METALS & ALLOYS

• Ferrous metals : wrought iron, caste iron, steel 
• Nonferrous metals : tin, zinc, aluminum etc. 

IRON ORE 
• Naturally occurring mineral aggregate from which one or more valuable constituent may be recovered by certain treatment 
• Impurities present in iron ore are 
1. Carbon 
2. Manganese 
3. Prosperous 
4. Sulfur


TYPES OF PIG IRON 

BESSEMER PIG  
• Obtained from hematite 
• Free from cu, P, S 
• Used in manufacture of steel 

GREY/FOUNDRY PIG 
• Raw materials burned at high temp 
• Soft variety 
• Used in manufacture of cast iron 

WHITE / FORGED PIG 
• Raw material Is burned at low temp 
• Hard &strong 
• Used in manufacture of wrought iron 

MOTTLED PIG
• Lies between grey pig and white pig


CAST IRON 
• 2 - 4 % carbon content 
• Made from remelting pig iron ( grey pig ) 
• Made in CUPOLA FURNACE 
• Impurities : Manganese, Phosphorus, Sulphur, Silica 

TYPES OF CAST IRONS 

1. GREY CAST IRON : made from grey pig, soft 
2. WHITE CAST IRON : hard, silvery, white, does not melt easily 
3. MOTTLED CAST IRON : intermediate between grey and white 
4. CHILLED CAST IRON : some portion made soft and other hard 
5. MALLEABLE CAST IRON : composition is adjusted to make it malleable 
6. SPHEROIDAL GRAPHITE IRON / DUCTILE : manganese treatment is given for making it ductile 
7. TOUGHENED CAST IRON : melting cast iron with wrought iron scrap 

 DEFECTS IN CAST IRON 

1. COLD SHORT : formed at junction where 2 streams of molten metal meats 

2. DRAWING : before the mould is completely filled up the metal becomes solid 

3. HOLES : due to insufficient vent air & gasses gets trapped 

4. HONEY COMBING : holes due to improper compaction 

5. LIFTS AND SHIFTS : external defect due to displacement of core 

6. SCABBING : scales seen on casting 

7. SWELLING : bulging due to over ramming 



WROUGHT IRON 
• Carbon content : not greater than 0.15 % 

MANUFACTURE OF WROUGHT IRON 

1. REFINING : pig iron melted - strong air current - agitated - impurities oxidized - product is called refined pig iron 

2. PUDDLING : converts pig iron to wrought iron using REVERBERATORY FURNAS, white spongy balls - puddle balls formed 

3. SHINGLING : the puddle balls are passed through squeezing machine - product obtained is called bloom 

4. ROLLING : the bloom is passed through rollers where flat bars are obtained, if poor quality rolled again with heat 

ASTONS PROCESS : molten steel poured into cool liquid slag - impurities are eliminated - puddle balls are obtained at 1370*c - shingling - rolling 


 DEFECTS 

1. COLD SHOT : due to excess of phosphor wrought iron shows brittle nature in cold 

2. RED SHOT : due to presence of excess Sulphur cracks are formed in hot condition 


STEEL 
• Carbon content : 0.25 - 1.5 % 

MANUFACTURE OF STEEL 

1. BESSEMER PROCESS : BESSEMER FURNACE is used - product is ingot 

2. CEMENTATION PROCESS : steel obtained is covered with thin bubbles - blister steel 

3. CRUISIBLE STEEL PROCESS : used for surgical instrument - final product is called cast steel 

4. DUPLEX PROCESS : combination of acid Bessemer process and basic open hearth process 

5. ELASTIC PROCESS : using electric furnace 

6. L - D PROCESS : using oxygen instead of air 

7. OPEN HEARTH PROCESS : using open hearth furnace 


DEFECTS IN STEEL 

1. CAVITIES OR BLOW HOLES : lack of vent holes 

2. COLD SHOT 

3. RED SHOT 

4. SEGREGATION : some portion solidify at early stage and separate from main portion 


MECHANICAL TREATMENT OF STEEL : done for converting steel to desired shape 

1. DRAWING : increasing length by reducing cross section 

2. FORGING : repeated blows under power hammer 

3. PRESSING : metal is pressed on the die and punch is lowered under high pressure 

4. ROLLING : passed through rollers 

HEAT TREATMENT PROCESS 

1. ANNEALING : heated metal allowed to cool slowly, in order to remove internal stresses and toughen it. Increase ductility 

2. CASE HARDENING : outer portion ductile, inner portion hard 

3. CEMENTING : skin of the steel saturated with carbon 

4. CYANIDING : adding C & N to the surface 

5. NITRIDING : saturating surface with N 

6. TEMPERING : improve ductility hardness , strength 

7. HARDENING : metal cooled fast 

8. NORMALIZING : restoring to normal condition

PREVIOUS YEAR REPEATED QUESTIONS BASED ON METALS & ALLOYS 

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