棒材軋機液壓系統設計說明書畢業論文-資料下載頁

　　

【正文】 he operator start and stop the various movement of legs and ram .Antiflushing shield :gives protection against falling debris form the roof or waste FUNCTIONSThe five main functions of a powered support are :1. to resist vertical loading 。2. to resist ,or acmodate .Lateral ( horizontal ) movement of the strata。3. to provide protection form waste flushing。4. to advance the AFC。5. to be selfadvancing。.TYPES OF MOTLONAL TRACES FOR THE LEADING EDGE OF THE CANOPYThis is the most monly recognized way of classifying the shield. Based on this criterion, there are three types, lemniscate, caliper, and ellipse.A. 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 leaning edge of the canopy moves up and down nearly vertically, thus maintaining a nearly constant unsupported distance between the face line and the leading edge of the canopy. This is a feature that is widely considered most desirable for good roof control. There are clear limits of mining height within which the leading edge of the canopy moves nearly vertically. These limits are strictly controlled by the dimentional and positional arrangements of the canopy, caving shield, lemniscate bars, and the base. Beyond these limits, the edges will move rapidly away from the faceline creating a large unsupported area.B. Caliper. In a caliper shield and the base are connected by a single hinge. When the hydraulic legs are raised, the leading edge of the canopy moves in an are away from the face, thus increasing the unsupported area. This is considered by most users the least desirable feature of the caliper shield. But in practice if the seam thickness varies little, the dimentional and positional arrangement of canopy, caving shield, and the base can be so designed that the distance change of unsupported area will not be significant, on the other hand, when the legs are lowered, it reduces the unsupported area.C. Ellipse. In this type the caving shield and the base are so connected that when the hydraulic legs are moved up and down, the leading edge of the canopy follows an elliptical trace. This type is seldom used.CHOCK SHIELDThe chock shield bines the features of chock and the shield .as such it possesses the advantages of both .If all of the four or six legs are installed between the bases, it is called a chock shield. There are regular four or sixleg chock shields in which all legs are vertical and parallel. Others from V or X shapes. Some canopies are a single piece and some are two pieces with a hydraulic ram at the hinge joint. The chock shield has the highest supporting efficiency. They are suitable for hard roof.Roadway supportsThe setting and advancing of supports at the face is only one aspect of effective strata control. It is also essential to set supports in the roadways so keeping roads safe from the shaft to the coalface.The packs on the side of the roadway and the girders supporting the roof in the roadways and permanent supports. They remain in position until the seam or district is worked out or until they have to be removed to enable the roadway to be repaired.There are various shapes of roadway in use underground, depending on the type of strata encountered and any advantages that can be taken from local conditions. However, the majority of roadways leading to longwall faces are supported by arched girders. These not only support the roof but the sides of the roadway as well.Where there is much convergence, stilts are attached to the legs of the arches. As the roof in the roadway gradually lowers, the arch is forced down the stilt instead of being damaged.Struts of steel or wood are placed between the flanges of the arches to ensure that each girder is properly spaced from its neighbors and to prevent the arches form buckling.To prevent loose rocks falling in the roadway, the space between the arch and the roof and sides is covered in with lagging。 pieces of wood, corrugated steel sheets or wire mesh sheets.In the USA, roof bolts are being used as a form of support in square roadways. This is done either by fastening a weaker bed to a stronger bed above, or by fastening a weaker bed to a stronger to form, in effect, one roof beam string enough to support the excavation. In Britain, this system of support has been used mainly in roadways with solid coal sides and the principle of binding strata together by bolts has been used as an extra support to the normal standing support. Floor bolting is also practiced at times.Roadway supports in use undergroundWhere the roadway in a seam meets the coalface, there is usually a change in height depending on the thickness of the coal and the height of the roadway. In most seams, extra height is obtained in the roadways by breaking down the stone just behind the coalface and over the roadway, which forms the roof of the seam. This operation is known as ‘ripping’ the face of rock exposed is known as the ‘ripping face’ and the edge as the ‘ripping lip’. In the space between the last roadway arch and the ripping face, special supports are set to secure the roof and to prevent accidents form falling stones. These supports consist of two girders (forepoling or horse head girders), which are suspended from the roadway supports by special brackets (horse head brackets). Pieces of wood are placed above the fore poling girders and wedged against the roof. Beneath the ripping lip, the roof is supported by girders and props, the girders extending from the face, or by girders and props, which are set parallel to the face. In addition to these girders, chocks are often set to ensure adequate support.The face of the ripping is also secured to prevent stones falling. This is often done by suing Lbars supported by fullwidth girders and props and packed behind with wood covering pieces.All persons who work on the face must pass beneath this area. Therefore, it must be made particularly secure if accidents are to be prevented.To prevent the collapse of roadway supports if a fall of roof should occur near the ripping face, it is necessary to secure the arches by using struts, which tie them together. Therefore, any force imposed upon the arches near the ripping face is transmitted along the line of arches in the roadway and the force is resisted.How powered support workThe plete unit is so designed that by operating control valves, the armored flexible conveyor and support units are moved forward to their new positions without hindrance to coal getting.STEP A The vertical supports are extended to bring the roof beam into contact with the newly exposed roof.STEP B the powerloader has passed on the loading run and the doubleacting ram is extended, pushing forward the conveyor.STEP C the vertical supports are lowered.STEP D the ram is set into reverse and the support is drawn up to new face line. It is then to the roof.Development of coalface supportsThe early types of coalface supports consisted of wood props and wood bars. The bars were usually halfround, being made by splitting props of suitable size.Owing to the weakness of wood supports, steel was eventually introduced and both steel props and steel bars were used. The steel bars were corrugated to increase their strength. In order to prevent the steel props from slipping underneath the corrugated steel strap, lips, made of pieces of soft wood, were set between the prop and the bar. The lid gave some measure of yield in the support and helped to prevent the prop and bar from being damaged.The props were usually set square between the floor and roof but sometimes, in inclined seams, they were under set.These supports were called “rigid supports”, although all supports yield a little under the pressure from roof or floor strata.With the introductio