Capital Equipment News September 2018

CRUSHING – PART 2

TALKING POINTS

says Ravenscroft. Van Rensburg says it’s not easy to con- trol the shape of the aggregate; different host rocks will break differently. “If for instance the material is flaky, then you can introduce specialised equipment like a VSI to break down the edges of the stone and make them more cubical,” he says. While most mining operations require ore to be crushed as fine as possible, Van Rensburg says this is not always the case. “Where fines must be kept to a minimum, there is need for less aggressive crushing, or the ore must be screened or scalped before crushing takes place to minimise further fines generation,” adds Van Rensburg. Pruewasser says every stone has a crystalline shape which is normally hex- agonal. He says impact crushing systems crush the material along this crystalline structure because it is the easiest part of the rock to crush. “This always gives a better shape than crushing with shearing or pressing forces offered by cone and jaw crushers,” says Pruewasser. Scherf says this can depend on the rock characteristics and the plant layout. However, as a general rule, the HSI and VSI crushers offer the best shape. “Often a three-stage plant consisting of 1 x jaw crusher and 2 x cone crushers will also produce a cubicle product. The type of cone crusher will have a significant effect on the results. A Metso HP crusher, for ex- ample, can produce a very cubicle product when utilised correctly, which a Symons type cone crusher, for example, cannot offer,” says Scherf. Due to the hardness and abrasive nature of most of the rock in southern Africa, Scherf says the VSI is the preferred option when it comes to a cubicle product, and would be used as a tertiary or quaternary crusher. “The main advantage the VSI has over the HSI crusher in this application, operating costs aside, is the consistency in the end product. As soon as you start feeding an HSI crusher you start having wear in the chamber, which means you require constant adjustment to achieve the same results,” says Scherf, adding that on the VSI, the wear on the rotor has a minimal effect on the product PSD, meaning you have a consistent product. Close partnership To come up with the best crushing solution for the application at hand, a closely knit cooperation between the supplier and the customer is of utmost

“The desired product shape will determine the type of crushers required. Should a high quality shape be required, an impact crusher will be necessary to get the end product into specification.”

Tyron Ravenscroft, Finlay product manager at Bell Equipment

“At Weir Minerals Africa, we understand that the more we help our customers become profitable, the more relevant we are. We do this by maintaining our machines and collaborating with clients continuously to find innovative ways to increase their production, using their existing infrastructure.”

JD Singleton, process director at Weir Minerals Africa

“Often a three-stage plant consisting of 1 x jaw crusher and 2 x cone crushers will also produce a cubicle product. The type of cone crusher will have a significant effect on the results.”

Sandro Scherf, CEO of Pilot Crushtec International

asphalt (or cement) is required in produc- tion, thereby reducing costs significantly,” he says. Scherf adds that since flaky material doesn’t compact as tightly as cubicle aggregate does, one is left with voids or spaces between the material, which is then filled with tar from the asphalt. In hot climates the tar will soften, and this can cause deformation of the road surface when exposed to heavy traffic. “Cubicle product adds value to your end product, however many construction projects don’t require high specification aggre- gate, so the added expense of shaping the end-product does not make financial sense,” argues Scherf. Shape in question If the shape of the stone is a major spec

requirement, what crusher achieves the best product shape? JD Singleton, process director at Weir Minerals Africa, says if optimum shaped product is an obligation, the VSI crusher is the optimum shape- producing crusher. The same view is shared by Heath Dickson, national mining sales manager at ELB Equipment, who says, without a doubt, a VSI, and in some cases a horizontal shaft impact (HSI) crusher, will help shape up the product. Ravenscroft is of the view that an impact crusher will give the best quality shape to a stone. “An impact crusher reduces the amount of flaky material from the feed ROM and or flakiness produced from the jaw and cone crushers. It re- moves the brittle pieces from the stones, creating a more high quality cubic shape,”

CAPITAL EQUIPMENT NEWS SEPTEMBER 2018 10