1、中文 3258 字 英文原文 Self-Advancing Hydraulic Powered Supports Modern longwall mining employs hydraulic powered supports at the face area . The support not only holds up the roof , pushes the face chain conveyor , and advances itself , but also provides a safe environment for all associated mining activit
2、ies . 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 powered support usually accounts for more than half of the initial capital for a longwall face . There
3、fore both from technical and economic points of view , the powered support is a very important piece of equipment in a longwall face . The application of modern powered supports can be traced back to the early 1950s . Since then , following its adoption in every part of the world , there have been c
4、ountless models designed 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 or
5、 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 - if a caving shield is included , the support is a “ shield ” type , otherwise , a frame or a chock ； (2) n
6、umber and type of arranging the hydraulic legs - 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 verti
7、cal 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 support , that is , the frame ,
8、 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 retreatin
9、g or advancing systems , and they are available in standard , one-web-back , and immediate forward support ( IFS ) versions . With the standard system , the winning 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
10、 . 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 fixed distance from the conveyor .This allows easy access through the face and employ
11、s the standard method of advancing ； i. e. , pushing the conveyor first , and then advancing the support . With the IFS system , the support unit is advanced to the conveyor immediately after the cutting machine has passed , and the forward canopy of the support unit is long enough to support both t
12、he 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 s
13、upports .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
14、a circular steel shoe welded at bottom of each leg or a solid base connecting both legs (Fig . 8.8) . 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 instal
15、led between each set . The piston of the ram is connected to the secondary set and the cylinder to the primary set . During support advance ( Fig. 8. 9) , 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 , t
16、he 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. (0.500.91m) . Fig . 8.8 Frame support a-primary set b-secondary set A B C Fig . 8.9 Method of advancing the frame support The frame sup
17、port 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 the
18、y 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 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 designed for thin seams with two legs in the front and four legs in the rear , separated by a
