Summary for cadmium plating and sil glyde Discussion
Cadmium plating and sil glyde are both discussed as possible contributors to stripped or damaged threads in stainless screws used with PEM locking nuts, but the thread does not give a definitive root cause. George says the nuts are cadmium plated per the PEM catalog, the screws are stainless steel, and Sil-Glyde is used to prevent seizing before the parts are painted and baked at 275°F. He reports that the threads are often damaged after removal. In a follow-up, he adds that the PEM nuts are 300-series stainless, cad plated, and that a RoHS-compliant version uses a dry-film lubricant of molybdenum disulfide (LAC-032-2MD). He also notes flaking material during installation and poor function after the first use. The excerpt does not include a final diagnosis, but it suggests the issue may involve the plated locking feature, lubricant choice, or the interaction of the assembly process with heat and reuse.
Q. Hi My name is George, I am quality assurance manager for a sheet metal company in New York.
We are using locking pem nuts in many of our products. The screws are stainless steel and to avoid seizing we are using Sil glyde
⇦ on
or
Amazon [affil link] in the nuts. This product is often painted and then baked in an oven (275 deg). What we notice often is that the screw threads are stripped and or damaged after removal- Could anyone tell me if this could be from Cad plating, sil glyde, or what may be causing the problem.
George Schoettlin
quality manager – Rockaway, New Jersey
March 24, 2010
A. Hi, George. What cad plating? You said the screws are stainless. Are the stainless steel screws cad plated? Are the nuts cad plated steel?
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Q. Hi Ted,
(I know you won’t remember me, I worked at Flextronics in Parsippany some years back. I ran the chem film tank line there for a year).
Sorry for the confusion. The pem lock nuts (LAC-032-2) are 300 grade SS. They are Cad plated per the Pem catalog.
The screws are SS. I understand that now they make a RoHS-compliant Pem nut which has a dry film lubricant of Molybdenum disulfide. That is LAC-032-2MD. When we install the screws we see some flaking material. Also does not function properly after first installation.
George Schoettlin [returning]
– TALLMAN, New York, USA
March 29, 2010
A. Hi, George. Nice to hear from you again. Sorry, but it’s difficult to figure out quite what is going on. Cadmium plating is virtually always chromate conversion coated; the ‘book’ limit for chromate conversion coatings is 140 °F. Although this can be exceeded by some chromate conversion coatings, especially after curing time (which will have elapsed long before you get the PEM nuts), it is one possible source of the problem. But the Sil-glyde is not intended for baking either.
I am no expert on this subject, but I’d be inclined to believe that switching to the dry-film lubricated, non-plated, nuts is the best solution.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.