Corrosion issue with OTEVA 70 steel springs
Corrosion issue with OTEVA 70 steel springs
(OP)
In an automotive application we have a spring made of OTEVA 70 (55SiCr6); the spring is clamped between two Ergal plates. During its life the component is subject to pressurized air up to 4 bar; there could be moisture in the air.
On a 30% basis we find that the spring terminals (were the spring is in contact with the Ergal plates)are heavily corroded (red rust). This compromises completely the spring functionality.
I would like to understand:
1) why this happen?
2) why on 30% basis(I am investigating also the customer operating conditions)?
3) and what action I can take to prevent this from happening (coating or different material ecc).
Thank You
[img d:/temp/DSCN3447.JPG]
On a 30% basis we find that the spring terminals (were the spring is in contact with the Ergal plates)are heavily corroded (red rust). This compromises completely the spring functionality.
I would like to understand:
1) why this happen?
2) why on 30% basis(I am investigating also the customer operating conditions)?
3) and what action I can take to prevent this from happening (coating or different material ecc).
Thank You
[img d:/temp/DSCN3447.JPG]





RE: Corrosion issue with OTEVA 70 steel springs
RE: Corrosion issue with OTEVA 70 steel springs
RE: Corrosion issue with OTEVA 70 steel springs
I think your spring may need a more functional coating like zinc flake + organic or PTFE, expecially if you can't have contamination.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Corrosion issue with OTEVA 70 steel springs
I like the idea of a synthetic lube also. This might prevent the fretting in the first place.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Corrosion issue with OTEVA 70 steel springs
RE: Corrosion issue with OTEVA 70 steel springs
A Zn-5%Ni coating offers more corrosion & wear resistance than plain Zn and is galvanically compatible with the Al. A higher Ni content offers even more protection, but above 12% Ni no longer galvanically protects steel.
Per ASTM B841 (electrodeposited Zn-Ni alloys), to avoid hydrogen embrittlement, a spring steel of hardness > 31 HRC requires both a pre-plating stress relief (per ASTM B849 or ISO/DIS 9587) and a post-plating hydrogen bake-out (per ASTM B850 or ISO/DIS 9588).
RE: Corrosion issue with OTEVA 70 steel springs
I would like to add some more info.
The application is quasi-static, i.e. the spring displacement is in the order of 0,1 mm therefore there is no friction at all with the plates. The spring is retained by two Ergal plates guided by inside diameter. Spring dimensions are roughly,
external diameter 14mm
internal diameter 8mm
length uncompressed 24mm.
The spring is located in a chamber were compressed air is blown by the engine turbocharger.
RE: Corrosion issue with OTEVA 70 steel springs
I would investigate a zinc + aluminium flake coating like:
Delta MKS 3000 series from Dörken
http://www.doerken-mks.de
or Magni 565 from the Magni Group:
http://www.themagnigroup.com
They offer excellent corrosion resistance for the steel, and they are formulated to prevent galvanic corrosion of aluminium parts that are in contact. Plus, they offer versions that are lubricated, which will reduce the tendency for wear.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Corrosion issue with OTEVA 70 steel springs
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm