Reasons for the occurrence of "edge cracks" and "tower shaped" coils in copper

Defect 1: Edge cracks in plate and strip rolling
Edge cracks can occur in both hot and cold rolling processes.
Hot rolled edge cracks:
Cause of occurrence:
1. Low heating temperature of ingots
2. Poor metal plasticity
3. There are organizational defects at the edges of the ingot
4. High cooling strength during hot rolling
5. Improper timing of the upright roller edge
6. Poor control of roller shape, resulting in cracks caused by additional tensile stress at the edges
7. Low final rolling temperature
Exclusion measures:
1. Change heating and hot rolling process parameters according to alloy characteristics, and appropriately increase the temperature of ingot discharge from the furnace
2. Reduce cooling and lubrication amount
3. Use the vertical roller edge one or two passes in advance
4. Appropriately increase the final rolling temperature
  02
Cold rolled edge cracks:
Cause of occurrence:
1. Cracks on the edge of the incoming material
2. Coarse grain size of incoming materials
3. High pass processing rate
4. High overall processing rate
5. High rolling tension
Removal measures:
1. Cut off any cracks on the edges of the incoming material
2. Reduce the pass processing rate. Depending on the equipment, the pass processing rate generally does not exceed 30%
3. Cold rolling to a certain extent requires timely annealing. The total processing rate of copper and low zinc alloys above H90 can exceed 90%, while the total processing rate of other alloys generally does not exceed 80%, and some even do 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 high.
Defect 2: Tower shaped with curls
Cause of occurrence:
During the coiling process, loose or uneven coiling, as well as unstable coiling tension, can all lead to the formation of a "tower shaped" coil.
1. The lateral tolerance of the incoming material is significantly larger, causing deviation from the centerline (deviation) during strip rolling
2. The incoming material head is wide and skewed, causing deviation when the head is loosened
3. Unreasonable adjustment of roll gap or roll shape, resulting in strip deviation
4. Inappropriate tension and fluctuation, causing strip deviation
Removal measures:
1. Hot rolling should be centered as much as possible to ensure the uniformity (symmetry) of the head and tail (tongue) and avoid tilting to one side
2. Adjust the roll gap and roll shape during hot rolling to ensure good lateral tolerance control of the strip billet
3. The tension during coiling should be appropriate and uniform
4. When there is slight deviation during the rolling process, adjust the pressure on both sides in a timely manner to correct it and ensure the flatness of the coil.
5. Reasonable selection of strip coiling tension in cleaning, cutting and other processes, and control of strip coiling tension to meet the requirements of strip coiling uniformity and constant tension coiling
Defect three: Surface adhesion of plate and strip materials
Cause of occurrence:
The defect of adhesion between the layers of certain copper and copper alloy thin strip coils produced during the annealing process.
1. The surface of the strip is too rough
2. Excessive coiling tension, wrapping too tightly
3. Annealing temperature too high or holding time too long
4. Uneven heating during the heating process, resulting in varying thermal expansion between layers
5. During the cooling process, the cooling speed is relatively fast, resulting in different coefficients of contraction between the outer and inner coils during cooling
Removal measures:
1. During coiling, especially before annealing, the tension should be moderate during the final coiling process
2. Strict control of heating and cooling rates is required in the annealing process
3. Properly reduce annealing temperature or shorten holding time
4. Appropriately increase the smoothness of the rolling mill