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  1. #1
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    Question Weakining Spring Steel??

    I need to weaken a compression coil spring. It is made from a special corrosion resistant steel [C 72 UNI 3545:confused:] so nipping down to the local "small coil spring making shop" of which there isn't one anyway, is not an option...thus the need to "fix" this one.
    I was hoping that it could be annealed to some extent or something similar.
    If there is anyone who has any knowledge of spring steel and how to work it please share your knowledge.

    Fingers crossed,
    Phill.

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  3. #2
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    Spring steel is typically the same as any medium/high carbon steel/alloy and of course can be annealed to whatever you want it to be.

    That is a spring serial number, not the kind of steel it is, so it's pretty hard to find what temperature it needs for annealing, hardening or tempering.

    What's wrong with the spring? Has it died, too strong or something else?

    Can you get a replacement for it, or do you need to change this particular spring?

    The problem being, that if it is in fact, an oddball steel, you might shatter it using water or oil as a quench, nothing might happen, you could completely ruin, etc, etc.

    I guess I am saying, more info about your valve is required.

  4. #3
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    Schtoo,
    from what I can see the C72 IS a grade of spring steel.....the following from relevant sites...."The standard materials used in the manufacture of rollers is chrome steel. Depending on quantity, Moore International can supply rollers amde in Carbon Steel C72, Tool Steel S2, Stainless Steel AISI 420, AISI 302 and AISI 316."
    and "Rubber: Vibrostop Elastomer with metal insert.Spring: C72 spring steel with powder coated epoxy coating."
    I looked up the other number sequence and it refers to, I think, a Silicon Chrome formula ?? "SiCr 8 UNI 3545" and another "SiCrMo 6. UNI 3545"
    All way above my head but may mean something to someone in the know.
    Phill.

  5. #4
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    This may narrow it down a bit if anyone understands the meaning of it??
    UNI 3545 45SiCrMo6
    Alloy spring steel. Standards:
    EN89-71(Pr) - DIN17221 – UNI 3545 - ASTM

    This spring is from a PRESSCONTROL pressure pump controller and is available in only one strength. It is what controls the "no-flow" pressure in the water pipes and is too high for my application. To lower the pressure I need a weaker spring. It is made in such a way that it is ground flat on each end so as to apply even pressure around its circumference, so I can't just cut a bit off one end. Does anyone know if compressing it in a vice and heating it would shorten the un-compressed length without totaly destroying the springiness?
    Thanks,
    Phill.

  6. #5
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    You can put it on a brick and heat it to dull or bright red and let it cool to anneal it, though it will probably work-harden later.

  7. #6
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    Quote Originally Posted by ptrott
    This may narrow it down a bit if anyone understands the meaning of it??
    UNI 3545 45SiCrMo6
    Alloy spring steel. Standards:
    EN89-71(Pr) - DIN17221 – UNI 3545 - ASTM

    This spring is from a PRESSCONTROL pressure pump controller and is available in only one strength. It is what controls the "no-flow" pressure in the water pipes and is too high for my application. To lower the pressure I need a weaker spring. It is made in such a way that it is ground flat on each end so as to apply even pressure around its circumference, so I can't just cut a bit off one end. Does anyone know if compressing it in a vice and heating it would shorten the un-compressed length without totaly destroying the springiness?
    Thanks,
    Phill.

    If you anneal it the spring will loose it's ability to spring back to its orignal shape. To reduce the springs force you would need to reduce the thickness of the spring without over heating the spring and annealing it. Very difficult to do because you will need to reduce the thickness over the whole length of the spring otherwise you creat a weak section that will eventually fail.

    One way of possibly reducing the springs thickness is to "jamb" the spring onto a piece of round wood. Then lightly rotate it on a beltsander without over heating it.

    Sounds more like you should try and find a supplier of springs on the internet and see if you can find a spring with the same dimensions that exerts less force.

  8. #7
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    That's funny, I got nothing on any of it, but I did get a hit on the C72 UNI3545, which is why I know it came from a valve. A flow control needle valve made by an Italian mob is what I got.

    If that's the case, 72 typically means that the steel is 0.72% carbon.

    Thinking about it, changing it's temper isn't going to do what you want it to do. You need to either add more coils and/or use smaller wire to change the spring rate.

    How big is the spring? How long, spring diameter, wire diameter, how many coils? I think that you might be able to find a sprig to do the job much easier than fooling around with you current spring, which might not actually accomplish anything.

    Sorry about the previous post, it was late, but I should have realized what you wanted to do anyway, and what the solution is.

    If it comes down to it, you might get a crash course in spring winding. Not that difficult to do, and you can then make springs however you want them.

    (Mental note, add spring winder design to lathe)

  9. #8
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    Trying to re-treat an exotic alloy spring is pretty much a one-way road to ruin. The big boys have ovens, optical pyrometers, timers, shelding gas etc. & do them in batches.

    Over-stressing the spring in a vice for a while may have some effect -ie - squish it all the way down & leave it for a few hours/days.

    The more 'normal' way would be to cut off the spring one turn at a time, bend the fresh end down into place & grind a new flush face, then refit - possibly after stretching the spring back to the ame length as it originally had. Then repeat if needed.

  10. #9
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    Phil,
    all the pump controllers I've seen have some form of adjustment for both the cut in and the cut out. Is there no adjustment at all, or is the adjustment not enough? I'm assuming the spring holds a pair of contacts open (or closed). Is it not possinle to bend the contacts to change the pressure exerted by the spring?

    Mick
    "If you need a machine today and don't buy it,

    tomorrow you will have paid for it and not have it."

    - Henry Ford 1938

  11. #10
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    Quote Originally Posted by bsrlee
    The more 'normal' way would be to cut off the spring one turn at a time, bend the fresh end down into place & grind a new flush face, then refit - possibly after stretching the spring back to the ame length as it originally had. Then repeat if needed.
    The thing is, while you may end up with a spring that will still fit, you just increased the rate of the spring, in effect, going in a whole other direction than what was intended.

    Mick, from what I saw googling last night, I think it might be a needle valve with some kind of backflow thingy. IIRC, it limits flow in one direction, and wide open in reverse direction, there was a minimum pressure to make the backflow valve work, and I am guessing Phil wants to reduce the pressure needed for the open back flow to kick in.

    Wether or not changing the spring will work or not is a whole other can of worms, but might as well give option A a shot huh?

  12. #11
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    The spring is 100mm long at rest. It has 10 coils of 5mm thick 'wire'.
    It is in a chamber and presses on a diaphram which has a water chamber on the opposite side to the spring. When the water pressure exceeds the spring strength, the diaphram moves and operates a megnetic reedswitch. There is a 'flow-switch' in series with the reed switch, so if there is some flow the pump will not cut off when the diaphram compresses the spring back, if there is no flow then the cct. is complete and the pump controller switches the pump off. I want the pump to switch off at a lower pressure. To achieve that I need a weaker spring. (There is no adjustment) Shortening it may do the trick, but I need to know how to bend the cut end down to the next coil so I can grind a flat circle for it to seat with. If that fails I will have to find a spring maker and get one made if it is not cost prohibitive. The other option is a pressure reducer, but one with sufficient flow would cost a mint.
    I cannot afford to have it loose its 'springiness' so heating seems to be NOT the way to go??
    Reducing the diameter of the 'wire' may be an option, if it doesn't matter that the wire won't be round anymore. I could put it in the lathe with a 'former' inside it and turn it slowly while grinding it??
    Thanks,
    Phill.

  13. #12
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    Grinding it down might do the trick. Make sure when you are done that it's effectively polished, because if you have lots of scratches in the spring, there's lots of stress raisers and the spring might well break. Go slowly and test often, because there's a good chance you might go too far and render the spring useless.

    I'd have to think you should be able to find a spring somewhere off the shelf that will suffice though. What kinda OD is the thing. Someone might know where to find one, with any luck that is.

  14. #13
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    You say the spring is 100mm at rest but how long is it compressed to in the chamber ??

    Altering the spring in any way will only make the pressure higher and increase the chance of a stress fracture.

    However there is more than one way to skin a cat , if you can modify the chamber so it is slightly longer it will reduce the switching pressure without altering the spring, also is it possible to move the reed switch slightly to make it operate earlier, or maybe increasing the magnet strength to make the reed operate at a lower pressure.

    I would try these or get another spring alltogether , modified springs never last
    long.

    Good luck
    Iligitimus non carbourundum

  15. #14
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    Twodogs, I would think that if it is is 10 coils of 5mm thick wire then it would be close to 50mm long when compressed, although I have not compressed it to see. Modifying the chamber or the switching gear is not an option.
    Schtoo, the OD is 32mm but that is not critical. There is room for a bit larger coil. One 'off the shelf' would need to be of a similar material which is Highly Corrosion Resistant.
    It would certainly be convenient to get one 'off the shelf', that's why I tried Davery Pumps first, but no go.
    Phill.

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