Principal factors influencing equipment selection can be grouped into five basic categories. Tonnage Requirements, Ore and Waste, Topography and Property Line Considerations, Ore Control Requirements, Physical Characteristics of Ore and Waste, and Climatic Conditions.
Specialized Machines: This type of equipment generally operates on the principle of leverage uprooting and mechanical breakage of fallen vegetation. It is used in areas where little or no revenue can be derived from the sale of the vegetation removed.
Bulldozers – Crawler, with Special Attachments: Attachments available for this type of clearing equipment are: brush rakes, stump plows, rippers, demolition and multi-purpose buckets, and grapples. Vegetation is usually uprooted, then dozed into convenient piles for removal or burning. The most economical dozing range for this type of trash cleanup is a distance of 100 to 150 yards.
Drills – Jackhammers, Airtracs: These units are principally used in the process of building drill roads or in blasting of surface boulders.
Bulldozers – Crawler: These units are confined to preparing a level surface to support large rock drills, rock breaking equipment, or loading equipment. The larger bulldozers are generally equipped with rippers and tilt blade for use in building drill roads in rocky or mountainous terrain.
Drills – Large Diameter (Percussion): Since these drills have a relatively high unit cost per foot, their use is generally confined to rock formations having compressive strengths in excess of 40,000 pounds per square inch. These rigs are self-propelled, mounted either on tracks or on special wheeled carriers. The wheeled carriers are used where a high degree of mobility is required and overall penetration rates are not critical.
Loading equipment of various types and capacities is readily available from a number of manufacturers. This permits an operator to select a design which is tailored to a specific loading application.
Power Shovels, Engine Driven: Engine driven machines are used primarily on jobs of short duration, remote location, or where electrically powered or control¬led equipment is impractical. Mobility of these machines is good. However, production rates of these machines are hampered by mechanical control devices and mechanical wear. These machines share the advantages common to all power shovels, i.e., high production rates, capability of handling diverse material, and the ability to operate in a generally adverse digging environment.
Power Shovels, Electric Motor Driven: Electric shovels have the advantage of unified control systems, efficient utilization of power, fewer energy conversion devices, and faster cycle times.
Haulage or transportation costs commonly account for some 50 percent of total mining costs, thus, the compelling need to carefully plan and engineer the transportation system. The principal systems in use today are railway, truck, conveyor, tramway, and hydraulic.
Railway Locomotives, Diesel-Electric: Rail haulage can be economically attractive when mine access gradients of 4 percent compensated or less can be maintained and when overall one-way haul distances exceed 3 to 5 miles.
Rolling Stock, Side Dump Cars: Dump mechanisms on open pit side dump cars are of the integral air/hydraulic ram type. The shear bulk of the dumping mechanism reduces total car carrying capacity and increases rolling stock maintenance. However, this type can be used for both ore and waste haulage.
Two Axle, 20 to 55 cubic yard, Struck, Diesel: Units of this type generally utilize power shift transmissions and torque converters. Final gear reduction to the drive wheels is accomplished through a “SUN GEARED” planetary axle drive. Torque retarder braking systems are incorporated in nearly all models produced. Suspension systems are either leaf spring, air cushion, or controlled rubber cushion. These trucks are normally operated over grades up to 15 percent.
Field Support and Service
Field support and service equipment is an integral part of any successful open pit operation. Investment in equipment for these purposes usually comprises about 15 to 20 percent of the cost of equipping the mine.
Cranes, Utility, 8-15T Rating: Cranes in this class are usually mounted on a special four-wheel, self-propelled carrier. All wheeled carriers are equipped with lateral support outriggers, either manually or hydraulically operated, and have a full 360-degree swing. Pipe laying cranes in this capacity range have booms generally side mounted on counter-weighted crawler tractors.
Field Service Truck, Mechanical: Units of this type are usually in-shop built on 1-½- to 3-T rated truck chassis. These are further described in the section on Utility Vehicles.
Field Service Truck, Tire Maintenance: These trucks consist of a heavy-duty chassis upon which are mounted a flat bed body, a central jib crane of 2,000- to 10,000-pound capacity, a high pressure air compressor, and an enclosed tool crib.
Water Trucks – Road Sprinkler: Units are available from manufacturers, but the majority are fabricated at the mine by converting spare or uneconomic haulage trucks to water tankers. Even the manufactured units are derived from a basic earthworking machine. Tank capacities are as varied as the trucks; however, the most used sizes range from 5,000 to 20,000 U. S. gallons.
Explosive Trucks, ANFO mixtures: These units are available with gravity, mechanical screw or chain, and pneumatic discharge systems. The gravity type trucks, requiring a hydraulic jack assembly, find minimal use. Both the mechanical and pneumatic type trucks normally incorporate a metered fuel oil system and some type of volumetric discharge indicator. Some models are equipped with a grinding mill to increase detonation sensitivities and velocities of the ANFO. Standard mixer trucks, such as used in the preparation and delivery of ready-mix concrete, have been also utilized for explosive loading.
Explosive Trucks, Slurried Products: Explosive dispensers of this type are normally custom built to fit the characteristics of a particular slurry mix. Slurries are delivered under pressure to the bottom of a blast hole by means of a flexible conduit.
Explosive Trucks, Utility: Vehicles in this class are normally standard or slightly modified models of a flat bed truck in the 1-½- to 3-T capacity range. They are used to transport men, miscellaneous equipment, detonating cord, fuse, and primers. Detonating caps are always transported to the blasting area in a separate vehicle.
The maintenance program is vital to the success of any open pit mining operation. Repair and maintenance can be expected to account for 40 to 50 percent of direct mining costs.
The need for careful initial planning often goes unrecognized, and this leads to underestimation of personnel and facility requirements. In a well balanced mine organization, maintenance personnel will comprise approximately 40 percent of the total.