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"Not wearing out"
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Most conveyor belts in severe duty applications typically do not just wear out. More often, they experience a shortened lifespan from catastrophic events, whether it is a significant impact, splice failure or piercing damage, or they suffer from chronic issues, such as mistracking or frozen idlers. In addition to correcting such problems to extend belt life, a concern to many bulk material handling operations is the damage from loading, belt wear from cleaning devices and the difficulty of cleaning damaged belts.
Figure 1. Engineered chutes direct material flow to the receiving belt,
Belt wear from loading
Since the belt is a major cost element in the process of conveying bulk materials, much attention is focused on reducing wear and damage. In general, loading wear occurs over a long period of time from the discharge of material onto the belt and from contact with conveyor components, such as idlers and belt cleaners. Belt wear from loading includes both impact damage and frictional wear.
Damage to the belt can be a single event, such as that from tramp metals or oversized lumps in the material flow stream. Such sudden damage can result in catastrophic failure that requires immediate attention, demanding a system shutdown. The negative effects of long-term wear are less dramatic, and replacement can generally be scheduled for planned outages to avoid affecting conveyor availability.
Figure 2. General wear of rubber, based on impact angle.
One key to understanding belt wear from loading is the chute. The development of discrete element
The primary objectives of a chute design are to direct an uninterrupted flow of the bulk solid from the chute to the receiving belt,
Figure 3. Three different chute design approaches.
While the interaction between the belt and the bulk material is complex, in general, troubleshooting belt wear caused by chute design can take advantage of some simple relationships. The first is the general relationship between material impact angles and the wear rate of rubber. Figure 2 shows that, as the impact angle increases, the wear generally decreases.
The second fundamental
Common chute configurations include rock boxes, inclined flat chutes and curved chutes, as shown in Figure 3 where Ve is the exit velocity of the bulk material stream from the chute and Vb is the belt speed.
Figure 4. Comparison of loading velocities and vertical component Vey.
Other factors to consider when designing the optimum chute for a given application include drop height and preferred liner materials, but in general, belt wear from the choice of chute design is greatest with rock boxes, which do little to slow the material’s velocity and introduce a large amount of disruption as the load cascades from one shelf to the next, then lands on the moving belt at a near-perpendicular angle.
Flat inclined chutes help shift the load in the general direction of the receiving belt’s
Figure 5. A single scratch can contain significant carryback.
Belt wear from loading impact is generally
Figure 3 is a
While belt wear is the main concern, a significant amount of attention should be paid to the selection of liners to prolong chute life. Given the relative cost of the belt compared to the chute in most applications, the wear liners should be considered sacrificial components; attention would be better spent on improving chute design, selecting lower friction liners and making the
Cleaning of damaged belts
Cleaning efficiency is related to the material properties,
The US Mine Safety and Health Administration (MSHA) estimates that 85% of all conveyor problems – including wear – come from fugitive materials. Fugitive materials are those that escape the conveyor other than at the discharge, including spillage,
Since carryback is a significant source of fugitive materials, which, in turn, is a significant contributor to belt and component wear, it makes sense to focus on adequate belt cleaning. Much attention is paid to the price of belt cleaners and replacement blades. Like chute liners, belt cleaner blades should be considered sacrificial components, and the focus – rather than being on price – should be on installing an adequate number and appropriate type of belt cleaners that can be easily serviced. Cleaning damaged belts
With a belt in good condition and professional maintenance, a belt cleaning station can usually control carryback to within 10 – 100 g/m2. The Conveyor Equipment Manufacturers Association (CEMA), in its seventh edition of Belt Conveyors for Bulk Materials has established a system for rating the difficulty of the belt cleaning application and for desired levels of carryback
- ALDRICH, J. and ZHANG, Y., ?Minimizing Belt Wear and Damage from Optimized Chute Design' Conveyor Dynamics Inc.; Bellingham, Washington, USA.
This is an excerpt from an article that was first published in World Coal October 2016. To register and receive your free trial of the magazine, click here.
Read the article online at: https://www.worldcoal.com/handling/30032017/not-wearing-out/