Engineered Surfaces for Exceptional Performance
Engineered Surfaces for Exceptional Performance

Electronics Industry

Article Index

Page 3 of 9

Earthing of Resin Insulators

The conductivity of thermal sprayed coatings is also used to help connection to resin resistors/insulators or graphite heating rods where aluminium or aluminium bronze coatings are very commonly applied.

Reason for use: To produce an integral earth screen.

The high voltage resin insulators required when using switch-gear between 3.2 KV and 38KV can sometimes give rise to problems of air ionisation between metal components and the resin insulators.

This ionisation is due to the corona or electrical discharge appearing around the surface of the charged conductor being insulated. It is possible to counteract this problem by using the Metallisation Arc or Flame Spray Process to apply a sprayed zinc integral earth screen around the offending areas of the resin insulators.

Equipment: In this case Arc Spray Equipment was used.

Materials: 99.99% Minimum Purity Zinc Wire.

Cleaning

Degrease by solvent vapour process if equipment available, removing all traces of release agent used in moulding process.

Preparation

  1. Mask all surfaces adjacent to area requiring treatment with heavy duty masking tape.
  2. Thoroughly inspect for imperfections or contamination prior to blasting.
  3. Thoroughly blast with n° 50-60 grade aluminium oxide grit.
  4. Ensure that areas requiring treatment are thoroughly blasted.

Application

  1. Check thoroughly that area to be sprayed is free from all contamination and debris
  2. IMPORTANT: Area to be sprayed should not come into contact with chains, rope slings, hands or any other contaminants, spraying should be completed as soon as possible after blasting.
  3. The Arc Spray Equipment should be set up in accordance with the MSSA manual for spraying Zinc Wire.
  4. The resin insulator should be rotated evenly, either mechanically or by hand, in front of the Flame spray Pistol keeping the surface being sprayed at as near as possible to 90° from the spray-stream of zinc, until a complete coating of 50-70μm is achieved.

Spraying Parameters of Zinc

  1. Range: 150-200mm (6” – 8”)
  2. Nozzle Air Pressure: 5.20 bar (75 psi)
  3. Voltage: 19-21 when spraying
  4. Amperage: 100-150 Amps

Note: Parameters may differ in accordance with type and length of power cables and hoses being used.

Demasking

  1. Remove all masking tape.
  2. Remove all over-spray, taking care to prevent coating damage.

Finishing

No finishing required, component to be used in the As-Sprayed condition.

Final Inspection

Check for cracks, defects in sprayed coating i.e. large pores, protrusions and loose particles.