mechanical engineering
Thursday, 28 January 2016
Wednesday, 20 January 2016
automobile braking mguniversity
Braking System
Brakes are employed to stop or slow down the speed of vehicle.When brake applied to wheel braking force is created that force oppose the speed of wheel or rotation of force.
Braking requirement:
1)The vehicle must stop in smallest distance.2) It must act suddenly in emergency.
3)It must have strong braking force.
4)It must neither slip nor skid the vehicle.
And less heat production.
5)It must operate on least effort.
Types of brakes:
Breaks are divided into seven types as per there uses, functionality, locations etc.1) On the basis of purpose saved.
a) Main brake.
b) Parking brake.
2) On the basis of location.
a) Wheel mounted.b) Transmission mounted.
3) On the basis of drivers ergonomics.
a) Foot brake.b) Hand brake.
4) On the basis of actuating.
a) Mechanical brake.
b)Hydraulic brake.c) Air brake.
d)Electric brake.
5) On the basis of construction.
a) Drum brake.b)Disc brake.
6) On the basis of application of brake efforts.
a)Manual brake.b)Power brake.
c)Power assisted.
7) On the basis of action of brake shoes.
a)Internal expanding brake.b)External contracting brake.
Brake Drum:
Construction of Brake Drum:The brake drum is mounted on axle hub and whole assembly is hold in wheel to brake shoes are handed on the back plate by mines of pin expander is fitted in between shoes.
The friction material is pasted or biretta on brake shoes the expanded (cam) expander.
The brake shoe and press on drum. Due to friction action brake will get applied.
Brake drum is shown in figure.
Brake Drum
Following parts used in break drum1) Brake drum.
2) Back plate.
3) Brake shoe.
4) Brake lining.
5) Expander.
6) Anchor.
7) Returning spring.
8) Adjuster.
Disc brake:
Construction of disc break:1) Caliper or cylinder casing.
2) Rooter disc.
3) Piston.
4) Friction pad.
5) Pad supporting plate.
6) Bleeder plug.
Working of disc break:
Disc brake is shown in figure.
Disc brake
The disc brake are appeaser hydraulically when the vehicle is to brake the brake fluid pumped by the master cylinder it them flows and pushes the piston and pad which makes friction with rooter disc and due to frictional action brake will get applied.Mechanical brake:
This brake system is operated by mechanical linkage.This brake system applied light vehicle two wheeler and some three wheeler this system required more efforts from driver and applied less force to the brake system to that system doesn’t used on four wheeler or heavy vehicle.
Hydraulic brake system :-
In this system the brake is operated with the help of oil pressure in this system master cylinder and wheel cylinder is most important part.This system is very popular on four wheeler vehicle basically light and medium vehicle.
Working of hydraulic break system :-
The diagram of hydraulic brake system is shown in figure.Hydraulic brake
The brake system is fitted with brake oil when driver presses the brake pedal the master cylinder creates oil pressure and sent to wheel cylinder.Piston in wheel cylinder get expands due to oil pressure and the brake shoes also get expand and rub on brake shoes.
Also get expand and rub on brake drum so that brake will get apply.
Master cylinder:
Master cylinder it is having following part:1) Cylinder body.
2) Piston.
3) Primary cup.
4) Secondary cup.
5) Check valve.
6) Return spring.
7) Push rod.
8) Dust cover.
Working of master cylinder:
The diagram of master cylinder is shown in figure.
Master cylinder
When driver depress the brake pedal the push rod pushes the piston forward and oil get compresses due to pressure the brake fluid open the hole of check valve and flows to wheel cylinder when driver release the brake pedal brake flied come back and pushes the check valve return spring and piston back ward and oil stores in reverie.Wheel cylinder:
The diagram of wheel cylinder is shown in figure.Wheel cylinder
As driver pressure the brake pedal and increases the pressure of oil that oil inters in the wheel cylinder it expand the piston towards outside they expand brake shoe and applies the brake.
When release the spring pushes the piston tension and flows the oil return to the master cylinder like this brake get release.
Pneumatic or air brake system :-
In this brake system air pressure is used to apply brake.Parts or components used in air brake system :-
1) Air compressor.
2) Reservoir air tank.
3) Water and oil separator.
4) Brake valve.
5) Air pressure gauge.
6) Safety valve.
7) Brake chamber.
8) Pipes.
Working of air brake system :-
The diagram of pneumatic or air brake system is shown in figure.
Pneumatic or Air Brake System
Mostly it is used heavy vehicle the compressor run by engine sucked air from atmosphere and the piston of compressor compress the air and supplied to air tank.
In between compressor and tank water separator is used which remove the water partial from air the air tank stores the air with pressure up to 8kg/cm2.the safety valve is used in the tank to manifold constant air pressure.
The pipe is connected from tank to brake valve and from brake valve to brake pedal the brake valve get open and pressure air flows from tank to brake chamber as soon as the air pressure inter in brake chamber the diaphragm get deflect which pushes the push rod for tarring the cam as the cam get turned it expand the brake shoe and brake will get applied.
When driver release the brake pedal the brake valve gets closed and air pressure cannot supplied to the brake chamber so that brake will get not applied.
Brake lining:
The brake lining are high friction material beings used rub again the rotating brake drums and to stop them will the brake are applied for on efficient braking and longer lifer they are expect to have high standard of quality they are required to full fill various requirement such as given below:-1) No water swells.
2) Low heat swells.
3) Low wear rate.
4) The high coefficient of normal and hot friction.
5) High strange and physically properties.
Brake lining material:
The brake lining are made of asbestos, rubber, metallic particles, resin, minerals, and coefficient of friction modifies among these the asbestos is most important there for brake.Lining are commonly known as asbestos brake linings.
1) Chrysalides asbestos fibers are comparatively cheap posses the hot coefficient of friction around 0.33 to 0.40 in the temperature range of 200 to 300’.
2) The metallic partial of aluminum brass and zinc are used for high heat dissipation and better antiwar characteristics.
3) The asbestos can resist temperature up to 350’ without folding.
Types of brake linings:
On the basis of manufacturing the brake lining are group in to following types.1) Rigid molded.
2) Flexible molded.
3) With metallic partial.
4) The wealth out metallic partial.
1) Non asbestos brake lining.
i) Flexible.
ii) Roll lining.
Rigid molded asbestos brake lining :-
Rigid molded asbestos brake lining has a random asbestos filigrees friction material with metallic inclusion in the form of steel wool brass chips.The coefficient of friction is well maintained even at higher temperature it is suitable for used under dry operating condition only it offer exceptional resistance to wear wealth out any penalty in the form of drum damage it finds application in light the medium and heavy commercial drum brake such a lining are two types:-
With Metallic Partial
Without Metallic Partial
Flexible molded roll brake lining :-
The flexible molded non metallic roll brake lining are of a dark gray in color having a random asbestos they have a random asbestos they have a high level of friction with a good anti squall properties and excellent temperature and wear resistance they are produce in roll and liner form and are suitable used under a dry operating condition only its material is manufactured with a good finish on both the surface suit may be bounded on inter surface.Wire meshed roll lining:
The molded rubberized and flexible wire meshed backed and with medium coefficient of partition these brake lining are suitable car and light commercial vehicle running in cities and also for agricultural tractors.Woven brake lining:
These are solid non magically using women the configuration of abbots fabric this lining do not feed up to 250 to 300 wire inclusion is also done for better heat transfer the turnery since copper or this alloys are preferred there coefficient of friction morally lies in the vicinity of 0.4.The wear properties of brake lining:
The wear resistance is a very important properties aliening should have the backing efficient will be have only of the timing are capable of sustaining a large number of braking stroke at a elevated temperature a test report conducted on lining at a 400 if show that the lining are stable or a long period of time and there is no reduction in brake effective even a after 100 cycle of inter brake operation a good brake lining should work well over about 800 km.Sunday, 10 January 2016
HEAT AND MASS TRANSFER
Differential equation of heat transfer
In order to find out the rate of heat transfer ,let consider an element from the bulk
Heat flowing in x direction
During the
time dt =-kx
dz dy ∂T/∂x dt
Heat flowing
in x direction in time dt = Qxdt
By expansion of the equation
(f(x+h))
=fx +h f’x+h2f’’x+………..
Then Q(x+dx)
= Qx+(∂ Heat flowing in x direction is Qx = -kx
dz dy ∂T/∂x
Qx/∂x) dx
Then heat
accumulation = Qx+dx– Qx
QX + ∂QX/∂X - Qx
(∂Qx/∂x) = (∂(-kdzdy)/∂x) × ∂T/∂x × dt dx
= -kx ∂2T/∂x2
dx dy dz dt
Similarly
Heat
accumulated due to heat flow in y direction
Ky
∂2T/∂y2dxdydzdt
Total heat
accumulated = sum of heat accumulation in all direction
=(kx∂2T/∂x2
+ ky∂2T/∂y2 +∂2T/∂z2)dxdydzdt
If q.
is the heat generated in differential element /volume
Then heat
generated in time dt is= q.dxdydzdt
Net heat
accumulation =
(kx∂2T/∂x2+ky∂2T/∂y2+kz∂2T/∂z2+q.)dxdydzdt 6
Due to heat
accumulation body temperature changes by dT
Q= mCpdT
=D×dxdydz×CpdT
7
Equating 6 and 7
D CpdT = (kx∂2T/∂x2+ky∂2T/∂y2+kz∂2T/∂z2+q.)dt
Dividing by dt
(kx∂2T/∂x2+ky∂2T/∂y2+kz∂2T/∂z2+q.
)= DCp∂T/∂t
For isotropic material k= constant
K(∂2T/∂x2+∂2T/∂y2+∂2T/∂z2+q./k) = DCp∂T/∂t
(∂2T/∂x2+∂2T/∂y2+∂2T/∂z2+q./k) = 1/(k/DCp) ×∂T/∂t
1/(k/DCp) = thermal diffusibility =1/α
HEAT AND MASS TRANSFER
HEAT TRANSFER BY CONDUCTION
Fouriers law of conduction
Q is proportional to area perpendicular to heat flow
and is directly proportional to temperature differential dT
and inversely proportional to thickness dx
there fore fouriers law of heat conduction is
Q =kAdT / dx
k= thermal conductivity of material
conduction by.....
free electrons : contribute to thermal conduction
lattice vibration produce lattice wave
Q is proportional to area perpendicular to heat flow
and is directly proportional to temperature differential dT
and inversely proportional to thickness dx
there fore fouriers law of heat conduction is
Q =kAdT / dx
k= thermal conductivity of material
conduction by.....
free electrons : contribute to thermal conduction
lattice vibration produce lattice wave
variation of thermal conductivity of material with temperature
For solids in general the variation is shown in graph
For liquids and gases the variation in general is as follows
In liquids and gases conduction occur due to molecular collisions
Wednesday, 30 December 2015
static force analysis
static force analysis continu......
Similarly a three force member will be in equilibrium if the vector sum of all these forces equal to zero and to satisfy the vector sum of all the moments about any arbitrary point equal to zero, their line of action should meet at a point.
Figure 4(a) shows a body subjected to three forces Also the line of action of coincide at point O. Hence the resultant of must F1 and F2 must pass through point O and it should be equal and opposite to force F3 . Hence for equilibrium, line of action of F3 should pass through point O as shown in Figure 4(b). In figure 4(c) the forces are shown to form a close polygon (triangle) and one may use Lami’s theorem (sine rule of tringle) to find the unknown forces if atleast one force is known both in magnitude and direction and the line of action of one more force is known. According to this theorem
where , and αβ γ are angle as shown in figure 4(c).
For more than three forces one may draw force vector polygon or resolve the forces and moments to get the required force components.
static force analysis
Static Force Analysis conti...........
Static equilibrium:
Hence a two force member as shown in figure 3(a) will be in equilibrium if (i) both forces are equal and opposite and (b) their line of action coincide. If the forces are equal and opposite but not collinear as shown in Figure 3(b) they will form a couple and body will start to rotate. Hence these two forces should be equal, opposite and collinear.
static force analysis
INTRODUCTION TO STATIC FORCE ANALYSIS
Free-body diagram
A free body diagram is a sketch or drawing of the body, isolated from the rest of the machine and its surroundings, upon which the forces and moments are shown in action. In case of the four bar mechanism shown in figure 1 the free body diagram
When a link or body is subjected to only two forces it is called a two-force member and when it is subjected to 3 forces it is called a three-force member. Similarly one may consider multi-force member also.
Static equilibrium: A body is in static equilibrium if
• the vector sum of the forces acting on the body is zero i.e., ΣF=0
• the vector sum of all the moments about any arbitrary point is zero i.e., ΣM=0
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