文献翻译自移式液压支架Word格式文档下载.docx

1、Self-Advancing Hydraulic Powered SupportsModern 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 activities . Therefore

2、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 . Therefore both from t

3、echnical 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 countless models d

4、esigned 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 props , and base

5、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） number and type of

6、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 vertical installation b

7、etween 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 , chock , shield , a

8、nd 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 syste

9、ms , 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 . The support units

10、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 employs the standard method

11、 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 the recently and newly

12、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 set

13、ting 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 we

14、lded 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 installed between each set . Th

15、e 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 , the secondary set is set a

16、gainst 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 supporta-primary set b-secondary setA B CFig . 8.9 Method of advancing the frame supportThe frame support is very simple , but more

17、 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

18、frequent maintenance .CHOCKIn 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

19、 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 walkwais also used in the shields and chock shie

20、lds .Again , all hydraulic legs are installed vertically between the base and the canopy （Fig. 8. 10） . 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 y （Fig. 8.10c） . For the six-leg chocks , the canopy is generally hi

21、nge-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.A B CFig . 8.10 Schematics of various chock supportIn most chock supports , there are

22、 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 t

23、he 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

24、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 roc

25、k 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 hor

26、izontal 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 m

27、ining 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 shi

28、elds , 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 MOTIO

29、NAL 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 （Fig. 8. 11） .A . Lemniscate.L B . Caliper.C C . Ellipse.EFig . 8.11 Three types of motional traces

30、for leading edge of the shield canopyA . 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

31、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 heigh

32、t 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 .B . 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 consider