What is the cause of the straight pipe in seamless steel tube?

　　What is the cause of the straight pipe in seamless steel tube?

　　1. The influence of the rolling temperature of the seamless steel pipe: the rolling temperature is high, pressure is small, and the head wear is small, so that the inner straight defects are also reduced. However, the rolling temperature is too high, and the surface of the plug is easily burned to adhere to metal and iron sheets, which causes an increase in internal straight defects. Generally, the seamless steel pipe rolling temperature is about 1050 degrees Celsius.

　　2. The effect of the amount of deformation: generally, the amount of deformation is large, and the defects of the inner straight track are increased. When the total elongation coefficient is constant, the first pass extension coefficient is increased, and the second run length coefficient is decreased, so that the inner straight track defect can be reduced. Therefore, the second deformation can eliminate the inner straight path generated during the first deformation. However, the straight path at the roll gap cannot be eliminated because the head is not in contact with the metal here.

　　3. The effect of the lubricant: in order to reduce the coefficient of friction between the seamless steel pipe and the plug, it is possible to reduce the straight-line defects in the seamless steel pipe by spraying the lubricant into the capillary tube before feeding it to the rolling mill. When no lubricant is used, the number and depth of defects increase.

　　4. The shape of the head: the use of the spherical head can reduce the inner straight defect, because the ball top has many processing faces, the reduced wall area is narrow, the rolling force is small, and the metal and iron skin are not easily adhered on the head.

　　5. Rolled seamless steel pipe steel. Steel grades with high deformation resistance are likely to cause internal straight-track defects due to large rolling pressure.

　　6. The surface state of the head: it's mainly determined by heat treatment, the surface of the head should have a certain hardness and no cracks.

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