Investing in Prevention
Proper conveyor system application and maintenance improves safety and your bottom line.
July 25, 2013 By Edward Whipple Emerson Industrial Automation
In the aggregates processing industry, plant operators commonly relocate
mechanical conveyor systems in an effort to reuse existing equipment in
In the aggregates processing industry, plant operators commonly relocate mechanical conveyor systems in an effort to reuse existing equipment in new applications. While their intentions may be good – going green in an attempt to recycle – this practice often leads to misapplication of conveyor systems, creating a ripple effect that starts with unplanned maintenance and inefficient operations and ends with increased cost of ownership and safety risks. The operation of a conveyor system in this manner is not recommended, especially where safety is a concern.
|Excessive sheave wear is an indication of a misaligned v-belt.
Jeremy Chessell, health and safety manager at Lafarge Canada knows first-hand the importance of proactive maintenance in the prevention of injuries. “People are much more likely to get hurt when they’re reacting to emergencies, as opposed to being proactive and preventing the situation in the first place,” stressed Chessell.
If a conveyor goes down while running 400 tons per hour (TPH), operators must be prepared to deal with a large amount of aggregate trapped in the conveyor system. Scenarios like these greatly add to the complexity of repairs to the system – requiring gravity take-ups to be de-energized, complex lock-outs on multiple pieces of equipment to isolate failures, and proper management of stored energy to keep the belt under tension.
“Anything that takes you into an unplanned maintenance situation is cause for a safety concern. But, if you’re able to understand the dynamics of the whole system, you will be much better equipped to predict and respond to failures,” said Chessell.
Operators will regularly tolerate subpar conveyor systems to meet their short-term production schedules. Often, what starts with a temporary fix turns into a permanent situation, complete with problem areas in the system that require repeated repairs, such as frequent changes to bearings, belts and other components of the system – all symptoms of misapplication.
Eventually, operators must decide if settling for their current system misapplication is worth the sacrifices in efficiency and safety, or if they could reduce the total cost of ownership by deploying a conveyor system and preventive maintenance program properly specified to their current application needs. And, as importantly, operators must decide if fixing the current inefficiencies is within their internal expertise, or if it’s time to bring in an expert or consult the equipment supplier to resolve the issue.
Misalignment Leads to Systematic Mechanical Degradation
Like the components in the human body, the components in a conveyor drive system are all interconnected. Misuse of one component has a ripple effect that results in negative consequences in multiple areas of the system. When operators overlook the whole system in an attempt to improve productivity by altering one variable, they may face these common misalignment issues.
Misaligned v-belt drive: The v-belt drive connects the motor to the gearbox. Misalignment can result in v-belt wear and premature failure, worn sheaves, misalignment on gearbox input shaft and oil leakage. A properly aligned v-belt will always have four points of contact across both sheaves.
Gearbox misalignment: Signs of gearbox misalignment include excessive wobble, oil leaking from the gearbox, running hot (at >160 °F), metallic fragments in the gear oil, and worn gear teeth on one side only. Proper torque arm mounting is achieved at a 90° angle and in proper tension; these factors are critical for gearbox alignment.
Dynamic bearing misalignment: Typically, bearing failures can be attributed to the use of an undersized shaft and resulting shaft deflection. The resulting shaft deflection causes the bearing to operate under varying misalignment angles. When dynamic misalignment is present, rolling elements are not centred properly, which can cause bearings to run hot with increased friction and grease wear. The additional stress on the locking mechanism causes vibration, wobble and potential loss of locking capability.
Lubricate Gear Reducers and Bearings According to the Plant’s Operating Conditions
One of the biggest contributors to conveyor drive system failure is the contamination of lubrication. This if often attributed to using the wrong type of lubrication or not implementing the proper lubrication schedule (either too much or not enough). Reducer lubricant can be sampled and tested as an alternative to changes. Operators should follow a re-greasing schedule for bearings that’s dependent upon the conditions in their plant, based on temperature, contamination exposure and bearing speed.
To achieve an optimal re-greasing schedule, operators should co-ordinate with the equipment manufacturer and the lubrication specialist, and then trust their own experiential knowledge to arrive at the prescription that works best for their particular scenario.
Rely on Remote Monitoring for Predictive Analysis
Advanced remote monitoring capabilities give plant operators an invaluable tool for analysis and predictive maintenance. Wireless monitors provide “state-of-change” indications and condition reports, and tell operators if something is overheating or if vibrations/harmonics are changing. This allows peak values to be sent to the plant operator (notified via alarm or e-mail), often providing operators enough notice to dispatch an experienced technician to assess the situation and mitigate the issue.
The Real Cost Is Production Lost
The ultimate cost of conveyor system misapplication is a loss in production. For example, a misaligned torque arm that causes gearbox seal and bearing failure on a conveyor running 600 TPH can halt production for one full day, resulting in 7,200 tons of lost production. When a system with undersized shafting results in pulley loss and bearing failure, it could take up to two days to source parts and perform repairs/installation. Trying to process 900 TPH on a system designed for 500 TPH can result in complete system failure, resulting in up to five business days of lost production.
Chessell concurred that unplanned downtime causes severe – and often far-reaching – disruptions in business, especially if major repairs result in extended production stoppages. “If catastrophic failure occurs while you’re in a sold-out position, then the week off could account for lost sales and even market share loss,” said Chessell.
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