Main equipment and process flow of pickling line

The pickling line plays a key role before the cold rolling production in the field of iron and steel metallurgy. Its main function is to remove the scale and dirt on the surface of the strip steel coil from the hot rolling mill with the help of mechanical and chemical effects. Strip with clean surface.

Pickling line
1. Steel coil preparation station
For the pickling line with only one decoiler, in order to shorten the auxiliary time of the unit and increase the output, a coil preparation station can be set up. Usually, the coil preparation station is arranged at the inlet end of the unit and is arranged in parallel with the unit, and is equipped with pre-uncoiling equipment, head straightening machine, cutting head shears, angle cutting shears and material head collecting devices. After the coil preparation station is set up, the cutting head and corner cutting shears are not required to be set online, but usually in order to organize production more flexibly, the online head cutting and corner cutting shears can also be reserved. Generally set up coil preparation station to increase production by 10%. Corner cutters are push-pull pickling lines.

2. Welding machine
Welders are very important equipment in continuous pickling lines. At present, domestic pickling lines are usually equipped with flash welders and laser welders.

1. Flash welding machine
Flash welders and narrow lap welders are both resistance welding. Narrow lap welding machine is used for welding cold rolled sheet or hot rolled sheet after descaling (below 4.0mm), while flash welder can weld hot rolled strip without descaling, the welding machine power is higher, and the equipment price is also higher expensive. The flash welder uses the inherent resistance of the strip itself and the resistance of the end of the strip to cause heating and burning of the metal when current is applied. When the end face is melted, a strong spark is emitted. Then the current is interrupted, a large upsetting force is given, and the two ends of the strip are forged and connected together under high pressure. Strip flash butt welding consists of two processes: flash and upsetting. Flash welder can weld CQ, DQ, DDQ, HSS, HSLA steel grades

2. Laser welding machine
The laser welding machine adopts the "self-fusion welding" technology without filler metal. After the head and tail of the two coils of strip steel are centered and clamped in the welding machine, they are continuously burned by the laser moving laterally along the welding surface of the strip steel, so that the two coils of strip steel are welded together. together. When the welding seam is subjected to post-heat treatment and flattening roller correction, the welding seam synchronous tracking detection can be carried out (it can detect defects such as missing welding and over-thickness of the welding seam).

In terms of welding time, laser welding machines are similar to flash welding machines. The heat affected zone of a laser welder is smaller than that of a flash welder. The laser welding machine can not only weld CQ, DQ, DDQ, HSS, HSLA steel grades, but also suitable for the welding of high carbon steel, high alloy steel, Si/Mn steel, TRIP and other special steel grades. The cost of laser welder equipment is relatively higher than that of flash welder.

3. Tensile straightening machine
The pickling line stretch straightening machine is mainly used to improve the shape of the plate, and also has the function of descaling. For hot rolled sheet, there are 2 additional functions:

1. It is beneficial to improve the anisotropy of strip steel. The yielding of deep-drawn sheets of mild steel is often anisotropic in both the longitudinal and transverse directions. Therefore, when the sheet is deep drawn, due to the different extension of each part, the thickness of each part of the punched part will be uneven, which will cause the punched part to produce skirt-like lace defects. This condition can be improved after straightening by stretch bending.

2. It has a certain effect on eliminating the yield platform. The stretch leveler is suitable for continuous pickling configurations. Due to the large tension required by the tension leveler, the setting and threading of the tension rollers are more complicated, and the domestic push-pull pickling lines are rarely configured at present.

4. leveling machine
Compared with the tension leveler, the leveler has the following functions in addition to the ability to improve the shape of the plate slightly worse:
1. Improve the internal metallographic structure of the strip, eliminate the yield platform, and improve its stamping performance;
2. Improve the surface quality of strip steel and control its surface finish;
3. Improve the thickness accuracy of the strip and reduce the thickness tolerance. For example, Ningshan Iron and Steel uses a skin pass mill to improve the wedge shape of the hot-rolled strip. In addition to the continuous pickling line, the push-pull pickling line has also been equipped with a levelling machine in recent years. This arrangement improves the quality of the finished product of the unit, and can produce hot-rolled pickled sheets similar to cold-rolled sheets to replace some less demanding cold-rolled products; it can also be used to coat the substrate after processing. In construction, automobile manufacturing, home appliances and other industries. A levelling machine is set in the exit section, and a tension roller set can be set before and after the levelling machine; or a tension roll set can be set only in front of the levelling machine, and the tension roll set and the coiler together provide tension for the levelling machine.