【正文】 08年第25卷第2期[20] 葉江 符寒光 李明偉 .[M]. 中國冶金設(shè)備南京有限公司 清華大學(xué)先進成形教育重點實驗室 重慶市川深港務(wù)機械制造有限公司聯(lián)合出版，2007年第27卷第1期[21] .[M]. 湖南婁底市：漣源鋼鐵集團有限公司，[22] [J].雜談，[23] .[M]. 北京：機械工業(yè)出版社，[24] [M].哈爾濱：哈爾濱工業(yè)大學(xué)出版社，2001[25] [M]. 北京：機械工業(yè)出版社，1980[26] [M].重慶：重慶大學(xué)出版社，1996[27] [J].中國液壓氣動密封件工業(yè)協(xié)會，2001年第3期外文資料INTRODUCTION OF POWERED SUPPORTBase: provides a firm foundation which spreads the load over its floor area.Legs: transmit the load form the roof beam or canopy to the base ,and are extendable .Roof beam or canopy :its broad area offers protection and carries the roof load ,transmitting it to the legs .It is often in two section ,the front canopy and the main rear canopy .The front section ,nowadays ,has an extension bar which gives protection to men if they are required to work ahead of the support .Ram: ttached to flexible conveor, it provides the power to push the AFC forward and to pull the powered support into its advanced position .Hydraulic flow lines: there supply the hydraulic fluid (an oil and water emulsion ) which operates the system .Control value :used by the 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 。3. to provide protection form waste flushing。5. to be selfadvancing。 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 introduction of mechanization