Views: 0 Author: Site Editor Publish Time: 2024-11-18 Origin: Site
Control of weld gap of malleable cast iron pipe fittings
Strip steel is fed into the welding pipe unit, and after multiple roller rolling, the strip steel is gradually rolled up to form a round tube blank with an open gap. The pressing amount of the extrusion roller is adjusted to control the weld gap to 1~3mm, and the two ends of the weld are flush. If the gap is too large, the proximity effect is reduced, the eddy current heat is insufficient, and the intercrystalline bonding of the weld is poor, resulting in unfused or cracked. If the gap is too small, the proximity effect is increased, the welding heat is too high, causing the weld to burn; or the weld will form a deep pit after extrusion and rolling, affecting the surface quality of the weld. Malleable cast iron pipe fittings
Welding temperature control
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to formula (2), the high-frequency eddy current thermal power is mainly affected by the current frequency. The eddy current thermal power is proportional to the square of the current excitation frequency; and the current excitation frequency is affected by the excitation voltage, current, capacitance, and inductance. The excitation frequency formula is:
f=1/[2π(CL)1/2]...(1)
Where: f-excitation frequency (Hz); C-capacitance in the excitation circuit (F), capacitance = charge/voltage; L-inductance in the excitation circuit, inductance = magnetic flux/current
From the above formula, it can be seen that the excitation frequency is inversely proportional to the square root of the capacitance and inductance in the excitation circuit, or proportional to the square root of the voltage and current. As long as the capacitance, inductance or voltage and current in the circuit are changed, the excitation frequency can be changed, thereby achieving the purpose of controlling the welding temperature. For low carbon steel, the welding temperature is controlled at 1250~1460℃, which can meet the requirements of 3~5mm penetration of the pipe wall thickness. In addition, the welding temperature can also be achieved by adjusting the welding speed. Malleable cast iron pipe fittings
When the input heat is insufficient, the edge of the heated weld cannot reach the welding temperature, and the metal structure remains solid, resulting in unfused or incomplete welds; when the input heat is insufficient, the edge of the heated weld exceeds the welding temperature, resulting in overburning or molten droplets, causing a molten hole to form in the weld.
Control of extrusion pressure
After the two edges of the tube billet are heated to the welding temperature, under the extrusion of the extrusion roller, a common metal grain is formed to penetrate and crystallize each other to form a solid weld. If the extrusion pressure is too small, the number of common crystals formed is small, the strength of the weld metal decreases, and cracks will occur after being stressed; if the extrusion pressure is too large, the molten metal will be squeezed out of the weld, which not only reduces the strength of the weld, but also produces a large number of internal and external burrs, and even causes defects such as weld overlap.
Regulation of the position of the high-frequency induction coil
The high-frequency induction coil should be as close to the extrusion roller as possible. If the induction coil is far away from the extrusion roller, the heating time is long, the heat-affected zone is wide, and the weld strength decreases; on the contrary, the weld edge is not heated enough, and the forming is poor after extrusion.
The impedance is one or a group of welded pipe magnetic bars. The cross-sectional area of the impedance should usually be no less than 70% of the inner diameter cross-sectional area of the steel pipe. Its function is to make the induction coil, the edge of the pipe blank weld and the magnetic bar form an electromagnetic induction loop, produce a proximity effect, and the eddy current heat is concentrated near the edge of the pipe blank weld, so that the edge of the pipe blank is heated to the welding temperature. The impedance is dragged in the pipe blank with a steel wire, and its center position should be relatively fixed near the center of the extrusion roller. When the machine is turned on, due to the movement of the pipe blank, the impedance is greatly worn by the friction of the inner wall of the pipe blank, and needs to be replaced frequently.
After welding and extrusion, the weld seam will produce weld scars, which need to be removed. The removal method is to fix the tool on the frame and scrape the weld scar flat by the movement of the weld pipe. The burrs inside the welded pipe are generally not removed.
Process example Now take the welding of φ32×2mm straight seam welded pipe as an example to briefly describe its process parameters:
Strip steel specifications: 2×98mm bandwidth is expanded according to the middle diameter plus a small amount of forming allowance
