Rack plating - process description 2

[PQE]

Hello All. This is my first thread and please be lenient. I have a problem with rack plating. my supplier produce for my shells with tin cover - rack plating. In places when shells have contact with rack tin have value below tolerance and appear a black stains. Will great iif somebody will help me in this case - how improve this defect? I try to find also a description for rack palting method . Thanks for help. Regards

 

[MikeHalloran]

In rack plating, the parts are supported by a rack, not unlike a dishwasher rack, that carries them through all the process steps and tanks. It's inevitable that the area of contact with the rack will end up different from the rest of the plate, because the electrochemical field is different in the contact area.

Contrast that with barrel plating, where parts are placed in a perforated plastic barrel that is continuously rotated as it carries the parts from tank to tank and within the tanks, so points of electrical contact move around as the parts tumble within the barrel, and the plating comes out uniform, or at least without contact scars. If the parts tangle with each other, this process may not be appropriate.



Mike Halloran
Pembroke Pines, FL, USA

 

[kenvlach]

Mike is correct; rack marks are inevitable with most plating. But, it is standard racking practice to minimize rack marks by using hidden surfaces & holes whenever possible. This is something you should discuss with the supplier.

Aerospace companies usually indicate on their blueprints acceptable spots for racking for anodizing or plating.

By a black stain, do you just mean a bare spot with no plating? Stains can also appear from inadequate rinsing -- sometimes the racking pins impede rinsing from holes, so trapped liquids may cause staining vertically downward from the hole. What is the substrate material? To what plating specification?

 

[PQE]

Hi. Many thaks for yours support. In black stains case, I have a pictures and if its possible send you by mail or attached to post but im not sure that is possible? What you think about it? By the way I measure a Tin on the black stains and normal value in 8-12 micro but on stains is 3,5. ist below spec.

 

[kenvlach]

Please give the substrate material, whether any underplating of another metal was used, what tin plating specification (e.g., ASTM B545), whether bright or dull tin, and whether fluoboric acid, MSA, stannous sulfate, alkaline stannate or some other plating bath was used.

To show pictures, you must upload to some free service and get a URL ending .jpg. Then, to include in Eng-Tips, type

(see below after clicking 'Preview Post.'

Also, to get many professional platers to review your problem, post a 'Hotline Letter' with all details at

http://www.finishing.com/Letters/cgimail.html

I'm not sure how to post photos, give URL or email to the editor?

 

[PQE]

Thanks for help.I try to do this.