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What kind of galvanizing for a hollow metal door



October 27, 2008

We are a hollow metal door manufacturer from the island of Puerto Rico. I need to know, what are the advantages of using electrogalvanized steel over hot dipped galvanized steel for manufacturing a steel door.

Please note that we are in a island in the caribbean and are constantly surrounded by sea water. The humidity average level is 85% all year round and the average temperature is also around 85 degrees.

Normally after the door has been manufacturer, some drilling, welding and grinding may occur.

My actual question is;

1 - What galvanizing is better for the climate conditions that we have?
2 - Which galvanizing process will respond better after we drill, weld and grind the steel door?
3 - Is it true that hot dipped is a better galvanizing process for a finish product, but electrogalvanizing is a better process for a product that still needs to be work on?

Joaquin Taule
Manufacturer - Trujillo Alto, Puerto Rico



October 31, 2008

The term "electrogalvanized" is a misleading one, often subject to interpretation. Lest assume you meant pregalvanized sheet steel?

In any case, the corrosion protection is proportional to the thickness of the zinc coating. Double the coating thickness and double the life.
Any free metallic zinc coating will give sacrificial protection, even to cut edges, up to about 5mm from the zinc.
Hot dip galvanizing gives coating thicknesses of 80-200 microns, depending on the steel thickness. In a sheetmetal door, I guess you might get 50-80u

If using pregalv sheet steel, you might have 20-30u
Electroplated zinc might give 8-10u

The surface finish of hot dip galvanizing is not aesthetically good. By the nature of dipping steel in a bath of molten metal there will be surface roughness.
Pregalvanized sheet steel is mechanically wiped to get a smooth surface. Electroplated is the smoothest.

Hot dip galv will mean that the door design might be required to be changed to accommodate zinc entering and leaving the inside, but you'll get both inside and outside coated.

geoff_crowley
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
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