煤矿英语-液压支架

9-1 Introduction

Modern longwall mining employs self-advancing hydraulic powered supports [1] (which will simply be called powered supports in this book) at the face area. The supports not only hold up the roof, push the face chain conveyor（AFC）, and advance themselves, but also provide a safe environment [2] for all associated mining activities. Therefore their successful selection and application are the prerequi

site for successful longwall mining. Furthermore, due to the large number of units required, the capital invested for the powered supports 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 supports are very important piece of equipment in a longwall face.

9-2 Classification of Powered Support

The application of modern powered supports can be traced back to the early 1950s. Since then, following their adoption in every part of the world, there have been countless models designed 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 components (i.e., canopy, caving shield, hydraulic legs or 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 a caving shield [3]—if a caving shield is included, the support is a “shield”type, otherwise i t is a frame or a chock; (2) number and type of arranging the hydraulic legs [4]—since support capacity is generally proportional to the 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 highest efficiency of application whereas an inclined installation between the base and the caving shield has the least efficiency in supporting the roof.

Based on this concept, there are four types of powered supports, those are, frame [5], chock [6], shield [7], and chock shield [8], in order of evolution of their development. However, it must be noted that the trend of their development in each type is such that it becomes less distinguishable in terms of application.

A. 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 [9] to hydraulic props or legs vertically in tandem that are connected at the top by a single or two segmented canopies [10]. The two-segmented canopies can be hinge-jointed [11] 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 the bottom of each leg or a solid base [12] connecting both legs. If the steel shoes are used, spring plates [13] connecting the legs are used to increase the stability.

Generally a frame support consists of two or three sets of hydraulic legs. The set that moves first is the secondary set; the set that moves later is the primary set. There is a double-acting ram [14]

installed between each set. The piston [15] of ram is connected to the secondary set and the cylinder [16] 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 set 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).

Thus the frame support is very simple, but more flexible or less stable structurally. There is a considerable uncovered space 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.

B. Chock

In a chock support, the canopy is a solid piece and the base may be either a solid piece or two separate parts connected by steel bars [17] 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 set up is also used in the shield and chock shield.

Again, all hydraulic legs are installed vertically between the base and the canopy [18]. The number of legs ranges from three to six, but the four-leg chock is by far the most popular one. The six-leg chock is designed for thin seams with two legs in the front and four legs in the rear, separated by a walkway. For the six-leg chock, the canopy is generally hinge-jointed above the walkway [19]. Most chocks are also equipped with a gob window [20] 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 [21], it is reinforced mostly with a box-shaped steel frame [22] between the base and each leg. A leg-restoring device [23] is installed around each leg at the top of the box-shaped steel frame.

The chock is suitable for medium to hard roof. When the roof over hangs well into the gob and requires induced caving [24], the chock can provide access to the gob [25].

C. Shield

Shield, a new entry in the early seventies, is characterized by the addition of a caving shield at the rear end between the base and the canopy. The caving shield, which in general is inclined, is hinge-jointed to the canopy and the base making the shield a kinematically stable support [26], a major advantage over the frame and the chock. It also completely seals off the gob [27] and prevents rock debris [28] from getting into the face side of the support. Thus the shield-supported face is generally clean.

The hydraulic legs in the shield 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 the hydraulic leg pressure is available for supporting the roof, the actual loading capacity [29] 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 [30] to be developed for all kinds of shields. The types of motional traces [31] of the canopy tip, leg positions and orientations [32], number of legs, canopy geometry [33], and other optional designs and devices can be clearly specified by the terminology.

D. Chock Shield

The chock shield combines the features of the chock and the shield. 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 is regular four-or six leg chock shield 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 [34]. It is suitable for hard roof.

9-3 Common Elements of Powered Supports

The modern powered supports, regardless of the type, consist of the following common components:

Load-bearing unit [35]. These include the hydraulic legs,

canopy, base plate, caving shield, lemniscate bars [36], and joint pins.

Hydraulic rams. These include hydraulic rams for (a) pushing

the chain conveyor and advancing the powered supports, (b) operating the front canopy or face guards [37], (c) balancing or limiting the position of the canopy, and (d) operating other auxiliary equipment such as leg recovering devices [38] and side shields [39].

Control and operating unit [40]. These include internal control

valves such as check and yield valves [41] in the hydraulic legs, unit control valves [42], and high pressure hydraulic tubings [43].

D. Auxiliary devices. These include leg recovering, gob windows, face guards, base-lifting [44], lighting [45], and so on.

E. Hydraulic fluid [46]. This is the emulsion [47] for operating the powered supports. Most popular hydraulic fluid is the water emulsion with 5% oil and 95% water.

9-4 Setting Load [48] and Yield Load [49]

During setting the support, the control valve is firstly turned to “setting” position, which allows the pressurized fluid [50] to enter into the front chamber of the leg piston. As the pressurized fluid continues to flow, the leg continues to rise until the canopy touches the roof. After that, the pressurized fluid in the front chamber of the piston rapidly increases to the working pressure of the hydraulic pump [51]. At that time, the control valve is turned off and the fluid is locked in [52]. The fluid is now operating at the working pressure of the pump. This is the setting pressure of the support. The force exerted by each leg under setting pressure is called setting load.

After setting, when the roof converges, the fluid pressure in the piston chamber will be increased. As the roof convergence [53] increases further, so does the fluid pressure in the piston chamber. To protect the hydraulic cylinder and piston from damage, a maximum allowable pressure [54], called yield pressure, is preset [55] for each support. This is usually provided by installation of a yield valve. When the fluid pressure in the piston chamber exceeds the yield pressure, the yield valve opens and fluid leaks out [56], which causes the fluid pressure in the piston chamber to drop rapidly below the yield pressure. This process repeats again and again if the roof continues to converge. The force exerted by each leg under yield pressure is called yield load.

9-5 Hydraulic Control Systems

High-pressure hydraulic fluid is used in each support to raise and lower the legs, advance the support, push the conveyor forward, set extension canopy and ¤ or face guard (sprag) [57]. Leg raising and lowering and support advance generally follow each other in order to advance and reset the support. But the other functions could be performed either before or after or simultaneously [58] with the support advance and reset. All of these functions are performed by the unit control valves. Depending on the designs of the control valves, there are various types of control systems. The types of hydraulic control systems are as follows:

Unit manual control [59].

Simple adjacent control [60].

Bi-directional adjacent control [61].

Batch or bank control [62].

Sequential control [63].

Electrohydraulic on-face control [64].

Electrohydraulic on-entry remote control [65].

NOTES TO THE TEXT

[1] self-advancing hydraulic powered supports：自移式液压支架

[2] safe environment：安全的环境

[3] caving shield：掩护梁

4] hydraulic legs：液压柱腿

[5] frame：节式液压支架

[6] chock：垛式液压支架

[7] shield：掩护式液压支架

[8] chock shield：支撑掩护式液压支架

[9] setting up：固定，调定

[10] segmented canopies：分割的顶梁

[11] hinge-jointed：铰链连接的

[12] solid base：整体式底座

[13] spring plates：弹簧钢板

[14] double-acting ram：双作用千斤顶

[15] piston：活塞

[16] cylinder：液压缸

[17] steel bars：钢条，钢棒

[18] canopy：顶梁

[19] walkway：人行道

[20] gob window：挡矸帘

[21] longitudinal stability：纵向的稳定性

[22] box-shaped steel frame：箱形钢架

[23] leg-restoring device：柱腿复位装置

[24] induced caving：人工放顶

[25] access to the gob：采空区通路

[26] kinematically stable support：运动学稳定的支架

[27] seals off the gob：封闭采空区

[28] rock debris:碎石堆

[29] loading capacity：承载能力

[30] terminology：术语，专门名词

[31] motional traces：运动轨迹

[32] orientations：定向，方位

[33] canopy geometry：顶梁的几何形状

[34] supporting efficiency：支护效率

[35] Load-bearing unit:承载部件

[36] lemniscate bars：双纽线联杆，四联杆

[37] face guards：工作面护壁装置

[38] leg recovering devices：柱腿复位装置

[39] side shields：侧防护板（掩护支架）

[40] control and operating unit：控制和操纵部件

[41] check and yield valves：单向阀和屈服阀

[42] unit control valves：液压支架控制阀

[43] high pressure hydraulic tubings：高压液压管

[44] base-lifting：底座升起装置

[45] lighting：照明

[46] hydraulic fluid：液压液

[47] emulsion：乳化液

[48] Setting load：初载荷，初撑力

[49] yield load：屈服载荷，工作阻力

[50] pressurized fluid：压力液

[51] hydraulic pump：液压泵

[52] locked in：被锁在里面

[53] roof convergence：顶板移近，顶板下沉

[54] maximum allowable pressure：最大容许压力

[55] preset：预先设定

[56] fluid leaks out：液体泄出

[57] sprag (face guard)：护壁装置

[58] simultaneous：同时发生的

[59] unit manual control本架手工控制

[60] simple adjacent control：简单邻架控制

[61] bi-directional adjacent control：双向邻架控制

[62] batch or bank control：分组或分段控制

[63] sequential control：顺序控制

[64] electrohydraulic on-face control：在工作面的电液控制

[65] electrohydraulic on-entry remote control：在区段平巷的电液遥控