Standard_Parts_Catalogue

Page 2172 | Surface Treatments Nickel-Plating Powder Coating Steam Oxide Coating This term is a collective term for dif- ferent processes that are used to apply nickel to metallic substrates. Nickel-plating is divided mainly into galvanic and chemical nickel-plating. With galvanic nickel-plating accord- ing to DIN EN ISO 1456, nickel ions are deposited from an electrolyte by the application of an electrical volt- age. The layer created in this way ap- pears silvery with a light yellow shade and is resistant to water and diluted acids and bases, but does not protect against tarnishing. Corrosion protec- tion is also only provided to a limited extent, as the layers, which are less than 25 μm thick, are usually porous and are therefore susceptible to pit- ting. Multi-layer systems with chromi- um as the top layer are more resistant in this respect. Chemical nickel-plating, on the other hand, is not an electrochemical pro- cess. It is a reduction reaction of the surface of the part in the electrolyte bath, in which a uniform, non-po- rous nickel layer is formed. The end result provides very good protection against corrosive media, good abra- sion resistance, and high hardness – including for parts with complex geometries with interior surfaces. The nickel layer created in this way can be soldered and is non-ferromagnetic. Powder coating, also known as plas- tic coating, usually refers to the elec- trostatic process variant. The powder, consisting of pigmented thermoplas- tic polymer or reactive binding agents made of epoxy resin, polyester resin, or acrylic resin, is applied to the work- piece. Inside the spray nozzle, the powder accumulates a negative electrostat- ic charge, flows along the field lines to the grounded workpiece, and also reaches the rear of the workpiece. The electrostatic charge reduces overspray and ensures adhesion of the powder up to its thermal fusion. The actual closed and homogeneous layer, with a thickness in the range from 80 to 160 µm, is not created until this step in the process. Depending on powder type, the layers are highly resilient, weatherproof, and cor- rosion-resistant. They also can be produced in a wide variety of colors. Powder coating is very popular due to the ease of automation of the process and its economic feasibility. This process is used for the post-treatment of hardened sintered parts for which black oxide coating using a saline solution cannot be used. With steam oxidation, the sintered part is treated with water vapor at temperatures in excess of 350 °C. The result is a thin, almost black homoge- neous oxide layer of about 1 μm. Steam oxide coating only increases corrosion resistance to a small extent. Finishes continued