Fullway copper industry

In the process of uncoiling copper strips, surface tearing and deformation can often be seen, resulting in bonding defects. Bonding is easy to deform, reduce the plasticity of the copper tape for cable, and reduce the stamping performance, which will seriously affect the pass rate of the product.

1 Causes of bonding

The chemical composition of the surface of the copper strip, the temperature and time of the annealing process, and the compressive stress between the coils may be the reasons for the bonding of the copper strip with the cable. The specific performances are:

(1) Chemical composition of copper strip. The different microstructures of the strips with different chemical compositions affect the grain boundary migration speed on the contact surface, which in turn affects the interlayer bonding of the copper strip roll.

(2) Cleanliness of copper strip surface. The remaining volatile organic compounds on the surface, such as emulsions, rolling oil, etc., have little effect on the bonding of the strip; the copper shavings and oxides attached to the surface of the strip will increase the local stress between the layers of the copper strip. Strip bonding has a greater impact.

(3) Holding temperature and time. The higher the holding temperature and the longer the holding time, the better the diffusion of atoms between the roll layers. As long as the copper strip can be recovered and recrystallized, the holding temperature and time should be strictly controlled as much as possible.

(4) Cooling strength. In the cooling stage, if the cooling rate is too high, the temperature difference between the outer layer and the middle layer will be too large, which will increase the compressive stress between the layers and lead to bonding. It is necessary to control the cooling strength reasonably.

(5) The width of copper tape coil ring. The larger the width of the copper tape winding ring, the heat transfer effect of the outer layer and the middle layer, the left and right parts and the middle part will become worse and worse, resulting in a larger temperature gradient.

(6) Curl tension of copper strip. Copper strip has a large curling tension and a large compressive stress between the roll layers, which will increase the bonding tendency of the strip.

(7) Thickness and shape of copper strip. Uneven thickness difference of copper strip or bad shape will increase local stress between layers.

(8) Surface roughness of copper strip. The smoother the surface of the copper strip, the closer the lamination is, which is conducive to atomic diffusion and increases the bonding tendency of the copper strip.

2 solutions

(1) The copper strip is annealed in a low hydrogen atmosphere, and the insulation temperature is continuously adjusted, the duration of insulation, the cooling temperature, the temperature at which the product is released, and the cooling time. Using metallographic structure analysis, until the finished strips have completed the recovery and recrystallization process, and there is no abnormal phenomenon

(2) Before entering the bell furnace, adjust the curling tension of the copper strip to make the shape of the winding tower good; and make the strip edges and surface free of burrs, copper scraps and oxides.

(3) Adjust the shape width according to the surface roughness.

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