Scratch Defects of Galvanized Steel Sheet

Substrate scratches
Substrate scratches are scratches on the surface of cold-rolled substrates due to rolling or unwinding. Since the zinc-iron reaction rate at the substrate scratch is significantly higher than that of the normal surface, the defects on the substrate will become more pronounced after hot-dip galvanizing. By strengthening the process on the quality of the inspection, can eliminate the scratched substrate into the galvanized line.

Sink roll scratches
Sunken roller scratches the strip out of the zinc pot on the board after the intermittent or continuous strip of roller prints, if the roller is lighter and no handle can be degraded, if the feel was scratched only do waste disposal , Must stop for roll. It is believed that the direct cause of this failure is that the speed between the strip and the sunken roller is different, and the roller system does not turn or rotates, so that the strip is in contact with the roller body. The strip surface is scratched by the roll surface. The reason for this phenomenon is multifaceted, because the sunken roller in the zinc pot of zinc in this special location, no transmission equipment, but a driven steering roller, completely by the process section of the tension and friction rotation. Therefore, it is the result of a common or single effect by factors such as mechanical structure specificity, production process control, installation and use of sunken rolls.

The solution is: Process improvement:
(1) Zinc pot zinc solution temperature control (460 ± 5) , in order to increase the mobility of zinc liquid.
(2) At any time to control and adjust the chemical composition of zinc liquid content, the general control of iron content below 0.05%, aluminum content should be controlled between 0.15% to 0.22%. In the production of thin strip due to the smaller tension, the board is easy to sink sink roll. At this point may be appropriate to add aluminum ingots to reduce the iron content, which will help reduce the viscosity of zinc liquid to increase the mobility of zinc liquid.
(3) Control speed and tension can not change too fast.

Equipment installation and use of the improvement: (1) roller processing after installation to check the surface roughness and groove is chamfering, with or without burr, with or without injury. (2) check the roller static balance, the appropriate increase in counterweight. (3) installed after the preload to the test platform (imitation zinc platform), check the level of parallelism to meet the installation requirements of the drawings. (4) sunken roll in the use of zinc into the pot before the first must be placed in the oven preheat, the temperature is close to the temperature of zinc is appropriate. Preheating purposes: First, through the slow preheating to reduce the temperature difference between the zinc pot is too large lead to burst burst and parts of the sudden deformation, improve service life; the second is to prevent the hot surface of the dross is not easy to remove, (5) roller into the zinc pot must be the surface of the zinc pot scum fishing net, bearing position and shaft hole can not stick slag, to prevent the roller stuck does not turn.

Other roller scratches
Other roller scratches are scratches caused by full-line rollers, steering rollers, tension rollers, roll-off rollers, which are divided into drive rollers and non-drive rollers. The main reason for this type of scratches is that the roller speed of the contact strip is not consistent with the running speed of the strip, and the scratches caused by the relative sliding of the strip and the roller.
The solution is: If you find a scratch, you should immediately confirm whether the scratch before plating or plating after scratches, and then determine the scratch area. The scratches caused by the drive rollers can be resolved by speed matching; scratches caused by non-drive rollers are notified to the mechanical maintenance personnel to check the roller bearings. If the bearing is not problematic, by increasing the tension in the area, With the transmission friction to reduce the scratches.