What is Hard Anodizing?
Because of its lighter weight and non-conductivity, anodized aluminum has become a popular alternative to steel in manufacturing circles. But many applications call for a process called anodizing to give aluminum a stronger surface. Essentially, anodizing involves immersing aluminum in a bath of sulfuric acid, called an electrolyte, and running a low-voltage electric current through the acid solution. The result of normal anodizing is a thin coating of aluminum oxide (rust) on the surface of the original aluminum sheet. If the acid solution is cooled to the freezing point of water and the amount of electric current increased substantially, however, the process is called hard anodizing. Hard anodizing is more commonly found in industrial or commercial applications than in consumer products. Some aluminum cookware may be processed through hard anodizing, but regular anodizing generally produces the durable non-stick coating preferred by consumers. Hard anodizing produces a much thicker c
Developed more than forty years ago, hard anodizing is an electrochemical process that involves placing an aluminum part into an electrolytic bath and applying electrical current through the bath. This process forms an oxide coating (sapphire-hard) on the aluminum part. This oxide coating can be harder than casehardened steel and provide excellent abrasion resistance; it is protective to the aluminum part and can be very durable. However, a number of factors can affect the quality, durability and density of the coating. This electrochemical process generally creates polarization of the cathode and anode in the electro-chemical process. This normally generates large amounts of oxygen at the anode and hydrogen at the cathode. This polarization fills the pores of the oxide coating and builds resistance to the electrical current. As a result, progressively more voltage has to be applied in order to maintain adequate current densities. These high voltages generate dangerously high temperatu
The anodizing process is an electrochemical process of oxidation, where a hard aluminium oxide (alumina) coating grows on the surface of the aluminium component being processed. This coating is not a surface layer like plating. The coating is created by the chemical reduction of the aluminium. Consequently, the bond strength of the coating is as strong as the aluminium and will not peel or blister. Special processing procedures in a low temperature, weak electrolyte, result in a very compact coating structure with smaller pores than conventional anodizing. Subsequent sealing of these pores on the very hard film can provide high chemical resistance, as well as other excellent properties. The Hard Anodizing process is suitable for aluminum alloys with limited alloy composition.
