Electric mining shovels
Table 3 lists the electric mining shovels over 200 t in weight offered by major manufacturers.
The use of solid state electronics in electric mining shovels continues to increase: static power conversion and control systems to replace motor generator sets are becoming well accepted. Both Marion and P&H apply this system to con vert ac input to dc operating power. Marion's latest Statitrol II system, for example, incorporates micro-processor electronics to reduce operational elements, forced air cooling instead of cumbersome liquid cooling and plug-in printed circuit boards which facilitate maintenance.
A fundamental change in electric mining shovel design came in 1980 when the first B-E excavator to use the Acutrol system with ac drive motors was put to work. This first unit of the new 838 t 395-B, equipped with Acutrol, operates at a copper mine near Tucson, Arisona and subsequent units have been sold to open pits in Australia, Yugoslavia and Canada. A two stage ac to dc and dc to ac system of conversion is required to provide adjustable voltage and frequency to control ac motors. Squirrel-cage induction motors (with-cut) commutators) and carbon brushes) are operated by controlled frequency current through switches connected to external solid state electronic circuits automatically sensing, and instantaneously supplying, the correct amount of power required for load variations. Regenerative power is used for braking even in an emergency during loss of outside current. By the end of 1983 a total of fourteen Acutrol equipped 395-B, 295-B II and 290-B II machines were in operation as well as the first 680-W walking dragline using the same system.
The smallest P&H electric mining shovel, the 1400/DE weighing up to 172 t, which first appeared in 1944, is now only made by Kobe-Steel in Japan. P&H up-dated the 2300 and 2800 to XP (extra performance) versions in 1981 and 1982 respectively. Both of these models are available with single or dual motor propel in the lower works; extra power has been provided end new designs of boom with a wide foot, and a dipper stick which can take a wider bucket, are incorporated. Two units of the largest model of shovel on two crawlers have now been shipped by P&H. The 5700 LR, which began stripping work in 1978 at the Captain Mine, Illinois, was joined in 1981 by a 5700 truck-loading version at Bloomfield Collieries mine in the Hunter Valley of New South Wales, Australia.
Soviet electric mining shovels have included the EKG-81 and EKG-12.5 for some years, the latter model being unusual is that it has four 13 m full-length crawlers in pairs on each side of the lower works. These were joined in about 1980 by the first two units of a larger machine, the EKG-20 made by U ZTM. The EKG-20 weighs some 800 t and has a 20 m3 standard bucket on a single dipper stick with its crowd motor attached to the boom. Solid state conversion is used for do drive.
Hydraulic excavators
Whereas the dramatic increase in size of cable excavators during the last forty or so years took place with a long-established technical base, the equally significant development of large hydraulic mining shovels and backhoes has been achieved from scratch in a relatively short period of time. There are now at least twenty-three models of hydraulic excavator in excess of 100 t weight: of these, the two largest are around 500 t, three are around 270 t, eight are between 150 and 190 t and the remaining ten are between 100 and 150 t (Table4).
Already by the end' of 1981 some eight hundred units о this type of machine had been produced and the large hydraulic excavators now challenge, and at times replace, the smaller sizes of cable excavators used in surface mining. Although manufacturers in the USA produced hydraulic excavators in the region of 100 t during the 1970s, it was French and German companies which led the industry into the mining field. Japanese, Soviet and larger American models appeared in the late 1970s and early 1980s. Since 1979 a number of manufactures have introduced hydraulic machines over 100 t for the first time. In the USA B-E made the 500-H in 1981 and 550-HHS in 1982, and Marion the 3560 in 1982. In Japan, Komatsu introduced the PC 1500-1 in 1982. Mitsubishi the MS1600 in 1982 and Kobelco the K975 in 1984. Other recently introduced models from established manufacturers of large machines are the Mannesmann Demag H185 and the O&K "Tri Power" RH120C and RH75C – all appeared in 1983 (fig. 13).
