"Tim" wrote in message
...
On Mon, 21 Nov 2011 20:27:40 -0800, stans4 wrote:
On Nov 21, 9:11 pm, Eli the Bearded wrote:
Last week the garage door torsion spring snapped. It was at least
twenty-five years old and no one lamented it's short life. So a day or
two later we got the spring replaced, and a new garage door opener for
good measure. The door is wood, single car sized, and quite heavy. I
don't have any specs, but the spring is clearly metal, so here I am.
I was not there when the installer was, but I was told he recommended
oiling the spring with WD-40 every three months. Now, to me "oiling"
and "WD-40" are not the same thing, but I can see people confusing
them.
I can see two theories behind why you'd want to oil the spring: 1) a
light coat of thin oil will keep it from rusting; and 2) as the door
opens and closes, the tension put on and released from the spring
causes it to rub against itself.
With the previous install, the rollers were occaionally -- perhaps
yearly -- lubricated with white lithium grease but that's it. At the
end of the life of the old spring, it had a small amount of rust, but I
don't think it caused the spring to fail early. Nor did the spring look
like it had worn down much, so I'm not sure the rubbing action is very
significant.
So what should I plan on doing?
Elijah
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even if this isn't metalworking, it's metal
He wants to sell another job, so WD-40 is the recommendation. You don't
want rust, pits will start fatigue cracks in that highly stressed
spring. I don't think friction between the coils would cause that much
fretting wear. I would probably use LPS 3 for coating the spring if I
lived in a really humid area, a good grade of automotive grease would
probably work most any other place. Repeat if it shows bare metal.
WD-40 probably wouldn't hurt that much but it's sure not either a
lubricant or a rust preventative. Maybe he's depending on the brown
crud buildup to shield things from moisture.
I knew a guy who used to be a systems engineer* for an aerospace
company. He did lots of interesting things. While you didn't want to
get him started on the stories of making side stick controller grips out
of condoms and RTV, he did once tell me that he did a _long_ study of
WD-40 and found out that it's a water attractant.
It's made to penetrate into cracks, even when they're wet -- so it has
stuff in it to disperse into water, and that stuff attracts water (don't
ask me what, I do not know).
I'd wipe it down with plain old oil, or if I was feeling really inspired
I'd get some of that black crap with moly in it that Christopher was
talking about, mix it with some kerosine, and wipe it on. The kero would
help it disperse over the spring, then it would evaporate leaving a
protective film behind. 30W oil stolen from the lawnmower (before you
run it _through_ the lawnmower) would probably be at least as good.
And yes,
AFAIK, rust = stress risers, and stress risers = bad.
* In aerospace companies, you get the title "systems engineer" if you're
really dumb but energetic enough to be invaluable, or if you're so damn
smart that no one knows what you're doing but they know it's invaluable,
or both**.
** You have to know guys with PhD's to understand the 'both', there.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
================================================== ============
Coincidentally, I replaced my garage-door (tension) springs last winter.
They were around 50 years old, I think. They had a pretty thick layer of
rust, which is a good place for cracks to start on a steel spring. (BTW, do
NOT skip replacing the safety cables inside of the springs!)
WD-40 does NOT "disperse into" water. It displaces water. It seems unlikely
that it "attracts" water, either. But the oil it leaves behind, when the
volatiles dry out, is just light mineral oil. It doesn't provide much
protection against rust and it's a lousy lubricant. Another BTW: oiling the
rollers with a few drops of motor oil is a lot easier than using grease, and
it will penetrate into the bearings a lot better. I do it twice a year.
I sprayed one of the LPS rust inhibitors on my springs. I'll tell you in 50
years if it held up as well as leaving them dry. g
--
Ed Huntress (who would be 113 in 50 years...)