Summary for unpassivated galvanized steel Discussion
Unpassivated galvanized steel is the focus of this thread, where Joe Lee asks what it means, how to specify it for RoHS compliance, whether it can be bent, and whether the surface must be cleaned for conductivity. Ted Mooney explains that passivation is a treatment that lowers the activity of the zinc and often changes its color away from the normal metallic zinc appearance. He says galvanized zinc is ductile, so bending about 30 degrees should generally be possible, but recommends checking the bend area with a magnifier for cracks if there is any doubt. On conductivity, Ted states that the zinc-coated surface is conductive. A second contributor adds an anecdotal note that zinc-coated mild steel left in a drawer for two years showed no visible corrosion, suggesting the coating can remain protective over time.
Q. I have specified the following for metal covers used in our product:
MATERIAL: STEEL SHEET ZINC-COATED (UNPASSIVATED GALVANIZED) AS PER ASTM A653/A653M-01, CS STEEL (TYPE A OR B), COATING DESIGNATION Z275, MINIMIZED SPANGLE (MAX. SPANGLE 1/8 INCH) NOT CHEMICALLY TREATED.
0.94 mm THICK (20 GAUGE).
The need for ‘unpassivated galvanized steel’ comes from a requirement to be compliant to the EU RoHS directive.
I contacted a steel producer and they informed me that ‘unpassivated galvanized steel’ is the only compliant galvanized steel.
1. What is ‘unpassivated galvanized steel’?
2. How do I ensure I get ‘unpassivated galvanized steel’?
3. Can ‘unpassivated galvanized steel’ be bent(~30 deg) and still provide rust protection?
4. The ‘unpassivated galvanized steel’ has to be electrically conductive; does it have to be cleaned to ensure a good conductive surface?
Regards,
Joe Lee
– Ottawa, Ont. Canada
2006
A. Dear Sir
1-Galvanized steel-zinc coated-passivation mean to lower the activity, Most of the time passivation will change the colour ,other than the zinc, metallic colour.
3-Zinc is ductile, I believe yes you can bend, if in doubt check after bending with a magnifier for cracks.
4- Yes it is conductive.
Good luck
Khair Shishani
aircraft maintenance – Al Ain, UAE
2006
Q. Mr. Khair Shishani: Thank you for your response.
The EU has granted an exemption pertaining to HexChrome (VI) for one year, but China has no exemptions.
The unpassivated galvanized sheet steel; non-oiled, will probably exhibit ‘white rust’ after a period of time, which would affect the surface conductivity that I need.
The questions is, how long would it take for the ‘white rust’ to appear in a climate controlled environment; telco central offices?
regards,
Joe Lee
– Ottawa, Ont. Canada
2006
A. Joe,
I happened to be in attendance just yesterday during a panel discussion at a technical conference session on chrome substitutes at Sur/Fin 2006 where the question came up of what to do about galvanized parts that require RoHS-compatible passivation. At least one of the suppliers of the new TCP treatments designed for aluminum (who include SurTec, Luster-On, Metalast and Henkel) reported successful experience in applying this coating to galvanized parts. Please follow up with them and you may find that the answer already exists. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
2006
A. I don’t know if this would help; but I have left a piece of mild steel coated with zinc from a alkaline bath for two years in a drawer in the office and there was no noticeable sign of corrosion. Good luck
Khair Shishani
aircraft maintenance – Al Ain, UAE
2006
A. Might want to try selecting a CRS with trivalent chromium in the passivate instead of hexavalent chromium. Trivalent chromium is RoHS compliant.
Abu Dhabi
– Linthicum, Maryland, USA
2006