Rollers 

Conveyor rollers can be a major source of the noise produced by high-speed conveyor systems. Most conveyor rollers are hollow metal tubes that resonate as conveyed materials move over them. In many high-speed roller conveyor systems, there is a constant “ringing” sound emanating from the roller tubes. This ringing can be reduced by using a plastic tube material or by covering or lining the tube with a sound absorbing material or vibration damping material.With roller conveyors, the noise level is also a function of speed; as speed increases, the noise level increases. A 50% increase in speed can cause a 3 to 5 dB increase in noise level. At double the original speed, the level is 6 to 7 dB higher. At very high speeds the noise increases stop or level off, i.e., the noise versus speed curve flattens out, and slight reductions in noise levels have been observed at even higher speeds. This implies that the noise versus speed curve is convex and has a peak. 

Roller Bearings 

Factors which influence noise generated from bearings includes; the smoothness of the raceway (ground or unground), the level of precision of the ball (roundness and variation in diameter), ball separators (cages) and types of lubricant. In general, noise levels decrease as the quality of the bearing increases.There are typically three types of bearings used in conveyor rollers. Stamped commercial grade cageless bearings utilize hardened unground steel balls and raceways with a full compliment of balls.These are the most economical bearings used in conveyor rollers. The next step up in quality is the stamped commercial grade “semi-precision” bearing. These bearings have hardened unground steel balls and raceways but utilize a stamped sheet metal cage to separate the balls. The highest quality bearings used in conveyor rollers are ABEC-1 precision bearings. They utilize hardened and ground balls and raceways with a caged ball complement. In most clean area applications, ABEC-1 precision bearings also offer longer life and lower maintenance and operating costs compared to traditional bearings.Noise reductions can be significant when ABEC-1 precision bearings are used versus stamped commercial grade cageless bearings. At lower speeds the individual balls in a cageless bearing will “fall” in the raceway causing a readily identifiable “pinging or tinkling” sound. At higher speeds the balls are held against the raceway by centrifugal force and this sound is not present. ABEC-1 bearings have a caged ball compliment which eliminates any noise from the balls regardless of speed.The difference in noise levels at varying speeds between commercial grade cageless bearings and ABEC-1 precision bearings. The results will vary greatly depending on bearings, method of securing roller shafts in frames, frame material and design, and method used to drive the rollers.  

Roller Shafts 

Shaft clatter can be another significant contributor to noise from conveyor rollers. While the manufactured roller is reasonably round, there will be some ovality and some imbalance. These issues are accentuated at high speeds. As speed increases, rollers begin to bounce in the frame creating noise. Several techniques are available to prevent shaft noise. Threaded shafts with either male threads or tapped holes are popular in Europe. Metal clips to secure shaft ends are also available. Alternatively, plastic, rubber or polymers can be used as inserts into a frame or adapters over a metal shaft to prevent metal to metal clatter.