Multi-pass method and apparatus for cold-drawing of metallic tubes

Claim 1

In an apparatus for cold-drawing metallic tubes, a combination comprising a series of discrete draw benches each having a diameter-reducing die surrounding a space whose crosssectional area exceeds the cross-sectional area of the space surrounded by the next-following die, each of said draw benches further having means for admitting a pressurized lubricant between the respective die and the portion of a tube within the respective die, at least two successive draw benches including floating mandrels spacedly surrounded by the respective dies and defining therewith annular reducing passages for successive increments of a tube, the floating mandrel in the preceding one of said two successive draw benches being provided with a channel for admission of a pressurized lubricant into a tube between said mandrels; a plurality of discrete tube advancing means each disposed downstream of a different one of said dies and each comprising a rotary element having an endless surface engaging with at least one convolution of the tube to be cold-drawn and motor means for driving the respective rotary element in a direction to pull the tube through the preceding die; means for regulating the speed of said motors so as to subject the tube to oppositely directed tensional stresses acting on the tube upstream and downstream of each die whereby the tensional stresses acting on the tube upstream of said dies reduce the resistance which the tube offers to a reduction of its diameter during travel through the respective dies; a source of metallic band material; and tube forming means disposed between said source and the foRemost draw bench to convert the band material of said source into a tube which is caused to pass through the dies of successive draw benches.