Either spot, seam or projection welding, the welding surface must be clean before, to ensure joint quality and stability.

Mechanical cleaning methods cleaning and chemical cleaning sub-two. Mechanical cleaning methods are commonly used blasting, shot peening, polishing and so on with gauze or wire brush.

Different metals and alloys requires the use of different cleaning methods. Described as follows:

Aluminum and its alloys on the surface cleaning is very strict, due to aluminum on a strong chemical affinity of oxygen, just cleaned surface will soon be oxidized to form aluminum oxide film. Therefore, the surface cleaned before welding is allowed to remain in the time is strictly limited.

Aluminum oxide film is mainly used to remove chemical methods in alkaline solution to the oil and washed the workpiece into the phosphoric acid solution is corrosive. To slow down the growth rate and the new film new film filled pores in the purification of corrosion at the same time. Purification of the most commonly used agents are potassium dichromate and sodium dichromate (see Table 1). After purification in addition to the oxide film is not at the same time, resulting in excessive corrosion of the surface.

Corrosion after washing, and then the lighting solution in nitric acid treatment, after washing again. After washing temperature of 75 ℃ in the dry room dry, utilize hot air dryer. This clean-up after the workpiece before welding can be maintained in 72h.

Aluminum can also be mechanically cleaned. If using gauze No. 0-00, or with electric or pneumatic wire brush and so on. However, in order to prevent surface damage, wire diameter must not exceed 0.2mm, wire length should not be less than 40mm, the brush pressing force on the workpiece must not exceed 15-20N, and must be cleaned no later than within 2-3h welding.

In order to ensure the stability of the welding quality, the factory is currently in the chemical cleaning up after the wire brush to clean up before welding and then overlap the inner surface of the workpiece.

Aluminum clean-up required to measure the release of two aluminum alloy workpiece total resistance between two electrodes, R. Method is to use a dedicated device similar to spot welding, an electrode above the insulation on electrode holders, in two specimens pressed between the electrodes, so the R value can be measured most objectively reflects the quality of surface cleaning. For LY12, LC4, LF6 aluminum should not exceed 120 micro-ohms R, just clean up after the 40-50 micro-R generally in Europe, for better conductivity LF21, LF2 aluminum alloy and sintering the material class, R must not exceed 28 -40 micro-ohms.

General use of chemical cleaning of magnesium alloy, the corrosion solution and then purified in the chromic anhydride. This treatment will form a thin dense surface oxide film, it has stable electrical performance can be kept 10 days and nights or longer, the performance remained almost unchanged. Magnesium can also use a welding wire brush cleaning.

Copper alloy can be processed in nitric acid and hydrochloric acid, then neutralize and remove welding residue.

Stainless steel, high temperature nickel alloy welding wire, keeping the height of the surface cleanliness is very important, because the oil, dust, paint the presence of sulfur can increase the possibility of embrittlement, so that the joint defects. Laser cleaning methods are available, shot peening, steel wire brush or chemical corrosion. For the particularly important parts, sometimes with electrolytic polishing, but this method is complicated and low productivity.

Titanium oxide, in hydrochloric acid, nitric acid and sodium phosphate mixed solution to remove corrosion depth. Can also use a wire brush or shot peening.

Low carbon steel and low alloy steel in the atmosphere, corrosion resistance is low. Consequent, these metals in the transport, storage and processing of oil is often used corrosion protection. If the surface is not coated with oil or other plant of the stolen goods contaminated with undesirable conductive material, the pressure of the electrode, the film easily pushed open, will not affect the joint quality.

Steel supplier states are: hot rolled, not pickled; hot rolled, pickled and oiled; cold. Not pickling hot-rolled steel welding, must be sand blasting, shot peening, or removed by chemical methods of corrosion oxide, sulfuric acid and hydrochloric acid in solution, or phosphate-based solution of urea but contains sulfur corrosion in the the latter component can be effectively coated the same time oil and corrosion.

A coated steel plate, with few exceptions, generally do not have a special clean-up can be welded, aluminized steel is required or chemical corrosion with a wire brush cleaning. Steel plate with a phosphate coating, the surface resistance to the ground electrode will be high pressure, the welding current can not level. Only the higher pressure can be welded.

keywords: Low Alloy Steel Electrode