среда, 21 августа 2019 г.
Maintenance and Operation of Lubricant Systems
Maintenance and Operation of Lubricant Systems Activity 1 Explain the purpose and the applications of three different types of lubricant. Greases: are solid or semisolid lubricants and generally consist of soaps, mineral oil, and various additives. These are highly viscous ad adhere well to metal surfaces. Although used extensively in machinery, greases are of limited use in manufacturing processes. Graphite: is weak in shear alone its basal planes and therefore has a low coefficient of friction in that direction. It is an effective solid lubricant, particularly at elevated temperatures. In a vacuum or an inertgas atmosphere, friction is very high; in fact, graphite can be abrasive in these situations. We can apply graphite either by rubbing it on surfaces or by making it part of a colloidal (dispersion of small particles). Glasses: is a solid material, glass becomes viscous at elevated temperatures and, therefore, can serve as a liquid lubricant. Viscosity is a function of temperatures, but not of pressure, and depends on the type of glass. Poor thermal conductivity also makes glass attractive, since it acts as a thermal barrier between hot work pieces and relatively cool dies. Glass lubrication is typically used in such applications as hot extrusion and forging. Activity 2 Describe the operation and maintenance of three different lubrications systems. Oil circulatory systems: In Oil circulatory systems, the oil is continuously supplied to various moving parts and bearings. In such systems, oil acts both as lubricant and also as coolant by earning away heat generated in the bearings/moving parts. The oil after lubrication is returned to reservoir either directly or through filters. These systems are large, employing reservoirs of capacity ranging from few hundreds of liters to thousands of liters. The pumps are heavy duty, intended for continuous running, with flow rate ranging from few tens of LPM to few thousands of LPM. These systems are widely used for plants like Cement, Sugar, Paper, Power generation. Steel as well as heavy duty machineries. Full Force Feed systems: In a full force-feed lubrication system, the main bearings, rod bearings, camshaft bearings, and the complete valve mechanism are lubricated by oil under pressure. In addition, the full force-feed lubrication system provides lubrication under pressure to the pistons and the piston pins. This is accomplished by holes drilled the length of the connecting rod, creating an oil passage from the connecting rod bearing To the piston pin bearing. This passage not only feeds the piston pin bearings but also provides lubrication for the pistons and cylinder walls. This system is used in virtually all engines that are equipped with full-floating piston pins. Force Feed systems: A fairly more complete pressurization of lubrication is achieved in the force-feed lubrication system Oil is forced by the oil pump from the crankcase to the main bearings and the camshaft bearings. Unlike the combination system the connecting-rod bearings are also fed oil under pressure from the pump. Oil passages are drilled in the crankshaft to lead oil to the connecting-rod bearings. The passages deliver oil from the main bearing journals to the rod bearing journals. In some engines, these opening are holes that line up once for every crankshaft revolution. In other engines, there are annular grooves in the main bearings through which oil can feed constantly into the hole in the crankshaft. The pressurized oil that lubricates the connecting-rod bearings goes on to lubricate the pistons and walls by squirting out through strategically drilled holes. This lubrication system is used in virtually all engines that are equipped with semifloating piston pins. Activity 3: Describe the operation of one seal, one type of packing and two different types of bearing with a typical application for each one. Seal: End face seals: This type of seal uses both rigid and flexible fundamentals that maintain contact at a sealing interface and slide on each other, allowing a rotating element to a pass through a sealed case. The elements are hydraulically and mechanically loaded with a spring or other device to maintain contact. In general the end face seal is sealed to the pump end plate by a gasket or O- ring and also the rotating seal face runs against the stationary seat (the opposing surface lapped to high degree of flatness). An end face mechanical seal, also known as a mechanical face seal but usually simply as a mechanical seal, is a type of seal utilised in rotating equipment, such as pumps and compressors. Packing: O-ring: Is a packing and it is also known as tonic joint, it is a mechanical gasket in the shape of a torus. It has a cross-section with a disc-shaped; it is also a loop of elastomer. O-rings are one of the most common seals used in machine design because they are inexpensive and easy to make, reliable, and have simple mounting requirements. They can seal tens of megapascals (thousands of psi) pressure. An O-ring is basically defined by its section diameter and the inner diameter of the O-Ring. O rings have many advantageous features including Low cost suit static dynamic duties space efficient seals in both directions fluid pressure assists sealing Suitable for all fluids-using appropriate elastomers. Two different types of bearings: Plain bearing: In general plain bearing have rubbing surfaces usually with lubricants. The stiffness of plain bearing are Good, provided wear is low, but some slack is normally present. It also has a very low speed to a very high sleep. Plain bearing is the simplest type of bearing, widely used, relatively high friction, suffers from stiction in some applications. Some bearings use pumped lubrication and behave similarly to fluid bearings. At high speeds life can be very short. Rolling-element bearing: A rolling-element rotary bearing uses a shaft in a much larger hole, and cylinders called rollers tightly fill the space between the shaft and hole. As the shaft turns, each roller acts as the logs in the above example. Yet, since the bearing is round, the rollers never fall out from under the load. A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces. The relative motion of the pieces causes the round elements to roll with very little rolling resistance and with little sliding. It is the earliest and best-known rolling-element bearings are sets of logs laid on the ground with a large stone block on top. As the stone is pulled, the logs roll along the ground with little sliding friction. As each log comes out the back, it is moved to the front where the block then rolls on to it. Activity 4: Describe two different types of screwed fasting and two different types of rivet giving a typical application for each one. Two different types of screwed fasting: Bolts and Nuts: Bolts and nuts can be made from steel, brass, aluminum alloys and plastic. There are all sorts of bolts and nuts with different sizes for example: M6x25 high tensile bolt BZP M2 full not zinc The above metric blots and nuts and specified as steel. The specifications for bolts and nuts: Example: M8x1.550: M specifies that it is metric. The number next to the letter M which is 8 specifies the diameter in millimeters. 1.5 specifies the tread pitch in millimeters. 50 specifies the length of the shank in millimeters. There are other bolts for example: Tap bolt A bolt that is threaded all the way to the head. Eye bolt A bolt with a looped head. Toggle bolt A bolt with a special nut known as a wing. It is designed to be used where there is no access to side of the material where the nut is located. Usually the wing is spring loaded and expands after being inserted into the hole. The strength of the bolts Can be identified by reading the numbers stamped on the head of the bolts, these are referred to the grad of the bolt used in certain applications with the strength of the bolt. High-strength steel bolts usually have a hexagonal head with an International Organization for Standardization(ISO) strength rating stamped on the head. Studs and nuts: Studs: Road studs: These are generally used on hard surfaces, such as roads or very had ground. They are normally 4 to 6 sided, small and flat in size and blunt. Ice studs: these are also designed for use on hard surfaces, but generally have a longer, sharper point than road studs, to provide traction on slippery surfaces. Grass studs: are also known as bullet studs , they come in many different lengths but are always larger and shaper than road studs and generally narrow so they can dig into hard, dry ground. Mud Studs: are used on extremely soft or wet riding surfaces where deep traction is needed. They are bigger thanRoad Studsbut often rounded on top and come in several different lengths.Mud Studscan also be square in shape, known asBlock Studs.SomeMud Studsare knownasOlympic Studs*which are long and sharp and used for extremely slippery ground Two different types of rivets: Blind rivets. These types of blind rivets have non-locking mandrels and are avoided for critical structural joints because the mandrels may fall out, due to vibration or other reasons, leaving a hollow rivet that will have a significantly lower load carrying capability than solid rivets. In addition, because of the mandrel they are more horizontal to failure from corrosion and vibration. A drive rivet: A drive rivet is an appearance of blind rivet that has a little mandrel protruding from the head that is driven in with a hammer to flicker out the end inserted in the hole. This is usually used to rivet wood panels into place since the hole does not need to be drilled all the way through the panel, producing a beautiful pleasing appearance. They can also be used with plastic, metal, Other materials and require no special setting tool other than a hammer and possibly a backing block. P5-Decribe the operation of two different types of cam and followers and two different types of linage mechanism. Two different types of cam and followers: Cam followers are comparable to needle or cylindrical roller bearings with a thick-walled external ring. The crowned outer surface of the outer ring prevents border stresses if the roller runs in a twisted or inclined location. They are grease full ready-to-mount units appropriate for all types of cam drives, tracks and conveyor systems. In its place of an inner ring cam followers have a hard threaded pin to permit the cam follower to be quickly and easily attached to the machine mechanism by means of a hexagonal nut. Axial guidance is provided through an essential flange on the external ring at the top of the pin and a side. Cam followers are obtainable in three different internal designs. Usually, the cam followers have concentric seating on the pin, but some are also accessible with a strange collar shrunk on to the stud. Cam follower bearings with collar allow an optimum interaction with the cam and allow fewer stringent developed tolerances for the mechanism. Two different types of linkage mechanism: A mechanical linkage is a sequence of rigid links linked through joints to shape a closed series, or a series of closed chains. Every linkage has two or more joints, and the joints have a variety of degrees of freedom to allow movement between the relations. A linkage is called a mechanism if two or more links are movable with respect to a fixed link. Four-bar linkage mechanisms: The four-bar linkage is one more mechanism which finds general uses. It is establish in applications such as windscreen wiper drives, Vehicle suspension units and Everyday uses such as the hinges on kitchen cupboard doors and squeeze-mop mechanisms. Two of the links spin about fixed centers and are connected by a coupler linkage. The fourth link is shaped by the frame or bed plate that contains the permanent centers of rotary motion. It must be noted that the number of inversion of machinery is equal to the number of links, which in this case is four links. Reverse motion linkage. As the top bar moves to the left the base bar moves to the right. The bars move in reverse directions. an additional way of describing this linkage is the direction of movement in one bar is reversed in the other rod. The fixed pivot is the centre of rotation. (P6): describe the arrangement and operation of Two different kinds of belt drive: Flat belts: Flat belts are used mostly for transmitting light tons. Since they are flexible, this makes them appropriate for applications where there is some misalignment among shafts; they possibly will be crossed to give opposition directions of turning round to the pulleys. They can also be twisted to attach shaft which are not in the same plane. Vee belts: Vee belts (also recognized as V-belt or wedge rope) solved the slippage and arrangement problem. It is currently the essential belt for power transmission. They offer the best mixture of grip, pace of movement, load of the bearings, and long service life. They are usually continuous, and their common cross-section shape is trapezoidal. The V shape of the belt tracks in a mating groove in the pulley (or sheave), with the effect that the belt cannot slip off. The belt also tends to hold into the groove as the load increases the larger the load, the larger the wedging action improving torque transmission and making the vee belt an helpful solution, needing less width and tension than flat belts. Two different kinds of chain drive: A chain is a method of transferring rotary motion between two parallel shafts. The chain drive is positive, efficient and high torques can be transmitted. The chain is generally made from steel although plastic chains have been developed. Roller Chain: Roller chain or bush roller chain is the type of chain most frequently used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery. It is a straightforward, dependable, and efficient means of power transmission. Two different kinds of gear train. Epicyclic gearing or planetary gearing is a gear system that consists of one or more external gears, or planet mechanism, rotating about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear. Epicyclic gearing systems may also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears. (P7): Describe the arrangement and operation of: Two different kinds of transmission shaft Power transmission shafts are mainly used in two wheeler and four wheeler vehicles. These shafts consist of metal joint elements and a metal pipe connected to each other. To provide more rigidity to shafts, a plastic pipe is inserted into metal pipe thus forming a composite power transmission shaft having more strength and rigidity. Automotive transmission shafts are especially designed and used in two wheelers as well as four wheelers. These shafts are integral hollow type shafts that maintain a perfect balance between static strength and fatigue strength. Two different types of Couplings: Shaft couplings are used in machinery for several purposes, the most common ones are: To provide for the connection of shafts of units those are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alternations. To provide for misalignment of the shafts or to introduce mechanical flexibility. To reduce the transmission of shock loads from one shaft to another. Rigid Slip Couplings: This type of coupling has no flexibility; therefore it is necessary for the shafts that aretobe connected to be in good alignment, both laterally and angularity, in order excessive loadson the coupling, on the shafts, or on the shaft bearings.Rigid couplings do not accommodate misalignment and consequently should not be usedindiscriminately. Types of Rigid Couplings: Sleeve or muff coupling: It is the simplest type of rigid coupling, made of cast iron. Itconsists of a hollow cylinder whose innerdiameter is the same as that of the shaft. It is fitted over the ends of the two shafts by means of a gibhead key. Clamp coupling: Clamp coupling is sometimes called a compression coupling or a ribbed coupling. Clamp coupling is a modification and an improvement of the sleeve coupling. This coupling is made in two parts which are machined to fit the shaft and are finished off around the periphery and on both ends. Flange coupling: A flange coupling usually applies to a coupling having two separate cast iron flanges. Each flange is mounted on the shaft end and keyed to it. The faces are turned up at right angle to the axis of the shaft. Two different kinds of clutch: Dog clutch: is a type ofclutchthat couples two turning shafts or other rotating mechanism not byfrictionbut by interference. The two parts of the clutch are designed such that one will push the other, causing both to rotate at the same speed and will never slip. Dog clutches are used inside manual automotive transmissions to lock different gears to the rotating input and output shafts. Cone clutch: serves the same purpose as a disk or plateclutch. However, instead of mating two spinning disks, the cone clutch uses two conical surfaces to transmit torque by friction. The cone clutch transfers a higher torque than plate or disk clutches of the same size due to the wedging action and increased surface area. Cone clutches are generally now only used in low peripheral speed applications although they were once common in automobiles and other combustion engine transmissions. Two different kinds of breaks: Disc brakes: are made of cast iron or ceramic composites. The use of these types of breaks ate to stop or slow the rotation of a wheel. Hydraulic brakes: use brake fluid, and normally containing ethylene glycol the reason for this is because to transfer pressure from the controlling unit and also to brake mechanism which is normally near the wheel. (P8): Describe with the aid of diagrams the general layout operation of a Pneumatic actuation system: Pneumatic systems provide a softer action and are also not able to deliver such large forces. Besides the disadvantages pneumatic systems have some advantages which are: Simplicity of Design and Control Machines are easily designed using standard cylinders other components. Control is as easy as it is simple ON OFF type control. Reliability Pneumatic systems tend to have long operating lives and require very little maintenance. Because gas is compressible, the equipment is less likely to be damaged by shock. The gas in pneumatics absorbs excessive force, whereas the fluid of hydraulics directly transfers force. Storage Compressed Gas can be stored, allowing the use of machines when electrical power is lost. Safety Very low chance of fire (compared to hydraulic oil). Machines can be designed to be overload safe. The process of the pneumatic system that is shown above: The compressor receives filtered air form air filter and delivers through an after-cooler to the compressed air receiver. Then the air is distributed to different applications as well as the pneumatic cylinder. Pneumatic systems employ gas that is compressed under extremely high pressure. For some applications where the air must be perfectly dry, the system also contains a moisture separator. The practical use of pneumatics comes in putting that compressed gas to use, at its most basic level a pneumatic system holds compressed gas in a specially designed tank and then we release some of that gas into an expandable chamber. The expandable part of the chamber has a rod attached to it so that as it expands the rod moves outward. Hydraulic actuation systems: Air has a low density and is compressible at the same time as hydraulic oil has a much higher density and is almost incompressible. Therefore, hydraulic systems are capable to function at much advanced pressure and deliver the very huge positive forces which are necessary in applications such as hydraulic presses and lifts. Hydraulic actuation system has advantages which are listed below: Advantages of hydraulics Liquid (as a gas is also a fluid) does not absorb any of the supplied energy. Capable of moving much higher loads and providing much higher forces due to the incompressibility. The hydraulic working fluid is basically incompressible, leading to a minimum ofspringaction. When hydraulic fluid flow is stopped, the slightest motion of the load releases the pressure on the load; there is no need to bleed off pressurized air to release the pressure on the load. The process of the Hydraulic actuation systems that is shown above: The system has motor-driven pump which draws filtered oil from the tank and distributes it through a pressure regulator to the positions where it is necessary. The pump runs constantly and the excess oil which is not necessary for procedures is diverted back to the tank by the pressure regulator. It must be noted that the organization generally supplies a relatively little work area in the locality of the pump and tank. It is not realistic to provide oil under pressure over large distances for the reason that of pressure drop and the need for a return pipe. A manual or automatic control valve supplies oil to the actuation cylinder and directs return oil to the reservoir. A mechanical handling system: The transfer of material, components and assemblies through the manufacturing stages often takes position on roller or belt conveyors. Mechanical handling has a broad variety of handling. Lifting gear used in developing business is broad and in some cases it is extremely meticulous. The roller conveyer is most expected the easiest form where manufactured goods are passed among work stations along a track having rollers. Materials are regularly shifted through a motor-driven belts conveyer. The belts are from frequently maintained on concave roller so that is falls in the center. (P9): Describe with the aid of diagrams the general layout and operation of Steam power generation plant: Though the main process in steam power station is the conversion of heat energy into electrical energy, it comprises of many steps for its proper working and good efficiency. The whole arrangement of a steam power station could be divided into following steps: The steam generating plant consist of boiler and its auxiliary equipments for the utilisation of flue gases. Boiler: The heat produced by the burning of coal in the boiler is used to produce steam at high temperature and pressure. The flue gases produced at the time of combustion is passed through the super heater, economiser, air- preheater and finally exhausted into the atmosphere through chimney. Super Heater: The steam produced in the boiler has got moisture content so it is dried and superheated (i.e. steam temperature is increased above boiling point of water)by the flue gases on the way to chimney. Super heating ensures two benefits at first the overall efficiency of the system is increased and secondly the corrosion to the turbine blades due to condensation in later stages is prevented. The superheated steam from superheater is fed to steam turbine by means of a main valve. Air preheater: Air preheater increases the temperature of the air supplied to coal for combustion using flue gases. Air is drawn in using a forced draught fan and is passed through preheater before supplying it to the boiler. This process increases the thermal efficiency and steam capacity per square meter of the boiler surface. Steam Turbine: The dry and super heated steam from superheater is fed to the turbine by means of a main valve. Due to the striking or reaction impact of the steam on the blades of turbine it starts rotating i.e. heat energy is converted to mechanical energy. After giving heat energy to the turbine the steam is exhausted to a condenser which condenses the exhausted steam by means of a cold water circulation. Alternator: The steam turbine is coupled to an alternator; the alternator converts the mechanical energy into electrical energy. The electrical output is transferred to the bus bars through transformer, circuit breaker and isolators. Feed Water: The condensed water produced in the condenser is used as feed water, some amount of water may be lost in the cycle but it is compensated using an external source and the cycle repeats and gives a better efficiency to the system. Cooling Arrangement: Inorder to increase the efficiency of the plant the steam coming from the turbine is condensed using a condenser. The water circulation for cooling steam in condenser is take from a natural source like river, stream etc and the out coming hot water from condenser is discharged in some lower portion of the water source. In scarcity of water the water from the condenser is cooled and reused with the help of a cooling tower. Refrigeration system: There are several heat transfer loops in a refrigeration system as shown above. Thermal energy moves from left to right as it is extracted from the space and expelled into the outdoors through five loops of heat transfer: Indoor air loop. In the left loop, indoor air is driven by the supply air fan through cooling coil, where it transfers its heat to chilled water. The cool air then cools the building space. Chilled water loop. Driven by the chilled water pump, water returns from the cooling coil to the chillers evaporator to be re-cooled. Refrigerant loop. Using a phase-change refrigerant, the chillers compressor pumps heat from the chilled water to the condenser water. Condenser water loop. Water absorbs heat from the chillers condenser, and the condenser water pump sends it to the cooling tower. Cooling tower loop. The cooling towers fan drives air across an open flow of the hot condenser water, transferring the heat to the outdoors. There are two fundamental types of refrigeration system. They are the; Vapour-compression system The vapour-absorption system. The two types are used for commercial purposes and domestic refrigerators and the two of them work on the standard that when a liquid vanishes, it takes in concealed heat from its surroundings. The liquids used in refrigerators and freezers are called refrigerants. They are made to evaporate at a temperature below 0 degrees Celsius and in doing so; they take in latent heat and maintain the cold space at a sub-zero temperature. A refrigerant must have a low freezing point so that it does not solidify or form slush in the low temperature part of the refrigeration cycle. Also it should have a high value for its latent heat of vaporisation to maximise the transfer of heat energy during the cycle. Compression refrigeration cycles take advantage of the fact that highly compressed fluids at a certain temperature tend to get colder when they are allowed to expand. If the pressure change is high enough, then the compressed gas will be hotter than our source of cooling (outside air, for instance) and the expanded gas will be cooler than our desired cold temperature. In this case, fluid is used to cool a low temperature environment and reject the heat to a high temperature environment. Vapour compression refrigeration cycles have two advantages. First, a large amount of thermal energy is required to change a liquid to a vapor, and therefore a lot of heat can be removed from the air-conditioned space. Second, the isothermal nature of the vaporization allows extraction of heat without raising the temperature of the working fluid to the temperature of whatever is being cooled. This means that the heat transfer rate remains high, because the closer the working fluid temperature approach es that of the surroundings, the lower the rate of heat transfer. An air condition system: An Air-condition system is the full automatic control of the indoor atmosphere to maintain comfortable and healthy conditions. Its objective is to provide clean, fresh air at a temperature and humidity level that is comfortable to the occupants. The essential ingredients in an air conditioning system are a fan to blow air around, a cold surface to cool and dehumidify the air, a warm surface and a source of water vapour. In a large system there will also be a tangle of tubes to distribute the air and collect it again. Notice that the cold surface has two independent jobs to do: it is used to cool the air and it is also used to dehumidify, by condensing water from the air. Advantages of Pneumatic systems over Hydraulic systems: Extremely cheaper then hydraulic systems. The force transmitter, air, is freely available. Cleaner systems as air leakage do not create a mess. Due to high pressure Hydraulic oil becomes very hot after continuous use. It can cause injury/burns if someone comes in contact with it. Usually has open circuits and we dont have to worry about the return circuit. (D1): Justify the use of shell tellus oil 27 lubricant and the splash lubrication system in the lathe machines in the college machine shop: Shell tellus oil 27and 37 lubricants: Shell Tellus Oils oil 27 are premium quality hydraulic oils generally acknowledged to be the standard-setter in the field of engineering hydraulic and fluid power lubrication. Shell tellus oil 27 has high lubrication properties and excellent low friction characteristics in hydraulic systems operating at low or high speed. Prevents stick-slip problems in critical applications enabling very fine control of machinery.Because of the reasons mentioned above shell tellus oil 27 is rated one of the best lubricant for lathe machine. Shell Tellus Oil 37 is an improved version of shell tellus oil 27. Shell Tellus Oi