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  1. #1
    Join Date
    Jan 2005
    Norfolk, U.K
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    Copper plating?????

    overhauling a compressor on one of the plants i look after and the big end bearing shells (white metal) look to me as if the may have some copper plating, i was wondering if any one else has seen this before and is it down to moisture in the system?

    Any thoughs or ideas appriciated.
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  2. #2
    rbartlett's Avatar
    rbartlett Guest

    Re: Copper plating?????

  3. #3
    rbartlett's Avatar
    rbartlett Guest

    Re: Copper plating?????

    Quote Originally Posted by Marc O'Brien
    Heat firstly, secondly, excessively close tollerances between surfaces, thirdly, moisture/acid.
    uninstantiated statement??



  4. #4
    Join Date
    Aug 2005
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    Re: Copper plating?????

    Acid is generally created in the system by a combination of the following; heat, moisture, contamination admitted during installation or service (flux, etc.), or non-condensable gas.

    The hottest location in the system is the compressor discharge valves. If the entering suction vapor has a higher temperature (increased suction superheat), this heat is greatly magnified during compression. In effect, any increase in suction superheat also increases the discharge temperature.

    Continued operation with this condition can contribute to acid formation, which I believe occurs from the high discharge valve temperature, water, and oil breakdown.

    Leaking (or broken) discharge valves can also greatly increase the discharge temperature, since the gas is continually being compressed and re-expanded in the cylinder.

    Non-condensable gas increases the overall discharge pressure, which increase the actual discharge temperature.

    When the acid content begins to reach a specific level of contamination, the acid begins to strip copper alloy out of the piping. I have seen this leaching behavior before with certain heat transfer fluids. The copper is then deposited on the bearing surfaces, since I think the copper alloy is in suspension with the oil.

    There is probably some form of electro-plating occurring also with stray electrical currents similar to an anode and cathode.

    I have seen the internal gears of oil pumps that are copper plated, besides the bearing surfaces. This is why I think the oil is the transport mechanism.

  5. #5
    Join Date
    Feb 2005
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    Re: Copper plating?????

    What was the type of refrigerant used in the system?
    Was it R22 with mineral oil?

  6. #6
    Join Date
    Jun 2005
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    Re: Copper plating?????

    Marc, can you elaborate a bit more? I don't claim to know a lot about copper plating.

    It's a lovely day to pump some gas

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