What you need to know about belt and chain drive maintenance
By By Steve GahbauerMachinery and Equipment Maintenance
In any plant, the efficient and reliable transmission of power depends on the proper function of drive components. When they fail, the resulting work stoppage can be costly. Chain and belt drives are vulnerable, and diligent maintenance pays...
In any plant, the efficient and reliable transmission of power depends on the proper function of drive components. When they fail, the resulting work stoppage can be costly. Chain and belt drives are vulnerable, and diligent maintenance pays sizable dividends.
In a day-long education seminar last November, convened by the Hamilton, ON, Section of the STLE, the Society of Tribologists and Lubrication Engineers, presenters from Tsubaki of Canada Ltd. and Gates Canada Inc. provided some useful insights and points to consider about mechanical drive component maintenance.
Jeff Murray, district sales manager for Tsubaki of Canada in Mississauga, ON, says the major reasons for chain drive failures are elongation, corrosion and erosion, fatigue, overload, lack of proper lubrication, misalignment, pin wear and plate fracture.
Over a period of time, all chain drives stretch about 1.5%. In very long drives, that can add up to a substantial elongation that can be corrected by removing one or more links. Corrosion is evident when bush and roller have worn wafer-thin, pins exhibit excessive wear, and plates show side wear and pitting. The solution is to improve lubrication or to switch to a corrosion-resistant chain material.
Bush fatigue failures and permanently stretched outer plates are the result of severe overload.
Misalignment causes rubbing wear on the side plates and the pin faces. To correct misalignment, realign the chain drive before the damage to the chain becomes too severe and the chain has to be scrapped.
The most common failure is pin wear. Over a period of time, pins gradually wear until the 1.5% chain elongation is reached. Plate fracture is common as well when excess working loads are applied repeatedly.
Belt drives often fail prematurely, too. Tony Lavalle, industrial district manager, Ontario, of Gates Canada Inc. in Brantford, ON, says that analyzing belt failures does not require a lot of tools. The resulting benefits include better drive performance, longer belt life, greater efficiency, energy cost savings and reduced downtime.
When properly installed and tensioned, V-belt drives operate at 93% to 97% efficiency. This efficiency level can be sustained as long as all drive components are properly maintained. Belts can deliver up to five years of service when well looked after. When a V-belt has reached the end of its useful life, it will pull apart or break.
The major factors affecting V-belt life are poor maintenance (42%), improper installation (20%), incorrect handling (2%) and defective components (1%).
Poor maintenance is the most common cause of premature belt failure. V-belts need a large surface area of contact and a high coefficient of friction and tension. Time and neglect can easily compromise these requirements. Too much or too little tension, worn pulleys, and misalignment are key indicators of improper maintenance. To keep a belt drive performing as it was designed requires regular inspection, proper alignment and correct tensioning.
Improper installation is the next major reason for belt failure. The drive must be properly aligned. Misalignment causes drive instability and shortens belt life. Common causes of misalignment include non-parallel driver and driven shafts, out-of-line sheaves, and sheaves that wobble or tilt while running. Check correct alignment by using a straight edge and string, or a laser alignment tool.
It is also vital that belt drives are properly mounted. Avoid prying or rolling the belt onto the sheave as this can damage the tensile cords and reduce belt life. Always check sheaves for wear or damage before mounting a belt. Nicks, worn sheaves and sharp edges can damage belts.
Excessive heat and contamination are two additional causes of abnormal belt wear. The ideal operating temperature is approximately 60°C.
Also remember that belts should be stored on a flat surface to avoid crimping. Hanging V-belts on hooks can shorten service life.
Detailed troubleshooting requires shutting down the drive and conducting a thorough inspection of all drive components. Stiff belt surface and surface flaking are indicators of excessive wear. Sheave damage could result from incorrect installation or debris falling into the drive. Install a drive guard to avoid this problem.
Competent installation, regular inspection for wear, and diligent maintenance are the keys to better-performing and longer-lasting drives, says Lavalle.
Steve Gahbauer is an engineer, a freelance writer, and an regular contributor of technical articles to MRO Magazine.