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Setting of Compression Spring when Compressed for Long Period

03/30/2014 6:06 AM

When a properly designed compression spring is compressed for a long period of time, say 15 to 20 years, do they set permanently or else function normally even after?

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#1

Re: Setting of compression spring when compressed for long period

03/30/2014 7:19 AM

Yes they take a little set, yes they still function normally.
Del

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#2

Re: Setting of compression spring when compressed for long period

03/30/2014 8:30 AM

The spring constant of the material should be reasonably consistent but 15 to 20 years is a long time for anything to happen along the way. Take the suspension springs of an automobile for an example. A couple of decades of a car sitting in a garage will likely have the bumper at the same height above the garage floor. However, just a few years of poor driving habits over rough terrain (pot holes) can ruin a suspension. The suspension springs will be one of the last things to show fatigue in a suspension but my point is still valid.

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#3

Re: Setting of compression spring when compressed for long period

03/30/2014 8:39 AM

these things can be tested and verified

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#4

Re: Setting of compression spring when compressed for long period

03/30/2014 9:14 AM

All comes down to what happened to the spring and its assembly within those years, right?

Spring steel can rot fairly quick in certain environment. Was/is the environmental component part of the design?

Which one is it? Are we talking dry or wet, fresh air, dirt, salt?

Is the assembly being used? What is the function of the spring after 20 years? Why is it not used before?

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#5

Re: Setting of compression spring when compressed for long period

03/30/2014 11:25 AM

From a practical point, the answer is as Del said, they function normally.

I have ammunition clips for semi-automatic pistols that are 20 years old and still function properly. Yes, they were stored with the springs in the fully (15 round) compressed condition. (an empty clip is of no use, except to throw at someone)

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#14
In reply to #5

Re: Setting of compression spring when compressed for long period

03/31/2014 6:08 AM

Indeed true. I am only now removing ammo from clips that I loaded in 1989. Yes it was an oversight but the springs are strong and work well. Actual spring material used and conditions of storage may effect your outcome significantly, but in a properly designed system 20 years under compression should not be a problem.

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#25
In reply to #5

Re: Setting of compression spring when compressed for long period

03/31/2014 3:16 PM

Wow! ... you carry guns too ... what a Man.

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#26
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Re: Setting of compression spring when compressed for long period

03/31/2014 3:23 PM

Never said that, Dork.

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#30
In reply to #25

Re: Setting of compression spring when compressed for long period

03/31/2014 9:22 PM

Why so surprised? Don't you?

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#6

Re: Setting of Compression Spring when Compressed for Long Period

03/30/2014 11:39 PM

Dear Mr.pc,

A properly designed spring, will retain its character as long as the stretching remains with in the Hooke's Law definition. Once this limit is crossed it will be no longer a spring.

As regards the compression it will retain its spring character.

DHAYANANDHAN.S

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#9
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 3:10 AM

I think a hard working spring like a valve spring in a car engine will take a little set over time, but that will be within the design parameters.
A light usage spring can be designed to take no set.

Del

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#7

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 1:20 AM

I don't know that there is any empirical data available on this subject, but I would expect, over that period, for some creep to take effect and the spring rate to deteriorate slightly.

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#8

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 3:09 AM

if the elastic limit of the steel has not been exceeded then it will just spring back nicely and work like new (if it hasn't rusted or been damaged)

Plenty of ICEs that were moth balled in working order start up no problem and the valves don't leak when started up after 20 years.

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#17
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 8:23 AM

The valve springs in my 1942 Chevrolet truck seem to be working fine after 72 years.

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#10

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 4:37 AM

It would depend upon the abrasion and corrosion that takes place on the spring in that time.

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#12
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 4:58 AM

Yes your right, the worst example is compressor discharge valve's springs. In fact in addition to abrasion and corrosion, heat and cycles of operation makes them to retire fast.

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#11

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 4:49 AM

Dear PC, It is very difficult to say without any experiment or evidence in literatures for the same. The probability to function normally will greatly depend on material specification, spring design and environment it is kept. So why don't you take up this research project and apply to some University for a Ph.D. It will generate required literature on this issue for future generations.

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#13

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 5:01 AM

The question actually answers itself...

"Properly Designed"

a) If the design requires no set during the design life, then self evidently a 'properly designed' spring will have no set.
b) If some small set (say 0.01 per inch of length) is acceptable, then a propperly designed spring will fall within that tollerance.
The reason for the distinction is spring a) will probably be heavier, larger and more expensive than spring b).

Size and inertia and cost are important considerations in my example of the valve spring.

Del

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#15

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 7:19 AM

I know springs in gas regulators (oxy acetylene) do lose set if left in the loaded position. These springs are in a dry, normal atmosphere. Maybe the regulators are pre war vintage and the spring steel not so good. Because of this effect I have got in the habit of backing them off each time I finish the job and so I don't know if modern regulators lose their set. I guess that a regulator is a very sensitive spring tester as well. The old time usual practice, as opposed to best practice, was to set the oxy at 60PSI for cutting and a regulator left at that setting would slowly drop pressure.

Just occurred to me this may have been due to stretch of the diaphragm as well.

Jim

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#16
In reply to #15

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 7:48 AM

That practice of backing off gas/air regulators when not in service and checked to be so before cracking open the HP was also drilled into me. Some old codger normally doing the drilling.

As I was reading your post Jim, I too was thinking that it may have more to do with unloading the diaphragm.....

...but then there's a safety aspect too. If the regulator is backed right out then, for air, there is no chance of damaging any downstream actuators and what not "by accident", and for gas, the safety aspect is pretty obvious.

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#18

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 9:29 AM

Modulus, hook's law, and gun clips are one thing; creep is another. There is no creep-proof spring material. At one time it was thought that springs made from quartz were totally creep resistant and people made precision scales from it. It was subsequently learned that even quartz creeps to some extent. Creep resistant alloys of beryllium copper were used to make creep-proof barometers and bellows, but they still require calibration to compensate for creep.

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#19
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 9:44 AM

You didn't answer the question, which was, "do they set permanently or else function normally even after?

The correct answer is no, and yes.

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#22
In reply to #19

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 10:16 AM

The answer to the question is that all springs creep (change length over time). They may have the same spring rate (elastic modulus) as they did initially, but the length of every spring will change as a function of time. This will be true at any temperature and any stress (except 0).

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#24
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 2:16 PM

So, will the spring get longer, or shorter.

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#27
In reply to #24

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 6:23 PM

Iff that's a question, the answer is yes. It will get longer - or shorter depending on whether it's pulled or pushed.

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#29
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 6:40 PM

Withdrawn.

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#20

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 9:46 AM

C'mon you tightwads... where are my GAs.
I need to get some more to exchange for bitcoins or tuna scraps (whichever has the better exchange rate)
Del

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#21
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 9:49 AM

I might give you a CA, if a cute/clever answer button existed.

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#28
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Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 6:37 PM

Ask an elevator repairman whether cables that by law must be within their elastic limit, experience creep over time. Or better yet, close to where I live, we have a railroad bridge that is raised and lowered a few times a day. Every few years they must replace the stretched cables. These cables are specified by both military, ASM, ASME, and a few other organizations. Yet, the cables still stretch - a lot.

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#23

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 11:24 AM
  1. I would thiink that spring steel is not immune from some form of internal mettalurgical change of the steel alloy.Old houses that are deconstructed were put together with cut nails, and they cannot be reusued until they are retempered;they are too brittle and will snap off like glass.I have seen parts from old tractor lift arms and steering sectors that are bent, and would snap when trying to straighten them, unless pre-heated first.

Then on the other hand, those same tractors had no problems with the valve train components,however, these were designed for a 50+ year useful lifetime from the start,and these springs are seldom put to the test of maximum rpm where valve floating would be evident.

When rebuilding new engines,or race engines,valve spring heighth and compression strength is compared to specs to check for fatique or set of the springs.

I guess it depends on a lot of factors,and a simple yes or no is not appropriate in all cases.

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#31

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 11:51 PM

Thanks a lot for your valuable input.

But it seems there is no clear answer.

But my personal opinion (though there no proof) that the spring should behave normally when "properly designed". Which means the stress induced when pressed to solid length are within safe limits. Ther is proper greasing to prevent corrosion

but, there is this Creep, wheep i am not fully aware of. I think the best bait, as someone said, is to overdesign.

This is all I found on net-

"Depending on design and space limitations, compression springs may be categorized according to stress level as follows:

  • Springs which can be compressed solid without permanent set, so that an extra operation for removing set is not needed. These springs are designed with torsional stress levels when compressed solid that do not exceed about 40 percent of the minimum tensile strength of the material.
  • Springs which can be compressed solid without further permanent set after set has been initially removed. These may be pre-set by the spring manufacturer as an added operation, or they may be pre-set later by the user prior to or during the assembly operation. These are springs designed with torsional stress levels when compressed solid that do not exceed 60 percent of the minimum tensile strength of the material.
  • Springs which cannot be compressed solid without some further permanent set taking place because set cannot be completely removed in advance. These springs involve torsional stress levels which exceed 60 percent of the minimum tensile strength of the material. The spring manufacturer will usually advise the user of the maximum allowable spring deflection without set whenever springs are specified in this category."

I guess i will go for first design, where the induced torsional stresses are not more than 40% of UTS of spring material.

But, then what about Torsional spring, where induced stresses are bending. Should I also design them with Induced bending stress 40% of UTS of spring material.

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#32
In reply to #31

Re: Setting of Compression Spring when Compressed for Long Period

03/31/2014 11:56 PM

You should design them, if that is truly your intent, to the best engineering practices for spring design.

I suspect that you are a paid consultant and are asking us, again, to do your work for you.

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#33
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Re: Setting of Compression Spring when Compressed for Long Period

04/01/2014 12:04 AM

I do have actually. I have designed springs for many applications. I find them them fascinating. May be that's why I try to push them in my every design

This application is actually a Relocker design for a Safe. A relocker operates when Safe is attacked and the attack may not happen over a lifetime or may be after 20 years.

I am designing a new one. Its already tested and found to be successfully operating. But then one of our production guy came up and asked this "simple question". And since I love springs, I must know whether this can really happen. But there is no such article on internet, that's weird!!

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#34
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Re: Setting of Compression Spring when Compressed for Long Period

04/01/2014 12:27 AM

Well then, good enough.

My position is still that, empirically, springs in compression, properly designed, will work for "a very long time".

After careful consideration, and recollection and some records checking, my clips/springs are actually over 35 years old.

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#35
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Re: Setting of Compression Spring when Compressed for Long Period

04/01/2014 12:30 AM

There's a government grant and a Phd in that ....

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#36

Re: Setting of Compression Spring when Compressed for Long Period

04/01/2014 10:20 PM

Properly designed compression spring, compressed for last 46 years in safety valves of reciprocating compressors are working satisfactorily. This is the practical example we had in one of our plants. Safety valve's set pressure is 325 bar and re-sets at 309 bar. These are installed in Synthesis gas compressors manufactured and supplied by M/s KOBE in 1967. There are nine safety valves at different pressure settings and till date we had not replaced spring in any of these valves.

The right term, which you had specified is "properly designed". Free length of these springs had reduced by few mm but the springing action is still functioning well.

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#37
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Re: Setting of Compression Spring when Compressed for Long Period

04/02/2014 12:08 AM

was it compressed to solid length for 46 years?

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#38
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Re: Setting of Compression Spring when Compressed for Long Period

04/02/2014 1:13 AM

In safety valves as you know, springs are never compressed to solid length.

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