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topic 41802

Problems with Powder Coat over Tin Plating



A discussion started in 2006 & continuing through 2017

(2006)

Q. As a commercial plating shop, it is not unusual for us to plate tin over copper bus bars. In certain instances, there are problems with powder coat adhesion. We have seen varying degrees of (apparent) tin oxidation on the powder coated components. It is reported that they bake the parts at 375 deg F. The customer is frustrated, the powder coater is pointing his finger at us and we are stuck in the middle - trying to come up with answers. How suitable a surface is tin for powder coat? What can be done to help insure success and eliminate adhesion problems?

Murray Ritland
Commercial Plater - Minneapolis, Minnesota, USA


(2006)

A. How fast is the temperature increasing by starting the powder coating burning process? Also, do you use an adhesion agent after tin plating? Are the parts clean prior to the powder coating and do the workers wear gloves while racking the parts? When you write that you have adhesion problems, could you figure out where it comes from (check also the plating process)?

Regards,

Dominik Michalek
- Mexico City, Mexico



November 3, 2017

Q. We have been powdercoating over tin plating for the past several months and occasionally have an outgassing type event occurring on the parts which leaves volcano type bubbles on the surface. Parts are aluminum plated in matte tin using the Alstan 88 process.

The big difference I see between parts that are good vs. bad, would be the base layer. Good parts use a copper cyanide base where the parts that typically cause issues use a bronze type base. Any ideas why one would net better results or is that just a coincidence?

Ryan Carter
Engineer - Cincinnati, Ohio United States


November 4, 2017

A. I'm not too savy on why one material is yielding more out-gassing than the other, but I have found that most of our out-gassing issues are with cast parts, aluminum or iron. We use a prebake process that consists of full cure temperature and time, then apply the powder coat while it is still hot. This way, the part is out gassed before the powder coat is applied and the finished product is smooth as intended. Although, I wouldn't trust all of our coaters to "coat it hot". It's an art form in itself to guess the correct powder thickness when the powder is melting as you apply it. The heat skyrockets the transfer efficiency and you could end up at 15 mils before you know it. Additionally, if more than one coat of powder is in the process, like using a primer or needing a clear coat, only the first coat needs to be coated hot.

Kayla Fagen
production manager - Cedar Rapids, Iowa, USA



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