There are various types of welding electrodes, which are generally classified in three ways: by application, by main chemical composition of the coating, and by properties of the slag formed after the coating melts.      By application, electrodes are categorized into structural steel electrodes, heat-resistant steel electrodes, stainless steel electrodes, hardfacing electrodes, low-temperature steel electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes, aluminum and aluminum alloy electrodes, and special-purpose electrodes.