- Created: Monday, 07 March 2011 10:08
- Published: Monday, 07 March 2011 10:08
Telescoping conveyors and truck unloaders increase efficiencies when loading and unloading aggregate and mineral ores.
By Carol Wasson
Maritime transport is playing an ever-increasing role in the cost-effective delivery of aggregate and mineral ores. From port to port, the economic advantages of shipping by inland barges or ocean freighters increase as the tonnage and distance of transport increases.
Consider that at any one time, one of the largest U.S. aggregate producers has nearly a quarter-million tons of material on barges heading down the Mississippi River, for example. Commonly holding 1,500 tons of aggregate, barges can be grouped into tows of 30 to 40 barges depending upon the width and depth of the waterway.
In addition, ocean freighters average tonnages between 60,000 to 120,000 tons, which equals the volume carried by 3,000 to 6,000 20-ton dump trucks. Consequently, more producers are cashing in on the advantages of waterborne shipment – and more customers’ trucks are being loaded at port facilities with materials produced hundreds or even thousands of miles away.
Total Picture The true cost-efficiencies of maritime transport can only be achieved by looking at the total picture. If an operation is elevating its costs by loading and unloading vessels with outmoded, unwieldy or labor-intensive methods; or stockpiling with loaders and haul trucks – arguably, what is gained from a maritime transport strategy is bit-by-bit being given away.
“To capitalize on the competitive advantages of waterborne transport, one’s material handling, stockpiling, and loading/unloading systems at each port facility must be equally as efficient,” said Bob Domnick, vice president of sales, marketing and engineering for Superior Industries, a Morris, Minn.-based manufacturer of conveyor systems and components for the aggregate, mining and marine material handling industries. Among its offerings, the company designs customized loading and unloading systems that include automated telescoping radial stacking conveyors combined with a number of transfer point mobility options, truck unloaders, tripper systems and more.
Domnick cites several examples of the use of this equipment at port facilities. A Quebec-based shipper is operating four Superior Industries TeleStacker conveyors. The portability of the equipment allows the company to serve more ports while reducing capital costs by avoiding the need to buy fixed equipment for all of its ports. Also, the TeleStacker conveyor creates larger volume stockpiles in a variety of configurations, which maximizes stockpiling capabilities in ports where space is restricted.
An Oregon-based producer has a 150-ft. TeleStacker Conveyor mounted on a dock structure located 360-ft. out into the river where there is adequate water depth. This loading operation provides an ability to raise and lower the conveyor to adjust to the different heights of the river throughout the year, while also adjusting the discharge height as the weight of the load causes the barge to lower in the water.
Domnick explains that when road-portable telescoping radial stacking conveyors are used in combination with portable truck unloading systems, port facilities can realize even greater cost-per-ton savings via improved cycle times, minimized loader use, reduced labor requirements, and ensured product quality control by removing any extra handling of material. The next detailed example illustrates his point.
Agencia Aduanal Vejar is a cargo-handling logistics solutions company in air, rail and maritime transport. Currently it operates out of two Mexican ports – one at Guaymas, Sonora; and the other in Lazaro Cardenas, Michoacan, Mexico. The company ships iron ore, copper concentrate, petroleum coke (petcoke), and other bulk materials via barge and ocean freighters.
It operates three 170-ft. TeleStacker conveyors and four Superior Industries RazerTail truck unloaders. Offering 90-second truck cycle times, these portable truck unloaders, can quickly transfer material onto a conveyor or onto another truck, thus reducing or eliminating the use of loaders. The units require a minimal 22- to 32-in. earthen ramp that takes minutes to build.
Owner Gabriel Vejar said that prior to operating the new equipment; it would take up to four days to load 10,000 tons of material onto a vessel. His previous method involved the use of a flatbed trailer with two 10-ton buckets onboard. Loaders would fill the buckets before transport to the vessel site where a crane and a six-man crew would hook up the bucket and lift it over the hold.
Another six-man crew inside the hold would partially unhook the bucket to unload the cargo. With two buckets, that meant the method required a total of 12 people on the ground and 12 people in the vessel. “It was a long and painfully slow process,” said Vejar.
Now, flash forward to his current method. Dump trucks travel from the mines to the Guaymas port and unload material onto two truck unloaders which feed two TeleStacker conveyors. Each works simultaneously to load two ship holds at a time. “The TeleStacker conveyors swing left to right, up and down, safely loading and trimming the cargo,” said Vejar, adding that with the use of this equipment, he has reduced his loading time by 75 percent, while requiring only one-third of the labor force he had needed previously.
The new equipment has also allowed Vejar to expand his service offerings into the transfer of material from specialized vessels which have a self-contained discharge system that feeds an onboard discharge conveyor. Material is transported from this conveyor at a rate of 1,000 tph.
In the past, a number of excavators were used to stockpile the discharged material, and the vessel had to shut down the feed system and reposition along the dock every two hours. Now the discharge system can operate without any downtime via the use of a TeleStacker conveyor, which is fed by the discharge system.
Material is then stockpiled in one large-volume configuration to await shipment by rail cars.
Truck unloaders are placed on a platform above the rail tracks where they are used to feed the rail car hoppers. Vejar said that the method has reduced unload/load time at this port by more than 50 percent. E
Mobility, Mobility, Mobility
Bob Domnick, vice president of sales, marketing and engineering for Superior Industries, explains that there are three key travel modes that should be considered when considering a telescoping radial stacker in effective marine material handling:
- An inline travel mode;
- A dock travel or transverse travel mode with a 360-degree rotation; and
- A radial travel or tow mode.
Superior Industries, said Domnick, can combine its TeleStacker conveyor with a “mobile pivot base” that allows free-ranging transfer point mobility. Essentially, the mobile pivot base features a fixed-width head axle with a swiveling wheel carriage that allows rotation into each mode. Axle jacks relieve the weight, a hydraulic pin is released, and the unit swivels into the next position.
Domnick stresses that marine material handling facilities should view the telescoping radial stacking conveyor as a “system” that can be custom-configured, via a wide range of available options, to meet the requirements of a specific application.
“As an alternative to the use of labor-intensive cranes and clamshell buckets, cable stackers and other more costly stationary ship loading systems – the custom-configured telescoping radial stacking conveyor delivers the advantages of a lower capital investment, shorter lead times and quick onsite assembly,” he said.
From port to port, these types of systems are increasing the efficiencies of maritime logistics.