Crushing Method And Assembly

Field of the invention

The present invention relates to a crushing method and assembly. More particularly, the invention relates to a method for crushing rocks or the like that includes monitoring of particles resulting from the crushing method and adjusting crushing parameters in response to monitored characteristics.

Background to the invention

Methods for the grinding and crushing of rocks, sch as using high-pressure grinding rolls (HPGR), are known. HPGR technology, which will be discussed herein for reference only, was first introduced on an industrial scale in the mid 1980's in the cement industry. Since that time, HPGR has been utilised in a variety of industrial applications for processing of a wide range of ore types. The key rationale for the wide usage of HPGR includes reduced energy consumption and increased crushing efficiency compared with more traditional methods of rock crushing, such as using tumbling mills.

Conventional HPGR 10, an example of which is illustrated in Figure 1 , include a pair of counter-rotating rolls 11 and 12. One roll 11 of the pair is fixed, while the other roll 12 is adapted for horizontal movement facilitated by hydraulic cylinders 13 that engage the movable roll 12. Material 14, such a rock fragments, is fed into a gap 15 between the two rolls 11 and 12. Normally, the material 14 is force (choke) fed via a small hopper 16 positioned above the gap 15.

Generally, the rolls 11 and 12 include studded surfaces 17 that grip the material 14 (rock fragments) and effectively drag it between the rolls 11 and

12. The material 14 is then subjected to increasing amounts of pressure as it passes between the rolls 11 and 12, resulting in crushing of the material 14 into smaller particles 14'.

As noted, one of the rolls is a fixed roll 11 and therefore rotates on a fixed axis, while the other is a moveable roll 12. The moveable roll 12 is forced up against the material 14 in the gap 15 by an hydraulic oil cylinder system including two or four cylinders 13, depending on the manufacturer. The oil pressure transmits grinding force over the diameter of the rolls 11 and 12 to the bed of material 14 formed in the gap15.

The amount of material in the gap 15, or compression zone, may be manipulated to a limited degree in order to optimise operating conditions. Generally, this will be a function of the ore type, roll diameter and surface characteristics.

Rock crushing that occurs in HPGR occurs under confined conditions within a compressed bed of particles. Under such conditions there is unavoidable shearing along the particles which, through friction, causes heating of the contacting or fractured surfaces. If the force applied exceeds the desired intensity, the HPGR will drop the force applied to the material. Sudden drops in force applied, if excessive or if applied for too long a period, may result in particles dropping through the gap between the rolls without being subjected to grinding. In that case, the particles falling through the gap will not be substantially affected by friction or shearing forces.

The invention advantageously provides a crushing process and a method for monitoring a crushing process that advantageously facilitate optimization of the process, or that provide an indication of a lack of economy during the crushing process generally due to a lack of crushing pressure.

Summary of the invention

According to one aspect of the invention there is provided a method of crushing a particulate material including: passing the particulate material through a crushing zone in which the particulate material is subjected to a crushing process; thermally imaging the particulate material within a predetermined time after the particulate material exits the crushing zone; and controlling at least one process parameter of the crushing process in response to the imaging step.

As used herein, the term "particulate material" refers to any material that may be subjected to a crushing process in order to reduce particle size, such as rock fragments, independent of the size of the fragments, ores, or other rigid materials.

As used herein, the term "predetermined time" refers to any time within which the heat of the particulate material reflects the heat induced during the crushing process.

As used herein, the term "controlling" refers to maintaining the process parameter at a particular level, or adjusting the process parameter to a particular level.

The invention essentially requires thermally imaging the particulate material within a predetermined time after the particulate material exits the crushing zone with the proviso that the heat at the time of thermal imaging reflects the heat induced during the crushing process. In that regard, the heat of the particulate material at the time of thermal imaging does not have to be the same as when the particulate material exits the crushing zone. It is sufficient

that the heat be within a relatively close range of the heat when the particulate material exits the crushing zone. To that end, in a preferred embodiment the thermal imaging step is preferably carried out while the particulate material is in free flight after is exits the crushing zone, or within a short period after the particulate material completes its free flight trajectory after exiting the crushing zone. For example, the thermal imaging step may be conducted while the particulate material is in free flight, or within 5 seconds of completing its free flight trajectory, more preferably within 1 second of completing its free flight trajectory, after exiting the crushing zone. Advantageously, this provides an indication of the efficacy of the crushing process and may also provide an indication as to whether the particulate material is passing through the crushing zone without being exposed to sufficient crushing pressure.

Preferably, the imaging step includes thermally imaging the particulate material in free flight after the particulate material exits the crushing zone. More preferably, the particulate material is thermally imaged immediately after the particulate material exits the crushing zone. Generally, the particulate material is thermally imaged using at least one infrared camera.

As noted above, during the crushing process the particulate material is subjected to shearing forces that result in heating of the particulate material. The heat that is imparted to the particulate material may be identified by thermal imaging and will provide an indication of the efficacy of the crushing process.

It will be appreciated that the crushing process is not particularly limited and that the invention may be suitably applied to any process that involves shearing-type forces applied to the material being crushed or ground. For example, the crushing process may be a high pressure crushing process.

As previously described, the controlling step may include maintaining and/or adjusting crushing pressure of the crushing process. This may be in response to heat detected in the particulate material during thermal imaging. More particularly, the crushing pressure employed during the crushing process is preferably increased if the heat detected in the particulate material is beneath a predetermined minimum. The crushing pressure may also be decreased if the heat detected in the particulate material is higher than a predetermined maximum.

Generally, in order to provide real time control of the crushing process, a computer control system will be provided. Therefore, the thermal imaging and controlling steps are preferably conducted in real time using a computer control system.

In some instances, the crushing process may be affected by influences other than process parameters. For example, if the surface of one of the rolls in a HPGR system becomes worn, the particulate material being subjected to the crushing process may fall through the pair of rolls with minimal or no shearing forces being applied to the particulate material. The invention may also be employed to identify such circumstances so that maintenance may be carried out on the crushing assembly in question as desired to improve crushing efficacy.

As such, according to another aspect of the invention there is provided a method of monitoring a crushing process including: passing the particulate material through a crushing zone in which the particulate material is subjected to a crushing process; and thermally imaging the particulate material within a predetermined time after the particulate material exits the crushing zone.

Again, according to this aspect of the invention, thermally imaging of the particulate material is conducted while the particulate material is in free flight after the particulate material exits the crushing zone. More preferably, the particulate material is thermally imaged immediately after the particulate material exits the crushing zone, for example using at least one infrared camera.

Likewise, the type of crushing process is not particularly limited. For example, the crushing process may be a high pressure crushing process.

According to a further aspect of the invention there is provided a crushing assembly for crushing a particulate material including: a feed inlet through which the particulate material is fed; a crushing zone in communication with the feed inlet and in which the particulate material is subjected to a crushing process; and at least one thermal imager for imaging the particulate material within a predetermined time after the particulate material exits the crushing zone.

As will be appreciated from the above description, the crushing process may be a process using HPGR. Therefore, according to one embodiment of the invention the crushing zone includes a pair of opposed counter-rotating rollers, at least one of the rollers being a moveable roller that is capable of translation in a lateral plane towards and away from the other of the rollers.

The thermal imager may be positioned to image the particulate material after it completes its free flight trajectory after exiting the crushing zone. Preferably at least one thermal imager is positioned to thermally image the particulate material in free flight immediately after the particulate material exits the crushing zone.

Most advantageously, the crushing assembly is capable of imaging the particulate material in real time as it exits the crushing zone so that the crushing process may be immediately adjusted in response. Therefore, in a preferred embodiment the crushing assembly includes a computer control system for controlling the movement of the moveable roller towards and away from the other roller in response to heat detected in the particulate material during thermal imaging in real time. As with previous embodiments, the thermal imager is preferably an infrared camera.

In other embodiments, the crushing process may not involve HPGR. In such cases, it is again preferred that the thermal imager is an infrared camera positioned to thermally image the particulate material in free flight immediately after the particulate material exits the crushing zone.

Detailed description of the invention

A more detailed description of the invention will now be provided with reference to the accompanying figures. It should be appreciated that the following detailed description is provided for exemplification only and should not be construed as limiting on the invention in any way.

In the Figures:

Figure 1 is a cross-sectional representation of conventional HPGR, including the hydraulic spring system; Figure 2 is a photograph of the experimental set up according to the invention;

Figure 3 is an infrared image illustrating large numbers of fragments passing through the HPGR without being crushed;

Figure 4 is an infrared image illustrating a relatively small number of fragments passing through the HPGR without being crushed;

Figure 5 is an infrared image illustrating cold (un-crushed particle) followed by the hot flake;

Figure 6 is an illustration of the pressure time history for test illustrated in Figure 3; Figure 7 is an infrared image illustrating fragments passing through the HPGR and past a scanline with a relatively low percentage being crushed;

Figure 8 is an infrared image illustrating a higher proportion of crushed fragments passing the scanline; and

Figure 9 illustrates a graph of the scanline temperature as recorded during the processing imaged in Figures 7 and 8.

In the following more detailed description of the invention specific reference will be made to operations involving HPGR. The ambit of the invention may not be so limited.

It is envisaged that infrared imaging may be useful for monitoring the efficacy of operation in HPGR processes. In such processes, there is clear pattern of periodicity in the appearance of cold fragments in the stream of rock that is emitted from the HPGR. In some instances, these fragments appear to be of approximately the same temperature as rock that has not been subjected to HPGR. This could be due to periodical relaxing of load of the HPGR, which increases the gap between loading surfaces allowing particle to fall through the HPGR without being crushed. Embodiments of the invention will advantageously allow for on-line monitoring of efficacy of crushing occurring within HPGR.

In an effort to prove the usefulness of infrared imaging in increasing the efficacy of a crushing process, such as HPGR, a number of tests were performed using laboratory scale HPGR. The rock crushed was basalt from a local quarry, used regularly as reference rock for crushing studies. Six samples of the same mass were crushed at different force levels (from 20

bars to 60 bars). Pressure was kept nominally constant during each test. Each test was monitored using an infrared camera, Silver™ produced by Cedip Infrared Systems, which is sensitive to infrared radiation from 2-5 microns. Infrared radiation was sensed by the cooled infrared focal array. Due to its cooled nature detection capability of the camera is about 0.02 ⁰ C.

Crushing was observed from a distance of about 1.5m, with the camera directed towards the discharge outlet of the HPGR and collection tray, as illustrated in Figure 2. Recordings were performed with speeds of 25 and 50 frames per second. The reference temperature for the rock was measured prior to crushing using a thermocouple, as well as during crushing by recording infrared images of large rock fragments of the same type located next to the collection tray. Some of the collected frames are presented in Figures 3, 4 and 5. Time history of the pressure acting on the material passing through the HPGR was also obtained and an example is provided as Figure 6.

The recorded pressures indicate significant variability resulting in uncontrolled passing of rock fragments through the HPGR without exposure to any significant force. It will be appreciated that this may dramatically affect the efficacy of the crushing process.

For example, with reference to Figure 3, it can be readily appreciated that cooler fragments of rock are passing through the HPGR without being exposed to shearing forces. In particular, a number of the particles at the top of the image are quite dark, indicating that the particles are relatively cool. Conversely, Figure 4 provides an indication of a process where the rock fragments are being effectively crushed in the HPGR. This can be appreciated from the bright fragments falling through the HPGR, indicating relatively high temperatures. In Figure 5, cold uncrushed particles are falling through the HPGR, followed by hot flake. This too is indicative of conditions within the crushing zone.

Based on the invention, therefore, the real time (on-line) verification of the efficacy of rock crushing in HPGR is possible. The ability to obtain real time information on the appearance of non-crushed rock makes it possible to adjust operating parameters of the HPGR or perform maintenance work, such as replacement of wear-off surface of the rolls, in a timely fashion and in order to maximise efficacy of the process. The information relating to the temperature of the crushed rock may also be used to finely tune operating parameters of the HPGR.

Figure 6 illustrates that the pressure within HPGR is not constant, but is variable. This variability may be responsible for some particles of the particulate material, for example rock fragments, not being crushed during a crushing process.

Further validation of the process of the invention was obtained through monitoring of a crushing operation involving a copper ore in a laboratory scale HPGR machine. The results are provided in Figures 6, 7 and 8.

The temperature of fragments crossing a scanline (6) positioned just under the HPGR discharge point were monitored. The recorded temperature was compared with a sample of unfractured rock (5). The results are graphically recorded in Figure 8.

It will be appreciated from Figure 8 that the minimum temperature recorded along the scanline was in fact lower than the temperature being the onset of the crushing process. Interestingly, the average minimum temperature was also slightly less than the average temperature of the unfractured rock of the same type. This confirmed that the fragments exiting the HPGR at a relatively cold temperature had not been subject to any force involving friction. When force was applied, as illustrated in Figure 8, the temperature of the fragments

passing through the HPGR was substantially higher due to the friction imparted on the fragments.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to those of skill in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.