Hydraulic pump and welding technology
In recent years, with the continuous development of liquid newspaper industry, as one of the hydraulic cylinder hydraulic components also towards the large diameter and large thickness, strip pressure direction, the hydraulic cylinder of the welding technology and quality of Dong also put forward the requirements of tea. In the past, in the CO: Welding often appear root penetration, welding cracks in the first layer and other defects, resulting in hydraulic cylinder leakage, cylinder head off and other serious phenomenon.
The accompanying problem is the solution, and the generation and application of CO2 welding technology provides a perfect solution for the above problems of hydraulic pump.
The hydraulic cylinder is composed of cylinder head, cylinder and tube joint seat welded structures such as the material of cylinder head and cylinder of 45 steel, medium carbon steel containing carbon is butt welding characteristics of children, is after welding the weld metal carbon structure of hydraulic cylinder 1. cylinder 2 cylinder head, 3. simple tube joint seat the amount is relatively high, the weld heat affected zone is easy to produce low plastic hardening structure, the result is not only easy to produce hot crack, but also prone to cold crack.
The thickness of the workpiece is larger, more rigid, this phenomenon is more serious in D according to this characteristic, we first select the U groove in the weld groove, the purpose is to reduce the matrix metal melted weld metal ratio, thereby reducing the carbon content in weld metal, to prevent hot crack; second, preheating before welding is the most effective means to eliminate the weld metal and base metal crack.
Because the preheating reduces the cooling speed of the base metal weld metal and heat affected, favors escape of hydrogen in the weld metal, avoid cracks; at the same time to reduce the weld shrinkage; finally, tempering after welding can reduce the heat affected zone of the strip strength, eliminating welding stress, prevent during welding and the crack after welding, ensure the stability of the structure size of the weld, eliminate harmful cold hardening, get the special requirements of mechanical properties and metallographic structure, improve the mechanical properties of welded joints.
When the root is not penetrated, when the welding current is too small, the wire extension is too long, the welding torch angle is not correct, etc., it is easy to cause the root penetration defect. For these reasons, we have taken the following measures: first, choose special nozzle to ensure that the dry extension of wire is within the specified range. Second, choose partial high current to compensate the fluctuation of power grid. The position of welding torch is correctly placed, and the angle of welding wire is strictly controlled.
The first layer of weld crack when the welding current is too large, the arc voltage is too low, although it can solve the lack of root penetration, but the T deep penetration, prone to cracks in the weld center line, and the base metal melting to weld to increase the proportion, and the welding speed is too fast, will make the welding pool change long grain, nearly straight to the weld axis to the growth of segregation in the weld junction form the weak plane; at the same time because of the increase of welding speed, weld width, weld shape coefficient decreases, fast cooling speed of the first layer of seam welding, which will make the weld centerline crack by D test the right choice, groove type, preheating before welding, the first layer of the small welding method of welding standard slow slow cooling speed, can avoid the occurrence of cracks in weld layer and the first solution.
The porosity practice shows that the porosity is mainly caused by the insufficient purity of the protective gas, the workpiece is not clean, and the dry extension of the welding wire is too long. Therefore, as long as the purity of the 0 gas is guaranteed, the gas is purified for 12 times before use, and the X piece is clean without oil pollution and other sundries, and the dry extension length of the welding wire is guaranteed within the prescribed range, and the blowhole can be overcome.
