Page 48 - HUB-4 Magazine Issue 89

Quarrying
A practical measured approach to
conveyor upgrades
R. Todd Swinderman, President Emeritus / Martin Engineering
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, many operators simply speed up the conveyor. Rather than increasing capacity as intended, speeding up the conveyor often results in reduced capacity, because changes in the trajectory of the discharged material can cause build up and clogging of hoppers or chutes, leading 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, which may weigh more, requiring structural changes and potentially additional space, limiting access for maintenance.
As plant engineers, operators and maintenance mechanics make undocumented or unproven changes, over time, the conveyor operation and physical characteristics can morph the system. In some cases, the proper answer to the question, "Can we increase capacity on the existing conveyor?” should be “No, we need to start over.”
Adjustments in belt speed and load volume should be accompanied by an in-depth assessment of the system. © 2024 Martin Engineering
Conveyor Design
Conveyor design is an iterative process. Purchasing a conveyor at the lowest capital cost, 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 OEM’s goal is to win the low bid and make it through the warranty period without costly rectifications. If the goal was 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. The 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. The most recent Conveyor
Equipment Manufacturers Association (CEMA) design guide Belt Conveyors for Bulk Solids 7th edition requires predicting power requirements within -0 to +10% of actual. [1] Much research and development for conveyor power requirements has taken place, resulting in several low-cost design software options. [Fig. 1]
Figure1 - Simplified Conveyor Iterative Design Flow Chart
This graphic might show the iterative design intent more clearly © 2024 Martin Engineering
Upgrade Design
First, define the problem the conveyor upgrade plan is trying to solve. It may seem obvious, but a lack of understanding for the primary reason(s) for an upgrade could cause specifiers to address symptoms rather than root causes. The new design might not address the primary need for a performance upgrade.
For example, if the chutes are plugging or there is spillage, then it might not be a conveyor issue, but instead an operator or maintenance issue. If the problem is belt damage, mistracking or tripping the breakers, it 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.
Component Standardization
It is usually desirable to try to use belting, idlers and other components that are available elsewhere at the 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 might escalate idler loads, rolling components may require a higher
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