Farm Machinery and Equipment-I 3(2+1)

Lesson 2 Materials of construction of farm equipment

II Classification of materials:

Broadly there are two groups of materials namely metallic and non-metallic

Metallic		Non-Metallic
Ferrous	Non-Ferrous	Wood (timber)
Iron: Cast iron           Wrought iron	Copper (Cu)	Rubber
Steel: Steel           Steel Alloys	Zinc (Zn)	Leather
	Lead (Pb)	Plastics
	Tin (Sn)	Fiberglass
	Aluminum (Al)	Teflon
	Brass (Cu+Zn)
	Bronze (Cu+tin)
	White metal or Babbit (Tin+Cu)
	Solder (Tin+lead)

 

III  What is an Alloy?

It is a substance that has metallic properties and is composed of two or more chemical elements, of which atleast one is a metal. There is infinite number of alloys. They are made by fusion of metals. Common groups of alloys are:

a)  Alloy steels using manganese, chrome, nickel, tungsten etc. as alloying elements.

b) Non-ferrous alloys:

Bronze

Brass

Babbit or antimony, solder

Aluminum alloys

 

IV Classification of Steels:

 Steel is an alloy of carbon and iron. Steels are classified according to:

 

a) Manufacturing Process:

    Bessemer Steel

    Open Hearth Steel

     Electric Steel

b)  Carbon Content:

      Low Carbon (upto 0.25% c)

      (Easy to bend, forge and shear)

       Medium Carbon Steel (0.25% to 0.50% c)

       High carbon steel (0.50 to 1.2% c)

 c)   Alloy steel (mixture of two or more chemical substances one of which is a metal)

 d)   According to Uses:

      Structural Steel

      Tool steel

 e)  According to Method of Forming:

      Rolled Steel

      Forged Steel

      Cast Steel

      Formed Steel

 

V Purpose of Alloying Substances:

a) Manganese: Used for cutting tools and high grade ball bearings. It imparts hardness

b) Chromium: Same as manganese

c) Tungsten: Helps in maintaining sharp edge even when the cutting tool is hot.

d) Nickel: Helps in making steel elastic and ductile.

 VI  Application of Steel:

a) Low carbon steel: Used extensively in the construction of farm machinery. Frames and most of other members are made out of low-carbon steel.

b) Medium carbon steel: Used for greater strength and hardness. Members such as shafts, connecting rods etc. are made of medium carbon steel.

c) High carbon steel: It is very hard and is used for making tools, ball and roller bearings, cutting tools etc.

 VII Alloy Steels and Their Composition:

S.No.	Types of Alloy Steels	Composition
1.	Boron Steel	Contains small amount (2.3%) Boron. Boron increases harden-ability of steel. Parts made: Axles, wheel spindles, steering nickel arms, cap screws, studs etc.
2.	Manganese Steel	Contains 11-14% manganese & 0.8-1.5% carbon It has extreme hardness and ductility. Can be cast in desired shapes and finished by grinding. Parts made: Machine parts subjected to severe wear e.g. feed grinders
3.	Nickel Steel	Contains 2-5% nickel & 0.10-0.5% carbon They are strong, tough and ductile Parts made: Used to make parts subjected to repeated shocks and stresses.
4.	Vanadium Steel	Contains 0.20% vanadium It is added for higher tensile strength and elasticity. Comparable to low and medium carbon steels.
5.	Chrome-Vanadium Steel	Contains 0.5-1.5% chrome, 0.15-0.3% vanadium and 0.15-1.10% carbon Parts made: Used for hard and malleable machinery casting, forgings, springs, shafts, gears and pins.
6.	Tungsten	Contains 3-18% tungsten and 0.2-1.5% carbon. Parts made: used for dies and high speed cutting tools
7.	Molybdenum Steel	Properties similar to tungsten steel
8.	Chrome Steel	Contains 0.5-2% chrome and 0.10-1.5% carbon Parts made: used for high grade balls, rollers, races for ball and roller bearings 14-18% chrome used to produce variety of stainless steels
9.	Chrome-Nickel Steel	Contains 0.3-2% chrome, 1.0-4.0% nickel and 0.10-0.60% carbon Parts made: used for gears, forgings, crankshafts, connecting rods and machine parts
10.	Stainless Steel	Contains 16-18% chrome, 7-8% nickel and less than 0.15% carbon Parts made: ********?
11.	Tool Steel	Tool steel means high carbon steel which is used for making tools. It is extremely hard by quenching from a temperature of 800-850°c. Degree of hardness can be altered by heating at lower temperature.

 

VIII Cast Iron: It is also an alloy of carbon and iron. The percent of carbon varies between 2.4-4.5%. It is very hard and brittle. There are five general types of cast iron:

1. Grey Cast Iron: Carbon occurs in the form of graphite flakes which imparts it grey colour and leads to crystalline structure.

2. White Cast iron: Carbon remains in a chemically combined form and gives it a characteristic white colour when fractured.

3. Chilled Cast Iron: It is made by chilling or rapid cooling of certain portions of the casting. Chilled parts have the characteristics of white cast iron and slowly cooled parts exhibit characteristics of gray cast iron. Example: Mould boards (only one side is hardened)

4. Malleable Cast Iron: It is made by subjecting the white casting to annealing or “softening” process. Cast iron is heated to temperature of about 900°c and is held in the oven for sufficiently long period and is then cooled quite slowly. This changes the chemically combined carbon into free carbon in an “amorlous” form but not in the crystalline form as in the gray cast iron.Casting made out of malleable cast iron are tough, strong and easy to machine.Examples: Mower guards, ledger plates, control pedals (clutch brake), chain links etc.

5. Malleable Cast Iron: It was developed in 1949. It is a high-grade iron produced by adding magnesium alloy to molten iron prepared to produce gray cast iron. Magnesium acts as a desulphurizer when added in controlled amount, it produces spheroidal carbon instead of flake carbon (graphite) as in the case of gray cast-iron.   Examples: Sprockets, gears, plow shares, mower guards, parts of hay-bailer knotter mechanism etc.

IX Non-Ferrous Metals: uses of non-ferrous metals and alloys are discussed below:

1. Copper (Cu): tubing, wires, windings etc

2. Brass: It is an alloy of Cu (60-90%) and Zn (10-40%). Used for making radiator pipes, brass welding rods, screen for fuel lines, instrument parts etc.

3. Bronze: It is an alloy of Cu (80-95%) and Tin (5-20%) Zinc is also added sometimes. Used for making bushings, springs, pipe fittings, valves, pump pistons and bearings.

4. Babbit: it is a tin-based alloy with small amount of copper Cu (7-8%), Antimony (8-9%) and Tin (80-84%). Used for making bearings.