Modern Quarrying Q2 2019

KEY TAKEAWAYS

Quality parameters in aggregate production are normally based on strength, size and shape of the end product

The final product requirement is the cornerstone of equipment selection and plant design

If optimum shaped product is an obligation, the VSI crusher is the ideal shape-producing crusher

Apart from costs, the main advantage of the VSI compared with the HSI crusher when it comes to production of a cubicle product is the consistency in the end product

An impact crusher reduces the amount of flaky material from the feed ROM and/or flakiness produced from the jaw and cone crushers.

crushers required to produce the desired product sizes in the acceptable crushing ratios,” says Ravenscroft. “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,” adds Ravenscroft. More quality considerations Sandro Scherf, CEO of Pilot Crushtec International, says one critical consideration is the end application of the aggregate produced. Some basic examples where shape and size or product size distribution (PSD) is critical to include are filter sands, road construction and asphalt topping, to mention a few. “Filter sands require very strict product curves. With too much fine material, the fil- ter sand turns to clay, which doesn’t allow water to flow through. With too little fine material, the water passes through too easily and particles aren’t filtered out,” explains Scherf. For road base construction, Scherf says the Colto specs on G1 and G2 base and sub-base material require at least 4-12% of 0,075 mm material, all produced from clean parent rock. “The micro fines basically act as a lubricant when compacting the road-base to ensure that you get the correct compaction levels and have a sturdy base on

job at hand, project considerations always have to start at the end. “This means that all tooling deliberations have to be informed by the quality demand of the final product, and then go step by step from the end of the process to the primary crushing stage,” says Pruewasser. Dewald Janse van Rensburg, MD of B&E International, says the final product requirement is the cornerstone of equipment selection and plant design, and certain combinations of jaw crushers and secondary crushers have proved to be more effective in achieving certain outcomes. “Customer requirements will also specify the grading envelope that must be achieved, which is the ratio between the coarser and finer aggregates. For any operation, the intended throughput rate is another key consideration in the choice of crushers and their sizes, and with commercial operations the market will dictate the level of demand to be satisfied, or the draw-off requirement for a specific project,” says Van Rensburg. Tyron Ravenscroft, Finlay product manager at Bell Equipment, says the strength of the material determines the crushing ratios acceptable to that material and how many crushers will be required to crush the run of mine (ROM) to the desired product sizes. “The size of the ROM will determine the size of the primary crusher to accept the ROM. The ROM size will also determine the number of

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QUARTER 2 - 2019 MODERN QUARRYING