Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/403276
TIONS ILLUSTRATED OUR EXPERTS Crushing for Particle Shape November 2014 Bradly Estes is the plants manager for the Western Re- gion of Granite Construction. Based in the Seattle, Wash., area, he oversees the mate- rials business for Granite's Washington region, includ- ing numerous aggregate, recycle, and HMA facilities. Estes started with Granite in June 2003 and has held positions in engineering, plant management, and materials management over the past 11 years. He holds a bachelor's degree in min- ing and mineral engineering from Montana Tech, of the University of Montana. George Fensome is the area manager, Americas, for Sandvik Construction's crusher product line. He is based in Chilcompton, United Kingdom. Fensome has more than 23 years in the crushing and screening industry. His experience within Sandvik goes back to 1991, when he joined Svedala, a company later acquired by Sandvik, and has included several positions in product line and sales management. During this time, he has also been in- volved in the development of several crusher components patented by Sandvik. The main job of the primary crusher is to reduce the particle size, with product shaping taking place at the secondary or tertiary stages. Some operations may fi nish the product at the secondary stage, but most will require at least three stages of crushing. Closing the circuit at the third or fourth stage also will help to refi ne particle shape because it allows for crushing at a lower reduction ratio, which improves shape. To a degree, geology dictates the type of crusher required to produce cubical aggregate products. For instance, limestone has lower abrasion characteristics and is softer than granite or basalt. For limestone production, primary and secondary horizontal shaft impact (HSI) crushers will help produce cubical product. With granite and basalt, compression crushing through a primary jaw and secondary cone is often required. Modern, high-speed cones can produce a cubical product, where their older-style counterparts cannot, due to the fact that they create rock-on-rock crushing within the chamber. The key to success is to ensure the cone is consistently choke fed, with an aim toward a lower reduction ratio. A benefi t is that a modern cone crusher also is economical to operate over time because wear costs are typically low. It may seem counterintuitive, but the faster the speed with a VSI, the lower the throughput — with greater production of undesirable crusher fi nes. Every crushing chamber has an ideal speed at which it produces the best mix of product qual- ity and production rates. Slowing a VSI crusher will improve product shape while producing fewer minus-200s and provid- ing greater tonnage per hour. Setting the stage 2 3 Geology plays a part 5 A few thoughts on cones 6 Success with a VSI