Mechanical breaking system

Mechanical breaking sytem

A brake is defined as a mechanical device that is used to absorb the energy possessed by a moving system or mechanism by means of friction .The primary purpose of the brake is to slow down or completely stop the motion of a moving system , such as a rotating drum , machine or vehicle .it is also used to hold the parts of the system in position at rest . An automobile brake is used either to reduce the speed or the car or to bring it to rest. The energy absorb by brake can be either kinetic or potential or both .In automobile application the brake absorbs the kinetic energy of the moving vehicle .In hoists and elevators the absorbs the potential energy released by the objects during the braking period .The energy absorbed by the brake is converted into heat dissipated to the surroundings. heat dissipation is a serious problem in brake applications .

Brake are classified into following three groups . 

Mechanical Brakes - Mechanical brakes are operated by mechanical means such as levers , springs and pedals ,Depending upon the shape the friction material the mechanical brakes are classified as block brake ,internal or external shoe brake .disk brake and band brake .Brakes are also classified into two groups according to direction of the actuating force ,namely ,radial brakes and axial brakes .Internal and external shoe brakes are radial brakes , while disk brakes are axial brakes.

Hydraulic brakes - Hydraulic brakes are operated by fluid pressure such as oil pressure or air pressure.

Electric brakes -  Electrical brakes are operated by magnetic forces and include magnetic particle brakes, hystersis brakes,and eddy current brakes .

Read More

KEYS & COUPLING

 A key is a piece of mild steel inserted between the shaft and hub or boss of the pulley to connect these together in order to prevent relative motion between them. It is always inserted parallel to the axis of the shaft. Keys are used as temporary fastenings and are subjected to considerable crushing and shearing stresses. A key way is a slot or recess in a shaft and hub of the pulley to accommodate a key.

Types of keys 

The following types of keys are important from the subject point of view 

1. Sunk key 

2. Saddle key 

3. Tangent key 

4. Round key 

5. Splines  key 

1. Sunk key - The sunk key  are provided half in the keyway of the shaft and half in the keyway of the hub or boss of the pulley  . The sunk keys are of the following types :

1. Rectangular sunk key - 

2. Square sunk key 

3. Parallel sunk key 

4. Gib-head key

5. Feather key 

6. Woodruff key 

2. Saddle key - The saddle are the two following type :

1. Flat saddle key 

2. Hollow saddle key 

3. Tangent key - These are used in large heavy duty shaft .

4. Round key - The round key  are circular in section and fit into holes drilled partly in the shaft and partly in the hub . 

5. Splines

Read More

WORM GEAR

WORM GEAR 

The worm gear drives are used to transmit power between two non-intersecting shafts . which are in general at right angles to each other . The worm gear drive consists of a worm and a worm wheel . The  worm is threaded screw , while the worm wheel envelope the threads on the worm and give line contact between mating parts. 

The advantages of worm gear .

1. The most important characteristic of worm gear drives is their high speed reduction .A speed reduction  as high as 100;1 can be obtained with a single pair of worm gear .

2. The worm gear drives are compact with small  overall dimensions ,compared with equivalent spur or helical gear drives having same speed reduction .

3. The operation is smooth and silent .

4. Provision can be made for self-locking operation .Where the motion is transmitted only from the worm to the worm wheel . This is advantageous in application line cranes and lifting devices .

TERMINOLOGY OF WORM GEAR

1. Axial Pitch - The axial pitch (p)  of the worm is defined as the distance measured from a point on one thread to the corresponding point on the adjacent thread , measured along the axis of the worm .

2. Lead -  The lead (I) of the worm is defined as the distance that a point on the helical profile will move , When the worm is rotated through one revolution .It is the thread advance in one turn .For single thread the lead is equal to the axial pitch .For double -start threads ,the lead is twice the axial pitch and so on .

3. Lead angle -  The lead angle ( Γ ) is defined as the angle between a tangent to the thread at the pitch diameter and a plane normal to the worm axis .

4. Helix angle - The helix angle ( Ψ )  is defined as the angle between a tangent to the thread as the pitch diameter and the axis of worm .The worm helix angle is complement of worm lead angle .

5. Pressure angle - The tooth pressure angle (α ) is measured in a plane containing the axis of the worm and it is equal to one-half of the thread angle . The pressure angle should not be less than 20° for triple and multi-start worms .

Read More

BEVEL GEAR 

The bevel gear are used to transmit power between two intersecting shafts . There are two common types of bevel gear - straight and spiral .The element of the teeth of straight bevel gear are straight lines . which converge into a common apex point .The element of the teeth of the spiral bevel gears are spiral curves which also converge into a common apex point . Involute profile is used for the form of the teeth for both types of gears . Straight bevel gears are easy to design and manufacture and give reasonably good service when properly mounted on shafts . However , they create noise at high-speed conditions .Spiral bevel gears on the other hand are difficult to design and costly to manufacture .for they require specialized and sophisticated machinery for their manufacturing .Spiral bevel gears have smooth  teeth engagement .which result in quiet operation even at high speeds .They have better strength and are thus used for high-speed . They have better strength and are thus used for high speed high power transmission .

TERMINOLOGY OF BEVEL GEAR 

A bevel gear is in the form of the frustum of a cone . The dimensions of bevel gear are illustrated .Following terms are important in design of bevel gears ;

1. Pitch cone - Pitch cone is an imaginary cone , the surface of which contains the pitch lines of all teeth in the bevel gear .

2. Cone center -  The apex of pitch cone is called cone center .It is denoted by 0.

3. Cone distance -  Cone distance is the length -cone element .It is also called pitch-cone radius .It is denoted by A

                                         O

4. Pitch Angle - The angle that the pitch line makes with the axis of the gear is called the pitch angle .It is denoted by λ .The pitch angle is also called center angle .

5. Addendum Angle - It is the angle subtended by addendum at the cone center .It is denoted by α .

6. Dedendum Angle - It is the angle subtended by dedendum at the cone center .It is denoted by delta .

7. Face angle - It is the angle subtended by the face of the tooth at the cone center .

8. Root angle - It is angle subtended by the root of the tooth at the cone center .

9. Back bone - The back cone is an imaginary cone and its elements are perpendicular to the element of the pitch cone .

10. Back cone Distance - It is the length of back cone element .It is also called back cone radius . 

Read More

HELICAL GEAR

There are basic difference between spur and helical gears . while the teeth of spur gear are cut parallel to the axis of the shaft , the teeth of helical gear are cut in the form of a helix on the pitch cylinder. In spur gear the contact between meshing teeth occurs along the entire face width of the tooth resulting in a sudden application of the load . In helical gear the contact between meshing teeth begins with a point on the leading edge of tooth and gradually extends along the diagonal line across the tooth .

Read More

TERMINOLOGY OF SPUR GEAR 

The terminology of gear includes number of terms peculiar to gear and it forms the basic of gear language .The terminology applied to spur gear is illustrated . 

gear terminology consist following terms ;

1. Pinion - A pinion is smaller of the two mating gears .

2. Gear - A gear is larger of the two mating gears .

3. Velocity ratio - Velocity ratio is the ratio of angular velocity of the driving gear to the 

angular velocity of the driven gear . It is also called the speed ratio .

4. Transmission ratio - The transmission ratio is the ratio of the angular speed of first driving gear to the angular speed of the last driven gear in a gear train .

5. Pitch Surface - The pitch surface of the gears are imaginary planes cylinders or cones that roll together without slipping .

6. Pitch circle - The pitch circle in the curve of intersection of the pitch surface of revolution and the plane of rotation . It is an imaginary circle that rolls without slipping with the pitch circle of a mating gear . The pitch circles of a pair of mating gears are tangent to each other .

7. Pitch circle diameter - The pitch circle diameter is the diameter of pitch circle .The size of the gear is usually specified by pitch circle diameter . It is also called pitch diameter .The pitch circle diameter is denoted by 'd' .

8. Pitch point  -  The pitch point is a point on line on line of centers of two gears at which two pitch circles of mating gears are tangent to each other .

9. Top land - The top land is the surface of the top of the gear tooth ..

10. Bottom land - The bottom land is the surface of the gera between the flanks of adjacent teeth .

11. Involute - An involute is a curve traced by a point on a line rolls without slipping on a circle .

12. Base circle - The base circle is an imaginary circle form which the involute curve of the tooth profile is generated .the base circles of two mating gears are tangent to the pressure line .

13. Addendum circle - The addendum circle is an imaginary circle that borders the tops of gear teeth in the cross-section .

14. Addendum - The addendum is the radial distance between pitch and the addendum circles .addendum indicates the height of tooth above the pitch circle . '

15. Dedendum circle - The dedendum circle is an imaginary circle that borders the bottom of  spaces between teeth in the cross-section . It is called root circle .

16. Dedendum - The dedendum is the radial distance between pitch and the dedendum circles . The dedendum indicates the depth of the tooth below the pitch circle .

17. Clearance -  The clearance is the amount by which the dedendum of a given gear exceed the addendum of its mating tooth .

18. Face of tooth  - The surface of the gear tooth between the pitch cylinder and the addendum cylinder in called face of tooth .

19. Flank of tooth - The surface of the gear tooth between the pitch cylinder and the root cylinder in called flank of tooth .

20. Face width - Face width is width of the tooth measured parallel of the axis .

21. Fillet radius - The radius that connects the root circle to the profile of the tooth is called fillet radius .

22. Circular tooth thickness - The length of  the arc on pitch circle subtending a single gear tooth is called circular tooth thickness . Theoretically , circular tooth thickness is half of circular pitch .

23. Tooth space -  The width of the space between two adjacent teeth measured along the pitch circle is called the tooth space . theoretically tooth space is equal to circular tooth thickness or half of circular pitch .

24. Working Depth - The working depth is the depth of engagement of two gear teeth , that is the sum of their addendums .

25. Whole depth  - The whole depth is the total depth of the tooth space that is the sum of addendum and dedendum . Whole depth is also equal to working depth plus clearance .

26. Center Distance - The center distance is the distance between centers of pitch circles of mating gears . It is also the distance between centers of base center of mating gears .

27. Pressure Angle - The pressure angle is the angle that the line of action makes with the common tangent to the pitch circles . The pressure angle is also called the angle of obliquity ,It is denoted by α .

28. Line of action - The line of action is the common tangent to the base circles of mating gears . The contact between the involve surface of mating teeth must be  on this line to give smooth operation . The force is transmitted from the the driving gear to the driven gear on this line .

29. Arc of  contact - The arc of contact is the arc of the pitch circle through which a tooth moves form the beginning of contact until the point of contact arrives at the pitch circle .

30. Arc of approach -The arc of approach is the arc of the pitch circle through which a tooth moves form its beginning of contact until the point of contact arrives at the pitch point .

31. Arc of Recess - The arc of recess is the arc of the pitch circle through which a tooth moves form the contact at the pitch point until the contact ends .

32. Contact ratio - The number of pairs of teeth that are simultaneously engaged is called contact ratio .

33. Circular pitch - The circular pitch (p) is the distance measured along the pitch circle between two similar points on teeth .











This article was taken by V.B. BHANDARI 

Read More

Introduction to the Clutch and classified ?

CLUTCHES 

The clutch is mechanical device, that is used to connect or disconnect the source of power form the remaining parts of the power transmission system at the will of  the operator . An automotive clutch can permit the engine to run without driving the car . This is desirable when  the engine is to be started or stopped or when the gears are to be shifted .

CLUTCHES ARE CLASSIFIED INTO THE FOLLOWING FOUR GROUPS ;

1. Positive contact clutch - They include square jaw clutch ,spiral jaw clutches and toothed clutches ,In these clutches power transmission is achieved by means of interlocking of jaw or teeth . Their main advantage is positive engagement and once coupled they can transmit large torque with no slip  .

The jaw are clutches have following advantage .

1. They do not slip and engagement is positive .

2. No heat is generated during engagement or disengagement .

2. Friction clutch - They include single and multi -plate clutch cone clutches and centrifugal clutches . In these clutches power transmission is achieved by means of friction between contacting surfaces . 

advantage of friction clutches ;

1. The engagement is smoothly made by gradual increase in the normal force .

3. Electromagnetic clutch - They include magnetic particle clutches , magnetic hysteresis clutches power transmission is achieved by means of the magnetic field .

4. Fluid clutch - In these clutches power transmission is achieved by means of  hydraulic pressure . A fluid coupling provides extremely smooth starts and absorbs shock .

Read More

HELICAL SPRING

HELICAL SPRING

The helical spring are made up of a wire coiled in the form of a helix and in primarily intended for compressive or tensile load .The cross-section of the wire from which the spring is made may be circular ,square or rectangular.The two forms of helical springs are compression helical spring & torsion helical spring.

The helical spring have following advantage .

1. The are reliable .

2. These are easy to manufacture .

3. These have constant spring rate.

4. These are available in wide range .

5. These performance can be predicted more accurately .

Material for helical spring 

The material of the spring should have high fatigue strength ,high ductility ,high resilience and it should be creep resistant . It largely depends upon the service for which they are used severe service , average service or light service.

Severe service - severe service means rapid continuous loading where the ratio of minimum to maximum load is one-half or less , as in automotive valve springs .

Average service - average service includes the same stress range as in severe service but with only intermittent operation .as in engine governor springs and automobile suspension springs.

light service - light service inculdes springs subjected to loads than are static or very infrequently varied . as in safety valve springs. 

TERMINOLOGY OF HELICAL SPRING 

The main dimensions of a helical spring subjected to compressive force . They are as follows  .

          d    = wire diameter  of spring (mm)

          Di  = inside diameter of spring coil (mm)

          Do = outside diameter of spring coil (mm)

          D   = mean coil diameter (mm)

Therefore ,

                      D 1 + D 2

          D =    ----------------

                             2

DESIGN OF HELICAL SPRING 

There are three objective for design of the helical spring.

1. It should posses sufficient strength to withstand the external load .

2. It should have the required load-deflection characteristic .

3. It should not buckle under the external load .

This artical was taken by  v b  bhandari & r.s. khurmi ,j.k. gupta .

Read More

SPRING

SPRING 

A spring  is defined as an elastic machine element that deflects under the action of the load and returns to its original shape when the load is removed .It can take any shape and form depending upon the application .The important functions and application of the spring are as follow.

1. Springs  are used to absorb shocks and vibration vehicle suspension springs .railway buffer springs in elevators & vibration mounts for machinery .

2. Springs are used to store energy springs used in clocks ,toys , circuit breakers and starters ..

3. Springs are used to apply force & control motion.

TYPES OF SPRING

1. Helical spring 

(a) Compression spring 

(b) Extension spring

SPRING MATERIAL 

The selection of material for the spring wire depends upon following factors .

1. The load acting on the spring.

2. The range of stress through which the spring operates .

3. The limitations on mass & volume of spring.

4. The expected fatigue life .

SPRING SPECIFICATION 

1. material = oil-hardened and tempered steel wire of grade -VW

2. wire diameter = 3.6mm

3. mean coil diameter = 18mm

4. free length = 125mm

5. total number of turns = 26

6. style of ends = square and ground 

Read More

HEAT TREATMENT OF STEEL

HEAT TREATMENT OF STEEL

The heat treatment process consists of controlled heating and cooling of component made of either plain carbon steel or alloy steel , for the purpose of changing their structure in order to obtain certain desirable properties like hardness , strength or ductility .The major heat treatment process are follow .

1. Annealing - It consist of heating the component to a temperature slightly above the critical temperature .followed by slow cooling .It reduces hardness and increases ductility .

2. Normalizing  -It is similar to annealing except that the component is slowly cooled in air. It is used to remove the effects of the previous heat treatment process .

3. Quenching -It consists of heating the component to the critical temperature and cooling it rapidly in water or air. It increases the hardness & wear resistance However during the process the component becomes brittle & ductility is reduced .

4. Tempering -It consists of reheating the quenched component to a temperature below the transformation range, followed by cooling at a desired rate . It restore the ductility & reduces the brittleness due to quenching . 

This artical was taken by VB BHANDARI 

Read More

MACHINE DESIGN

MACHINE DESIGN

Machine design is defined as the use of scientific principle technical information & imagination in the description of a machine or a mechanical system to perform specific function with maximum economy and efficiency .This definition of machine design contains following important features .

1. A designer uses principle of basic engineering sciences such as physics mathematics , statics & dynamics , thermodynamics and heat transfer , vibration and fluid mechanics ,Some of the example of these principle are 
1. D' Alembert's principle 
2. Carnot cycle 
3. Bernoulli's principle
4. Newton's laws of motion 


2. The designer has technical information basic element of machine. These element in clude fastening devices ,chain belt and gear drivers bearing ,oil seals and gaskets ,springs  Shaft ,keys .A machine is a combination of these basic element .The designer knows the relative adavatange & disadavantages  of these basic element & their suitability in different application .


3. The designer uses his skill and imaginatioin to produce a configuration ,which is a combination of these basic element .However this combination is unique and different part of constructing a proper configurartion is creative in nature .



Machine design  is the creation of plans for machine  to perform the desired function. 

Basic procedure of machine design 

The basic procedure of machine  consist of a step by step approch from given specification about the function requirement of a product .

1. Market survey 

2. Define specification of product 

3. Study alternative mechanisms for product & select proper mechanism 

4. prepare general layout of configuration 

5.Design individual components 

6. prepare assembly and detail drawing 

This artical was taken by Design of machine element 

Read More

SHAFT

A shaft is a rotating machine element which is used to transmit power from one place to another .
the power is a delivered to the shaft by some tangential force and the resultant torque set up within the permits the power to be transformed to various machine linked up to the shaft .In order to transfer the power from one shaft to another the various members such as pulleys gears etc. are mounted on it . Theses member along with the forces exerted upon them causes the shaft to bending .In order words ,we may say that a shaft is used for the transmission of torque and bending moment.The various member of torque and bending moment .The various member are mounted on the shaft by means of keys or splines.

MATERIAL USED IN FOR SHAFT
1.It should have high strength.
2.It should have a good machinability.
3.It should have low notch sensitivity factor.
4.It should have good heat treatment properties.
5.It should have high wear resistant properties.


MANUFACTURING OF SHAFT
shaft are generally manufactured by hot rolling .The cold rolled shaft are stronger then hot rolled shaft but with higher residual stresses.

TYPES OF SHAFT
1.Transmission shaft :-The shaft transmit power between the source and the machines absorbing power.
2.Machine shaft:- These shaft form an integral part of the machine itself .The crank shaft is an example of machine shaft.


STRESSES IN SHAFT
1.Shear stresses due to  the transmission of torque.
2.Bending stresses due to the forces acting upon machine elements like gears,pulleys  etc.
3.Stresses due to combined torsional and bending loads.

Read More

NOTCH SENSITIVITY

In cyclic loading ,the effect of the notch or the fillet is usually 'ess than predicted by the use of the theoretical factor as discussed before.The different depends upon the stress gradient in the region of the stress concentration and on the hardness of the material The term notch sensitivity is to the behaviour. It may be defined at the degree to which the theoretical effect of stress concentration is actually reached.The stress gradient depends mainly on the radius of the notch,hole or fillet and on the grain size of the material .Since the extensive data for estimating the notch sensitivity factor is not available therefore the curves may be used for determining the value of q for two steels.










When the notch sensitivity factor q is used in cycle loading then fatigue stress concentration factor may be obtained from the following relations .
                                                     Kt=1+q(Kt - 1)
                                                     Kfg=1+q(Ktg -1)


THIS ARETICAL WAS TAKEN BY R.S. KHURMI AND J.K. GUPTA

Read More