外文翻译--液压支架-液压系统(编辑修改稿)

外文翻译--液压支架-液压系统(编辑修改稿)内容摘要：

eyor and the chock in a whole unit, respectively, a distinctive difference from the frame support. This setup is also used in the shields and chock shields. Again, all hydraulic legs are installed vertically between the base and the canopy. The number of legs ranges from three to six, but the fourleg chocks are by far the most popular ones. The sixleg chocks are designed for thin seams with two legs in the front and four legs in the rear, separated by a walkway. For the sixleg chocks, the canopy is generally hingejointed above the walkway. Most chock are also equipped with a gob window hanging at the rear end of the canopy. The gob window consists of several rectangular steel plates connected horizontally at both ends. In most chock supports, there are hinge joint connections between the legs and the canopy and between the legs and the base. But in order to increase the longitudinal stability, it is reinforced mostly with a boxshaped steel frame between the base and each leg. A leg restoring device is installed around each leg at the top of the boxshaped steel frame. The chocks are suitable for medium to hard roof. When the roof overhangs well into the gob and requires induced caving, the chocks can provide access to the gob. Shield Shields, a new entry in the early seventies, are characterized by the addition of a caving shield at the rear end between the base and the canopy. The caving shields, which in general are inclined, are hingejointed to the canopy and the base making the shield a kinematically stable support, a major advantage over the frames and the chocks. It also pletely seals off the gob and prevents rock debris from getting into the face side of the support. Thus the shieldsupported face is generally clean. The hydraulic legs in the shields are generally inclined to provide more open space for traffic. Because the canopy, caving shield, and base are interconnected, it can well resist the horizontal force without bending the legs. Thus, unlike the solid constraint in the frame/ chock supports, the pin connections between the legs and the canopy , and between the legs and the base in a shield support make it possible that the angle of inclination of the hydraulic legs varies with the mining heights. Since only the vertical ponent of hydraulic leg pressure is available for supporting the roof, the actual loading capacity of the shield also varies with the mining heights. There are many variations of the shield supports. In the following, six items are used to classify the shields , which enables a unified terminology to be developed for all kinds of shields. The types of motional traces of the canopy tip, leg positions and orientation, number of legs, canopy geometry, and other optional designs and devices can be clearly specified by the terminology . Types of motional traces for the leading edge of the canopy. This is the most monly recognized way of classifying the shield. Based on this criterion, there are three types, lemniscate, caliper , and ellipse. Lemniscate. This is the most popular type. The caving shield and the base are jointed by two lemniscate bars which have a total of four hinges. As the hydraulic legs are raised and lowered, the dimentions of the lemniscate bars are selected such that the leading edge of the canopy moves up and down nearly vertically , thus maintaining a nearly constant unsupported distance between the faceline and the leading edge of the canopy .This is a fe。