WHY RAILWAY BRIDGES ARE MADE UP OF STEEL RATHER THAN CONCRETE ??

Trains are quite heavy and they generate high frequency vibrations when moving through the bridge.

Bridge can be made up of 2 materials i.e steel or concrete.Concrete is brittle in nature as a result small vibrations may break it.For example you might have seen jack hammer.How does it break concrete on which it is used? Does it generate very large force? No. It vibrates very quickly and splits up concrete into smaller chunks. This is because of brittle nature of concrete and low fatigue value.

But steel is not brittle, it is ductile. It can sustain such oscillations and has higher fatigue strength. As a result it can absorb high vibrations and sustain.

WHY TIRES ARE BLACK IN COLOUR ??

Although the natural colour of rubber is a milky white, the black colour we see is because of carbon black.Actually Carbon Black is not added as a coloring agent,it is a filler. 

Vulcanized rubber does not have very good wear resistance and hence a tire made of pure vulcanized rubber would wear out soon.

Carbon Black also increases the damping properties of rubber, thus transferring less shock loads to the automobile.

In addition to this Carbon Black is a good conductor of heat and would help conduct heat away from the surface with contact to the road and help maintain a healthy tire temperature.

An added bonus is that addition of carbon black increases the coefficient of friction with the road surface thus making it safer to drive.

RELATION BETWEEN RPM AND TORQUE EXPLAINED !!

Torque is the twisting or rotating force that the engine exerts on the crankshaft; it is expressed in N-m or Kg-m.

It is generally measured at a radius of one meter from the crankshaft's center.

Torque and Speed ( RPM) Are inversely proportional with each other

Here is the torque-speed curve.

As the RPM Of an engine increases, torque increases upto a certain value of RPM. And as the RPM goes on increasing, torque starts decreasing.

To understand this behaviour, you need to understand one more term which is called as “ Low-End torque”. Low -End Torque is the amount of torque produced at Low RPM range of an engine ( around 1000–2000 rpm) .This low end torque is very crucial when moving a vehicle from stand-still or driving in slow-speed conditions such as in traffic. If the greater amount of torque is generated at the lower end of engine rpm, it implies that the engine has more ‘low-end-torque’ or better pulling ability at slow speeds.

It also implies that vehicle can move very quickly from rest/stand still.

Now as the engine speed keeps increasing, torque starts to decrease because of the increase in friction between engine’s moving parts.

Engine torque is also related to the gearing. The lower the gear, greater is the pulling ability of an engine and hence greater the torque because lower gears are greater in diameter and we know that,

Torque=Force x Perpendicular Distance(Larger diameter of smaller gear).

So at lower RPM we get maximum torque as we are in smaller gear.Torque helps the wheels to turn that is why it is suggested to start vehicle in first gear as toque is maximum at that point of time.

If you know the Horsepower (HP) of an engine, then you can calculate the torque using the formula :-

Torque = (HP*5252)/RPM

TECHNICAL ROUND QUESTIONS OF MARUTI SUZUKI INDIA LIMITED !!

1. The purpose of jigs and fixtures are to

a. Increased production rate
b. Increased machining accuracy
c. Facilitate interchangeable manufacturing
d. Enable employ less skilled operators
e. All of the above

Ans:e

2. Tool life of the cutting tool is most affected by

a. Cutting speed
b. Tool geometry
c. Cutting feed and depth
d. Microstructure of material being cut
e. Not using coolant and lubricant
Ans:a

3. A feeler gauge is used to check

a. Radius
b. Screw pitch
c. Surface roughness
d. Unsymmetrical shape
e. Thickness of clearance
Ans:e

4. Metal in machining operation is removed by

a. Tearing chips
b. Distortion of metal
c. Shearing the metal across a zone
d. Cutting the metal across a zone
e. Pushing the metal with tool
Ans:c

5. Ductility of material can be defined as

a. Ability to undergo large permanent deformation in compression
b. Ability to recover its original form
c. Ability to undergo large permanent deformation in tension
d. All of the above
e. None of the above
Ans:a

6. Inconel is an alloy of

a. Nickel, chromium and iron
b. Nickel and copper
c. Nickel and chromium
d. Nickel and zinc
e. Nickel and lead

Ans:a

7. Casting defects caused by the molten metal is

a) Blow holes
b) Swell
c) Scab
d) All of the above
Ans.: d

8. Forming operation which does not involve rotation of work piece is

a) Spinning
b) Thread rolling
c) Ring rolling
d) Upsetting
Ans.: d

9. Greater forging capacity is achieved with

a) Mechanical press
b) Power hammer
c) Hydraulic press
d) None of them
Ans.: c

10. Which of the following welding process uses consumable electrodes

a) TIG
b) MIG
c) Thermit
d) Laser
Ans.: b

11. The crystal structure of alpha iron

a) BCC
b) FCC
c) HCP
d) Cubic
Ans.: a

12. Severe quenching can cause

a) Blow holes
b) Warping
c) Inclusions
d) Non of them
Ans.: b

13. Glass bead peening on components done to

a) Improve creep strength

b) Improve fatigue strength

c) Improve finish

d) Impart further coating

Ans.: b

14. Trajectory of a robot mean :

a) Path traced by the end effectors

b) Kinematics of Robot

c) Robot joints

d) Robot programming
Ans: a

15. Rayleigh’s method of computing the fundamental natural frequency is based on

a)Conservation of energy

b)Conservation of momentum

c)Conservation of masses

d)Laws of statics

Ans: a

Source-https://www.freshersworld.com/

WHY PETAL DISC BRAKES ARE USED INSTEAD OF ROUND DISC BRAKES?

Generally the disc of disc brake is round in shape but few disc brakes have petal shaped disc.What is the reason behind this?We will try to find out the answer of this question in this article.

When we apply brakes the kinetic energy of the wheels is converted to heat energy.As brake pads are in direct contact with the disc, so disc gets heated up.Now, if this heat is not properly dissipated then the disc may get overheated and might change its property.For this purpose, holes are provided in disc brakes.But in extreme conditions we require additional mechanism to remove this heat.For this purpose cuttings are provided in disc in the form of petal,as a result the diameter of disc remains same so effective braking is achieved with enough cooling.

You can notice that not all discs are given petals. Some discs are the usual round ones while only some get petals and there is a good reason for it. The reason petals are given is if the disc is expected to undergo heavy braking forces and has to dissipate a lot of heat a lot quickly or else if the disc is of a smaller size and the area is not enough to handle to heat dissipation rate.

Also petal discs look cooler and they add an extra aesthetic value to the entire thing.

CLICK "HERE" TO DOWNLOAD THIS ARTICLE IN PDF FORM 

KNOW WHY BEER BOTTLES ARE GREEN OR BROWN IN COLOUR !!!

You might have imagined why beer is sold in brown or green bottle?Why not in transparent bottle?This article will give you the answer.

In earlier days beer was sold in clear bottles which was transparent. The manufacturers noticed that the liquid in the clear bottles was getting affected by the sunlight and smelled very bad. This is because the UV rays coming from sun reacts easily with the acid in beer when stored in clear bottles. So when light enters beer bottle it breaks down the acid in the hops and this reacts with the already present sulphur, making the beer taste horrible. In order to solve this problem brands started using brown colour for beer bottles as brown stops the UV rays to react with the liquid inside the bottles.

After World War II there was a shortage of brown bottles and hence European manufacturers of beer began to use green bottles. Eventually these green bottles became a symbol of sophistication because most of these Euro beers were of extremely high quality. And so we got to the brown and green variants of a typical beer bottle.

WHY TUBELESS TIRES ARE NOT USED WITH SPOKE WHEELS ??

Now-a-days most of the vehicles are using tubeless tires with alloy wheels but when it comes to spoke wheels we don't see tubeless tires fitted to them. though some top of the line adventure superbikes come with tubeless tyres even on spoke wheels.In this article we will find out the reason why tubeless tires are not generally used with spoke wheels.

The spoke wheels have spoke fitted with the rim.When these spokes are fitted with the rim it leads to formation of small gap between spoke and the rim.If we fit tubeless tires with the spoke wheels the air will escape through these small gaps but in case of tubed tires there is a tube to hold the air so this problem does not arise in spoke wheels.

But there is a solution to this problem which is to seal the part where rim and spoke nipples are fused together. The rim strip is removed, cleaned for any dirt or rust and then the inside of the rim is sealed. One of the common sealants used to seal the wheels are 3M Marine adhesive sealant 5200 or 3M 540 polyurethane adhesive sealant. But this is again not a long term solution.