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.