- 上一篇：过硫酸盐在无污染含水层材料中的持久性英文文献和中文翻译
- 下一篇：分类机英文文献和中文翻译
Multiple feed particles
Previous trials with the NCRC were conducted using only single feed particles where there was little or no interaction between particles. Although very effective, the low throughput rates associated with this mode of comminution makes it unsuitable for practical applications. Therefore it was necessary to determine the effect that a continuous feed would have to the resulting product size distribution. In these tests, the NCRC was continuously supplied with feed to maintain a bed of material level with the top of the rolls. Figure 5 shows the effect that continuous feed to the NCRC had on the product size distribution for the Normandy Ore. These results seem to show a slight increase in P80 with continuous (multi-particle) feed, however the shift is so small as to make it statistically insignificant. Similarly, the product size distributions would seem to indicate a larger proportion of fines for the continuously fed trial, but the actual difference is negligible. Similar trials were also conducted with the granite samples using two different roll gaps, as shown in Figure 6. Once again there was little variation between the single and multi-particle tests. Not surprisingly, the difference was even less significant at the larger roll gap, where the degree of comminution (and hence interaction between particles) is smaller.
All of these tests would seem to indicate that continuous feeding has minimal effect on the performance of the NCRC. However, it is important to realise that the feed particles used in these trials were spread over a very small size range, as evident by the feed size distribution shown in Figure 6 (the feed particles in the Normandy trials were even more uniform). The unilormity in feed particle size results in a large amount of free space, which allow:s for swelling of the broken ore in the crushing chamber, thereby limiting the amount of interaction between particles. True "choke" feeding of the NCRC with ore having a wide distribution of particle sizes (especially in the smaller size range) is likely to generate much larger pressures in the crushing zone. Since the NCRC is not designed to act as a "'high pressure grinding roll" a larger number of oversize particles would pass between the rolls under these circumstances.
Roll gap
As with a traditional roll crusher, the roll gap setting on the NCRC has a direct influence on the product size distribution and throughput of the crusher. Figure 7 shows the resulting product size distribution obtained when the Aurora Gold ore (mill scats) was crushed at three different roll gaps. Plotting the PSO values taken from this graph against the roll gap yields the linear relationship shown in Figure 8. As explained previously, the actual roll gap on the NCRC will vary over one revolution. This variation accounts for the difference between the specified gap setting and product Ps0 obtained from the crushing trials. Figure 8 also shows the effect of roll gap on throughput of the crusher and gives an indication of the crushing rates that can be obtained with the laboratory scale model NCRC.
The NCRC is designed to operate with minimal interaction between particles, such that comminution is primarily achieved by fracture of particles directly between the rolls. As a consequence, the roll force only needs to bc large enough to overcome the combined compressive strengths of the particles between the roll surlaces. If the roll force is not large enough then the ore particles will separate the rolls allowing oversized particles to lall through. Increasing the roll force reduces the tendency of the rolls to separate and therefore provides better control over product size. However, once a limiting roll force has been reached (which is dependent on the size and type of material being crushed) any further increase in roll force adds nothing to the performance of the roll crusher. This is demonstrated in Figure 9, which shows that for granite feed of 25-3 Imm size, a roll force of approximately 16 to 18 kN is required to control the product size. Using a larger roll force has little effect on the product size, although there is a rapid increase in product P80 if the roll force is reduced bek>w this level.