Metal pickling

Powder coating is distinguished by quality and durability. However, a great role in the application of powder on metal is played by the preliminary preparation of things for painting.

Due to the fact that the particles of the powder settle on the product due to the electric field, contamination with high electrical resistance can interfere with the application of paint.

Therefore, before applying powder paint, it is necessary to pre-clean the metal of oil, grease and other mechanical contaminants.

One of the types of preparation for dyeing is metal pickling. This procedure removes oxide films, scale and rust. Also due to pickling increases adhesion and additionally protects the part.

Methods of metal pickling

Pickling metal things can be electrolytic (electroplating), chemical and plasma method.

The first option is suitable for quick cleaning of products. The metal is placed in a salt or acid solution. It is converted into a cathode (negative electrode) or anode (positive electrode). Therefore, galvanic pickling can be cathodic or anodic.

Cathodic digestion removes scale from carbohydrate steels. The anode in this case is lead, the electrolyte is a salt, sulfur solution or alkali metal salts. Note that during cathodic pickling, the product may become more brittle. Therefore, it is not recommended for thin workpieces.

Anode pickling is most common in mechanical engineering. In this case, the anode is the product itself. From it with the help of oxygen mechanically breaks off the oxide film. And the metal molecules are mixed with the electrolyte. As in the previous method, the electrolyte is a solution and the cathode is lead, copper or other metal. During anode pickling, the product turns out to be a little rough.

Chemical pickling of metals is required in order to process ferrous metals, stainless and heat-resistant steels, titanium and its alloys, and aluminum. In a special pickling solution withstand the product from 1 to 120 minutes. Purification in this case occurs by chemical reaction of acid and metal. In order that the metal of the product itself is not dissolved in acid, inhibitors are added to it.

During plasma pickling, inert gas ions seem to bombard pollution on metal. But this method is mainly used for machining parts required for microelectronics.

Metal pickling solutions

The basis of pickling solutions can be sulfuric, hydrochloric, phosphoric, nitric acid and caustic nitrate. In order for the pickling to be uniform and to clean the entire surface, it is necessary to slow down the process of dissolving the already treated areas. This is done by inhibitors that are added to the pickling solution.

Hydrocarbon steels are pickled in sulfur (8-20%) or saline (10-20%) solution. It must necessarily include inhibitors.

Stainless steel and heat-resistant steel are treated with hydrochloric (12%), sulfuric (12%) and nitric (1%) solutions. In this case, the pickling of the metal by acid can occur in several stages. First it is placed in a solution of hydrochloric acid, and then nitric.

Aluminum (10-20%) and acidic solutions are treated with aluminum products. Adding sodium to the alkali will make the process more uniform.

Titanium is first immersed in sodium oxide and then treated with sulfuric, nitric or hydrofluoric acid.

Copper is treated with hydrogen peroxide and chromic acid. Salts are used for this. Metal pickling with chlorine iron, chlorine copper and ammonium persulfate is possible.

During the metalworking process it is thus necessary to pay attention not only to the composition of the solutions but also to the precautionary measures. Still work with acids. It is important that the room is well ventilated and must have a neutralizing reagent nearby!