Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/945822
24 AGGREGATES MANAGER / March 2018 Adjust screen speed and stroke as needed T he concept of avoiding a bottleneck altogether is a misnomer. The real question is whether you have the bottleneck you want or desire, explains Phil Gosnell, eastern divisional production manager at Rogers Group Inc. "All plants have at least one bottleneck," he says. "You can't simply remove the bottleneck, because another one will take its place — the basic law of physics. The best you can hope for is making the bottleneck what you want." The typical ideal design for any aggregates operation is to have the fi nal crusher in a plant be the bottleneck, because it represents the most expensive asset to replace for further throughput improvements. As the market and demands change, aggregates opera- tions are "forced to push products in a different direction," Gosnell explains. Using Rogers Group as an example, he says that many of the company's historical plants were designed around the demands of large highway projects, so producing a base product was paramount. However, the plants have had to be modifi ed through- out the years to push base forward, creating multiple new bottlenecks from screens to conveyors. "Finding bottlenecks is easy, though," he says. "If the plant is properly automated, watch the human-machine interface (HMI). If it's not automated, talk to the plant op- erator. Most operators will list off the fi rst three bad things that will happen when the feed rate increases. Otherwise, grab a shovel, call the quality control (QC) technician, and start turning feeders up." It's critical that operations personnel and those respon- sible for QC are constantly observing all aspects of the ag- gregates facility, points out Joe Schlabach, vice president of marketing and sales for Deister Machine Co. Inc. "There are conditions every day that can affect effi cien- cy," he says. "Where it's coming out of the pit can vary from one blast to the next — whether it's dry weather or wet weather — it all can affect the performance of crush- ing and screening. [The] operations [team] will learn by experience what to do and what the starting point is to make sure material stays in spec." There are many factors — not just one answer — to how issues causing bottlenecks need to be handled to run at a certain amount of effi ciency, Schlabach says. He de- scribes it as "the measure of the amount of material going through the screen divided by the amount of material available to go through the deck." Although the goal is typically to get more tons per hour across the screen, "the real key to optimum screening," he adds, "is maximizing capacity without losing quality and effi ciency." The Art of Handling Bottlenecks Adjust the speed on screens to help travel velocity of material to help unload the screen faster, but note it can reduce effi ciency. If repurposing screens from their initial setup for a scalping application to a fi n- ish screen, fi ne-tune stroke and speed. Decreasing the stroke reduces the bounce from each particle, improving effi ciencies on fi nish size products. De- pending on screen type, inclination, and bed depth, change the direction of rotation — forward to un- load the screen faster and backwards to increase ef- fi ciencies. Perform a vibration analysis and examine X, Y, and Z axis data to determine why the screen is a bottleneck and how to correct it. 1