Conveyors, packaging equipment, storage systems and other equipment in a warehouse can breakdown or completely stop functioning at some point. That's a given. But when equipment fails unexpectedly, maintenance costs rise while warehouse productivity suffers from unscheduled downtime.

Fortunately, there's a solution. Predictive maintenance programs are designed to monitor the operating condition of most types of machinery and identify any changes in their operating condition that may cause concern or require further evaluation. Implementing a combination of predictive maintenance techniques delivers the greatest effectiveness, and, when done correctly, exposes the root cause of the problem

The underpinning of predictive maintenance is consistent and accurate data gathering that detects trends in a machine's operation and anticipates a problem before it occurs. As a result, the experts say the most successful programs adhere to a strict monitoring schedule and rely on knowledgeable, well-trained personnel to analyze the data.

According to a survey published in the Plant Engineer's Handbook, benefits of predictive maintenance include: a 55% reduction in the number of catastrophic machine failures; an average reduction of 60% in repair time; a 30% increase in the useful operating life of equipment; as well as increased operating time and improved safety.

Despite these benefits, many warehouses do not practice predictive maintenance. Expense (system costs range from $1,000 to $60,000) and the need for long-term use of these practices are the most common reasons. Nevertheless, experts say the benefits easily exceed these requirements.

While many technologies are available, those best suited to warehouse equipment include vibration analysis, infrared thermography, oil analysis and ultrasonic analysis. Here's where each one fits in the world of predictive maintenance.

Used on rotating equipment and related electro-mechanical equipment such as conveyors and automatic storage/retrieval systems, vibration analysis monitors a machine's vibration amplitudes and signatures. Vibration monitoring and trending is based on the principle that every machine, when operating in perfect condition, has a naturally occurring vibration signature created by a series of unique frequency components. But when a loose or bent shaft, a bearing fault or an unbalanced rotor occurs, the frequency's amplitude increases. By measuring the deviation in vibration, the cause of the change can be identified.

In the case of a Cincinnati, Ohio bulk mail center of the United States Postal Service, shaft looseness in a conveyor system was identified and repaired before causing serious damage and costly downtime. According to the case history from DLI Engineering (800-654-2844), a vibration program identified serious intermediate shaft looseness or impacting problem in a critical conveyor drive. Monitoring and trending the drive's vibration levels over time revealed increased vibration levels, indicating that the problem was worsening. Once maintenance technicians replaced the unit and disassembled the defective gearbox, they found a broken tooth that had been causing an impact each time it meshed with the gear on the output shaft.

How often a machine should be monitored with vibration analysis techniques depends on the technology used and how critical the machine is to a facility. Keith Mobley, president of The Plant Performance Group (865-539-9300), states that 'thirty days is the maximum interval recommended for vibration monitoring. As the criticality of the system increases, so should the monitoring frequency.'

Infrared thermography is one of the most popular forms of predictive maintenance due to its versatility. Used on components such as electrical motors, gearboxes, and bearings, to name three, the technology measures heat energy, looking for 'hot spots.' For warehouse equipment, it is particularly useful to detect temperature disparities caused by loose or worn parts or excessive friction. By using infrared instruments, operators monitor the surface temperature of a machine's components and pinpoint those hot spots.

An instrument commonly used for predictive maintenance is the infrared camera often referred to as a 'point-and-shoot' instrument. This tool focuses on a specific spot on a machine's surface. It captures infrared images and displays them with a color scale representing the temperature levels.

While systems such as the camera are inexpensive and relatively easy to use, infrared thermography is complex and involves many variables that can prevent accurate readings. For instance, the atmosphere between a machine in the infrared instrument may have water vapor and other gases that absorb infrared radiation. Users of infrared thermography must be well-trained in acquiring and interpreting the data.

Suggested monitoring intervals are weekly for critical systems and bi-monthly for less essential equipment, according to Mobley. And many predictive maintenance experts, including Bob Madding, director of Infrared Training Center (978-901-8405), emphasize that 'thermography should focus primarily on equipment that is considered vital to a facility's operation or representative of the biggest safety concern.'

Oil analysis is a beneficial predictive maintenance tool for any type of lubricated equipment in a warehouse. These include packaging machinery and other equipment with large reservoirs of oil. Lubricants can become contaminated and lead to costly wear of a machine's bearings or other parts. To avoid equipment downtime, a machine's lubricating oils should be monitored and reconditioned or replaced when necessary.

A suggested interval for monitoring oil is quarterly or semi-annually. Sampling locations must be carefully selected and sampling conditions must be uniform for samples to accurately represent the oil condition.

Testing oil's viscosity, oxidation and fuel dilution levels are some techniques used in oil analysis. But in order for oil analysis to actually detect failures and their root cause, the process should include a wear particle analysis. This type of analysis involves studying and tracking the condition of particle shapes, composition, sizes and quantities to provide information about wearing conditions inside of machines. As a result, it is often advisable for warehouse personnel to work with a reliable laboratory or outsource the entire oil analysis service to a highly experienced technician.

Another predictive maintenance tool is an ultrasonic monitor. In a warehouse, it can often detect damage to components such as bearings, gears and valves and also spot vacuum and pressure leaks in pressurized systems.

Ultrasonic monitoring is similar to vibration analysis in that machines generate both audible and ultrasonic vibration frequencies, which can be measured and trended for any change. For instance, when a pump in a pressurized system has a leak, the uncontrollable two-way flow of air and liquid becomes turbulent, creating an ultrasonic noise.

Many types of equipment emit ultrasonic noise, making this type of testing very useful. Some tools such as an ultrasonic gun are also generally less expensive and complex than vibration analysis systems. However, while many ultrasonic detectors can identify irregular vibrations in equipment, they often cannot distinguish the cause of those vibrations. For a predictive maintenance program to be effective, Mobley advises facilities to 'use ultrasonic monitors in conjunction with other tools to evaluate overall performance.'

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