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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 10:1 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.9323
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Keywords: Comminution; crushing
INTRODUCTION
Conventional roll crushers suffer from several disadvantages that have led 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 developed at the University of Western Australia in order 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
surfaces. 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 10:1 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 various other factors that influence 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 effecting the performance of a roll crusher. Smaller nip angles
are beneficial since they increase tl〜e likelihood of parlictes being 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 the 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
I lie roll profiles. The final shapes of the NCRC rolls are shown in Figure I. One of the rolls consists {si an
alternating arrangement of plane and convex surfaces, while the other is formed from an alternating