In this regular column, experts from specialist bulk materials engineering firm DYNA Engineering solve some common issues associated with materials handling. In this edition, the firm’s managing director Graeme Greaves, explains the latest innovations available to correct mistracking belts and improve productivity by reducing unscheduled conveyor stoppages and downtime.
When a conveyor belt is not properly aligned it can rub and wear against the surrounding structures, which eventually results in severe damage to the conveyor belt, the idler frames and even the conveyor structure itself.
Belt mistracking is one of the most common causes of belt stoppages and occurs when the conveyor belt is not properly centred on the conveyor frames. There are several simple checks which can be performed to find some of the common belt tracking issues and may uncover underlying mechanical issues.
1. Is the belt in poor or worn condition?
If the belt is badly worn or stretched, shows signs of cracking or wear through the rubber cover, the belt may no longer be straight which makes tracking problematic.
2. Is the belt ripped, torn or damaged?
If the belt has rips, holes or any sort of structural damage to the belt carcass, the belt could catch on idlers or other parts of the conveyor, causing it to run off centre and no longer be straight.
3. Is the belt splice in poor condition?
Inspect the splice and make sure it is in good condition, has no flaps, loose items or abrupt edges that may become caught on idlers or other components.
4. Is the conveyor pulley lagging worn or material build-up on the pulleys?
If the pulley lagging is worn or material builds up around the lagging, this can alter the effective diameter across the pulley. This will likely lead to the belt wandering off centre, increased instability and may result in the belt running off the edge of the pulley.
5. Has material built-up on the idlers?
Material build-up around the idlers may result in the belt being steered off centre, running to one side and contacting other components along the conveyor.
6. Are all the idlers rotating smoothly?
If idlers cease running or become jammed, the stationary roller may act as a brake on that part of the belt. This can cause the belt to run off to one side.
7. Are the trainers in good condition and effectively training the belt?
Mistracking can also occur if the trainers are in poor condition or not effectively training the belt to run in the centre of the structure. Inspect the trainers closely to spot if they are worn or tired.
Tracking Rollers
Tracking rollers are designed to minimize belt mistracking and are usually fitted on the return run of the conveyor belt but can also be fitted on the carry side of the belt. Tracking rollers assist in keeping the belt aligned and centred on the conveyor system.
One of the most common methods of assisting to correct belt tracking is a pivot belt tracking frame, which can be seen in figure 1. These frames use the standard conveyor rollers with the addition of a horizontal centre pivot and side guard rollers to steer the belt back towards the middle of the conveyor when the belt wanders to one side.
However, in this type of design, there is often a gap between the belt and the side guide rollers which creates a delay in the response to the movement of the belt. This may result in an overcorrection in the conveyor belt which will continue to wander from one guide roller to the other.
In extreme cases, the pivot design can be a potential liability. When a severe tracking event occurs, the pivoting frame can move to a point where the pivot reaches its limit and the conveyor belt can be forced up and over the side guide roller, potentially damaging the belt or surrounding equipment.
If the centre pivot becomes worn or seized and consistently rubs and wears against the side guide rollers, it can lead to belt mistracking and premature wear of the edges of the belt when it comes into contact with traditional tracking rollers.
It’s common to see the older style tracking rollers, or “trainers” as they’re sometimes called, tied with rope or supported with other devices because they simply don’t steer the belt correctly. The belt keeps tracking off centre, causing the edge of the belt to become damaged and frequently trip the belt drift safety switches.
When issues continuously reoccur, conveyor operators tend to take matters into their own hands and work around these issues as best they can. The work arounds are usually effective for a short period of time, however they are sometimes unsafe and not a long-term solution.
DYNA-TRAC Tracking Rollers
DYNA-TRAC tracking rollers are a relatively low cost and low maintenance solution to belt mistracking. Easily installed on most conveyor systems, DYNA-TRAC Tracking Rollers are self-aligning and self-adjusting.
The self-adjusting mechanism uses belt forces provided by gravity, friction and balance to keep the belt aligned and centred while the belt is in motion. The design steers the belt towards the centre of the conveyor without the need for side rollers or pivot frames.
By using conveyor belt forces to adjust the tracking, the tracking roller is constantly adjusting any small changes in the belt alignment, eliminating any delay response typical of traditional tracking rollers. The intuitive steering mechanism streamlines the correct steering response based on the force applied which helps to prevent overcorrection.
Another important feature of the DYNA-TRAC tracking roller is the belt edges no longer need to come in contact with side guide rollers. Side rollers have been made redundant on the DYNA-TRAC due to its design, eliminating potential damage and wear to the conveyor belt.
All DYNA-TRAC tracking rollers are supplied with diamond grooved rubber lagging to improve grip on the belt. This improves the steering performance in a variety of conditions including dry, wet and muddy. Diamond grooved rubber lagging enables more positive and reliable tracking than the traditional plain steel rollers.
Additionally, DYNA-TRAC training rollers have enhanced dust sealing which ensures greater service life of the steering mechanism when compared traditional tracking rollers. Traditional tracking rollers frequently suffer from pivot bearing failure due to dust and other contaminates entering the pivot bearing. The redesigned mechanism combined with improved dust sealing, resists the entry of water, dust and other forms of contamination.
DYNA-TRAC Tracking rollers are available to suit conveyor belt widths (in millimetres) of:
400, 500, 650, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600.