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The Bergforsk Annual Meeting, 5 May 2011

Increased production systems effectivenessthrough condition monitoring and prognostics

Rajiv Dandotiya,FilipBerglund LuleåUniversity of Technology Optimum maintenance of mill liners

Miningindustriesusesheavy‐duty equipment thatmustwork around theclock inhighly

abrasiveenvironments.Autogenous(AG)millsusedintheminingindustryandoredressing

plants are examples of major bottlenecks in the context of downtime concerning theproductioneconomy.Rubberlinersinsidethemillarecriticalcomponentinthecontextof

shellprotectionandoregrinding.Replacementandinspectionsofthemilllinersaremajor

factorsregardingmillstoppagesandcorrespondingproductionlossesduetomillstoppage.

ThepresentresearchpresentstheusefulnessofLifeCycleCost(LCC)andLifeCycleProfit

(LCP) analyses for the mill liners of the mining industries and demonstrates decision

modelsforeffectivemaintenanceplanning.Theresearchispresentedintwoparts.Part 1 dealswithoptimum replacement interval for group replacementofmill liners. It

brieflydescribestheinterrelationbetweenmaintenanceandprocessparameters.Thestudy

showstheimpactofmaintenancestrategiesongrindingprocesswhichleadstosignificant

savingsofthemill.Thephysicalexplanationofeachparameter(power,metaloutput,liner

wear,inspectionpolicy,oredensity,torqueetc)isprovidedtogiveindepthpictureof theeffect of maintenance decisions on the process economy. Based on the knowledge and

interactionbetweentheseparameters,amathematicalmodelforLCPhasbeendeveloped

foroptimizingoptimumreplacementintervalofgroupofmillliners.Thepresentresearch

simulatedtheLCPmodelfordifferentoretypesandoptimumreplacementintervalforthe

replacementofmilllinersisobtained.Theresultsofthisstudyobservedsignificantsavings

whensuggestedmaintenancepolicyisintroduced.SeeFigure1

Profit fraction Vs Optimum replacement interval

0,965

0,97

0,975

0,98

0,985

0,99

0,995

1

1,005

0 100 200 300 400

Optimum replacement interval (days)

P r o f i t f r a c t i o n

290

Figure1.Profit fractionversusoptimumreplacement interval




Part2dealswithdetailedanalysisofmilldowntimeasitfocusedatmillstopsduetomajorandminorreplacementofmillliners.Thereasonsofmultiplestopsareduetodifferentlife

cycleperiodofdifferentpartsofmillliners.Thisminorstopnotonlyleadstoproduction

lossesduringreplacementbutalso leads to losseswhichoccur duringstartuptime.The

replacementofallpartsofthemilllinersalltogetherisnotpossibleduetotechnicaland

economicalreasons.TheaimofthisstudyistominimizetheLCCbyoptimizingthegrouping

forjointreplacementandwear lifeperiodofdifferentparts ofmill liners.Theoptimized

maintenance decisions are basedon the tradeoff analysis betweenmonetary savings by

reductionofmillstopsandthecostincurredforimprovingthelifeofthepartofthemill

liners.Dynamicprogramminghasbeenusedtodeterminethelifecyclecost(LCC)foreach

feasiblescenarioformaintenancescheduling forvarious life improvementsof mill liners

parts. The scenario with minimum LCC provides the optimum grouping for joint

replacementand necessary life improvement of different partsofmill liners. The resultshowsthatanoptimumlifeimprovementcanfurtherreducetheLCC.Ademonstratorhas

beendevelopedformakingthesecosteffectivemaintenancedecisions.

Condition monitoring of fatigue cracks in rotating mining millsInfrared thermography and fatigue damage sensors have been investigated as non

destructivetestingmethodsforhealthmonitoringofrotatingminingmills.Theideaofthe

thermography method is to monitor the thermal differences on the mill surface with

thermalcamerain ordertodetectandmaintaincracksandothermaterialdamagein the

millmaterial.Figure2showthermalimagestakenduringoperationonacrackedmillhead.

The fatigue damage sensors are attached to the tips of a fatigue crack andmeasure its

propagation.Thesensorsconsistofthinconductivewireswhichbreakoneaftertheother

as the crackpropagates through the sensor, see Figure 3. To test the usefulness of the

methods, real lifemeasurementswith IR‐camera and fatigue damage sensors have been

performedon theminingmills atLKABdressingplants.Preliminaryresults indicate that

infraredthermographyisafast,easyandrelativelycheapinspectionmethodwhichcanfind

and monitor fatigue cracks and material damage in rotating mining mills. The fatigue

damagesensorsmeasuretherealcrackpropagationbutarenoteasytoplaceduotowiring

and connectivity setup. The large and fast propagating cracks together with the harsh

miningenvironmentmakethemethodnotsuitableformonitoringofmills

Figure2.Thermal imagesof amill head,crack free portiontotheleft and cracked portiontotheright




Figure3.Fatiguedamagesensor

Keywords:Maintenancedecisions;Mill liners;LifeCycleCost (LCC);LifeCycleProfit (LCP);Productioneconomy;Optimization;Replacement decision,Wear measurement device, fatiguecracks,infrared thermography,conditionmonitoring

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