Lecture 3 Material Handling Equipment (Hoisting Equipment)

Material Handling Equipment lecture 3 out of 5

1. MATERIALS HANDLING EQUIPMENT LECTURE Three Hoisting Equipment Outlines Theory of hoisting equipment Flexible hoisting appliance Pulleys, sprockets, Drums and Load handling attachments Arresting gear and brakes Hoisting and travelling gear By: Amanuel DIriba 06-Sep-19 1 By: Amanuel Diriba

2. Theory of hoisting equipment The hoisting is a device used for lifting or lowering a load by means of drum or lift – wheel around which rope or chain wraps . It may be done with a wide range of equipment from the small hand operated simple screw or hydraulic – jack to modern high powered cranes and elevators. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium. Hoisting equipment can be a stationary, portable or travelling. There are different types of hoisting equipment whose accurate classification is difficult. 06-Sep-19 2 By: Amanuel Diriba

3. Cont.. There are three groups of hoisting equipment having the following main distinctive features. Hoisting machines a group of periodic action devices designed as self-lifting gears for hoisting and moving loads. 06-Sep-19 3 By: Amanuel Diriba

4. Cont.. Cranes a combination of separate hoisting mechanism with a frame for lifting and/or moving loads 06-Sep-19 4 By: Amanuel Diriba

5. Cont.. Elevators - a group of periodic action machine intended for raising loads with guide – ways. 06-Sep-19 5 By: Amanuel Diriba

6. Cont.. The main technical parameters of hoisting machines are : lifting capacity : the maximum safe load a machine is designed to handle Dead weight of the machine : the total weight of the machine without load Speed of various movements: this may be the hoisting speed, the bridge travel speed and the trolley traveling speed lifting height : the height to which the load is intended to be raised; 06-Sep-19 6 By: Amanuel Diriba

7. 06-Sep-19 7 Flexible hoisting appliances Hemp – rope Welded loaded chains Roller chain Steel wire ropes Fastening of chains and ropes Load handling attachments Hook’s Electric lifting magnets grabs By: Amanuel Diriba

8. Flexible hoisting appliances The needs of hoisting machinery in flexible members are met widely by hemp rope, welded and roller chains, and steel wire ropes. 1. Hemp – Ropes Because of their poor mechanical properties (rapid abrasion, inadequate strength, rapid damage from sharp materials and atmospheric effects, etc ), they can be recommended only for hand-operated hoisting machinery (rope pulleys). The diameters of the sheaves over which the rope runs should be at least 10d,where d is the nominal rope diameter. 06-Sep-19 8 By: Amanuel Diriba

9. Cont.. By the mode of manufacture and number of strands , hemp ropes are classified as plain-laid cable-laid T he latter being from twisted from three ordinary ropes twisted from three ordinary ropes. 06-Sep-19 9 By: Amanuel Diriba

10. Cont.. 2. Welded loaded chains They are widely used in hoisting installations as flexible members. Depending on the ratio between the pitch and the diameter of the chain bar, welded chains are classified into Short – link chains with t ≤ 3d Long – link chains with t ˃ 3d 06-Sep-19 10 By: Amanuel Diriba

11. Cont.. Manufacturing accuracy divides welded chains into: Calibrated – with permissible deviation from the nominal size within t +/- 0.03d and B+/- 0.05d Uncalibrated – with permissible deviation from the nominal size within t +/- 0.1d and B +/- 0.1d Links for welded chain are formed most commonly hammer (forge) and electric resistance welding. Because of the short comings, welded chains are used only in some hand – operated mechanism (where Dmin > 20d) and in few power drive mechanism (where Dmin > 30d) They are employed for low capacity hoisting machines (hoists, winches, hand – operated cranes, etc ) 06-Sep-19 11 By: Amanuel Diriba

12. Cont.. Advantage of welded chain Good flexibility in all direction Possibility to use small diameter pulleys and drums Simple design and manufacture Disadvantages of welded chains Heavy weight Susceptibility to jerks and overload Sudden failure Concentrated wear at the link joints and Low safe speed f movement. 06-Sep-19 12 By: Amanuel Diriba

13. Cont.. 3. Roller chains Roller chains are composed of plates hinge – jointed by pins and rollers. For light loads , t wo plates are used. For very heavy loads the number of plates can be increased upto 12. The maximum allowable speed of roller chain is V = 0.25m/s Roller chains are used for hand operated hoists , power – driven winches and hoisting mechanisms of high load lifting capacity , operating at low speed, if the weight is lifted between guide – ways. 06-Sep-19 13 By: Amanuel Diriba

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15. Advantage of roller chains Roller chains are superior to welded chains in a number of ways such as: The reliability of operation is higher since the plates are solid. Roller chain have good flexibility The friction in the joints is considerably less than that in the joints of welded chains. But roller chains should not be allowed: To carry weight acting at an angle to the plate(to prevent excessive wear and pin breakage) To be used in dusty premises (unless the chain is sealed by cover which would cause excessive wear) 06-Sep-19 15 By: Amanuel Diriba

16. Cont.. 4. Steel wire Ropes The steel wire ropes are extensively used in hoisting machinery as flexible lifting appliance. The wire is drawn cold and given heat treatment as well as chemical treatment between the drawing stages in order to obtain required strength, structure, appearance and surface finish. They are most popular types used in hoisting machinery. Normally steel wire ropes consist of 6 or 8 strands and a core. 06-Sep-19 16 By: Amanuel Diriba

17. Cont.. Comparing to chains they have the following advantages:- Lighter weight Less susceptibility to damage from jerks Silent operation even at high speeds Greater reliability in operation 06-Sep-19 17 By: Amanuel Diriba

18. Cont.. Non –spinning wire ropes Each individual wire and strand being laid is performed to correspond to its disposition in the rope. As a result of unloaded wires are not subjected to internal stresses and tend to spin . Advantages of non – spinning wire ropes over the general purpose ropes :- Uniform load distribution over the individual wires, which reduces internal stresses to a minimum Better flexibility Less wear of the wire ropes running over drum or sheaves Greater operation safety. The disadvantage of non- spinning wire ropes is that it is more expensive. 06-Sep-19 18 By: Amanuel Diriba

19. Cont.. 4. Fastening of chains and Ropes Various methods are used to secure the ends of chains and ropes. 06-Sep-19 19 By: Amanuel Diriba

20. A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a rigid cable or belt, or transfer of power between the shaft and cable along its circumference. Pulleys are used in a variety of ways to lift loads, apply force, and to transmit power. Pulleys 06-Sep-19 20 By: Amanuel Diriba

21. Classification of pulleys Pulleys are either fixed or movable in design. 1. Fixed Pulleys Fixed pulleys are used to change the direction of the flexible appliance. Disregarding the resistance of the pulley, the pulling force Zo equals Q (weight to be pulled) I.E Zo = Q, without considering pulley resisting. 06-Sep-19 21 By: Amanuel Diriba

22. Cont.. 2. Movable pulley M ovable pulleys are used to gain mechanical advantage or speed/force. Movable pulleys are classified into two Pulleys for gain in force: Used t o increase amount of force applied and it doesn’t change direction of the force. The distance that effort moves is double that of the load, and the speed at which the load is raised is half of that of the effort. S = 2h C = 2v Figure : Single movable pulley for a gain in force Where C= Speed of force v = speed of load s = distance the force moves h = distance the load moves 06-Sep-19 22 By: Amanuel Diriba

23. Cont.. Pulleys for gain in speed Used to increase amount of load speed and it doesn’t change direction. The effort is applied at the axle of the pulley and moves at half the speed of the load. The distance moved by the load is twice that of the effort. s = c = Z=Q = So   Figure : Single movable pulley for a Gain in speed 06-Sep-19 23 Where C= Speed of force v = speed of load s = distance the force moves h = distance the load moves By: Amanuel Diriba

24. Cont.. 3. Block and Tackle pulley A block and tackle is a pulley system made up of fixed and movable pulleys. 06-Sep-19 24 By: Amanuel Diriba

25. Cont.. Pulley Systems Several fixed and movable pulleys are combined in order to form a pulley system for a gain in force or a gain in speed. Figure: pulley system for a gain in force Figure: pulley system for a gain in Speed 06-Sep-19 25 By: Amanuel Diriba

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27. 06-Sep-19 27 Flexible hoisting appliances Hemp – rope Welded loaded chains Roller chain Steel wire ropes Sheaves Sprockets Drums Sheaves Used for ropes and welded chains Sprockets Used for welded chains and Roller chain Drums used for Hemp rope and steel wire ropes By: Amanuel Diriba

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29. Sheaves A sheaves is a pulley with a grooved wheel for holding belt, wire rope or rope. A sheaves are grooved rims used for guiding ropes or chains. The sheaves are usually mounted freely on their axles. 06-Sep-19 29 By: Amanuel Diriba

30. Cont.. Rope life depends on the material of the groove. Practical experience goes to show that ropes operating over steel sheaves wear down more rapidly than those used in conjunction with cast-iron sheaves apparently due to higher contact stresses and poorer conditions of slipping of the rope over the steel sheave. To increase rope life , sheave grooves are lined with aluminum, rubber, and plastics. Sheaves for welded chains: These sheaves are usually made of cast iron. They are mainly used for hand operated hoists and rarely they are used for power driven devices. 06-Sep-19 30 By: Amanuel Diriba

31. Sprockets A sprocket or sprocket-wheel is a profiled wheel with teeth, that mesh with a chain, track or other perforated or indented material. As a rule , sprockets are manufactured with a small number of teeth and are small in size ensuring compactness and low cost of the driving mechanism . 06-Sep-19 31 By: Amanuel Diriba

32. Cont.. Sprockets for welded chains: Sprockets are used as driving chain wheels of hand operated hoists and winches . Sprockets for rollers chains: Sprockets are manufactured from cast iron and forged steel casting. They are mainly used for hand- operated hoists and winches. 06-Sep-19 32 By: Amanuel Diriba

33. Drums Drums is a grooved wheel on which the rope is wound in more than one layer. During operation the drum is subject to the combined action of torsion bending and compression. The machined grooves increase the drum bearing surface, prevent friction between the adjacent rope turns and consequently reduce the contact stresses and rope wear. 06-Sep-19 33 By: Amanuel Diriba

34. Cont.. 06-Sep-19 34 By: Amanuel Diriba

35. Friction Drums of ropes F riction drums are rope – driving drums in which motion is transmitted by friction between the rope and drum. They have the advantage of being able to raise loads for great height. Are used for winches and railway cars. Friction drums are capable of handling long ropes by means of a small drum. 06-Sep-19 35 By: Amanuel Diriba

36. Cont.. There are three types of friction drums Simple friction drums They are provided with helical grooves for the rope, which coil around in one or several turn. Double drum friction drive In this case the rope is wound several times around two parallel drums rotating in the same direction and driven by a single motors. Capstan Capstans are usually arranged vertically, driven by electromotor through a worm gear drive and used to move railways cars. 06-Sep-19 36 By: Amanuel Diriba

37. 06-Sep-19 37 Flexible hoisting appliances Hemp – rope Welded loaded chains Roller chain Steel wire ropes Fastening of chains and ropes Load handling attachments Hook’s Electric lifting magnets grabs Sheaves Sprockets Drums By: Amanuel Diriba

38. LOAD HANDLING ATTACHMENTS The load is usually handled by many various methods. 06-Sep-19 38 By: Amanuel Diriba

39. Cont.. They are three most commonly used load handling attachment Hook’s Electric lifting magnets Grabs Hook’s The load is usually handled by means of chain or rope slings attached to hooks. One – piece forged hooks are used for lifting loads upto 100 tons while triangular and laminated hooks can be employed to carry over 100 tons. Hook are forged from low carbon steel. 06-Sep-19 39 By: Amanuel Diriba

40. Cont.. In the process of production hooks are carefully annealed after forging and machining. Generally hooks have trapezoidal section made wider on the inside for better material utilization. 06-Sep-19 40 By: Amanuel Diriba

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42. Cont.. Electric Lifting Magnets . Lifting magnets are used to handle magnetic materials of diverse form (ingots, beams, rails, steel sheets and plates, scrap, metal chips etc.). These drastically reduces the time required for manual suspension of loads . 06-Sep-19 42 By: Amanuel Diriba

43. Cont.. Grabs These are the holding attachments which are special type of buckets which mechanically grab and automatically dump the materials. The grabs are designed considering the type of material to be bold . 06-Sep-19 43 By: Amanuel Diriba

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45. 06-Sep-19 45 Flexible hoisting appliances Hemp – rope Welded loaded chains Roller chain Steel wire ropes Fastening of chains and ropes Load handling attachments Hook’s Electric lifting magnets grabs Sheaves Sprockets Drums By: Amanuel Diriba

46. Arresting Gear Arresting gear is used to hold the being lifted without interfering in the hoisting process but preventing the load from coming down due to gravity. They are three most common arresting gear types:- Ratchet gearing Friction arresters Roller ratchets Arresting gear and brakes 06-Sep-19 By: Amanuel Diriba 46

47. Cont.. Ratchet gearing Ratchet gearing consists of ratchet gear and pawl . The teeth in the ratchet(internal teeth or external teeth) and so arranged that the ratchet gear runs free when the load is being raised. The pawl engaging the ratchet assist its motion when the load is being lowered. 06-Sep-19 By: Amanuel Diriba 47

48. Cont.. Friction Arresters Friction arresters operate noiselessly compared to the operation of toothed arresting gear. However, the pressure on the pawl pivot and shaft is considerably high. They have a limited application. To avoid unidirectional action , the arrester is always provided with two pawls arranged at diametrically opposite points. 06-Sep-19 By: Amanuel Diriba 48

49. Cont.. Roller Ratchets This mechanism arrest the load within a minimum distance . The whole system relies on friction for its successful operation. A roller wedged between the follower and the driver is subjected to the action of normal forces N 1 and N2 and tangential friction forces µ 1 N 1 and µ 2 N 2 . With the roller in equilibrium, the resultant force R 1 = R 2 . for equilibrium N 1 = N 2 06-Sep-19 By: Amanuel Diriba 49

50. Brakes A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping of moving vehicle, wheel axle or to prevent it’s motion, most often accomplished by means of friction. In hoisting machinery, brakes are employed for controlling the speed of load lowering and holding the suspended load at rest . 06-Sep-19 By: Amanuel Diriba 50

51. Cont.. Depending on the purpose, brakes can be classified as Stopping brakes – These bring the drive at rest at the end of motion. Regulating brakes – These are serving to maintain the speed of motion within prescribed limits . From operational aspect they can be classified as Automatic brakes – These brakes are applied automatically irrespectively of the operator’s will at the-instant the motor of the mechanism is de-energized. Controlled brakes – These are set and released by the operator irrespectively of whether or not the relevant drive is in operation. 06-Sep-19 By: Amanuel Diriba 51

52. Hoisting and Travelling Gear In any lifting drive the hoisting mechanism is considered to be the vital element. Hoisting mechanisms are subdivided into three groups Hand power drives Individual power drives A common drive for several mechanisms 06-Sep-19 By: Amanuel Diriba 52

53. Cont.. Hand power drives A hand drive" is employed in mechanisms with a low lifting capacity, or where the load has to be moved a short distance, or for occasional lifts; Application area of Hand drives are:- winches with small lifting height, in jacks, and sometimes in travelling overhead and gentry cranes and in light-duty rotary cranes. 06-Sep-19 By: Amanuel Diriba 53

54. Cont.. Individual electric drives An electric motor driven hoist has one or two rope drums for coiling and uncoiling the hoisting wire rope. The hoisting motor drives the drum through a planetary gearing system . Electrically driven cranes designed to handle up to 2000 tons are available. The drives can be hydraulic drive , pneumatic drive , diesel electric drives etc . 06-Sep-19 By: Amanuel Diriba 54

55. Cont.. Electric motor is generally preferred in most hoisting installations owing to the following advantages. Immediate readiness for operation. Possibility of driving every motion by a separate motor. Higher economic efficiency as compared with other drives. The ease of speed control over a wide range. Convenient reversing of motions. Safe operation, simplicity of construction, and high reliability of safety devices. Ability to cope with short-time overloads of significant magnitude. 06-Sep-19 By: Amanuel Diriba 55