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Basic Conveyor Belt Behavior

A wide variety of different flaws in the design or maintenance of a conveyor belt can lead to mistracking. However, all of these problems stem from a few basic principles about conveyor belt behavior.

These concepts underlie the entire practice of belt training, which is the process of adjusting conveyor structure, rolling components, and load conditions to correct any tendency for the belt to run off-center. Understanding these principles can better prepare operators to address the issue, and potentially allow them to prevent belt mistracking entirely.

The fundamental rule of conveyor belt tracking is that the belt will move toward the side that has more friction, or the side that reaches the friction first.

Friction between the belt and, generally, the rollers serves to slow down the movement of the belt. If this friction is distributed unevenly across the belt, one side will slow down while the other attempts to continue at the same speed. This causes the belt to “turn,” leading to mistracking.

There are four requirements of a rolling component to steer the belt correctly.

This kind of imbalance can be created by a variety of factors, but two common causes are angled rollers and unleveled rollers. In each instance, the belt comes across one side of the roller before the other, leading to a small imbalance in friction that can eventually be exaggerated over the course of the conveyor if not corrected.

This principle can be demonstrated by rolling a book along a round pencil on a flat surface. If the pencil is perpendicular to the direction of motion, the book will travel straight forward. However, if the pencil is angled, the book will move slightly toward the nearer end of the pencil.

An illustration showing how a book rolled over an angled pencil will shift towards the lower end of the pencil.
The basic rule of belt training can be demonstrated by laying a book on top of a round pencil. When pushed away, the book will shift to the left or right depending upon which end of the pencil is closer to the person doing the pushing: that is, the end the book is contacting first.

This principle applies equally to flat and troughed idlers, however, there is a separate force unique to troughed idlers. Because the sides of a trough are suspended in the air, each side of the belt is constantly being pulled downward by gravity. If the belt becomes misaligned and the trough becomes unequal, the gravitational force on either side becomes unequal, pulling the heavier side down toward the middle of the conveyor. This gravitational tracking force is so pronounced that bulk conveyors usually depend upon it as their major tracking influence.

Aside from specific applications, these principles illustrate that conveyor belts are primarily affected by misalignments and other flaws upstream—where they came from—than downstream—where they are going. When looking to address mistracking, operators should always look upstream to identify the problem.

Topics: Conveyor Belt Mistracking

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