Zinc temperature of galvanizing pot
High temperature galvanizing (also called delta galvanizing) is a hot-dip coating process where steel is dipped in a zinc bath at 1040-1165°F (560-630°C) to form a coating comprised of a thin gamma layer with a compact delta layer on top. As a result, a very hard, rough, and thin coating is produced with similar properties to a traditional hot-dip galvanized coating. Depending on the customers specification, high temperature galvanizing can also be controlled to produce coating thicknesses ranging from 1-3.1mils (25-80?m) in accordance with ISO 1461, but not meeting ASTM A123 or A153 requirements.
Although high-temperature galvanizing is not a common coating process seen in North America, in Europe high temperature galvanizing is typically specified for sheet products in the automotive industry or for certain hardware items where both superior corrosion protection and precise fit-up (controlled coating growth) is required. Often times, the reason a customer may wish to utilize high temperature galvanizing for their project is that they have concerns over fit-up between parts, ease of painting over HDG, and/or abrasion resistance. So what can you tell your customer that has heard high-temperature galvanizing can provide these benefits, and requests you provide this service? First of all, it is not possible to simply raise the zinc bath temperature. Due to the high reactivity between molten zinc and steel at these temperatures, a ceramic-lined steel kettle is used. Additionally, bath alloying additions which are helpful at certain concentrations at standard galvanizing temperatures may become detrimental or at best ineffective at higher bath temperatures.
Instead, it may be possible the customer is unaware of how traditional hot-dip galvanizing can be used to achieve the same benefits. You can educate the customer regarding each of their concerns: