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英文原文
Self-advancing hydraulic powered support
Modern 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 1950’s. 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.
FRAME
The 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.
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 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.
SHIELD
Shields, 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 SHIELD
The 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.
中文譯文
自移式液壓支架
現(xiàn)代長壁工作面采煤已經(jīng)在開采區(qū)使用液壓支架。液壓支架不僅支撐頂板，推動(dòng)刮板輸送機(jī)工作面和自移式支架本身，而且還為相關(guān)的采煤設(shè)備提供一個(gè)安全的工作環(huán)境。因此正確的選擇和應(yīng)用液壓支架是長壁工作面采煤成功的先決條件。此外，由于對液壓支架需求數(shù)量很大，對液壓支架的投資經(jīng)常要占到長壁采煤工作面初始投資的一半以上。因此，從技術(shù)和經(jīng)濟(jì)兩方面的觀點(diǎn)看，液壓支架是長壁采煤工作面設(shè)備中十分重要的一部分。
現(xiàn)代液壓支架的應(yīng)用可以追溯到上個(gè)世紀(jì)50年代早期。從那時(shí)開始，隨著液壓支架在全世界各個(gè)領(lǐng)域的使用，各個(gè)國家都設(shè)計(jì)和制造了無數(shù)的液壓支架。但是，到現(xiàn)在始終沒有一個(gè)統(tǒng)一的分類系統(tǒng)。
這里使用一個(gè)簡化的液壓支架的分類。由于液壓支架由四個(gè)主要部分組成(即頂梁，掩護(hù)梁，液壓支柱和底座)，因此根據(jù)這些結(jié)構(gòu)的相互關(guān)系給液壓支架分類。在其中，有兩個(gè)因素是最重要的：(1) 是否使用掩護(hù)梁—如果使用了掩護(hù)梁，那么液壓支架屬于掩護(hù)式液壓支架，否則，支架就屬于節(jié)式支架或者垛式支架。（2）液壓支架所使用立柱的數(shù)量與類型— 由于液壓支架的支護(hù)能力一般與液壓立柱的數(shù)目成正比，所以確定液壓支架立柱的數(shù)目是很重要的。另外，液壓支柱的安裝方式也很重要，例如，立柱垂直安裝在底座和有掩護(hù)梁的頂梁之間，此時(shí)對頂板具有最小的支護(hù)效率。
基于這個(gè)概念，按照液壓支架發(fā)展進(jìn)化的順序，把液壓支架分為四類，即：節(jié)式支架，垛式支架，掩護(hù)式支架和支撐掩護(hù)式支架。然而，必須指出的是，每一種支架的發(fā)展趨勢在應(yīng)用方面的區(qū)別在逐漸變小。
這四種類型的液壓支架不僅可以用于后退式長壁回采工作面和前進(jìn)式開采工作面，還可以用于標(biāo)準(zhǔn)方式、滯后支護(hù)方式和即時(shí)支護(hù)方式。
對于標(biāo)準(zhǔn)支護(hù)方式，采煤機(jī)作切割或分段運(yùn)動(dòng)，工作面輸送機(jī)由裝在液壓支架上的推移千斤頂推動(dòng)前進(jìn)。液壓支架比輸送機(jī)先移動(dòng)。對于滯后式支護(hù)方式，支架不可能靠近輸送機(jī)，因?yàn)橛幸粋€(gè)裝置自動(dòng)的使支架前端與輸送機(jī)保持一定的距離。這就要求要有貫穿工作面的緩溝，并且采用前進(jìn)式標(biāo)準(zhǔn)支護(hù)，比如：先推動(dòng)刮板輸送機(jī)，然后再讓液壓支架前進(jìn)。
對于即時(shí)支護(hù)方式，液壓支架在截煤機(jī)過去之后立即跟隨刮板輸送機(jī)前進(jìn)，液壓支架前面的頂板有足夠的長度來支護(hù)采過和將要采的頂板部分。在液壓支架前進(jìn)以后，刮板輸送機(jī)也被推移前進(jìn)。
節(jié)式支架
節(jié)式液壓支架是一種擴(kuò)展單體液壓支柱的常規(guī)使用的支架。它是現(xiàn)代自推進(jìn)式液壓支架發(fā)展的第一個(gè)類型。它包括一前一后垂直安裝的支柱，支柱連接在單一或分割的頂梁的頂端。兩塊分割的頂梁可以鉸接在兩立柱之間或在前立柱之前的任意點(diǎn)。兩根液壓支柱的底部是焊接在每個(gè)支柱末端的一只金屬環(huán)形底靴或者固體底座連接兩根支柱。
一般來說，節(jié)式液壓支架由兩套或三套液壓立柱組成。先移動(dòng)的是次要裝置，后移動(dòng)的是主要裝置。每根支柱之間有雙作用液壓缸。液壓缸的活塞連接到次要之柱上，缸底連接到主要支柱上。支架前進(jìn)過程中，當(dāng)次要支柱降低并通過活塞推動(dòng)向前移動(dòng)時(shí)，主要支柱使頂梁平衡。當(dāng)?shù)竭_(dá)新位置以后，次要支柱支撐頂板，主要支柱降低并且由缸筒拉動(dòng)前進(jìn)。每次移動(dòng)的前進(jìn)距離為20到30英尺。（即0.5到0.91米）。
節(jié)式液壓支架結(jié)構(gòu)很簡單，但是在結(jié)構(gòu)上柔韌性過強(qiáng)而缺少穩(wěn)定性。兩塊頂板下有相當(dāng)大的未覆蓋區(qū)域，這段區(qū)域允許碎石落入。因此，節(jié)式液壓支架不適合較弱頂板。由于缺少穩(wěn)定性和需要頻繁維護(hù)，節(jié)式液壓支架現(xiàn)在已經(jīng)很少使用。
垛式液壓支架
在垛式液壓支架中，頂梁是一個(gè)堅(jiān)固的整體結(jié)構(gòu)，而底座則可能是堅(jiān)固的整體結(jié)構(gòu)或者兩個(gè)獨(dú)立的部分，它們用金屬桿在其前端或尾部連接起來。在這兩種情況下，兩垛式支架之間將有一個(gè)很大的空間，并在其中部安裝雙作用立柱，這種立柱將把刮板輸送機(jī)和垛式液壓支架作為一個(gè)整體進(jìn)行推移，這就是垛式液壓支架與節(jié)式液壓支架的不同。這種方式同樣應(yīng)用于掩護(hù)式液壓支架和支撐掩護(hù)式液壓支架當(dāng)中。
和節(jié)式液壓支架一樣，所有的液壓立柱垂直安裝在底座和頂板之間。立柱的數(shù)目在3到6之間，但4柱支架目前應(yīng)用最多。六柱式垛式支架是為薄煤層設(shè)計(jì)的，兩個(gè)支柱在前，四個(gè)在后，中間是人行走的通道。對于六柱式支架，頂梁在通道的上方鉸接。大多數(shù)垛式支架在其頂梁末端都裝有擋矸簾。擋矸簾由一些矩形的金屬片組成，這些金屬片的兩端水平連接。
在大多數(shù)垛式支架中，液壓支柱與頂梁和液壓支柱與底座之間都采用鉸接式連接。但是為了增加支架的縱向穩(wěn)定性，通常在底座與各支柱之間安裝箱形金屬框用來加強(qiáng)穩(wěn)定性。在金屬框上方的立柱周圍安裝復(fù)位裝置。
垛式液壓支架適用于各種堅(jiān)硬頂板。當(dāng)部分頂板已經(jīng)完全懸掛在采空區(qū)時(shí)，需要引導(dǎo)其塌落，這時(shí)垛式液壓支架就可以提供一條通向采空區(qū)的通道。
掩護(hù)式液壓支架
掩護(hù)式液壓支架是在七十年代新出現(xiàn)的一種液壓支架，它的特點(diǎn)是在底座和頂梁尾端增加了掩護(hù)梁。掩護(hù)梁一般是傾斜的，鉸接在頂梁和底座之間，從運(yùn)動(dòng)學(xué)上說，它是穩(wěn)定的，這也是掩護(hù)式支架優(yōu)于節(jié)式支架和多式支架的一個(gè)主要方面。掩護(hù)式支架可以完全封鎖采空區(qū)，防止巖石碎片落入支架的工作面。因此，掩護(hù)式液壓支架的工作面一般都比較清潔。
掩護(hù)式液壓支架的立柱一般都是傾斜的，這樣可以為運(yùn)輸提供更多的空間。由于頂板、掩護(hù)梁和底座是相互連接的，所以掩護(hù)式液壓支架可以更好的抵抗橫向力，而不需要使立柱彎曲。這樣，與節(jié)式支架和垛式支架固定約束不同，掩護(hù)式液壓支架中支柱與頂梁和支柱與底座之間是通過銷軸連接的，使液壓支柱的傾斜角度隨著采煤高度的不同而變化成為可能。由于只有液壓立柱的垂直分量起支護(hù)頂板的作用，掩護(hù)式液壓支架的承載能力隨著采煤高度的變化而變化。
掩護(hù)是液壓支架有很多種類。在下面的介紹中，有六項(xiàng)可以用來給掩護(hù)是液壓支架分類，這六項(xiàng)可實(shí)現(xiàn)所有類型掩護(hù)式液壓支架統(tǒng)一術(shù)語的發(fā)展。頂梁端部的運(yùn)動(dòng)軌跡，液壓立柱的定位于定向，液壓立柱的數(shù)目，頂梁的幾何形狀，以及其他的可以任意選擇的設(shè)計(jì)方法和理念都可以用專業(yè)術(shù)語詳細(xì)的說明。
頂梁端部的運(yùn)動(dòng)軌跡的形式
這是公認(rèn)的最普遍的對掩護(hù)是液壓支架的分類方法?；谶@種標(biāo)準(zhǔn)，掩護(hù)是液壓支架可以分為三種類型：雙紐線形，圓弧形和橢圓形。
雙紐線形：這是最常用的一種類型。掩護(hù)梁和底座通過含有四個(gè)鉸鏈的雙紐線形運(yùn)動(dòng)的連桿連接起來。隨著掩護(hù)式液壓支架立柱的升起和下降，選擇好雙紐線桿的尺寸，就可以使頂梁前端近乎垂直的作上升和下降運(yùn)動(dòng)，這樣就可以保持頂梁前端與煤壁之間未支撐的距離為一常量，這種特性對很好控制頂板來說是廣泛考慮的最合乎要求的。當(dāng)采煤高度有明顯限制時(shí)，頂梁前端垂直運(yùn)動(dòng)。頂梁、掩護(hù)梁、雙扭線桿和底座的尺寸及位置的布置都嚴(yán)格約束了這種限制。如超出這個(gè)限制，頂梁前端將會(huì)迅速的遠(yuǎn)離采煤線，從而產(chǎn)生一個(gè)很大的未支護(hù)面積。
圓弧形：在圓弧形掩護(hù)式液壓支架中，掩護(hù)梁和底座之間通過單一的鉸接連接。當(dāng)液壓支架立柱升起時(shí)，頂梁的前端將按圓弧型軌跡遠(yuǎn)離煤壁，這樣使未支護(hù)面積增大。這就是大多數(shù)用戶所考慮的，圓弧型式掩護(hù)式液壓支架最不合適的地方。但在實(shí)際應(yīng)用中，如果煤層厚度變化幅度較小，則頂梁、掩護(hù)梁和底座的尺寸及位置可以按這種形式設(shè)計(jì)，未支護(hù)面積處的縱向距離變得不重要。另外，當(dāng)降低液壓支柱時(shí)，未支護(hù)面積將會(huì)減少。
橢圓形：在橢圓形掩護(hù)式液壓支架中，掩護(hù)梁和底座采用這種方式連接，當(dāng)液壓支架的立柱作上升和下降運(yùn)動(dòng)時(shí)，支架頂板的前端沿橢圓形軌跡運(yùn)動(dòng)。這種形式的液壓支架現(xiàn)在已經(jīng)很少應(yīng)用了。
支撐掩護(hù)式液壓支架
支撐掩護(hù)式液壓支架結(jié)合了垛式液壓支架和掩護(hù)式液壓支架的特點(diǎn)。所以，支撐掩護(hù)式液壓支架具有以上兩者所具有的優(yōu)點(diǎn)。
如果所有的四根或六根液壓立柱都安裝在頂梁和底座之間，則稱這種支架為支撐掩護(hù)式液壓支架。常規(guī)的四柱或六柱支撐掩護(hù)式液壓支架所有的立柱都是垂直安裝、互相平行的。另外還有V型和X型的安裝形式。有些頂梁是一個(gè)整體，而有些頂梁則是由通過鉸接并在鉸接處安裝一液壓千斤頂?shù)膬刹糠纸M成的。支撐掩護(hù)式液壓支架具有最高的支護(hù)效率，因此適用于堅(jiān)硬頂板。