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WHY HEAT TREATMENT IS REQUIRED ? CHECK OUT THE ANSWER !!

Heat treatment is the process of heating (but never allowing the metal to reach the molten state) and cooling a metal in a series of specific operations which changes or restores its mechanical properties.




WHY HEAT TREATMENT IS REQUIRED?

Welding, cutting, or even grinding on metal produces heat, which in turn has an effect on the structure of the metal. These change in structures affect the properties of the material. Heat treatment makes the metal more useful by making it stronger and more resistant to impact, or alternatively, making it more malleable and ductile.



However, no heat-treating procedure can produce all of these characteristics in one operation; some properties are improved at the expense of others. For example, hardening a metal may make it brittle, or annealing it may make it too soft.


STAGES OF HEAT TREATMENT :

You accomplish heat treatment in three major stages:

• Stage l — Heat the metal slowly to ensure uniform temperature.
• Stage 2 — Soak (hold) the metal at a given temperature for a given time.
• Stage 3 — Cool the metal to room temperature.


VARIOUS TYPES OF HEAT TREATMENT PROCESSES :

All heat-treating processes are similar because they all involve the heating and cooling of metals. However, there are differences in the methods used, such as the heating temperatures, cooling rates, and quenching media necessary to achieve the desired properties.

The heat treatment of ferrous metals (metals with iron) usually consists of annealing, normalizing, hardening, and/or tempering. Most nonferrous metals can be annealed, but never tempered, normalized, or case hardened.


1.)ANNEALING: Anneal metals to relieve internal stresses, soften them, make them more ductile, and refine their grain structures. The process includes all three stages of heat treatment already covered (heat the metal to a specific temperature, hold it at a temperature for a set length of time, cool it to room temperature), but the cooling method will depend on the metal and the properties desired.


2.)NORMALIZING: The intent of normalizing is to remove internal stresses that may have been induced by heat treating, welding, casting, forging, forming, or machining. Uncontrolled stress leads to metal failure; therefore, you should normalize steel before hardening it to ensure maximum results. Normalizing applies to ferrous metals only, and it differs from annealing; the metal is heated to a higher temperature, but then it is removed from the furnace for air cooling.

3.)HARDENING: The purpose of hardening is not only to harden steel as the name implies, but also to increase its strength. However, there is a trade-off; while a hardening heat treatment does increase the hardness and strength of the steel, it also makes it less ductile, and brittleness increases as hardness increases. To remove some of the brittleness, you should temper the steel after hardening.



4.)TEMPERING: After hardening by either case or flame, steel is often harder than needed and too brittle for most practical uses, containing severe internal stresses that were set during the rapid cooling of the process. Following hardening, you need to temper the steel to relieve the internal stresses and reduce brittleness.

Tempering consists of:

• Heating the steel to a specific temperature (below its hardening temperature)
• Holding it at that temperature for the required length of time
• Cooling it, usually in still air.

The difference from other heat treatment process is in the temperatures used for tempering, which will affect the resultant strength, hardness, and ductility.

5.)QUENCHING: Quenching is a process of hardening a metal substance beyond its natural hardness level. In this process, a metal/alloy object is heated to a temperature till it becomes RED hot i.e. sub-boiling temperature and then is suddenly sunk into a fluid of room temperature or lesser eg, Water.

The main objective behind this process is to increase the hardness of the material. This takes place by making the micro grain structure homogenous and improving the strength of the metal. This process makes the metal brittle. The tensile strength of the material is reduced heavily.

WHY GAPS BETWEEN RAILWAY TRACKS ? CHECK THE ANSWER HERE !!


In traditional railway construction, rails are laid down over sleepers, clamped to them and then fastened to one another by means of fishplates. These fishplates not only help the whole track structure to maintain its integrity but also ensure that a certain (small) distance between rails is kept. This is due to thermal expansion.



All metals expand when heated. If two railway tracks are laid together without any gap between them they will push against each other when they expand in the day time because of the heat of the sun, and when they cool down in the night they will contract and return to their original state pulling against each other.  This constant pushing and pulling against one another when they heat and expand in the day time and cool down and contract in the night will result in the weakening of the joints between the two tracks and after a few days the two tracks may also break free from one another. Such a situation will result in the derailment of the trains causing major accidents and loss of lives.



So, the railway engineers always leave a small gap between two rails to compensate for the expansion of the rails during the hot day time and contraction during cold nights.

Modern railways employ continuous soldered rails and track expansion devices at regular intervals (and usually at the start and end of bridges, tunnels, and other structures) to avoid the maintenance problems posed by rail thermal expansion and to increase rolling comfort.

FACTORS AFFECTING EXHAUST SOUND OF AN ENGINE EXPLAINED !!!

You might have heard different exhaust note of motorbikes and cars. For example, the exhaust sound of the Royal Enfield Classic 350 is completely different from Kawasaki Ninja 300. In this article, we will discuss various factors that affect the exhaust sound of an engine.



But, before we discuss that, a brief primer on sound: It originates as vibrations that cause air-pressure disturbances that hit our eardrums. The frequency, or Hertz (Hz), of a sound wave—how many times the wave oscillates in a second—determines how our brain processes and interprets it as a distinct pitch. A higher frequency makes for a higher pitch, and vice versa. A car’s engine under load plays a range of frequencies, but its root note—the pitch its musical chord is built on—is defined by its so-called dominant frequency.


These sound-generating vibrations derive from the combustion in each cylinder and the corresponding pressure waves in the intake and exhaust systems. They are all keyed to the engine’s rotational speed; as revs rise and fall, the pitch goes up and down.

FOLLOWING FACTORS AFFECT THE EXHAUST SOUND OF AN ENGINE:


1.) Air induction-  In most cars, this is damped heavily. If you have a k+N universal one, you will hear the hiss. Carb engines made a much more delightful noise. Seen an Alfa or was it a Ferrari with triple carbs. Intake manifolds also play a part in the induction noise.



2.)Top Part of Engine- More parts means more music or noise - double overhead cams should make more interesting sounds. Belt driven cars are a little quiet. It all depends on tolerances and valve lifts. Pushrod engines generally sound harsh at high speeds. So, camshaft, valves and other parts of an engine which are located at the upper part of the engine also determines the sound of an engine.



3.)Bottom Part of Engine- It depends on bore, stroke and the number of cylinders. If an engine is having a larger stroke, we will get thump like sound that we get in Royal Enfield. If the number of cylinders in an engine is more than one it will produce better sound as compared to single cylinder engine.



4.)Exhaust- The exhaust construction is a big influence: which cylinders are combined into one pipe, separate exhausts per bank or combined or separate with a balance pipe, material.




5.)Turbo- It actually muffles the car, produces hiss sound when the turbo comes on.



MG HECTOR !! 5 FACTS YOU MUST KNOW !!

MG Motor recently announced the name of its SUV for the Indian market. Called the MG Hector, the new SUV will be officially released in mid 2019. Prior to its launch, the carmaker has released a teaser video showing minor details about the vehicle, while testing in extreme climate conditions. Here are 5 interesting facts about the MG Hector SUV that you should know.



1. MG: A ‘NEW’ carmaker for India

Operational since 1924 (pre-Independence era), MG a.k.a Morris Garages was founded in the UK (95 years old) and is known for its classic sports cars and cabriolets. MG was acquired by China’s state-owned SAIC Motor Corporation (SAIC, formerly Shanghai Automotive Industry Corporation) in the late 2000s.



According to the British automaker, the name ‘Hector’ takes inspiration from a couple of sources, all with reference to Europe. First off, the Hawker Hector which served as a biplane in the British Royal Army back in the 1930s. Second, Prince Hector of Troy, the warrior who fought valiantly in the Trojan War.

2. Competitive pricing and rivals

MG is targeting 75 per cent localisation with the Hector at launch. It is expected to be priced between Rs 15 lakh to Rs 20 lakh, similar price range as the Jeep Compass. The MG Hector will also go up against the Tata Harrier, Hyundai Tucson and the Mahindra XUV500.


3. Will get both petrol and diesel engines at the time of launch

The MG Hector will be powered by the same Fiat 2.0-litre Multijet diesel engine as the Jeep Compass. There will also be a petrol engine on offer, but MG Motor is yet to reveal any details about it. We believe that it could be a 1.5-litre turbocharged petrol, as seen on the China-spec Baojun 530. While the is there no confirmation regarding the automatic diesel variant, the petrol-powered Hector is expected to get an automatic version in India.

4. More than 45 MG dealerships at the time of launch

At the time of Hector’s launch, MG will have around 45 dealerships up and running across the country and almost as many service centres. Moreover, MG Motor will also set up a brand-owned dealership in Gurugram for those who want a more in-depth understanding of the brand. The carmaker says all MG owners will be part of an exclusive club as well. The carmaker has already announced 4 dealerships for Punjab, in Chandigarh, Jalandhar, Ludhiana and Amritsar.

5. BIGGER THAN TATA HARRIER

Compared to its arch rival – Tata Harrier, the MG Hector is 57mm longer and 54mm taller. While the former measures 4598mm in length and 1706mm in height, the latter is 4655mm long and 1760mm tall. In terms of width, however, the Harrier takes a lead. While the Harrier is 1894mm wide, the Hector measures 1835mm in width.


The launch of the Hector has been confirmed to take place in Mid 2019, which could be in June 2019. MG will have 100 sales and service touchpoints in place by May 2019.

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WHAT IS TSI ENGINE ?? CHECK OUT HERE !!

If you have kept up with updates of the automotive industry throughout the past few years, you have probably heard of Volkswagen TSI engines. It is likely you know about TDI Clean Diesel, but you may be wondering about TSI as well. So, what is Volkswagen TSI, exactly? We will discuss TSI in this post.


TSI stands for “Turbo Stratified Injection.”Volkswagen TSI engine uses a combination of turbocharging and direct fuel injection to offer high efficiency. 

With this technology, these engines can be designed smaller, allowing them to achieve high fuel economy. The direct-injection combined with a turbocharger gives high performance. Allowing the smaller engine to provide an incredible amount of horsepower and torque. With smaller designs and incredibly efficient combustion, the TSI engines are able to provide maximum power with minimum fuel consumption. Most Volkswagen models are equipped with TSI engines including the 2016 Jetta, 2016 Golf GTI, 2016 Beetle, and 2016 Tiguan.


ADVANTAGES :

Some advantages of TSI engines:
  1. Better fuel distribution and better fuel charge inside the combustion chamber
  2. During the injection process, the fuel gets evaporated, cooling the cylinder chamber
  3. The cooling effect of the pressurized fuel allows for use of a lower octane fuel leading to cost savings for the end user
  4. Higher compression ratios, which translates into more power
  5. Increased fuel combustion efficiency
  6. Higher power during pick-up of vehicle


DISADVANTAGES :


  1. Huge rise in the number of emitted exhaust particles
  2. More expensive - much higher pressure fuel pumps are required to inject the fuel directly into the cylinder. This requires fuel pressures of up to 200 bar, much greater than a traditional multiport injection setup.


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LEARN HOW TO READ WELDING SYMBOLS !!

The ability to read and understand weld symbols is very important in the manufacturing industry. Like other aspects of drafting, there’s a set of symbols for welding to simplify the communication between designer and builder (i.e. the welder).In this article, we will discuss various welding symbols and their meaning.


Let us begin with the constituents of a welding symbol. A typical welding symbol is shown below.


These figures represent the core structure of every drafting specification for a weld to be performed. The welding symbol has an arrow, which points to the location on the drawing where a weld is required. The arrow is attached to a leader line that intersects with a horizontal reference line. Finally, there's a tail at the opposite end of the reference line that forks off in two directions. The tail is optional and needed only for special instructions.

TYPICAL WELDING SYMBOLS AND THEIR MEANING :

1.) The weld symbol may also be placed above the reference line, rather than below it. This placement is important. When the weld symbol hangs below the reference line, it indicates that the weld must be performed on the "arrow side" of the joint. For example, in the figure shown below, a fillet weld is specified on the arrow side. You can see the actual weld in the second depiction.


2.) If the weld symbol appears on top of the reference line, then the weld should be made on the opposite side of the joint where the arrow points.It is represented in the figure below.


3.) If the weld symbol appears on both sides of the reference line, as shown below, it specifies that a weld must be performed on both sides of the joint. This is represented in the figure below.


4.) Each type of weld has its own basic symbol, which is typically placed near the center of the reference line (and above or below it, depending on which side of the joint it's on). The symbol is a small drawing that can usually be interpreted as a simplified cross-section of the weld. In the descriptions below, the symbol is shown in both its arrow-side and other-side positions.



5.) A weld symbol may also specify an angle, root opening or root face dimension. This is common when the base metal to be welded on is thicker than 1/4 inch. The following example is a symbol and drawing calling for a V-groove joint:


6.) Sometimes, a series of separate welds is specified, rather than a single long weld. This is common when thin or heat-sensitive metals are welded on, or where the joint is a really long one. In the following symbol and drawing, 3-inch intermittent fillet welds are specified and shown in figure below.


7.) Numbers are also a big part of a welding specification. The width, depth, root opening and length of a weld, as well as the angle of any beveling required on the base metal before welding can all be communicated above or below the reference line.

In most cases, the weld width (or diameter) is located to the left of the weld symbol (expressed here in inches), while its length is written to the right. (The weld's width is the distance from one leg of the weld to the other.) Often, no length is indicated, which means the weld should be laid down from the beginning to the end of the joint, or where there's an abrupt change in the joint on the base metal.


Dimensions written below the reference line, of course, apply to the joint on the arrow side, while dimensions written above apply to the joint on the other side. In the image above, welds are indicated for both sides of the joint.

8.) Optional Tail = Special Instructions

As you just saw in the case of the backing strip, the forked tail of the welding symbol is used to convey details that aren't part of the normal parameters declared on the reference line. For instance, the engineer or designer might want the welder to use specific welding ( for example SMAW), or another welding process. Or there may be other information to convey:

Of course, when no special instructions are needed, the tail is omitted from the welding symbol, leaving just the reference line, arrow and leader line.

Apart from these, there are other symbols but these are some of the mandatory symbols that every welding specification contains.

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LAB VIVA/INTERVIEW QUESTIONS OF THERMODYNAMICS !!

LAB VIVA/INTERVIEW QUESTIONS OF THERMODYNAMICS :


1. A quantity of matter of fixed mass and identity which is bounded by a closed surface. 

2. An enclosure which permits thermal interaction. 

3. An enclosure which prevents thermal interaction.

4. A system in which all the measurable variables have the same value as they had inside an enclosure after a long time, irrespective of the interaction that may have taken place. 

5. A region of interest, that is involved in the analysis.

 6. Any change of state occurring in a system. 

7. A region in space or control volume or quantity of matter upon which attention is focussed for study. 

8. A change of state which occurs while the system is adiabatically enclosed. 

9. Any observable characteristic of the system. 

10. A type of reversible process, characterized by the fact that the system is at each instant arbitrarily close to equilibrium. 

11. A study of the transfer and conversion of energy. 

12. If a thermodynamic system undergoes an adiabatic process, the net amount of work performed by it depends only on its initial and final states, and not on the sequence of intermediate state or path. 

13. Depends solely upon the state of the system and not upon how that state was reached. 

14. A change in the state of a system which occurs without any work being done. 

15. It is impossible to construct a device which, working in a complete cycle, will produce no other effect than the transfer of a quantity of heat from a cooler to a hotter body. 

16. Two states of two systems characterized by an absence of heat flow even when there is no adiabatic wall between them.

17. The loci of points corresponding to states of the same temperature.

18. A system going through some process whose initial and final states are the same. 

19. A system which exchanges heat and work with its surroundings while operating in a cyclic process. 

20. A hypothetical machine whose operation would violate the laws of thermodynamics.

ANSWERS:

1. system 2. diathermic 3. adiabatic 4. equilibrium state 5. system 6. process 7. thermodynamic system 8. adiabatic process 9. property 10. quasistatic 11. thermodynamics 12. first law of thermodynamics 13. property 14. free motion 15. Clausius statement 16. thermal equilibrium 17. isotherms 18. cycle 19. thermodynamic machine 20. perpetual-motion machine