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Belt DriftBelt Drift

Gary James Gary James Director Minerva EngineersDirector Minerva Engineers

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Main Causes of DriftMain Causes of Drift

Poorly designed or made takePoorly designed or made take--ups.ups.Poor Alignment of idlers & pulleys.Poor Alignment of idlers & pulleys.Bent Belt & splices.Bent Belt & splices.Poor Loading (not covered here).Poor Loading (not covered here).Build up in pulleys & idlers (not covered here).Build up in pulleys & idlers (not covered here).

There are other causes. Please consult references There are other causes. Please consult references such as CEMA or equipment suppliers installation such as CEMA or equipment suppliers installation manualsmanuals

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TakeTake--upsups

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TakeTake--ups Cause Belt Driftups Cause Belt Drift

Unstable.Unstable.Under square.Under square.Too flexible or sloppy gaps in guide Too flexible or sloppy gaps in guide system.system.Poorly aligned or not balanced.Poorly aligned or not balanced.No adjustment of guide system.No adjustment of guide system.

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Mass

Vertical Loop Take-up

Mass

Common problems

Under square

Flexible guides & frame system

Big gaps? Are there any slots or is there other evidence that the designers/installers tried to get straight and vertical rails?

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Mass Mass

Pendulum effect gives stability.

Small gaps

System now over-square

Align guide rails

THE FIX

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Typical under-square trolley

Under Square Trolley Systems

Single rope pull. (may

also have a sheave)

Are there any slots or is there other evidence that the designers/installers tried to get straight and vertical rails?

Is the wheel riding up on an inverted V angle?

Does the trolley have side guide wheels or are V wheels used with an inverted angle?

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Mass

Sheaves

Double rope take-up tower

Does a two rope system help ? No!

Mass jams in tower

Better to take loads out at ground level & not in the tower

Torque/couple

Wheel up liftLarge angle of rotation & forces

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THE FIX

Make Over Square

Align rails

Improve trolley stiffness

Reduced angle of rotation & side loads

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Idler AlignmentIdler Alignment

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TYPICAL IDLER ALIGNMENTTYPICAL IDLER ALIGNMENT

Not aligned, but the net effect typically gives Not aligned, but the net effect typically gives reasonable tracking. reasonable tracking. Most of the time. Most of the time. More power required, more wear.More power required, more wear.

Tracking changes with loading, weather or Tracking changes with loading, weather or water sprays.water sprays.

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THE REASON FOR BAD THE REASON FOR BAD ALIGNMENTALIGNMENT

Structure not straight or level.Structure not straight or level.Equipment, idlers, pulleys etc have never Equipment, idlers, pulleys etc have never been aligned. They need to be accurately been aligned. They need to be accurately surveyed. surveyed. Twisted frames. Twisted frames. Bad feetBad feetHammersHammers

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Twisted framesTwisted framesThe frames can be manufactured out of tolerance. If the sequenceThe frames can be manufactured out of tolerance. If the sequence of of welding is the same on each frame, there can be a common error. welding is the same on each frame, there can be a common error.

Common errors work together to cause large belt drifts.Common errors work together to cause large belt drifts.

Side view on conveyor

Stringer

Common twist

Carry Belt

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Bad FeetBad FeetSlots encourage use of a hammer. The surveyed alignment is lost. The idler frames end up all over the place. Tracking can be erratic.

Idler Roll

Idler frame

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This is a better Approach. This is a better Approach. Slotting both ways allows the frames Slotting both ways allows the frames to be aligned on bent support structures. The common support stto be aligned on bent support structures. The common support structural ructural

tolerances ( to Aust Standards) are poor if you consider the strtolerances ( to Aust Standards) are poor if you consider the structure is part of a ucture is part of a machine.machine.

Get the supplier to slot frame transverse as shown

Slot stringer parallel to the conveyor

Frame

Roller

Use ProkConveyliner to align or similar

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PulleysPulleys

Use SG iron bearing housings, Use SG iron bearing housings, reduces risk of foot breakage if fully reduces risk of foot breakage if fully tensioning bolts on not flat support. tensioning bolts on not flat support. Make site standard or label position & Make site standard or label position & pulley with stainless information pulley with stainless information plate. Cast iron housings are ok plate. Cast iron housings are ok provided the mount surface is flat.provided the mount surface is flat.

Pulleys Pulleys ctdctd

If possible, mount bearings horizontal, If possible, mount bearings horizontal, allows simple alignment.allows simple alignment.Align with survey tools or similarAlign with survey tools or similarHold bearing housing down with fully Hold bearing housing down with fully tensioned minimum Grade 8.8 bolts, to tensioned minimum Grade 8.8 bolts, to prevent fatigue. Use hydraulic prevent fatigue. Use hydraulic tensionertensionerjack on bolts M30 and above.jack on bolts M30 and above.

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After Careful Alignment, After Careful Alignment, Measure Actual Belt MovementMeasure Actual Belt MovementSo, prove that all is correct by taking So, prove that all is correct by taking measurements when the belt is running.measurements when the belt is running.

Check by taking signature.Check by taking signature.Check for bent belt, splice or offset due to Check for bent belt, splice or offset due to poor support alignment.poor support alignment.

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The belt drift signature allows the The belt drift signature allows the root cause to be determined. root cause to be determined.

Offset is due to pulley or idler alignment, take-up alignment, structural support & feed error

Plot of drift at a point over time

Mark the belt. After several rotations of the entire belt loop, repeat patterns will appear. This pattern is due to bent belting from factory or a bent belt splice. ( Ie belt not lined up properly when the belt segments spliced together in the field.

Measurement equipment. The two sensors eliminate errors due to changing belt width.

Minerva Equipment.

(A video camera and ruler is an alternative)

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Last ResortLast ResortIf all else fails, & you are under pressure If all else fails, & you are under pressure to ensure flow.to ensure flow.

Use a tracking device ESS, PROK etc etc, can Use a tracking device ESS, PROK etc etc, can even use active tracking.even use active tracking.or Tilt sets forward 3 deg Max. ( Power & or Tilt sets forward 3 deg Max. ( Power & wear)wear)

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