Considerations to make when upgrading your conveying system

Many operators simply speed up a conveyor when greater production is needed to meet rising demand, or when lower quality raw materials require more tons to be processed per unit of output to retain the same level of production.

Rather than increasing capacity as intended, speeding up a conveyor often results in reduced capacity because changes in the trajectory of the discharged material can cause buildup and clogging of hoppers or chutes. And this leads to unscheduled downtime.

More tonnage means more carryback, dust and spillage, degrading workplace safety and increasing labor costs for cleanup. Greater volume and weight could also require a more powerful drive that may weigh more. And this may require structural changes and potentially additional space, limiting access for maintenance.

As plant engineers, operators and maintenance mechanics make undocumented or unproven changes, the conveyor operation and physical characteristics can morph the system over time. In some cases, the proper answer to questions regarding whether capacity on an existing conveyor can be increased should be: “No, we need to start over.”

Original design

Prior to the modification of a conveyor, engineers recommend verifying that the current system is operating in an environment and on an application for which it was originally designed.

The existing conveyor may have been repurposed over the years by modifying chutes, adding feed points or changing the slope to accommodate process changes. In situations where conveyors are many decades old, the original design specifications and drawings could be incomplete or lost.

Conveyor design is an iterative process. Purchasing a conveyor at the lowest capital cost is generally accompanied by significant design compromises. Even if it matches previous conveyor structures, the design is likely to use the maximum loading capacity on the narrowest belt traveling at the maximum speed for the raw material, while meeting only the minimum safety standards and codes.

When sold on lowest price, the supplier’s goal is to win the low bid and make it through the warranty period without costly rectifications. If the goal is to design a conveyor with the lowest cost of ownership over its intended life, it was likely designed with less than maximum loading, a slightly wider belt and the capacity to run at a reasonable speed, while exceeding minimum safety standards and code requirements. A best practice is to re-establish the original design intent and compare it to the existing conveyor.

Conveyor technology changes over time, particularly in belting and calculation methods. Until the 1980s, without the aid of computers and design software, conveyors were designed using hand calculations and experience. It’s amazing how many conveyor designers still use an edition of the Conveyor Equipment Manufacturers Association’s (CEMA) Belt Conveyors for Bulk Solids design guide from the 1970s or earlier. The fifth edition relies on research from the 1940s.

The sixth edition of the guide indicates that the hand calculation method was an inaccurate predictor of the actual power needed for proper conveying. The most recent seventh edition requires predicting power within -0 to +10 percent of actual. Much research and development for conveyor power requirements has taken place, resulting in several low-cost design software options.

Upgrade design

With a conveyor upgrade plan, a problem must first be identified that needs solving.

This may be obvious, but a lack of understanding of the primary reasons for an upgrade could cause specifiers to address symptoms rather than root causes. The new design, for example, might not address the primary need for a performance upgrade.

Consider, for instance, if the chutes are plugging or there is spillage. This might not be a conveyor issue but rather an operator or maintenance issue. If the problem is belt damage, mistracking or tripping the breakers, the problem may be due to misalignment of the structure and idlers. Surge loading the conveyor in an attempt to catch up for lost time spent cleaning could result in more spillage.

The bulk material

Another critical early step in an upgrade project is understanding the physical properties of the material handled.

Knowledge of properties such as solid density, bulk density and particle distribution are critical to a well-designed conveyor. Original test results for material are likely out of date due to changes in the sources and variations in the extracted raw cargo over time.

Discrete element modeling software programs help model the flow of bulk solids through chutes and onto conveyors. Laboratories can perform the tests, or operators can conduct their own basic tests using the information in the ANSI/CEMA Standard No. 550: Classification & Definitions of Bulk Materials publication.

Component standardization

It is usually desirable to try to use belting, idlers and other components that are available elsewhere at a site or are common supplier stock items.

This may not always be possible, but the capital cost alone should not force a less-than-optimum design solution. Because increased tonnage may escalate idler loads, rolling components may require a higher load capacity to obtain an acceptable life. Consider the life cycle costs of your design and component selections.

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