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Pilot study on the influence of the eccentric speed on cone crusher production and operation
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Abstract • There are many different machine design parameters and variables that affect the'' production of cone crushers in a minerai processing piant. One of these variables is the speed at which the cone gyrates. In June 2012, pilot tests were conducted to determine the production and operating conditions over a wide spectrum of speeds. Mining operations will have variations in the ore characteristics and feed rates that result in nonoptimal use of the crushing energy and inconsistent process control. This study documents the measured variation in production and energy efficiency with two operating modes. Overall, the results match the theory, and the capacity and power fluctuated by 25% and 17%, respectively, when operated at full capacity, with an overall trend of slightly coarser discharge size distribution as the speed decreased. Using a fixed feed rate, the crushers had 4-14% higher production when operating at the optimal speed. Secondary analysis showed that the power draw consistency and magnitude of power spikes could also be improved by optimizing the cone speed. Varying the speed of the crusher can be used to tune the crusher during commissioning, adapt to changing ore conditions over long periods of time or be used as a dynamic input into an advanced control system. Each action above would serve to make the crusher(s) more productive, more energy efficient, improve process control and would also have mechanical benefits for the machine. Mining Engineering, 2013, Vol. 65, No. 12, pp. 50-56. Official publication of the Society for Mining, Metallurgy and Exploration, Inc. = = i = 31812
Introduction There are many parameters that af- fect the production and efficiency of a high-speed cone crusher. One of these variables is the eccentric speed, or gyra- tion frequency, of the moving crushing member (head). For the majority of in- stallations today, the eccentric speed is a set parameter and is rarely changed once the machine is commissioned. D. Jacobson is manager at Metso, Waukesha, Wl, and N. Lamminmaki is research engineer at Metso, Tampere, Finland. Paper number TP-12-045. Original manuscript submitted November 2012. Revised manuscript accepted for publication August 2013. Discussion of this peer-reviewed and approved paper is invited and must be submitted to SME Publications by March 31,2014. However, since each application will have a most advantageous speed for crusher production and efficiency, op- erating at a single speed over the life of the crusher does not allow for the op- timal crusher arrangement at all times. At the start of operation, it is pos- sible that a crusher is not set up with the most optimal speed due to misapplica- tion and/or inaccurate assumptions of ore properties, feed size and reduction desired. Furthermore, the operation will see fluctuations in crusher loads that are frequent (short periods of higher or lower loads) and long-term (varying ore hardness, blasting strategy or a change in circuit design and/or pro- duction requirements). An extensive pi- lot campaign with a 150-kW (200-hp) high-speed cone crusher (Nordberg HP200) was executed in order to mea- sure the production differences of the cone crusher when operated at maxi- mum capacity (at the volumetric capac- ity or choke-fed condition), as well as with the feed tonnage rate to the crush- er held at a fixed rate, as is common for many mining operations. TTiis paper discusses crushing dy- namics and the effect that gyration fre- quency has on capacity, reduction and power use. Theory: effect of eccentric speed on crusiier operation There are a number of parameters of the crusher setup that affect how material flows through the chamber, how much reduction is achieved and how much power is needed to achieve this. A short list of the most influential crusher parameters would include: ec- centric speed, closed side setting (CSS), crushing throw and chamber profile. This paper seeks to isolate the eccentric speed to measure the effect of this pa- rameter only; in this regard, the throw and chamber profile during the testing