外文翻譯--自移式液壓支架-液壓系統(tǒng)-文庫吧
2025-04-17 05:59 本頁面
【正文】 r. This allows easy access though the face and employs the standard method of advancing。 i. e. , pushing the conveyor first, and then advancing the support. With the IFS system, the support units is advanced to the conveyor immediately after the cutting machine has passed, and the forward canopy of the support units is long enough to the support both the recently and newly exposed roof sections. After the supports have been advanced, the conveyor is pushed over. FRAME The frame support is an extension of the single hydraulic props conventionally used underground. Thus it is the first type developed in modern selfadvancing hydraulic powered supports. It involves setting up two hydraulic props or legs vertically in tandem that are connected at the top by a single or two segmented canopies. The two segmented canopies can be hingejointed at any point between the legs or in front of the front leg. The base of the two hydraulic legs may be a circular steel shoe welded at bottom of each leg or solid base connecting both legs. Generally, a frame support consists 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
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