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Describe the operation of two different types of cam and follower and two different types of linkage mechanism
There are three types of cam followers, and since the type of follower influences the profile of the cam it is worthwhile considering the advantages and disadvantages of each type. The three types are the knife-edge, the roller follower and the flatfoot or mushroom follower.
The knife edge follower:
This is the simplest type, is not often used due to the rapid rate of wear. When it is adopted, it is usually for reciprocating motion, running in slides and there is considerable side thrust, this being a component of the thrust from the cam.
The roller follower:
This eliminates the problem of rapid wear since the sliding effect is largely replaced by a roller action. Some sliding will still take place due to the varying peripheral speed of the cam profile, due to the changing radius of the point of contact. Note also that the radial position of the contact between the cam and the roller, relative to the follower center, will change according to whether a rise or fall motion is taken place: this fact has to be considered when constructing the cam profile. Again, with the roller follower, considerable side thrusts are present, a disadvantage when dealing with reciprocating motions. This side thrust will be increased when using small rollers.
The flat foot or mushroom follower:
This has the advantage that the only side thrust present is that due to the friction between the follower and the cam. The problem of wear is not so great as with the knife-edge follower, since the point of contact between the cam and follower will move across the face of the follower according to the change of shape of the cam. A trick to lessen further the effect of wear is to design the follower to be capable of axial rotation and arrange the axis of the follower to lie to one side of the cam. Thus the contact with the cam will tend to cause rotation of the follower. The cam profile, to work with a flatfoot follower, must be convex at all parts, in order to prevent the corners of the follower digging into the cam profile. The minimum cam radius should be as small as possible to minimize sliding velocity and friction.
It must be appreciated that this type of cam, where the follower is in contact with the edge of the cam disc, is only capable of imparting positive motion to its follower in one direction, that is, during the rise portion of the cam movement. During the fall portion of the cam movement the follower must be maintained in contact with the cam either by the mass of the follower and its mechanism or, more usually, by a spring. Both methods have their advantages
Cylindrical cams are used when motion has to be transmitted parallel to the axis of rotation of the cam. The cylindrical or barrel cam consists of a rotating cylinder with a helical (screw shaped) groove in its curved surface. A follower with a tapered roller end is located in the groove. As the cylinder turns, the follower moves in a straight line parallel to the axis of the rotation barrel cam. This type of cam is often used to guide thread on sewing machines, looms and fabric making machines.
Reverse Motion Linkage
As the top rod moves to the left the bottom rod moves to the right. The bars move in opposite directions. Another way of describing this linkage is the the direction of movement in one rod is reversed in the other rod. The fixed pivot is the centre of rotation
Crank and Slider Linkage
The rods move forwards and backwards in slider. The fixed pivots anchor the linkages to one place.
Mechanisms and mechanical devices - sourcebook
Neil Sclater, Nicholas P. Chironis
Belt and chain drives are used for the transmission of power when the centre distance between drives are relatively large and need not be very precise.
Belts are machine elements that use friction for the transfer of energy. Belts drives can absorb shock and vibration and relatively quiet. Chain drives offer the advantages of positive drive (no slip) and therefore greater power capacity.
Flat- belt. The flat as shown in Fig. is mostly used in the factories and workshops, where a moderate amount of power is to be transmitted, from one pulley to another when the two pulleys are not more than 8 metres apart. They are the simplest and the least expensive. They are used at high speed and relatively low power. They can operate on pulley diameters too small for V-belts; thus used extensively in business machines.
V- belt. The V-belt as shown in Fig. is mostly used in the factories and workshops, where a great amount of power is to be transmitted, from one pulley to another, when the two pulleys are very near to each other.
When the primary consideration is high power,V-belts are used instead of flat belts. In terms of low cost and space, v-belts provide the best overall power transmission capability for the normal range of power requirements
The roller chain is used to transmit motion between rotating shafts via sprockets mounted on the shafts.Roller chains are generally manufactured from high specification steels and are therefore capable of transmitting high torques within compact space envelopes. Compared to belt drives the chain drives can transmit higher powers and can be used for drives with larger shaft centre distance separations.
Leaf chains generally have greater tensile strength than roller chains, and run over sheaves rather than sprockets. They are most often used as counterweight chains for machine tools, elevator and oven doors, fork lift truck masts, spinning frames and similar lifting or balancing applications. BL series can, in most instances, replace the older AL series Leaf chains; consult U.S. Tsubaki for interchange information.
These chains are supplied with male or female terminations to allow addition of various clevises as desired.
A SPUR GEAR is cylindrical in shape, with teeth on the outer circumference that are straight and parallel to the axis (hole). There are a number of variations of the basic spur gear, including pinion wire, stem pinions, rack and internal gears.
A helical gear is similar to a spur gear except that the teeth of a helical gear are cut at an angle (known as the helix angle) to the axis (or hole). Helical gears are made in both right and left hand configurations. Opposite hand helical gears run on parallel shafts. Gears of the same hand operate with shafts at 90-degrees.
Transmission Shaft and Coupling
A flexible coupling is used to connect two shafts, end-to-end in the same line, for two main purposes. The first purpose is to transmit power that is torque from one shaft to another, thereby causing both to rotate in unison, at the same RPM. The second purpose is to compensate for small amounts of misalignment and random movement between the two shafts. Flexible couplings are made of elastic materials, like rubber, or have various other configurations. During rotation, flexible couplings can accommodate misalignment and motion.
How flexible coupling operates
It is a known fact that in any direct mechanical drive system, there is the need to couple the variety of driven elements that are included. The majority of drive elements which include gear reducers, lead screws, and a host of other components, are driven by shafting. The shafting is supported by multiple bearings. This allows the shafting to be held extremely straight and rigid while rotating which at the same time avoid any kind of possible balancing and support problems. Because of this rigid support, it practically becomes impossible to avoid slight misalignments between a driving and driven shaft when they are connected
Rigid coupling Rigid couplings are used to connect rotating members such as shafts. They are compact, economical components for the timing, joining or aligning of shafts and provide transmission of torque and motion. They are used at lower speeds, particularly where zero backlashes is desired. These type of couplings do not allow for angular or parallel misalignment. Rigid couplings are also not intended for use as a critical part of a drive line or as a substitute for flexible or universal joints. They are also not meant for other power transmission devices. They are basically used for aligned shafts only. They are the most cost-effective coupling option suitable for all rigid shaft connections. These couplings comprise simple hollow cylinders having internal diameters of the proper size which can fit over the shaft ends being joined. The length of the coupling depends on the desired shaft gap between ends. For light applications, setscrews are used to attach the shafts to the coupling. This type of coupling do not accommodate for misalignment
Internal Expanding Brakes
Internal expanding brakes are used almost exclusively as wheel brakes, but can be found on some cranes. This type of brake permits a more compact and economical construction. The brake shoes and brake-operating mechanism are supported on abacking plate or brake shield attached to the vehicle axle. The brake drum, attached to the rotating wheel, acts as a cover for the shoe and operating mechanism and furnishes a frictional surface for the brake shoes. The brake shoe of an internal expanding brake is forced outward against the drum to produce the braking action. One end of the shoe is hinged to the backing plate by an anchor pin, while the other end is unattached and can be moved in its support by the operating mechanism. When force from the operating mechanism is applied to the unattached end of the shoe, the shoe expands and brakes the wheel. A retracting spring returns the shoe to the original position when braking action is no longer required.
The disc brake is a device for slowing or stopping the rotation of a wheel. A brake disc is usually made of cast iron or ceramic, is connected to the wheel or the axle. To stop the wheel, friction material in the form of brake pads (mounted in a device called a brake calliper) is forced mechanically, hydraulically or pneumatically against both sides of the disc. Friction causes the disc and attached wheel to slow or stop.
The main components of a disc brake are:
The disc brake is a lot like the brakes on a bicycle. Bicycle brakes have a caliper, which squeezes the brake pads against the wheel. In a disc brake, the brake pads squeeze the rotor instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down.
A moving car has a certain amount of kinetic energy, and the brakes have to remove this energy from the car in order to stop it. How do the brakes do this? Each time you stop your car, your brakes convert the kinetic energy to heat generated by the friction between the pads and the disc. Most car disc brakes are vented.
Vented disc brakes have a set of vanes, between the two sides of the disc,that pumps air through the disc to provide cooling.
Clutch is a mechanical device used to engage or disengaged the driving and driven shaft instantaneously without stopping it using clutch pedal.
There are many different vehicle clutch designs but most are based on one or more friction discs, pressed tightly together or against a flywheel using springs. The friction material is very similar to the material used in brake shoes and pads and contained asbestos in the past. Also, clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient, however these have a "grabby" action and are unsuitable for road cars. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate, depending on type, and the friction plate is released and allowed to rotate freely.
While engaging the clutch, the engine speed may need to be increased from idle, using the manual throttle, so that the engine does not stall (although in most cars, especially diesels, there is enough power at idling speed that the car can move although fine movements with the clutch are needed). However, raising the engine speed too high will cause excessive clutch plate wear and cause a harsh, jerky start. This kind of start is desired in drag racing and other competitions, however.
Wet and dry clutches
A 'wet clutch' is immersed in a cooling lubricating fluid, which also keeps the surfaces clean and gives smoother performance and longer life. A 'dry clutch', as the name implies, is not bathed in fluid that robs it of some energy. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch disks can compensate for slippage. Most Moto Guzzi and BMW motorcycles use a triple plate clutch like a car.
Pneumatic systems are usually good for work which requires tow discrete states, such as in gear shifters, lifters, brakes, and on anything which requires a significant amount of force or displacement.
A - Compressor: a pump which compresses air, raising it to a higher pressure, and delivers it to the pneumatic system (sometimes, can also be used to generate a vacuum).
B - Check valve: one-way valve that allows pressurized air to enter the pneumatic system, but prevents backflow (and loss of pressure) into the compressor when it is stopped.
C - Accumulator: stores compressed air, preventing surges in pressure and relieving the duty cycle of the compressor.
D - Directional valve: controls the flow of pressurized air from the source to the selected port. Some valves permit free exhaust from the port not selected. These valves can be actuated either manually or electrically (the valves typically provided in the FIRST kits use dual solenoids to change the direction of the valve, based on input signals from the control system).
E - Actuator: converts energy stored in the compressed air into mechanical motion. A linear piston is shown. Alternate tools include rotary actuators, air tools, expanding bladders, etc.
The Hydraulic Actuator is quite similar to the Pneumatic Actuator, but it is simpler than the Pneumatic Actuator. The Hydraulic Actuator has a cylinder. The cylinder contain a piston and on one side it has a spring which pushes the piston down and the other side the cylinder is filled with hydraulic fluid.
The Fluid is passed through 'Hydraulic Supply and Return line'. The fluid pushes the piston up and takes the stem along. The stem is under motion and positions the control valve. Control valve is positioned to its position that the operator demanded. The hydraulic Fluid can be adjusted by 'Hydraulic Supply and Return line', which also adjust the piston and also the 'Control valve'.
MECHANICAL HANDLING SYST
- Refrigeration is the removal of heat from a material or space, so that its temperature is lower than that of its surroundings.
- When refrigerant absorbs the unwanted heat, this raises the refrigerant's temperature ("Saturation Temperature") so that it changes from a liquid to a gas - it evaporates. The system then uses condensation to release the heat and change the refrigerant back into a liquid. This is called "Latent Heat".
- This cycle is based on the physical principle, that a liquid extracts heat from the surrounding area as it expands (boils) into a gas.
- To accomplish this, the refrigerant is pumped through a closed looped pipe system.
- The closed looped pipe system stops the refrigerant from becoming contaminated and controls its stream. The refrigerant will be both a vapor and a liquid in the loop.
There are four main components in a refrigeration system:
- The Compressor
- The Condensing Coil
- The Metering Device
- The Evaporator
Two different pressures exist in the refrigeration cycle. The evaporator or low pressure, in the "low side" and the condenser, or high pressure, in the "high side". These pressure areas are divided by the other two components. On one end, is the metering device which controls the refrigerant flow, and on the other end, is the compressor.
Air Conditioning System
The Compressor transports the refrigerant atthe required pressure through the air conditioning system. The refrigerant is a low-pressure gas as it enters the Compressor from the Evaporator.
The Condenser works in the opposite way to the Evaporator. The refrigerant gives up its heat generated by the Compressor by passing cold air across its fins and tubes by ram air or by an extra fan.
Depending on the type of air conditioning system fitted, this item can be called a Receiver Drier or an Accumulator.(The Accumulator is fitted onthe low-pressure gas line of an air conditioning system between the Compressor and the Evaporator and is used in conjunction with an orifice tube)
The Expansion Device comes in many forms. It can be a brass internally or externallyequalised valve,a block type valveor an orifice tube (the latter being part of an Accumulator type air conditioning system).
As soon as the liquid pressure drops, the refrigerant begins to boil (R134A refrigerant boils at approximately -26 degrees centigrade).
1. Coal and ash handling plant
The coal is transported from different places to the station by means of rails or road and is stored in a coal storage plant.
2. Steam Generating Plant
The steam generating plant consists of boiler and its auxiliary equipments for the utilisation of flue gases.
- 2.1 Boiler
The heat produced by the burning of coal in the boiler is used to produce steam at high temperature and pressure.
2.2 Super Heater
The steam produced in the boiler has got moisture content so it is dried and superheated (ie steam temperature is increased above boiling point of water) by the flue gases on the way to chimney.
Economiser is a feed water heater. It uses the heat produced by the flue gases for this purpose.
2.4 Air preheater
Air preheater increases the temperature of the air supplied to coal for combustion using flue gases.
3. Steam Turbine
The dry and super heated steam from superheater is fed to the turbine by means of a main valve.
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.
5. 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.
6. Cooling Arrangement
In order to increase the efficiency of the plant the steam coming from the turbine is condensed using a condenser. In scarcity of water the water from the condenser is cooled and reused with the help of a cooling tower.