Metallurgy question

S

SR_matt

Joined
Jan 4, 2007
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Hey everyone, been a while since ive been around but got a slightly off topic metallurgy question that i figure y'all would know the answer to.

What causes a spring to wear out/break in/weaken? Is it due to just being 'cycled' fully or does the force at which the spring is compressed matter? I.E. if you have a spring you compress fully by hand once is it the same as if the spring is cycled once by being slammed with a huge amount of force that completes a full cycle?

thanks
 
Both can happen, but usually a one tme compression failure is due to a defect in the spring. Thats called a fracture. Being hiot with a over rated weight that fully compresses it causes damage. A spring has a rated weight per inch of compression up to binding.

Springs usually fail due to high number of cycles causing the material to create a point defect that leads to failure in a section. Its called fatigue.

The usual culprits for spring wear out are: impact, heat, chemical attack, fatigue. A properly over-designed spring SHOULD be able to last an incredibly long time at full compression/extension at its rated RPM. most springs are not desigend to see full compression/extension and work at a portion of their rated capacity.

Not sure I helped.

Larry
Tinkerer
 
I was referring more so to 'breaking in' or a softening of the spring as apposed to it failing.

Basically if a spring is cycled through its designed and rated distance with just enough force to complete the cycle vs it being cycled with a much higher level of force and speed (but still within the design specs), is there going to be any difference in the wear on the spring between the 2 cycles?
 
There are a lot of variables in your question.

Many springs, like folder springs, have to "wear in", not due to any internal change, but due to needing the mating surfaces to burnish until they slide back and forth easily. Friction is added to the spring energy. Thus, a new folder may seem stiff ( spring plus friction), but after a few hundred opening/closing cycles,the spring seems less strong. In truth, the spring is the same, it is the friction of the spring and blade that has been reduced. Oil helps both the wear in as well as to reduce the friction. The better the polish and flatness of the mating surfaces, the less friction there is to counter. Proper hardness matters a lot here,too.

The basic mechanism of a spring loosening its "Springiness" is the changes in the grains and boundaries in the steel. If the spring is heated to a high enough temperature ,we all understand that the spring will loose some strength. What is not always understood is that heat energy isn't the only energy that can make changes in the grains. Kinetic energy can also make changes. Grains can re-crystallize at room temperature if enough energy is added. This makes larger grains. This often is called work hardening. Bending a coat hanger back and forth is the common example. It gets hot due to the grains growing, changing, and the molecular friction caused when they shear. The larger grains make the metal more brittle, and starts shearing the grain boundaries. It isn't the heat that makes the change, it is the change that makes the heat. As the grains change, and start to become more brittle, this causes fractures to form. A few micro-fractures, and there is little change. A few more, and the spring gets weaker ( just as the hanger bends easier), a lot more, and it fails catastrophically ( breaks).
The funny thing about all this is that the metal in the spring is actually getting stiffer as the grains grow, but the shearing makes for less physical attachments between the grins, so the spring gets weaker.
 
Apelt Sensei is right that in what you're asking is one of those situations whereby there are stacked variables that inevitably lend to eventual failure.
However, the prime suspect time and again is the heat caused by plastic deformation over time as a direct result of torsion and flex while the vehicle is under use:
Ex. Drive your car for a quarter mile over flat, even road and then for a quarter mile over rough terrain--the springs will be two different temps by the end of the drive.

I'm including a link that demonstrates exactly how much heat can be generated by compression, flex, and torsion:
http://www.youtube.com/watch?v=2Px5JhFToss

The man at the hammer and anvil is Larry Hagberg, and within 42 strikes, strikes a smoke off a piece of spring steel heated strictly by cold working.

Given enough time and use, we have to expect grain boundary fail and phase shift--with some areas of a spring actually getting somewhat harder and others softer, we find that the lifespan of individual leafsprings can be altered by such things as placement in the stack, the kinds of terrains frequently traveled, or exposure to the elements.

This is one of the primary reasons why many of us choose to warn new makers against using leaf springs from used vehicles--if one tries to find an appropriate make and model vehicle that used 5160, say like a 70's series Chevy, the possibility for internal fractures grows exponentially. The new maker may work his kiester off, only to have a blade fail because it had cracks already forming when it was forged.
 
Thanks for the responses, its just not exactly getting to what i am trying to figure out.

I am specifically interested in coil springs if that will matter in any way to the physics (i am purposefully trying to not list the exact situation as there is A LOT of pre conceived notions on the specific situation from people when it is discussed, but its not a knife spring, and don't worry i will tell you all what it is in a bit just want some unbiased science first) A good comparison to the situation i am looking at is if you had a a vehicle with coil spring suspension; if you take the vehicle and slowly lower it down to max out the suspension to the bump stops once, then take the same vehicle and drop it from a few feet in the air that will make it max out the suspension to the bump stops when it his, do those 2 cycles do the wear and tear to the springs or would the drop cause more wear?

basically is it the movement of a spring that causes the micro cracks/work hardening/etc or is it the force at which that movement is done that causes it all?
 
If the SAME amount of energy was added to the spring in each case, then the springs will react the same and wear the same.

Where there is a variable that may be missed is that if you slowly press down with your hands to compress the spring by 100 pounds ( just an example) it will bottom out. If you drop the car from a few feet, the energy absorbed by the spring may be 100 pounds. but the spring will bottom out by receiving 3000 pounds of impulse energy for a fraction of a second. The spring actually gets a far greater stress, but deflects the same.

If that was where you were going, then yes, the higher the force applied for the same flex/compression, the more wear/damage. This would be called shock fatigue in mechanical engineering.
 
ok yes that answers the question, thank you very much.

now a follow up, if the spring travel is limited by something to prevent it from 100% compression and that 'stop' is what is what takes the force of the "bottoming out" does that change anything or is the fatigue from the initial forceful hit as apposed from the extra force trying to compress the spring when it is fully compressed.
 
Coil binding does impart great mechanical stresses and can make a spring go out of column creating further flex distortion. It should be avoided at all costs. Bump stops can be solid object, like on a car or can be another seconday spring, creating a progressive spring rate.

As far as changing the fatigue stresses, I'll let the edumacated smarty folks discuss it.


-Xander
 
The peak stress level that a material sees while being repeatedly cycled will influence the total number of cycles to failure. Higher peak stress = lower total lives. This may not be dramatic for springs which are designed for high strains. I haven't pulled any data on common spring materials. It is often important for non-spring applications though, in which strains are low (and the materials thus have a lower threshold). The "S-N" curve for a material shows a graphical depiction of this behavior. For your 'hypothetical' application, limiting the spring to less that 100% compression should improve its life, since this reduces the peak stress in the coiled wire.

Additionally, the ratio of the peak stress to the average stress also influences the total number of cycles to failure. Assuming identical maximum stress, the material which sees a greater fluctuation as it's loaded and unloaded will have a shorter life than the one with smaller fluctuation.

-Mike
 
thanks,

I think i am just muddling the waters with not just saying the application, i am specifically talking about the recoil spring in a semi-auto pistol (i didn't want to come right out because i didn't want to get the non technical answers that i kept seeing on gun forums of just "no its different"). Basically does hand cycling wear it the same as shooting it? I know there are much higher forces but since the springs are never fully compressed during cycling does the fact the round hits with more force initially cause extra wear or not?
 
Put it this way. You will wear out long before your hand cycling will. The recoil springs on quality firearms are meant to handle 10's of thousands of rounds. In fact Sig does 10k and 20k testing on their new production handguns. The force of the shot will not overstress the spring and will last for most normal shooters lives. If you are into ipsic or 3gun comps were you shoot 1-2k in a weekend you might need to replace your recoil spring occasionally. There are other factors like shooting light loads that might require a change for proper operation. On cheaper firearms the heat treat may not be properly executed so all bets are off. But even then most will function for thousands of rounds. Hand activation of the slide will cycle the spring but not significantly reduce the lifespan of said spring. I like to dry fire in the LR. Just make certain there is no ammo anywhere near you.
 
The is a huuuuge difference between the chrome-vandium in car springs, and the smaller silicon chrome springs seen in pistols.

The type of pistol will vary too--the "standard" reply to questions about break-in for semi-custom 1911s (such as Kimber or Wilson) is between 500-750 rounds, and then determined by the type of load shot.
I've seen some factory recoil springs, like Kimber which uses a 16# spring, begin failing around 2k rounds, but using medium recoil target loads--+P defense loads would cut it down considerably.
I personally use a Wolff 18.5# spring in my 1911s, and have seen them last upwards to 5K rounds before giving out, again using just light to medium target rounds.

I am seriously piqued about this--typically we clip springs rather than try to secure and compress as it not only cramps the minimal spacing around the guide rod and spring, but will cause timing issues. If you're talking about hand cycling a gun to break it in, you better be prepared to do about 10K cycles.
Remember this--the heat dampening effects of Si in recoil springs is there to dampen not only heat conduction from the barrel, but the force of cycling.
I don't want to make a call on a type of spring to substitute without knowing the gun, for example, a StormLake or Wolff 18.5# recoil spring in a Glock 26 will affect cycling and timing considerably between the two brands--Lake uses a 1/2" loop at 6", the Wolff is also 6-6.5" (at least they were when I last replaced one 5 years ago) but the coils are separated by 1/4". Using a Lake spring requires clipping coils to fit a Glock and cycle cleanly.
 
Yeah the specific reason i am asking is because of an issue i am having with cycling on cheaper target ammo that people claim as 'weaker' and I have seen the issue resolving for some with more 'breaking in' but since i don't have the money right now to go buy a bunch of ammo to run through the gun i was trying to find out if hand cycling would help at all or if i would just be using a glock as a resistance work out ;)

The threads on some of the gun forums i saw were saying that hand cycling a few hundred times wouldn't do much compared to just shooting a couple of mags through but like i said i didn't know if the info was valid since it is coming from some people that also talk about springs getting "set" from being left compressed which I had heard was false from more reliable metal working sources.

Ed, its a glock 36 and I've seen the replacement springs from LWI, just trying to get the stock stuff working at minimal cost. I have shot enough to be past the "break in" (but then again since I'm not using NATO spec rounds as the factory probably assumes it might not be as much as they expected) but just trying to see if hand cycling it at this point can accomplish anything other than a good arm work out (heck honestly if 10,000 hand cycles will accomplish something then i actually might give it a try, i got plenty of time on my hands but not much cash and i can use some extra exercise ;) ).

I know this isn't knife related exactly, and if we have gone to a point where this needs to be moved mods please do so, but i figured it was metal related and i would get more of educated answers based on metallurgy/science here than other places.

Thanks
 
Heh, figured a G26 or 36, they're tetchy out the box (I'll spare you the 1911er's ribbing--tis neither the time nor "forum" for such ;)) but as another .45 man, don't worry--within 250-500rnds she'll calm down. HSM or Rem PMI yellow box will take care of that--last time I checked win whitebox was costing at 32 box a hundred. Trust me, I know the hurt on .45ACP, but we could be worse off--look at what .30 Carbine or 5.7x28 folks are paying.
To close you out--I still suggest you be patient and throw'em down the pipe rather than hand cycling, letting a slide slam home on any pistol without pushing a round in the chamber is never good for the gun. Lookit like this--buying a 16# spring, futzing installing and then retuning the cycle rate (and all the headaches that can entail) can be better set to use practicing with the pistol.
 
yeah. The short of it is that i kind of doubt my issue is totally related to a stiff main spring but i figure making sure it is broken in well will confirm/deny that.

Thanks for the helps guys, i know it wasnt knife related but i knew those with the metallurgy knowledge would be here.
 
Recoil spring--Glock's don't have a mainspring like a 1911 since it's a striker fired pistol.

I sent you an email with some instructions on break in check, you can hit me up through there if you need further help.
 
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