Question

Discuss the suitability and limitation of the following insulating material for use on board ships and state suitable application in each case.

Pure rubeer

Paper.

Mica.

Porcelain.

Ebonite.

Rubber. Rubber in the pure form is very soft and to make it tough and hard, 5% sulphur and other mineral materials, such as zinc oxide, red lead and some colour are added to it. It is then known as vulcanised rubber it does not absorb moisture up to a certain limit and serves as a good insulation and protective covering for conductors for low and medium voltages. It melts easily and can be moulded into any shape. It is flexible, resistant to abrasion, chemicals and the affects, of oxygen. It is inflammable but has low conductivity. Therefore, it is used as an insulating material in various electrical appliances, insulation on wires, rubber gloves, hard rubber battery containers, etc.

Ebonite or Vulcanite It is a good insulator and can be moulded into any shape, it is manufactured by mixing 30 to 50% sulphur with vulcanized rubber and then heating it 3 to 4h at about 150degC. It is a hard substance and becomes soft at 70degC It is used for making covers for resistance boxes, containers of lead acid batteries, panel frames.

Mica It is a very good insulator and is widely used as an insulating material in electrical and electronic industries. It has very high specific resistance and dielectric strength. It is fireproof and does not absorb moisture. Mica is obtained from mines in big solid sheets. Thin sheets can be obtained of thickness 0.0005 in. On account of it being available in thin sheets, it can be rolled and used where the space is limited. Mica starts softening at 1200°C. However, at 600°C it is very stable. Therefore, it can be used as an insulating material where the temperature is not to increase beyond 600°C. In between 600° and I200°C mica starts disassociating. Therefore, it cannot be used at an insulator beyond 600°C. For temperatures above 600°C it is mixed, with shellac or a resin adhesive known as micanite, which can withstand higher temperature. A mixture of mica and adhesive pasted on paper or cloth is known as micanite paper or micanite cloth. Micanitc can be bent into any shape when it is heated Mica is used as an insulator in electric irons, between commutator segments, slot Lining for high voltage machines, condensers and for many other electrical and electronics work.

Porcelain it is made from china clay and quartz: stone and can be moulded into any shape. It is white or brown in colour and is not as brittle as glass. It is not affected by chemical fumes and the atmosphere- Porcelain is glazed to make it non absorptive of moisture- It is used for making low, medium-

and high-tension insulators of overhead lines, bases of switches, kit-kat fuses, holders, transformer bushings, etc

Paper it is hygroscopic, but when treated with insulating oil or wax, it becomes a good insulator, it is. cheaper than rubber and has replaced rubber insulation in oil-filled power cables It is used as a dielectric in condenser and insulating strands of cables