Metal cleaning by final polishing is used to improve products' appearance and to make them more consumer demanded. Polishing adds decorative brightness to products and is also used to prepare surface for coating.
Types of final polishing
Mechanical methods for final polishing of metal surfaces have a long history and are still widely applicable in metallurgy. Such metal treatment is based on the use of abrasive wheels and tapes in combination with pastes or on the use of round type vibratory machines.
By chemical final polishing, metal surface has an exposure to solution and galvanic couples. It causes passivating film formation.
Electrochemical final polishing consists in smoothing and adding brightness to product surfaces. This type of final polishing is achieved by immersion of parts in the electrolyte (chemical solution) of special composition with parallel connecting to positive power supply.
Electrolyte-plasma final polishing presents a pure precise method of surface treatment, allowing to process almost all types of metals and their alloys: metal and semiconductor products, workpieces made from brass, zink, titan, silicone, stainless carbon steel, copper and aluminum alloys. Along with high performance, electrolyte-plasma technology provides higher product processing speed and absence of abrasive particle penetration in workpiece surface. Roughness value by such final processing can reach level 14, and at the same time within one stage defatting and surface polishing take place.
Metal finishing applications
Many of former USSR industrial enterprises use products made from aluminum as component parts. Thus, in the Republic of Belarus in Barysaw at the motor and tractor electrical equipment factory aluminum starters are used; in Baranavichy at the "Torgmash" factory aluminum frameworks are used for commercial equipment; at the Brest enterprise "Gasapparat" gas and electrical equipment is produced using polished parts from aluminum (100 000 a year); at the Kobryn furniture factory handles, chandeliers and furniture fittings parts are also produced from aluminum. In motor industry alone, having a large range of products, subject to final polishing, the number of aluminum parts reaches hundreds of thousands and millions of pieces. For example, among such parts are injection ramps in up-to-date motor engines, produced by the Dimitrovgrad Auto Aggregate Plant in Russia, fuel equipment parts, pistons and etc.
Traditionally, aluminum parts polishing is carried out in toxic electrolytes, comprising concentrated acids, and, by deburring, labour-consuming mechanical methods are used. Introduction of highly productive electrolyte-plasma polishing method will allow not only to improve quality and application properties of products but also to obtain considerable economic and social effect.
It is advisable to use electrolyte-plasma polishing technology in two stages. In the first stage rough surface treatment by energy-efficient methods is carried out, and then, in the second stage, short-duration final polishing by electrolyte-plasma method is applied. Thus, in the first stage, by polishing of stainless-steel parts, one of the following treatment types is applied:
- Treatment with course wire brush.
- Sand blasting with cast-iron grit.
- Underwater hand grinding with waterproof sandpaper with particle size in 50–80 microns.
- Electric melting in 10% oxalic acid solution with the voltage of 12 V for 5–10 minutes with current density of 2 A/cm2.
At the same time, in case of prior mechanical surface polishing energy saving makes up about 40%.