外文翻譯--自移式液壓支架-液壓系統(tǒng)-展示頁(yè)
2025-05-27 05:59本頁(yè)面
【正文】 ts of two or three sets of hydraulic legs. The set moving first is the secondary set, the set moving later is the primary set. There is a doubleacting ram installed between each set. The piston of the ram is connected to the secondary set and the cylinder to the primary set. During support advance, the primary set is set against the roof while the secondary set is lowered and pushed forward by the piston. Having reached the new position, the secondary set is against the roof while the primary set is lowered and pulled forward by the cylinder. The distance of each advance ranges from 20 to 36 in.( ~ ) The frame support is very simple, but more flexible or less stable structurally. There are considerable uncovered spaces between the two pieces of canopy which allows broken roof rock to fall through. Consequently, the frame support is not suitable for a weak roof. Frames have bee seldom used because they are less stable and require frequent maintenance. CHOCK In a chock support, the canopy is a solid piece and the base may be either a solid or piece or two separate parts connected by steel bars at the rear and/or the front ends. In both cases a large open space is left at the center for locating the doubleacting hydraulic ram which is used to push and pull the chain conveyor 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
畢業(yè)設(shè)計(jì)相關(guān)推薦
鄂ICP備17016276號(hào)-1