Mechinopedia For Mechanical Engineers

  White cast Iron contains carbon exclusively in the form of cementite (Iron Carbide). This is obtained by the presence of relatively large quantities of manganese , a very small amount of silicon, and by rapid cooling. The ordinary rate of cooling in sand produces free graphite while rapid cooling helps to produce cementite. More over, manganese encourages the formation of carbide. The white cast iron is very hard (the hardness ranges from 400 to 600 BHN) and brittle, and its fractured surface has a silvery metallic appearance. From the engineering point of view, white cast iron  has limited application. This is due to its un machinability and to its having , in general , relatively poor mechanical properties. It is widely used in the manufacture of wrought Iron. White cast Iron is also cast as the intermediate material for making malleable cast iron.  White cast iron does not rust so much as the grey kind.  

Phosphorus in cast iron aids fusibility and fluidity but induces brittleness. It is rarely allowed to exceed 1.0 percent . Phosphoric Irons are useful, however, for castings when cheapness is essential. 

Manganese tends in a different way to whiten and harden cast iron by encouraging the formation of  carbide. It is therefore, often kept below 0.75 per cent. But it helps to exert a controlling Influence over the harmful effect of Sulphur , and for any particular purpose these two impurities should be considered in conjunction.   

Sulphur is generally regarded as harmful in cast Iron. It lowers the viscosity of the melt and tends to make the cast iron hard and brittle. So it should be kept well below 0.1 percent for most foundry purposes. In wrought iron, 0.01 to 0.04 per cent of  Sulphur produces shortness-that is , the metal becomes brittle and unworkable at red heat, although possessing the usual qualities when cold.  

Silicon in cast iron may be present up to 2.5 percent. It promotes the formation of free graphite which makes the Iron soft and easily machinable. At the same time, this element Inhibits the pick - up of carbon during the melting of Iron. It also produces sound castings free from blow holes because of its high affinity for oxygen. A very small amount of  silicon makes wrought Iron hard, brittle and unforgeable.

When Carbon is dissolved in Liquid Iron, and if the solution is solidified slowly the carbon tends to separate out giving a structure which is a mixture of pure iron and graphite. This gives a fairly tough iron which breaks with a dark glistering fracture. It is easily machined. If the same iron is cast and cooled quickly, it is hard , has a higher tensile strength , is difficult to machine and breaks with a close, white fracture. The white constituent is Iron Carbide , called cementite.   

 In the Aston or Byers process , to produce wrought iron, the pig iron is first melted in a cupola furnace and refining of molten metal is done in a Bessemer converter . At the same time, a quantity of iron silicate slag in prepared in an open hearth furnace. The refined Iron so made in the Bessemer converter is poured at predetermined rate into a ladle containing the molten slag already prepared. After the excess slag is poured from the ladle, the remaining mas of iron and slag is taken to a press where some slag is removed. The rectangular block is formed in the press is known as bloom . The hot bloom as before is immediately passed through rolling mills to produce products of wrought Iron of different shapes and sizes. 

What is puddling Process ?And How it is Used In Wrought Iron?   Pig Iron for this purpose is first subject to a preliminary process of refining, the object of which is to remove silicon as completely as possible together with the greater part of the phosphorous, and to convert the graphite into combined carbon and this produces White Iron. The next Process is to convert the white Iron into wrought Iron. To do this the slabs of the white Iron are broken into pieces and taken to the puddling furnace which is coal fired reverberatory furnace. The products obtained is known as blooms having a mass of about 50 kg. The hot metal is then passed through grooved rollers which convert blooms into bars called muck bars or puddle bars, which have a cross-section of approximately 15 to 100mm. These bars are cut into short length, fastened together in piles, reheated to a welding temperature and again rolled into bars.  

What is Wrought Iron ? How it is Made ?  Wrought Iron is highly refined iron with a small amount of  slag forged out into fibers. The chemical analysis of the metal shows as much as 99 percent of Iron. The slag characteristic of wrought Iron is useful in blacksmithing operations and gives the material its peculiar fibrous structure. The non - corrosive slag constituent causes wrought iron to be resistant to progressive corrosion. Moreover, The presence of slag produces a stricture which diminishes the effect of fatigue caused by shocks and vibrations.  It is tough , malleable , ductile and has an ultimate tensile strength of about 35 kg-f per mm2. ( 350 Newton per mm2). It cannot be melted, but at a white heat, it becomes soft enough to take any shape under the hammer, i.e., it can be forged. It admits readily of being welded. This iron has the property with being able to withstand sudden and excessive shock loads with - out permanent Injury. It rusts more quickly than cast iron but st

MANUFACTURING OF MEEHANITE CAST IRON :  Cast irons, in which metal has been treated with calcium silicide, are known by the trade name of meehanite. Calcium Silicide used to graphitize and fine graphite structure giving a cast Iron of  excellent mechanical properties. The high qualities of meehanite Iron are , however , not solely due to the use of calcium silicide but also due to careful control of all the factors in the melting of iron in the copula or electric furnace and in the molding of the casting. Very little calcium silicide remains in the iron after solidification. The metal used is low in silicon, moderately low in carbon which is limited about 2.5 to 3 percent. This normally would be white if cast, but graphitizing by meehanite system of control provides a range of materials to meet the broad requirements by engineering industries. There are in all more than twenty six types of  meehanite metal available at the present under five broad classification :  (a) General Engineer

Alloy Cast Iron have been developed in recent years to overcome certain inherent deficiencies in ordinary cast Iron and to give qualities more suitable for special purposes. The addition of nickel, chromium, molybdenum, titanium, silicon, copper and other alloying elements confer special properties to this cast Iron. The use of 1 or 2 percent of nickel is suitable good quality iron offers a simple and effective means of improving the properties to this cast iron. It ensures machinability and uniformity of structure of the cast iron. By the use of nickel of the order of 25 percent, enhanced life can also be obtained in parts subjected to abrasive wear. Cylinders or cylinder liners of all sizes form the smallest to the largest afford outstanding examples. Nickel Cast Iron is also used in withstanding caustic corrosion. For this reason. It is widely employed for making caustic pots, pipes and other castings in contact with  caustic liquor. The addition of only 1 percent of nickel gives a

Quick Cooling is called "Chilling" and the iron so produced is "Chilled Iron" . All castings are chilled at their outer surface by coming in contact with the cool sand in the mold. Since cast Iron has a higher thermal conductivity than sand, the chilled portions of  the casting undergo rapid solidification and cooling and, thereby produce a herd surface. But this hardness only penetrates about 1 to 2 mm in depth. Sometimes a casting is chilled intentionally and sometimes becomes chilled accidentally to a small depth. Intentionally chilling is carried out by using cast Iron Instead of sand for those portions of the mold where hard surfaces are required. Where these are touched by the m olten metal , its surface is suddenly cooled and converted into the white cast Iron. Chills are used on those castings where some parts are required to have the hardness of white cast iron, While others are required to have relatively soft and tough core of grey cast Iron. 

Spheroidal graphite iron , also called modular cast iron, is of  a higher grade because graphite is precipitated not in the form of flakes but in the form of spheroids. This can be achieved by various methods, e . g., by the addition of one of the following elements : magnesium, cerium, calcium, bismuth, zinc, cadmium, titanium or boron. Ferro - Silicon is also used as an inoculant. Spheroidal cast iron can be producer in thicker pieces than those produced by malleable cast Iron. Outstanding characteristics of spheroidal cast iron are high fluidity, which permits the castings of intricate shapes, and an excellent combination of strength and ductility. The tensile strength of this iron is about   33 kg-f per mm2 (330 Newton per mm2). This material is also known as Ductile Iron.  Spheroidal cast iron is widely used in cast parts where density and pressure tightness is a highly desirable quality. They Include hydraulic cylinders , valves , pipes, and pipe fittings, cylinder head for com

 The Ordinary cast Iron is hard and brittle. It is therefore, unsuitable for articles which are thin, light and subjected to shock and vibration or for small castings used in various machine opponents. The application of the term "malleable" to castings is rather a misnomer because they are not very malleable when compared with the standards of malleability. When compared with grey iron castings, however , which are fairly brittle, malleable castings do possess a degree of toughness, and this is probably why they have been so named. Malleable Castings are first made from an  iron having all of its carbon in the combined form. i.e., from white cast iron. Two methods are then used for malleablizing the castings : (1) White heart, and (2) black heart. The names refer to the color of the fracture given by castings produced by each method. The approximate chemical compostions are  White Iron  Carbon - 3.2% , Silicon - 0.4 -1.1% , Manganese - 0.1to 0.4 % , Sulphur - 0.10 to 0.3

This is obtained by allowing the molten metal to cool and solidify slowly. On Solidifying , The iron contains the greater part of carbon in the form of  graphic flakes. Grey cast Iron contains large quantities of carbon and relatively small quantities of the other element, e.g., silicon phosphorous , Sulphur and manganese. It presents a dull grey crystalline or granular structure and a strong light will give a glistering effect due to the reflection of the free graphite flakes. The presence of this free graphite is also seen when filing or machining cast iron as it makes hands black. The Cast Iron is brittle and may easily be broken if a heavy hammer is used. The strength of  Iron is much greater in compression than in tension. The ultimate tensile strength of  Cast Iron varies between 12 to 13 kg-f per mm2 (120 to 300 Newton per mm2) and depends on the composition of the Iron. In compression , Gray cast Iron will withstand about 60 to 75 kg-f  per mm2 (600 to 750 Newton per mm2) bef

Cast Iron is Pig Iron re-melted and thereby refined together with definite amount of  limestone, steel scrap, and spoiled castings in cupola or other form of re-melting furnace, and poured into the suitable molds required shape. It contains about 2to 4 percent of carbon , a small percentage of silicon, Sulphur, phosphorous and manganese and certain amount of alloying elements, e.g., nickel chromium, molybdenum, copper and vanadium. Carbon in cast iron usually exists in two forms associated together : (1) as the compound cementite i.e., in a state of chemical combination and the iron is known as white cast iron, and (2) as free carbon , i.e., in a state of mechanical mixture. Carbon in the first form is called "combined carbon" , and in the latter is called grey cast iron. An Intermediate stage between these two varieties of  Iron shows patches of grey in the white structure . This Iron is Mottled Iron. The Quality of cast iron thus depends not upon the absolute amount of carb

Electric Pig Iron furnaces are becoming popular where suitable metallurgical coke is not available in sufficient quantities and where electricity is cheap. The advantage with the furnace is that coke consumption is reduced by 50 percent, as heating is done by electricity and only reduction of the iron ore is done by coke. A medium sized furnace of the type can produce 100 to 110 tons per day. Charging of raw materials and other operation principles are practically same as that of the other common methods. Now-a-days , low shaft blast furnaces being developed to make use of low grade coke and iron ore. Oxygen also is used to help the reaction. Another process which is also being developed is the sponge iron process. This new process for treating low grade iron ore by direct reduction , in place of the conventional blast furnace method, is being fast developed. It will be of great advantage to a country like India where large quantities of low grade iron ore remain unused.  A certain a

 The Blast furnace is the vertical furnace designed for continuous operation. The smelting room of the blast furnace comprises a throat, stack, body, bosh and hearth. The Raw materials (alternate layers of ore, coke , flux) , known as the charge, are taken to the top of the furnace by a specially designed bucket called "skip" running along an incline. The charge is then introduced into the throat of the furnace by means of a double bell and hopper arrangement to prevent the escape of blast furnace gas which is used as a fuel. The proportions of the raw materials are approximately one-half iron ore, one-third fuel, and one sixth flux. It may be pointed out , for instance to make 100 tons of pig iron it requires about 180 tons of iron ore, nearly 95 tons of coke, 50 tons of flux, and about 350 tons of preheated air blast. In addition to pig iron, about 60 tons of slag and 50 tons of gas are produced.   A hot blast is forced into the furnace through a number of nozzles called T

All iron and Steel Products are derived originally from pig iron. This is the raw material obtained from the chemical reduction of iron ore in a blast furnace. The process of reduction of iron ore to pig iron is known as smelting. The main raw materials required for pig iron are :  (1) Iron Ore  (2) Cooking coal (3) Flux.  Iron ores are generally carbonates, hydrates or oxides of the metal, the latter being the best. These Iron ores are found in India in Several States namely, Bihar, Orissa, Madhya Pradesh, Andhra Pradesh, Karnataka, Tamil Nadu, and Some other places.  The coke used in the blast furnace should be very high class hard coke obtained from good quality coking coals containing as low phosphorus and Sulphur as possible. It is produced by heating what is commonly called as "dry distillation" of the coking coals in coke ovens made of silica bricks in the absence of air to avoid giving off valuable gases. A light porous , sufficiently firm fuel which burns well is thu

 Ferrous metals and alloys are widely used because of the development of a technology that has produced thousands of different alloys and grades that provide a wide range of properties not found in any other family of materials. Further, they are economical on a basis of cost per unit of length. The Latin word of iron is ferrum. So metals which contain iron are classified as ferrous metals. The principle ferrous metals used in engineering are classified under the following groups : 1. Pig Iron  2. Cast Iron. 3. Wrought Iron. 4. Carbon Steel. 5. Alloy Steel.