Getting the belt to track in the center of the conveyor’s structure and components is a process of adjusting idlers and loading conditions to correct any tendency of the belt to run outside the desired path. The first step is to get the structure into alignment with the belt’s theoretical centerline, as identified in the system survey. Once the structure is aligned, all the pulleys and idlers must be aligned so they are level and square to the center line. Then attention can be given to getting the belt to run true. When training a belt, only one person should be in charge of the procedure.
Belt mistracking can be caused by a number of factors, but all mistracking leads to subsequent problems if not identified and resolved.
When more than one person adjusts the conveyor at the same time, it can lead to conflicting “corrections” that make the belt’s path more difficult to correct. It is important that records be kept, noting the conveyor’s problem areas and detailing the corrective steps taken. This will prevent, or at least identify, the problems arising from correction, re-correction, over-correction, and counter-correction when problems return to a specific area.
Procedure for Training
The following is a step-by-step process for training the belt to correct for component alignment and loading problems.
Determine Areas of Belt Tension
Adjustments to components in the low tension areas have the highest impact on correcting the path of the belt. By identifying and starting in the low-tension areas, the training process can have the greatest impact with the least amount of changes. In high-tension areas, there is too much tension on the belt for relatively minor adjustments to have significant impact on the belt path. Belt tension is usually highest at the drive pulley. The area of lowest tension will vary on the location of the snub and take-up pulleys. The low tension areas are completely dependent on the individual conveyor and must be identified for each application. Conveyor Equipment Manufacturers Association’s (CEMA) BELT CONVEYORS for BULK MATERIALS, Sixth Edition, or an experienced conveyor engineer can be consulted for additional information.
It is important to make sure the takeup weight is applying the correct tension required by the current belt and capacity ratings. If the belt is inadequately or improperly tensioned by the take-up pulley, it is likely to have severe variations in its path.
Determine Locations of Mistracking
It is best if inspection for mistracking begins with the first rolling component directly after the highest-tension area (typically where the belt leaves the drive pulley), as the tension will usually be lower in that area, and continues along the path of the belt until a point where the belt is visibly off track.
Belt tracking devices sense mistracking and react accordingly to correct its path.
It is important to remember that the track of the belt at any given point is affected more by the idlers and other components upstream (the points where the belt has already passed) than the components downstream (the points the belt has not yet reached). This means where mistracking is visible, the cause of mistracking is at a point the belt has already passed.
Therefore, corrective measures should be applied at points the belt passes before the area where it shows visible mistracking. The movement of one idler generally has its greatest training effect in an area within 5 to 8 meters (15 to 25 ft) downstream.