Large Flanges used for Welding Metals with Good Thermal Conductivity
The welding of large flanges can also be called large welded flanges. Two large welded flanges, between which gasket seal is inserted, can be used for connecting the end of one pipe to the end of another pipe. Bolts can be used through the holes of two welded flanges for fastening such two flanges. Welded flanges are disc-shaped parts, which are commonly used in pipeline construction.
During welding process for metals with good thermal conductivity, large flanges require very high upset speed (150-200mm/s). As for welding the same metals, the greater temperature gradient of joint area becomes, the quicker cooling speed of the joint will be; at the same time, increasing upset speed is also required. Upsetting force per unit area can be expressed by upsetting pressure. Upsetting pressure should be appropriate for ensuring extrusion of liquid metals from internal surface of joint area and certain plastic transformation at contact area.
Too low upsetting pressure will result in insufficient deformation and decreased strength of welding joint, while too high upsetting pressure will cause severe deformation, excessive crystal grain bending degree and decreased impact toughness of welded joint. Because higher flash welding speed will result in greater temperature gradient, metals like copper and alloys with good thermal conductivity should be welded through high upsetting pressure (150-400Mpa) imposed on special steel flanges.
Apart from abovementioned factors, preheating flash butt welding should also take preheating temperature and preheating time into consideration. Preheating temperature varies with cross section of workpieces and material properties. During the welding process for low-carbon steels, the preheating temperature should not be more than 700-900 °C.
Since large flanges have good integrated performance, they are widely applied in foundation engineering, such as chemical engineering, construction, water supply, water drainage, petroleum, light and heavy industry, refrigeration, sanitation, heating engineering, fire protection, electric power, spaceflight, shipbuilding and so on.