Extrusion amount refers to the extrusion amount of the weld metal when the edge of the tube billet passes through the extrusion roller after high frequency heating. The simple measurement of extrusion amount is the difference of the circumferential length before and after welding.
Extrusion amount is one of the important factors affecting the welding quality, just like the heat input. Appropriate extrusion amount can increase the contact surface of the metal to be welded, make enough metal particles produce intergranular interaction, affect the size of welding pressure, affect the size of metal streamline rising angle, and thus affect the welding strength.
The welding quality is unstable, and the welding defects such as undercut, inclusion (black overburned oxide), top arc (white overburned oxide) and insufficient fusion are easy to appear. Increasing the extrusion amount appropriately narrows the range of allowable heat input, reduces the width of heat affected zone and increases the metal flow However, when the extrusion amount is too large, it not only reduces the welding strength, but also increases the amount of internal and external burr, which makes the metal on the edge surface with high plasticity extrude out of the weld, resulting in difficult removal. Due to the low temperature, the molecular diffusion ability of the metal particles on the fusion line is weakened, which affects the solid phase recrystallization process, and is easy to cause welding defects.
When the heat input is constant, the width of heat affected zone and the width of fusion line decrease with the increase of extrusion amount, and the range of allowable heat input decreases with the decrease of extrusion amount, and increases with the increase of extrusion amount. When the extrusion amount is less than 0 . When the extrusion amount is 1.5mm, the range of allowable heat input is very narrow . When the extrusion amount is more than 2 mm, the allowable heat input range is wide . When the temperature is less than 0 mm, the increase of allowable heat input range is not obvious.
Therefore, in the actual production, the wall thickness should be fully considered, and the extrusion amount should be controlled at 2.0 ~ 3.0 mm. For thick wall pipe such as welded pipe over 8 mm, the extrusion amount can be increased by 1 ~ 2 mm. When the welded pipe strength is high, the extrusion amount should also be increased. In experience, the extrusion amount is usually calculated as 40% ~ 50% of the wall thickness
Influence of welding temperature on welding quality
The welding temperature should be controlled at 1250 ℃ ~ 1460 ℃. In actual production, the suitability of welding temperature can be judged and adjusted by observing the flame color and burr shape. When the extrusion roll is just out, the color of normal weld is orange red. If the temperature is too high, the color is red and white. If the temperature is too low, the color is dark red.
After the extrusion roll, the normal shape of the outer burr of the welded pipe should be thin and straight, with smooth top and discontinuous protruding points on the burr line. If the outer burr is not convex, the weld is flat, and the two sides are serrated, it means that the temperature is too high. If the top of the outer burr is not smooth, and there is no discontinuous protruding point on the burr line, it means that the welding temperature is too low.
The welding temperature can also be measured by using the non-contact temperature measuring instrument with new optical fiber technology. It can not only output accurate and linearized on-site analog signal, but also form a closed-loop control system with automatic adjustment control and real-time sound light alarm through the reasonable combination of PLC and high-frequency welding machine, so as to increase the control accuracy of welding temperature.
