Wrought iron

Cast Iron

Pig iron along with scrap iron, coke and limestone is melted in a vertical furnace called cupola. Here also the carbon and other impurities present oxidise in presence of a little amount of air, to form slag. The molten iron obtained from cupola furnace can be cast into moulds. It is, therefore, known as cast iron. It consists of 93-94% Fe, 2-4% carbon and a little of S, P, Si and Mn impurities. It is vary hard and brittle. It is cast into covers of manholes, drain-pipes, frames of machines etc.'

Wrought Iron
Wrought iron is the purest form of iron containing not more than 0 • 2 peri jnt carbon and 0-3 percent of other impurities, i.e., sulphur, phosphorus, silicon and manganese.

Manufacture
It is obtained from cast iron by removing the major portion of its impurities by the well known puddling process. The cast iron along with some scrap iron is heated on the hearth of a reverberatory furnace lined with haematite. Fe₂0₃. The hot gases and flames reflected from the roof of the furnace falls upon the charge placed on the hearth. The cast iron melts down and the molten mass is stirred or puddled at intervals by means of a long pole introduced through an inlet in the wall of the furnace. The haematite supplies the oxygen required to oxidise the carbon, sulphur, silicon, manganese and phosphorus present in the cast iron.
Carbon and sulphur are oxidised to carbon dioxide and sulphur dioxide, respectively. Silicon and manganese are oxidised to silica and manganous oxide, which combine to form manganous silicate.
3Si + 2Fe₂0₃ —* 3Si0₂ + 4Fe 3Mn + Fe₂0₃ —» 3MnO + 2Fe MnO + Si0₂ —» MnSi0₃

Slag
Phosphorus is oxidised to phosphorus pentoxide which forms ferric phosphate slag with haematite.
P₂0₅ + Fe₂0₃ —* 2FeP0₄

Slag
As the impurities are eliminated, the melting point of the metal rises and iron becomes pasty. The pasty mass is stirred which forms "balls" or "blooms" which are spongy in texture due to large amounts of slag. The balls are taken out from the furnace and the slag is squeezed out by hammering. Finally, iron is rolled into sheets or forged into bars.

Wrought iron is soft, grey, tough and can be welded. It is malleable and has a fibrous structure due to the presence of thin films of slag between layers of pure iron. The presence of slag makes it extremely tough and resistant towards rusting



and corrosion. It softens at 1000°C and melts at 1530°C. It is used to make articles which are subjected to sudden and repeated stresses such as chains, anchors, wires, bolt, agricultural implements and cores of electromagnets. It has now been largely replaced by mild steel owing to its high cost.

Metric System Chart

About Metric System:

• Metric system is an International system of measurement used commonly for measuring units in the world.
• Metric system exists in various choices of fundamental units although the choice of base units does not get affected in any form.
• Metric units are used universally in scientific work around the world for all forms of personal and commercial purposes.
• Standard set of prefixes in powers of ten are used to derive larger and smaller units from the base units.
• Goal of the metric system is to prescribe a single unit for every physical quantity so as to avoid the need for conversion factors.
• Meter is the basic unit used to measure lengths and distances. This unit is converted to many other units such as inches, feet, yards, fathoms, rods, chains, furlongs, miles, nautical miles, leagues, etc.
• Early metric system includes several fundamental or base units and other quantities are derived from the base units. For example the basic unit of speed is calculated as meters per second.
• The metric system is also called as decimal system because all multiples and sub multiples of the base units are basically factors of powers of ten.
• In a formal representation fractions are not used to represent Metric units.

Advantages of a decimal system:

• They substitute other non-decimal systems too apart from metric system of measurements.
• All derived units use a set of prefixes for each multiple such as kilo for mass (kilogram) or length (kilometer) both indicating a thousand times the base unit.

Metric System Chart

Quantity	Unit	Symbol
Length	Millimeter Centimeter Meter Kilometer	mm cm m Km
Mass	Milligram gram Kilogram Ton	mg g Kg T
Time	Second	s
Temperature	Degree Celsius	oC
Area	Square meter hectare square kilometer	m2 Ha Km2
Volume	Millimeter cubic centimeter liter cubic liter	ml cc L Cl
Speed	Meter per second Kilometer per second	m/s km/s
Density	Kilo gram per cubic meter	Km/cc
Force	Newton	N
Pressure	Kilo Pascal	K Pa
Power	Watt, kilo watt	W KW
Energy	Kilo joule, mega joule	KJ MJ
Current	ampere	A

Prefixes used in Metric System Units

Giga	G	109
Mega	M	106
Kilo	k	103
Centi	c	10-2
Milli	m	10-3
Micro	μ	10-6
Nano	n	10-9

Pig iron productions

Introduction :

Pig iron is the intermediate product which is obtained during the smelting of iron ore with coke, in this process limestone is used as flux. Pig iron has maximum carbon content, it is around 3.5–4.5% which improves the brittleness of iron. In olden days, the Chinese Zhou dynasty were making pig iron in Europe. The plant used for the pig iron production is sinter plant.There will be use of two furnaces for the pig iron production. The word pig iron comes from old casting blast furnace iron method into moulds which are arranged on the beds of sand.

Pig iron production:

Blast furnace used for pig iron production:

Pig iron production is done by blast furnace method which involves the smelting of iron ore like hematite, i.e.
Fe₂O₃ + 3CO → 2Fe + 3CO₂

A blast of preheated air is blown through the furnace which reacts with carbon which is in the form of coke to produce carbon monoxide and also a large amount of heat is produced. The produced carbon monoxide reacts with the iron ore to form molten iron and carbon dioxide. Unreacted carbon monoxide, nitrogen which is present in the blown air and hot carbon dioxide are fed into the reaction zone as a fresh feed so that there will be preheating of fresh feed using counter current gases and also there will be the decomposition of limestone to calcium oxide and carbon dioxide and starts to reduce iron oxide in the solid state. So formed calcium oxide reacts with some of the acidic impurities which are present in iron which form a slag called calcium silicate. The reactions involved in the pig iron production are

C + O₂ → CO₂
CO₂ + C → 2CO
CaCO₃ → CaO + CO₂
SiO₂ + CaO → CaSiO₃(slag)

The pig iron obtained by this method has high carbon content so which increases the brittleness by that it has limited commercial applications. If there is a need to reduce the carbon content, pig iron undergoes further processes.

Applications of Pig iron:

• Pig iron sometimes used to produce cast iron and Gray iron which is achieved by smelting the pig iron.
• Pig iron is used to produce steel metal.

Iron Steel Manufacturing

Introduction :
Iron produced in the blast furnace is known as pig iron or cast iron.  Pig iron is the iron which contains 4% of carbon and some other impurities.

Carbon contents present in pig iron are reduced by burning off carbon as carbon monoxide and carbon dioxide. Impurities present as sulphur, manganese etc are oxidised as their oxides. There are three methods of burning carbon for production of steel.

(i) Bessemer Process
(ii) Open Hearth Process
(iii) Electric Furnace Process

Bessemer Process of Manufacturing:

This was the first process for the mass-production of steel from molten iron. Henry Bessemer invented this process in 1855.

Principle: Removal of impurities from iron by oxidation is the key principle of this process. The oxidation also raises the temperature and hence melts the iron.

Process: In this process, burning takes place in a pear shaped furnace called Bessemer Converter. This furnace is coated with basic mixture of calcium oxide or magnesium oxide (CaO / MgO). Hot air is introduced through holes. The temperature of furnace is maintained at 1873K. Manganese in the iron is removed as manganese silicate, (which is called as slag).

2Mn + O₂ ----------> 2MnO

Si + O₂ -----------> SiO₂

MnO + SiO₂ -----------> MnSiO₂

Phosphorus present as impurity is removed by formation of slag. This slag is called Thomas slag. Thomas slag is very useful fertilizer.

4P + 5O₂ -----------> 2P₂O₅

3CaO + P₂O₅ -----------> (Ca)₃(PO4)₂    Thomas Slag

Open hearth process of manufacturing:

This process can be used for rapid manufacture of large quantities of steel. The steel producd by this process can be used for the construction of the high buildings. This process complemented the Bessemer process to produce steel. It is easier to control because it is a slow process.
In this process, cast iron, iron scrap, haematite and lime is taken in open hearth furnace. This furnace is heated at temperature of 1873 K. This furnace is heated with (CO+N₂). (CO+N₂) is called producer gas. Impurities are removed by oxidation with haematite.

Fe₂CO₃ + 3C ----------> 2Fe + 3CO

2Fe₂O₃ + 3S -----------> 4Fe + 3SO₂

5Fe₂O₃ + 6P ------------> 10Fe + 3P₂O₅

2Fe₂O₃ + 3Si ------------> 4Fe + 3SiO₂

3CaO + P₂O₅ ------------> Ca₃(PO4)₂ (Slag)

Electric Arc Furnace

 In this method, iron is heated electrically. Normally thesedays, steel is prepared by open hearth process. About 39% of the steel manufactured in US is produced from the electric furnace. The stel produced by this process is not very pure or of high quality.

Energy Consumption: An electric arc furnace consumes an energy of 350 - 700 kWh/ton of steel produced. We can reduce the energy consumption to 425 kWh/ton by using oxy-fuel burners.
This process is used for the electric production of steel. It is used for remelting of steel scrap. This process is useful for those markets where the quality of steel is not critical.

Air speed

Introduction :
It is the speed of an air related to the aircraft among them the qualifying airspeed are Calibrated airspeed, Indicated aircraft, Equivalent air speed, true airspeed and finally the density airspeed. This aircraft speed is measured by the airspeed indicator which is shortly and popularly known as ASI. These are connected to the pitot static system. Types of the airspeed are Indicated airspeed, Calibrated airspeed, Equivalent airspeed, True airspeed. In this article we will know types of articles and how to calculate the airspeed.

Air speed Types

Indicated airspeed is abbreviated as IAS. This indicator reads directly form the airspeed indicator by the pitot static system on the aircraft. This is the airspeed related to the CAS that is calibrated airspeed it is corrected for the installation errors and the instrument.

These IAS are very much important for the pilots for the various purposes like calculation of the limited speeds and so on. This plays an important role in the airspeed.

Calibrated air speed is for the instrument errors and position errors and the installation errors. This equation shows the installation and the minus position.
Where, Vc is the calibrated airspeed
qc is the impact pressure
Po is static air pressure. Measures 29.92126 inches Hg at sea level.
ao is speed of sound. Measures 661.4788 knots at standard sea level.

Equivalent & True airspeed

Equivalent airspeed: This produces dynamic pressure as the true speed at the altitude where the vehicle is flying. It is forward to the flight for the effects of compressibility. Compressible impact pressure makes a function of calibrated airspeed. At standard sea level equivalent airspeed and calibrated airspeed are equal.

True airspeed is also called as TAS, it is the physical speed of the aircraft. The relation between true airspped and speed is Vg.
Vt = Vg - Vw
Where Vw is the wind speed vector.
To compute true airspeed using a function of mach number
V_{t =} a_o.M`sqrt(T/(To))`
Where:
a_o= Speed of sound(661.4788 knots) at standard sea level
M = Mach number
T = Temperature in kelvins
T_o= (288.15 kelvins)Standard sea level temperature

Speed of Light and Sound

Introduction :

Light and sound are the essential part of our life and with an absence of one; we will not be able to communicate or to detect properly as we can do with help of these two. Light and sound both are the sensations produced by energetic particles with the help of which we will be able to see or listen. 

Difference between Speed of Light and Sound :

Regarding the speed of light and sound we can say the following points

1. Speed of light is much faster than the speed of sound in air.
2. Light do not require the medium to travel with its speed while the sound require medium to propagate.  
3. Speed of light is much less in transparent than what it had in vacuum.  While the speed of sound is much, fast in solid medium such as steel then in air.

Speed of light and sound : Conclusion

Why speed of sound Differ in different mediums means solid, liquid and air?

Explanation:
Since sound require medium particles to propagate properly, hence the medium having particles much closer will enhance the movement (speed) of sound wave rather than the medium which have a long gap between the particles. Since, the molecules spacing for solid, liquids, and gases are different in that gas molecules are more spread apart & free to move, liquids are a little more structured, and solids are very compact.             

The other reason for the different speed in different mediums is the elasticity of the medium. More the elasticity in the medium more will be the speeds of sound as we can understand with ball, more the elasticity of the ball more will it jump. Since steel is more elastic than air, so sound travels 19 times much faster in steel than its speed in air. E.g. if we put your ear on rail track we can hear the vibration of the train movement in the track much before than the whistle of the train which travels through air.

Aircraft speed of sound

Introduction :
Air crafts with propellers in the initial stages were not able to perform well when they approached the speed of sound. This problem resulted into deep research into jet engines conducted mainly by Frank White of England and Hans van Ohain of Germany. They carried out this research in their respective countries.

Breaking Sound Barriers

Various sources claimed to have broken the sound barriers. Claims were made that air crafts ran smoothly at the speed of sound without any turbulence but there were many disputes against these claims. These claims were made as early as 1945. Man has attempted to break the sound barriers since the time the first plane was invented by the Wright Brothers. Bell X-1 was the first flight to travel faster than the speed of sound and this happened on 14^th October, 1947 under Captain Charles Yeager.

Speed of Sound

The exact speed of sound is not known but it is considered that it varies according to the height above sea level or what we call as altitude. It is 761 mph at sea level and at 20000 feet above it is 660 mph.

Modern Aircrafts and their speed

Today there are several air crafts like fighter jets that travel at speeds faster than the speed of sound regularly. When the aircraft reaches close to the speed of sound what happens is quite interesting in respect of the movement of air around the wings of the plane. It is called the Prandtl-Glauert singularity and it is quite photogenic.

Conclusion to aircraft speed of sound

In two decades ranging from 1947 to 1967 there were appreciable efforts by man to reach the speed of sound and there are crafts that are unmanned and cross the speed of sound easily and that is quite a remarkable achievement. There will be further developments and we all have to wait and watch how fast air crafts will become.