JP3325335B2 - Manufacturing method of branch joint for electric welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a branch pipe joint for electric fusion in which a branch pipe integrally projects from an upper surface of a saddle curved in a substantially semi-cylindrical shape, and a heating wire is buried at a predetermined interval on the back surface of the saddle. And a method for producing the same.

[0002]

2. Description of the Related Art Generally, a method of manufacturing a branch pipe joint of this type for electric fusion includes a step of forming an electric heating mat and a step of setting the electric heating mat in a mold and injecting a molten resin into a mold cavity. Has become. That is, in the first step of forming the electric heating mat, a spiral groove is provided on the upper surface of the synthetic resin sheet having a through hole in the center at a predetermined interval from the peripheral edge of the through hole on the outer peripheral side. A heating wire is fitted along with the heating wire to form a heating mat. Next, the electric heating mat is placed on a lower mold having a substantially semi-cylindrical curved surface, the mold is closed, and then the molten resin is injected into the mold cavity.

[0003]

However, in the case of this conventional manufacturing method, when the molten resin is injected into the mold cavity, the heating wire drawn from the inner peripheral portion of the spiral groove is applied to the spiral groove. There was a risk of being formed while being in contact with the fitted heating wire.

As a method for preventing short-circuiting of the heating wire, for example, a method of fitting a heating wire coated with a synthetic resin into a spiral groove (Japanese Utility Model Laid-Open No. 1-121994), is drawn out from the inner peripheral portion of the spiral groove. A method has been proposed in which a synthetic resin sheet is interposed between a heating wire and a heating wire fitted in a spiral groove to insulate the heating wire (Japanese Patent Publication No. 2-62379). Some success has been achieved.

[0005] However, in the case of the above-mentioned conventional method, a new problem has been raised that the heating wire cannot be buried at a certain depth on the back surface of the saddle. That is, a rigid heating wire is spirally wound around a thin synthetic resin sheet to form an electric heating mat, and the electric heating mat is curved and placed on a lower mold having a substantially semi-cylindrical curved surface. At times, the electric heating mat may be set in an undulating state without adhering to the mold surface. When the molten resin is injected into the mold cavity in such a state, the molten resin may be interposed between the electric heating mat and the lower mold, and the heating wire may not be buried at a certain depth on the back surface of the saddle. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and provides a method of manufacturing a branch pipe joint for electric welding in which a heating wire can be embedded at a certain depth on the back surface of a saddle.

[0007]

The present invention comprises a step of forming an electric heating mat and a step of setting the electric heating mat in a mold and injecting a molten resin into a mold cavity. In the process of forming the mat, the synthetic resin sheet is bent into a substantially semi-cylindrical shape, and the central ridge line perpendicular to the bending direction is formed to be thick, and the thickness is gradually reduced from the ridge line toward both curved hem sides. It forms so that it may become. Also,
A through-hole is provided substantially at the center of the synthetic resin sheet, a spiral groove is provided on the outer peripheral side at a predetermined interval from the periphery of the through-hole, and a heating wire is fitted along the groove to form an electric heating mat. Form. Next, the electric heating mat is placed on a lower mold having a substantially semi-cylindrical curved surface, the mold is closed, and then the molten resin is injected into the cavity.

[0008]

The electric heating mat is formed of a synthetic resin sheet whose thickness is thick at a central ridge portion perpendicular to the bending direction and gradually becomes thinner from the ridge portion toward both hem sides. When placed on the mold, it is set in close contact with the semi-cylindrical mold surface, and when the molten resin is injected into the mold cavity, the molten resin does not enter between the electric heating mat and the lower mold. .

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a mold apparatus used in the present invention, FIG. 2 is a sectional view taken along line XX of FIG. 1, FIG. 3 is a plan view of an electric heating mat, and FIG. Y-line enlarged sectional view, FIG. 5
1 is a cross-sectional view of a branch pipe joint for electric fusion obtained by the present invention, in which 1 is a synthetic resin sheet, 2 is a heating wire, 1
a is an electric heating mat in which the heating wire 2 is spirally wound on the upper surface of the synthetic resin sheet 1.

The present invention comprises a molding step of the electric heating mat 1a and a molding step of setting the electric heating mat 1a in a mold and then injecting a molten resin, and is curved into a substantially semi-cylindrical shape as shown in FIG. A branch pipe 82 integrally projects from the upper surface of the saddle 81, and a heating wire 2 is buried at a predetermined interval on the back surface of the saddle 81, and a conductive terminal 3 connected to an end thereof is embedded in a plug terminal 83. This is to manufacture a branch pipe joint for fusion.

First, in the first forming step of the electric heating mat 1a, the synthetic resin sheet 1 which is curved in a substantially semi-cylindrical shape is formed. The synthetic resin sheet 1 is formed by bending a sheet made of polyethylene, polypropylene, polybutene, or the like into a substantially semi-cylindrical shape, forming a central ridge portion A perpendicular to the bending direction to a large thickness, and forming both curved portions from the ridge portion A. It is formed so as to become gradually thinner toward the hem side. Further, a through hole 11 is provided substantially at the center of the synthetic resin sheet 1, and a spiral groove 12 is provided on the upper surface of the sheet 1 at a predetermined interval from the peripheral edge of the through hole 11 to the outer peripheral side. A heating wire 2 such as a nichrome wire or a copper-nickel wire is fitted along the wire to form the heating mat 1a.

It is important that the synthetic resin sheet 1 is formed such that the back surface curved in a substantially semi-cylindrical shape has an arc surface substantially matching the curved surface of the lower mold 5.
Can be appropriately set according to the wire diameter of the heating wire 2 and the like. 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 set to 0.6 to 1.5 mm.
The width of the groove 12 may be appropriately selected within a range of 5.0 mm, and the width of the groove 12 may be substantially equal to or slightly larger than the diameter of the heating wire 2. The thickness t of the bottom of the groove 12 is formed so as to be substantially constant irrespective of the variation of the thickness of the sheet 1. After the heating wire 2 is fitted into the groove 12, the opening of the groove 12 is heated by a heater or the like. The part may be melted and partially closed. When the groove 12 is partially closed by the fusion part B in this manner, the heating wire 2 can be reliably prevented from escaping from the groove 12.

Next, a spiral groove 1 into which a heating wire 2 is fitted.
2. Pull out both ends of the heating wire 2 from the inner and outer peripheral portions of
A conductive terminal 3 is connected to an end of each heating wire 2. At this time, it is important that the drawn-out length of the heating wire 2 has some allowance. If the drawn-out length is too short, the conductive terminal 3 is closed when the mold is closed as described later. There is a problem that the upper mold 6 cannot be fixed. Further, if necessary, the surface of the end portion of the heating wire 2 drawn out from the groove 12 may be covered with an adhesive of an insulating thermosetting resin such as a two-component polyester resin or an epoxy resin.

Therefore, the electric heating mat 1a is placed on a lower mold 5 having a substantially semi-cylindrical curved surface, and a projection 51 provided at the center of the upper surface of the lower mold 5 has a through hole of the electric heating mat 1a. 11 is fitted and set so as not to shift. Further, the terminal holding member 4 is inserted into the conductive terminal 3 connected to the end of the heating wire 2, and the terminal holding member 4 is inserted into a support hole 61 provided in the upper die 6. That is, the upper mold 6 is divided into half molds 6a, 6a.
b, the support holes 61 are provided on the mating surfaces of the half halves 6a and 6b, so that the terminal holding member 4 is inserted into the support holes 61 while closing the half halves 6a and 6b. Fix it.

After the lower mold 5 is covered with the upper mold 6 and the core mold 7 is hung over the projections 51 of the lower mold 5 to close the mold, polyethylene and polypropylene are placed in the mold cavity. Inject molten resin such as polybutene. Then, the molten resin fills the cavity and the electric heating mat 1
fused together with a. At the time of this injection molding, the end of the heating wire 2 drawn from the inner periphery of the spiral groove 12 passes above the ridge A of the thick sheet 1 and is drawn to the outer periphery. Since the end of the heating wire 12 is loose,
There is no short circuit due to contact with the heating wire 2 fitted in the back of the heating wire 2. Further, since the back surface of the curved electric heating mat 1a and the upper surface of the lower mold 5 are in close contact with each other, no molten resin enters between them.

Finally, after the molten resin injected into the cavity is solidified, the upper and lower molds 5, 6 and the core mold 7 are opened, and the terminal holding member 4 is pulled out from the conductive terminal 3. Thus, the branch pipe joint for electric fusion shown in FIG. 5 is obtained.

[0017]

As described above in detail, according to the present invention, the synthetic resin sheet constituting the electric heating mat is curved so that the back surface of the sheet can be set in a state of being in close contact with the upper surface of the upper mold. When the molten resin is injected into the mold cavity, the molten resin does not enter between the sheet and the lower mold. In addition, the heating wire drawn from the inner peripheral portion of the spiral groove passes above the ridge portion of the thickened sheet and is drawn to the outer peripheral side, so that the end portion of the heating wire is spirally wound. There is no danger of short circuit due to contact with the heating wire. Therefore,
ADVANTAGE OF THE INVENTION According to this invention, the heating wire is buried in the back surface of a saddle at a fixed depth, and the branch pipe joint for electrofusion which is stable in quality without a short circuit of the heating wire can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a mold apparatus used in the present invention.

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

FIG. 3 is a plan view of an electric heating mat.

FIG. 4 is an enlarged sectional view taken along line YY of FIG. 3;

FIG. 5 is a sectional view of a branch pipe joint for electric fusion obtained according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synthetic resin sheet 2 Heating wire 3 Conductive terminal 4 Terminal holding member 5 Lower mold 6 Upper mold 7 Core mold 12 Spiral groove 1a Electric heating mat

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-145113 (JP, A) JP-A-3-278919 (JP, A) JP-A-6-305048 (JP, A) JP-A-6-305048 94179 (JP, A) JP-A-4-321819 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/14 F16L 47/02

Claims (1)

(57) [Claims] When manufacturing a branch pipe joint for electric welding in which a branch pipe integrally projects from an upper surface of a saddle curved in a substantially semi-cylindrical shape, and a heating wire is embedded at a predetermined interval on a back surface of the saddle, A method for producing a branch pipe joint for electric fusion, comprising the following molding steps. The synthetic resin sheet is bent into a substantially semi-cylindrical shape, and a central ridge line perpendicular to the bending direction is formed to be thicker and gradually thinner from the ridge line toward both curved hem sides, In addition, a through hole is provided substantially in the center of the sheet, a spiral groove is provided continuously on the outer circumference side at a predetermined interval from the periphery of the through hole, and an electric heating mat is formed along which the heating wire is fitted. Then, placing the electric heating mat on a lower mold having a substantially semi-cylindrical curved surface, injecting the molten resin into the cavity after closing the mold,