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英文原文Self-advancing hydraulic powered supportModern longwall mining employs hydraulic powered supports at the face area. The supports not only holds up the roof, pushes the face chain conveyor, 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 long wall face.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.A simplified classification is used in this section. Since a powered support consists of four major components(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: (1) presence or absence of caving shield- if a caving shield is included, the support is a “shield” type, otherwise, a frame or a chock; (2) number and type of arranging the hydraulic legs- since support capacity is generally proportional to number of hydraulic legs, it is important to specify the number of hydraulic legs that a support has. Furthermore, the way the hydraulic legs are installed is important; for example, a vertical installation between the base and the canopy has the caving shield has the least efficiency in supporting the roof.Based on this concept, there are four types of powered support, that is, the frame, chock, shield and chock shield, in order of evolution of their development. However, it must be noted that the trend of development in each type is such that it becomes less distinguishable in terms of application.The four types of roof supports can be obtained for either longwall retreating or advancing systems, and they are available in standard, one-web-back, and immediate forward support (IFS) versions.With the standard system, the wining machine takes a cut or a slice, and the armored face conveyor is pushed over by the hydraulic rams that are fixed to the support units. The support units then are advanced sequentially to the conveyor. With the one-web-back system, a support is set back from the conveyor by a device that automatically keeps the leading edge of the support at a fix distance from the conveyor. 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.FRAMEThe frame support is an extension of the single hydraulic props conventionally used underground. Thus it is the first type developed in modern self-advancing 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 hinge-jointed 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 double-acting 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.(0.50 0.91m)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 become seldom used because they are less stable and require frequent maintenance.CHOCKIn 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 double-acting 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 four-leg chocks are by far the most popular ones. The six-leg chocks are designed for thin seams with two legs in the front and four legs in the rear, separated by a walkway. For the six-leg chocks, the canopy is generally hinge-jointed 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 box-shaped steel frame between the base and each leg. A leg restoring device is installed around each leg at the top of the box-shaped 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.SHIELDShields, 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 hinge-jointed to the canopy and the base making the shield a kinematically stable support, a major advantage over the frames and the chocks. It also completely seals off the gob and prevents rock debris from getting into the face side of the support. Thus the shield-supported face is generally clean.The hydraulic legs in the shields are generally inclined to provide more open space for traffic. Because the canopy, caving shield, and base are interconnected, it can well resist the horizontal force without bending the legs. Thus, unlike the solid constraint in the frame/ chock supports, the pin connections between the legs and the canopy, and between the legs and the base in a shield support make it possible that the angle of inclination of the hydraulic legs varies with the mining heights. Since only the vertical component of hydraulic leg pressure is available for supporting the roof, the actual loading capacity of the shield also varies with the mining heights.There are many variations of the shield supports. In the following, six items are used to classify the shields, which enables a unified terminology to be developed for all kinds of shields. The types of motional traces of the canopy tip, leg positions and orientation, number of legs, canopy geometry, and other optional designs and devices can be clearly specified by the terminology .TYPES OF MOTIONAL TRACES FOR THE LEADING EDGE OF THE CANOPY.This is the most commonly recognized way of classifying the shield. Based on this criterion, there are three types, lemniscate, caliper , and ellipse.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 leading 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 face-line creating a large unsupported area.Caliper. In a caliper shield, the caving 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 arc 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. 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 combines the features of the chocks and the shields. As such it possesses the advantages of both.If all of the four or six legs are installed between the canopy and the base, it is called a chock shield. There are regular four or six-leg chock shields in which all legs are vertical and parallel. Others form 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.中文译文自移式液压支架现代长壁工作面采煤已经在开采区使用液压支架。液压支架不仅支撑顶板，推动刮板输送机工作面和自移式支架本身，而且还为相关的采煤设备提供一个安全的工作环境。因此正确的选择和应用液压支架是长壁工作面采煤成功的先决条件。此外，由于对液压支架需求数量很大，对液压支架的投资经常要占到长壁采煤工作面初始投资的一半以上。因此，从技术和经济两方面的观点看，液压支架是长壁采煤工作面设备中十分重要的一部分。现代液压支架的应用可以追溯到上个世纪50年代早期。从那时开始，随着液压支架在全世界各个领域的使用，各个国家都设计和制造了无数的液压支架。但是，到现在始终没有一个统一的分类系统。这里使用一个简化的液压支架的分类。由于液压支架由四个主要部分组成(即顶梁，掩护梁，液压支柱和底座)，因此根据这些结构的相互关系给液压支架分类。在其中，有两个因素是最重要的：(1) 是否使用掩护梁如果使用了掩护梁，那么液压支架属于掩护式液压支架，否则，支架就属于节式支架或者垛式支架。（2）液压支架所使用立柱的数量与类型由于液压支架的支护能力一般与液压立柱的数目成正比，所以确定液压支架立柱的数目是很重要的。另外，液压支柱的安装方式也很重要，例如，立柱垂直安装在底座和有掩护梁的顶梁之间，此时对顶板具有最小的支护效率。基于这个概念，按照液压支架发展进化的顺序，把液压支架分为四类，即：节式支架，垛式支架，掩护式支架和支撑掩护式支架。然而，必须指出的是，每一种支架的发展趋势在应用方面的区别在逐渐变小。这四种类型的液压支架不仅可以用于后退式长壁回采工作面和前进式开采工作面，还可以用于标准方式、滞后支护方式和即时支护方式。对于标准支护方式，采煤机作切割或分段运动，工作面输送机由装在液压支架上的推移千斤顶推动前进。液压支架比输送机先移动。对于滞后式支护方式，支架不可能靠近输送机，因为有一个装置自动的使支架前端与输送机保持一定的距离。这就要求要有贯穿工作面的缓沟，并且采用前进式标准支护，比如：先推动刮板输送机，然后再让液压支架前进。对于即时支护方式，液压支架在截煤机过去之后立即跟随刮板输送机前进，液压支架前面的顶板有足够的长度来支护采过和将要采的顶板部分。在液压支架前进以后，刮板输送机也被推移前进。节式支架节式液压支架是一种扩展单体液压支柱的常规使用的支架。它是现代自推进式液压支架发展的第一个类型。它包括一前一后垂直安装的支柱，支柱连接在单一或分割的顶梁的顶端。两块分割的顶梁可以铰接在两立柱之间或在前立柱之前的任意点。两根液压支柱的底部是焊接在每个支柱末端的一只金属环形底靴或者固体底座连接两根支柱。一般来说，节式液压支架由两套或三套液压立柱组成。先移动的是次要装置，后移动的是主要装置。每根支柱之间有双作用液压缸。液压缸的活塞连接到次要之柱上，缸底连接到主要支柱上。支架前进过程中，当次要支柱降低并通过活塞推动向前移动时，主要支柱使顶梁平衡。当到达新位置以后，次要支柱支撑顶板，主要支柱降低并且由缸筒拉动前进。每次移动的前进距离为20到30英尺。（即0.5到0.91米）。节式液压支架结构很简单，但是在结构上柔韧性过强而缺少稳定性。两块顶板下有相当大的未覆盖区域，这段区域允许碎石落入。因此，节式液压支架不适合较弱顶板。由于缺少稳定性和需要频繁维护，节式液压支架现在已经很少使用。垛式液压支架在垛式液压支架中，顶梁是一个坚固的整体结构，而底座则可能是坚固的整体结构或者两个独立的部分，它们用金属杆在其前端或尾部连接起来。在这两种情况下，两垛式支架之间将有一个很大的空间，并在其中部安装双作用立柱，这种立柱将把刮板输送机和垛式液压支架作为一个整体进行推移，这就是垛式液压支架与节式液压支架的不同。这种方式同样应用于掩护式液压支架和支撑掩护式液压支架当中。和节式液压支架一样，所有的液压立柱垂直安装在底座和顶板之间。立柱的数目在3到6之间，但4柱支架目前应用最多。六柱式垛式支架是为薄煤层设计的，两个支柱在前，四个在后，中间是人行走的通道。对于六柱式支架，顶梁在通道的上方铰接。大多数垛式支架在其顶梁末端都装有挡矸帘。挡矸帘由一些矩形的金属片组成，这些金属片的两端水平连接。在大多数垛式支架中，液压支柱与顶梁和液压支柱与底座之间都采用铰接式连接。但是为了增加支架的纵向稳定性，通常在底座与各支柱之间安装箱形金属框用来加强稳定性。在金属框上方的立柱周围安装复位装置。垛式液压支架适用于各种坚硬顶板。当部分顶板已经完全悬
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