It is a method to produce seamless tubes. The piercing machine consists of two taper rolls and a cylindrical hot billet passed between these rolls over a mandrel as shown in Figure 21.12. Both the rolls revolve in the same direction and the billet is centre punched. The hot billet is pushed forward into the rolls. The rolls grip the billet and pull it. The axes of rolls are crossed at 10°–12° so that they revolve the billet as well as draw it in forward direction and force onto the mandrel. The mandrel can also revolve in its own position. The combination of the revolving motion of the billet and mandrel together with the axial advancement of the billet provides a helical rolling effect of the billet material over the mandrel. If tube of larger bore is required, a second piercing operation is required after the completion of first piercing operation.
Figure 21.12 Piercing or Seamless Tubing
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