Studied by 44 people
uhmm ano, ehe hihiihi
SHAFT
•A ______ is a rotating member usually of circular cross-section (solid or hollow), which transmits power and rotational motion.
•Machine elements such as gears, pulleys (sheaves), flywheels, clutches, and sprockets are mounted on the shaft and are used to transmit power from the driving device (motor or engine) through a machine.
•Press fit, keys, dowel, pins and splines are used to attach these machine elements on the shaft.
SHAFT
•The _____rotates on rolling contact bearings or bush bearings.
•Various types of retaining rings, thrust bearings, grooves and steps in the shaft are used to take up axial loads and locate the rotating elements.
•Couplings are used to transmit power from the drive shaft (e.g., motor) to the driven shaft (e.g. gearbox, wheels).
AXLE
•used for shafts that support rotating elements like wheel, hoisting drum or rope sheave and which is fitted to the housing by means of bearing. It is subjected to bending moment due to transverse loads like bearing reactions and does not transmit any useful torque.
SPINDLE
•a short rotating shaft. It originated from the round tapering stick on the spinning wheel on which the thread is twisted. Spindles are used in all machine tools such as a small drive shaft of lathe or the spindle of a drilling machine.
COUNTERSHAFT
•it is a secondary shaft, which is driven by the main shaft and from the power is supplied to a machine component. It is driven by the main shaft by means of a pair of spur or helical gears and the route counter to the direction of the main shaft. It is used for multistage gearboxes.
JACKSHAFT
– it is an auxiliary or intermediate shaft between two shafts that are used in transmission of power. Its function is the same as the countershaft.
LINE SHAFT
consists of a number of shafts which are connected in axial direction by means of coupling. Line shafts were popular in workshops using group drive.
Shear stresses
due to the transmission of torque (i.e. due to torsional load).
Bending stresses
(tensile or compressive) due to the forces acting upon machine elements like gears, pulleys etc. as well as due to the weight of the shaft itself.
Transmission shafts
These shafts transmit power between the source and the machines absorbing power. The counter shafts, line shafts, overhead shafts and all factory shafts are transmission shafts. Since these shafts carry machine parts such as pulleys, gears etc., therefore they are subjected to bending in addition to twisting.
Machine shafts
These shafts form an integral part of the machine itself. The crank shaft is an example of a machine shaft.
Torsional rigidity
is important in the case of camshaft of an I.C. engine where the timing of the valves would be affected. The permissible amount of twist should not exceed 0.25° per meter length of such shafts. For line shafts or transmission shafts, deflections 2.5 to 3 degree per meter length may be used as limiting value. The widely used deflection for the shafts is limited to 1 degree in a length equal to twenty times the diameter of the shaft.
Lateral rigidity
It is important in case of transmission shafting and shafts running at high speed, where small lateral deflection would cause huge out-of-balance forces.
is also important for maintaining proper bearing clearances and for correct gear teeth alignment. If the shaft is of uniform cross-section, then the lateral deflection of a shaft may be obtained by using the deflection formulae as in Strength of Materials.
A KEY
can be defined as a machine element, which is used to connect the transmission shaft to rotating machine elements like pulley, gear, sprocket or flywheel. A keyed joint consisting of shaft, hub and key. There are two basic functions of the key. They are as follows
Keyway
A recess or slot machines either in the shaft or in the hub to accommodate the key is called a keyway. The keyway is usually cut by vertical or horizontal milling cutters.
results in stress concentration in the shaft and the part becomes weak. This is the main drawback of keyed joints
Saddle key and sunk key
fits in keyway of the hub only (no keyway on the shaft
Square key and flat key
half of the thickness of key fits into the keyway of the shaft
Woodruff key
is a sunk key in the form of almost semicircular disk
Feather key
is a parallel key, which is fixed either to the shaft or to the hub
COUPLINGS
A mechanical device that permanently joints two rotating shafts to each other. The shafts that are connected by the coupling can be disengaged only after dismantling the ________
Rigid coupling
connects two shafts which are perfectly aligned. Following types of rigid coupling are important from the subject point of view:
Flexible coupling
connects two shafts having both lateral and angular misalignment. Following types of rigid coupling are important from the subject point of view:
BEARING
a machine element which supports another moving machine element (known as journal). It permits a relative motion between the contact surfaces of the members, while carrying the load.
radial bearings
the load acts perpendicular to the direction of motion of the moving element
thrust bearings
- the load acts along the axis of rotation
sliding contact bearings
the sliding takes place along the surfaces of contact between the moving element and the fix element. It is also known as plain bearings.
rolling contact bearings
the steel balls or rollers are interposed between the moving and fix elements. the bowls of a rolling friction at two points for each ball or roller.
full journal bearing
When the angle of contact of the bearing with the journal is 360° then it is called full journal bearing. This type of bearing is commonly used in industrial machinery to accommodate bearing loads in any radial direction
partial journal bearing
when the angle of contact of the bearing with the journal is 120 degrees is said to be partial journal bearing. This type of bearing has less friction than full journal bearing, but it can be used only where the load is always in one direction. The most common application of partial journal bearing is found in railroad car axles.
fitted journal bearing
when a partial journal bearing has no clearance letter example the diameter of the journal and bearing are equal it is called fitted bearing.
thick film bearings
the thick film bearings are those in which the working surfaces are completely separated from each other by the lubricant. Such bearings are also called hydrodynamic lubricated bearings.
thin-film bearings
the film bearings are those in which all the lubricant is present, and the working surfaces partially contact each other at least part of the time. Such bearings are also called boundary lubricated bearings.
Zero film bearings
are those which operate without any lubricant present.
hydrostatic or externally pressurized lubricated bearings
are those which can support steady loads without any relative motion between the journal and the bearing. This is achieved by forcing externally pressurized lubricant between the members.
compressive strength
the maximum bearing pressure is considerably greater than the average pressure obtained by dividing the load to the projected area. Therefore, the bearing material should have high compressive strength to withstand this maximum pressure so as to prevent extrusion or other permanent deformation of the bearing.
fatigue strength
the bearing material should have sufficient fatigue strength so that it can withstand repeated loads without developing surface fatigue crack. it is a major importance in aircraft and automotive engines.
conformability
it is the ability of the bearing material to accommodate shaft deflections and pairing inaccuracies by plastic deformation (or creep) without excessive wear and heating.
embeddability
the ability of bearing material to accommodate (or embed) small particles of dust, grit etc., without scoring the material of the journal.
bondability
many high capacity bearings are made of bonding one or more thin layers of a bearing material to a high strength steel shell. Thus, the strength of the bond is an important consideration in selecting bearing materials.
corrosion resistance
the bearing material should not corrode away under action of lubricating oil. This property is of particular importance in internal combustion engines where the same oil is used to lubricate the cylinder walls and bearings. In the cylinder, the lubricating oils come into contact with hot cylinder walls and may oxidize and collect carbon deposits from the walls
thermal conductivity
the bearing material should be of high thermal conductivity so as to permit the rapid removal of heat generated by friction
thermal expansion
The bearing material should be of low coefficient of thermal expansion so that the bearing operates over a wide range of temperature, there is no undue change in the clearance.
lubricants
are used in bearings to produce friction between the rubbing surfaces and to carry away the heat generated by friction; it also protects the bearing against corrosion. can be classified as liquid, semi-liquid like grease, and solid lubricants like graphite.
Viscosity
measure of degree of fluidity of a liquid. It is a physical property by virtue of which an oil is able to form, retain and offer resistance to shearing a buffer film under heat and pressure. The greater the heat and pressure, the greater viscosity is required of a lubricant to prevent staining and squeezing out of the film.
Oiliness
is a joint property of the lubricant and bearing surfaces in contact. It is a measure of lubricating qualities under boundary conditions or base metal to metal is prevented only by absorbed film. There is no absolute measure of oiliness.
Density
the property has no relation to lubricating value but is useful in changing the kinematic viscosity to absolute viscosity
viscosity index
is used to denote the degree of variation of viscosity with temperature
flashpoint
- the lowest temperature at which an oil gives off sufficient vapor to support a momentary flash without actually setting fire to the oil when a flame is brought within 6 mm at the surface of the oil
fire point
the temperature at which an oil gives off sufficient vapor to burn it continuously when ignited
freezing point
Temperature at which an oil will cease to flow when cooled.
Solid journal bearing
- is the simplest form of journal bearing it is simply a block of cast iron with the whole for a shaft providing running fit. The lower portion of the block is extended to form a base plate or sole with two holes to receive a bolt for fastening it to the frame. an oil hole is drilled at the top for lubrication.
Bushed bearing
- is an improvement of solid bearing in which a bush of brass or gunmetal is provided. The outside of the bush is driving a fit in the whole of the casting whereas the inside is a running fit for the shaft.
Split bearing or plummer block
It is used for shafts running at high speeds and carrying heavy loads. A ____bearing consists of a cast iron base, a gun metal, phosphor bronze brasses, butches or steps made into halves and cast-iron cap
Thrust bearing
it is used to guide or support the shaft which is subjected to a load along the axis of the shaft.
Footstep or pivot bearings
suitable for slow running and lightly loaded shaft. If the shaft is not steel, its end must be fitted with a steel face.
Collar Bearing
the shafts continue through the bearing. The shaft may be vertical or horizontal, with a single collar or many collars. The colors are either integral parts of the shaft or rigidly fastened to it.
Rolling Contact Bearing
- In ______, the contact between the bearing surfaces is rolling instead of sliding as in sliding contact bearings. It is an outstanding advantage of a rolling contact bearing over sliding bearing that it has low starting friction. Due to this low friction offered by rolling contact bearings, these are called antifriction bearings.
GEAR
is a kind of machine element in which teeth are cut around cylindrical or cone shaped surfaces with equal spacing. By meshing a pair of these elements, they are used to transmit rotations and forces from the driving shaft to the driven shaft.
Spur Gear
Gears having cylindrical pitch surfaces are called cylindrical gears. Spur gears belong to the parallel shaft gear group and are cylindrical gears with a tooth line which is straight and parallel to the shaft.
Helical Gear
gears are used with parallel shafts similar to spur gears and are cylindrical gears with winding tooth lines. They have better teeth meshing than spur gears and have superior quietness and can transmit higher loads, making them suitable for high speed applications.
Gear Rack
Same sized and shaped teeth cut at equal distances along a flat surface or a straight rod is called a gear rack. A_______ rack is a cylindrical gear with the radius of the pitch cylinder being infinite.
Bevel Gear
have a cone shaped appearance and are used to transmit force between two shafts which intersect at one point (intersecting shafts). A_____gear has a cone as its pitch surface and its teeth are cut along the cone.
Spiral Bevel Gear
bevel gears are bevel gears with curved tooth lines. Due to higher tooth contact ratio, they are superior to straight bevel gears in efficiency, strength, vibration and noise.
Screw Gear
are a pair of same hand helical gears with the twist angle of 45° on non-parallel, non-intersecting shafts. Because the tooth contact is a point, their load carrying capacity is low and they are not suitable for large power transmission
Miter Gear
are bevel gears with a speed ratio of 1. They are used to change the direction of power transmission without changing speed.
Worm Gear
A screw shape cut on a shaft is the worm, the mating gear is the worm wheel, and together on non-intersecting shafts is called a ______
Internal gear
have teeth cut on the inside of cylinders or cones and are paired with external gears. The main use of internal gears are for planetary gear drives and gear type shaft couplings.
cast iron
is widely used for the manufacture of gears due to its good wearing properties, excellent machinability and ease of producing complicated shapes by casting method
The steel
used for high strength gears and steel may be plain carbon steel or alloy steel.
phosphor bronze
______is widely used for worm gears in order to reduce wear of the worms which will be excessive with cast iron or steel.
Grasping Mechanism
Use two spur gears of the same diameter in mesh so that when the driver gear is reversed, the driven gear is also reversed
Intermittent Motion Mechanism
There is the Geneva mechanism as an intermittent motion mechanism. However, because of need for the specialized mechanical components, it is high priced. By using the missing teeth gears, a low cost and simple intermittent mechanism can be obtained.
Special Power Transmission Mechanism
By mounting a one-way clutch (a mechanism that allows rotational motion in one direction only) in one stage of a gear train of a gear speed reducer, you can create a mechanism which transmits motion in one direction but idles in reverse.
Note
Flashcard