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As mentioned previously, the feed size distribution has a significant effect on the pressure generated in the crushing chamber. Ore that has a finer feed size distribution tends to "choke" the NCRC more, reducing the effectiveness of the crusher. However, as long as the pressure generated in not excessive the NCRC maintains a relatively constant operating gap irrespective of the feed size. The product size distribution will, therefore, also bc independent of the feed size distribution. This is illustrated in Figure 10, which shows the results of two crushing trials using identical equipment settings but with feed ore having different size distributions. In this example, the NCRC reduced the courser ore from an Fs0 of 34mm to a Ps0 of 3.0mm (reduction ratio of 11:1), while the finer ore was reduced from an Fs0 of 18mm to a Pso of 3.4mm (reduction ratio of 5:1). These results suggest that the advantages of using profiled rolls diminish as the ratio of the feed size to roll size is reduced. In other words, to achieve higher reduction ratios the feed particles must be large enough to take advantage of the improved nip angles generated in the NCRC.
Some grinding circuits employ a recycle or pebble crusher (such as a cone crusher) to process material which builds up in a mill and which the mill finds hard to break (mill scats). The mill scats often contain worn or broken grinding media, which can find its way into the recycle crusher. A tolerance to uncrushable material is therefore a desirable characteristic for a pebble crusher to have. The NCRC seems ideally suited to such an application, since one of the rolls has the ability to yield allowing the uncrushable material to pass through.
The product size distributions shown in Figure 1 1 were obtained from the processing of mill scats in the NCRC. Identical equipment settings and feed size distributions were used for both results, however one of the trials was conducted using feed ore in which the grinding media had been removed. As expected, the NCRC was able to process the feed ore containing grinding media without incident. However, since one roll was often moving in order to allow the grinding media to pass, a number of oversized particles were able to fall through the gap without being broken. Consequently, the product size distribution for this feed ore shows a shift towards the larger particle sizes, and the Ps0 value increases from 4ram to 4.7mm. In spite of this, the NCRC was still able to achieve a reduction ratio of almost
摘要 低的破碎比和高的磨损率是与传统的破碎机相联系的很常见的两个特性。因为这点,在矿石处理流程的应用中,很少考虑到它们,并且忽略了很多它们的优点。本文描述了一个已被发展起来的新颖的对辊破碎机,旨在提出这些论点。作为NCRC,这种新式破碎机结合了两个辊筒,它们由一个交替布置的平面和一个凸的或者凹的表面组成。这种独特的辊筒外形提高了啮合角,使NCRC可以达到比传统辊式破碎机更高的破碎比。用一个模型样机做的试验表明:即使对于非常硬的矿石破碎比任可以超过10。另外,既然在NCRC的破碎处理中结合了辊式和颚式破碎机的作用,那就有一种可能:那种新的轮廓会带来辊子磨损率的降低。