The shape of cold-rolled steel strips that factors analysis affected
1 original sheet effects: include thickness fluctuations, hardness fluctuations, the original plate shape.
2 cold rolling itself effects: factors have roll cold rolling itself crown (including thermal crown), roll wear, rolling force, rolling temperature, rolling lubrication.
Generally, roll crown is convex roll diameter value that is the difference between the middle and the end of the representation. Comprehensive rolling crown means mechanical crown early, thermal crown, rolling force and bending machine with a given roll bending together the crown.
Flatness defects
Mainly due to the poor operation of rolling and roll design due to the unreasonable, in addition, the poor quality of the strip itself, pickling, improper heat treatment will have a plate-shaped defects, a common plate-shaped defects:
Camber strip length direction within the horizontal plane bending one side.
Reason: strip on both sides of the uneven reduction; strip on both sides of the thickness difference is too large or uneven hardness, roll is not installed correctly (on the center line of the lower rollers are not parallel or cross-); uneven distribution of lubricants; strip pickling uneven; roll of thermal expansion on both sides of the temperature difference is too large, roll wear is not the same on both sides of the center line of tension as well as the rolling line is not correct and the like.
(2) waves along the rolling direction of the strip segment to the horizontal undulating wave-shaped bend, and projections (peak) and depressed (trough) alternate regularly distributed in the entire length of the strip or local.
Reason: roll through the large convex or reduction is too small; roll surface thermal expansion is too big, too small tension, improper lubrication technology.
Solution: Take the coolant cooling roll surface, increasing the tension and increasing reduction, or the rational use of a lubricant (for thin strip is particularly effective). Little effect as described above, then roll improper or "fall slot" serious and should roll change.
(3) wave wrinkle tilt the rolling direction undulating bent appear on one or both sides of the strip, the strip shape You Ruhai waves wrinkle appeared in the strip on one side called unilateral waves wrinkled, appeared in both sides called bilateral waves wrinkled, appears in the middle part is called intermediate waves wrinkled.
Reason unilateral wrinkled waves generated: The main reduction is uneven sides or ends of the roller body cooling is not good, or tapered rollers, and lubrication is uneven, uneven thickness of the blank. Prevent and eliminate methods to control the thickness of the blank, adjustment and lubrication pressure on both sides to maintain consistent cooling and lubricating the ends of the roll body.
Reason bilateral waves generated wrinkle: The main is a roller-type projection is too small or no crown, or roller-type intermediate was badly worn concave, and two roll neck poor lubrication and cooling body roll ends well and so on. To prevent and eliminate: Increase roll crown value, timely exchange worn roll, holding two roll neck and the roll ends oiled body cooling is good.
Intermediate wave wrinkle causes: mainly through the large convex roll, or reduction amount is too small, and the tension is too small. Prevention method: using reasonable roll crown, due to increase tension.
Transverse occur (4) buckling strip along the arc bent.
Cause: The main reduction amount is too small or too large convex roll, leaving the non-uniform deformation of the strip in the transverse direction, or strip the central and edge cooling conditions are inconsistent, and the blank thickness or hardness uneven.
3 mechanical properties of defects
Mostly rolling process or heat treatment process is not correct due to the mechanical properties of the main defects of the following aspects:
(1) strip of high tensile strength Chilled state extends inadequate
Cause is the total reduction ratio is too high, such as the total reduction ratio is correct, it may be annealed before finishing incomplete, so that is not divisible before finishing work hardening, or cold-pressed middle processes, the annealing process is not correct, as well as affect the annealing is incomplete.
Tensile strength is too low (2) extending exceeded chilled state
The cause is the lack of overall reduction rate, so that the degree of hardening does not meet process requirements. In addition, the annealing process can cause incorrect low tensile elongation after cold rolling excessive degree.
(3) Tensile strength is too low, the extension
It causes the strip material itself is bad, or the hot rolling finish temperature is not correct, the incorrect annealing.
(4) The mechanical properties of unevenness causes uneven annealing or cold rolling reduction is incorrect, resulting in rolling pressure suddenly suddenly small, resulting in different parts of the degree of hardening of each strip.
Because of this convexity is appropriate, make changes in the shape of the strip, in the actual operation to control the shape of the following essentials.
1) Select the best mechanical crown roll.
2) controlled rolling roll cooling. Hot rolling deformation of the roll of the mechanical crown change significantly, such a thermal crown is controlled by adjusting the rolling oil and cooling water.
3) Adjust the roll deflection (crown control). In the control roll crown in order to improve its sensitivity, the work roll bending hydraulic mandatory, this method is called roll benders.
4) adjusting the rolling force. By controlling the rolling force to adjust the amount of deflection rollers, but also to control the shape of the method commonly used.
