While efficient belt-cleaning systems alone cannot ensure trouble-free production, they do contribute to the successful outcome of on-going operations. Comprised of belt fasteners, belt cleaners and other accessories, belt conveyors serve a single mission – to maintain or increase production. Because each of these components serves distinctly different duties, each must be selected carefully to operate with the compatibility needed to achieve peak efficiency.
At the outset, careful consideration must be given to selecting cleaners and fasteners that will work together effectively. The same holds true for belt selection and the development of routine and specialised maintenance procedures.
There are two key goals of effective belt-conveyor maintenance:
1. prevent surprise belt failures and
2. keep maintenance downtime to a minimum. Belt splicing is among the most critical parts of a conveyor system. First, it is one of the few components that constantly experiences heavy abrasive wear. Second, a failed splice not only stops the operation, it drops materials; in fact, cleanup can sometimes be worse than the repair.
Mechanical versus vulcanised splicing
Although some operators prefer vulcanised splicing, mechanical belt splicing has been gaining popularity for decades as it continues to prove – and improve – its reliability, while offering lower cost, quicker installation and easier visual monitoring to prevent surprise failures. In addition, the effective combinations of fasteners and cleaners enable mechanical fasteners to serve as a suitable alternative to vulcanisation.
Mechanical fasteners, which are recognised as an efficient tool for getting failed belts running as soon as possible, are proven in high-tension applications up to 350kN/m. In addition, they can be installed in a fraction of the time required for vulcanised splicing.
For example, it can take six to eight hours to vulcanise a 100mm-wide belt, depending on conditions. That does not include time lost waiting for the vulcanisers to reach the site and set up their equipment, or the potential for inclement weather conditions. Materials and labour may cost several thousand dollars, and the result can steal about 2.5 metres of belting out of take-up reserve.
In contrast, a belt the same size can be mechanically spliced in less than one hour. An on-site belt crew using simple tools – often for less than $100 in material – can accomplish the repair. Plus, a mechanical-fastener repair sacrifices only a small amount of belt.
Once installed, mechanical fasteners allow visual inspection for wear and damage, which is helpful in preventative maintenance programs based on planned downtime. In comparison, vulcanised-splice deterioration or a vulcanised splice (installed incorrectly) will not be visible in its early stages. This may result in catastrophic belt failure, if not caught in time. Vulcanising also works best on new belting. On older, worn belts (where most emergency splicing is done), vulcanising often becomes more difficult, and is less reliable than mechanical splicing.
The correct interface of cleaners and fasteners improves belt-conveying performance and prolongs belt life. In addition, properly functioning belt cleaners facilitate the cost-effective operation of a conveyor system. When the mechanical selection and installation of cleaners is done correctly, the relationship between belt cleaners, splices and maintenance becomes an important factor for maximising conveyor-belt productivity.
Component selection requires a thorough knowledge of the composition of the fasteners, the cleaners and the belt itself. What’s more, there are numerous fasteners, cleaner designs and blade types to choose from.
For example, fasteners with ‘scalloped edges’ feature concave, scalloped-shaped edges, which allow the fastener plate ends to embed deeper into the belt with less effort while reducing the splice height. Reducing the splice profile allows belt cleaners to easily ramp up and over the plates without hard-edge impact. However, be aware that belt splices that sit above the normal height of the belt’s top cover can be picked up by the cleaner tips, causing inefficient belt cleaning and increased risk of damaging the belt, the splice or the cleaner.
Also, the problems encountered between fasteners and cleaners can be avoided by skiving: removing a strip of rubber top cover to lower the fastener plates below or even with the belt surface. On heavy top-cover belts, countersinking positions the fasteners closer to the belt carcass. In addition, this creates synergy between the belt and the mechanical fastener, at the same time reducing the prospects for chips or damage to the cleaner blade.
Belt cleaners work most effectively when part of a systems approach. Multiple types of belt cleaners may comprise a single system, starting with a precleaner or primary cleaner mounted on the head pulley where carry-back can be removed and easily kept in the process stream.
Secondary cleaners are placed anywhere the belt leaves the head pulley (along the returning conveyor line) to remove fine sticky materials, or carryback from the belt. If these materials are not removed, they can accumulate on return idlers and rollers causing belts to mistrack, which can result in further damage to belt edges and premature component failure.
Belt cleaners are available in many designs, and each type functions differently to remove product from the belt. Although most cleaners are effective for a short time, long-term efficiencies will vary based on several factors.
First, cleaners must be designed to work with mechanical fasteners. Manufacturers who produce both fasteners and belt cleaners are in a good position to evaluate this situation and design their products accordingly.
Second, correct installation is the key to belt cleaner performance. If a cleaner is not installed properly, it has failed before it has begun. The belt cleaner must be installed so that it maintains a constant blade pressure on the belt, thus ensuring peak efficiency.
Tensioning is perhaps the most important component in a belt-cleaning system; cleaners that are properly tensioned ensure that the blade maintains constant blade-to-belt contact without putting excessive pressure on the belt, which can cause premature blade wear. Cleaners that incorporate spring-tensioning systems allow mechanical fasteners to pass easily under the blades by momentarily releasing the cleaner blades to move away as the splice passes underneath. This is done with minimal cleaning disruption and without damage to the splice, cleaner blades or the belt.
Also deserving consideration are the relief points, or degrees of freedom that involve the interaction of the belt, the cleaner and the splice. This abrupt interaction creates considerable kinetic energy, which is received in short intervals when the splice hits the cleaner. Proper cleaner/fastener interface requires receiving and dissipating this energy without damaging the splice or the cleaner. Multiple tensioning elements, which provide energy absorption/relief, are needed to store and dissipate this energy while keeping the cleaner blades in contact with the belt.
Cleaners are available that incorporate four tensioning elements (for relief points) that allow the blades to maintain contact with the belt and mechanical fasteners and, at the same time, dissipate harmful impact energy. That energy can damage belts, mechanical fasteners and cleaner blades.
When properly selected, installed and maintained, the combination of mechanical fasteners and cleaners form an effective working team. While their roles differ, each component shares a common purpose, one that keeps belt conveyors moving toward greater productivity.
Kevin Finnegan is product manager for Flexco and Bill Hoogewind is product manager for the Parramatta Group.