Page 87 - MetalForming-Oct-2018-issue

variation, which often requires differing amounts of tension. Following are effects of low and high belt tension, as well as possible causes.
Low Belt Tension
• Abrasive belt tracking problems. Here, the belt randomly tracks off of the head in either direction due to a poor grip on the tracking wheel/roll. Do not confuse this with a belt tracking off in the same direction, which may indicate wear on the tracking wheel/roll or tracking-mechanism parts, or side-to- side length variation on the belt.
• Printing on the back of the belt shows a high degree of wear. This indi- cates a belt slipping on the drive roll, which will wear away the print.
• Parts being processed have “skip” marks where the belt has slowed or stopped during grinding/sanding. This can occur when a belt randomly slips on the drive roll for short periods of time, which typically occurs when the head encounters higher workload.
• Short-term high-pitched whining sound with the grinding/sanding head in start-up mode and/or when pro- cessing parts. This may be a symptom of the belt slipping on the drive roll and likely has significantly less tension as compared to the above scenario.
• Belts folding over on themselves and typically breaking. This occurs under low belt-tension conditions; how- ever, it also can result from wear on any of the rolls that the belt runs over, or a combination of these two conditions.
• Belts breaking at the joint where the joining tape is on the back side of the belt. This can be caused by the belt slipping on the drive drum, causing excessive wear to the joining tape.
• Reduced belt life. This can result from abrasive grain not breaking down and resharpening due to a reduced amount of pressure/force being applied between the workpiece and the grain particles when belt slippage takes place.
High Belt Tension
• Abrasive belt tracking problems. Here, high tension overwhelms the tracking cylinder, which typically is
much smaller than tension cylinders. • Premature bearing wear on the head’s drive, tracking, and/or idler rolls. The higher the belt tension on any type of grinding/sanding equip- ment, the more wear on all related bearings. This results from the over- tensioned abrasive belt pulling the OD of the rolls or roll shafts against the outer race of the bearings at higher pressures than recommended. This
creates higher pressure between the ball/rollers and the inner and outer bearing races, resulting in dangerously high bearing temperatures, followed by bearing failures. On sanding oper- ations that develop combustible par- ticulate, such failures can become fire hazards.
• Belt breakage. High belt tension reduces the belts ability to absorb high or fluctuating shock loads. Breakages
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