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Plastic vs metal gears / parts

  1. Jan 14, 2015 #1
    Hello,
    I wonder whether I can replace the Metal gears and other parts with Plastic material? If so, what kind of plastic material should I use? There is no heat and the force is also not that great but the speed is.
    This is not for toy but industrial machinery, with gear diameter of about 10 inches.
    Thank you.
     
  2. jcsd
  3. Jan 14, 2015 #2

    OldEngr63

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    Gold Member

    To answer this question properly, you need to do two things (at least):
    1) Evaluate the loads on the gears (actual number) at nominal condition and at max condition;
    2) Design a plastic gear, and compute the stresses and wear resistance potential.
    When both of these are done, you should have an answer to your question.
     
  4. Jan 14, 2015 #3
    Maybe, what specifically is the application? The force and speed being great or not is really relative.
     
  5. Jan 14, 2015 #4
    Here is what I'm trying to prototype using plastic gears and other components.

     
  6. Jan 14, 2015 #5


    1] I guess the load is just to rotate the gear, which initially have mass resistance of 4-5 lb, I guess. Not more than that. I don't see any other load coming in except the tension of the rope/thread from the bobbin.
    2] Little difficult for me. Will have to ask an engineer. But considering above machine. I think not much load is there.

    But had anyone used the Plastic gear in industry? I'd like to know the kind of plastics I can use. Better/Best etc? Their names? Which would be cheaper than Steel/Iron/Aluminium?
     
  7. Jan 15, 2015 #6

    jh0

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  8. Jan 15, 2015 #7
    Thank you, that was good one.
    Can I use the mold to make plastic gear or is there any other technique to create a gear? Like metal gears are made on machine?
     
  9. Jan 16, 2015 #8

    jh0

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    Plastic gears can be milled in the same manner as metal ones. Feed rates are greater and production is faster and cheaper.
    I do not see why they could not also be made by injection moulding for mass production, if the plastic is suitable and very high precision is not needed for the particular application.
    I don't know much about plastics, but I believe that many plastics absorb humidity and the dimensions can change in the process, also thermal expansion is greater than steel, so for very precise gears plastic (even machine milled) could be a problem.
     
  10. Jan 16, 2015 #9
    Well for the machine shown in video, these gears are in back side of the machine. One gear is driven by motor and that in turn rotates all gears in clock-anti clockwise fashion alternately, which touch each other. I'll have to calculate the resulting load of all these gears on the driving one and then decide whether plastic or steel. As of now don't know how much load the plastic gears can with stand if they are made up of Nylon - 6 or 66 who has 8 inch diameter and possible largest gear pitch.
     
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