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Five points that should be paid attention to in the tempering square tube of Shenzhen Steel Plant

Phosphating is a chemical and electrochemical reaction to form a phosphate conversion membrane. The phosphate conversion membrane formed is referred to as a phosphate membrane. It can play a big role in improving the rust resistance of the rectangular tube. Shenzhen Steel Plant should pay attention to the following five points when phosphating the square tube:

(1) overflow washing

It is best to wash the overflow water to ensure that the square tube is fully cleaned and the stringing phenomenon is reduced. When overflowing, water should be introduced from the bottom, and the overflow hole on the diagonal line overflows.

(2) Phosphating and slag removal

For any kind of phosphating solution, more or less sediment will be produced. The phosphating and slag removing device should be indicated when the process is designed. Especially when the other party's rectangular tube is spray phosphating, the slag removing device is indispensable. Typical slag removing devices are: sloping plate precipitator, high-position sedimentation tower, centrifugal slag remover, paper bag filter residue, etc. are all available for selection.

(3) Interval

If the interval between the various processes is too long, it will cause the square tube to rust during the operation. Especially in the pickling process, the pipe is easily oxidized and rusted in the air after pickling, and it is better to provide water film protection between the processes to reduce rust. The interval time is short, and it is not possible to drain the water completely and effectively, causing a stringing phenomenon and even destroying the bath. Therefore, when considering the process interval of the rectangular tube, an appropriate interval should be selected according to the situation.

(four) tank heating tube

Although the choice of material for the tank heating tube is not the content of the process design, if not reminded, it may cause negligence of the equipment designer. For the acidification of sulfuric acid and hydrochloric acid, the tank material can only be selected from FRP, granite and plastic. The heating tube can only be used with lead-bismuth alloy tube and ceramic tube, but stainless steel. If it is washed with phosphoric acid, the tank body and heating tube material can be made of stainless steel, of course, glass fiber reinforced plastic, plastic, granite.

(5) Process hole

For rectangular tubes that are easy to form dead angles, the process holes must be drilled at appropriate locations to ensure that the water can be fully drained in a short period of time. Otherwise, it will cause a series of grooves or be drained in the air for a long time, causing secondary rust and affecting the phosphating effect.

Sometimes there is a delamination problem in the square tube blank, which leads to flaw detection. To prevent this deficiency, we can take the following three measures:

(1) Optimizing the cooling time

Optimize the slow cooling process of square tube slabs, mainly for stacking temperature and stacking duration. After the steel plate has a thickness of not more than 80 mm and the steel plate is hot-straightened, the residence time in the cold bed shall not exceed 5 min. Steel plates with a thickness greater than 80 mm can be extended to 10 min to ensure that the temperature of the steel plate before it is formed is above 500 °C. The steel plate thickness is not more than 50mm, the steel plate slow cooling time is 12h; the thickness of the steel plate with thickness greater than 50mm is 24h, it is forbidden to disassemble and finish in advance.

(2) Optimized control cooling

The appearance of bainite in the square tube slab is generally caused by the excessively fast cooling rate. When the cooling rate is reduced to 3-5 ° C / s, the bainite structure of the steel core segregation zone no longer appears, forming a conventional pearlite structure. After the control cooling optimization, the microstructure stress of the core segregation zone of the slab is significantly reduced, and the microcracks generated by the tissue stress are greatly improved.

(3) Centralized furnace system

In the actual production, the difference in length and width of the rolled steel sheet is large, and there is a situation in which the stacking is not uniform when the steel sheet is slowly cooled, resulting in unqualified inspection of the edge of the ultra-wide panel or unqualified inspection of the head of the super-long board. Through the establishment of a centralized furnace charging system, the contracted rolling of steel plates with different lengths and widths is arranged to ensure the tidy stacking of subsequent steel plates. If necessary, the outer tube of the rectangular tube is wrapped with asbestos cloth to enhance the insulation effect.