What is belt conveyor tracking?
Belt conveyor tracking is the practice of keeping the conveyor belt travelling along the path as it is required. A conveyor belt should not drift off path as it would cause the conveyor to work incorrectly. When installing a new belt there can often be tracking issues, these require adjustments to counter any tracking problems to ensure the conveyor maintains optimal performance. It is best practice to do any belt tracking adjustments whilst the belt conveyor is running. A belt may also need additional tracking adjustments as it is worn in.
Before considering belt conveyor tracking methods it may be of use to give a brief overview of what a belt conveyor consists of. Each of these parts play a role in ensuring correct belt conveyor tracking.
Parts of a Conveyor Belt
The belt is the material on which the products are transported. They're available in numerous materials such as thermoplastics, metal, rubber, fabric and leather. A number of these are available with different weaves and coatings. The goal of conveyor tracking is to ensure this belt runs straight.
When referring to conveyor systems, pulleys are sometimes also known as drums.
The head pulley usually drives the conveyor. It is important for this pulley to have good traction, for this reason is is often lagged. Lagging is where the face of the pulley is coated with a material such as rubber or ceramic coating which increases traction. During conveyor maintenance the lagging should be checked to ensure it is still generating friction and hasn't become worn down.
Located at the opposite end of the belt to the head pulley. Often an idler pulley but can be driven in some cases. The tail pulley can take the role of the take-up pulley in shorter conveyor belts.
A snub pulley increases a drive pulleys traction by increasing the wrap angle.
A Drive Pulley has an external power source which rotates the pulley and thus drives the conveyor belt. They're often used as the head pulley, however centre drive conveyors are common.
An Idler pulley rotates freely and is driven by the belt only, it has no drive function of its own.
A bend pulley is used for changing the direction of the belt.
These are adjustable pulleys to allow for proper belt tensioning
A Basic Conveyor Belt
At the most basic level a conveyor consists of two pulleys; a drive pulley, an idler pulley, and a belt that wraps around them. In many applications however a standard belt conveyor without any additional tracking measures would be insufficient. For example when loading items onto the belt, the belt can be shifted off centre, without tracking measures in place the belt would run off and become damaged.
Belt tracking measures ensure that this does not happen and any issues can be fixed before the conveyor becomes unusable . As well as saving in the cost of repeatedly buying replacement belts, correct belt conveyor tracking can decrease overall maintenance and downtime. A modular conveyor however does not have these tracking issues.
What causes tracking problems?
Conveyor belt tracking problems are often blamed on the belts themselves. This is not always the case. Usually the problems can be blamed on poor installation, such as pulleys and rollers not being properly adjusted, or using the wrong belt tracking measures. Sometimes however it's simply just faulty conveyor design.
Factors that can effect belt tracking include:
- Uneven foundations
- Pulleys not parallel or square with the frame
- Seized or out of round rollers
- Transverse forces such as tight belt scrapers
- Dirt or build up anywhere in the conveyor
- Damaged idler frames
- Belts being loaded off centre
- Worn pulleys
- Belt making insufficient contact with rollers
- Poor belt quality or incorrect weave direction
- Under or over tensioning
- Belt too stiff or damaged, warped or bowed
Belt tracking considerations
As a rule, the belt moves to the side of the pulley or idler that it first comes into contact with. If the pulley is slanted down on the left side, the belt will move to the left. If the pulley is slanted down on the right side, the belt will move to the right. A basic belt conveyor tracking adjustment involves gradually repositioning the pulleys to aid the belt in realigning. It takes several revolutions of the belt to see if the adjustment has been successful, therefore any adjustments should be carried out incrementally and slowly to avoid any drastic effects which could damage the belt.
How to Fix Belt Conveyor Tracking Problems
To ensure correct belt tracking:
- The structural support must be stable, rigid, and able to withstand forces including belt tension, product weights, uneven flooring etc
- Pulleys and rollers should be fitted at right angles to the belt running axis. Any adjustable parts should be set up once the belt has been adequately run in.
- Any part that comes into contact with the belt is required to be kept clean, either by design including protection or by access to allow cleaning.
Belt tracking measures can be quite basic, they're used to maintain a correctly aligned belt in position. In other cases however, additional measures may be required.
Further Tracking Measures
A crowned or tapered pulley can aid in belt tracking
As mentioned above, usually a belt will follow a path moving towards the edge of the roller it meets first. In the case of a belt on a crowned pulley, it will travel towards the centre. Whichever side the belt is tracking to, due to the shape the central area is where the belt tension will be higher. As the belt grips onto the central area and the roller pulley continues to turn the belt is re-aligned centrally.
Once the belt reaches the centre however the tension should be even as there is an equal amount of slack on each side of the belt. If the belt begins to go off centre for any reason, the crowned pulley will naturally guide the belt back into the centre. The taper ideally should be very gradual, as you can imagine any angular parts the belt will run over could cause damage to the belt. When performing belt conveyor tracking, there should be enough tension in the conveyor for the belt to conform to the crown pulleys if used.
A guiding pulley, or control pulley, is a snub pulley that is adjustable. As previously mentioned a snub pulley increases the wrap angle of the belt over the drive pulley which improves the traction. These pulleys can be coated with a material to improve friction. Ideally the area of contact for the belt on the guiding pulley should be a minimum of 30 degrees of the pulley circumference.
A guiding profile is a shaped wedge that is added onto running side of the belt. Often V shaped, though other shapes are sometimes used. They are not recommended for general use as belt conveyor tracking assistance as they incur higher productions costs and have a limited scope for use.
A guiding profile is not usually utilised for belts running at high speed as the guiding profiles have a tendency to slip from their running groove. They are suitable however to lessen the effects of transverse forces on the belt, such as occasions where side loading is required. In wider belts, or belts of thinner material it is recommended to use two guiding profiles, one located at each edge of the belt rather than one centrally.
Where a belt has a v-guide in the underside, often the pulley will be straight faced, as there is no need for the pulley to have a crowned shape, the guide alone should keep the belt centred as required.