Fitting Shop

Fitting work is a very important work in engineering. In fitting shop unwanted material is removed with the help of hand tools. It is done for mating, repair and manufacturing purposes. The person working in the fitting shop is called a fitter. A fitter should have the complete knowledge of the tools used in the shop. Commonly used tools are hacksaw, files, chisels etc.

PHYSICAL PROPERTIES OF METALS

As different types of metals are used  in fitting shop, therefore, it is necessary for the students to have some knowledge about the physical properties of the metals.

Luster

It is the ability of a metal surface to reflect light rays.

Color

It is the property of the metal to show a specific surface appearance. It depends upon the composition of the metal.

Density

It is defined as the mass per unit volume of the metal. It is measured in Kg/cm^3.

Melting point

It is the temperature at which a metal flows like a fluid is known as melting point. Melting point of iron is 1539 C.

Boiling point

The temperature at which a metal starts boiling is known as the boiling point of the metal.

Plasticity

By this property of the metal it can be converted into required shape and size for commercial use either by application of heat or pressure or both.

Elasticity

It is the property of the metal by which it can resist permanent deformation in new shape and size due to external pressures.

Stiffness

Due to this property material resists deflection due to external loads.

Malleability

It is the property by which metal can be elongated in all directions by the application of external pressure, due to this property metal can be converted into sheets.

Toughness

Due to this property metal can withstand bending without failure.

Ductility

By this property metal can be drawn in the form of wires, without failure.

CLASSIFICATION OF METALS

a. Ferrous metals example: mild steel, cast iron, high speed steel etc.
b. Non-ferrous metals example: copper, brass, aluminium, tin etc.

FERROUS METALS

In these metals the percentage of iron is very high. These are commonly used for engineering purposes. Some other materials like carbon, sulphur, nickel etc. are also mixed into ferrous metals to change their properties. Ferrous metals are magnetic in nature and have more hardness.

STEEL:

Steel is mixture of iron and carbon. It is very widely used in engineering for different purposes.

ALLOY STEEL:

It is made by combining some percentage of additional elements into plain carbon steels. The material to be mixed depends upon the properties required from alloy steel. Generally strength, hardness, resistance to corrosion are the main desirable properties. Nickel, phosphorus, silicon, chromium, molybdenum etc. are added to make alloy steels.

CAST IRON:

The iron containing carbon more than 2% is known as cast iron. It is hard and brittle material. It is generally used for making beds and heavy parts of machines. It is mainly of two types:
a. Grey cast iron: Grey cast iron is self lubricated material and is easy to machine due to free graphite’s.
b. White cast iron: White cast iron is difficult to machine due to the presence of cementite.

WROUGHT IRON:

It is almost pure iron containing 99.9% of iron. The percentage of carbon is low. It is ductile and soft. It can be rolled into sheets or drawn into long wires. Iron rivets are made of wrought iron.

HIGH SPEED STEELS:

These are used for making cutting tools working at high speeds. They are able to retain the hardness at high temperatures. The composition of high speed steel is 18% tungsten, 4% chromium, 1% vanadium and 0.7% carbon.

SPRING STEEL:

It is used for making springs or blades. It contains 0.5-0.6% carbon.

NON-FERROUS METALS 

The metals which contains negligible or no quantity of iron are known as non-ferrous metals. Copper, aluminium, brass, bronze, tin, lead are some of the common examples of it.

COPPER:

It is widely used in engineering industry. Copper is very soft, ductile having reddish brown color. It has high electrical and thermal conductivity. It is commonly used for electrical purposes. Sulphur, nickel, tin and cadmium are added to it to change the properties of copper.

BRASS:

Brass is an alloy of copper and zinc. There is no effect of corrosion on brass. It can be easily soldered this is also soft and ductile material.

BRONZE:

It is an alloy of copper and tin. Bronze have a good resistance to atmospheric corrosion and have no effect of water on it. It is a wear resistant material.

GUN METAL:

It is an alloy of copper, tin and zinc. Tin is 10% and zinc is 2% in it. It is used for making castings.

ALUMINIUM:

It is a soft material with a white color. It is very light and have good electrical and thermal conductivity. Aluminium is used for electrical and decorative work.