided in the mold matching surfaces of a and 6b.

In this way, the electric heating mat 1a is set between the lower mold 5 and the upper mold 6, the core mold 7 is hung, and the lower end of the core mold 7 is fitted into the through hole 11 of the sheet 1 to form the mold. Close it. Then, when a molten resin such as polyethylene, polypropylene, or polybutene is injected from the gate 62 into the cavity, the hot-melt type adhesive b applied to the surface of the sheet 1 is melted, and the synthetic resin sheet is passed through the adhesive b. 1 and the molten resin are integrally joined.

Finally, waiting for the molten resin injected into the cavity to solidify, the molds 5 and 6 and the core mold 7 are opened, and the terminal holding plug 4 is pulled out from the terminal pin 3, as shown in FIG. As shown, the branch pipe 82 integrally projects from the upper surface of the saddle 81 curved in a substantially semi-circular shape, and the heating wire 2 is spirally embedded in the back surface of the saddle 81 at a predetermined interval in a spiral shape. Is obtained.

[0014]

As described in detail above, the electric heating mat of the present invention is a hot-melt type mat on which the heating wire is fitted along the spiral groove provided in the synthetic resin sheet and which surrounds the through hole. Since this adhesive is applied, when the mat is set in the mold and then the molten resin is injected into the cavity, the adhesive melts and the synthetic resin sheet and the molten resin are integrated through the adhesive. To join.

Therefore, fine cracks do not occur due to poor fusion between the synthetic resin sheet and the molten resin, and the fluid in the pipe originates from the fine cracks generated in the conventional branch pipe joint for electric fusion. It is possible to prevent accidental leakage and leakage of the material.

[Brief description of drawings]

FIG. 1 is a plan view of an electric heating mat showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a cross-sectional view of a state where an electric heating mat is set in a mold.

FIG. 4 is a sectional view taken along line YY of FIG.

FIG. 5 is a cross-sectional view of a branch pipe joint for electrofusion obtained according to the present invention.

[Explanation of symbols]

 1a Electric heating mat 1 Synthetic resin sheet 11 Through hole 12 Spiral groove 13 Annular groove 2 Heating wire 3 Terminal pin b Hot melt type adhesive

Claims (1)

[Claims] 1. A through hole (11) in a synthetic resin sheet (1).
And the spiral groove (12) is provided on the surface of the sheet (1) around the through hole (11), and the heating wire (2) is fitted along the spiral groove (12). Sheet (1) which is an electric heating mat and surrounds the through hole (11)
An electric heating mat, characterized in that a hot-melt type adhesive (b) is applied to the surface of the.