Shovel PDF - L13 | 6/9/2023

L13: Shovels 6/9/2023 Shovel Course Instructor Dr. Sunit...

L13: Shovels 6/9/2023 Shovel Course Instructor Dr. Sunita Mishra Assistant Professor Department of Mining Engineering Indian Institute of Technology Kharagpur Kharagpur, West Bengal - 721302. 1 Introduction Shovel made their first appearance as early as 1835, and were mounted on the rail tracks and powered by the steam engine at that time. Those shovels were slow in action and were very clumsy. As the time passed they become stronger, faster and lighter and left the rails to move on crawler tracks and sometimes on rubber tyres. Shovels can be visualized on the following three structural divisions. The top or revolving unit is the head. The mounting or travel unit are the legs and The other attachments are the arms and hands. 2 Prof. Sunita Mishra 1 L13: Shovels 6/9/2023 General Construction A shovel consists of bucket (dipper) rigidly attached to the end of a steel structure known as a dipper stick. The dipper stick, which can play forward and backward, is held in position by a cable on the bucket side while it is supported by a pinion on the other. The pinion and rack on the underside of the dipper stick is in constant mesh. These pinions are held in position on a heavy structural member known as boom. The boom is pivoted at its underside with the turntable, while the top of the boom is held in position by means of a cable known as the boom hoist cable. The superstructure or the turntable supports all the equipment necessary to operate the shovel, including the operator’s control room, mechanism for hoisting, swinging and travelling of the shovel. A crawler mechanism supports the whole shovel and also provides motion to the shovel for travelling, including the steering of the machine. 3 Classification Shovels are classified considering the following factors: working agent, bucket size and working mechanism. According to working agent they are regarded as: Diesel shovel Electric shovel Hydraulic shovel According to bucket size they are: Commercial type power shovel, bucket capacities in the range 0.275 cu m to 1.8 cu m. Quarry mine type shovel, bucket size 1.8 cu m to 15 cu m or more. Large quarry mine type shovel, bucket size 15.0 cu m to 75 cu m or more. According to working mechanism they are: Rope shovel Non-rope shovel In rope shovel the front attachment such as bucket, dipper stick and boom are controlled by rope, while in the non-rope shovel they are controlled by a piston-cylinder arrangement. 4 Prof. Sunita Mishra 2 L13: Shovels 6/9/2023 Diesel Shovel This is one of the oldest types of shovels used in open cast projects. A general shovel consists of the following units: Prime mover (Diesel engine) Power transmission system including crowd and hoist mechanism, travel mechanism, swing mechanism Undercarriage unit Front attachment 5 Diesel Shovel 6 Prof. Sunita Mishra 3 L13: Shovels 6/9/2023 Power Transmission System The engine delivers power to three different shafts through a torque converter and the first chain sprocket. The shafts are: Crowd and bucket hoist shaft (C.B.H. shaft) Boom hoist shaft (B.H. shaft) Swing and propel shaft (S.P. shaft) 7 Power Transmission System 8 Prof. Sunita Mishra 4 L13: Shovels 6/9/2023 Crowd and Bucket Hoist Shaft The crowd and bucket hoist shaft is placed at the farthest end from the engine. The figure indicates that the rotation of the swing and propel shaft and crowd and bucket hoist shaft remain in the same direction as that of the engine shaft. The bucket is raised by engaging the drum band clutch, which connects the freely rotating hoist drum with the shaft (C.B.H. shaft). If the bucket has to be stopped or held in a raised position, the drum band clutch is disengaged and the brake is applied simultaneously. The bucket is usually allowed to fall down by its own weight and the speed is adjusted by the brake. The dipper stick and the bucket are forced forward, that is, crowding which is done by engaging the band clutch to the twin sprocket. When the twin sprocket begins to rotate with the shaft. One of the sprockets of the twin sprocket is connected to the shipper shaft. 9 Crowd and Bucket Hoist Shaft There are two crowd pinions mounted on the shipper shaft, which are in a clockwise direction thereby producing the crowd motion of the dipper stick. Retraction of the dipper stick is effected by engaging the cone clutch with the B.H. shaft and when the shipper shaft turns counter-clockwise. During this action the band clutch on the C.B.H. shaft remains in a disengaged position. 10 Prof. Sunita Mishra 5 L13: Shovels 6/9/2023 Boom Hoist Shaft To lift the boom a jaw is engaged with the free boom drum and the cone clutch is engaged with the B.H. shaft there by hoisting the boom. The boom drum is prevented from rotation by disengaging the cone clutch and simultaneously applying the brake on the drum as provided. Lowering of the boom is achieved by its own weight and is controlled by the brake. 11 Swing and Propel Shaft The swing and propel shaft is connected to the engine shaft, which directly receives power from the engine crank shaft through the first reduction. Two cone clutches, L and R, are mounted on this shaft. By engaging these clutches bevel gears L and R can be made active respectively. If the right hand side clutch R is engaged only, the swing and propel vertical shaft rotates in the clockwise direction, thereby enabling the mechanism to swing or travel in one direction. When the left hand side clutch L is engaged, the swing and propel vertical shaft rotates counterclockwise which helps to swing or travel in the opposite direction. Power from the swing and propel vertical shaft is taken into the swing shaft. At the top end of this shaft, there are the swing brake and the swing clutch, while at the bottom end the swing pinion is attached. By engaging the swing clutch, the swing pinion is allowed to rotate about the ring gear, there by swinging the turntable. The reversing of the motion is done by engaging either the L and R clutch. To stop swinging, the swing brake is used. 12 Prof. Sunita Mishra 6 L13: Shovels 6/9/2023 Swing and Propel Shaft 13 Swing and Propel Shaft To start the propelling of the machine, the swing clutch is disengaged and the propel clutch is engaged simultaneously. During this operation, by applying the swing brake the turntable is secured in its fixed position. The power from the propel shaft now is taken to the chains sprocket by the bevel gears and the jaw clutches L and R. The chain sprockets deliver power to the driving sprocket of the crawler mechanism. When the machine is to travel in a straight or forward direction both jaw clutches L and R are actuated simultaneously, so that both the driving sprocket receive power equally. To steer the machine to the right or left, the jaw clutches R or L are disengaged accordingly. To reverse the direction of travel, the cone clutch L or R is engaged as needed. 14 Prof. Sunita Mishra 7 L13: Shovels 6/9/2023 Swing and Propel Shaft Two designs are available for the actuation of the clutches. In one design the actuation of all the clutches is done by compressed air operation, while the other design permits the actuation of cone clutches on S.P. shaft by the electromagnetic principle, popularly known as magneto- torque. This design helps in reducing the swing time, hence the shovel cycle time. The maintenance of this design is also simpler in comparison with other design. The swing and propel mechanism actuation is so designed that they cannot be engaged simultaneously. This helps in restoring machine stability; otherwise unbalanced forces would come into play to disturb the balancing of the equipment. 15 Undercarriage Unit This is also known as the crawler travel unit. This unit consists of two shovel track assemblies fitted with a sprocket, an idle sprocket, track rollers. The whole of the track assembly is mounted on a track frame. There is a provision for adjusting the tension on the track near the idler of the assembly. This serves the following purposes: Supports the whole machine, Helps in the marching of the machine and Helps in steering the machine. The two track assembly are rigidly fixed by the main frame of the equipment. In between the track assembly a bull gear is attached to or mounted on the frame. The turntable is mounted on the structure of the bull gear through a ball race, which supports the turntable and at the same time permits rotational motion of the turntable over the bull gear. There is a central pin known as the centre pintle supported vertically on the main frame, which is attached to the turntable. The turntable rotates about this central pin. The track usually consists of flat shoes hinged and pinned together at their ends. 16 Prof. Sunita Mishra 8 L13: Shovels 6/9/2023 Front Attachment This unit consists of a boom, a dipper stick and a bucket. The bucket is rigidly attached to the front end of the dipper stick, while the dipper stick and bucket combination is held by rope at one end and the stick is supported at the other end by the crowd pinion. There are two such crowd pinions, which are mounted on the skipper shaft or the crowd shaft. The crowd shaft is powered by a chain sprocket arrangement receiving power in turn from another chain sprocket arrangement. 17 Front Attachment 18 Prof. Sunita Mishra 9 L13: Shovels 6/9/2023 Shovel-In Pit Crushing Arrangement 19 Next Class: Draglines 20 Prof. Sunita Mishra 10