Can lubricant actually damage spring steel? 3

[PackardV8]

From a couple of automotive replacement spring websites,

Grease has an adverse reaction to spring steel which causes the steel to degrade and weaken the spring, so we do not recommend using grease/graphite between the leaves.

If this is in fact true, can anyone explain the chemistry?

jack vines

 

[MiketheEngineer]

Nope - must be from the spring mfg - they want them to wear out!!

 

[swall]

Utter nonsense. Just look at valve springs--running in oil, a lubricated environment. Valve spring failures (fatigue) I have seen are due to nicks, pre-existing seams in the wire and overstress due to improper installation or operating parameters.

 

[GregLocock]

The only explanation I can think of would be that the grease and dust and grit forms grinding paste.

I'll ask in the workshop, we've been building leaf spring cars for 50 years or more, someone will know.

Cheers

Greg Locock


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[PackardV8]

Thanks for the replies. I don't get it either, but Eaton, a major supplier of springs has on their FAQ: Link

Prior to the mid fifties grease was put between the spring leaves, in fact springs of many pre-50 cars were wrapped in metal liners to hold the grease in. Some cars had hollow center bolts with a grease fitting so the springs could be lubed on the car. The idea behind lubing between the leaves was to reduce inter-leaf friction.

Then in the early 50's the type of steel used to manufacture springs was changed to SAE5160 and the practice of lubricating between the leaves stopped.

Grease has an adverse effect on 5160 steel. The chemicals in the grease react with the steel and causes the steel to breakdown.

Take a look at the front springs on the next large truck you see leaning. There's a good chance the power steering unit will be leaking onto the low side spring.

Eaton makes a lot of springs for OEMs and the aftermarket, but is it likely a large truck/heavy equipment OEM would put a SAE5160 spring on equipment where lubricant leaks are a fact of life, knowing it would result in deterioration?

jack vines

 

[MintJulep]

5160 is steel. There isn't anything particularly exotic about it. It has the things that most other steels have in it. There is rather a lot of chromium, but not enough to classify it as stainless.

Grease is applied routinely to all sorts of things made out of steel. In much more demanding environments than between leafs of a leaf spring stack.

Grease is routinely smeared on steel things that shouldn't rust in storage or shipping.

So I'm inclined to call BS.

 

[rmw]

Even if the grease had some chemical or soap in it that reacted with or etched the surface of the steel, I can't imagine it having any worse adverse effects than road salt, MgCl, etc. And it would be a surface effect and I can't imaging it penetrating into the spring and degrading it.

And grease and ATF are similar in that they are lubricants, but other than that, quite different; different additives to petroleum products so that annecdote sounds like hokum.

So unless this is a case of SCC due to chlorides, I'm with the BS call.

rmw

 

[patprimmer]

I'm pretty well of the opinion that greases are mostly formulated to protect as well as lubricate steel. While it might hold onto abrasive particles that find there way in there, it also helps keep them out in the first place and reduces the harm they do while there.

I call BS.

Regards
Pat
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[pontiacjack]

Merely "thinking out loud"...

Does this question possibly arise from the reduced internal frictional damping of a greased leafpack? To illustrate my ignorance, does a standing wave ever occur in a leaf spring if excited in some particular manner? Even if the center (or whatever point) is well damped by a separate damper ("shock absorber")? I just don't know...

 

[patprimmer]

The friction between leaves makes the ride a bit harder but reduces rebound control so the leaf spring loses some of its inherent self dampening effect.

Regards
Pat
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[Tmoose]

Here in Massachusetts all the (less than a dozen, probably) busted springs I've seen ( and essentially all the unbroken ones, too) are quite rusty, but worn significantly where the ends of the leaves (leafs) rub.

page 83 here makes it pretty clear how badly rusted steel is impaired.

http://www.timken.com/en-us/Knowled...s/Timken_Practical_Data_For_Metallurgists.pdf

 

[swall]

Thanks for the Timken handbook, Tmoose. I have the paper version, but it was a little out of date (1983).

 

[140Airpower]

First of all, plain petroleum lubricants will not attack steels. I think that the only problem would have to come from an additive that is corrosive. I think that a lube maker would be crazy to put a corrosive or caustic additive in his product. Three very common additives are Lithium, Molybdenum Disulfide and Graphite. These should not hurt steels.

 

[MikeHalloran]

Now, add salty water and re-evaluate those lubricants.


Mike Halloran
Pembroke Pines, FL, USA

 

[140Airpower]

Mike, adding salt water to greases generally results in very poor penetration to the metal surface. In other words, greases and oils tend to repel water. This is fairly well known. Conversely, adding salt water to bare metals has an accelerated corrosive effect. This is also fairly well known.

 

[patprimmer]

I think from some vague memories that greases are typically soaps or metal salts of large molecule organic acids that are mixed into a paste with fine clays.

I guess if a metal was used it could dissociate and form a galvanic cell with the iron or more likely some other component of the steel alloy, however the reactive metal would be the sacrificial one and this (having the metal in the grease being the sacrificial one) would certainly seem to be an objective when formulating grease. Anyway, from my experience, grease protects rather than corrodes metals.

Regards
Pat
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[140Airpower]

Pat, Petroleum greases are heavy hydrocarbons mixed with soaps.
The additives I mentioned are non-reactive with steels, as they would have to be in order not to corrode the metal surfaces. In other words, they would be no good if they reacted with the metal and would be anathema as a lubricant additive.

 

[drwebb]

Despite the source, the careless wording of the recommendation suggests it may be single tech service engineer repeating 'conventional wisdom'. After all, there are a host of different grease chemistries- some even non-petroelum- and if ALL were deleterious to 5160 steel it would be far too fragile to use in the application. Furthermore, power steering units normally are filled with hydraulic oil, so if that (as the FAQ claims) is also harmful why isn't exposure to petroleum in general (including engine oil and tar from the road) recommended against? It sounds a little apocryphal.

 

[1gibson]

Claiming grease has an "adverse chemical reaction," why then also suggest to avoid using graphite in the same sentence? Does graphite have an "adverse chemical reaction" as well? Power steering fluid too? Any lubricant, solid or liquid, ever?

There must be a mostly mechanical answer. Lubricants decrease the friction, maybe the spring operates at a lower temperature and fatigue characteristics are worse. Maybe it is more prone to "sag" when it sits at rest because interleaf friction is much lower. I'd buy that actually.

"It just doesn't work and we don't know why" can be explained by black magic, or 99% of the population will also accept "an adverse chemical reaction" because they don't know the difference between the two.

A lot of people know that a lot of things "just don't work" and for most, "that's how everyone does it" is a good enough explanation. For engineers it is not.

But everyone knows mechanical engineers hate chemistry, so points for effort on this one.

 

[Compositepro]

Graphite and iron do experience strong galvanic corrosion in the presence of salt water. A mitigating factor is that it is difficult to maintain electrical contact between iron and graphite particles as corrosion occurs.