Dispelling Myths Through Training

Solving conveyor belt problems requires re-education on the root causes.

By: R. Todd Swinderman, Contributor

Most belt tracking issues result from misalignment of the structure, pulleys and idlers. Photo courtesy of Martin Engineering.

Conveyor belts form the critical artery through any bulk processing operation, carrying materials between each phase of a production plant. Yet much of the assumed knowledge about conveyor system design and operation is inconsistent, incomplete or inaccurate, leading to all-too-common problems of spillage, buildup, dust and belt damage.

The source of such issues can be traced back to informal design axioms (or ‘rules of thumb’) that have emerged through historical trial-and-error and passed down through generations to become accepted as fact. These ‘rules’ are often based on successfully treating the symptoms of a conveyor problem rather than addressing the root causes.

To truly understand the root causes of conveyor problems and get conveyors performing as desired requires technical knowhow and decades of lived experience. And there is a need to equip the next generation of designers and engineers with the right knowledge and skills to avoid repetition of the errors associated with the handed-down design rules. Training based on a combination of industry experience and engineering expertise is proven to greatly improve design decisions, resulting in higher productivity, fewer safety incidents and reduced unplanned outages.

HISTORICAL DESIGN AXIOMS

Many design principles are undoubtably the result of the early years of conveyor use. Others emerged in codes developed in the early 20th century, typically following catastrophic equipment failures and serious safety incidents. Since then, different industries, operators and even individual plants have come up with their own ‘rules’ which have become etched into company specifications.

However, since the development of the modern conveyor in the early 1900s much has changed in its construction, performance and regulation so, when it comes to design, doing “the same as we’ve always done” isn’t good enough, especially when many conveyor design guidelines appear to contradict each other. The following sections outline examples of some of the issues relating to materials, sealing systems and tracking.

MATERIAL SIZE AND SHAPE MATTERS

When the quantity, quality or source of the bulk material changes, the design must be adapted to new handling challenges. For example, as minerals from a particular source are depleted, material typically needs more processing to remove unwanted residues and fines to achieve the right size for processing. The cost of raw materials can also drive processors to accept alternative materials with differing consistencies and a higher percentage of fines. And the actual ‘lump size’ in production is frequently much larger than the design specification, a discrepancy that’s often the result of adjustments to crushers, screens or other parts of the plant to increase production.

The lump size and percentage of fines provide guidance on selecting the belt width and skirtboard width and height. Maximum lump size influences idler selection due to impact forces but also depends on how the material tends to fracture. Bulk materials are hard enough to handle when consistent in size, physical properties and percentage of fines. But for ‘slab’ or ‘rod’ shaped materials, the lump size could vary significantly. Lump or slab mass is a direct variable in the calculation for idler and impact cradle selection, as well as belt selection, chute size and slope.

In-person training is an effective way to ensure root causes can be addressed through good design. Photo courtesy of Martin Engineering.

SKIRTBOARDS AND SEALING SYSTEMS

Skirtboard width and length guidelines were developed long before dust was a concern, most likely by observation and experience to determine sufficient height to contain the turbulent material long enough to allow it to settle into a stable profile after the belt is loaded. When covers started being used to control dust, there likely weren’t any changes to the height or length guidelines. Instead, the same general rules based on either belt width or belt speed continued to be used.

Eventually it was recognized that the velocity of the air in the skirtboard enclosure had to be controlled to reduce dust emissions. At the same time, suppliers and engineers began paying more attention to the wear liner and skirtboard sealing details to reduce leakage and spillage.

For the width of the skirtboards and free belt edge calculations, there are omissions and inconsistencies between even the most well established specifications (eg CEMA and ISO). Sealing system designs also vary, so the adequate edge distance in the load zone depends on the actual dimensions of the sealing system specified. Examining all the factors that go into an engineered loading of material on the belt is a complex and lengthy topic of its own.

BELT TRACKING AND IDLERS

Theoretically, a properly installed and aligned conveyor system using a belt within manufacturing tolerances, with square splice(s) and center loading, should track without the need for training idlers. If most of the training idlers are tied off, they are either ineffective or the belt must be constantly re-centered to compensate for structural and component misalignment or belt damage. Too many training idlers can interfere with each other and often make tracking worse. Additionally, the rule of installing training idlers a standard distance apart regardless of the quality of the installation and operation does not consider whether they are even needed or how much correction each training idler can generate.

For a start in locating training idlers, the most critical positions are before the belt enters the tail pulley, after the loading zone, before the belt discharges and before the belt enters the take-up. Portable and underground conveyors may require more training idlers because of the installation tolerances or distortion of the structural alignment when portable conveyors are moved. Most belt tracking problems are related to misalignment of the structure, pulleys and idlers, and not the absence of enough training idlers.

CONCLUSION – TRAINING IS KEY

From these examples alone, there are many inputs required to ensure a safe and productive conveyor, most of which are not included in the generally accepted design rules. Unless those dealing with conveyor issues have a detailed understanding of how to treat root causes rather than perpetuate temporary fixes, problems will almost certainly continue. With the retirement of many experienced operators and mechanics it’s critical to educate younger colleagues, at least on the basics of conveyor design and operation.

Fortunately, there are many options for professional and comprehensive conveyor training. Many companies offer in-person classes, virtual training and one-on-one support. The most effective approach to training examines a plant’s specific conveyor challenges and helps operators run safer, cleaner and more productively by learning on the job and addressing the root causes of conveyor problems. One axiom that always rings true: “If you think education is expensive, try lack of knowledge.” WMHS

R. Todd Swinderman is CEO Emeritus of Martin Engineering, a global leader in bulk material handling for more than 80 years. Martin Engineering continuously develops new solutions to make high-volume conveyors cleaner, safer and more productive. The company’s series of Foundations™ books is an internationally-recognized resource for safety, maintenance and operations training and can be downloaded as free PDFs from the Martin website. Martin Engineering products, sales, service and training are available worldwide. Visit: www.martin-eng.com.