JP2003019746A - Inner mold for molding bent pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inner mold for molding a bent pipe capable of simply performing drawing-out work after bending processing. SOLUTION: In the inner mold used for molding the bent pipe by heating a straight pipe comprising a synthetic resin pipe to bend the same at a predetermined bending angle, a plurality of panel materials 21, etc., having flexibility are stacked to form a structure having a shape coming into contact with the inner surface of the synthetic resin pipe 1 at a part easy to generate deformation in the pipe but not coming into contact with the inner surface of the pipe at other part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner die for forming a bent pipe used for forming a bent pipe of a synthetic resin pipe.

[0002]

2. Description of the Related Art Polyvinyl chloride pipes (vinyl chloride pipes) are generally used as synthetic resin pipes. Also, polyethylene pipes (polyethylene pipes) have been used for a long time. The amount of polyethylene pipes used has been expanding in recent years.

As another synthetic resin tube, an inner layer made of a synthetic resin formed into a tubular shape, a reinforcing layer formed by spirally winding a stretched polyolefin resin sheet on the outer peripheral surface of this inner layer, and A composite pipe having a synthetic resin outer layer laminated on a reinforcing layer has been proposed. Since the composite pipe using such a stretched polyolefin resin sheet has excellent internal pressure resistance, it is characterized in that it can be made thinner than a synthetic resin pipe made of a single material.

When forming a bent pipe of these synthetic resin pipes, a method is adopted in which a straight pipe of the synthetic resin pipe is heated and softened and then bent. In such a bending pipe forming method, in order to prevent the synthetic resin pipe from being deformed during the bending process, the bending process is performed with the inner die inserted in the synthetic resin pipe.

As an inner mold for forming a bent pipe, conventionally, as shown in FIG. 7, an inner mold (laminated body) having a structure in which a round bar having an outer diameter substantially equal to the inner diameter of the synthetic resin pipe 101 is sliced into a predetermined width.
102 is used.

[0006]

By the way, when the round bar-shaped inner die shown in FIG. 7 is used, the contact area between the inner surface of the synthetic resin pipe to be bent and the outer surface of the inner die is increased, and the bending work is performed. It becomes difficult to remove the inner mold after completion. In particular,
When processing a large-diameter synthetic resin pipe, the contact area between the inner surface of the pipe and the outer surface of the inner mold becomes large and the contact resistance becomes considerably large, so that it may be impossible to pull out the inner mold.

The present invention has been made in view of such circumstances, and even in the case of bending a large-diameter synthetic resin pipe, a bent pipe capable of easily performing a drawing operation after the bending work. The purpose is to provide an inner mold for molding.

[0008]

The inner mold of the present invention is a method for forming a bent pipe by heating a straight pipe of a synthetic resin pipe and then bending the straight pipe to a predetermined bending angle. It is an inner mold to be inserted into a synthetic resin pipe and has a structure in which a plurality of flexible plate materials are laminated, and contacts the inner surface of the pipe where the synthetic resin pipe is likely to be deformed during bending, It is characterized by being shaped into a shape that does not come into contact with the inner surface of the pipe in the other portions.

The inner mold for forming a bent pipe of the present invention can be used for forming a bent pipe of a synthetic resin pipe made of a single material or a bent pipe of a composite pipe having a reinforcing layer. You can

According to the inner mold for forming a bent pipe of the present invention,
Since it has a structure in which multiple flexible plate materials are laminated, when a synthetic resin pipe is bent while it is inserted into a synthetic resin pipe (straight pipe), the inner pipe is bent according to the bending of the synthetic resin pipe. The entire mold is curved. Therefore, it can be used as an effective inner mold when molding a bent pipe.

Moreover, since the synthetic resin pipe is shaped so as to come into contact with the inner surface of the pipe in a portion where deformation is likely to occur during bending and not to contact the inner surface of the pipe in other portions,
The contact area with the inner surface of the pipe can be reduced as compared with the round bar-shaped inner mold. As a result, it is possible to easily perform the drawing work after the bending work.

Here, the inner die for forming a bent pipe of the present invention has a portion which does not come into contact with the inner surface of the synthetic resin pipe, so that the plate material may come apart during bending. As a method for preventing this, for example, a method of binding a plurality of laminated plate materials with a stretchable cloth or the like, or as shown in FIG. The method of connecting with each other can be mentioned.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 1 shows an example of a synthetic resin pipe (composite pipe) to which the present invention is applied.

The composite pipe 1 shown in FIG. 1 comprises a polyethylene resin inner layer 11 formed in a tubular shape, and an outer peripheral surface of the inner layer 11,
The reinforcing layer 12 is formed by spirally winding the stretched polyethylene resin sheet 12a, and the polyethylene resin outer layer 13 is laminated on the reinforcing layer 12.

The reinforcing layer 12 laminated on the inner layer 11 is a stretched polyethylene resin sheet 12a in the form of a strip having an appropriate size.
Is spirally wound at an inclination angle of 30 to 90 ° with respect to the tube axis of the inner layer 11, and a stretched polyethylene resin sheet 12a is further spirally wound thereon so that the inclination angle is opposite. It has a wound two-layer structure.

In the composite pipe 1 having such a structure, the reinforcing layer 12 formed by spirally winding the stretched polyethylene resin sheet 12a having excellent tensile strength is laminated on the inner layer 11 made of polyethylene. The inner layer 11 is reinforced by the reinforcing layer 12. Therefore, the composite pipe 1 has excellent pressure resistance, and even if a high-pressure fluid flows inside the inner layer 11, there is no risk of damage.

A method of forming a bent pipe using the composite pipe (synthetic resin pipe) 1 having the above-mentioned structure as a raw pipe will be described with reference to FIGS.

First, an embodiment of the inner mold 2 used for bending will be described with reference to FIGS. 2 and 3. Note that FIG.
FIG. 6 is a sectional view taken along line XX in FIG. 4.

The inner mold 2 of this example is a member formed by laminating a plurality of flexible belt-shaped plate members 21.
When the (synthetic resin pipe) is bent, it is inserted into the composite pipe 1. As shown in FIG. 2, the inner mold 2 has a portion where the synthetic resin pipe 1 is likely to be deformed during bending, that is, a portion inside the bending (compression portion) and a portion outside the bending (tensile portion) inside the pipe. It is processed into a shape (oblong shape) that contacts the surface and does not contact the inner surface of the pipe in other parts.
The inner mold 2 is entirely covered with a stretchable cloth 22 so that the plate members 21 ...

As shown in FIG. 3 (A), when the inner mold 2 is in a state in which no external force is applied (straight state), a bending force is applied to the entire inner mold 2, as shown in FIG. 3 (B). Plate material 2
1 ... 21 are displaced from each other so that the whole is bent.

Examples of the plate material 21 constituting the inner mold 2 include a PE plate and an ultra high molecular weight PE plate. A suitable thickness of the plate material 21 is about 5 mm to 10 mm. The stretchable cloth 22 may be, for example, a cloth made of synthetic fiber such as nylon.

Next, a specific example of bending of the composite pipe 1 will be described with reference to FIGS. 4 and 5. For the bending work in this example, the inner die 2 described above and the press dies 3a and 3b for the bending work having the shape shown in FIG. 5 are used.

First, while the composite pipe 1 (straight pipe) is heated by a heating furnace or the like (not shown) to be softened, the inner mold 2 is inserted into the composite pipe 1 as shown in FIG.

Next, as shown in FIG. 5, the composite pipe 1 is set in the upper and lower press dies 3a and 3b and pressed to bend the composite pipe 1 to a predetermined bending angle.

During this bending process, the inner mold 2 inserted into the composite pipe 1 bends according to the bending of the composite pipe 1 (see FIG. 3). Further, since the outer peripheral surface of the inner mold 2 contacts the pipe inner surfaces of the portion inside the bend (compressed portion) and the portion outside the bend (tensile portion) of the composite pipe 1, the composite pipe 1 is prevented from being deformed. it can.

After the above bending and cooling of the composite pipe 1 are completed, the inner mold 2 is pulled out from the composite pipe 1 (bent pipe). At this time, since the outer surface of the inner mold 2 is in contact with the inner surface of the composite pipe 1 at two places, and the contact area is small, the inner mold 2
Can be easily pulled out.

Here, in the above embodiment, the cross section of the inner mold 2 is an oval, but the cross section of the inner mold 20 is not limited to this, and as shown in FIG. Alternatively, the inner surface of the composite pipe 1 (synthetic resin) may be in contact with four places.

In the above-mentioned embodiment, the plate members 21 ... Are covered with the cloth 22 so as not to come apart, but instead of this, as shown in FIG. The parts may be connected to each other by pins 23.

In the above embodiment, an example in which the inner mold of the present invention is applied to the molding of the curved pipe of the composite pipe 1 having the reinforcing layer 12 has been shown. In addition to this, a synthetic resin composed of a single material is used. The inner mold of the present invention can also be used for forming bent pipes.

[0031]

As described above, the inner die for forming a bent pipe of the present invention has a structure in which a plurality of flexible plate materials are laminated, and the synthetic resin pipe is deformed during bending. Since it is formed in a shape that makes contact with the inner surface of the pipe in the easy portion and does not contact the inner surface of the pipe in other portions, it can be used as an effective inner mold for forming a bent pipe. Moreover, since the contact area of the inner die with the inner surface of the pipe is small as compared with the case of using the round rod-shaped inner die, the drawing work after the bending can be easily performed.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a composite pipe.

FIG. 2 is a vertical cross-sectional view of an embodiment of an inner die for forming a bent pipe of the present invention.

FIG. 3 is a diagram schematically showing a deformed state of the inner mold.

FIG. 4 is an explanatory diagram of a method for forming a bent pipe.

FIG. 5 is an explanatory diagram of a method for forming a bent pipe.

FIG. 6 is a vertical cross-sectional view of another embodiment of the inner die for forming a bent pipe of the present invention.

FIG. 7 is a longitudinal sectional view showing a conventional example of an inner die for forming a bent pipe.

FIG. 8 is a vertical sectional view (A) and a plan view (B) of another embodiment of the inner die for forming a bent pipe of the present invention.

[Explanation of symbols]

1 composite pipe (synthetic resin pipe) 11 inner layer 12 Reinforcing layer 13 outer layer 2 Internal type 21 Plate material 22 Stretchable cloth 3a, 3b Press type

Claims (2)

[Claims] 1. A method for molding a bent pipe by heating a straight pipe of a synthetic resin pipe and then bending the synthetic resin pipe at a predetermined bending angle, which is an inner die to be inserted into the synthetic resin pipe when performing the bending work. With a structure in which multiple flexible plate materials are laminated, the shape that contacts the inner surface of the synthetic resin tube where bending is likely to occur and does not contact the inner surface of the other sections Inner mold for bending pipes, characterized by being molded into. 2. The inner mold for forming a bent pipe according to claim 1, wherein a plurality of laminated plate materials are bound by a stretchable cloth.