破碎机偏心速度英文文献和中文翻译(2)

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were held constant and the closed side setting was adjusted only to track speed change effects in multiple applications. To understand the theory behind eccentric speed in crusher design, each of the factors above must be considered to de- termine the consequence of varying the speed. The capacity, reduction and power utilization of a cone crusher depend on how the particles fiow through the cham- ber and what is the final opening that the particles need to pass in order to exit the chamber. The eccentric speed will be a significant factor in how far a particle can drop during one gyration cycle; this drop is referred to as one crushing zone. TTie speed at which the crusher would have the theoretical maximum capacity is known as the critical speed. High-speed cone crushers are operated at super-critical speed, in the range of the speed versus capacity curve where the capacity is dropping as the speed is increasing (Fig. 1). Note that the shape and magnitude of this curve will be slightly different for each crusher, setting, feed size, ore properties, etc. As can be seen by the curve in Fig. 1, for a high-speed cone crusher, the volumetric capacity of the machine should decrease as the eccentric speed is increased (all other things considered equal). If capacity was the only important output, it could be deduced that operating at the lowest speed pos- sible would yield the most optimal outcome. However, the speed also affects the number of crushing zones and how the particles drop through the crushing zones; so, for a given closed side setting, varying the speed will change the reduc- tion (discharge size distribution), power used and particle shape of the discharge. A higher eccentric speed can result in an increase in the number of crushing zones and more im- pact in the parallel zone (lower portion of chamber near the CSS). Reduced speed and the resulting increase in capacity also result in an increase in work being done, which is seen in the power used to operate the crusher. Finally, increas- ing the quantity of crushing zones down a chamber in effect decreases the reduction in each zone, which is beneficial to particle shape and can reduce the resultant crushing force. There are limits to the work that can be done with the crushers. The first limit is the volumetric limit of the machine, which means the feed rate has met or exceeded the physical fiow rate limit for material passing through the chamber. This is considered to be the ideal situation for the crusher. The second limit is the power limit. Each crusher is designed with a certain amount of power transmission in the mechanical de- sign, and exceeding this limit will put stress on the drive com- ponents. The third limit is the force limit; most crushers have a system to relieve the crushing forces to protect the frame and internal components. Exceeding the force limit can put stress on the machine and cause fiuctuation in discharge size. For this study, a fourth limit is considered: the lubrication, bearing surfaces and drive equipment are designed based on a specific speed range, and operating outside this range may cause fatigue stress or failure of crusher components. These four limits will need to be monitored and adhered to during operation. One final factor toward cone crusher production is the level of material that is filling the chamber, or what is re- ferred to as cavity level. As the cavity level increases in the crushing chamber, the bed of particles above the chamber helps to push the ore through the chamber and increase interparticle comminution in the chamber due to elevated particle density (Jacobson, 2010). In many mining operations, due to fiuctuating size distribution of the run-of-mine, chang- ing ore characteristics, plant design and production require- ments from the crushing section, there is simply not enough feed to effectively and consistently keep the crusher choke fed at the volumetric limit. This leads to a decrease in overall productivity and efficiency of the cone crushing station. This situation was specifically simulated in this study to measure the benefits that can be seen during these conditions. Using eccentric speed to manipulate production as part of a monitoring and control system has been previously dis- cussed and documented, with a study on the use of dynamic control of the eccentric speed to increase production and liner life for a 224-kW (300-hp) cone (Hulthen, 2011). There are also many instances in full production applications where a simple change to a different speed has altered production compared to the originally installed speed.