JPH0420715B2 - - Google Patents

Description

[Detailed Description of the Invention] <Object of the Invention> Industrial Field of Application The present invention relates to an impeder mandrel used for high-frequency induction welding of ERW pipes, and more specifically, it relates to an impeder mandrel used for high-frequency induction welding of ERW pipes, and more specifically, it is a method for forming a metal band such as a steel band into a cylindrical shape. , an impeder mandrel that is inserted inside to increase the induced voltage and welding current during high-frequency induction welding, and the inner core is made of silicon carbide with excellent insulation, heat resistance, and thermal shock resistance. The present invention relates to a mandrel that is surrounded by a covering layer of continuous woven fibers and can be used for a long time without damaging the core.

Conventional technology Generally, when manufacturing ERW pipes by high-frequency induction welding, a steel strip is sequentially formed into a cylindrical shape using breakdown rolls, and then finished in the pipe circumferential direction using finishing rolls such as side rolls and in-pass rolls. The steel strip is rolled down to form a stable V-shaped edge between both ends of the steel strip, and a high-frequency induced current is concentrated at the welding point at the apex to perform fusion welding. Thereafter, both end surfaces are abutted against each other using a squeeze roll and a top roll to expel oxidized non-metallic inclusions present in the molten part during welding to the outside, and form a tubular-sized blank pipe.

At this time, in order to stably form the ERW pipe, it is necessary to balance the rolling force between finishing rolls such as side rolls and fin pass rolls, and also to increase the induced voltage and welding current. In order to increase the resistance, a ferrite core called an impeder is inserted inside the electric resistance welded tube in a manner supported by a mandrel.

That is, FIG. 3 is an explanatory diagram of the high frequency induction welding mode of the electric resistance welded pipe, in which the steel strip is curved with a predetermined curvature in the width direction using a breakdown roll or the like as described above so that the side end surfaces 1a face each other. In addition, the cylindrical pipe 1 has a V-shaped edge portion 2 between its side end surfaces 1a. Further, an induction coil 3 is wound around the outer circumference of the pipe 1, and when a high-frequency current is passed through the induction coil 3, the current cannot flow through the V-shaped edge portion 2, and the current is V as shown by reference numeral 4. It flows in a detour to the top 2a of the mold edge 2. Therefore, the top portion 2a is used as the welding point, and the side end surfaces 1a are brought into contact with each other by melting and joining, thereby producing an electric resistance welded pipe.
At the time of manufacturing, an impeder mandrel 5 is inserted inside the pipe 1 from an increase in welding current due to an increase in induced voltage, and a ferrite core called an impeder is attached to this mandrel 5. The presence of this ferrite core increases the induced voltage and increases the welding current, making it possible to stably perform high-speed welding with a small capacity. This mandrel 5 usually has a ferrite core supported inside a cylindrical body made of a composite material such as glass fiber, and in particular, as the induced voltage increases, an induced current flows through the cylindrical body and is likely to generate heat. It is usually made of glass fiber, which has excellent insulation properties. However, as the induced voltage increases, the corresponding part of the welding point that is heated by high frequency during welding is exposed to considerably high temperatures and becomes extremely hot, even if it is made of insulating material such as glass fiber. Glass fibers and the like, which have low heat resistance and poor thermal shock resistance, are easily damaged, and the internal ferrite core is also damaged, resulting in extremely short service life. For this reason, the production line has to be frequently stopped to replace the mandrel, leading to a decrease in productivity and making it difficult to produce thick-walled tubes that require a large amount of current.

Problems to be Solved by the Invention The present invention aims to solve the above-mentioned drawbacks, and specifically, in an impeder mandrel used for manufacturing ERW pipes by high frequency induction welding. problems such as the fact that it is easily damaged, that its service life is extremely short due to this ease of damage, that it is difficult to weld thick-walled pipes that require a large welding current, and that it is difficult to increase the speed of the production line. The purpose is to resolve the points.

<Structure of the Invention> Means for Solving the Problems and Their Effects That is, the mandrel according to the present invention has a silicon carbide material on at least the surface corresponding to the welding point on the impeder mandrel used during high frequency induction welding of ERW tubes. A coating layer made of continuous fibers is provided so as to cover it without any gaps.

Therefore, this configuration and its operation will be explained in more detail with reference to the drawings as follows.

First, FIGS. 1 and 2 are a perspective view of a mandrel according to an embodiment of the present invention and a sectional view thereof taken along the line A-A, and the reference numeral 10 indicates a mandrel according to an embodiment of the present invention. Generally indicated. The mandrel body 11 of the mandrel 10 is made of, for example, epoxy resin and has a cylindrical shape, as in the conventional example. A ferrite core 12 is installed inside the center of the main body 11, the tip of the ferrite core 12 is held down by an internal truncated conical part 11a, and a stator (not shown) is screwed into a threaded part 11b at the rear end. A carbide tip (not shown) is attached to the tip of the main body 11 via a screw 11c, and this carbide chip removes burrs during welding. Surround with hard chips.

On the surface of this main body 11, a coating layer 13 is provided so as to cover at least the surface corresponding to the welding point, that is, the portion corresponding to the welding point 2a at the apex of the V-shaped edge portion (see FIG. 3) without any gaps.
This covering layer 13 is composed of continuous fibers made of silicon carbide, and these continuous fibers can be constructed as woven fabrics such as plain weave, satin weave, and twill weave.

When the covering layer 13 is made of silicon carbide continuous fibers, even if the main body 11 is made of conventional synthetic resin, it is made of silicon carbide which has excellent heat resistance and thermal shock resistance and has insulation properties. Since it is made of continuous fibers, it can be fixed to the synthetic resin body with adhesive without any gaps, and since it is made of continuous fibers, it can be fixed even when wrapped around the body.

In other words, the electrical resistivity of silicon carbide fibers is 10 ohm-cm, and silicon carbide fibers exhibit approximately the same insulation properties as glass fibers (electrical resistivity of 10 ⁸ to ^{10 10} ohms-cm), and the induced voltage Due to the increase in , almost no induced current flows even when a large current is passed.
On the other hand, the heat resistance strength of glass fiber is generally
Approximately 100-120Kg/ ^mm2 , thermal shock at 1200℃ in air
Ceramics break when a load of 12 kg is applied for 10 seconds, and ceramics break when subjected to thermal shock at 400°C/hour. In contrast, the heat resistance strength of silicon carbide fiber is 250 to 350 kg/
mm ² , and can withstand thermal shock at 1000℃/min without breaking. When surrounded by reinforced continuous fibers made of silicon carbide, the interior is completely insulated and fixing with adhesive is sufficient, and even if the corresponding part is exposed to high temperatures, it can withstand thermal shock during welding. The main body can be protected by an enveloping layer without any gaps.

Note that it is not necessary to cover only the portion corresponding to the welding point 2a, but may cover the entire surface of the main body 11, and the main body may be a pipe made only of silicon carbide fiber reinforced resin.

<Effects of the Invention> As described above, since the mandrel according to the present invention has at least the portion of the surface of the main body 11 corresponding to the welding point 2a covered with a coating layer made of continuous fibers made of silicon carbide, high frequency Because it is exposed to high temperatures during induction welding, and the coating layer 13 itself has excellent insulation, heat resistance, and thermal shock resistance,
The lifespan is more than doubled, thick-walled pipes can be manufactured, and the production line speed is more than twice that of the conventional example.

In other words, when welding an ERW tube by inserting an impeder mandrel inside using high-frequency induction welding, the induced power increases as described above, making it possible to weld large currents and welding thick-walled tubes. . However, in reality, when welding with a large current, the part of the impeder mandrel corresponding to the welding point 2a is exposed to extremely high temperatures, and in the conventional example,
This part is damaged, making it virtually impossible to weld thick-walled pipes. On the other hand, in the impeder mandrel having the above structure, the covering layer 13 is made of silicon carbide fiber and has excellent heat resistance, and is also insulative, so that this portion does not conduct electricity at all. For this reason,
Even if a large current flows due to an increase in induced voltage, almost no induced current flows through the coating layer, and no heat is generated.The internal ferrite core will not be damaged for a long period of time. It will not be damaged even if you use it.

Note that, although the above description has mainly focused on application examples of high-frequency induction welding, the present invention can also be applied to other applications, such as manufacturing electric resistance welded pipes using high-frequency resistance welding.

[Brief explanation of drawings]

FIGS. 1 and 2 are a perspective view of a mandrel according to one embodiment of the present invention and a cross-sectional view thereof taken along line A-A, and FIG. 3 is an explanatory diagram of a high-frequency induction welding mode of an electric resistance welded pipe. Code, 2a... Welding point, 10... Impeder mandrel, 11... Main body, 11b, 11c...
...Mounting screw, 12...Ferrite core, 13...
Covering layer.

Claims (1)

[Claims] 1. High-frequency induction welding of electric resistance welded tubes, characterized in that a coating layer made of continuous woven fibers made of silicon carbide is provided on at least the surface of the impeder mandrel provided at the time of high-frequency induction welding of electric resistance welded tubes at the welding point so as to cover the surface without gaps. Impeder mandrel sometimes served.