SERVICE TIP

Tracking A Conveyor Belt

Basic Rules For Conveyor Belt Tracking

1. The basic rule of tracking a conveyor belt is the belt moves toward that end of the roll/idler that it contacts first (see Figure 1). The reader can demonstrate this rule very simply by laying a round pencil on a flat surface in a skewed orientation. Lay a book across the pencil and gently push it with your finger in a line directly away from you. The book will tend to shift to the left or right depending upon which side of the pencil the moving book contacts first.
2. The conveyor structure must be "TRUE" (relative to the centerline) and LEVEL (side to side).
3. ALL pulleys, snub rollers, carrying idlers and return idlers must be SQUARE with the frame (perpendicular to the belt centerline) and parallel to each other. Check this by measuring diagonals, which should be equal.
4. BELT TENSION must be great enough to:
   A. Prevent slippage between the drive pulley and the belt.
   B. Force the belt to conform to the crown on the crowned pulleys.
5. CLEANLINESS is essential to good belt tracking. Foreign matter creates a new roll or pulley face – adversely affecting tracking.
6. The CONVEYOR BELT must be straight (less than ½ percent camber) and ends must be squared and laced properly. Check this by measuring diagonals, which should be equal.

Measuring Belt Camber

If unbalanced warp tensions exist in a conveyor belt, that belt will usually assume a "crescent" or "banana" shape when laid flat upon a horizontal surface. This deviation from a straight line is defined as "camber."

Unroll the belt on a flat surface such as the floor, a flat horizontal driveway, etc. Grasp one end of the belt and drag it in a perfectly straight line for 10-20 ft., (3-6 m). If the belt is too heavy for one person to move, clamp one end of the belt to a forklift and follow the same procedure. After pulling, the belt should be flat. (If the belt assumes a "crescent" or "banana" shape, unequal and unresolved warp tensions exist in the belt).

Note: It is extremely important that the procedure described above be followed closely. It is difficult to have both edges of the belt at the same thickness – particularly wide belts. According, if the belts is unrolled on a flat surface, that belt will always unroll in a banana shape – due to geometry, not unbalanced warp tensions. "Dragging" one edge of the belt for 10-20 ft., (3-6 m) eliminates this geometrical consideration and shows whether the belt is cambered.

Camber is measured by drawing a taut line along one edge of the belt (inward camber edge) and measuring the maximum deviation from the center point of the line to the belt. The percentage of camber is computed using the following formula:

% camber = Maximum Deviation (inches) x 100

Length of Taut Line (inches)

It is recommended that if the percent camber exceeds ½% on a polyester warp belt construction, or 1% on a nylon warp belt construction, the belt manufacturer should be contacted.

Skew or Bow

The fill yarns (horizontal yarns) in the belt carcass will usually lie perpendicular to the centerline of the belt. Any deviation from perpendicular by the fill yarn is termed "skew" or "bow."

A skewed pick in a square weave is cause for concern since it is usually indicative of unbalanced warp tensions and generally goes hand-in-hand with a significant camber.

In a straight warp or solid woven carcass designs, such as Georgia duck used in Polyvinylok and Wearlok belting construction, skew is of little significance. In this case skew is a cosmetic defect and is not indicative of a cambered belt.

7. The NORMAL SEQUENCE of belt training is to start with the return run, working toward the tail pulley; following with the top run in the direction of belt travel. Start with the belt empty. After tracking is completed, run the belt with a full load and recheck tracking.
8. TRACKING ADJUSTMENT is done while the belt is running and should be spread over some length of the conveyor preceding the region of trouble. Permit the belt to run for several minutes and at least three full belt revolutions after each idler has been adjusted to determine if additional adjustment is required. If the belt is over corrected it should be restored by moving back the same idler, and not by shifting additional idlers or rollers.
9. TRACKING EFFECTIVENESS of a roll/crown is approximately proportional to the length of the unsupported span of belt approaching the roll up to a maximum of approximately 10 ft., (3 m). If there is no such span, tracking effect of the roll is virtually non existent. However, such a roll can induce camber into the belt as it leaves the roll.

Posted 24 July 2000