LOCKED AND LOADED

The Australian Mining Review - - TRANSMISSI­ON TESTING -

Load test­ing of power trans­mis­sion units is a proven cost sav­ing tool as any prob­lems can be eas­ily iden­ti­fied and rec­ti­fied prior to on­site in­stal­la­tion. Loaded and un­loaded test­ing of crit­i­cal gear drives proves that in­di­vid­ual com­po­nents and com­plete as­sem­blies are fit for ser­vice be­fore ex­pen­sive trans­port, labour and down­time is in­curred.

The AMR vis­ited Gear Drive Ser­vices (GDS), in Wan­gara, WA, to look at the process of dis­as­sem­bling, check­ing, re­fur­bish­ing and load test­ing gear­boxes and drives com­monly used in min­ing ap­pli­ca­tions.

Gear Drive Ser­vices spe­cialise in in­dus­trial power trans­mis­sion ser­vice and re­pair. The com­pany re­cently de­signed and built a 6000m2 work­shop specif­i­cally to ac­com­mo­date over­haul, re­fur­bish, load test and en­gi­neer all types of in­dus­trial re­duc­ers, speed in­creasers, wind tur­bines and fluid cou­plings.

STRIP AND AS­SESS

The first step in the process is to strip down the drive unit and as­sess its con­di­tion. This step is com­pleted on ev­ery com­po­nent which comes in for over­haul.

A de­tailed re­port is com­pleted on the gear­box to in­clude a min­i­mum of gear mesh con­tact, gear mesh back­lash, bear­ing/shaft end floats, vis­ual in­spec­tion on ev­ery com­po­nent, di­men­sional in­spec­tion on ev­ery com­po­nent and non­de­struc­tive test­ing (crack de­tec­tion) on gear­ing, shafts, cou­plings and hous­ing.

The con­di­tion of all com­po­nents is pho­tographed and a de­tailed writ­ten re­port com­pleted.

All com­po­nents must ad­here with OEM tol­er­ances and spec­i­fi­ca­tions.

The qual­ity of re­paired or man­u­fac­tured com­po­nents meets or ex­ceeds OEM spec­i­fi­ca­tions.

ASSEM­BLY

Assem­bly on ev­ery com­po­nent is car­ried out fol­low­ing strin­gent pro­ce­dures and a very high stan­dard of work­man­ship. Bear­ing/shaft end floats are checked and set to OEM spec­i­fi­ca­tions.

Spi­ral bevel gear sets are setup to achieve the op­ti­mum blue con­tact/ gear mesh and the cor­rect back­lash, al­ways while con­sid­er­ing things such as ther­mal growth, the type of bear­ings in­stalled and the di­rec­tion of thrust caused by a com­bi­na­tion of left or right­hand gear­ing and di­rec­tion of ro­ta­tion.

He­li­cal gear­ing back­lash and blue con­tact is checked, while con­sid­er­ing gear tooth pro­file cor­rec­tions such as crown­ing and tip re­lief.

All di­men­sional mea­sure­ments and set­tings are recorded, pho­tographed and dou­ble-checked by an­other tech­ni­cian.

LOAD TEST­ING

Load test­ing is com­pleted on all over­hauled drives and fluid cou­plings. Gear Drive Ser­vices have a highly ad­vanced test­ing fa­cil­ity and some of the most rig­or­ous test­ing pro­ce­dures in Aus­tralia, with the ca­pa­bil­ity of test­ing in­dus­trial re­duc­ers, speed in­creasers, wind tur­bines and fluid cou­plings.

Their ad­vanced con­trol sys­tem can test dif­fer­ent styles of power trans­mis­sion gear­boxes and sim­u­late ex­act op­er­at­ing con­di­tions on­site, with the abil­ity to test gear­boxes with a power range from 10kW to 3500kW rang­ing from ra­tios of 5:1 to 900:1.

Test­ing such a broad spec­trum of power and ra­tios has its chal­lenges. Ev­ery setup must be care­fully thought out con­sid­er­ing that some load tests ex­ceed 250,000Nm of torque at the gear­box out­put shaft.

Load test tool­ing, adap­tions, test shafts, cou­plings and mount­ing brack­ets need to be specif­i­cally en­gi­neered for ev­ery load test with ex­pected power and torque fig­ures kept in mind. The lat­est up­grade to the fa­cil­ity will per­mit the test­ing of full drive as­sem­blies. This means that a com­plete drive assem­bly, such as a ship loader or bucket wheel drive, can be load tested util­is­ing the fi­nal in­stalled mo­tor and cou­pling ar­range­ment.

The cus­tomer’s mo­tor will be con­nected and tuned to our con­trol sys­tem so a load test can be car­ried out on the en­tire assem­bly.

Load test­ing has proven to be a vi­tal and crit­i­cal step of the over­haul process as any mi­nor prob­lems can be cap­tured and rec­ti­fied prior to in­stal­la­tion on­site, thus sav­ing trans­porta­tion costs, in­stal­la­tion and re­moval costs on­site and ul­ti­mately un­ex­pected down time and loss of pro­duc­tion. Our lat­est up­grade will fur­ther­more prove that all com­po­nents are fit for ser­vice prior to ar­riv­ing on­site and im­prove the re­li­a­bil­ity of cus­tomers’ core com­po­nents.

Gear Drive Ser­vices have as­sisted in de­vel­op­ing a con­trol sys­tem specif­i­cally for load test­ing in­dus­trial drives. The main ob­jec­tive for the con­trol sys­tem is to sim­u­late the ex­act op­er­at­ing con­di­tions any drive would see while in ser­vice.

The way in which dif­fer­ent types of in­dus­trial drives ex­pe­ri­ence loaded con­di­tions in ser­vice is ac­tu­ally very dif­fer­ent with dif­fer­ent types of drives. For ex­am­ple, when look­ing at a con­veyor drive, the in­put shaft/high­speed shaft is driven by the in­stalled mo­tor.

When con­sid­er­ing a wind tur­bine gear­box or power gen­er­a­tor, the high­speed shaft is ac­tu­ally the out­put shaft and is driv­ing the gen­er­a­tor, there­fore op­er­at­ing in a brak­ing type sce­nario. These dif­fer­ent sce­nar­ios re­quire dif­fer­ent pro­gram­ming and dif­fer­ent con­trol mea­sures to ac­cu­rately sim­u­late each test.

GDS’s sys­tem op­er­ates in torque con­trol mode, which means the torque on the high-speed shaft is main­tained and will not fluc­tu­ate more than 1 New­ton­meter (Nm) for any test car­ried out.

The sys­tem has the flex­i­bil­ity to main­tain the driv­ing torque or the brak­ing torque. This is how the sys­tem has the ca­pa­bil­ity to ac­cu­rately test a con­veyor drive as well as a wind tur­bine gear­box.

With any given test, one mo­tor will fluc­tu­ate power/torque to achieve accurate torque con­trol on ei­ther the driv­ing mo­tor or the brak­ing mo­tor. The same ac­cu­racy is main­tained in re­la­tion to the speed (RPM) of the high­speed shaft.

The sys­tem has 100pc con­trol of the rpm “ramp” rates and torque “ramp” rates. This means GDS can pro­gram how fast the torque is ap­plied and how quickly the drive reaches the de­sired rpm.

Hav­ing this flex­i­bil­ity makes it pos­si­ble to sim­u­late the torque/power fluc­tu­a­tions a drive might see while in ser­vice. This has been a very valu­able con­trol mea­sure on cer­tain load tests. GDS have set up strain gauges for cer­tain load tests and sim­u­lated a load spike com­ing onto a gear­box to record ex­actly how the gear­box is act­ing.

Test­ing such a vari­ance of dif­fer­ent size drives means the sys­tem needs to have ad­vanced safety mea­sures in place to en­sure no dam­age is in­curred dur­ing any load test.

The con­trol sys­tem has sev­eral pages where the gear­box pa­ram­e­ters must be pro­grammed be­fore a test can start, as well as a test pro­gram which is cus­tomised to suit ev­ery dif­fer­ent gear­box tested.

All the dif­fer­ent setup pages work to in­sure that the cus­tomer’s gear­box is never over­loaded. The safety lim­its are con­trolled via four main cri­te­ria: torque; power; speed and tem­per­a­ture. If any of the pro­grammed values are ex­ceeded, the test will au­to­mat­i­cally shut down.

While any test is run­ning, the load test cell is log­ging the data and col­lect­ing it in 1-sec­ond in­ter­vals for the du­ra­tion of the test. The main data streams col­lected in­clude mo­tor speed, torque, power and gear­box tem­per­a­ture.

It also cap­tures all the pa­ram­e­ters which were en­tered on ev­ery setup page as well as the test­ing pro­gram writ­ten for the test. When a load test is com­plete, there is also an op­tion to cre­ate a test re­port.

The load test cell takes the recorded data and gen­er­ates a con­densed PDF re­port. This re­port in­cludes the test pro­gram, the gear­box tem­per­a­tures reached and the power and speed fig­ures which were at­tained. The data is trans­lated into colour-coded graphs for a vis­ual rep­re­sen­ta­tion of the test re­sults. The load test re­port is then sub­mit­ted to the cus­tomer.

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