aluminium coated tubes

In general, the existence of metal micro crack is inevitable, but under the condition of the same material, cracks depends on the tensile stress components. Affects the tensile stress can be either in the external load components, can stainless steel tube 304 also exist in residual stress of components. After cold drawing, after the empty pull, the residual stress is bigger, show the product near the surface of the outer tangential and axial tensile stress, its value can be up to a larger value. Based on the mechanism of the open crack resistance and can draw near the surface of the aluminium tube outer tangential residual stress of longitudinal cracking of plays a key role.
Aluminium tube longitudinal cracking for many reasons, both the material reason, also for process reasons. If the product is low plasticity or annealing, the probability of longitudinal cracking will increase, but aluminium coated tubes the root cause is cold drawn pipe residual stress. According to the concept of crack mechanics, the component of the cracking is the result of the inside of the micro crack formation and propagation. Aluminium tube basic for brittle crack, longitudinal crack its crack form to open mouth.
As long as the material is alloy steel pipes, including heat resistance, high voltage, low temperature resistant alloy steel tube, are emphatically on the welding process to implement to avoid produce martensite structure due to the welding of high temperature, the tendency of cracks, the craft is general requirements, electrode to choose good, and baking to welder use, according to the requirements on both sides of weld welding before going to oil, water, rust, debris, clean, welding line energy as less as possible, to minimize the swing welding process, after the arrangement of a welding seam annealing heat affected zone for as much as possible. Slow cooling after welding, cover good measures with asbestos cloth, etc.
Thick wall precision steel pipe welding skills what points, according to the use of thick wall precision steel tube such as general purpose and high temperature and high pressure, the latter with tubes are often alloy steel, you need to consider and solve the problem of welding seam shrinkage crack in the welding process and the heat affected zone of tubing mechanical properties is not too big change due to welding operation effect. According to the pipe wall thickness, steel strip made of thin materials such as pipe can use high frequency welding, some thin wall pipe can use the method of shielding gas, welding; Wall thickness greater than 2 mm pipe can use manual welding. According to the size precision of steel tube diameter, small diameter of only one side welding and technicians to implement two sides welding can drilling pipe. One-side Cold Drawn Seamless Tubes welding for welding technique request, can do two one-side welding forming, through ball test, guarantee capacity and weld cross-sectional area have both comply with the design requirements.