Pickling process and principle of rapid scale removal
Fasteners made of carbon steel or medium-low carbon alloy steel are easy to rust in humid environment. Black and dense oxide scale will be formed during hot heading and red punching, which not only affects the appearance, but also brings inconvenience to the later treatment. Usually, methods such as sand blasting, shot blasting, hot pickling and normal temperature pickling can be used to remove rust and scale. A pickling process for quickly removing oxide scale is introduced below.
1, basic formula
According to the literature "Practical Technology of Chemical Cleaning", "Pickling Chemistry of Iron and Steel Materials" and "Pickling Rust Removal Technology", the basic formula (1l solution) of normal temperature pickling process with hydrochloric acid as the main component was established as follows:
420ml hydrochloric acid, 5g urotropine, 5g sodium dodecyl sulfate, 5g oxalic acid, OP- 100g, additive 10ml and phosphoric acid 14ml.
Hydrochloric acid is the main component; The addition of phosphoric acid can improve the pickling speed; Oxalic acid can be complexed with fe2+ and fe3+ to accelerate the dissolution of oxide scale. The additive can also be complexed with fe2+ and fe3+, which obviously accelerates the dissolution of oxide scale. Sodium dodecyl sulfate plays the role of lubrication and penetration; Op- 10 has the function of permeation and fog suppression.
2. Determination of content
Hydrochloric acid pickling increased from 420ml hydrochloric acid to 1000ml. Results It took 48 minutes to completely remove the scale, and the weight loss per unit area was 1 18g/m2. When the basic formula of hydrochloric acid is 420ml, it takes 23min to completely remove the scale, and the weight loss per unit area is 10 1g/m2.
The addition of urotropine not only reduces the removal rate of oxide scale, but also increases the pickling time. The addition of 1g to 5g slightly increased the corrosion of the matrix, resulting in pits and pits.
In the experiment of adding sodium dodecyl sulfate from 1g to 5g, only adding 1g accelerated the pickling speed, and the pickling speed was not obvious when the dosage continued to increase.
In the experiment of adding oxalic acid from 1g to 5g respectively, with the increase of oxalic acid content, the removal speed of scale will be accelerated, and the pickling speed will not increase obviously after 5g.
Op- 10 increased from 1g to 10g respectively. When 1g is added, the scale removal speed is accelerated, and then it continues to increase. The speed increase is not obvious, and the acid fog is obviously reduced after adding it.
When the additive amount is 1g ~ 10g, the dissolution speed of oxide scale is accelerated, but when the concentration is greater than 10ml, the speed increase is not obvious.
The additive is produced by Jinan Taige Chemical Co., Ltd. ..
Adding water to 14, 28, 42, 56, 70 and 140ml phosphoric acid can speed up the scale removal. The increase of phosphoric acid concentration accelerated the descaling speed, but the speed did not increase obviously when it exceeded 56ml. Therefore, the content of phosphoric acid is determined to be 56 ml/L, and the descaling time of this formula is about 16min, which saves 30% compared with hydrochloric acid pickling and greatly shortens the descaling time.
3. Conclusion
The best formula of this process (1l solution): 42ml hydrochloric acid; Sodium dodecyl sulfate10g; ; Oxalic acid 5g; op- 10 10g； Additive10ml; ; 56 ml of phosphoric acid.
This formula is 70% faster than hydrochloric acid solution in descaling.