MINE MACHINARY ASSIGNMENT

MINE MACHINERY

BYABHISHEK MISHRA

BELT AND CHAIN DRIVING SYSTEMSBELT CONVEYORThe belt conveyor is basically an endless belt in a straight line stretched between two drums, one driving the system and the other acting as a return drum. The system of transport by belt conveyors consists of the following: BeltIdlersStructure of angle ironTension arrangementDrumsDrive headBELTBelt is an endless thick flat strip of woven cotton, rayon or nylon fabric laid up in piles or layers and their surfaces and sides covered with rubber, plastic or P.V.C. Belts having nylon fabric are strong as nylon offers very high resistance to longitudinal tearing and damage due to edge turn up. Cotton carcass is more susceptible to moisture and it rots on account of fungus formation in the presence of moisture.

Belts covered by a layer of P.V.C instead of rubber are fireproof and only such belts are to be used in underground mines. A belt conveyor with rubber coating is capable of working on a limiting gradient of 1 in 5 without any braking arrangement ;with thruster brake the limiting gradient is 1 in 3. The maximum angle of inclination for conveying coat on piled P.V.C. belting is 16 degrees.Belt speed varies from 45m/min to 150m/min 60m/min is preferred.Belt widths varies from 0.60 m for face conveyors to 1 m for trunk conveyors in underground coal mines but surface installations may have width as 1.2 m or even more at Nayvelli lignite mines . The maximum size is 1.5 m.The carrying capacity of troughed belt conveyor is given by T=abv where , T=carrying capacity(tonnes per sec) a=average cross sectional area of material(m2) b=the bulk density (te/m3) v=speed of conveyor belt(m/s) Care of Belt

Protect conveyor belt from direct sunlight during storage and keep it away from steam pipes or other places of heat.Use drive drums and delivery as well as tail end drums or adequate size so that sharp bending of the is avoidedIDLERSThe idler is a long pulley moving on its own axle and ball bearings and filled with grease.Idlers at the transfer points have to beat the impact of falling mineral and they are of special construction with thick corrugated rubber layer on their surface to take up the impact and provide cushioning.The direction of axles of the idlers, delivery-end drum and the tail-end drum should be at right right angles to the direction of belt travel, otherwise shifts of the centre line for part of its length and its troughing is upset resulting in spillage of the contents.

TENSION ARRANGEMENTSThe belt should be in proper tension . If it is loose or slack on the driving drum , the later will not be able to transmit the power to the belt.The tension end of the belt conveyor of a small length is the return drum mounted in a steel frame work to which hooks are fitted for tensioning by means of Sylvester prop withdrawer or by tensioning screws.The tension arrangement is provided near the drive head and it consists of weights placed on movable pulley or drum over which the belt passes.Very tight loop tension will cause excessive stresses in the loaded belt which is liable to break or damage joints and shorten the life of belt.DRIVE HEAD This consists of an electric motor or compressed air motor ,fluid coupling , gear coupling, gear wheels and a drum . The drum drives the belt by friction and snub pulleys are employed to increase the area of contact.CHAIN CONVEYORA scraper chain conveyor consists of stationary steel troughs each usually 2 m long ,connected together end to end and an endless chain with flights moving in troughs ,which are nearly 450mm wide at the top and 300mm at bottom. Each trough is slightly dished at one end so that the next one fits in to form a flush joint.Chain consists of links and after every 3-4 links a flight is provided so that the flights are 2-2.5 m apart.The return end of the conveyor ,with its totally enclosed sprocket-drum , is provided with a telescopic trough by which the tension of the chain can be adjusted through Sylvester chain.ADVANTAGES OF CHAIN CONVEYORIt is much stronger and can withstand more rough handling than the belt conveyorIt can be readily dismantled, moved forward, extended or shortened.DISADVANTAGES OF CHAIN CONVEYOR It is fairly high in cost and power consumptionIt has too many moving parts.It is noisy in operation and tends to increase the percentage of small coal.