Why Aluminium Windings are not being used in Motors ?

(2 Min Read)

• Resistivity of Copper  is 1.68 x 10-8 Ohm
• Resistivity of Aluminium 2.65 x 10-8 Ohm
• Aluminium/Copper  = (2.65 x 10-8) / (1.68 x 10-8) = 1.6

    Aluminum’s resistivity is 1.6 times higher than copper’s resistivity. To compensate, aluminum windings cross-section must have 1.6 times larger and diameter must be 1.26 times of copper windings to offer the same conductance.This means windings wound with aluminum wire will likely have greater volume compared with an equivalent copper wire motor.

    It is possible to match the power performance of a motor wound with aluminum to a motor wound with copper.But since aluminum requires more turns and/or a larger diameter wire,the size of the motor will go bigger, this may not always be feasible in some applications. In situations where efficiency and volume are not issues such as where the motor only has to work occasionally or for very short periods of time, aluminum windings make an acceptable motor.

Cu vs Al

What is Relation between Hardness,Ductility,Malleability&Brittleness...

HARDNESS:

 Hardness is a measure of the material’s resistance to localized plastic deformation (e.g. dent or scratch).

DUCTILITY:

 Ductility measures the amount of plastic deformation that a material goes through by the time it breaks.

Ductility is said to be the property of a material to stretch without getting damaged. Metals having ductile property can be stretched into wires. An example is copper wire.

MALLEABILITY: 

Malleability is said to be the property of a material to deform under compression. The metals having malleable property can be rolled or beaten into sheets. An example is aluminium foil.In more simple words, ductility means stretching to wires and malleability means beating to sheets.

Ductility means that a metal can be changed to another form by pulling, compression or twisting.On the other hand,Malleability means that a metal can be changed into another form by beating or hitting it hard.

Ductility also refers to the ability of a metal to change its form under tensile stress. Malleability refers to the ability of a metal to change its form under compressive stress.

A metal’s ductility is measured by looking at its tensile strength. The tensile strength inspects how far a metal could stretch without breaking. A metal’s malleability is measured by looking at how much pressure it can withstand without breaking.The bend test is the commonly used test for determining the ductility of a metal.Gold and silver are the top ranking ductile and malleable metals.

The two properties of Malleability and ductility do not always correlate in metals. For example, gold is both malleable and ductile and lead is only malleable.

BRITTLENESS:

A material is Brittle if, when subjected to stress, it breaks without significant deformation (strain). Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.

TWO MEASURES OF DUCTILITY:

1) Percent Elongation (%El )

2) Percent Reduction In Area

• Highly ductile metals can exhibit significant strain before fracturing, whereas brittle materials frequently display very little strain.

• An overly simplistic way of viewing ductility is the degree to which a material is “forgiving” of local deformation without the occurrence of fracture.

Brittle materials: %EL £ 5% at fracture

Ductile materials: %EL and %RA both ³ 25%.

What is Ductile to Brittle Transition...??? How it related to Titanic Sinks...???

                At low temperatures some metals that would be ductile at room temperature become brittle. This is known as a ductile to brittle transition.

          The ductile to brittle transition temperature is strongly dependant on the composition of the

metal.Steel is the most commonly used metal that shows this behaviour.

          For some steels the transition temperature can be around 0°C, and in winter the temperature in some parts of the world can be below this. As a result, some steel structures are very likely to fail in winter.

                                    

Example of Brittle Failure:

            Ductile fracture is always a preferred mechanism of failure. Many cases have occurred through history where catastrophic failures have occurred as a result of brittle fracture. The most infamous of these is the sinking of the Titanic.

           The sinking of the titanic was caused primarily by the brittleness of the steel used to construct the hull of the ship. In the icy water of the Atlantic, the steel was below the ductile to brittle transition temperature.

           In these conditions even a small impact could have caused a large amount of damage. The impact of an iceberg on the ship's hull resulted in brittle fracture of the bolts that were holding the steel plates together.

          Nowadays engineers know more about this phenomenon and the composition of the steels used is much more controlled, resulting in a lower temperature at which the ductile to brittle transition occurs.

What is Magnet wire?

    Magnet wire or enameled wire is a copper or aluminium wire coated with a very thin layer of insulation. It is used in the construction of transformers, inductors, motors, speakers, hard disk head actuators, electromagnets, and other applications that require tight coils of insulated wire.
    The wire itself is most often fully annealed electrolytically refined copper. Aluminium magnet wire is sometimes used for large transformers and motors. The insulation is typically made of tough polymer film materials rather than enamel, as the name might suggest.
    Annealing: In metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling.