Conveyor belt tracking requires systematic approach
Tracking a heavy-duty conveyor belt must be approached with the entire system in mind. All major pulleys including head, tail, drive, snubs, bends and take-up should be parallel and square before beginning, according to Walt Bond, Georgia Duck and Cordage Mill technical sales and engineering manager. “Also expect to have the belt loaded in the center,” he said. “All idlers and pulleys need to be clean and functioning. Self-training idlers on the carry side and the return side should be installed in the proper direction.”
“The new belt may have some internal stresses from manufacturing. Therefore, the best procedure for a new belt is to let it run and put some tonnage on it to break it in,” he said. Breaking in a new belt may take anywhere from a few hours to a few days, but will relieve most manufacturing stresses that can occur during weaving, treating, calendering, assembly and curing. Full belt contact with all carry-side idlers is a necessity.
Crowned pulleys have been “sold as a tracking panacea,” according to Bond, who insists heavy-duty belt conveyors do not need them. Crowned pulleys may offer a minor contribution in tracking when the crowned face is on a low-tension bend pulley or on the tail, but they should not be used on steel cord belting. “High modulus belt fabrics like nylon, polyester and aramid do not respond to the centering forces of crowned pulleys, and in some cases they can actually have an adverse effect on the belt,” he said.
Self-training idlers should be on 100-foot centers on the return, unless the conveyor is old and the belt is tough to train, then 50-foot centers are needed. The locations of the self-training idlers are very important, Bond said. He recommends placing the first self-training idler on the return about 30 feet behind the head to allow the idler to align the belt coming out of the head and into the trainer. At least 30 feet of free run is needed on either side of a training idler to make it effective, although 20 feet will suffice on some slow-moving belts. Trainers can then be spread out across the return.
“A good rule of thumb is never skew an idler that has over 90 degrees of wrap to ensure that the high modulus belt fabric will not be stretched out of square,” Bond said. “This method will train the slack side belt, feed the tail square, then run true on the carry side because of the centering forces from the troughers.” Another approach to training the slack side of conveyors more than 500 feet long is using two roll-“V” return idlers. With this method, gravity is the training force and belt edges are not subjected to wear from the vertical arms on the self-trainers. Return run self-trainers can become a high maintenance item as belt edges tend to wear through the vertical arms.