Introduction to Mechanical Engineering PDF

INTRODUCTION TO MECHANICAL ENGINEERING 102902/CO100E DR. ATHUL SATHYANATH ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING Class hours: IME S1 ME B 1 2 3 4 5 6 MON TUE WED THU FRI SYLLABUS MARKING SCHEME TEXTBOOK...

INTRODUCTION TO MECHANICAL ENGINEERING 102902/CO100E DR. ATHUL SATHYANATH ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING Class hours: IME S1 ME B 1 2 3 4 5 6 MON TUE WED THU FRI SYLLABUS MARKING SCHEME TEXTBOOKS COURSE OUTCOMES  Power transmission  Movement of energy from its place of generation to a location suitable for extracting useful work.  General mode of transmission: Between shafts  Driver shaft – Shaft from which power is transmitted. Driven shaft – Shaft to which power is transmitted.  Focus: Transmission of mechanical power from one shaft to another – Mechanical drive Power transmission  General methods of mechanical drives: o Belt drive o Chain drive o Gear drive o Single plate clutch  The choice of drive depends on: o Distance between shafts o Amount of power o Speed ratio of shafts o Accuracy required Belt drive  Generally used when driving and driven shafts are at a considerable distance apart (up to 15 m).  Pulleys mounted on driver and driven shafts; Endless belt fitted tightly over the pulleys.  Factor responsible for power transmission: Frictional resistance between belt and pulley.  Amount of power transmission depends on: o Velocity of belt o Tension of belt o Arc of contact of belt and smaller pulley  Belt drive  Belts: o A thin inextensible band made of leather, rubber, balata, steel, cotton or fabric. o Must possess large strength, flexibility and life, and high coefficient of friction. o Types – based on shape: i. Flat belts ii. V-belts Belt drive Flat belts V-Belts For moderate power transmission For higher power transmission Distance between shafts: up to 10 m Distance between shafts: 1.5 times larger pulley diameter. Rectangular cross-section Trapezoidal cross-section Less frictional grip. Leads to slip More frictional grip. Lesser slip Used in sawmills, conveyors, electrical Used in automotive and agricultural generators. purposes. Belt drive Belt drive  Types of belt drives: Open belt drive Cross belt drive Used with shafts arranged in parallel and Used with shafts arranged in parallel and to be rotated in the same direction. to be rotated in opposite direction. Tension on belt will be different. Crossing of belts occurs. High tension side – Tight side To minimize wear, shafts to be placed at Low tension side – Slack side a minimum distance of 20b, where b is belt width. Speed of belt should be less than 15 m/s. Belt drive  Types of belt drives: Open belt drive Cross belt drive Chain drive  Consists of endless chain running over special profile toothed wheels called sprockets.  Consists of driver and driven sprockets.  Smaller sprocket – pinion; Larger sprocket – wheel.  Parts of chain: plates, pin, bushing. Material: High grade steel. Chain drive  Classification based on application: o Power transmission chains – for transmitting power from one shaft to another. o Hoisting chains – for lifting loads o Pulling chains – used in elevators and conveyors  Chain drive  Types of chains: i. Roller chain o Consists of rollers, bushes, pins, inner and outer plates. o Pin passes centrally through bush; Roller surrounds the bush. o Two adjacent rollers are held by two inner plates – Roller link plates. o Two adjacent pins are held by two outer plates – Pin link plates. ii. Silent or inverted tooth chain o Consists of special profile plates corresponding to profile of sprocket teeth. o Complex in design. o Employed for heavier loads and silent operation. Gear drive  Consists of toothed wheels called gears.  Gears are mounted on driving and driven shafts. Teeth of gears are in mesh.  Distance between shafts just sufficient to enable meshing of gears.  Gear teeth formed by: casting or machine cutting. o Machine cutting include milling, shaping, hobbing.  Gear material: Grey cast iron, cast steel, alloy steel, phosphor, bronze, nickel, etc.  Gear drive  Types of gears: i. Spur gears o Teeth cut parallel to axis of shaft. o Transmit power between parallel shafts. ii. Helical gears o Teeth cut inclined to axis of shaft. o Transmit power between parallel shafts.  Gear drive  Types of gears: iii. Bevel gears o To connect non-parallel shafts with intersecting axes. o Generally used to connect shafts at right angles. iv. Worm gears o To connect non-intersecting shafts at right angles to each other. o Consists of worm as driver and worm wheel as driven wheel. Gear train  Combination of gear wheels for power transmission from one shaft to another.  Types of gear train: i. Simple gear train ii. Compound gear train iii. Reverted gear train iv. Epicyclic gear train  Gear train  Simple gear train: o Each shaft carries one gear only. o Intermediate gears act as both driver and driven gears. o Intermediate gears are known as ‘idlers’. They have no effect on velocity ratio. o For odd number of idlers – driver and driven gears rotate in same direction; For even number of idlers – driver and driven gears rotate in opposite direction.  Gear train  Compound gear train: o Two or more gears rotate about same axis. o Intermediate shafts carry more than one gear. o Speed ratio depends on diameters of driver, driven and intermediate gears.  Gear train  Reverted gear train: o Axes of the first and last gears coincide. o Used in automotive transmissions, industrial speed reducers, clock (minute and hour hands are coaxial), etc.  Gear train  Epicyclic (or planetary) gear train: o Axis of rotation of at least one gear rotates about the fixed axis of rotation of another gear. o Ex: Differential mechanism in automobiles