【文章內(nèi)容簡介】 e require a plex gearing system which ， however ， offers the advantage that the motor power can be divided among the two drums and the haulage box as required . New machines such as ， for instance ， the EDW1502L are equipped with transverse motors fitted direct to the ranging arm .The advantage ，however ， is achieved at the expense of the power distribution the two drums which is no longer possible ， and the drum which is subjected to the higher load determines the traveling speed of the shearer by marking full use of its motor power . Haulage Units Hydraulic haulage units for power loaders have been used for nearly 30 years now .In the course of the decades they have been improved to a high degree of the shearer as a function of the lood on the motor and the haulage box (Eiatik).They prevent overloads and operate safely using flameresistant fluids . However ， the development of the semiconductor technique has progressed to a stage during the last decade that it is now possible to design electrical haulage units powered by . motors the speed of which is controlled by thyristors .Compared with hydraulic haulage units electric haulages are simpler and maintained via the use of plug in control units .In addition ， their various functions are monitored and they respond more rapidly to speed alterations than hydraulic haulage units . Amongst the first power loaders equipped with such electric haulage units are the Eickhoff doubleended ranging drum shearers EDW1502L， and the electric haulages have fully met the expectations from the very first installation. Chainless Haulage Systems After the use of haulage ropes and chains ， chainless haulage systems are now gaining ground .They offer the advantages of greater safety ， of a steadier machine operation ， and of multimachine operation on a face . In Great Britain， a number of various designs are used .A problem connected with some chainless haulage systems is the fact that they impede the flexibility of the face conveyor and can cause operational restrictions. The Eicotrack system of Gebr. Eickhoff has overe this problem， because contrary to other systems the rack sections have half the pan length ，so that displacements and deflections between the line pans have only half the effect between the rack sections .This unique advantage naturally entails higher costs . In special cases， however ， the flexibility of the face conveyor is still not considered sufficient .In such cases， the rack sections are not fixed to the face accessories ， but are slidingly arranged in a channel or at the trapping tube .This fully eliminates any effect on the flexibility of the conveyor .Depending on the conditions ， the line of rack sections is fixed at one or several points along the face. Existing haulage units can be converted for operation via Eicotrack .Haulage forces of up to 300 KN are currently ased for presentday power loaders . But even these forces are sometimes insufficient for heavy machines in steeply inclined seams. Higher haulage forces are obtained if booster haulage units are installed in addition to an existing haulage unit to house an additional hydraulic motor and with the follow up train of gear wheels .The oil flow from the pump in the main haulage unit is then distributed to the two hydraulic motors which transmit the power to the two rack wheels .This hydraulic arrangement ensures that both rack wheels exert the same force on to the rack .Higher haulage forces are therefore reached at the expenses of correspondingly reduced traveling speed. Gear Boxes Shearers powered by longitudinal motors need gearboxes to which the ranging arms with the plaary gearings can be mounted .The gearheads are built in different sizes in accordance with the existing motors and house the bevel wheels ， lubrication pumps and hydraulic pumps . Oil cooling is required for high ratings .Intermediate ， twospeed gearboxes are available when a lower drum speed is required . It is unavoidable ， however， that low drum speeds result im a higher torque load on the gearings at a given rating . All twospeed gearboxes known so far can therefore not operate at full load and should therefore be protected against overloads. However ， the trend for low drum speeds is quite obvious ， and n