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letter 31034

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



A discussion started in 2004 & continuing through 2017

(2004)

Q. Can Pure Acid Tin obtain 240 hours in Salt Spray Tests? How can we achieve this requirement? Our client requests 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 advise regarding the best procedure.

Thanks for your help.

Sergio Enriquez
Job shop - Guadalaja, Jalisco, Mexico


(2004)

A. Dear Sergio,

Yes, it can resist 240 hr in SS according ASTM B117 [link by ed. 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 [link by ed. to spec at TechStreet]:1986 coatings are classified in four categories; group 4 extremely 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 (included in ASTM B545 [link by ed. to spec at TechStreet] ) or ferroxyl test, plate some test parts and check corrosion resistance in the salt spray chamber to set up process parameters.

Danny Neidel
- Guadalajara, Jalisco, México


(2004)

Q. Dear Danny,

Thanks for your help. I'm not familiar with ISO 2093: 1986. what salt spray 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 recommendations? What about the use of sealers?

Gracias por tu ayuda,
Sergio

Sergio Enriquez [returning]
Job Shop - Guadalajara, Jalisco, Mexico


(2004)

A. 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 salt spray 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 lacquer. That is easy to make for rack parts, small parts in barrel tend to stick with each other. An 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


(2004)

thumbs up signDanny,

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

Thanks again

Sergio Enriquez [returning]
Job Shop - Guadalajara, Jalisco, Mexico



July 8, 2008 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi!

Our company has reel-to-reel plating of Au Ni, SnPB,& Ni finishes. Early this year, we plated a Sn-Ni finish on some electronics parts (Cu base). Plating specification is Sn = 2µm & Ni - 1.5 µm. Our practice on our finished products is to have a certain corrosion testing - High Humidity High Temp (HHHT) & Saltwater spray Test (SST). But we always encountered NO GOOD corrosion result in Sn plating when subjected to SST wherein development of black dots or discolorations were observed. HHHT result got no problem. Are Sn-Ni plated items appropriate for this kind of testing (SST)? Is this result after its corrosion test normal? Please advice.

Thanks ahead.

Diana Fe Espinosa
electroplating - Cebu City, Philippines


July 16, 2008

A. Hi Dianne,

Salt Spray test is not normal for tin coatings. Salt Spray test is a typical corrosion test for zinc or zinc alloy plating. Tin is not a common corrosion protection on parts that are exposed to severe environmental condition. For your application where tin is plated on components/parts NOT exposed to environmental condition, salt spray test may not be relevant.

Germie Maravilla
- Laguna, Philippines


August 18, 2009

A. Hi Dianne,

You don't mention the Salt spray test duration? But with the thickness that you mention, I don't think that the parts will sustain even 24 hours.

Moreover, with the thickness as you mentioned, this part only can be used in an indoor and dry environment (no condensation can occur). So, if you do Salt Spray test, it's normal if the result is failure.

Reynald Sukin
- Batam, Indonesia



May 23, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,

This is regarding the constant failures of the tin plating in our fasteners that we procure from our suppliers. These fasteners (nuts, bolts and screws) are made up of mild steel and are tin plated at another supplier's end.

Now, the problem of rust after some time has been reported from our esteemed customer and we are unable to come out of it after we have maintained the plating thickness up to 12 microns also. These fasteners are failing in salt spray test constantly. Now, the salt spray test is done for 48 hours and pics of the pieces found after it are attached.

57188

My queries are as below,
1. Is it correct to conduct the SST on tin plated parts ?
2. If yes, then how to overcome 48 hrs. of SST ?
3. If no, then how to test the durability of tin plating ?

Please help on the above such that we may overcome the same.

Hope for a quick reply from your side.

Regards,

Rishabh Rai
engineer - Noida, U.P., India


A. Hi Rishabh.

As you see, we appended your question to a thread that pretty much answers it for you. But if you now have more questions, please get back to us. Thanks.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 27, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am doing some electronic assemblies which have sheet metal parts.
Base material is CRCA, and then after doing Tin plating I am unable to get salt spray life more that 5 hours.
But our customer need salt spray life more than 72 hours.

Please guide .

Nilesh Hire
- Pune , Maharashtra , India


July 27, 2012

A. Hi, Nilesh.

As you see, we appended your inquiry to a similar thread. As you will read, you are going to require rather thick tin plating to solve this problem, and possibly an organic sealer if the specs permit.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 10, 2014

Q. Dear sir,

I am facing a severe rust issue on tin coated sheet gasket parts. This part is assembled in between engine exhaust manifold and elbow, and also a similar part is assembled in between elbow and silencer.

31034

1) What's the SST life of tin coated part?
2) Is it advisable to do Aluminum coating over tin coated sheet to enhance SST life?
3) Our requirement is 240 hours SST?
4) Can we do Heat resistant black paint over tin coated sheet gasket part?

Please suggest to improve SST of tin coated sheet gasket?

Regards,

Arumuga kumar
- CHENNAI , TAMIL NADU , INDIA



June 24, 2017

Q. If we have Tin plated (5 µm) on brass, then how much hours of Salt Spray Test to be recommended?
As our result I got Rust within 96 Hours -- How to Improve it?

Subrat Kumar Behera
- pune, MH, India



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