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  • Hydraulic System to prevent thermal expansion

    Discussion in 'The main mechanical design forum' started by arsal2607, Apr 1, 2014.

    1. arsal2607

      arsal2607 New Member

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      Hi,

      Is there any hydraulic system that can prevent the expansion of metal due to high temperature? I need this system for a closed vessel where space is also a constraint. So thickness required should be few mm?

      I will appreciate your guidance.

      Thanks
       
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    3. Erich

      Erich Well-Known Member

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      Prevent the expansion of what?

      I cannot visualize what you are trying to accomplish.

      Just a general comment. It is usually better to work with material properties than to fight them.

      Clever design can compensate for thermal expansion in some cases.

      Lastly there is a material called INVAR that has essentially 0 thermal expansion over certain temp ranges.

      It is a nickel-Iron alloy.
       
    4. Designdrive

      Designdrive Member

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      Use Helical Compression spring

      Hi,

      It can be done correctly if we know the full details, Its OK. Istead of going for a Hydraulic system, you can try fixing a Helical Compression spring against the expanding metal. This metal expansion cab be slowed and stopped by a compression spring.


      Designdrive
       
    5. JPfalt

      JPfalt Member

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      Unlikely

      The answer to your question will depend on the temperature swing experienced, the pressure inside the vessel and the material of the vessel.

      In any case, the difference between the dimension of the thermally expanded material and the dimension you want to maintain is the strain on the material. You need to back calculate the compressive stress on the material. In most cases where the temperature is high and the materials are fairly mundane, you will yield the material in compression and it will contract to a smaller size when cooled bakc down.

      This sort of problem is referred to as a stress calculation of a member with "built in edges".

      To use hydraulics to counteract expansion, you would need build another shell around the vessel and use an adaptive hydraulic control that would increase the hydraulic pressure as the internal shell heats. In the event that the hydraulic pressure exceeds the pressure inside the vessel due to high temperature of a low pressure working fluid, then you also need to take into account buckling of the internal vessel. Pressure vessels will fail at much lower pressures when externally pressurized.
       
    6. arsal2607

      arsal2607 New Member

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      Hi,

      Many thanks for your valuable inputs. I actually need an O-ring which will serve as a seal. This O-ring will be over aluminum or any other metal that will expand around 200 C. There will certainly lot of pressure as well which will try to displace the o-ring from the metal as in my application overburden will be lower than the internal pressure (I am trying to fracture a core by steam).


      Is there any material of the O-Ring that has lower coefficient of expansion than aluminum and will rather contract and stick to its place at higher temperature and pressure conditions? That will provide a better seal. I also tried to have mechanical clamps over the O ring rubber sleeve section but due to metal expansion they cut the rubber and seal was not intact.


      Thanks !
       
    7. JPfalt

      JPfalt Member

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      O ring seal

      I would suggest you look into using a Teflon backup ring with a high temp o ring. The backup ring will prevent the o ring from extruding and cutting. Size the depth of the groove to be correct at temperature.

       

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