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Re: galvanneal questions

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Posted By<" ">david schenken on March 14, 2002 at 00:26:26:

In Reply to: galvanneal questions posted bypeterN on January 30, 2002 at 13:25:37:

Zinc coating are electrochmically sacrificial. Since the expanse of zinc is much larger than the exposed area of the steel, little corrosion can occur on the steel until most of the zinc is gone.

On ship's hulls relatively small bars of sacrificial metal are used to prevent corrosion on the whole hull. Ships are generally advantaged in that the ocean is electrically conductive and will tend to even things out. If only small portions of galvanneal are exposed to corrosive elements there could be localized corrosion.

So, generally you would have no trouble; yes it is secondary; no it is not a full-penetration product.

: I am currently investigating 'galvanneal' and need to know whether the process is actually a galvanization process that leaves a galvanized 'skin' on cold rolled sheet metal, or whether the galvanneal process thoroughly impregnates the sheet metal.
: I believe 'galvanneal' to be a secondary process generally applied to cold rolled sheet before fabricators pierce, punch, fold, or form the sheet.
: I am concened that any piercing, punching, folding or forming would expose bare ('ungalvannealed') CRS and that these untreated areas would be liable to rust.

: 1. Can anyone confirm, deny, or summarize 'galvanneal' as a rust inhibitor, and whether 'galvanneal' is inherent WITHIN the full thickness of the CRS material, or whether it is just a protective coating?2. Should I be concerned about exposed CRS rusting, whether exposed CRS (i.e. punched holes or sheared edges.
: 3. Can or should parts be galvannealed, after punching or shearing to inhibit rust.

: Thanx in advance for your replies - Peter

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Subject: Re: Re: galvanneal questions

Comments:: : Zinc coating are electrochmically sacrificial. Since the expanse of zinc is much larger than the exposed area of the steel, little corrosion can occur on the steel until most of the zinc is gone. : On ship's hulls relatively small bars of sacrificial metal are used to prevent corrosion on the whole hull. Ships are generally advantaged in that the ocean is electrically conductive and will tend to even things out. If only small portions of galvanneal are exposed to corrosive elements there could be localized corrosion. : So, generally you would have no trouble; yes it is secondary; no it is not a full-penetration product. : : I am currently investigating 'galvanneal' and need to know whether the process is actually a galvanization process that leaves a galvanized 'skin' on cold rolled sheet metal, or whether the galvanneal process thoroughly impregnates the sheet metal. : : I believe 'galvanneal' to be a secondary process generally applied to cold rolled sheet before fabricators pierce, punch, fold, or form the sheet. : : I am concened that any piercing, punching, folding or forming would expose bare ('ungalvannealed') CRS and that these untreated areas would be liable to rust. : : 1. Can anyone confirm, deny, or summarize 'galvanneal' as a rust inhibitor, and whether 'galvanneal' is inherent WITHIN the full thickness of the CRS material, or whether it is just a protective coating?2. Should I be concerned about exposed CRS rusting, whether exposed CRS (i.e. punched holes or sheared edges. : : 3. Can or should parts be galvannealed, after punching or shearing to inhibit rust. : : Thanx in advance for your replies - Peter

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