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topic 13357

Best Malleable (Non-Flaking) Finish for 12L14



 

We have a 1" diameter cylindrical housing made of 12L14 and currently plated with zinc/clear chromate. The cylinder has plastic inserts set into an internal step on each end that are retained by a slight rolling of the housing ends after installation. We have an ongoing issue with plating flaking during this rolling operation that can cause electrical shorts if introduced into the assembly. We are looking for the best finishing option for the 12L14 that can give us equivalent (or better) corrosion resistance of 12 hour salt spray per ASTM B633 [affil. link to spec at Techstreet] , but must be extremely malleable to eliminate any possibility of flaking.

Any and all options are welcomed for consideration, thanks.

Mike McMonagle
- Houston, Texas


 

Zinc would not normally flake if I understood your process correctly. I feel that the problem is in the plating. You have a leaded steel and the preprocess should have a fluoboric acid dip to remove surface lead. Without that, you will have decent adhesion for many purposes, but not physical abuse. Another alternative is to go to a non free cutting steel. Machinists will whine, but proper inserts, coolants,feeds and speeds and you can nearly maintain current production levels

James Watts
- Navarre, Florida


After receiving advice on this forum (thank you) about the plating of 12L14, I asked our plater if they were using a fluoboric acid dip prior to plating. They told me they used a sulfuric acid dip and have never heard of fluoboric acid. Will the sulfuric acid work as well as the fluoboric acid on leaded steel? If so, do we have a different problem? Could the problem be that the part is case hardened? Does the high concentration of carbon near the surface prevent the zinc from sticking to the part?

Robb McMackin
Mr. Gasket - Carson City, Nevada


 

Sulfuric acid will not touch the lead. It will etch some of the iron away from the lead, leaving it on the surface in a greater percentage than originally. An etch is mandatory for adhesion. I have never seen a published process for leaded steel that did not encourage a fluoboric acid step. Some use a combined sulfuric fluoboric etch, but that would not be my preference, especially since it is used on non leaded parts also. Fluoboric acid is common! It is just not a common as sulfuric and hydrochloric.

Case hardened steel can be more difficult than unhardened to etch and to not smut.There are steps that can be taken, but that is getting out of the realm of this site and into consultants or good reference material. I am totally unimpressed by any plater that says they have never heard of fluoboric acid. Can you send a few parts to a better plater to see if they can do better. They need to know that it is leaded and that it has been case hardened!

James Watts
- Navarre, Florida

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