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May 22, 2009

Bucket Elevator Preventative Maintenance & Inspection Checklist

 

Insufficient consideration of preventive maintenance for bucket elevators will result in poor reliability, increased costs, safety problems, bad housekeeping, and unhappy employees.  Unscheduled downtime due to breakdowns will also result in lost production and unhappy management.

 But when should a preventive maintenance program start?  Let’s think outside the box for a few moments before we discuss specifics of a P.M. program.

 Preventative maintenance for bucket elevator legs really starts long before the unit is even commissioned.  Many of our ongoing maintenance headaches could have been prevented by properly sizing the elevator for future loads, specifying quality components appropriate to the application, installing a complete control monitoring system, and providing adequate space and access for maintenance personnel to actually get to the equipment.

 Second item out of the box is the installation and commissioning of the bucket elevator.  Control monitoring devices must be wired in before start-up. Elevator casing must be installed straight and plumb.  Head and boot pulleys must be perpendicular and plumb in relation to each other.  Inlets must provide for feeding of grain or other materials straight into the elevator buckets, at the proper elevation.  Fasteners must be tightened to the correct tension, especially bearing set-screws and pulley hubs.  Bearings and gearboxes must be lubricated properly, and drive components adjusted.  Most of these things must be verified several times during the commissioning process, so consult your owner’s manual for the manufacturer’s recommendations.

Third are the maintenance personnel themselves.  They must have training in order to accomplish the reliability mission, and procedures in place to know what to do, and how and when to do it, so that the entire maintenance division is doing the same thing the same way every time.  Consistency is the key to an effective preventative maintenance program.

And finally, management must think of preventive maintenance in terms of reliability, instead of a budget liability, and make it a priority, or preventative maintenance will not happen.  Put another way, which is more expensive, a fire extinguisher, or a fire truck?

Now we’re done thinking outside the box, and ready to talk about maintenance.  Be aware that the OSHA Standards for General Industry mandate regularly scheduled inspections of at least mechanical and safety control equipment, and lubrication and other maintenance in accordance with manufacturer’s recommendations, or as determined necessary by operating records.  The facility is required to maintain a certification record of each inspection.

It is a good idea for the certification record to take the form of checklists.  These should be pre-printed forms for consistency, and a separate checklist should be used for each bucket elevator in your plant.  A schedule for inspection must be made and, more importantly, followed.  Depending on usage, frequency of inspection may be anywhere from seasonal, to monthly or weekly.  Known problem areas may have to receive special treatment, such as a reducer known to walk on the head shaft, or a bearing known to run “hot”.

Some of the things on a proper checklist will require the unit to be shut down, and proper lock-out/tag-out procedures must be followed.  Safety first!

At a minimum, the following items must be checked: 

  • BEARINGS:  Check for excessive heat, unusual noises, excessive shaft movement, tight fasteners and locking devices.  Clean and lubricate as recommended by the bearing manufacturer.  Do not over-grease!
  • PULLEYS:  Check for tightness of pulleys on shafts, and that head shaft is level.  Check alignment of pulleys in casings, and alignment of head pulley to boot pulley.  Pulleys must be plumb to each other in both directions.  Lagging must be inspected for wear, tightness and cracks.  The pulley crown must be centered and adequate for proper belt tracking.  Pulley hubs, discs and edges must be checked for cracking or other signs of stress or fatigue.
  • BELTING:  Check for stretch, damage and wear on both front and back sides and ends of belting.  Check belt tracking on both pulleys, under both loaded and unloaded conditions.  Check for loose fasteners or wear on belt splices.
  • BUCKETS:  Check for condition of buckets, missing buckets and tightness of fasteners.  Check under operation to see if buckets are rubbing or banging against elevator casing. 
  • TAKE-UPS AND TENSIONING DEVICES:  Check for proper operation and adjustment. 
  • CASINGS:  Check for leaks, deterioration and obstructions.  Verify that casings have not shifted from a vertical position.  Check inspection doors for tightness, dust sealing and presence of safety grating.
  • HEAD AND BOOT SECTIONS:  Check for wear and condition of lining materials.  Periodically clean boot section to prevent infestation and cross contamination.  Check inspection doors for tightness, dust sealing and presence of safety grating.  Inspect head wiper. 
  • MOTORS AND DRIVES:  Check motor, reducer and drive components for proper operation, alignment, operating temperature, lubrication levels, and excessive vibration.  Check fasteners for tightness, and seals for deterioration and leaks.  If present, check backstops for proper operation.  Add oil or grease per the manufacturer’s specifications, or change if necessary.  Include jacking drives, if present, in these inspections. 
  • CONTROLS, MONITORING DEVICES AND ELECTRICAL:  Check lockouts, interlocks, ammeters and start/stop controls for proper operation.  Check slowdown switches, alignment sensors, bearing heat sensors and alarms for proper operation and adjustment.  Check bonding and grounding for continuity. 
  • EXPLOSION VENTING:  Check for proper function and obstructions.  Check explosion suppression and fire extinguishing systems, if present. 
  • ACCESS AND SAFETY EQUIPMENT:  Check ladders, safety cages, handrails, handrail gates and platform grating for safe condition, adherence to the OSHA standards.  Any platforms that do not provide adequate access to, and safe clearance around, the elevator leg components must be modified as necessary.
  • STRUCTURAL:  Check condition of support towers and bracing.  Check and adjust guy-wire bracing as necessary.  Check boot pits for cleanliness and water leaks.  Check sump pumps and drainage piping for condition and proper operation.
  • GENERAL CONDITION:  Check condition of paint or galvanizing.  Inquire of operators of any known problems not already reported.

Checklists should be modified as necessary for the specifics of your operations.  Deficiencies should be reported to management, prioritized for urgency and scheduled for repair or closer monitoring, depending upon the situation.

Finally, a few words about predictive maintenance.  One of our national accounts has greatly increasing their operational reliability by instituting a predictive maintenance program.  They’ve been able to make huge cuts in spare parts inventories, and schedule component replacement work in advance, instead of in panic mode.  We suggest you give serious consideration to these measures:

  • THERMOGRAPHIC SCANNING:  Infrared scanning reports actual operating temperatures, instead of a suspicion that a bearing, motor or gearbox is running “hot”.  It will also identify electrical devices like starters and switches running hot inside their enclosures, and can give you an idea how quickly something heats up, versus identical equipment.
  • LUBRICATION ANALYSIS:  Certainly cost effective for large gearboxes, gives advance warning of gear failure and allows replacement or repair of reducers before failure at critical times.
  • VIBRATION ANALYSIS:  Identifies bearings, reducers, shafts and other moving objects with excessive “shake”, and can often isolate the location of the problem device.

In addition to giving advance warning of impending failure, predictive maintenance can also reveal when something is not likely to fail.  That knowledge will save money in replacement parts and worker hours.  “If it ain’t broke, why fix it?

In conclusion, a good preventive maintenance and reliability program is a synergy of the right equipment, operated correctly, and regularly inspected and maintained by properly trained professional maintenance personnel.  You can’t afford not to.

 

 

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