In the pit-and-quarry industry, not all material is of the same consistency and value. The equipment needed to move it efficiently and profitably varies, and savvy producers study their operation and buy equipment suited to the task at hand.

An operator would not, for example, use a pneumatic cement-conveying system to move a pile of heavy rock. Nor would he move powder over a conveyor system exposed to high winds and weather extremes. In short, different materials require different transportation practices. This is easily noted when comparing the angles of repose and surcharge of various products.

Wet sand, for example, is sluggish compared to dry. If aerated, cement flows freely but compacts after the air is removed. Marble chunks are free-flowing, as is crushed traprock, but broken sandstone and bentonite are sluggish. In any case, the flowability of any material may change depending on factors such as the weather, temperature and storage conditions.

The best advice is to rely on the opinions of qualified manufacturers or consultants when deciding to buy a new system or add to an existing one to make it more versatile and efficient. Virtually all manufacturers employ in-house specialists who answer questions about system design and operation. It also is a good idea to take topography into account. The higher a system is off the ground, the harder it is to maintain.

Cost savings is always a goal. A well-engineered material-handling system may help producers spare the expense of additional payroll, heavy equipment and haul vehicles.

Belt conveyors

Conveyors come in permanent units for fixed applications and in portable configurations when mobility is desired. Either way, they are called upon to move tons and tons of material and should be inspected at least once a day. Belts tear, material gets trapped between the belt and the pulley and other problems develop, resulting in costly downtime. Like all equipment, conveyors should be maintained regularly.

Bearings may need to be greased (though not overgreased), and the belt may need to be cleaned. Scrapers and plows can be installed easily at the tail end of the return run. Simply clamp rubber slabs 1/2 to 1-in. thick between two wooden bars. A number of manufacturers provide belt-cleaning products and technologies. These range from rotating scraper blades and air-pressure systems to brushes, vibrators and steel belts. Belt-conveyor hoods also are available. They protect both the bulk material and conveyor components.

The belt conveyor is perhaps the most widely recognized conveyor in the pit and quarry industry. It traces its history to an 18th-century Delaware flour mill and was brought into widespread use in 1914 for assembly-line production by the Ford Motor Co.

Good belt conveyors operate at 90 percent or greater uptime. Belts are made from a variety of materials – steel cable and polyester, for instance – and are often covered with rubber or a rubberized coating. Steel belts are used for hot materials, and steel cable is used where extreme tensile strength is needed. No dramatic improvements in belt technology have been witnessed in the past decade, although incremental advances and material improvements have made today's belts better than those made a generation ago from cotton, rayon and other products.

Belt size varies according to the type and size of material being transported. In general, the larger the belt, the larger the material being moved. Sizes generally range from 18 to 96 in.

Electricity or internal-combustion engines power the conveyor. Belt-conveyor systems vary in length from a few feet to a number of miles--that's right, miles. A large, dam project in San Bernardino County, Ca., for example, used a 3.5-mile-long conveyor system in two separate lines. It transported millions of sq. yd. of material and was credited with replacing a fleet of 15 trucks and drastically reducing labor and equipment costs.