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Thread: The effect of lubricant on torque spec

  1. #1
    Join Date
    Dec 2015
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    Default The effect of lubricant on torque spec

    I finally got all my rollers installed on the bottom of my d6 with new CAT bolts and washers ( made in China....)

    The torque spec is between 150 and 170 ft lb. I used a moly type assembly lube on the threads. It is my belief that using lubricant on the fastener (bolt) increases the installed stress on the bolt given the same amount of tightening torque.

    Example : torque a lubricated bolt to 100 ft lbs. the stress on the bolt is - say - 75,000 psi
    Now torque the same bolt with no lube to 100 ft lb. the stress on the bolt is 30,000 psi.

    These numbers are just to make my point. And to lead to my question...... Must I consider the lube on my 9/16 NF carrier bolts when calculating a torque spec ? Assuming yes, who can suggest a torque spec based on the above info.?

    Thanks - don't want to break a bolt or have one come loose!

  2. #2
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    long island NY, Hancock Ma
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    i really can't speculate on a dozer machinery spec--but i would surmise that it would not be dependent on the lubrication of the threads--every mechanic would be using a different lubricant and amount applied My experience is with structural steel applications--our spec called for a 30000 lb load on a 7/8 diameter A325 bolt. we would take a load cell test each morning and calibrate a torque wrench for the number of foot lbs to achieve this tensile load with no lubricants--the contractor would always use an air impact wrench. I would take my manual torque wrench and calibrate it also, and then would spot check the contractors installations.
    As long as you stay below the ultimate tensile strength of the steel bolt and be in the yield strength range it shoudn't matter much where you are--
    does this make sense?? OM--your opinion please!
    Cat 941B, Cat D2 4U, Cat D3B, Cat D4 7U, Cat D6 9U

  3. #3
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    Use either one of these charts......

  4. #4
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    well what little i know about this is there a 30% difference between lubed and non lubed. so if your looking for 100 ft/lb when lubed it only takes 70 ft/lb to get the same stretch. but this has been when working with BIG stuff 2"-4" range bolts which where most of the time studs in drag lines not bolts. the rule of thumb is it would be a dry torque unless it tell you lubed it. now i know what kind of lube will change things. this is onsite passed down info so consider that when making your decisions as i have never read up myself. i don't know if i answered your question or just made more points to question's .

  5. #5
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    great tables! surprised at the big differential in the first table between lubricated and ant-seize
    Cat 941B, Cat D2 4U, Cat D3B, Cat D4 7U, Cat D6 9U

  6. #6
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    Dec 2015
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    Thanks all. I torqued them to 100 ft lb ( with lube) . I will run the machine for a few hours ( someday......)
    And the have Oilslick crawl under there and recheck them.

    Glad I axed that question!

  7. #7
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    That seems low by either chart using lubed threads.

  8. #8
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    The CAT hardware is made in China???

  9. #9
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    My Cummins manual shows to lubricate all the critical bolts and both sides of the washers.

    Iíll look tomorrow and see the torque difference between lubed and dry same size bolts.
    Attached Images Attached Images

  10. #10
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    Quote Originally Posted by ETD66SS View Post
    The CAT hardware is made in China???
    By the looks , not much they don't make in china .
    http://www.caterpillar.com/nl/compan...apd/china.html

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