Streamlining the Scale House
Welch says proportional controls are a major asset. “With on and off controls, you have to bounce the bucket back and forth. With proportional controls, you can open it just enough to get the right amount of sand out of the bucket depending on how slow or fast you move your joystick.”
Another adaptation to the mining environment is the slewing mechanism (for swinging the rotating head to the left or right). Currently, most cranes employ a turntable with bearings and a small pinion gear that turns a larger bull gear. “The problem,” Rathbun says, “is that the gears aren’t enclosed in oil. They’re open. They get lubricated and collect dirt and dust. We have a spindle to support our rotating head and a totally enclosed hydraulic motor with a planetary gear to provide slewing force. Our mechanism is sort of old-fashioned and may be a little heavier, but it doesn’t have exposed gears.”
The spindle shaft turns in a large bushing made of Nylatron, a cast nylon product from Quadrant Engineering Plastic Products, Inc., a German company with U.S. headquarters in Reading, Pa. “You grease it from the inside, so each time the clean grease ejects dirty grease and doesn’t let debris in,” Rathbun says.
Going the extra mile
At the Dolese Bros. Company’s St. Helena Sand and Gravel Mine in Pine Grove, La., a dredge in a 20-acre pond pumps sand, gravel, and pea gravel three-eighths of an inch in diameter from a depth of 20 feet. These materials are sorted into piles, from which wheel loaders fill commercial dump trucks. Loading takes place a full mile from the scale house. The mine installed a grapple loader in December 2006 and began using it in January 2007. “This is the first time I’ve ever been around one,” says Ricky Miley, plant manager. “I’m very impressed with it.”
He says the grapple loader paid for itself in its first six months of operation. Operating costs include electricity, filters, hydraulic oil, grease, and an occasional repair part. Such costs will vary based on a given machine’s intensity of use.
Rinker’s four Florida mines load 300 to 400 trucks a day, but the Davenport mine may load 600 in a day. At Lake Wales, Welch estimates his loader’s operating costs for electricity and maintenance at about $600 a month. Other operators report monthly operating costs ranging from a couple hundred dollars to $1,500, depending on type and frequency of use.
Like playing a video game
Cemex Florida Aggregates’ Inglis quarry consists of a 300-acre aggregate pit on a 900-acre site. Miners at the 75-feet deep pit produce manufactured sand. The quarry has two scale houses, one for aggregate and one for sand. Each has its own grapple loader. “We bought the first one in 2004 and the second in 2006,” says Billy Miller, assistant manager. “For the quarry as a whole, we’re gaining a good couple of hours a day in productivity.”
Training a new operator involves very little time and effort, he says. “It takes 15 to 30 minutes to show somebody how to run it, and three or four days for that person to get really good at it,” Miller adds.