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Conveyor Efficiency – More Than Just a Pipe Dream

Thursday, September 10th, 2009

Even today, the troughed belt conveyor is still seen as one of the mainstay methods used in the handling of bulk materials but the inherent problems of such conventional belt conveyors coupled with the continual pressures of environmental legislation has seen many forward-thinking companies such as The Greenbank Group’s Materials Handling Division investing heavily in the field of pipe conveyor technology, resulting in the ability to deliver much more efficient and economical transport solutions to today’s bulk handling industry.
Conventional conveyors have always been plagued with operational issues such as loss of material by wind scatter, velocity disturbance, spillage due to poor alignment, dust creation and spillage at transfer points along the conveyor system. As a direct result, significant focus has been placed on developing totally enclosed methods of belt conveyor, concentrating on such operational benefits as carrying material securely and accommodating difficult routing.
Paul Holt, Greenbank’s Conveyor Product Manager believes that the continuing evolution of pipe conveyors is key in tackling the issues faced by their customers,
“With increasingly stringent regulations regarding environmental planning, it is imperative that we [Greenbank] can provide solutions that help our customers meet their environmental & social responsibilities. Our pipe conveyor system is completely enclosed; this means there is minimal contamination to the surrounding environment through spillage or wind scatter of material.”
“Additionally, the structural design can generate significant economic savings. The general high level of cleanliness of the system means much lower maintenance costs and a pipe conveyor system can negotiate tight curves and rise at steep inclines, ultimately providing a more economical layout, meaning less need for costly and problematic transfer stations.”
The advantages of implementing a pipe conveyor system can be demonstrated across a number of operational areas, all of which represent considerable improvement over traditional open trough conveyor solutions.
Dust Control
In the current climate of environmental directives, the pipe conveyor is particularly fitting in the control of dust.
Because the belt is formed around the product, material dust cannot escape and therefore contamination of surrounding areas and plant is drastically reduced, resulting in much lower maintenance and cleanup costs. In fact it is only at the delivery and receiving ends where it may necessary to provide covers to eliminate dust creation as these are the only areas of a similar design as those of conventional conveyors. In addition to providing delivery and receiving end covers, dust control filters can also be installed to further reduce dust creation.
Reduction in Noise Pollution
The drive motors in a pipe conveyor system are typically designed to give a noise level of 85dbA, conventional conveyors are similar however the noise level of along the route of a pipe conveyor has been measured to be much less than that of a conventional conveyor.
Belt Speed Capacity
It is quite common for pipe conveyors to run much faster than their troughed counterparts. This is possible because the material is fully enclosed and is also due to the tubular belt being inherently stiffer which results in less belt sag between idlers, thus preventing disturbance of the material being transported. It should be noted that belt speed is wholly dependent on idler diameter and rotational speed and since the life of the idler bearing is inversely proportional to its rotational speed, there is an upper limit to belt speed. This is normally set at an idler rotational speed of 1000 RPM.
For operational purposes, belt speeds should be kept below this figure and it is recommended that idler rotational speeds are set between 500 and 700 RPM. This gives belt speeds in the order of 150 m/min on smaller diameters and up to 250 m/min on the larger diameter conveyors.
Coping With Curves
In comparison to trough belt conveyors, a pipe system is able to negotiate horizontal and vertical curves of relatively tight radii thereby eliminating costly and problematic transfer stations.
Whilst the operational and economic benefits of curve handling are obvious, there are still implications of introducing such systems. At the standard panel spacing, curves up to 45° including angle require a curve radius of 300 times pipe diameter with increasing curve radius up to 600 times pipe diameter for a 90° turn. Should tighter radii be required, it is possible to reduce the factor to 200 times the pipe diameter by giving additional support to the belt by reducing the panel spacing. The difficulty is, of course, the deformation of the circular shape at the curve, which, apart from any possible damage to the belt, will reduce the carrying capacity.
As the Pipe Conveyor travels round a horizontal curve, there is a natural tendency for the belt to twist, displacing the overlap to the inside of the curve when loaded and to the outside of the curve when empty. For this reason it is necessary to cater for a straight length of conveyor before and after a curve to allow the belt to centre itself. This straight length depends on curve angle and the layout of the conveyor.
However companies like Greenbank, as part of an extensive R&D programme, are at the forefront in the research and testing of pipe conveyors systems with significantly reduced radii and at reduced idler spacing to address these restrictions.
Coping With Climbs
Along a similar vein as curve handling, pipe conveyors systems are much better suited to coping with steep inclines, enabling handlers to leverage the benefits of maximising the incline angles of their conveyor system. Because of the increased contact area between belt and material, much steeper angles can be negotiated, allowing a more economical layout. On average, a pipe conveyor will handle materials on an incline which is 50% greater than can be achieved with conventional troughed belt conveyors.
Carrying Capacity
In general, a pipe conveyor will carry an equivalent load to a conventional troughed belt conveyor which has a width in the order of three times the pipe’s diameter, however the maximum capacity of a conventional conveyor also depends on the troughing angle of the idler sets and the surcharge angle of the material being conveyed and as such a pipe system may prove even more efficient in particular implementations.
Power
Pipe Conveyors use approximately 10% of the power absorbed by pneumatic systems and, in theory, 10% to 15% more than a troughed belt conveyor. However in practice, where a straight pipe conveyor is alongside a troughed conveyor, it has been shown that the pipe system has absorbed 15% to 20% less power.
This saving can be attributed to three key factors; the cleaner environment of the enclosed conveyor which leads to less spillage and hence friction from the idlers, the idlers on the hexagon of the Pipe Conveyor are not constantly turning, and significantly there is less sag between idlers which reduces the lifting, lowering and disturbance of the material.
Belt Performance
As well as normal cover compounds, various other belt types are available to address such aspects as high temperatures, oil resistance, fire resistance, food quality and abrasion resistance. The majority of conveyor installations use a ply type belt and the materials used in the manufacture of pipe conveyors are identical to those used on conventional conveyors.
The difference between pipe and conventional trough conveyors is in the construction of the belt itself. Accurate control of the weft strength is critical to ensure the belt is flexible enough to form the pipe shape whilst still maintaining sufficient strength to prevent collapsing, support of the load and resistance of fatigue from flexing. In addition, the plies are closed up at the edges of the belt to reduce edge stiffness, which allows the overlap to form an effective seal.
Because limitations on the tensile strength are similar to those on conventional belts, steel cord belts are available for the larger capacity pipe systems. These are designed to give the same pipe forming characteristics as the ply belts with breaker plies being used to maintain the pipe shape.
Summary of Pipe Conveyor Benefits
• Ability to negotiate curves of relatively sharp radii (eliminating transfer points)
• Steeper incline angles can be accommodated
• Enclosure of the transported material
• Elimination spillage and wind scatter
• Containment and control of dust
• Product security
• No spillage or dust from return belt as this is enclosed
• Reduction in noise levels
Conclusion
Since the early 1980’s, the pipe conveyor has always proved to be a simple and reliable system but it is only recently that industry experts have started to acknowledge the fact that pipe conveyor systems are the only viable solution to jointly address both the economic and environmental demands faced by today’s materials handling market. As such, companies like The Greenbank Group who are actively expanding and enhancing their pipe conveyor product portfolio, are well placed to play a major role in shaping the future of bulk materials handling.

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