How to control the phosphorus slag content in the phosphating tank
Author: Robby
The key measures to control the phosphorus slag content in the phosphating tank include the following:
Maintain appropriate total acidity: the total acidity of the phosphating solution is an important factor affecting the generation of phosphating slag. Total acidity is too high will lead to phosphate film roughness, phosphate slag increase; total acidity is too low, the phosphate film formation rate is slow, it is difficult to form a high-quality phosphate film. Therefore, to maintain the appropriate total acidity is to ensure that the phosphating film normal film and prevent a large number of phosphate slag generation key.
Control of accelerator concentration: accelerators such as sodium nitrite in the phosphating treatment plays a role in promoting the reaction, but its concentration is too high will lead to an increase in the consumption of phosphating chemicals, resulting in a large number of residues. It is recommended that the pre-treatment line as much as possible to focus on production, stop the line without adding accelerant to prevent excessive waste and unnecessary slag generation.
Adjust the value of acid ratio: acid ratio refers to the ratio of free acid to total acid, which should normally be maintained in the range of 20 to 30. Too high or too low an acid ratio will lead to a decrease in the quality of the phosphated film and an increase in slagging. Therefore, the value of the acid ratio control in the appropriate range can effectively reduce slagging and ensure the quality of phosphating film.
Control of phosphating temperature: high temperature of phosphating solution will lead to increased dissociation of dihydrogen phosphate, increasing the generation of slag. Usually recommended the use of secondary heating outside the tank, control temperature does not exceed 60 ℃, in order to avoid direct heating caused by excessive slagging.
Adequate circulation of phosphating tank liquid: to ensure that the phosphate tank liquid concentration in all areas of uniformity and consistency, to avoid the local circulation of small or no circulation caused by the slag concentration is too high and slag sludge. Usually requires phosphating tank liquid circulation 2 ~ 3 times per hour to ensure uniform concentration.
Pay attention to dilution when using neutralising agent: neutralising agent such as NaOH added when adjusting free acid will produce a large amount of zinc phosphate precipitation. It is recommended to dilute the neutralising agent by 10 times and then add it to the bath slowly to avoid a large amount of slagging due to too violent neutralisation reaction.