Induction welding coils/Induction Coils

1.Application of Induction Coils

The process parameters of high frequency welded pipe production include welding speed (unit speed), welding temperature (high frequency power), welding current (high frequency frequency), extrusion force (die design and material), opening V angle, inductor (coil material, winding direction, and location) and the size and location of the resistor (bar magnet).

The induction coil is an important part of the production of high-frequency welded pipes, and the gap between it and the tube blank and the width of the opening have a great influence on the welding quality. Correct selection of induction coils is important for maximum welding efficiency.

2.The selection of induction coil

1)      The distance A between the coil and the squeeze roll depends on the design of the rolling mill and the diameter of the squeeze roll. The smaller the A, the better, and it is best not to exceed the diameter of the tube, as shown in the figure below.

2)      The inner diameter of the coil and its length should be equal and about 20% larger than the pipe diameter

3.Opening V angle reference list

4. Precautions

1)      If the speed is too high or too low, it will cause low temperature weld impermeability and high temperature overburning, and the weld will crack after flattening.

2)      When the extrusion force is insufficient, the welded edge metals cannot be pressed together completely, the remaining impurities in the weld are not easy to be discharged, and the strength is reduced. When the extrusion force is too large, the metal flow angle increases, the residue is easily discharged, the heat affected zone is narrowed, and the welding quality is improved. However, if the pressure is too high, it will cause large sparks and spatters, causing the molten oxide and part of the metal-plastic layer to be squeezed out, and the weld will become thinner after being scratched, thereby reducing the strength of the weld. Appropriate extrusion force is an important prerequisite for ensuring welding quality.

3)      The opening angle is too large, which reduces the high frequency proximity effect, increases the power loss, and reduces the soldering temperature. If the welding speed is constant, there will be no penetration; if the opening angle is too small, the welding current will be unstable and a small spatter will occur at the pinch point.

4)      The gap between the induction coil and the tube blank is too large, resulting in a sharp drop in the inductance efficiency.

5)      If the gap between the induction coil and the tube blank is too small, it is easy to generate electric discharge between the coil and the tube blank, and it is also easy to be damaged by the moving tube blank.

6)      If the width of the induction coil is too large, the welding temperature of the butt edge of the tube blank will be reduced. If the welding speed is fast, false welding and cracking are likely to occur after straightening.