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May 7, 2009

Drag Chain Conveyor Preventive Maintenance & Inspection Checklist

Insufficient consideration of preventive maintenance for drag-chain conveyors 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 any machinery really starts long before the unit is even commissioned.  Many of our ongoing maintenance headaches could have been prevented by properly sizing the equipment 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 equipment.  Control monitoring devices must be wired in before start-up. Trough sections must be installed straight, plumb and level, with properly aligned trough joints.  Sprockets must be perpendicular to the head and tail sections.  Inlets must be correctly designed to feed grain or other materials into the conveyor without plugging.  Fasteners must be tightened to the correct tension, especially bearing setscrews and sprocket 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. 

Now we’re done thinking outside the box, and ready to talk about maintenance.  A good maintenance program starts by base-lining the equipment to document the equipment’s condition at the program’s start, then periodically inspects, or certifies the machine if you will, to determine how it’s holding up and what needs fixed or adjusted.  You can accomplish these base-line and periodic goals by using checklists.  These should be pre-printed forms for consistency, and a separate checklist should be used for each conveyor 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”.

The periodic maintenance checklists should be retained to provide a record of how well the machinery is doing over time, and to provide a predictive tool to gage when major repairs or replacement may be necessary.

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, or you might be next!

At a minimum, the following items must be checked:

  • NOISE:  Employ the technique of “management by walking around” to determine if the conveyor is making any unusual banging or clanking noises while operating.  This needs to be done while both empty and under operating conditions.  By the way, good maintenance people, and good managers, develop the habit of listening to equipment for problems every time they walk past an operating machine, and this trait is not limited to drag conveyors!
  • 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!
  • SPROCKETS:  Check for tightness of sprockets on shafting, and that shafting is level.  Check alignment of sprockets in head and tail sections.  Tooth profiles must be in good shape without excessive “hook” to allow the chain to disengage properly from the sprockets, to help the chain transition back to the return system without hanging up.
  • CHAIN ASSEMBLY:  Check for proper chain tension and adjust as necessary.  Check for good disengagement from the head sprocket, and proper movement through the conveyor troughs.  Check for loose flights, and flights that need to be replaced.  If flights are bending, find out why and correct the problem.  Periodically check for chain “stretch”, although this does not need to be done as often as regular maintenance checks.  You’ll probably want to replace the chain assembly when stretch reaches 5%.
  • TAKE-UPS ASSEMBLIES:  Check for proper operation, lubrication and adjustment.  Check condition of take-up screws and keep them clean. 
  • TROUGH SECTIONS:  Check for leaks, deterioration and obstructions.  Verify that casings have not shifted from a level position.  Check condition of wear liners and trough bottom.  Check inspection doors for tightness, dust sealing and presence of safety grating.
  • RETURN ASSEMBLIES:  For idler return systems, check for condition of idler rollers or sprockets and shafting, and replace as necessary.  For return rail systems, check for condition of wear strips, that the rails are level.  For inclined conveyors with divided troughs, check guide rails in the bend sections, and condition divider pans.  Verify that rail and pan ends are aligned to provide smooth transition of the chain assembly through the troughs.
  • HEAD AND TAIL SECTIONS:  Periodically clean tail section to prevent infestation and cross contamination.  Check inspection doors for tightness, dust sealing and presence of safety grating. 
  • CONVEYOR COVERS:  Check for rusting and damage, and immediately replace missing covers to prevent injury to personnel.  Replace missing cover clamps or fasteners, paying particular attention to outside conveyors subject to high winds to prevent flying covers.  Check for dust sealing and repair or replace seals as necessary. 
  • 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.
  • DISCHARGE GATES:  Check solenoids and limit switches for proper operation and alignment.  Check air cylinders or proper operation, and regulator-filter-lubricators to ensure they are in fact regulating, filtering and lubricating.  Check electric operators to ensure proper operation.  Verify proper operation of percentage controllers or encoders if present in your system.
  • CONTROLS, MONITORING DEVICES AND ELECTRICAL:  Check lockouts, interlocks, ammeters and start/stop controls for proper operation.  Check slowdown switches, slack chain detectors, plug switches, bearing heat sensors and alarms for proper operation and adjustment.  Check bonding and grounding for continuity.
  • 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 conveyor components must be modified as necessary.
  • STRUCTURAL:  Check condition of conveyor support legs, support bridges and bracing.  Check surrounding area for cleanliness.
  • GENERAL CONDITION:  Check condition of paint or galvanizing.  Inquire of operators of any known problems not already reported.
  • OPERATOR ISSUES:  Check with the equipment operator to see if he has detected any operational issues that need to be addressed.

 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.