FEATURED PRODUCTCOAL CONVEYOR FOR A NEW AGE
The engineering of belt conveyors to move bulk materials has
changed little during the last 50 years. Granted, designers have
computers to help design them, and new materials to use in building
them, but the basic rules of thumb haven’t changed much in
this time. This “status quo” is still used in spite of the fact that
virtually every requirement for safety, regulatory compliance and
production performance has been raised in the same period.
As the saying goes, if you do what you have always done, you will get what you have always gotten. In the face of these changes in requirements (and the fact the requirements continue to change), a new approach to specifying, designing and purchasing belt conveyors is needed. It is time for new conveyor architecture.
The application of architecture
“Architecture” is the best term to describe this new design
standard and methodology. It can be defined as the science and art of selecting and interconnecting components to create systems to meet functional, performance and cost
goals. The time has come to “start over,” by redesigning conveyors from the ground up. By including elements that match customer needs for a clean, safe and productive
system, this new conveyor architecture can be cost-competitive, yet flexible enough to be easily upgradeable. A new priority of considerations that will rank the goals will be required. All design decisions are made based on this ranking.
the new hierarchy of design
This new design priority includes these ranked elements:
1. Design capacity: The system must deliver the required (tons/hour) output. If a system cannot reliably achieve its throughput goals, then that system does not achieve its performance goals and is not suitable for the application.
2. Safety: In the past, the approach to safety regulations has been to meet the minimum mandatory requirements. Now, most safety standards around the world are moving away from mandated minimums toward risk mitigation through risk analysis. The approach of the new conveyor architecture is to exceed the minimum mandated safety and incorporate technologies to make conveyors safer to operate and maintain.
3. Cleanliness: The control of fugitive material through improved design should be a high priority. Simple design decisions, such as where to run utilities so they will not interfere with the ability to safely clean around a conveyor, should be carefully considered.
4. Service-friendliness: A commitment to making it easy to reach, clean, adjust and repair components is essential to keeping a conveyor clean, safe and productive. Fundamentals such as the mounting of components on tracks for slide-in/slide-out maintenance, and systems that allow service from either side of the conveyor will simplify maintenance procedures.
5. Cost effective: The general practice for procurement in industry is to find the lowest price. But lifetime cost should be as important. By keeping accurate records on the cost of operating, cleaning and maintaining systems, minor design changes that improve safety and reduce fugitive material can be justified. With minimal initial penalty, the basic conveyor system can be outfitted with components some standard, some specialized — that make the system more affordable to operate, clean and maintain through the long term. More importantly, the designer should anticipate upgrades to components to solve specific problems that might occur. While it might not be cost-effective to
include from the beginning every problem-solving component that could possibly be fit onto a conveyor, it is cost effective to provide the clearances and allocate the space for upgrades in the initial design.
6. Upgradeable: Trying to upgrade an "old school" system is typically difficult and expensive. It often results in only minimal improvement in capacity or productivity, while increasing the generation of fugitive materials. The philosophy of new conveyor architecture is to anticipate at least one capacity increase of 10-15 percent during the system's initial specification.
Turning the hierarchy into design details
This prioritization should be incorporated into a number of design details on new conveyor architecture. Some of these details include:
Dust resistant structure. Conventional conveyor stringers are designed from C-channel with angle iron bracing. But these shapes allow dust and spillage to accumulate, leading to long-term corrosion and safety problems, as well as the costs of cleanup. In the U.S., OSHA is currently in the midst of a campaign that mandates the cleanup of accumulations of explosive dust thicker than a paper clip.
By orientating structural members at 45 degrees to horizontal, the accumulation of dust and spillage can be reduced, without an increase in the weight, (and cost) of the structure. For example, when the angle-iron cross braces are orientated "point up" they will tend to shed, rather than accumulate fugitive materials. Granted, these 45 degree surfaces can still accumulate some material, but not nearly as much as horizontal surfaces. As a bonus, they will be easier to clean.
The design selected for new conveyor architecture stringers combines the convenience of a standard C-channel with a fiat web section and the fugitive material shedding capabilities of a 45 degree flange. This Dust-Accumulation Resistant Structure has strength comparable to common C-channels at a similar weight, so there should be little cost differential. This stringer is predrilled (laser) with mounting and connecting holes on 6"( 150 mm) centers. These holes can accommodate the mounting of standard troughing and impact idlers, impact beds and sealing cradles.
Oversized terminal pulleys
The conveyor's head and tail pulleys are typically kept to a minimum size to reduce their price, but this can increase their lifetime cost. When a tail pulley is upsized and deeper drop brackets are used, it becomes easier to install, inspect and maintain tail pulley belt plows. Similarly, oversized head pulleys allow more room for installation, inspection and service of belt cleaning systems. By selecting larger diameter pulleys, the price is slightly increased, while the lifetime cost is reduced.
Removing the transition idlers
The required transition distance from the tail pulley to the first fully troughed idler is specific to the construction and tension of each belt Providing the proper transition distance will allow the belt to be fully-troughed before it receives any material. This eliminates transition while it improves transfer point sealing. Transition idlers should be installed before the loading zone only if dynamic analysis indicates they are necessary to control belt flap.
External wear liner
Wear liner is a sacrificial lining to reduce the abrasion of the cargo against the skirtboard and the pressure against the skirtboard sealing systems. Long-standing practice is the liners are installed on the inside of the chute and skirtboard. The new conveyor architecture proposes to install this "liner" on the outside of the skirtboard steel (yet still on the inside of the sealing system). This "external" wear liner allows easier installation, inspection and replacement, all without confined space entry. As always, wear liners must be accurately installed and well maintained to prevent trapping particles, which accelerates wear of the belt and seals.
Components ranging from belt cleaners to impart cradles can be designed with track-mounted or mandrel-style support structures, allowing them to be removed and replaced efficiently. A major prerequisite for using service-friendly designs is that there is sufficient access to take advantage of the benefits of these designs.
The sane conclusion
Clean, safe, productive material handling on conveyors is more a question of state of mind than cost. An overall approach that places more emphasis on cleanliness and safety than initial cost is critical to loading and conveying bulk materials at a high level of safety, cleanliness and performance. Dozens of simple yet significant design, operating and maintenance details become reasonable when following the design hierarchy of the new conveyor architecture.
According to Einstein, insanity is doing the same thing over and over again, and expecting a different result In the case of belt conveyors, this means the sane thing is to adopt the new conveyor architecture as the design standard. The result would be conveyors with improved overall performance in areas that include productivity, cleanliness, safety, environmental compliance and productivity.