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The drive motor for the hydraulic system was rewired. The loader tracks, and miscellaneous other components were repaired. A separate, major problem was the inadequate power of the tail conveyor hydraulic motor to drive the tail conveyor belt under conditions of maximum loading.
Figure illustrates the amount of coal on the conveyor system that lead to this failure. This problem was solved by increasing the pressure in the hydraulic line driving the motor, and mounting a series of small diameter rollers underneath the conveyor belt to reduce friction between the belt and the bedplate An apparently minor, but persistent problem, was the buildup of coal on top of the main conveyor bed plate, between the bed plate and the conveyor belt.
At the beginning of the surface testing program, this buildup was sufficient to cause excessive tension in the conveyor chain, which in turn stalled the conveyor. Two methods for eliminating this problem were tried. First, a snowplow scraper was installed on top of the belt, within the return bed, and immediately following the rubber covered return idler.
Next, an array of holes was drilled in the bod plate along the length of the main frame conveyor. The snowplow scraper was not effective, but the holes in the bed plate reduced the buildup significantly, by providing scraping edges against the belt and permitting any captured coal dust to pass through.
Following the successive incorporation of these repairs, modifications, and improvements, the loader was tested for several additional hours prior to shipment to the Spur Mine. A one-day surface testing program in a coal pile at the Spur Mine was also conducted at the completion of the underground testing in order to obtain additional noise measurements.
The results of the performance evaluations and acoustic measurements conducted during the surface testing program are discussed in Sections 4. This is a new mine which enters the coal seam at the base of a foot high wall of the old Squaw Creek strip mine. The coal seam is the Illinois No. Seven main entries have been driven past an area where six submains have been turned and are now being driven. The entries are generally 20 feet wide on 50 foot centers, both inby-outby and left to right.
However, during the time the underground test program was conducted, bad roof conditions had been encountered, requiring a limitation on entry width to 16 feet. Furthermore, the coal seam had pinched down to approximately inches in the working section. The limited entry height and width resulted in rather adverse operating conditions for the modified Joy 14 BUCH loader, which is approximately 11 feet wide, 28 feet long, and 45 inches high.
The top of the canopy was lowered to 48 inches to avoid jamming it against the roof, and consequently, the loader operator was unable to see the gathering arms and the conveyor foot section. This lack of operator visibility presented problems in clean-up work and in loading the shuttle cars.
Following approximately 23 hours of loader operation in the mine, the coal seam at the left side of the working section pinched down even more, preventing the loader from moving up to that working face. The decision was then made, in consultation with the Bureau of Mines, to terminate the underground testing program and the loader was taken outside.
The results of the performance evaluations and acoustic measurements conducted during the underground testing program are discussed in the two following sections. Conveyor Performance Following the modification of the tail conveyor during the surface testing program, the conveyor system performed very well, and was able to discharge coal satisfactorily even at the highest rates of loading attempted in the surface coal piles.
Towards the end of the underground testing program, during the visit by the Bureau of Mines representative, a problem with spillage became apparent at the transfer point from the main conveyor to the tail conveyor, caused by the inability of the tail conveyor to move as much coal as the main conveyor. When the loader was moved out of the mine shortly afterwards, it was discovered that the tail conveyor drive pulley was slipping on the drive shaft, causing the tail conveyor to operate at part speed.
The rubber belt under the conveyor chain on the main conveyor had been the subject of some concern. This belt, which is not independently powered, but is driven by the friction between it and the conveyor chain, typically travels at approximately one half the speed of the flight chain.
On examining the belt following the surface testing at M. Industries, it was found that no significant wear had been caused by coal and rocks, but some damage had occurred to the strip of belt riding under the conveyor chain.
This was probably caused at the tail roller, where the chain moves relative to the belt while turning around a small radius. To minimize the damage to the new belt installed for the underground testing, the flight chain takeup tension was reduced. The flight chain may have been excessively tensioned during the surface testing. Final examination of the belt indicated that this was successful, as shown in Figure We believe, however, that belt wear would be even further reduced if the belt traveled at the same speed as the flight chain.
Hence, we recommend that a belt drive be incorporated into future versions of this system. An additional modification that should be considered would consist of replacing the steel tail roller on the main conveyor with a roller covered by an approximately one-inch layer of hard rubber durometer.
This would reduce possible belt damage by the flight chain. The return idler and the rubber belt placed over the main conveyor return bed also performed satisfactorily. Some belt damage at the leading edge of the return bed occurred during the surface testing, when the return idler was mounted sufficiently low that the conveyor chain hit against this edge.
The holes drilled in the top bed plate to eliminate coal buildup under the conveyor belt were quite effective in reducing this problem to a manageable level. However, it is believed that the coal buildup can be further reduced by installing the snowplow scraper immediately adjacent to the foot section idler pulley rather than back by the rubber-covered return idler. By this means, the conveyor belt would be scraped clean of coal dust just before it turns around the idler pulley and onto the top of the bed plate.
The swing conveyor belt showed a tendency to ride over to one side while turned and loading, particularly when the conveyor was raised, causing the conveyor belt to ride on a transverse slope. This problem was minimized by maintaining proper belt adjustment and belt tension which, however, did not fully eliminate occasional scraping of the belt against the side of the conveyor.
No measurable belt damage was apparent or is expected by this failure to track properly, but the problem can probably be alleviated by installing tracking idlers along the sides of the conveyor belt. Noise Measurements The noise levels at several positions around the loader were measured during the surface and underground test programs. Measurements were made with the conveyors running empty and fully loaded with coal.
Table I presents a summary of the noise levels obtained during the test programs. Some problems were encountered with auxiliary loader components. The cause of this variation was eventually diagnosed as an inadequate hydraulic fluid supply tank. With the conveyor frame or the foot section in a raised position, the extended hydraulic lift cylinders drained the supply tank to the extent that hydraulic fluid passing through the pump contained an excessive amount of air.
This caused an uneven loading on the hydraulic pump vanes and dynamic imbalance of the pump and motor shafts, resulting in higher noise levels. During the final surface testing, a lead foam blanket was wrapped around the motor and pump, as shown in Figure The increased noise level while loading was presumably caused by coal scraping against the conveyor side plates, and by coal discharging from the main to the stub conveyor at the transfer point and from the end of the stub conveyor.
Table IIA shows that significant quieting of the loader, by about 15 dBA, was achieved by the modifications made. Table IIB is shown to illustrate the wide variations in noise measurements resulting from both changes in operating condition and changes in sensor location. The conventional Joy 14 BU10 low machine is a smaller loader and inherently less noisy than the 14 BUCH modified under this contract, but the data indicate a similarly broad range of noise measurements with similar correlation to operating condition and sensor location.
Conclusions and Recommendations The objective of this program was to develop a new conveyor system that could be adapted to existing continuous miners and loading machines and would exhibit a noise level of 90 dBA from the conveyor without reducing the performance of the machinery.
The modification to the particular loader of this program reduced noise levels by approximately 15 dBA. Capacity reductions observed in underground tests are attributable to mechanical failure belt drive pulley slippage on its shaft and to mine dimensions not well suited to the design of the particular machine used. The conveyor design modifications developed in this program can be applied to moderate or high coal.
The vertical dimension of the transfer point presents a limit to applications in low coal. Some belt damage was caused by the chain during the surface tests due to excessive chain tension. With lower chain tension, underground tests showed no additional wear.
These features are worthy of note because, besides providing effective quieting, they may be incorporated into a conventional swing conveyor machine with only minor alteration. The quieting achieved by the main belt, although measurable, was significantly less. The following recommendations for design improvement are the result of experience with the design developed in this program: a The design criteria for loaders and continuous miners are sufficiently diverse that future attempts at quieting conveyors should consider these applications individually.
The major noise contributor then would be the gathering arms which could be the target of another effort. By eliminating chains and flights, the height of the transfer point may be reduced by about 6 inches, thus making a machine suited for lower coal seams. There are indications from this program that a belt can adequately resist wear in this application.
The incorporation of a moving belt under the chain and flights is not recommended. The quieting achieved by this method, though measurable, is not justified by the complexity of the modification. The shorter the pitch the greater will be the number of sprocket teeth at a given pitch diameter.
The fluctuations in chain pitch line velocity chordal effect are inversely proportional to the number of sprocket teeth. These velocity fluctuations are the major source of vibration input at a sprocket and resultant chain slap. Following is a breakdown of these costs based on the test unit fabricated for this program. Drawings and , Sheets 1 and 2, illustrate the configuration built and tested. Note: These cost estimates are based on prices as of December, Appropriate forward pricing factor should be applied to these estimates for current equivalent.
The subject element concerns quieter conveyors for continuous miners and loaders. Noise measurement studies conducted in underground coal mines have shown that several mine occupations expose individuals to noise levels that result in shift noise exposures in excess of the safe standards established by the Walsh Healey criteria. In particular, operators of continuous miners and loading machines are subjected, during loading, to noise levels ranging from 89 to dBA.
The principal sources of noise on these machines are in the chain conveyor system. Efforts to date to eliminate or reduce the conveyor noise have been conducted along modifications of the existing mechanical system.
An alternate approach is to use a new conveyor design to reduce noise levels without reducing the performance of the machine. Foster-Miller Associates has been awarded a contract by the Bureau of Mines to develop a new conveyor system which can be adapted to existing machinery continuous miners and loading machines to reduce the noise from the conveyor to 90 dBA without reducing the performance of the machinery.
The work leading to the demonstration of a prototype conveyor system has been divided into three phases; a Initial design and component testing. This report presents the results achieved during the Phase I effort. Summary The basic objective of this program is to develop a new conveyor system which can be adapted to continuous miners and loaders to reduce the noise from the conveyor to 90 dBA without reducing the performance of the machinery.
The scope of the Phase I study included initial design and component testing to ensure that the system designed meets ail the operating requirements. The recommended design consists of a main conveyor and a tail conveyor. The tail conveyor, which is a simple rubber belt conveyor design, is mounted on a turn table bearing that is attached to the main conveyor by means of a cantilever bracket. Personnel from Joy Manufacturing Co.
Technical Discussion Conveyor Concepts The purpose of the conveyor system on a continuous miner or loading machine is to transport the coal from the base region to the material handling system behind the machine. In the case of a loading machine the capability of the conveyor system to transport the design load is a necessary and sufficient design consideration, i. For the continuous miner, however, there are additional performance requirements that must be taken into consideration.
Since the currently used chain conveyor system is such a sturdy device, which can suffer a great deal of abuse and still remain operational, the practice has developed to use the conveyor as a rock and coal breaker as well as a transport system. For example, if the cutting head breaks off a large piece of rock or coal from the mining face, the gathering arms will push it onto the conveyor chute, and the flights will move it along the chute until, if it exceeds the critical size, it will become wedged between the chute and the cutting head boom.
According to current miner operation practice, the flights will continue to move, breaking off and grinding down the material until it has been reduced sufficiently in size to pass through the restriction. Our diverse product range includes tripper cars on rails or on crawlers as a mobile link between dump conveyor and spreader, as well as hopper cars on rails or on crawlers between excavator and bench conveyor. Bench conveyors for mining and dumping are designed as shiftable conveyors, where the conveyor modules are equipped with steel sleepers and rails to allow for an easy shifting procedure.
Our product range also covers shifting head fabrication and testing in our specialized fabrication facility. Gearless drive technology TAKRAF is one of a very limited number of global conveyor manufacturers boasting an operating reference in the use of advanced gearless drive technology in mining conveyor systems and are proud of our association with our drive technology partner, ABB. Gearless drives eliminate the need for a gearbox, hereby significantly reducing the number of main wear parts, which results in increased efficiency and reliability, as well as less maintenance being required.
This incredible system, boasting a total installed drive power of 58 MW, transports crushed copper ore from underground storage bins to the surface along a 7 km underground tunnel that overcomes 1 km of vertical elevation. Once on the surface, the ore then travels along an overland conveyor that transports it the final 6 km to the distribution silo. The underground system comprising two conveyors of about equal length , as well as the overland conveyor, boast advanced gearless drive technology.
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Figure 3 is a side view of the swing conveyor. Figure 4 is a rear view of the machine and shows the conveyor system and transfer point. Figure 5 is a schematic of the machine showing all modifications that affect the noise level of the conveying system. Following conveyor fabrication and installation on the Joy loader at FMA, the machine was shipped to M. Industries, West Frankfort, Illinois, for installation of a canopy, system debugging, and surface testing as requested by U.
Repairs and modifications to the conveyor design resulted from these preliminary tests which involved operation of the loader in a surface coal pile at the M. After approximately 20 hours of surface testing, the loader was taken underground at the Spur Mine for testing in an operating section. The underground testing was only partly successful. The Joy loader was too large to maneuver easily in the 16 foot wide by 50 to 53 inch high entries. The canopy restricted visibility of the gathering arms.
Left side entries became inaccessible as a result of pinching of the coal seam. There was excessive coal spillage at the transfer point preventing shuttle cars from tramming up to the loader. This latter problem was eventually traced to slippage of the tail- conveyor-belt drive pulley on its shaft which reduced the belt speed, and caused the belt conveyor to be incapable of taking sufficient coal away from the transfer point.
For these reasons the underground testing was curtailed. The underground test conditions also showed the hydraulic fluid reservoir to be inadequate, which resulted in abnormal motor and pump noise levels. Measurements of the loader running empty tended toward the higher noise levels. Some belt damage sustained during surface testing was caused by excessive chain tension. Proper tension eliminated this damage. However, mine personnel were not convinced that the belt would hold up under prolonged service.
The moving rubber belt contributed dBA of quieting. In addition, the loader was operated within a lower coal seam than that suited for the particular loader used. Quantitative measurement of loading rates was not performed. The apparent cause of this excess noise was an inadequate fluid reservoir. The following future envelopments of the conveyor system are recommended: a For application to loading machines, the flight chain may be eliminated and the main conveyor belt driven by the foot or tail pulley.
Significant additional noise reduction is possible with this approach if attention is paid to noise generation by the gathering arms, motors, and hydraulic pumps. The height of the transfer section from the front to the mining conveyor may be significantly reduced in this way, making the loader potentially applicable to low coal machines. These changes are possible without changing the overall height of a miner. Because the chain forms a polygon around the sprocket rather than a circle, there are fluctuations in effective sprocket radius resulting in chain speed and tension fluctuations and a tendency for the chain to slap surfaces adjacent to its path.
Reduction of chain pitch permits more links to wrap on a given size sprocket, thereby reducing chordal action. The following modifications were made to the loader. See Drawing No. This bracket is the main support for the swing conveyor, as shown in Drawing No. The flight chain rides on the belt while on the top bed plate of the conveyor. As the flight chain turns around at the tail roller Figure 6 , the conveyor belt rides on the flights through the main frame return bed to within 2 inches of the chain drive sprocket.
There, an idler pulley, inserted in the conveyor bed, turns the belt back onto the conveyor bedplate as the flight chain is pulled around the drive sprocket and back on top of the rubber belting, as shown in Figure 7. To eliminate material buildup between the bed plate and the conveyor belt, holes were drilled in the top bed plate along the length of the main frame conveyor. To eliminate this impact, the new configuration includes an energy-absorbing pulley which is mounted in front of the return bed, as shown in Figure 8.
This causes the flight chain to be carried upward past the leading edge of the return bedplate and onto the rubber cover which is bolted to the leading edges of the bedplates of the main frame and the foot section. Swing Conveyor The Swing Conveyor consists of a roller bed, drive idler, pulleys, a rubber belt, a 24 HP hydraulic drive motor, a turntable bearing, and a double-acting swing cylinder.
The portion of the conveyor which lies under the main conveyor tail pulley, the point at which the coal is dumped by the flight chain onto the swing conveyor, is fitted with a deflector plate to protect the conveyor rollers from loading impact Figure 6. The deflector plate also allows easier swing conveyor start-ups less torque requirement when coal still remains on the unit. The swing conveyor is mounted on the turntable bearing which, in turn, is mounted on the cantilever bracket.
The maximum angle of conveyor swing is 40 degrees, as compared to 45 degrees for the original loader. Hence, it is raised and lowered in the same manner as a conventional conveyor system. Hydraulic Drive System The Joy loader hydraulic power supply consists of a 10 HP electric motor, a gear pump, and a 24 gallon reservoir.
This system is used to raise the foot section and main frame tail section hydraulic jacks. It also supplies power to the swing cylinder, which moves the tail section right or left. The pressure requirements of the conventional system are less than psi.
The swing conveyor belt drive hydraulic motor requires psi pressure so the 10 HP electric motor and pump were replaced by a 40 HP electric motor and a psi dual hydraulic pump, as shown schematically in Figure One pump supplies the belt drive motor at psi pressure, and the other supplies the cylinders described above. Test Program and Results The fabrication and installation of the new conveyor design on the Joy loader were performed at the Foster-Miller Associates facilities in Waltham, Massachusetts, and by local subcontractors.
The loader was then shipped to M. Industries in West Frankfort, Illinois, for installation of a canopy and methane monitor, and preliminary performance testing prior to the underground test program in the Peahody Spur Mine. However, at the recommendation of the Bureau of Mines and Peabody Coal Company, this was extended into a rather comprehensive surface testing program, in which the loader operated in a surface coal pile.
The surface and underground test programs are both described in the following sections. Surface Testing The surface testing program was conducted in a coal pile outside the M. Industries facilities, as shown in Figure The total operating time of the conveyor system at this site, including the initial conveyor and loader debugging, was approximately 20 hours.
The machine debugging became a considerably greater undertaking than was originally projected. This was partly due to the condition of the loader. Four hydraulic cylinders, were replaced. The drive motor for the hydraulic system was rewired. The loader tracks, and miscellaneous other components were repaired. A separate, major problem was the inadequate power of the tail conveyor hydraulic motor to drive the tail conveyor belt under conditions of maximum loading.
Figure illustrates the amount of coal on the conveyor system that lead to this failure. This problem was solved by increasing the pressure in the hydraulic line driving the motor, and mounting a series of small diameter rollers underneath the conveyor belt to reduce friction between the belt and the bedplate An apparently minor, but persistent problem, was the buildup of coal on top of the main conveyor bed plate, between the bed plate and the conveyor belt.
At the beginning of the surface testing program, this buildup was sufficient to cause excessive tension in the conveyor chain, which in turn stalled the conveyor. Two methods for eliminating this problem were tried. First, a snowplow scraper was installed on top of the belt, within the return bed, and immediately following the rubber covered return idler. Next, an array of holes was drilled in the bod plate along the length of the main frame conveyor.
The snowplow scraper was not effective, but the holes in the bed plate reduced the buildup significantly, by providing scraping edges against the belt and permitting any captured coal dust to pass through. Following the successive incorporation of these repairs, modifications, and improvements, the loader was tested for several additional hours prior to shipment to the Spur Mine. A one-day surface testing program in a coal pile at the Spur Mine was also conducted at the completion of the underground testing in order to obtain additional noise measurements.
The results of the performance evaluations and acoustic measurements conducted during the surface testing program are discussed in Sections 4. This is a new mine which enters the coal seam at the base of a foot high wall of the old Squaw Creek strip mine.
The coal seam is the Illinois No. Seven main entries have been driven past an area where six submains have been turned and are now being driven. The entries are generally 20 feet wide on 50 foot centers, both inby-outby and left to right. However, during the time the underground test program was conducted, bad roof conditions had been encountered, requiring a limitation on entry width to 16 feet.
Furthermore, the coal seam had pinched down to approximately inches in the working section. The limited entry height and width resulted in rather adverse operating conditions for the modified Joy 14 BUCH loader, which is approximately 11 feet wide, 28 feet long, and 45 inches high. The top of the canopy was lowered to 48 inches to avoid jamming it against the roof, and consequently, the loader operator was unable to see the gathering arms and the conveyor foot section.
This lack of operator visibility presented problems in clean-up work and in loading the shuttle cars. Following approximately 23 hours of loader operation in the mine, the coal seam at the left side of the working section pinched down even more, preventing the loader from moving up to that working face. The decision was then made, in consultation with the Bureau of Mines, to terminate the underground testing program and the loader was taken outside.
The results of the performance evaluations and acoustic measurements conducted during the underground testing program are discussed in the two following sections. Conveyor Performance Following the modification of the tail conveyor during the surface testing program, the conveyor system performed very well, and was able to discharge coal satisfactorily even at the highest rates of loading attempted in the surface coal piles.
Towards the end of the underground testing program, during the visit by the Bureau of Mines representative, a problem with spillage became apparent at the transfer point from the main conveyor to the tail conveyor, caused by the inability of the tail conveyor to move as much coal as the main conveyor. When the loader was moved out of the mine shortly afterwards, it was discovered that the tail conveyor drive pulley was slipping on the drive shaft, causing the tail conveyor to operate at part speed.
The rubber belt under the conveyor chain on the main conveyor had been the subject of some concern. This belt, which is not independently powered, but is driven by the friction between it and the conveyor chain, typically travels at approximately one half the speed of the flight chain. On examining the belt following the surface testing at M.
Industries, it was found that no significant wear had been caused by coal and rocks, but some damage had occurred to the strip of belt riding under the conveyor chain. This was probably caused at the tail roller, where the chain moves relative to the belt while turning around a small radius. To minimize the damage to the new belt installed for the underground testing, the flight chain takeup tension was reduced.
The flight chain may have been excessively tensioned during the surface testing. Final examination of the belt indicated that this was successful, as shown in Figure We believe, however, that belt wear would be even further reduced if the belt traveled at the same speed as the flight chain. Hence, we recommend that a belt drive be incorporated into future versions of this system.
An additional modification that should be considered would consist of replacing the steel tail roller on the main conveyor with a roller covered by an approximately one-inch layer of hard rubber durometer. This would reduce possible belt damage by the flight chain. The return idler and the rubber belt placed over the main conveyor return bed also performed satisfactorily.
Belt widths vary according to the material to be conveyed and capacity required together with the manner in which they are constructed. Depending on requirements, our conveyors can also integrate scales, detectors or material analyzers and sampling equipment.
Open-pit mine applications According to an open-pit mine's development, conveyors are also often required to be relocated or shifted and may include special features for extension requirements including belt storage at the tail end and a crawler-mounted drive station at the head end.
Other typical applications for open-pit conveyors are mobile transfer points like tripper cars, hopper cars and shuttle heads for material feed to several downstream conveyors. Our diverse product range includes tripper cars on rails or on crawlers as a mobile link between dump conveyor and spreader, as well as hopper cars on rails or on crawlers between excavator and bench conveyor.
Bench conveyors for mining and dumping are designed as shiftable conveyors, where the conveyor modules are equipped with steel sleepers and rails to allow for an easy shifting procedure. Our product range also covers shifting head fabrication and testing in our specialized fabrication facility. Gearless drive technology TAKRAF is one of a very limited number of global conveyor manufacturers boasting an operating reference in the use of advanced gearless drive technology in mining conveyor systems and are proud of our association with our drive technology partner, ABB.
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