Calculation method of welded pipe billet width

Welding allowance

After the welded pipe blank is formed into a cylinder, it enters the induction ring. Due to the skin effect and proximity effect of the current, the edge of the pipe blank is heated to a semi molten or molten state. Under the pressure of the extrusion roller, the molten metal of the two edges crystallizes together to achieve the purpose of welding. In order to weld firmly, during the extrusion process, a small amount of molten metal is extruded from the weld, on both sides of the weld The amount of metal extruded can be regarded as welding allowance if the negligible factor of edge oxidation of tube blank in welding process is excluded.

Sizing allowance

The roundness and diameter of the welded tube are different from the standard requirements, so the outer diameter of the tube needs to go through the reducing and rounding process to meet the standard requirements. Therefore, a certain reducing and finishing allowance (sizing allowance) should be left on the width of the strip steel.

Molding allowance

In the process of steel tube forming, the outer wall of the tube blank is strictly limited in a certain shape of roller groove. With the increase of the edge of the tube blank, the restriction on the inner wall of the tube blank becomes smaller and smaller. When the tube blank is rolled into a cylindrical shape, there is no restriction. In the process of the tube blank completing the inward bending deformation under this condition, there is a slight thickening phenomenon, which makes the tube blank narrow, It is necessary to increase a certain margin in the width of the strip, that is, the forming margin.

The tube blank is stretched during the whole forming process, which also makes the steel strip narrow. In general, the stretch will not exceed the elastic limit of the steel. This can be proved by the obvious yield point in the elongation test of low carbon steel finished tube. Therefore, the amount of narrowing caused by stretching will basically disappear with the process of tube blank rolling into cylinder. When considering the forming allowance, this factor can be used To be ignored.

By measuring the thickness of the welded pipe blank and the wall thickness of the finished pipe, it is easy to get the increase of the wall thickness in the production process of the welded pipe.

The increase of the thickness of the finished pipe compared with the tube blank is not only caused by the forming process, but also caused by the slight thickening of the tube wall during the reducing and finishing process of the sizing process. Therefore, the increase of the wall thickness of the finished pipe is the sum of the increase of the wall thickness in the forming process and the increase of the wall thickness in the sizing process.

There are several empirical formulas commonly used by various manufacturers to calculate the blank width, but the selection range of correlation coefficient in these formulas is wide, the calculation is complex, and a little carelessness will waste a lot of raw materials and man hours because the width does not meet the process requirements

Formula 1: blank width = π (finished pipe outer diameter + sizing allowance - blank thickness) + welding and forming allowance coefficient × blank thickness

In the formula, the sizing allowance coefficient is 0.7 ~ 1.5mm, and the welding and forming allowance coefficient is 0.5 ~ 2.5mm. The thinner the pipe wall is, the larger the diameter is, and the lower the carbon content is, and the larger the value is. Or according to the production experience, this formula is applicable to the welded pipe whose outer diameter of finished pipe is less than or equal to 114 mm.

Formula 2: blank width = π (outer diameter of finished pipe - thickness of blank) + forming allowance + welding allowance + sizing allowance, which is applicable to the circular deformation method.

Formula 3: blank width = (outer diameter of finished pipe - blank thickness) × 1.046 ~ 1.05

The range of 1.046 ~ 1.05 in the formula needs to be determined according to production experience. When the outer diameter of finished pipe is greater than 40mm, the coefficient is 1.04 ~ 1.045. When the outer diameter of finished pipe is smaller or equal to 40mm, the coefficient is 1.046 ~ 1.05. This formula is applicable to thin-walled pipe.