comparison of globoid and cylindrical shearer drums ... - .drums of a modern longwall shearer are

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  • The Journal of The South African Institute of Mining and Metallurgy VOLUME 106 REFEREED PAPER JANUARY 2006

    Introduction

    Recent improvements in longwall mining andtechnology have led to a significant increase inproduction speed and capacities up to40005000 tons/h and 45 milliontons/annum from a single face. Although thehigh production speed and capacities require acombined high performance of all longwallequipment, the shearer drum plays a key roleby cutting and loading the material onto thearmoured face conveyor (AFC). Although, thecutting action of shearer drums has beenimproved by increasing the motor power andusing enhanced drums equipped with heavy-duty picks and box, the loading action ofshearers is still a problem, particularly in thinseams.

    The loading action of shearer drums couldbe best compared with the short-length screwconveyor, as noted by previous researchers1,2.

    In this model, the screw conveyor has a largediameter shell and a relatively low height ofvein. The veins are terminated by a circularend plate (called as face ring) that has thesame overall diameter as the vanes. Thematerial is excavated by picks located on theface ring and vanes, then conveyed anddischarged onto the face conveyor with thehelp of veins. The face rings of the drumswhere 1225% of material is excavated in thevicinity, are formed with a 30 degree coneangle to enable easy conveyance of excavatedmaterial towards the face conveyor1. Thematerial conveyed between the vanes increaseslinearly from the face side to the back or to theconveyor side and reaches the maximum at thedischarge point of the drum. Since the amountof conveyed material reaches the maximum, inorder to protect the drum from excessive wear,some drum manufacturers weld special wearplates made of tungsten carbide to the sides ofthe vanes at the discharge point3.

    Previous researchers suggested that thevanes should be wrapped around the drumshell with a less than 360 and overlapped atleast 202,4. The higher wrap angle causesrecirculation of the excavated material insidethe drum aperture. In contrast, the small wrapangle prevents regular discharging of materialonto the AFC, increasing the number of vanesand material speed, consequently resulting inpoor loading efficiency5. The variables thateffect the loading efficiency of shearer drumsare vane angle, number and depth of vane,drum diameter and rotational speed, haulagespeed, seam thickness, face gradients, thedistance between drum and AFC and ancillaryloading device2,46.

    Extensive investigations were carried outon the loading performances of shearer drumsby the Mining Research and Development

    Comparison of globoid and cylindricalshearer drums loading performanceby M. Ayhan* and E.M. Eyyuboglu

    Synopsis

    Drums of a modern longwall shearer are manufactured to includevarious constructional features conveying extracted material ontothe face conveyor as efficiently as possible. Designing a drum with aconical shell or with reduced vane length, consequently with astepper vane angle, is the most widely employed method in anattempt to increase loading efficiency. This study compares loadingperformances of two such drums, one having a conical shell withmodified loading vanes, the other with a cylindrical shell withreduced vane length. Firstly, the loading performances of drums arepredicted and the maximum haulage rate attainable with the drumsare calculated. Then the performances of drum are compared bylong-term comprehensive underground trials with coal shearersunder similar conditions during the production operation of ParkTermik Cayirhan coalmine in Turkey. Although higher loadingperformance is predicted for cylindrical drums, the in situ trialspoint out that Globoid drums have a slightly higher loadingperformance than cylindrical drums. Furthermore, the relationshipbetween operational variables, i.e. extraction height, sumpingdepth, haulage rate and in situ loading performance, wereinvestigated statistically on the basis of data gathered during theunderground trials.

    Keywords: longwall mining, shearer drums, loadingperformance.

    * Mining Engineering Department, Dicle University,Turkey.

    Industrial Engineering Department, CankayaUniversity, Turkey.

    The South African Institute of Mining andMetallurgy, 2006. SA ISSN 0038223X/3.00 +0.00. Paper received May 2005; revised paperreceived Sep. 2005.

    Transaction

    Paper

    51

  • Comparison of globoid and cylindrical shearer drums loading performance

    Establishment of British Coal around 1980. A computerprogram was developed to predict loading performances ofdifferent drums that have various design properties in avariety of working conditions7. Recently, some firms havemanufactured shearer drums having different constructionalproperties in order to increase the loading performance. Oneof the most important designs is known as the Globoid drum.As a result of in situ comparison, it was reported that theperformance of the Globoid drum was better than thecylindrical one in terms of grain size, dust generation andhaulage rate8. However, the loading performances of drumswere not measured; it was observed visually that theperformance of the Globoid drum was better than thecylindrical drum. On the other hand, some companies havebeen manufacturing cylindrical shearer drums with reducedvane length in an attempt to improve loading performance ofshearer drums. Although these drums have been used widelyin longwall shearer machines, detailed investigations havenot yet been performed to compare the theoretical andpractical loading performance of drums.

    In this study, the loading performance of Globoid andcylindrical drums is predicted firstly, and then comparedunder the practical circumstances of use at Park Termik ASCayirhan Coal Mine in Turkey. Since the loading performanceof shearers is not satisfactory, a flitting run is necessarilyperformed after each cutting run, thus resulting in lostproduction and time, consequently decreasing productionvolume. Globoid and cylindrical drums designed in anattempt to increase the loading efficiency are compared undersimilar conditions. Furthermore, the effect of workingparameters on in situ loading performance at constantrotation speed was investigated statistically.

    Constructional specifications of the drums

    The Globoid drum is manufactured with several designfeatures in an effort to increase loading efficiency. The mostdistinctive feature of the drum is the conical shell shown inFigure 1. Due to the conical shell, the depth of vane beingminimal at the face side increases linearly across the cross-section of the drum, reaching maximum at the dischargepoint. Since the conveyance capacity of the drum is related tothe depth of the vein, it also increases across the cross-section. In practice, the amount of extracted material, hencethe conveyed material inside the drum aperture, increasesfrom the face side towards the discharge point. The Globoiddrum is designed with a conical shell in an attempt to satisfylarger volume requirements at the rear part of the drum.

    In addition to the drum shell, the vanes of the Globoiddrum are also formed in such a way as to increase theconveyance capacity towards the discharge point. The vanesof the drum are formed in a half elliptical shape at the goafside to increase the conveyance area, as shown in Figure 2.This arrangement enables a larger cross-sectional area atpoint B compared with point A; thus the conveyance capacityincreases towards the discharge point. Furthermore, thesurface of the drum aperture is shaped in a circular form inorder to decrease the friction between conveyed material andthe drum body, thus resulting in easy material flow.

    The second type of shearer drum has a cylindrical shell,as shown in Figure 3. The wrap angle of the drum is kept at200 in an effort to increase the loading performance. At alower wrap angle, the length of the vane decreases while thevane angle increases. With this arrangement, it is possible toraise the speed of the material inside the drum aperture.Hence, the drum is designed to take advantage of highmaterial speed to make the loading performance better. Thedrum has no additional design feature to improve loadingperformance other than the wrap angle.

    Comparison of drums loading performance

    The loading performance of drums is predicted and thencompared by long-term in situ underground tests.

    Prediction of drums loading performance

    The drum of a shearer can be thought of as a short-lengthscrew conveyor with a large diameter shell and vanes ofrelatively low height2. Loading efficiency depends on theconstructional properties of the drum and operationalparameters. The extraction and conveyance rate of a drum ismainly related to drum geometry, haulage rate and therotational speed of drum. The notations used for predictingloading performance of drums are presented in Figure 4.

    The loading performance of a drum can be calculated bythe equations given below.

    [1]

    [2]

    [3]

    [4]V SnQ W=

    I V VF F G= >/ 1

    V D - D VF L2

    T2

    Q= ( ) / 4

    V D TV SG W M FL=

    52 JANUARY 2006 VOLUME 106 REFEREED PAPER The Journal of The South African Institute of Mining and Metallurgy

    Figure 1Cross-section of globoid drum (all dimensions are in mm)

    Conical Shell

    Face Side

    Goaf Side

    Web

    950

    Min. Vane Depth

    Max. Vane Depth

    Cutting Diameter 1400

  • where;SFL : bulking factor of extracted material : fill factor of drum apertureIF : conveyance ratioS : pitch length of vane (m)In order to operate the drum at constant rotational speed,

    the conveyance rate must be greater than the extraction rate,i.e. IF = VF/VG>1. Otherwise the drum would become clogged.

    The optimum transverse speed of the

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