- Presented at the Third Western Regional Conference on Precious Metals, Coal and Environment, Rapid City, South Dakota, USA, September 23-26, 1987, published in proceedings, pp. 215-22
PREFACE
High angle conveying technology has grown out of its’ infancy and is beginning a successful maturing process. Two different systems for high angle conveying applications are discussed within this paper. With successful installations of both types of systems worldwide a broad spectrum of possibilities exist for the future of this technology.
INTRODUCTION
Development of the Sandwich Belt high angle conveyor concept has come a long way since its first introduction in the early 1950s. Over the approximate thirty-year development period significant advances had been few and had come only in spurts. Such advances did not significantly build on past developments, rather they were independent developments which soon reached their technical limitations and did not develop further.
The latest significant development of this technology, beginning in 1979, is the first to take a broad view of the industries to benefit from high angle conveyors, and of all significant developments to date. As a result, these latest developments limitations, address a broad market and offer a forum for further logical development or evolution.
Significant speculatory advances in HAC technology were made and documented in a in 1981 Bureau of Mines study [1]. The more significant of these, with regard to past developments and the governing theory, were further discussed in a paper entitled “Evolution of Belt High-Angle Conveyors” [2].
The latest HAC developments, at Continental Conveyor, USA, were further described and related to the governing theory in a paper entitled “Sandwich Belt High Angle Conveyors – HAC – Evolution to Date” [3]. The significance of the latter paper is that it documents real, not speculatory, HAC developments from the many engineering studies through the first large-scale prototype into the first commercial units. HAC have been in successful operation since June of 1983.
Further papers discuss HAC applications in open pit mining [4], storage and blending [4], and reveal the operational and economic advantages over the traditional haulage systems [1], [6].
The engineering studies prior to the HAC development conducted wide searches, in the literature and through industry contact, for the then state-of-the-art high angle conveying methods. Many methods were studied. In-depth study of the sandwich belt high angle conveyor technology at that time revealed much need for further development, but offered much promise for success if such development adequately and thoroughly addressed the governing theory and constraints of conventional conveyor belt and component technology. The resulting high angle conveyors would fulfill the needs of the mining and materials handling industries and would offer the most operationally appropriate and the most cost-effective solution.
The Sandwich Belt Principle
The Continental HAC represents evolution of the latest concepts in Sandwich Belt high angle conveying. The Sandwich Belt approach employs two, ordinary, rubber belts which sandwich the conveyed material. Additional force on the belts provides hugging pressure to the conveyed materiel in order to develop sufficient friction at the material-to-belt and material-to-material interface so that sliding back will not occur at the design conveying angle.
INSERT FIGURE 1 and FIGURE 2
A more realistic model is shown in Fig. 2. An ample belt edge distance assures a XXXled material package during operation even when belt misalignment occurs. A more comprehensive treatment of force interaction for a complex model along with the implications of driving both belts is not within the present scope and can be found in Refs [2] and [3].
Continental HACs
Though much development was needed, the Sandwich Belt concept clearly offered the greatest potential tor a cost-effective, operationally appropriate high angle conveying system to address the broad scope needs of the mining and materials handling industries.
Following the extensive Sandwich Belt conveyors, the governing theory and constraints, and development of the governing design criteria, a broad scope effort was undertaken in 1982 at Continental Conveyor & Equipment Company, Inc., USA, to develop the first Sandwich Belt high angle conveyor to needs. Towards this end, many mine and terminal operators and planners were consulted at various stages of development.
The resulting HACs, described in Figs. 3 to 8 and Tables 1 to 5, are truly evolutionary in judiciously selecting and advancing past desirable features, while omitting the non-desirable features. They are entirely conforming to the governing theory and constraint equations and to the development criteria.
The HAC fulfills all of the established operational requirements, HAC profiles can conform to a wide variety of applications. The HAC is well suited to a self-contained modular unit, utilizing nylon fabric belts to achieve short vertical radii of curvature, as it is to a single-run approach utilizing steel cord or aramid fiber belts requiring very large transition curves [3], [4].
Advantages of Sandwich Belt HACs
HACs can take on various forms (Fig. 3) and offer many advantages over other systems, including:
- Simplicity of Approach
The use of all conventional conveyor hardware means interchangeability of components, fast delivery of replacement parts. Operating experience thus far has revealed that HACs have very high availability and low maintenance costs.
- Virtually Unlimited in Capacity
The use of conventional conveyor components permits high conveying speeds. Available belts and hardware up to 120 inch (3,000 mm) wide make capacities greater than 15,000 short/tons/h (13,608 t(metric)/h) possible.
- High Lifts and High Conveying Angles
Lifts of up to 350 ft (107 m) are possible with standard fabric belts, and single-run lifts greater than 1,000 ft (305 m) are possible with steel cord or aramid fiber belts. High angles of up to 90° are possible without excessive wear because of the soft, floating, fully equalized hugging pressure.
- Flexibility in Planning and in Operation
The Continental Conveyor Sandwich Belt lends itself to multi-module conveying systems using self-contained units as well as to single-run systems using externally anchored, high angle conveyors. In either case, the conveyor unit may be shortened or lengthened or the conveying angle may be altered according to the requirements of a new location. High angle conveying modules may be mounted on rails, rubber tired or crawler-type transporters, or they may be equipped with walking feet for optimal mobility.
- Belts Are Easily Cleaned and Quickly Repaired
Smooth surface belts allow continuous cleaning by belt scrapers or plows. This is especially important in handling wet and sticky material. Smooth surface belts present no obstruction to quick repair of a damaged belt by hot or cold vulcanizing. Quick repair means less costly downtime.
- Spillage-Free Operation
During operation, the material is sealed between the carrying and cover belts. Well centered loading and ample belt edge distance result in no spillage along the conveyor length.
INSERT FIGURE 3
HAC Installations
HACS are now well into the commercial stage, with the first commercial unit in operation since June 1984 (Fig. 5, Table 2). Two additional significant HACs have been delivered (Fig. 6, Table 3, and Fig. 7, Table 4) an& engineering of the latest commercial unit (Fig. 8, Table 5) is presently under way.
The first large scale HAC, however, began operation in June 1983. It was at the 1,524 am (60 inch) belt width prototype (Fig. 4, Table 1) that a year long testing program was conducted to verify the theory and develop specific design criteria. Because of the versatility built into this unit, including various incline angles from 30 to 60 and various belt speeds, it was possible to investigate the limits of the concept.
The program included large scale testing of basic material properties and their relations to conveying characteristics with the HAC at various conveying angles, speeds and degrees of cross-sectional filling.
Materials tested included Texas lignite, Alabama coal (run-of-mine, lump, sized, size and washed), Arizona and Tennessee copper ores, river run gravel, soybeans, iron ore pellets and sandstone. Testing proved successful in all cases with all materials conveyed at various speeds up to a conveying angle of 60°. At the 60° angle, demonstrated conveying rates exceeded 1,814 t(metric)/h (2,000 short tons/h) with coal and lignite, 2,722 t(metric)/h (3,000 short tons/h) with copper ore, gravel, and sandstone, 51,000 bushels/h (1,795 m-/h) with soybeans, and 2,812 t(metric)/h (3,100 short tons/h) with iron ore pellets.
In addition, damage testing was performed on three USDA Grade 1 grains to demonstrate the gentle distribution of hugging pressure on the sandwich material. Five one-bushel samples were loaded into oversized burlap sacks from each of a common batch of soybeans, wheat and seed corn. The first bushel of each grain was set aside to serve as the control sample, while the next four bushels were conveyor eat 60°, the full length cf the HAC prototype, two, four, six and eight tines, respectively, for corresponding conveying distances of 45.7m (150ft), 91.4m (300£t), 137.2m (450ft) and 182.9n (600ft). Samples (2,555g) from each bushel sack were then analyzed at a State of Alabama Department of Agriculture laboratory for the various forms of damage and contamination, and at the Alabama State Seed Laboratory Department of Agriculture and Industries for germination potential. The results showed no damage to any of the three grains tested, as a result cf conveying in the HAC prototype.
Conveying up to 60° proved very successful and indicated no limit on conveying angles of up to 90° (vertical). HACs are thus offered with conveying angles of up to 90°, as in the latest commercial unit (Fig. 8, Table 5).
Success in testing and convincing demonstrations led to the sale of the first commercial HAC unit (main features described in Table 2) to a Western coal mining company in latter part of 1983. The HAC permits a short direct path to the company’s train loading silos, rather than the long route through the blending silos, as previously required. The unit was commissioned in June 1984 and has operated successfully to date. It has proven to be very reliable and requires very little maintenance. It operates today with all of its original components 10].
The second commercial HAC unit (main features described in Table 3 and illustrated in Fig. 6) was sold to a Yugoslavian copper company to be installed in a deep open pit copper mine. This HAC is part of an in-pit crushing and conveying system which incorporates in-pit trucking to portable crushers to an in-pit conveying system which feeds the HAC.
The HAC elevates the crushed ore from the pit onto an out-of-pit conveyor system to the coarse ore pile at the plant. Designed to permit installation of a second future unit to elevate ore from a deeper pit location onto the tail of the first HAC.
The third commercial unit (Fig. 7, Table 4) elevates all coal throughput of a Western U.S. coal mine at 2,903 t(metric)/h (3,200 short tons/h) from a slot storage barn to a sampling tower where it discharges to a silo feed conveyor. This unit began operation in January 1987.
Engineering is underway on a fourth unit (Fig. 8, Table 5) which will elevate sludge vertically along a C-profile at 50 t(metric)/h (55 short tons/h).
Summary and Conclusions
This and previous papers have described the broad-scope effort at Continental Conveyor, USA, which led to development of the Continental high angle conveyor – the HAC – in 1983.
HACs are now proven as a result of extensive testing, during development, followed by more than three years of proven performance in commercial applications.
Review of the commercial installation to date yields evidence of the HACs great versatility, varying in profile from S-to L- to C-shape (Figs. 4 to &), in elevating angle from 30° to 90°, in materials handled from coal, to coarse ore, to sludge, and in throughput rate from 50 to 4,000 t (metric)/h.
Because of the HACs great versatility and proven performance, its advantages may now be exploited with confidence in a wide variety of applications.
References
[1] Mevissen, E.A., A.C. Siminerio and J.A. Dos Santos: High Angle Conveyor Study. By Dravo Corp. for the Bureau of Mines, U.S. Department of the Interior, under BuMines Contract No. J0295002, 1981, Vol. 1, 291 pages, and Vol. II, 276 pages.
[2] Dos Santos, J.A., and E.M. Frizzell: Evolution of Sandwich Belt High-Angle Conveyors; CIM Bull. Vol. 576 (1983) No. 855, pp. 51-66.
[3] Dos Santos, J.A.: Sandwich Belt High Angle Conveyors – BAC – Evolution to Date; bulk solids handling Vol. 6 (1986) No. 2, pp. 299-314.
[4] Dos Santos, J.A.: Sandwich Belt High Angle Conveyors – Applications in Open Pit Mining; bulk solids handling Vol. 4 (1984) No. 1, pp. 67-77.
[5] Mitchell, J.J.: High Angle Conveyors Climb to the Top; Coal Mining, Maclean Hunter Publication Chicago, USA, (1984) Nov., pp. 39-43.
[6] Mitchell, J.J., and D.W. Albertson: High Angle Conveyor Offers Mine Haulage Savings. Beltcon 3, Int. Materials Hanlding Conf., Sept. 9-11, 1985, Johannesburg, Republic of South Africa.
[7] Belt Conveyors for Bulk Materials. Conveyor Equipment Manufacturers Association (CEMA), CBI Publishing Co., Inc., Boston, USA, 2nd Ed., 1979.
[8] Dos Santos, J.A., and Z. Stanisic: In-Pit Crushing and High Angle Conveying in Yugoslavian Copper Mine. Mining Latin America, Int. Mining Convention, Nov. 17-21, 1986, Santiago, Chile.
[9] Dos Santos, J.A.: Sandwich Belt High Angle Conveyors – Broad Horizons; Bulk Solids Handling Vol. 7 (1987) No. 2, pp. 229-239.
[10] Dos Santos, J.A.: High Angle Conveyor – HAC Provides Shortest Route to Train Loading Silos; Coal Prep 87, April 27-29, 1987, Lexington, Kentucky, U.S.A.
Table 1: Test and demonstration data of HAC® prototype unit
Material conveyed
Conveying angle
Design conveying rate
at an angle of 60°
Belt width
Belt speed
Elevating height
Overall conveyor length
HAC conveyor drives:
— top belt
— bottom belt
INSERT FIGURE 4
Fig 4:
HAC prototype
lignite, coal, copper ore and
waste rock, iron ore pellets, sand,
gravel, grain
variable from 30° to 60°
1,955, 2,468, 2,684 t (metric)/h
(2.155, 2,721, 2,959 short tons/h)
for.materials of a density of 0.8,
1.6, 2.4 t (metric)/m (50, 100,
150 Ib/ft9), respectively
1,524mm (60inch)
infinitely variable from 0 to
6.1 m/s (0 to 1,200 ft/min)
variable from 7.9 to 19.5m
(26 to 64 ft)
35m (115 ft)
74.6 kW (100 HP)
111.8 kW (150 HP)
Table 2: Data of HAC” far Triton Coal Co.
Material conveyed
Conveying angle
Conveying rate:
design
surge
Belt width
Belt speed
Elevating height, loading point to
discharge
Horizontal projection:
= loading point to
Sandwich entrance at a conveying
angle of 0°
sandwich entrance
to discharge
Overall conveyor
length
HAC conveyor drives:
— top belt
— bottom belt
coal
60°
1,814 t(metric)/h
(2,000 short tons/h)
1,966 t(metric)/h
(2,200 short tons/h)
1,524 mm (60 inch)
4.65 m/s (915 ft/min)
32.9 m (108 ft)
11.0 m (36 #)
: 25.6 m (84 ft)
56.7 m (186 ft)
112 kW (150 HP)
149 kW (200 HP}
Table 3: Data of HAC® for the Majdanpek copper mine,
Yugoslavia
Material conveyed
— type
— density
— lump size
Conveying angle
Conveying rate
Belt width
Belt speed
Elevating height
HAC conveyor drives:
— top belt
— bottom belt
copper ore
2.08 t(metric)/m* (130 Ib/ tt?)
250 mm (10 inch) max.
35.5°
4,000 t(metric)/h
(4,409 short tons/h)
2,000 mnt (78.7 inch)
2.67 m/s (525 ft/min)
93.5 m (307 ft)
450 kW (600 HP)
2x 450kW = 900 kW (1,200 HP)
Fig. 6: HAC at the Majdanpek copper
mine, Yugoslavia
Table 4: Data of HAC® for Western U.S. coal mine
Fig. 5: Triton Coal HAC, Western USA
Material conveyed
Conveying angle
Conveying rate
Belt width
Belt speed
Elevating height
HAC conveyor drives:
— top belt
— bottom belt
coal
35°
2,903 t(metric)/h
(3,200 short tons/h)
1,829 mm (72 inch)
4.57 m/s (900 ft/min)
29.0 m (95 ft)
149 kW (200 HP)
224 kW (300 HP)
Fig 7: HAC at Western U.S. coal mine
Table 5: Data of HAC® for sludge, Eastern USA
Material conveyed sludge
Conveying angle 90°
Conveying rate 50 t(metric)/h
(85 short tons/h)
Belt width 610 mm (24 inch)
Belt speed 1.40 m/s (275 ft/min)
Elevating height 20.4 m (67 ft)
HAC conveyor drives:
— discharge belt 11.2 KW (15 HP)
— receiving belt 5.6 KW (7.5 HP)
Fig 8: C-profile HAC for sludge, Eastern USA
PART II
INTRODUCTION
The transportation of bulk solid materials by conveyor belts dates back to the late seventeen hundreds. Primitive conveying systems of leather and canvass carried grains and other bulk solids short distances over flat or troughed wooden beds with enough efficiency to prompt further development of this technology [1]
In the early part of the twentieth century the marriage of bucket elevating technology with products from the rapidly growing rubber industry produced the first belted bucket elevators. Belt strength quickly limited the vertical lift component of these systems until World War II when the rubber industry was forced to create synthetic materials to replace dwindling supplies of natural rubber from southeast Asia. Still, technological problems had to be overcome before high angle conveying could replace the old reliable but expensive steel bucket elevators already in steady use around the world.
Simple economics have been the driving force in the research of high angle conveying systems during recent years. High capital costs for the installation of conventional conveying equipment high vertical lift situations and concerns about available space for such installations at existing facilities has prompted many operators to look at high angle conveying as a serious alternative to some of their materials handling problems.
The most recent developments and products in the field of bucket or pocket type high angle conveying systems have come from Scholtz Hamburg of West Germany.
The Pocket Principle
The success of high-speed, high-angled, pocket type conveying systems for delivering bulk solids hinged on solutions to several key problems. One particular element was the development of a successful system for discharging the material once it reached its prescribed point of delivery. With slow moving bucket type elevators the trajectory of discharged materials was quite easily determined. With increased speeds however centrifugal forces are introduced as the belting passed around the end wheel of the conveyor resulting in a very uncontrolled discharge of the material being carried. An apparent solution to the problem was to increase the diameter of the wheel at the discharge end of the conveyor. This was neither practical nor cost effective. The solution came with the development a conveying pocket with a flexible sidewall (see Figure 1) which would allow an “opening” of the pocket to occur as it passed around the end wheel.
FLEXOWELL -Grdaflen
FLEXOWELL – sizes
INSERT Figure 1
It was found that the pocket design also prevented material degradation and spillage since the material rests securely in the pocket after loading (see Figure 2). Abrasion of the surface of the belt is also reduced by the restricted movement of the material within the pocket [2].
Stollenprofile Qualitaten
Figure 2: Cleat profiles for pocket belt installation.
Applications
Although pocket type high angle conveyors designed by Scholtz have existed in the United States for about 20 years. The first mining application of the Flexowall (R) system in the U.S. was made during the tunneling of a sewer system in the city of Chicago. A vertical, lift of a little over 260 feet was made with Flexowall (R) belt installed by Scholtz of Hamburg, West Germany. Delivering 1100 sth of waste rock under very wet conditions it was felt this would be a good test of the system in a mining environment. Successful tests and operation of this system prompted the design and construction of the first coal mine installation at the Elkhart Mine approximately 20 miles northwest of Springfield, Illinois in 1982. The second Flexowall ® conveyor system installation was made at the Wyodak Mine in Gillette, Wyoming in 1983.
The Elkhart Mine
The Elkhart Mine was originally designed with a sloped coal conveyance system to move coal to the surface from a depth of approximately 330 feet (100m). Site investigation and drill hole date indicated substantial deposits of unconsolidated glacial till which would require special tunneling techniques. Cost estimates for the project ranged from $13 million (US) to $23 million (US). A decision was made by the Turris Coal Company to proceed with a vertical shaft through the unconsolidated Strata and to construct a continuous hoisting system rather than a skip hoist (see Figure 3).
INSERT FIGURE 3
Operating costs for the vertical conveyor were estimated to be lower than those for the skip hoist with the construction costs of both systems roughly equal [3].
Construction and Operation
Two Flexowall ® belts designed to carry 650 stph (590 t/h) were installed within the 20 foot diameter shaft which was sunk using conventional techniques. The mine operates 2-10 hour shifts per day, seven days per week, and produces approximately 3 million tons of coal per year [3]. Operating experience has very satisfactory according to Chief Engineer Paul Hollar. The complete coal handling system from the screen feed conveyor to the raw coal silo can be operated and maintained by one man per shift. Downtime attributed to the Flexowall ®
belt conveyor system delivering raw coal from the mine is less than 0.1%.
With the experience gained in the installation of the two belts within the hoisting shaft at the mine the Turris Coal Company installed a third high angled Flexowall ® conveyor system in the tipple area of the Elkhart Mine. This conveyor system lifts a stoker coal product 146 vertical feet to a storage silo. With a belt speed of 450 feet per minute the 36 inch wide belt was designed with pocket sizing to carry 100 stph (91 t/h). Actual production is approximately 80 stph (73 t/h) [3].
Summary
In both decisions to install high angled pocket type conveyors at the Elkhart Mine there were extenuating circumstances which precluded the use of conventional conveyance systems. In the case of the surface installation limited space was available because of existing structures.
Some dribble and carry back problems were encountered with the belts in the production shaft during: the start-up period. With this experience, design modifications were made on the discharge chutes of the stoker coal conveyance system before it was installed and the changes appear to have solved the problems [3].
All belts have performed their functions as anticipated and have been cost effective in both capital and operating costs when compared with other alternatives [3].
The Wyodak Mine
The Wyodak Mine in the Powder River Basin of Wyoming is a wholly owned subsidiary of Black Hills Corp. The mine produces approximately 3 million tons of sub-bituminous coal per year for power plant use and industrial processes. Two power plants located at the mine site consume nearly 70% of the coal produced by the mine and the balance is distributed to other consumers by rail and highway truck.
Due to increased sales volumes and problems with rail transportation to some consumers the amount of coal being shipped by highway truck was rising steadily. The existing truck loadout system was grossly inadequate and long lines of trucks waiting to be loaded were commonplace, On top of these problems some customers were requesting certain select qualities of coal for their particular boilers and furnaces.
The decision was made to construct a new truck loadout facility in the spring of 1982. The following operational needs were outlined and the engineering firm of Stone and Webster was selected to make the conceptual design.
1) Additional and faster truck loading capacity was needed
2) A batch weighing system was needed for accurate loading of trucks
3) Separate silos were needed for the selectively mined coal and stoker coal products
4) Interconnection with existing conveyor facilities would have to be done without interrupting normal production
Like the Elkhart Mine, Wyodak also had very limited space for the construction of conventional conveyance systems to feed the silos that were needed.
A review period followed submittal of the initial design and in January of 1983 a contract was awarded to Scholtz-EFS for the final design and construction of the truck loadout facility.
Construction and Operation
Three 1,000 ton silos were erected to feed the batch weighing systems for truck loading. Computer operated hydraulic slide gates load a desired amount of coal into each hopper. The truck driver then controls the loading of the pre-weighed coal into the truck. One silo contains stoker coal for domestic heating purposes. The other two silos contain selectively mined and blended coal for boilers which require coals with high or low temperature ash fusion firing characteristics. These two silos (Nos. 2 and 3) are fed by a high angle Flexowall ® conveyor with a capacity of 900 stph (816 t/h). The stoker coal silo (No. 1) is fed by another Flexowall ® conveyor with a capacity of 400 stph (362 t/h). Two 450 sthp (816 t/h) vibrating screens process the stoker coal with all over and under sized rejects delivered to the high angled belt feeding silos No. 2 or 3 [4].
A third high angled belt rated at 900 stph (816 t/h) feeds the entire system with coal diverted from the primary mine conveying system. Coal can be diverted around the screens to load silos 2 and 3 directly or can be processed into stoker coal when demand for that product increases.
Conveyor No. 1 (CNV-1) which feeds the screen building is a 48 inch wide steel cord belt which rises 64 feet at a 50 degree angle driven at 450 ft per minute by a 100 hp electric drive system. Conveyor No. 2 (CNV-2) which feeds bins 2 and 3 is similar to CNV-1 in design and function. Powered by a 200 hp system this belt rises at 45 degrees to a height of 125 feet. The Flexowall® belt feeding the stoker coal silo (CNV-3) travels at 450 ft per minute and is housed in a common gallery with CNV-2. All three conveyors are equipped with hydraulically operated tensioning systems operated by a series of pressure switches to maintain constant belt tension [4].
SUMMARY
All Flexowall® conveyors are operating according to design. Operating and maintenance costs have been difficult to determine but appear to be in-line with expectations [4]. Some spillage was encountered in the loading area of CNV-2 and CNV-3 and pocket lip wear was noted but both situations were improved with some chute modification and the addition of metal pocket lip guards. Clean-up operations are done with a central vacuum system and a water washdown.
The decision to install the pocket type high angle conveyors was based on several considerations. Most importantly was the available space around the existing facilities. Secondly was the cost of alternative measures to accomplish the same goals.
CONCLUSIONS
The comparable cost of installation, operation, and maintenance for pocket type high angle conveyors make this technology particularly attractive to operators with plans to add flexibility to existing coal systems.
INSERT FIGURE 4
REFERENCES
[1] Handbook of Conveyor and Elevator Belting. The Goodyear Tire and Rubber Company, Industrial Products Division; Akron, Ohio (1982).
[2] Anthony, James J.: High Angle In-Pit Conveying System. Mini Symposium – In Pit Crushing and Conveying, Session II. SME-AIME Fall Meeting; Salt Lake City, Utah (October 1983).
[3] Paelke, J.W., Germany and Emerton R.C., USA. Vertical Flexowell ® Conveyors With 330 ft (100M) Lift Carry Over 3 Million Tons Of Coal For Illinois Coal Mine; Bulk Solids Handling Vol. 6 (April 1986) No. 2.
[4] Paelke, J.W., Germany; Emerton, R.C. and Williams, J.A., USA. Wyoming Coal Mine Truck Load-Out Facility Carries 65,000 Tons Per Month On Flexowell ® Steep Angle Conveyors; Bulk Solids Handling Vol. 6 (April 1986) No. 2
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