clutch.Clutch is a transmission device of an automobile which is used to engage anddisengage the power from the engine to the rest of the system.
the types of friction clutches
Types of friction clutches are:
*Disc or plate clutches.
*Cone clutches.
*Centrifugal clutches.
centrifugal clutch.Centrifugal clutch is being increasingly used in automobile and machinesobviously it works on the principle of centrifugal force.
the types of flat drives The types of flat drives are:
*Compound belt drive.
*Stepped or cone pulley drive.
*Fast and loose pulley.
slip.Slip is defined as the relative motion between the belt and pulley.
law of belting.Law of belting states that the centre line of the belt, as if approaches the pulley liein a plane perpendicular to the axis of that pulley or must lie in the plane of the pulleyotherwise the belt will run off the pulley.
Rope drive: Utility.The rope drives are widely used when large power is to be transmittedcontinuously from one pulley to another over a considerable distance. One advantage ofrope drives is that a number of separate driver may be from the driving pulley
Belt drive: Utility.Belt drive is commonly used for transmission of power when exact velocity ratiois not required. Generally, belt drives are used to transmit power from one pulley toanother, when the two pulleys are not more than 10 meters apart.
the types of ropes The types of ropes are:*Fiber ropes.*Wire ropes.
Quarter turn left drive. The quarter turn left drive is used with shafts arranged at right angles and rotatingin one definite direction.
the velocity ratio of the belt drive.The velocity ratio of the belt drive is defined as the ratio between the velocities ofthe driver and the follower or the driven.
Advantages of V-belt.*Power transmitted is more due to wedging action in the grooved pulleys.*V-belt is more compact, quite and shock absorbing.*The V-belt drive is positive because of negligible slip between the belt and thegroove.*High velocity ratio may be obtained.
Disadvantages of V-belt.*It cannot be used with large center distances.*It is not as durable as flat belt.*It is a costlier system.
Circular belts or ropes.*Ropes are circular in cross section.*It is used to transmit more power.*Distance between two pulleys is more than 8metres.
Belt materials.BELT TYPES BELT MATERIALSFlat belts Leather, canvas, cotton & rubber.V-belts Rubberized fabric & rubber.Ropes Cotton, hemp & manila.
Name the types of friction.*Static friction.*Dynamic friction.
frictional force Force of friction is always acting in the direction opposite to the direction ofmotion.
self locking screws have lesser efficiency Self locking needs some friction on the thread surface of the screw and hence itneeds higher effort to lift a body and hence automatically the efficiency decreases.
static friction It is the friction experienced by a body, when at rest.
dynamic friction It is the friction experienced by the body, when in motion. The dynamic friction isalso called as kinematic friction.
screw jack.The screw jack is the device used to lift the heavy loads by applying acomparatively small effort at its handle. The working principle of screw jack is similar tothat of an inclined plane.
Square thread vs V-thread.*V-thread is stronger and often moves frictional to the motion than squarethreads.*A given load may be lifted by applying lesser force by square thread ascompared to V-threads.*V-threads are capable of taking more loads as compared to square threads
Tuesday, September 23, 2008
Monday, September 22, 2008
Basic mechanical engineering: gear
Define spur gear.A spur gear is a cylindrical gear whose tooth traces are straight line generation
of the reference cylinder. They are used to transmit rotary motion between
parallel shafts.
Define addendum and dedendum.Addendum is the radial distance of a tooth from the pitch circle to the top of thetooth.
Dedendum is the radial distance of a tooth from the pitch circle to the bottom of
the tooth.
Define circular pitch.It is the distance measured on the circumference of the pitch circle from a point
of one tooth to the corresponding point on the next tooth. It is denoted by Pc
Circular pitch Pc= P/DT
Where D = Diameter of pitch circle.
T = Number of teeth on the wheel.
Path of contact: It is the path traced by the point of contact of two teeth from the
beginning to the end of engagement.
Length of path of contact: It is the length of common normal cut- off by the
addendum circles of the wheel and pinion.
law of gearing.Law of gearing states that, the common normal at the point of contact between a pairof teeth must always pass through the pitch point.
conjugate action.When the tooth profiles are so shaped so as to produce a constant angular velocity ratioduring Meshing, then the surface are said to de conjugate.
angle of approach.The angle of approach is defined as the angle through which a gear rotates from the instant a pair of teeth comes into contact until the teeth are in contact at the pitch point.
the characteristics of in volute action.
a) Arc of contact.
b) Length of path of contact.
c) Contact ratio.
contact ratio.Contact ratio is defined as the ratio of the length of arc of contact to the circular pitch mathematically.
Contact ratio = length of arc of contact Pc
Where Pc = circular path.
the advantage of in volute gear The most important advantage of involutes gear is that the center distance for a pair of involute gears can be varied within limits without changing the velocity ratio.
the conditions to be satisfied for interchangeability of all gears.For interchangeability of all gears, the set must have the same circular pitch, module,diameter pitch, pressure, angle, addendum and dedendum and tooth thickness must be one half of the circular pitch.
gear tooth system.A tooth system is a standard which specifies the relationship between addendum,dedendum, working depth, tooth thickness and pressure angle to attain
interchangeability of gears of tooth numbers but of the same pressure angle and pitch
cycloid.A cycloid is the curve traced by a point on the circumference of a circle which rolls
without slipping on a fixed straight line.
clearance.The amount by which the dedendum of a gear exceeds the addendum of the mating
gear is called clearance.
in volute interference occurs.If the teeth are of such proportion that the beginning of contact occurs before the interference point is met then the involute proportion of the driven gear will mate a non in volute portion of the driving gear and involute interference is said to occur.
the principle reason for employing non standard gears
a) To eliminate the undercutting.
b) To prevent interference.
c) To maintain reasonable contact ratio.
the advantages and disadvantages of gear drive.
Advantages:
a) It transmits exact velocity ratio.
b) It has high efficiency.
Disadvantages:
a) The manufacture of gears require special tool and equipment.
b) The error in cutting teeth may cause vibrations and noise during operation.
helix angle (b).It is the angle between the line drawn through one of the teeth and the center line of the shaft on which the gear is maintained.
gear ratio.The quotient of the number of teeth on the wheel divided by the number of threads on
the worm.
gear train.A combination of gears that is used for transmitting motion from one shaft to another
shaft is known as gear train.
E.g. spur gear, spiral gear.
velocity ratio.Velocity ratio of a simple gear train is defined as the ratio of the angular velocity of
the first gear in the train to the angular velocity of the last gear.
epicycles gear train.In a gear train when the axes of shafts over which the gears are mounted move relative to a fixed axis is called epicyclic gear train..
the function of differential gear used in the rear drive of an automobile.
a) To transmit motion from the engine shaft to the rear driving wheels.
b ) To rotate the rear wheel of different speeds while the automobile is taking a turn.
bevel gears.The gears which are used to connect shafts whose axes of rotation intersect are called bevel gears.
limited slip differential.The coupling unit which is sensitive to wheel speed causes most of the torque to be directed to the slow moving wheel. This combination is called limited slip
differential
of the reference cylinder. They are used to transmit rotary motion between
parallel shafts.
Define addendum and dedendum.Addendum is the radial distance of a tooth from the pitch circle to the top of thetooth.
Dedendum is the radial distance of a tooth from the pitch circle to the bottom of
the tooth.
Define circular pitch.It is the distance measured on the circumference of the pitch circle from a point
of one tooth to the corresponding point on the next tooth. It is denoted by Pc
Circular pitch Pc= P/DT
Where D = Diameter of pitch circle.
T = Number of teeth on the wheel.
Path of contact: It is the path traced by the point of contact of two teeth from the
beginning to the end of engagement.
Length of path of contact: It is the length of common normal cut- off by the
addendum circles of the wheel and pinion.
law of gearing.Law of gearing states that, the common normal at the point of contact between a pairof teeth must always pass through the pitch point.
conjugate action.When the tooth profiles are so shaped so as to produce a constant angular velocity ratioduring Meshing, then the surface are said to de conjugate.
angle of approach.The angle of approach is defined as the angle through which a gear rotates from the instant a pair of teeth comes into contact until the teeth are in contact at the pitch point.
the characteristics of in volute action.
a) Arc of contact.
b) Length of path of contact.
c) Contact ratio.
contact ratio.Contact ratio is defined as the ratio of the length of arc of contact to the circular pitch mathematically.
Contact ratio = length of arc of contact Pc
Where Pc = circular path.
the advantage of in volute gear The most important advantage of involutes gear is that the center distance for a pair of involute gears can be varied within limits without changing the velocity ratio.
the conditions to be satisfied for interchangeability of all gears.For interchangeability of all gears, the set must have the same circular pitch, module,diameter pitch, pressure, angle, addendum and dedendum and tooth thickness must be one half of the circular pitch.
gear tooth system.A tooth system is a standard which specifies the relationship between addendum,dedendum, working depth, tooth thickness and pressure angle to attain
interchangeability of gears of tooth numbers but of the same pressure angle and pitch
cycloid.A cycloid is the curve traced by a point on the circumference of a circle which rolls
without slipping on a fixed straight line.
clearance.The amount by which the dedendum of a gear exceeds the addendum of the mating
gear is called clearance.
in volute interference occurs.If the teeth are of such proportion that the beginning of contact occurs before the interference point is met then the involute proportion of the driven gear will mate a non in volute portion of the driving gear and involute interference is said to occur.
the principle reason for employing non standard gears
a) To eliminate the undercutting.
b) To prevent interference.
c) To maintain reasonable contact ratio.
the advantages and disadvantages of gear drive.
Advantages:
a) It transmits exact velocity ratio.
b) It has high efficiency.
Disadvantages:
a) The manufacture of gears require special tool and equipment.
b) The error in cutting teeth may cause vibrations and noise during operation.
helix angle (b).It is the angle between the line drawn through one of the teeth and the center line of the shaft on which the gear is maintained.
gear ratio.The quotient of the number of teeth on the wheel divided by the number of threads on
the worm.
gear train.A combination of gears that is used for transmitting motion from one shaft to another
shaft is known as gear train.
E.g. spur gear, spiral gear.
velocity ratio.Velocity ratio of a simple gear train is defined as the ratio of the angular velocity of
the first gear in the train to the angular velocity of the last gear.
epicycles gear train.In a gear train when the axes of shafts over which the gears are mounted move relative to a fixed axis is called epicyclic gear train..
the function of differential gear used in the rear drive of an automobile.
a) To transmit motion from the engine shaft to the rear driving wheels.
b ) To rotate the rear wheel of different speeds while the automobile is taking a turn.
bevel gears.The gears which are used to connect shafts whose axes of rotation intersect are called bevel gears.
limited slip differential.The coupling unit which is sensitive to wheel speed causes most of the torque to be directed to the slow moving wheel. This combination is called limited slip
differential
for more basic concept see this
I found this is one of the very important link for the mechanical engineering student
http://www.engineersedge.com/Design_Data.shtml
http://www.engineersedge.com/Design_Data.shtml
Tuesday, September 16, 2008
Basic of mechanical :cam
cam
Cam is a rotating mechanical member used for transmitting desired motion to afollower by direct contact
Classification of cam
(i) according to cam shape
(ii) according to follower movement
(iii) according to manner of constraint of the follower
Classify cam based on a shape
(i) wedge cam
(ii) radial cams
(iii) spiral cams
(iv) drum cams
(v) spherical cams
classification of follower
(i) According to follower shape
(ii)according to motion of follower
roller followerIn place of a knife edge roller is provided at the contacting end of the follower
Spherical follower In the contacting end of the follower is of spherical shape
Angle of ascend The angle of rotation of the cam from the position when the follower begins to risetill it reaches its highest points
Angle of descend The angle through which the cam rotates during the time the follower returns to
Angle of dwell It is the angle through which the cam rotates while the follower remains stationary atthe highest or the lowest
Angle of action The total angle moved by the cam during its rotation between the beginning of riseand the end of return of the follower
radial or disc camsIn radial cams the follower reciprocates or oscillates in a direction perpendicular to thecam axis . The cams are all radial rams. In actual practice, radial cams are widely useddue to their simplicity and compactness.
dwell The zero displacement or the absence of motion of the follower during the motion of thecam is called dwell.
classification of followers according to follower shape
(i) Knife edge follower(ii) Roller follower(iii) Mushroom or flat faced follower and(iv) Spherical faced or curved shoe follower
classification of follower according to the motion of the follower
(i) Reciprocating or translating follower(ii) Oscillating or rotating follower15.What is classification of followers according to the path of motion ?(i) Radial follower and(ii) Offset follower
the motion of the follower The follower can have any of the following four types of motions(i) Uniform velocity(ii) Simple harmonic motion(iii) uniform acceleration and retardation(iv) cycloidal motion.
application of camClosing and opening of inlet and exit value operating in IC engine .
necessary elements of a cam mechanism(i) Cam-The driving member is known as the cam(ii) Follower-The driven member is known as the follower.(iii) Frame-It supports the cam and guider the follower.
translating angle The wedge is replaced by a flat plate with a groove . The plate cam moves back andforth imparting a translatory motion to the follower. Thus these cams are also known astranslating cams.
Cam is a rotating mechanical member used for transmitting desired motion to afollower by direct contact
Classification of cam
(i) according to cam shape
(ii) according to follower movement
(iii) according to manner of constraint of the follower
Classify cam based on a shape
(i) wedge cam
(ii) radial cams
(iii) spiral cams
(iv) drum cams
(v) spherical cams
classification of follower
(i) According to follower shape
(ii)according to motion of follower
roller followerIn place of a knife edge roller is provided at the contacting end of the follower
Spherical follower In the contacting end of the follower is of spherical shape
Angle of ascend The angle of rotation of the cam from the position when the follower begins to risetill it reaches its highest points
Angle of descend The angle through which the cam rotates during the time the follower returns to
Angle of dwell It is the angle through which the cam rotates while the follower remains stationary atthe highest or the lowest
Angle of action The total angle moved by the cam during its rotation between the beginning of riseand the end of return of the follower
radial or disc camsIn radial cams the follower reciprocates or oscillates in a direction perpendicular to thecam axis . The cams are all radial rams. In actual practice, radial cams are widely useddue to their simplicity and compactness.
dwell The zero displacement or the absence of motion of the follower during the motion of thecam is called dwell.
classification of followers according to follower shape
(i) Knife edge follower(ii) Roller follower(iii) Mushroom or flat faced follower and(iv) Spherical faced or curved shoe follower
classification of follower according to the motion of the follower
(i) Reciprocating or translating follower(ii) Oscillating or rotating follower15.What is classification of followers according to the path of motion ?(i) Radial follower and(ii) Offset follower
the motion of the follower The follower can have any of the following four types of motions(i) Uniform velocity(ii) Simple harmonic motion(iii) uniform acceleration and retardation(iv) cycloidal motion.
application of camClosing and opening of inlet and exit value operating in IC engine .
necessary elements of a cam mechanism(i) Cam-The driving member is known as the cam(ii) Follower-The driven member is known as the follower.(iii) Frame-It supports the cam and guider the follower.
translating angle The wedge is replaced by a flat plate with a groove . The plate cam moves back andforth imparting a translatory motion to the follower. Thus these cams are also known astranslating cams.
Wednesday, September 10, 2008
Basic mechanical engineering~kinematics
This site will help you to know the basics of Mechanical Engineering concepts and terms. We have tried our level best to make the definitions and explanations as simple as possible
This to know about the basic mechnaical concept behind the mechanical
- Kinematic link It is a resistive body which go to make a part of a machine having relativemotion between them.
- Kinematic pair.When two links are in contact with each other it is known as a pair.If the pairmakes constrain motion it is known as kinematic pair.
- Kinematic chain.When a number of links connected in space make relative motion of any point ona link with respect to any other point on the other link follow a definite law it is known askinematic chain.
- Klein’s equation for joints.
h-Higher pair joint
l-Number of links
j-Lower pair joint
- Degree of freedom.Of mechanism.It is defined as the minimum number of input parameters which must beindependently controlled inorder to bring the mechanism into a useful engineeringpurpose.
- Kutzbach’s relation.
n-Degree of freedom.
l-Number of links.
h-Higher pair joint
j-Lower pair joint
- Grashoff’s law.Sum of shortest link length and sum of longest link length is not greater than thesum of remaining link length.
- Inversion of mechanism.The method of obtaining different mechanism by fixing different links in akinematic chain is known as inversion of mechanism.
- Mechanical advantage of mechanism.It is defined as the ratio of output torque to the input torque also defined as theratio of load to effort.
- Transmission angle. The acute angle between follower and coupler is known as transmission angle.
- Toggle position. If the driver and coupler lie in the same straight line at this point mechanicaladvantage is maximum.Under this condition the mechanism is known as toggle position.
- few types of rocking mechanism Pendulam motion is called rocking mechanism.1.Quick return motion mechanism.2.Crank and rocker mechanism.3.Cam and follower mechanism.
- pantograph It is device which is used to reproduce a displacement exactly in a enlargedscale.
- application of crank and slotted lever quick return motion mechanism
1.Shamping machines.2.Siotting mechanism.3.Rotary internal combustion engine.
- structure It is an assemblage of a number of resistant bodies having no relative motion betweenthemand meant for carrying loads having straining action.
- simple mechanism A mechanism with four link is known as simple mechanism.
- equivalent mechanism The mechanism, that obtained has the same number of the degree of freedom,as theoriginal mechanism called equivalent mechanism.
- single slider crank chain mechanism A single slider crank chain is a modification of the basic four bar chain. It consist ofone sliding pair and three turning pair.
- double slider crank chain mechanism A kinematic chain which consist of two turning pair and two sliding pair isknown as double slider crank mechanism.
Classification of kinematic link
Classification based on relative motion between links.
1)Sliding pair.In a sliding pair minimum number of degree of freedom is only one.
2)Turning pair.In a turning pair also degree of freedom is one.when two links are connected suchthat one link revolves around another link it forms a turning pair.
3)Cylindrical pair.In a cylindrical pair degree of freedom is two.If one link turns and slides alonganother link it forms a cylindrical pair.
4)Rolling pair.In a rolling pair degree of freedom is two.The object moves both linearly andangularly.
5)Spherical pair.In a spherical pair degree of freedom is three.It can both move left and right,up anddown,and rotate along the same point.
Based on nature of contact.
1)Lower pair.If contact between two links is surface contact also having degree of freedom one,then the pair is known as lower pair.Example: Sliding pair.
2)Higher pair.If contact between two links is either point contact or line contact then the pair isknown as higher pair.Example: Point contact-Rolling pair.Line contact-Cylindrical pair.
3)Mechanical pair.
(a)Open pair.In this pair everything is open to the admosphere.
(b)Closed pair.In this pair everything is closed from the admosphere.
(B)Indexing mechanism.This type of mechanism is used in automatic lathe’ s etc.
- Snap action mechanism.It is used in calling bells, bicycle bells etc.
- Motion adjustment mechanism.The mechanism used to adjust or modify any one of the links in a mechanism isknown as motion adjustment mechanism. Differential screw used in bench vice, pipewrench, Lathe chuck and screw jack are some of the examples of motion adjustmentmechanism.
- Scott Russel mechanism.This is one of the mechanism to produce straight line motion mechanism.The mechanismin which the straight line is copied from a existing straight line constrain is known asScott Russel mechanism.
- Quick return motion are of two types.
They are,
1)Crank and slotted lever quick return motion mechanism.
2)Whitworth quick return motion mechanism
Crank and slotted lever quick return motion mechanism.
In this mechanism,the link AC forming the turning pair is fixed.The driving crank CBrevolves with uniform angular speed about the fixed center C.A sliding block attached tothe crank pin at B slides along the slotted bar AP and thus causes AP to oscillate aboutthe pivorted point A.A short link PR transmits the motion from AP to ram which carriesthe tool and reciprocates along the line of stroke R1R2.In the extreme positions,AP1 andAP2 are tangential to the circle and the cutting tool is at the end of the stroke.The forwardor cutting stroke occurs when the crank rotates from the position CB1 to CB2 in theclockwise direction.The return stroke occurs when the crank rotates from the positionCB2 to CB1 in the clockwise direction.Since the crank has uniform angularspeed,therefore
Time of cutting stroke
Time of return stroke =Since the tool travels a distance of R1R2 during cutting and return ,
thereforelength of stroke =R1R2=P1P2=2AP
Whitworth quick return motion mechanism.
In this mechanism,the link CD forming the turning pair is fixed.The driving crank CArotates at a uniform angular speed.The slider attached to the crank pin at A slides alongthe slotted bar PA which oscillates at a pivoted point D.The connecting rod PR carries theram at R to which a cutting tool is fixed.The motion of the tool is constrained along theline RD produced along a line passing through D and perpendicular to CD.When thedriving crank CA moves from the position CA1 to CA2 through an angle in theclockwise direction,the tool moves from left to right through a distance 2PD.Now whenthe driving crank moves from the position CA1 to CA2 through an angle in theclockwise direction,the tool moves back from right to left hand end.Since CA rotates atuniform angular velocity therefore time taken for return stroke is less than time taken forcutting stroke.then ratio between time taken for cutting and return stroke is,
Time of cutting stroke
Time of return stroke
- components of acceleration
i Radial component of accelerationii Tangential component of acceleration
- instantaneous center axis
Instantaneous axis is a line drawn through an instantaneous centerand perpendicular to the plane of motion.
- .What are the names of instantaneous center
i. Virtual center.ii. Centro.iii. Rotopole.
- objective of Kinematic analysis
The objective of Kinematic analysis is to determine the Kinematicquantities such as displacement,velocity and acceleration of the element in amechanism.
- two rules to locate Instantaneous center
a) When two links are connected by a pin joint the instantaneouscenter lies on the center of the pin.b) When two links have a sliding contact,the instantaneous centerlies at infinity in a direction perpendicular to the path of motionof slide.
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