Carryback is the material that remains on the belt after discharge and is perhaps the most common struggle among conveyor pulley. Typically all conveyors experience carryback to some extent, but given its potential for serious consequences, keeping it to a minimum is essential.
WHY CARRYBACK IS AN ISSUE
Carryback creates a messy and potentially hazardous work environment, as it gets into the undercarriage and surrounding area of the conveyor. This can cause outages and increase the time devoted to cleaning and maintenance.
Not only does carryback create a mess, but material allowed to build up on rollers, idlers, and pulleys degrades these components, causing excessive wear. Further, a buildup of carryback can also cause belt tracking issues, potentially wearing and damaging the belt.
WHAT CAUSES CARRYBACK
Carryback is largely a result of the conveyed material’s characteristics and propensity for sticking. In general, a material with a higher moisture content is more likely to stick to the belt. Similarly, carryback can be more of a problem in humid environments where hygroscopic materials pull moisture from the air, increasing the likelihood of sticking.
Sticking can also occur when condensation is produced as a result of extreme temperature differences between the material and the belt.
HOW TO PREVENT CARRYBACK
The best way to prevent carryback is to utilize one or more belt cleaners. Belt cleaners can be installed at both the head and tail pulley and serve to ride against the conveyor belt, dislodging any material that may be adhered to the belt. These devices substantially reduce buildup on the belt, and depending on the level of carryback, several options may be appropriate. Common options include a self-cleaning tail pulley, return side belt plow (v-plow), and dual belt cleaners.
Routine cleaning should also be prioritized as part of a conveyor head pulley maintenance program in order to minimize any remaining buildup on components.
CONVEYOR BELT MISTRACKING
Tracking, or training, refers to the way in which the belt rides on the rollers. Conveyor belts should always track centrally. Mistracking occurs when the conveyor rubber belt rides unevenly on rollers, favoring one side over the other.
Like carryback, mistracking can cause several issues in a conveyor system. This includes uneven belt wear, belt damage resulting from catching or rubbing on surrounding infrastructure, material spillage, warped belting or belts that are not square, and more.
Mistracking is also recognized as a safety violation by the US Department of Labor’s Mine Safety and Health Administration (MSHA). When a belt is not tracking properly, areas that are normally safe can become pinch points, presenting a hazard to workers. Mistracking can also cause material to fall off of the conveyor, falling on to workers and equipment, or creating piles that present a safety risk.
WHAT CAUSES MISTRACKING
Since conveyor bend pulley are carefully balanced, any number of factors may be the source of mistracking, making it difficult to identify the origin of the problem. Potential causes of mistracking include improper idler spacing, seized or worn rollers, a misaligned frame, material buildup on any part of the conveyor, excessive belt tensioning, and a worn or damaged belt, to name a few.
HOW TO PREVENT MISTRACKING
The range of possible mistracking causes make a blanket solution to prevention impossible. There are, however, measures that can help to reduce the potential for this issue to occur.
Conveyors can fall out of perfect alignment through normal wear and tear. As a result, routinely inspecting alignment of the conveyor structure and its many components helps to prevent mistracking. Off-center loading can also create an alignment issue, so ensure that chutes are positioned centrally over loading areas.
Since mistracking can be caused by material buildup, it’s also important to keep the belt conveyor, idlers, and pulleys clean. This will reduce wear on components, which could also cause mistracking.
Slight off-tracking issues can be remedied by “knocking idlers,” a practice in which idlers are skewed a small amount to correct an off-tracking belt.
Belt slippage typically occurs around the drive/head pulley and happens when the belt and pulley do not have enough grip to adequately turn the belt around the pulley.