The influence of extrusion force and temperature on welding quality

Squeeze amount refers to the amount of metal squeezed at the weld when the edge of the tube passes through the squeeze roll after high-frequency heating. A simple measurement of the amount of squeeze is the difference between the length of the circumference before and after welding.

The amount of squeezing is the same as the input heat, which is one of the important factors that affect the quality of welding. A proper amount of squeezing can increase the contact surface of the welded metal, so that enough metal particles can produce intergranular interaction, which affects the size of the welding pressure and affects The size of the rising angle of the metal streamline, thereby affecting the welding strength.

The amount of extrusion is small, the range of allowable heat input is narrow, the width of the heat-affected zone is large, the rising angle of the metal streamline is small, the welding quality is unstable, undercuts, inclusions (black overburning oxide), and top arcs (white overheating) are easy to appear. Welding defects such as burned oxide), insufficient fusion, etc., appropriately increase the amount of extrusion to narrow the allowable range of heat input, reduce the width of the heat-affected zone, increase the angle of metal flow line, and increase the welding quality, but when the amount of extrusion is too high When it is large, it not only reduces the welding strength, but also increases the amount of internal and external burrs, which makes the metal on the edge surface with high plasticity squeeze out of the weld, causing difficulty in removal. Due to the low temperature, the molecular diffusion ability of the metal particles on the fusion line is weakened. , It affects the solid phase recrystallization process and easily causes lap welding defects.

When the heat input is constant, the width of the heat-affected zone and the width of the fusion line decrease with the increase of the amount of extrusion, and the range of allowable heat input decreases with the decrease of the amount of extrusion. When the extrusion volume is less than 0.5mm, the allowable heat input range is very narrow. When the extrusion volume is 1.5mm, the allowable heat input range is wider. When the extrusion volume is greater than 2.0mm, the allowable heat input range is The increase in the input heat range is not obvious.

Therefore, in actual production, the wall thickness should be fully considered, and the extrusion volume should be controlled at 2.0 ~ 3.0 mm. For thick-walled pipes such as welded pipes above 8 mm, the extrusion volume can be appropriately increased by 1 ~ 2 mm. When it is high, the extrusion volume should also be appropriately increased. Empirically, the extrusion volume is often calculated as 40% to 50% of the wall thickness.

The influence of welding temperature on welding quality

The welding temperature should be controlled at 1250℃~1460℃. In actual production, the suitability of the welding temperature can be judged and adjusted by observing the flame color and burr shape. When the squeeze roll is just exiting, the color of the normal welding seam is orange. If the temperature is too high, the color is red and white, if the temperature is too low, the color is dark red.

After exiting the squeeze roller, the normal outer burr shape of the welded pipe should be a thin straight line with a smooth top and slightly intermittent protruding points on the line. If the outer burr is not raised, the weld is flat, and both sides are jagged, indicating the temperature Too high, if the top of the outer burr is not smooth, and there is no intermittent protrusion on the burr line, it indicates that the welding temperature is too low.

Welding temperature can also be measured by a non-contact temperature measuring instrument using the new optical fiber technology. It can not only output accurate and linearized field analog signals, but also through the reasonable combination of PLC and high-frequency welding machine, it can be automatically measured. Adjustable control, real-time sound and light alarm closed-loop control system, thereby increasing the control accuracy of welding temperature.

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