Phosphating is a process in which chemical and electrochemical reactions form a phosphate conversion film, and the formed phosphate conversion film is referred to as a phosphating film. It can play a big role in improving the rust resistance of square and rectangular tubes. When we phosphate the rectangular tube, we should pay attention to the following five points:

(1) Overflow washing

It is best to wash the overflow with water to ensure that the square tube is fully cleaned and reduce the phenomenon of cross-channeling. When overflowing, water should enter from the bottom, and an overflow hole is opened on the top of the diagonal to overflow.

(2) Phosphating and slag removal

 For any kind of phosphating solution, more or less sediment will be generated, and the phosphating and slag removal device should be indicated in the process design. Especially when the rectangular tube is sprayed and phosphate, the slag removal device is essential. Typical slag removal devices include: inclined plate settler, high-level sedimentation tower, centrifugal slag remover, paper bag filter residue, etc. are available.

(3) Interval time

If the interval between each process is too long, it will cause secondary rusting of the square tube during operation. Especially when there is a pickling process, the pipes are easy to oxidize, rust and turn green in the air after pickling. It is best to have water film protection between processes to reduce rust. However, the interval time is short, and the water cannot be completely and effectively drained, resulting in the phenomenon of stringing grooves, and even the bath liquid is destroyed. Therefore, when considering the process interval of square rectangular tubes, an appropriate interval should be selected according to the situation.

(4) Tank heating pipe

Although the selection of the material for the tank heating tube is not the content of the process design, if it is not reminded, it may cause the negligence of the equipment designer. When pickling with sulfuric acid and hydrochloric acid, the material of the tank can only be selected from fiberglass, granite, and plastics, and the heating tube can only be selected from lead-antimony alloy tubes and ceramic tubes, instead of stainless steel. If pickling with phosphoric acid is adopted, the material of the tank body and the heating pipe can be made of stainless steel, of course, glass fiber-reinforced plastics, plastics, and granite can all be used.

(5) Process hole

For square tubes that are easy to form dead corners and store water, it is necessary to choose an appropriate position to drill the process hole to ensure that the water can be fully drained in a short period of time. Otherwise, it will cause string grooves or drain in the air for a long time, resulting in secondary rust and affecting the phosphating effect.