Coincidentally, the 300th AC-VFD shuttle car – a 10SC32BC model – is being shipped to Jim Walter Resources’ underground coal mine in Brookwood, Alabama, not far from where the very first shuttle car of its type went into operation just four years ago at Drummond Coal’s Shoal Creek Mine in Adger, Alabama.
During those four years, Joy has shipped OPTIDRIVE AC-VFD shuttle cars to 10 countries: Australia, China, India, Italy, Mexico, Norway, Russia, South Africa, the United Kingdom and the United States.
According to Joy, these machines have been operating in some of the toughest, most rugged mining conditions in the world, successfully contending with significant amounts of rock and other seam-intrusive materials, tram-challenging slopes and muddy roadways and low seams that provided minimal operating heights.
Since the introduction of its OPTIDRIVE AC variable frequency drive in the spring of 2003, Joy reported shuttle car sales increasing steadily, while the percentage of units sold with OPTIDRIVE skyrocketed in just the second year.
In 2003, during which OPTIDRIVE was available for just more than half the year, 10% of the Joy shuttle cars sold had OPTIDRIVE AC-VFD. In 2004, that soared to 87% of the units sold and, last year, increased further to 91% of sold units.
Joy shuttle cars are available in eight models of six increasing capacities designed to accommodate virtually any underground wheeled-haulage requirement.
The smallest of the machines, the 21SC04, can haul nine tons (eight tonnes) of material, while the largest of the models, the 10SC32D, is rated at 33 tons (30 tonnes). Falling between the two extremes are the 10SC32AA and 10SC32A, both capable of hauling 12 tons (11 tonnes) of mined material; the 10SC32AB and 10SC32B, rated at 15 tons (14 tonnes) each; the 10SC32BC, with a capacity of 18 tons (16 tonnes); and the 10SC32C, capable of hauling 22 tons (20 tonnes).
More than 90% of the 2700 shuttle cars operating today worldwide are employed in underground coal mines, Joy said.
According to the company, OPTIDRIVE was a major breakthrough in applying AC variable frequency drive to shuttle cars and has resulted in significant increases in power, speed and productivity.
Prior to OPTIDRIVE, Joy says the mine operator had to choose one of three drives: AC drive if the mine had steep gradients or either AC/DC or DC drive if the mine was fairly level. OPTIDRIVE, Joy says, was designed to work well in all conditions, providing the needed power of the AC drive and the smooth acceleration of an AC/DC or DC drive.
With OPTIDRIVE, the shuttle car’s top speed of about four miles per hour (6km per hour) was increased to 6mph (9kph), the international standard allowable top speed, Joy said, adding that this 50% increase in the maximum speed has the potential to increase mine production by 10% which, in a typical situation, amounts to a difference of five additional loads per shuttle car, per shift.
Additionally, Joy said mine performance studies have shown Joy shuttle cars with OPTIDRIVE AC-VFD have less motor maintenance when compared to haulage vehicles having AC/DC drives or DC drives, primarily because DC traction motors have brushes that must be replaced about every six months.
“Shuttle cars also have lower maintenance costs than AC drives with soft start and they consistently outperform and have lower maintenance costs than battery and diesel powered haulers, as well as cascading chain haulage systems,” Joy said.
Inventory gains can also be made, Joy noted, with the interchangeability of OPTIDRIVE – a single, AC variable frequency for all Joy mining equipment.
OPTIDRIVE was introduced on longwall shearers in 1998, continuous miners in 2001, flexible conveyor trains in 2002 and, in 2003, shuttle cars.