Page 194 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Press board

It is widely used in windings to insulate parts which support windings. It is also used as spacers in electrical
devices and transformers.
Asbestos

A fibrous, incombustible, fire- proof material - used for panel boards and as frames for winding resistance wires
of regulators, rheostats etc.
Cotton
It is soaked in paraffin to avoid moisture. It is a good insulator for low voltages. It is used in conductors for
armatures and field coils.
Silk
Like cotton, it is used for small jobs like telephone coils.

Tapes
Tapes of various types are used, such as cotton, silk, jute etc either pure or in impregnated form.
Empire cloth
It is made by varnishing a cotton cloth, silk or paper. It is not effected by moisture. It is available in yellow and
black colours in different sizes. It is used as slots insulation in winding works and for coil insulation.
Press pahn
Press pahn is a form of paper made from hemp, rags, and wood pulp by special chemical treatment. It is widely
used for lining armature slots, insulating coil sides, etc.
Leatheroid
It is a tough material made from cotton rags with chemical treatment. It is unaffected by grease or oil and is used
for slot and coil insulation, transformer core coverings, etc.
Adhesive tape
It is used widely for taping of ends of conductors, leads and connections. Adhesive tape is made from cotton
fabric coated with a compound of rubber, bitumen, resin, gum, etc. It dries when exposed to air. It is available in
sizes “, 3/4”, 1” etc. These are also available as P.V.C. adhesive tape, cotton and bitumen tapes.
Bitumen
It is used for filling cable jointing boxes and for sealing the tops of the batteries etc. It is waterproof, but it will crack
under certain conditions. It can be valcanised in the same manner as rubber.
Mica
It is a mineral and available as large slabs. It can be easily separated into thin sheets. It is fireproof, waterproof,
and is a good insulator. It should be used carefully since it is liable to crack. It is used in heating elements of
electric iron etc.
Marble and slate

Marble and slate are mechanically strong insulators and are non- hygroscopic. When polished they form good
mountings for switchboards, switches, resistance frames, etc. Slate is used generally for low voltages.
Micanite

It is made by sticking together pieces of mica with insulating cement like shellac. It can be bent to any shape
by heating and pressing. Therefore, it is used as insulator for slots of armatures and to insulate the commutator
from the shaft.
Paraffin wax
It melts at 55°C and does not absorb water. It is used to impregnate paper, wood, pressboard etc to reduce their
moisture absorption.

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CITS : WCS - Electrical - Exercise 18