Letter 31034

Can we improve our tin plating to 240 hours Salt Spray? [Mexico]  

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Can Pure Acid Tin obtain 240 hours in Salt Spray Tests? How can we archieve this requierement? Our client request this and normally we plate to 24 hours, but not 240. The part is made of steel and processed in barrels, we don't know if we need to apply an undercoat of copper or nickel (thickness?) and what Tin thickness, as well as a chromate or sealer. Please advice regarding the best procedure .

Thanks for your help.

Sergio Enriquez
Job shop - Guadalaja, Jalisco, Mexico

I haven't received an answer to this question (31034)

Can Pure Acid Tin obtain 240 hours in Salt Spray Tests? How can we archieve this requierement? Our client request this and normally we plate to 24 hours, but not 240. The part is made of steel and processed in barrels, we don't know if we need to apply an undercoat of copper or nickel (thickness?) and what Tin thickness, as well as a chromate or sealer. Please advice regarding the best procedure .

Thanks for your help.

Sergio Enriquez
Job Shop - Guadalajara, Mexico

Dear Sergio,

Yes, it can resist 240 h in SS according B-117 [link is to spec at TechStreet]. It depends on thickness and porosity of the tin layer. Tin will protect steel only if it is pore-free. Where that is not the case, the iron becomes anodic and strong corrosion follows. According to ISO 2093, 1986 coatings are classified in four categories; group 4 extremly demanding conditions, group 3 demanding cond., group 2 moderate cond. and group 1 mild cond. Over steel the following thicknesses are required : 30, 20, 12 and 5 micron. Corrosion resistance can be improved by a copper-strike interlayer.

Test for porosity with Kesternich test (enclosed in ASTM B 545) or ferroxyl test, plate some test parts and check corrosion resistance in the SS- chamber to set up process parameters.

Danny Neidel
- Guadalajara, Jalisco, México

Dear Danny,

Thanks for your help. I'm not familiar with ISO 2093, 1986 what SS resistance is expected for each service condition 4, 3, 2 and 1 with the thicknesses mentioned?

We plated the Steel part with copper, then 8 microns of Tin and a chromate and got only 144 hours? Any recomendations? What about the use of sealers?

Gracias por tu ayuda,
Sergio

Sergio Enriquez
Job Shop - Guadalajara, Jalisco, Mexico

Hi Sergio,

In the standard mentioned you need to plate 30 micron(group 4), 20 micron(group 3), 12 micron(group 2) and 5 micron(group 1). To reach 240 hours in SS over steel you have to plate at least 20 micron. Chromates avoid staining in the parts, but it doesn't improve really corrosion resistance. If it is permitted (parts are not soldered after plating), you can use a organic sealer or laquer. That is easy to make for rack parts, small parts in barrel tend to stick with each other. A organic sealer improves corrosion resistance 2-3 times, commercial products are available from local vendors.

I hope that's helpful.

Saludos

Danny Neidel
- Guadalajara, Jalisco, Mexico

Danny,

Thanks for your help. I´ll try with the 20 microns and a sealer.

Thanks again

Sergio Enriquez
Job Shop - Guadalajara, Jalisco, Mexico

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