Welded pipe blank is the raw material for manufacturing welded pipe. Its mechanical properties and chemical composition have a far-reaching impact on the quality of welded pipe. Its width is an important factor to determine the weld strength. We usually say that the appropriate width of welded pipe blank refers to the width of a given thickness. The determination of the width is restricted by many factors.
Precision welded pipe is inseparable from accurate billet width. In order to obtain accurate welded pipe with the same thickness, it is necessary to consider the changes of billet in the forming process. The changes are: the amount of narrowing in the forming process, the amount of consumption converted into internal and external burrs in the welding process, and the amount of consumption reserved for reducing the diameter of welded pipe in the sizing process. The sum of these changes is the amount of wear The total variation of the pipe from the filler metal to the finished product.
Forming allowance (decrease) + welding allowance (decrease) + sizing allowance (decrease) = total consumption
Consumption of tube blank during forming
In the process of rolling straight strip into open tube (in front of extrusion roll), under the combined action of longitudinal rolling tension of forming unit and longitudinal tensile deformation of tube billet, the tube billet will produce more or less elastic extension and plastic extension in longitudinal direction. Although elastic-plastic compression occurs in some parts of strip, the general trend is that the extension is greater than the compression, according to the principle of equal metal flow per second Then, the width of the tube blank will be narrowed in this rolling interval, and the consumed width will be converted into the growth of the tube to be welded.
Billet consumption in welding
Forging welding of high frequency welding is completed by extruding the molten metal at the top of v-corner of tube blank with extrusion pressure by extrusion roller. In this process, some metal will be extruded, and the extruded metal is called welding allowance before the extrusion pressure is applied by extrusion roller, which is reserved for extrusion welding. When the tube blank to be welded is extruded, the circumference of tube blank will be smaller than the extrusion pressure On the other hand, some metal will be extruded, and the extruded metal will adhere to the inner and outer walls of the weld, which is a kind of internal and external burr.
Strictly speaking, the volume of welding allowance is the sum of the volume of spatter ball formed by metal vapor, the volume of internal and external burr and the volume of circumferential shrinkage.
It should be noted that the splashing steel ball and internal and external burr are the visual display of welding allowance, while the invisible consumption of circumferential compression volume is easy to be ignored, which requires us to attach great importance to the design and production adjustment of the unit.
Billet consumption in finishing and sizing
According to the production process and forming principle of welded pipe, in order to obtain the finished pipe with neutral layer diameter D, it is necessary to use welded pipe d'larger than the central diameter for shaping consumption, so the billet width consumed in forming is equal to (d'-D) π.
