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  • 1.  Mill bolts

    Posted 09-21-2023 01:19 PM
    Would any of he members have experience in bolt breakages in mills?
    Particularly on the discharge?

    I ask because I’m currently study what could cause these “pre-mature” bolt failures

    👷🏾‍♂️


  • 2.  RE: Mill bolts

    Posted 09-22-2023 06:53 AM

    Hi, I have no experience in mills however in the oil and gas industry, I have encountered studs/bolts failures due to the following;

    • Normal wear and tear usually due to corrosive environments. Degradation due to corrosion.
    • Application of improper torque values to studs/bolts during repairs. Too high a value for a particular stud/bolt material.
    • Re-torqueing of corroded studs/bolts to original values. In cases of small leaks on exchanger heads, we would usually re-torque studs if the gasket cannot be immediately changed.
    • if flange gaps are uneven all the torque would be applied to bolts/studs which may be under strain.

    Hope these helps.



    ------------------------------
    KAMARIA DUNCAN
    Mechanical Technician III
    P.P.G.P.L
    Point Fortin
    ------------------------------

    Original Message


  • 3.  RE: Mill bolts

    Posted 09-22-2023 07:53 AM

    Send me some picts of failures and I can hopefully give you some insight.

    Without seeing picts or knowing anything about the application, I can give some general things around bolt failures.

    • Most bolt failures are fatigue and specifically bending fatigue.  If it is a rotating bolt circle like on a roll or shaft then every revolution is a bending fatigue cycle.  Two choices - improve fatigue strength or reduce cyclic load on bolts.
    • About every bolt failure issue I've encountered has been solved by proper bolt preload procedures.  There are many things to do correctly in preloading a bolt.  Proper bolt preload getting joint clamp load is also the best prevention of bolt fatigue as well.  The resulting joint clamp load insulates the cyclic bending stress on the bolts.  
    • A few bolt preload (torque) tips - use lubricated torque conditions.  This improves preload scatter around the bolt circle.  Do star pattern tightening and ramp up torque in 4 stages to final assembly torque.  Rotate element on each tighten sequence.  Look at more accurate preload methods - turn of nut, ultrasonic.  
    • There are design improvements that can be done to improve service factor or design margins too if the external load of the application has increased or original design was small.  Some might be higher strength bolts - higher preload so higher fatigue resistance.  Load sensing bolts.  Bolt loosening washers - Nordlock is best.


    ------------------------------
    Randy Riddell, CMRP, PSAP, CLS
    Reliability Manager
    Essity
    Cherokee AL
    ------------------------------

    Original Message


  • 4.  RE: Mill bolts

    Posted 09-27-2023 03:00 PM
    Edited by Benjamin Prior 09-27-2023 03:00 PM

    HI Lesiba,

    I'm guessing you're having issues with your liner bolts on your discharge end (vs the shell / girth gear studs)? I agree with Kamaria and Randy. Most of the time these are due to preload issues during installation. It's fairly common practice to "re-torque" the liner bolts after around 24 hrs of operation. That'd be my first check.

    If it's only on the discharge end, it may point to some other issues. Have a look for washout of the mill shell behind the liners during the next reline.

    There are a few products that can help monitor these issues too, enabling you to act before the bolt breaks. "Smart" bolts with load cells inside the bolt are a good option here. There are a few companies with products in this area. BoltSense by Copper State is one I'm familiar with. Their product uses a bluetooth transmitter to send the bolt tension back to either a receiver or to a handheld device (e.g. cell phone). They have been used in exactly the application you've mentioned in the past and are a relatively cost-effective option.

    Copper State Bolt & Nut Co. :: Load Monitoring Fasteners

    This will only allow you to collect more data however, and obviously won't address the root cause of the breakages. Feel free to shoot me an email (or we can discuss here) if you'd like to chat further.



    ------------------------------
    Benjamin Prior CMRP, BEng, MBA
    Principal
    Priority Consulting Inc
    Berkeley CA
    ------------------------------

    Original Message


  • 5.  RE: Mill bolts

    Posted 09-28-2023 06:51 AM
    Hi Team

    This how the failures are looking 👀

    Regards

    ---------------------------------
    Lesiba Moja BEng
    Reliability Coordinator
    First Quantum Minerals
    Kempton Park
    ---------------------------------



    Original Message


  • 6.  RE: Mill bolts

    Posted 10-02-2023 02:21 PM

    Looks like reversed bending fatigue.  Looks like rather large bolts from the picts which would make low bolt preload more likely as well contributing to fatigue.  Do you have the proper tools and info for the proper bolt torque application to preload bolts? 



    ------------------------------
    Randy Riddell, CMRP, PSAP, CLS
    Reliability Manager
    Essity
    Cherokee AL
    ------------------------------

    Original Message


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