FAQs: Coating and Pre-melt Pots (for Galvanizing Applications)

What recent advances have been made in channel coating pot technology?

Castable refractory in the inductors has been replaced with dry vibratable refractories; wooden channel molds have been replaced with hollow metallic channel molds; and manual forking tools and hand-held electric tampers have been replaced with an electric form type vibrator.

What are the advantages of using dry vibratable refractory?

Dry vibratable refractory eliminates a lot of the variability and problem issues associated with cast refractory, such as: mixing in the correct proportions, mixing time, water quality, water temperature, ambient temperature, ambient humidity, having the right type of mixer and spares, having the right type of vibrators and spares, and so on. Dry vibratable refractory is quicker to install and sinters faster. Dry vibratable refractory is “self-healing” (if molten metal penetrates it, a new hot face can be formed to stop the fin from progressing towards the bushing or the case), whereas cast refractory is one solid body that usually cracks all the way through. Contact your refractory vendor for specifications, installation and curing procedures.

What are the advantages of using hollow metallic channel molds?

The hollow metallic channel mold does not need to be removed by combustion before mounting the inductor on the pot. This saves time and eliminates fumes. It also produces more consistent sintering of the surrounding refractory material, forming an impervious contact boundary to the molten metal to protect against leaks.

What are the advantages of using an electric form type vibrator?

The Electric Vibration System (EVS – Trademark of Allied Mineral Products, Inc.) takes the consistency of using dry vibratable refractory one step further by eliminating the variances caused by worker inexperience and fatigue when performing manual forking and hand-held electric vibration. It also further improves on the labor savings by eliminating the need for removal of the inductor side plate, coils, and core.

When should a channel pot be used and when should a coreless pot be used?

Channel coating pots provide reasonable life and reasonable cost for processing Galvanize (GI), Galvanneal® (GA), and Galfan® (GF) coatings. Inductotherm recommends coreless coating and premelt pots for Galvalume® (GL) and Aluminize (Type I and Type II) coatings due to the relatively short inductor life associated with these coatings from dross settling in the channels of the inductor. Inductotherm offers both channel and coreless coating and premelt pots.

What are the advantages of coreless pots?

The advantages of coreless pots include: round shape for structural integrity and equally distributed thermal stress; fast temperature response due to direct energy transfer; controlled stirring for temperature and alloy uniformity; smaller size (less metal and floor space are required); virtually unlimited power, therefore, higher production capability; can be emptied for alloy changes; shorter refractory installation and sintering time; lower holding power because there is less radiation loss; no emergency power requirement (other than for maintaining water flow through the coil); and longer refractory life for Galvalume® and aluminize coatings because there are no inductors to get clogged with dross.

Which costs more, channel coating pots or coreless coating pots?

While every application must be analyzed individually, generally speaking, the initial cost of coreless pots is 10% higher on average than channel pots. However, once the cost of spare inductors for future inductor replacements is factored in, coreless pots are less expensive in the long run.

Which type of pot has better temperature uniformity and alloy mixing, channel or coreless?

The electro-magnetic stirring action that is typical of coreless pots provides much better temperature uniformity and alloy mixing than is typical for channel pots. Furthermore, inductor placement or adding more inductors provides very little, if any, improvement since most of the metal movement in a channel pot comes from the motion of the strip passing through the bath.

Which type of pot has less bottom dross accumulation, channel or coreless?

Bottom dross accumulation has less to do with the type of pot and more to do with the following factors: cleanliness of the strip coming into the pot, temperature of the strip coming into the pot relative to the bath temperature, bath temperature stability, and aluminum level stability.

What are the reasons for using a pre-melt pot?

The reasons for using a pre-melt pot include: formation of Galvalume® alloy by melting zinc and aluminum ingots; keeping the surface dross created by melting ingots away from the coating process; and isolating the coating process from temperature changes caused by ingot insertion. Pre-melt pots are most commonly used for Galvalume® but are sometimes also used for Galvanneal®.

Which type of power supply is better for a channel inductor, tap changer or solid-state?

Tap changer power supplies provide an economical solution and reasonable contactor life when tight regulation of the bath temperature is not required. For higher quality coating processes and for minimizing dross formation, Inductotherm recommends its solid-state VIP® power supplies, which are capable of providing +/- 1 deg. C. bath temperature regulation. VIP® power supplies accept a balanced three-phase input (no Scott transformer required), operate at constant power factor and constant power output regardless of line or load conditions. And they are more reliable and require less maintenance because they contain no contactors. Inductotherm offers both tap changer and VIP® solid-state power supplies.

Which type of inductor cooling is better, air or water?

Water-cooled inductors offer the following advantages: more efficient and better regulated cooling of the refractory; quieter operation (by eliminating the blower motors); lower ventilation requirements in the pit area; enhanced capability to stop small molten metal leaks due to water cooling around the inductor mounting flanges and refractory bore openings; smaller overall size of the inductor and longer inductor coil life (less prone to arcing due to the coil insulation operating at a lower temperature). Inductotherm offers both air-cooled and water-cooled inductors.

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