Steel will rust slowly under natural conditions. Every year, there is a huge financial loss from steel rust. A metallic zinc coating on the surface of steel products can serve as a good anti-corrosion function. The process of hot-dip galvanizing is now widely available and used. The production process of hot-dip galvanizing is as follows: degreasing - washing - pickling - washing - plating - drying - galvanizing - cooling - passivation. The purpose of the hot-dip galvanizing process is to remove the iron oxide from the surface of the workpiece. When pickling hot-dip galvanized workpieces, the following should be noted.
1、Control the concentration of acid wash solution. During acid washing, the hydrochloric acid is consumed and the concentration of the acid wash solution gradually decreases. Therefore, hydrochloric acid should be supplemented and the concentration adjusted at any time. The concentration of the pickling solution should be controlled within the range of process requirements, so as to avoid excessive acid concentration, resulting in hot-dip galvanized workpiece over pickling, affecting quality.
2、Control the iron ions in the pickling solution. Iron is a variable element with common valencies of +2 and +3. When iron reacts with sulfur, copper sulfate solution, hydrochloric acid, dilute sulfuric acid, etc. it loses two electrons and becomes +2 valent. When the iron ions in the pickling solution reach 150-200 g/L, the pickling speed is greatly reduced. Although there is a certain amount of free acid in the tank, it no longer removes rust very well.
3、Control the temperature. Temperature shall be controlled in accordance with process specifications. Increasing the temperature speeds up pickling, but also increases the corrosiveness to the workpiece and equipment.
4. Stir appropriately. Acid wash generally requires stirring. During the pickling process, the pickling speed can be accelerated by changing the contact surface of hot-dip galvanized workpiece and pickling liquid once or twice in a row.
5, pay attention to the washing procedure. After pickling, the hot-dip galvanized workpiece is cleaned. Generally speaking, products that have been acid-cleaned by hot acid solution should be rinsed with hot water after being taken out. On the contrary, pickled parts at room temperature, taken out should be rinsed first by cold water, soaked, before rinsing with hot water. Washing must be thorough and no residual acid is allowed to remain on the surface of the part to avoid corrosion. Washing should be carried out in flowing water to avoid rapid accumulation of iron salts in the pool or cleaning is not clean and brought into the plating aid pool. Two washings with two pools is better.
6、The pickling process must be continuous. The process of acid washing and rust removal and all the processes before and after must be carried out continuously and should not be stopped in the middle, otherwise the quality and effect of rust removal will be affected.
7、Regularly remove the sludge from the acid wash basin. As the rust removal process proceeds, the pickling basin will gradually deposit sludge, blocking heating pipes and other controls and should be removed periodically.