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Thread: Deforming poweful springs for assembly

  1. #1
    Associate Engineer
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    Jun 2013
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    Deforming poweful springs for assembly

    Hello,

    I'm working on project to construct a custom mixing machine, and the assembly requires that a number of very powerful springs be deformed during assembly so that they will remain in compression at all times during the machine's operation. The most powerful set of springs consists of 16 die springs with an equivalent spring constant of about 10,000 lb/in- they only need to be deformed by half an inch during assembly, but the springs are much too strong to be deformed by hand.

    My current deisgn will allow a plate (around 50 lbs) to be placed above the strongest springs and screwed into place using nuts on 4 threaded rods, but the force required to do so will be extremely large. Some parts of this assembly may be unsafe, and I was wondering if anyone has experience or ideas for how to handle and manipulate powerful sets of springs without risk.

    Spring compressors might be a possibility, but because of the large number of springs they might be impractical.

    Thanks for your advice!

  2. #2
    Technical Fellow
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    Hi, interesting issue. As is so frequent here you have not supplied anywhere enough information.

    The diameter and length of the springs.
    The coils count and air gap between coils.
    The individual load when compressed that 1/2".
    How many times a day this has to happen for assembly.
    If once a day then a manual method may suffice, if 1000 times a day then automated is a must.

    Over to you.

  3. #3
    Associate Engineer
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    Jun 2013
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    I didn't mean to be vague- the machine has many different springs and I thought there might be some general guidelines, but this is the sheet for the strongest spring (16 of these act together):

    [URL]http://www.leespring.com/product_spec.asp?partnum=LHL2000B04+++++&springTyp e=C&subType[/URL]

    (diam 1.83 in, free length 4 in, 5.8 coils, spring rate 664 lb/in)

    the air gap is about 1/3 inch at free length.

    individual load on each spring = 664lb/in * 0.5in = 332 lb
    total load = 332 lb * 16 = 5,312 lb

    Assembly will happen only once, and probably once per month or so for maintenance, but no need for automation.

    Thank you

  4. #4
    Technical Fellow
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    This is sounding to be quite a complex thing and not something that can be generalized about.

    Are the spring ends in pockets at both ends?

    Do they have to be compressed all at one time? I know you stated that is how you are using threaded rod, but is it possible to do them one at a time?

    How much total spring deflection is there when the machine is operating? Could you have posts inside the spring that are just shorter than maximum deflection. Each post could have a cross-drilled hole such that each spring can be compressed (spring compressor) and a cross-pin used to hold it down until the assembly is in place then the pins removed one by one. They need only be held down by about 0.015" below fully-compressed working length.

    You also mention "parts of this assembly may be unsafe" which prompts me to suggest finding a local Engineer experienced in this kind of machinery design to assist with the basic design. There are probably a hundred different ways that this issue could be approached in the design, and to my thinking, way beyond the scope of this forum. Certainly compressing 16 springs with that amount of total force requires some very careful design considerations.

  5. #5
    Associate Engineer
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    Jun 2013
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    Good questions- the spring ends are in pockets, and the springs will need to be compressed at the same time- your suggestion about the cross-pins may be a possibility, however.

    I think maybe I should have mentioned sooner that I'm an intern trying to learn- I don't claim to be a master machinist, and it is likely that we will be contracting outide help in addition to the staff in our machine shop. I'm currently writing up a step-by-step guide for the construction of this machine, and soon I will be able to ask more specific questions (although probably not on a forum.)

    Thanks for your input

  6. #6
    Technical Fellow
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    Ha, funny you should mention the intern thing. I was coming in here this is morning thinking I would have to tread lightly with any further comments. Thinking more about it, it was sounding very much like a poor design approach to have so much pressure pre-loaded during assembly.

    An experienced Engineer will probably lead you towards the pre-loading being part of the start up process of the mixing machine, rather than at the assembly stage. Especially so if the springs are actively involved for monthly maintenance. Releasing the pressure is an area that would be prone to accidental uncontrolled release with great potential harm to human life and limbs.

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