Will strip into welded pipe unit, the multichannel roll rolling, strip steel rolled up gradually, there is an open space form of round billet, adjust the quantity of the squeezing roller, make the weld gap control in 1 ~ 3 mm, and the joint match on both ends. If clearance is too large, resulting in a decrease of proximity effect, eddy current heat is insufficient, the joint between the weld crystal bad and incomplete fusion or crack generation. Proximity effect such as the gap is too small a result, the welding heat is too big, cause the burning of the weld; Or weld after extrusion, rolling the deep pit formation, affect the surface quality of the weld.

2, welding temperature control

Welding temperature is mainly affected by high frequency eddy current thermal power, according to the formula (2), the high frequency eddy current thermal power is mainly affected by current frequency, the vortex heat power and current is proportional to the square of the excitation frequency; The current excitation frequency and the excitation voltage, electric current and the influence of the capacitance and inductance. Excitation frequency formula is:

F = 1 / (2 PI (CL) 1/2]... (1)

Type: f - excitation frequency (Hz); C - excitation circuit of capacitance (F), capacitance = power/voltage; L - excitation circuit of inductance, inductance = flux/current

On the type, the excitation frequency and the excitation circuit of capacitance, inductance is inversely proportional to the square root, or is proportional to the square root of the voltage, current, as long as change the capacitance and inductance of loop or voltage and current can change the size of the excitation frequency, so as to achieve the aim of controlling the welding temperature. For low carbon steel, welding temperature control in 1250 ~ 1460 ℃, the wall thickness 3 ~ 5 mm penetration can meet the requirements. In addition, the welding temperature can be accomplished by adjusting the welding speed.

When the heat input is insufficient, the heated weld edge short of welding temperature, metal organization remains solid, forming not fusion or lack of penetration; When the input heat is insufficient, the weld edge over welding temperature of the heated, burnt or drop, make the weld formation of melt hole.

3, the control of extrusion

Two edges of tube billet heating to welding temperature, under the extrusion of squeezing roller, forming a common metal grain interpenetrate, crystallization, eventually forming solid weld. If the extrusion pressure is too small, the amount of common crystal small, weld metal strength drops, stress produces after cracking; If the extrusion pressure is too large, will make molten metal being squeezed out of the seam, not only reduce the weld strength, and can produce a large number of inside and outside burr, even cause the welding seam defects such as.