Causes of "edge cracks" and "tower shape" in copper strip production and how to avoid them
Defect 1: Edge cracks during strip rolling
Edge cracks can occur during hot rolling and cold rolling.
Hot rolling edge cracks:
Causes:
1. Low ingot heating temperature
2. Poor metal plasticity
3. Ingot edge has structural defects
4. High hot rolling cooling intensity
5. Improper time of vertical roller edge
6. Poor roller shape control, additional tensile stress on edge causes cracks
7. Low final rolling temperature
Removal measures:
1. Change heating and hot rolling process parameters according to alloy characteristics, and appropriately increase ingot out-of-furnace temperature
2. Reduce cooling lubrication amount
3. Use vertical roller edge one or two passes in advance
4. Appropriately increase final rolling temperature
Cold rolling edge cracks:
Causes:
1. Cracks on incoming material edge
2. Coarse incoming material grains
3. High pass processing rate
4. High total processing rate
5. High rolling tension
Removal measures:
1. Cut off the cracks on the edge of the incoming material
2. Reduce the processing rate of each pass. Depending on the equipment, the processing rate of each pass generally does not exceed 30%
3. After cold rolling to a certain extent, timely annealing is required. The total processing rate of copper and low-zinc alloys above H90 can exceed 90%, and the total processing rate of other alloys generally does not exceed 80%, and even does not exceed 60%, such as HPb59-1.
4. Reasonably control the rolling tension to avoid cracks caused by edge defects when the tension is too large.
Defect 2: "Tower-shaped" strip coil
Cause:
When the strip is not rolled tightly, unevenly, or the winding tension is unstable, the strip coil will be "tower-shaped".
1. The lateral tolerance of the incoming material is obviously too large, causing the strip to deviate from the center line (deviation) during rolling
2. The incoming material head is wide and skewed, causing deviation when the head is loose
3. The roll gap or roll shape is not adjusted properly, causing the strip to deviate
4. The tension is not appropriate and fluctuates, causing the strip to deviate
Removal measures:
1. Try to center the hot rolling to ensure the uniformity (symmetry) of the head and tail (tongue) and avoid deviation to one side
2. Adjust the roll gap and roll shape during hot rolling to ensure good control of the lateral tolerance of the strip
3. The tension should be appropriate and uniform during coiling
4. When there is a slight deviation during rolling, adjust the two sides to press down and correct it in time to ensure the coiling uniformity of the strip. 5. Reasonably select the strip winding tension in the cleaning and shearing processes, and control the strip winding tension to meet the requirements of strip winding uniformity and constant tension winding
Defect 3: Plate and strip surface adhesion
Cause:
Some copper and copper alloy thin strips are produced in the annealing process. The defect of the strip layers sticking together.
1. The strip surface is too rough
2. The winding tension is too large and the winding is too tight
3. The annealing temperature is too high or the insulation time is too long
4. The heating process is uneven, and the thermal expansion between layers is different
5. The cooling speed is fast during the cooling process, resulting in different contraction coefficients between the outer and inner rolls
Removal measures:
1. The tension should be moderate during coiling, especially the last coiling before annealing
2. Strictly control the heating and cooling speeds during the annealing process
3. Appropriately reduce the annealing temperature or shorten the insulation time
4. Appropriately increase the smoothness of the roller
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