Preventive maintenance (PM) seems to be the phrase that comes to mind when we think about keeping our size reduction equipment in top shape. With the available tools of today this task has become much easier than before, relying more on the will and conviction of your maintenance crew. Obviously you need the support of management in making sure that proper man power and funds are allocated which should be fairly easy to justify. It is clear that a dollar spent today (in PM) will save you hundred fold down the road in losses of valuable product and repair of major failures. When we think of size reduction equipment the primary areas of concern will be the wear parts associated with mechanical rotating components (like bearings, belt drives and internal rotor components), seals as well as the electrical instrumentation and controls associated with these equipment.
Further breaking down the mechanical components it has become customary to place thermocouples/thermal switches on bearing housing which would alarm operators of excess temperatures one of the clear indicators of trouble developing. In addition to this time proven method newly available thermal imaging could further provide insight into the condition and exact location of the problems. The next level of protection for these rolling elements would be to monitor the vibration levels to make sure that any changes in operating conditions can quickly be identified without leading to a catastrophic failure. There are transmitters that can provide vibration amplitude as well as the frequency which again could be extremely valuable in identifying the source of the problem. Relying on monitoring alone could still result in premature failures; hence a routine maintenance program would be a necessary supplement where predetermined lubrication schedules can be implemented in order to extend the life of this equipment. Vibration monitoring can also be a good tool in identifying problems developing with the drive components like the belt drive parts, motors as well as the coupling mechanisms. Just like with bearings there still needs to be timely visual inspections where the belt quality (visual wear) and belt tension being the critical items that would need to be incorporated in to the maintenance program.
Size reduction whether it is wet or dry could generate a messy environment if not properly contained within the milling equipment which brings us to the importance of seal maintenance. Seals are in place to isolate the surrounding and the drive components (bearings) from the products that are being processed. There are numerous methods developed like addition of purges in tandem with seals to minimize the risk of contamination but simple measures like keeping minimal lubrication (suitable for the environment) on the seal contact surfaces could go a long way in extending the life of these simple parts. Just like with bearings higher temperatures again could signify problematic seal condition.
Size reduction being done via the use of high speed rotating components is susceptible to wear if processing abrasive materials. This brings us to the routine inspection of critical internal components to make sure that any parts (like bolts or pins) holding rotors together are in pristine condition since centrifugal forces developed at high speeds can easily be the cause of unexpected failures resulting in extreme damages to the internals of size reduction equipment. Once again vibration sensors could provide early warning if the wear levels are high and uneven which would manifest as unbalance loads. Beside from the mechanical components the instrumentation that monitors the condition of your size reduction equipment would need to be on proper maintenance schedule where by routine calibration of sensors (typically once a year) will provide the operator with the necessary confidence in the data monitored.
The last issue that would need to be considered is the proper storage of any equipment that is not being used for periods over several months. Each equipment manufacturer with their operational manuals should provide typical maintenance schedules as well as long term storage procedures that again would need to be incorporated in to preventive maintenance schedule/programs.