We are frequently asked about finishes in terms cost, corrosion resistance and where best to use each type. This is important since finishing seriously affects the functionality and cost of a product.
As a general guide, if Powder Coating has a cost of 1, Wet Spray painting has cost of 2, Alochroming a cost of 3, Plating a cost of 4 and Anodising a cost of 4.
Some finishes are specific to materials and further information can be found in Materials.
Parts are first degreased, hung on a conductive hook, sprayed with powder then passed though an over at about 200 degC for 10 mins. The powder melts, flows and cures resulting in a corrosion resistant, hard finish. Colours are normally RAL or BS standard colours in matt, semi-gloss or gloss finishes with optional thickening effects such as leatherette.
Powder coating is generally applied to zintec, aluminium (after alochroming) and stainless steel.
Wet Spray Painting & Stove Enamelling
With regards to sheet metalwork, wet spray tends be used where thin, hard wearing or very high quality gloss finishes are required or where there is a legacy issue such as with old military specifications.
As with Powder Coating, a wide range of RAL and BS standard colours are available in various finishes.
Painting is in small quantities in colours which are not popular can result is high minimum charges.
In Electoplating, the anode (positive) is made of the metal to be deposited (for example zinc) and the cathode (negative) is the part to be plated (for example steel). Both are immersed in a bath of conductive fluid called an electrolyte, current is then applied and plating takes place. The higher the current and the longer it is applied, the thicker the plating and the size of the part will be altered.
Electroless plating uses only one electrode and no external source of electric current or baths are used. Metal can be deposited on non-metallic surfaces as in PCB’s. The is a low cost process, the plating is of uniform thickness but it is slow and thick plating is hard to achieve.
A passivation process can be applied to Plating to further increase corrosion resistance and passivation can be clear, yellow or black.
In GW, the most common forms of plating are zinc plating mild steel for corrosion resistance and chromium plating to achieve a shiny surface.
The aluminium is pre-treated in an alkaline bath based on sodium hydroxide then rinsed clean. The anodisation process takes place in an elecrolytic bath based on sulphuric acid using the aluminium as the anode. This changes the suface of the aluminium to prevent further corrosion but does not seal it.
Because the suface is porous, the aluminium can optionally be coloured in a bath of organic dye typically blue, black, red, orange, green, purple or bronze to achieve attractive finishes.
An optional forth stage to Anodising is to seal the oxide layer by immersion in a bath containing a chemical sealant.
Alochromed parts retain their electrical conductivity, the process adds no weight nor is the component altered in size.
The alochrome film repairs itself if scratched, marks such as fingerprints wipe clean and parts are pleasant to handle. Alocroming also repels water providing excellent protection against moisture.
Anochromed aluminium parts are commonly used internally and externally in electrical and electronic products.