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ABSTRACT Low reduction ratios and high wear rates are the two characteristics ntost commonh" associated with conventional roll crushers. Because of this, roll crushers are not often considered Jor use in mineral processing circuits, attd many of their advantages are being largely overlooked. This paper describes a novel roll crusher that has been developed ipt order to address these issues.Relbrred to as the NCRC (Non-Cylindrical Roll Crusher), the new crusher incorporates two rolls comprised qf an alternating arrangement of platte attd convex or concave su@wes. These unique roll prqfiles improve the angle qf nip, enabling the NCRC to achieve higher reduction ratios than conventional roll crushers. Tests with a model prototype have indicated thar evell fi)r very hard ores, reduction ratios exceeding lO:l can be attained. In addition, since the comminution process in the NCRC combines the actions of roll arM jaw crushers there is a possibili O' that the new profiles may lead to reduced roll wear rates.2001 Elsevier Science Ltd. All rights reserved. 29295
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Keywords: crushing
INTRODUCTION Conventional roll crushers suffer from several disadvantages that have lcd to their lack of popularity in mineral processing applications. In particular, their low reduction ratios (typically limited to about 3:1) and high wear rates make them unattractive when compared to other types of comminution equipment, such as cone crushers. There are, however, some characteristics of roll crushers that are very desirable from a mineral processing point of view. The relatively constant operating gap in a roll crusher gives good control over product size. The use of spring-loaded rolls make these machines tolerant to uncrushable material (such as tramp metal). In addition, roll crushers work by drawing material into the compression region between the rolls and do not rely on gravitational feeci ~like cone and jaw crushers. This generates a continuous crushing cycle, which yields high throughput rates and also makes the crusher capable of processing wet and sticky ore. The NCRC is a novel roll crusher that has been dcveloped at the University of Western Australia in ordcr to address some of the problems associated with conventional roll crushers. The new crusher incorporates two rolls comprised of an alternating arrangement of plane and convex or concave surfaccs. These unique roll profiles improve the angle of nip, enabling the NCRC to achieve higher reduction ratios than conventional roll crushers. Preliminary tests with a model prototype have indicated that, even for very hard oics, reduction ratios exceeding 10:I can be attained (Vellelri and Weedon, 2000). These initial findings were obtained for single particle feed. where there is no significant interaction between particles during comminution. The current work extends the existing results bv examining inulti-particle comminution inthe NCRC. It also looks at 论文网
various othcr factors that influencc the perli~rmance of the NCRC and explores the effectiveness of using the NCRC for the processing of mill scats.
PRINCIPLE OF OPERATION
The angle of nip is one of the main lectors effccting the performance of a roll crusher. Smaller nip angles are beneficial since they increase tl~e likelihood of parlictes bcing grabbed and crushed by lhe rolls. For a given feed size and roll gap, the nip angle in a conventional rtHl crusher is limited by the size of thc rolls. The NCRC attempts to overcome this limitation through the use of profiled rolls, which improve the angle of nip at various points during one cycle (or revolution) of the rolls. In addition to the nip angle, a number of other factors including variation m roll gap and mode of commmution were considered when selecting Ille roll profiles. The final shapes of the NCRC rolls are shown in Figure I. One of the rolls consists is an alternating arrangement of plane and convex surfaces, while the other is formed from an alternating arrangement of phme and concave surlaccs.
The shape of the rolls on the NCRC result in several unique characteristics. Tile most important is that, lk)r a given particle size and roll gap, the nip angle generated m the NCRC will not remain constant as the rolls rotate. There will be times when the nip angle is much lower than it would be for the same sized cylindrical rolls and times when it will be much highcr. The actual variation in nip angle over a 60 degree roll rotation is illustrated in Figure 2, which also shows the nip angle generated under similar conditions m a cylindrical roll crusher of comparable size. These nip angles were calculated for a 25ram diameter circular particle between roll of approximately 200ram diameter set at a I mm minimum gap. This example can be used to illustrate the potential advantage of using non-cylindrical rolls. In order for a particle to be gripped, the angle of nip should normally not exceed 25 ° . Thus, the cylindrical roll crusher would never nip this particle, since the actual nip angle remains constant at approximately 52 °. The nip angle generated by the