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Powder Coating Alloy


Guest Dry Reach

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Guest Dry Reach

Another alternative to Anodizing but not regarded by many due to past failures.

 

Powdercoating is an excellent coating for alloy when done correctly.

 

The key to getting longevity (as long as Anodising) is to ensure that the powdercoater you chose has the correct 3,5,7, stage pretreatment system and preferably a chromate system that has a good a qaulity de greaser, and the correct deposition rates for the chromate.

 

The chromate pretreatment is the "surface treatment" that prevents corrosion and ensures longlasting adhesion of the polyester or Epoxy powdercoating to the alloy.

 

With the correct pre treatment and the correct film build of a good quality polyester powdercoating there is no reason why you could not get 20 years plus from this system.

 

Most of the alloy window frames and steel claddings on buildings have these systems applied and they all have shown great performance out past 20 years.

 

The Sky tower Silver coating is a PVF 2 powdercoating and is gaurenteed for 25 years (from memory).

 

HAving said all this there are people who hate the stuff because of failures such as masts, booms, ...

 

These failures are all linked back to application and pre treatment issues in nearly every case. (long "marine" objects that do not fit in the pre treatment baths)

 

1. Adhesion issues arise from the Pretreatment as mentioned above. But most issues are because the powdercoater has not cleaned or chromated properly or not at all!

 

2. The application issues pertain to either low or to high film Build (rare) or (mainly) undercure. Undercure will make the Coating brittle and chip or fracture easily because the thousands of 'particles' of powdercoaing are not cross linked (holding hands) correctly

 

I was invloved with several alloy engine beds for 2 of the original w60's that were SA2.5 grit blasted with a 75micron profile, Chromate pre treated, then powdercoated with a fusion bonder epoxy powdercoating.

 

pre Application salt spray (acidic)trials gave in excess of 20 years corrosion free, and the beds in the boats themselves are still in perfect condition many many years on.

 

The Steel Rebar used in the Manapouri dam (back vent project) is coated with FBE powder coating and will give 50 plus years corrosion free.

 

 

Powdercoating is a great alternative with a better colour and finish range. But Anodising is a product that has higher impact resistance.

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