外文翻譯--液壓支架-液壓系統(tǒng)-全文預(yù)覽
【正文】 whose position is held unchanged by the advancing rams, forces of the supports that are set on both sides of the support to be advanced. As soon as the support has been advanced to the designed position, the support is immediately reset against the roof. Finally, the advancing ram of the support in question is extended to push the conveyor forward and bees ready for the next cut. The sequential steps described are for the advance of an individual support in the direction perpendicular to the along the faceline direction, the conveyor cannot be advanced in a sharp step immediately after the shearer has passed it, due to the rigidity of the panline. Thus the fourth step is usually sometime after the shearer,s pass, resulting in a curved or snaked section. During panel development the panel entries are roof bolted as usual. But in the tailentry one or two rows of cribs are erected to supplement the roof bolting. During retreating mining, the roof at the headentry Tjunction area (up to 500 ft (152m) outby the face) is generally reinforced with supports of some type to increase support density to cope with the moving front and side abutment pressures. Modern longwall mining employs hydraulic powered supports at the face area. The supports not only holds up the roof, pushes the face chain conveyor(AFC), and advances itself, but also provides a safe environment for all associated mining activities. Therefore its successful selection and application are the prerequisite for successful longwall mining. Furthermore, due to the large number of units required, the capital invested for the power support usually accounts for more than half of the initial capital for a longwall face. Therefore both from technical and economic points of view, the powered support is a very important piece of equipment in a longwall face. Classification of powered supports The application of modern powered supports can be traced back to early 1950s. Since then, following its adoption in every part of the world, there have been countless models design and manufactured in various countries. But unfortunately, there still is no uniform system of classification. In this section a simplified classification is used. Since a powered support consists of four major ponents (i. e , canopy, caving shield, hydraulic legs and props, and base plate), the ways by which they are interrelated are used for classification. In this respect, two factors are most important: (a) presence or absence of caving shield if a caving shield is included, the support is a “shield” type, otherwise, a frame or a chock。他們在立即前移支護系統(tǒng)里通常從事以下幾步工作，為了盡可能快地支撐新暴露空間。支架一推進到設(shè)計的位置，支架就立即重新靠在頂板上。因此第四步通常是在采煤機通過之后的一段時間，導(dǎo)致了彎曲或矩形的方向。 現(xiàn)代長壁采煤工作 面使用自移式液壓支架（這種支架在這本書中通常被稱為液壓支架）。因而從技術(shù)和經(jīng)濟兩方面觀點看，液壓支架是長壁工作面非常重要的設(shè)備。 在這一段一個簡化的分類被使用。此外，立柱被安裝的方式是重要的；例 如，在支護頂板方面，在頂梁和底座之間垂直的安裝立柱有最高的應(yīng)用效率然而在底座和掩護梁之間傾斜的安裝立柱卻有著最低的效梁。 對于標(biāo)準(zhǔn)支護方式，采煤機作切割或分段運動，工作面輸送機由裝在液壓支架上的推移千斤頂推動 前進。 對于即時支護方式，液壓支架在截煤機過去之后立即跟隨刮板輸送機前進，液壓支架前面的頂板有足夠的長度來支護采過和將要采的頂板部分。它包含兩排串列的液壓支柱，在頂部由單個或兩個扇形頂梁所連接。 通常節(jié)式支架包含兩排或三排立柱。在支架推移期間，主要立柱支撐頂板而輔助立柱是低的并 且通過活塞向前推。在兩塊頂梁之間有相當(dāng)大的地方，不允許破落的頂板石塊落在那里。在這兩種情況里，一塊大的空地方是在中心的左邊，為了 定位雙作用液壓缸，用來在整個機構(gòu)里推拉刮板輸送機和垛式支架。六柱垛式支架的前面兩個立柱和后面四個立柱都設(shè)計的有細(xì)小縫隙，被一個通道分開。但是為了增加縱向的穩(wěn)定性，在底座和每個 立柱之間用一個箱形的鐵架來進行加固。 掩護式支架 掩護式支架，十七世紀(jì)早期的一種新的發(fā)明，以在后部，底座和頂梁之間增加一個掩護梁為特征。 掩護式支架的立柱通常是傾 斜的，可以為交通提供更多的窨。 掩護是液壓支架有很多種類?；谶@種標(biāo)準(zhǔn)，掩護是液壓支架可以分為三種類型：雙紐線形，圓弧形和橢圓形。當(dāng)采煤高度有明顯限制時，頂梁前端垂直運動。當(dāng)液壓支架立柱升起時，頂梁的前端將按圓弧型軌跡遠(yuǎn)離煤壁，這樣使未支護面積增大。 橢圓形：在橢圓形掩
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