Examen engineering

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(i) [pic] (ii) [pic]
Corrosive substance: a substance Caution: warning of an immediate
that may destroy living tissues. danger.

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Pyrometallurgy uses heat energy to separate ore, this principle is used during the
smelting of iron ore in the blast furnace.
Hydrometallurgy incorporates the use of aqueous solutions, or leaches, to extract
metals from their ores.

3l) Submerged arc welding, electro-slag welding, resistance welding are forms of
automatic welding.

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(d) A rack and pinion can be used in the steering mechanism of a car or
on a pillar drilling machine to raise or lower the table.

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(a) (i) Vacancy or vacant site defect: if there is an atom missing from thelattice, a distortion occurs as other atoms are forced toward the
vacant space.
(ii) Interstitial: a different type of atom moves into the spaces between
the atoms of the lattice.
(iii) Substitutional: the structure has foreign atoms in the lattice.
Distortion will be caused if these atoms are a different size.

(b) The differences between BCC and FCC structures:
In a BCC structure, atomsare arranged with an atom at the corner of a
cube and an atom in the centre of the cube. This structure is associated
with brittleness.
BCC FCC
In a FCC structure atoms are atoms at the corners of a cube and one atom
in the centre of each face of the cube. Atoms are more tightly packed
which allows metals to be more ductile. Slip is more likely to occur in an FCC
structure.

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(a) (i)Name: Tungsten Inert Gas (TIG) welding.
(ii) Operation: An arc is formed between the non-consumable electrode and
the metal being welded. The inert gas shielded arc is used to flux the
joint, Argon is often used to prevent oxygen getting to the joint area. A
filler metal is added manually to the weld pool when necessary. A high
frequency generator provides a path for the welding current.(iii) Application: Commonly used as a high quality welding process where
precision is needed. It allows aluminium and stainless steel to be welded.

(c) (i) Resistance spot welding:
The components to be joined are placed
between the electrodes and then
pressed together. A nugget weld is achieved as
current is passed through the electrodes
generating a large heat between the metals. It isvery effectively used to join sheet metal
together and is recognised by the distinctive
circular mark left at the site of the weld. Spot
welding gives a lower strength joint than other
forms of welding but it is energy efficient, giving little work deformation, it can be
easily automated and does not require a filler metal. It is commonly used in
sheet metal uses such as presses, filingcabinets and car body panels.

(ii) Metal inert gas welding: MIG welding is a semi-automatic process.
A consumable bare wire electrode is fed continuously into the weld pool area
through the welding torch. An inert gas, such as Argon, creates a protective shield
around the weld pool giving a fluxing action. The feed rate and flow rate of the
gas are set by the operator. This allows the operator toguide the torch along the
weld once the arc is generated between the electrode and the work. MIG welding
can be used on heavy plate as well as sheet metals, it does notproduce a slag on
the weld. [pic]

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(i) Basic Oxygen Furnace and Electric Arc Furnace.
(ii) Any one:
Mild Steel is produced in the Basic Oxygen
Furnace. The charge consists of scrap iron
and steel together with limeand molten pig
iron. Oxygen is blown at the surface of the
molten charge from a water cooled lance
which is lowered through the mouth of the
furnace. Impurities in the charge are oxidized
and form a slag on the surface. At the end of the
blow, the steel is poured off through a tapping
hole followed by emptying the slag through the
mouth of the furnace.

High Carbon Steel is produced in...
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