It's a fact that equipment and parts in every industry are subjected to abrasive wear and/or corrosive and erosive wear. This often leaves maintenance personnel with two options:
Anodic Coatings for the protection of iron and steel substrates are almost entirely limited to zinc and aluminum coatings or their alloys. Where coatings anodic to the substrate are applied, the corrosion protection is referred to as cathodic protection or sacrificial protection. The substrate is made to be the cathode and the coating the sacrificial corroding anode. The metallizing process is an excellent means of protecting iron and steel from corrosion to almost any desired degree, from long life coatings to inexpensive coatings which are competitive with organic coatings such as paint. Heavy coatings of zinc or aluminum can be applied to meet the most severe corrosion conditions and give 15 to 50 years life without any further maintenance. Aluminum has been found to be the most effective metal for protection of steel in offshore structures.
Cathodic coatings comprise a metal coating which is cathodic with respect to the substrate. A stainless steel or nickel alloy coating would be cathodic to a steel base. Cathodic coatings can provide excellent corrosion protection. There is a very wide choice particularly for steel base materials ranging from stainless steel to more exotic materials like tantalum to cater for the more extreme corrosive environments. However, a limitation of such coatings is that they must provide a complete barrier to the substrate from the environment. If the substrate is exposed to the corrosive environment, the substrate will become the anode and corrosion will be dramatically accelerated resulting in spalling of the coating. Generally, sealing of these coatings is always recommended. Processes, which provide the densest coatings, are preferred (HVOF, plasma and fus ed coatings). Thick coatings will provide better protection than thin coatings.
Neutral materials such as alumina or chromium oxide ceramics provide excellent corrosion resistance to most corrosive environments by exclusion of the environment from the substrate. Generally, a neutral material will not accelerate the corrosion of the substrate even if the coating is somewhat permeable, but any corrosion of the substrate interface with the coating should be avoided to prevent coating separation. Again, sealing of the coatings is recommended. The densest and thickest plasma sprayed coatings are recommended. When stainless steel type substrate materials are used where the exclusion of oxygen can cause crevice corrosion, nickel chromium bond coats are required.
TYPICAL COATING APPLICATIONS -
Thermal spray coatings are widely used in preventing corrosion of many materials, with very often additional benefits of properties such as wear resistance. Thermal spray coatings for corrosion protection fall into three main groups:
Parat Technologies offer Twin Wire Arc Spray, Wire Combustion Spray, Atmospheric Plasma Spray & Ceramic Rod Spray Coating Equipment for combating corrosion problems in different applications. As per the requirement of application we suggest most suitable equipment.