JPH03164225A - Preparation of composite pipe - Google Patents

Abstract

PURPOSE:To uniformize the adhesive strength of the resin layer covering the inner peripheral surface of a metal pipe by using an induction heating coil having a shape capable of generating density distribution in internal magnetic flux density after the welding of both side edges of a strip like metal material but before the coating with a resin to heat the metal pipe so as to provide heating intensity distribution thereto. CONSTITUTION:The molten resin sent into a resin flow pipe 20 is extruded into a cylindrical shape from the leading end 21 of the resin flow pipe 20 on the downstream side of the welding point due to a welding machine 40 to coat the inner peripheral surface of a metal pipe 71. The inner surface shape of this coating resin is molded by the leading end 51 of an insertion rod 50. An induction heating coil 90 is arranged between the welding point due to the welding machine 40 and the molten resin extruding part from the resin flow pipe 20 so as to surround the periphery of the metal pipe 71 and has a shape capable of forming density distribution in the magnetic flux density in the coil to forcibly provide distribution to the heating intensity of the metal pipe 71 in the circumferential direction thereof. As compared with the vicinity of a welding part 73, the metal pipe is strongly heated on the opposite side thereof and the non-uniformity of temp. distribution in the circumferential direction is eliminated and the whole is uniformly heated to the vicinity of the temp. of the molten resin.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a composite pipe in which the inner peripheral surface of a metal pipe is covered with a resin layer, and more specifically, it relates to a method for manufacturing a composite pipe in which the inner peripheral surface of a metal pipe is covered with a resin layer. The present invention relates to a method for manufacturing a composite pipe in which the inner circumferential surface of a metal tube is coated with a resin by extruding an adhesive resin in a molten state toward the inner circumferential surface of the metal tube after the tube is manufactured.

In recent years, composite pipes in which the inner peripheral surface of metal pipes is coated with plasticine have been developed as piping materials for hot water supply, hot water heating, drainage, etc.

One of the manufacturing methods for such composite pipes is to use gold F in the form of a strip.
rA Temporary side edges are brought together to form a circular tube, and the joined portions are welded together to produce a continuous tube, and from a mold inserted into the tube through the opening before welding, There is a method in which molten resin is extruded into a cylindrical shape into a metal tube after welding, and the inner peripheral surface of the tube is coated with a blast layer (see, for example, Japanese Patent Laid-Open No. 80511/1983).

In this method, the extrusion mold for molten resin is mainly a resin flow tube inserted into a metal tube, and when forming the bottom of the metal band into a circular tube, the mold is used to extrude the molten resin through the opening before forming. The tip of the resin flow tube through which the molten resin flows is positioned inside a welded circular tube, and the molten resin is extruded from the tip of the flow tube in a cylindrical shape and adhered to the inner circumferential surface of the metal tube. A layer is formed.

(Problem to be Solved by the Invention) According to such a manufacturing method, the base end of the resin flow pipe is necessarily located at a U-shaped cross section where the metal plate is not closed in the tubular shape. Therefore, the base end of the resin flow tube, the welded metal tube, and the tip end of the resin flow tube are arranged in this order in the flow direction of the material in the tube manufacturing process.

On the other hand, when metal tubes are butt welded, heat is generated mainly at the welded portion. Therefore, the resin is bonded to the metal tube while the temperature distribution is non-uniform in the circumferential direction. This non-uniformity in the temperature distribution of the metal tube causes variations in the adhesive force of the resin applied to the inner peripheral surface of the metal tube in the circumferential direction.

High-frequency welding, TIG welding, etc. are used to weld metal pipes, but in any case, the temperature is approximately 700°C for aluminum at the welding point, as it is basically fusion joining of metals.
In iron-based materials, the temperature rises to about 1200°C. Since the metal is tubular, the temperature difference between the welding point and the welding point is quite small at a short distance from the welding point due to heat conduction, but there is a considerable temperature difference between the welding point and the opposite side. will occur.

Melting on the inner surface of the metal tube? & It is known that the adhesive strength of the resin to be covered varies considerably depending on the temperature of the metal to be coated, even if the resin itself has adhesive properties with the metal. It is necessary to match the temperature. When the metal surface temperature is low, the molten resin solidifies the moment it is extruded onto the metal surface, resulting in a significant decrease in adhesive strength.

One way to make the temperature of the metal tube uniform is to heat a band-shaped metal plate in advance in a heating furnace, etc.
If heating is performed before welding, the heat generated during welding will have low thermal conductivity and will be difficult to conduct in the circumferential direction of the tube, resulting in a wider temperature distribution.

Therefore, heating for uniformity must be carried out after bonding and before covering the resin. However, as mentioned above, due to the arrangement of the resin flow tube base, metal tube weld, and resin flow tube tip, the tip of the resin flow tube is inside the welded metal tube. There is no way to support the resin flow tube, so the resin flow tube has no choice but to be cantilevered at the base end. Therefore, the longer the distance between the welded part and the resin covering part, the longer the resin flow pipe will need to be.However, if the resin flow pipe is lengthened, it may bend due to its own weight.
There is a risk that the resin layer covering the inner circumferential surface of the metal tube may become uneven in thickness. Due to this arrangement, if uneven thickness occurs, it is impossible to adjust it from the outside, so the coating work is temporarily stopped and the position of the tip of the resin flow pipe is changed to
Must.

In this way, when inserting a heating furnace between the welded part and the resin covering part, in order to raise the temperature of the metal tube to the resin melting temperature, it depends on the tube manufacturing speed and the type of heater used. , a space of several meters is required, and it is impossible to use it together with a cantilever-supported resin flow pipe.

In the end, as a method of heating the gold G4 tube between the welded part and the resin covered part, as shown in FIGS. 5(a) and (b), a heating coil 93 for induction heating is provided, and There is no choice but to pass 7L of metal tube through it.

However, in induction heating by passing through the center of the ordinary heating coil 93, the uneven temperature distribution caused in the circumferential direction of the metal tube 71 due to welding cannot be resolved, and the resin on the inner peripheral surface This results in variations in the adhesive strength of the layers.

The present invention has been made in view of the above circumstances, and its purpose is to make the adhesive force of the resin layer covering the inner circumferential surface of the metal tube uniform in the circumferential direction of the metal tube. The object of the present invention is to provide a method for manufacturing a composite pipe that allows the following.

(Means for resolving the problem) The method for manufacturing a jointed pipe of the present invention involves injecting molten resin into a cylindrical tube inside a metal tube that is continuously produced by sequentially butting and welding both side edges of a band-shaped metal material. A method for manufacturing a fitting pipe in which the inner peripheral surface of a metal pipe is coated with a resin by extruding the pipe into a shape, the method comprising:
Before covering the inner circumferential surface of a metal tube manufactured by welding both side edges of a metal tube with resin, the metal tube is subjected to induction heating in a shape that can generate a dense and dense distribution of magnetic force density inside. It is characterized by passing through the inside of the metal tube to reduce the circumferential temperature distribution of the metal tube produced by welding, thereby achieving the above object.

(Function) In induction heating, the heating temperature is determined according to the density of magnetic lines of force generated by the heating coil. By devising the shape of the heating coil, we create a density distribution in this magnetic force density, and force a distribution of heating intensity in the metal tube passing through the coil, which increases the temperature compared to the part where the temperature increases due to welding. By heating the opposite side more strongly, the temperature distribution in the circumferential direction of the metal tube as a whole can be made substantially uniform.

(Example) FIG. 1 is a longitudinal section of a manufacturing apparatus used for carrying out the method of the present invention.

The band-shaped metal material 70 is sequentially paid out from a roll forming device or a mold for forming (not shown) and conveyed.
During its transportation, it is shaped from a flat plate to a U-shape to a circular tube, and is butt-welded by a welding machine 40 to form a metal tube 7l.

The mold for coating the inner surface of the metal tube 7l with resin includes a mold main body 10 located in a portion where the band-shaped metal material 70 is formed into a U-shape, one end supported by the mold main body lO, and the other end supported by the mold main body lO. A resin flow pipe 20 whose end extends beyond the welded part and into the inside of the metal tube 7l which is butt welded, and a resin flow pipe 20 whose end is supported by the mold body 10 and which are concentric with a predetermined gap in the resin flow pipe 20. It has an inner insertion rod 50 inserted in a shape.

A resin flow passage l1 communicating with the resin flow pipe 20 is formed in the mold body lO, and molten resin is fed into the resin flow pipe 20 via this resin flow passage 11.

The molten resin sent into the resin flow pipe 20 is transferred to the welding machine 4.
On the downstream side of the welding point by 0, the resin flow pipe 20
It is extruded into a cylindrical shape from the tip h=21 and covers the inner peripheral surface of the metal tube 7l. The inner shape of this coating resin is
It is shaped by the tip 5l of 0.

An induction heating coil 90 is disposed between the welding point by welding R40 and the molten resin extrusion portion from the resin flow pipe 20 so as to surround the metal pipe 7l.

This heating coil 90 does not uniformly heat the metal tube 71 like a conventional ordinary heating coil, but has a shape that can form a density distribution in the magnetic flux density inside the coil.
As a result, the heating intensity in the circumferential direction of the metal tube 7t is forcibly distributed.

2(a) and (1)) are a front view and a side view showing an example of the shape of this heating coil 90. FIG.

In this example, the heating coil 90 is elliptical or egg-shaped, and the positional relationship with the metal tube 71 inserted inside the heating coil 90 is such that the welded part 73 at the top of the metal tube has a wide distance from the coil 90, and the opposite side has a wide distance from the coil 90. 90, the positional relationship is such that they are closer to each other.

With this structure, the opposite side of the welded part 73 is heated more strongly than the vicinity of the welded part 73, and the uneven temperature distribution in the circumferential direction of the metal tube 73 caused by welding is eliminated, and the entire part is melted almost uniformly. It is heated to around the resin temperature.

The metals used for the central joint pipe include Fe, AI, and C.
Although the material may be uS, SUS, or an alloy thereof, it is preferable to have an appropriate surface condition since the resin is adhered to the inner surface of the tube.

In addition, coating resins that have good adhesion to metal include acid-modified polyethylene, silane-modified polyethylene, etc., and also include polyvinyl chloride (PVC), chlorinated polyvinyl chloride (C-pvc), etc. , polyethylene (P
For resins having poor adhesion to metals such as E), a resin having adhesion to both these resins and metals may be used as the adhesive layer.

As a method for forming the band-shaped metal material into a circular tube shape, a method of passing the band-shaped metal material through a mold having a shape that sequentially changes from a plate shape to a circular tube shape, a method of sequentially forming with rolls, etc. can be adopted. For continuous welding of the joints of tubular metal materials, a welding method suitable for the metal used is adopted; for example, for Fe-based metals, high-frequency welding, direct ATIG welding, electron beam welding, etc. , for AI-based metals, cross-cut T I G welding, ~ high pulse TI
G welding etc. are suitable. Further, the induction heating device may be a device using the general principle of high-frequency induction heating, in which an alternating current is passed through a Cu tube coil wound spirally around the outside of a metal tube, and the metal tube is heated by the generated magnetic lines of force.

In addition to the shape shown in FIG. 2, the shape of the induction heating coil in the present invention may be a more extreme oval shaped coil 91 as shown in FIGS. 3(a) and (1)), or a As shown in Figures (a) and (b), the coil 92
is circular in the circumferential direction as before, but the way it is wound in the axial direction is different, with the upper part of the film where the welded part 73 of the metal tube 7l is located wider, and the lower part more closely spaced. There is. By having such a shape, the heating coil 9
The lines of magnetic force generated above the inside of the coil 92 rise from the gap between the coils 92 and become sparse, while the lines of magnetic force generated below the inside of the coil 92 are generated parallel to the metal tube 71 and become dense.

Next, actual measurement results will be described.

High frequency output 25kW, oscillation frequency S as induction heating device
A heating coil with OKHz capability was used, and the heating coil was a Cu tube with a diameter of 10 cm wound in an oval shape as shown in Figure 3. A rolled one was used.

The metal tube is made of Fe-based hot-rolled steel plate with a thickness of 1.6 mm and an outer diameter of 8 mm.
It was formed to have a length of 9m, and DC TIG welding was used for welding.

The clearance between the metal tube and the heating coil is 12ll at the top (welded part side)! II1, and the lower part was designated as lOLIII1.

The resin is silane-modified PE (MI = to. 3
g/10min. ), and the molding temperature was 200°C.
Adhesive coating was performed in order of thickness 2.0. The tube manufacturing speed was 1.0 m/min. Closed.

As a result of transporting the Fe tube with the output voltage of the induction heating device at 125V, the temperature at the top of the tube was 220°C and the temperature at the bottom was 17.
The temperature difference was 50°C. The adhesive strength of the resin in this case was evaluated by dividing the circumferential direction of the tube into 12 equal parts and calculating it by il + separation strength, which was 22 kg / 2 cm ~ 25
kg/2cm. Regarding this, if an induction heating device is not used, the temperature at the top of the Fe tube will be 18
5°C1 Lower part, visibility is 43°C, temperature difference is 142
It was ℃. When the adhesive strength of the resin was evaluated in the same manner, it was 5 kg/2 cm to 22 kz/2 cm, and only adhesive strength with large variations in the circumferential direction was obtained.

(Effects of the Invention) As explained above, according to the present invention, when coating the inner circumferential surface of a metal tube continuously produced by sequentially butt welding both side edges of a strip metal material with a resin, welding Afterward, and before coating with resin, the metal tube is heated with a distribution of heating intensity using an induction heating coil shaped to generate a dense and dense distribution in the internal magnetic flux density. Because the temperature distribution in the circumferential direction of the metal tube is small, the adhesive force of the resin applied to the inner circumferential surface is uniform in the circumferential direction of the tube, resulting in a composite tube with excellent durability. be able to.

4゛no! H Fig. 1 is a longitudinal cross-sectional view of a manufacturing apparatus used to carry out the method of the present invention, Fig. 2(a) is a front view of the shape of the induction heating coil 90, and Fig. 2(b) is a side view thereof. FIG. 3(a) is a front view of another shape of the induction heating coil, FIG. 3(b) is a side view thereof, FIG. 4(a) is a front view of still another shape of the induction heating coil, and FIG. FIG. 5(b) is a side view thereof, and FIG. 5 is a diagram illustrating the shape of a conventional conventional induction heating coil.

10...Mold body, ti...Resin flow path, 20...
・Resin flow pipe, 40... welding machine, 50... inner insertion,
70... Band-shaped metal material, 7l... Metal tube, 73...
Welding section, 90, 91, 92...induction heating coil.

that's all

Claims (1)

[Claims] 1. Manufacture a composite tube in which the inner circumferential surface of the metal tube is coated with resin by extruding molten resin in a cylindrical shape into the interior of a metal tube that is continuously produced by sequentially butting and welding the edges of both sides of the metal strip. A method of
A composite tube characterized in that the metal tube is passed through an induction heating coil having a shape capable of generating a dense/concentrated distribution of magnetic force density inside to reduce the circumferential temperature distribution of the metal tube resulting from welding. manufacturing method.