US 4,002,048 A · Method of stretch reducing of tubular stock

Abstract

The disclosure relates to a new procedure for the stretch reducing of tubular stock, in a manner to reduce the so-called crop end loss off of specification product at the ends of a tube section. In the process of the invention, a multi-stand stretch reducing mill is provided with a plurality of speed variable mill stands, at least at the upstream or entry end of the multi-stand mill. As the head end of a finite tubing section enters the upstream end of the mill, and as the tail or trailing end of the finite section enters the mill, programmed speed variations are made in the selected mill stands, to compensate for the fact that the head end or tail end sections of a finite length of pipe are acted upon at any given instant by fewer mill stands than intermediate sections of the tube. In the process of the invention, selected mill stands are speed controlled such that certain ones thereof apply maximum pulling force to the tube end section, while certain other mill stands apply maximum retarding force. At one or more intermediate mill stand locations, mill stand speed is controlled to establish a substantial equilibrium of such pulling and retarding forces. within this general procedure, a limiting condition at all times is that a predetermined stretch factor, for a given workpiece, is not exceeded at any mill stand. Realization of desired wall thickness, without either maximum force effectiveness or maximum stretch factor, can also be a limiting condition, particularly when rolling the tail end section. The procedure of the invention may require the selected upstream mill stands to be either speeded up, or slowed down, or sometimes both speeded up and slowed down at different moments, in relation to steady-state speed.

Claims12

Dependent claims

A process for the stretch reducing rolling of tubular stock of finite length in a multiple stand rolling mill in which at least a plurality of mill stands at the upstream end of the mill are of variable speed, which comprises

a. driving said mill stands at predetermined steady-start speeds during rolling of central portions of said finite length of tubing, and
b. during rolling of at least one end region of the finite length of tubing, variably controlling the speeds of said upstream plurality of mill stands, whereby,
1. one or more upstream mill stands are driven at less than steady-start speed to exert a maximum restraining force on said tubing while avoiding significant slippage,
2. one or more downstream mill stands are driven at greater than steady-start speed to exert a pulling force on said tubing while avoiding significant slippage, and
3. where necessary, one or more intermediate mill stands are driven at controlled speeds, less than steady-start speeds, to maintain the stretch factor of the tubing in the immediate region of said intermediate mill stands, below a predetermined maximum.

2 more elements

A process for the stretch reducing rolling of the head end of tubular stock of finite length, in a multiple stand rolling mill in which at least a plurality of mill stands at the upstream end of the mill are of variable speed, which comprises

a. upon passage of the head end extremity through the first speed controlled mill stand commencing to run said first mill stand at a speed below steady-state speed,
b. upon passage of the head end extremity through successive subsequent speed controlled mill stands, initially running said mill stands successively at speeds greater than steady-state speed and thereafter controllably changing the successive mill stand speeds to steady-state speeds,
c. said vaiable speed mill stands being controlled such that, during at least a portion of the head end rolling sequence, maximum restraining force is being exerted by at least one upstream mill stand and maximum pulling force is being exerted by at least one downstream mill stand, and
d. at least one intermediate mill stand, between said upstream and downstream mill stands, being controlled to establish substantial equilibrium of pulling forces on opposite sides thereof while maintaining the stretch factor of the tubing wall below a predetermined maximum.

1 more element

Dependencies are inferred from the claim text.

Method of stretch reducing of tubular stock

Life of this patent

Method of stretch reducing of tubular stock

Life of this patent

Abstract

Claims12