Surface Enhancement

By using the Metallisation Arc or Flame spray Process, it is possible to remove this major source of spark hazard by applying a thin layer of phosphor bronze onto the offending surface. One of the most common components to be treated in this way is crane hooks, but it is also possible to apply this type of coating to steel fan housings or forklift truck forks. Metal spraying is an economic method of producing a spark resistant surface on any standard manufactured steel component.

Equipment: In this case Arc Spray Equipment was used.

Materials: Phosphor Bronze Arc Wire - Easily machinable material, very good for bearing surfaces and giving an excellent anti-spark coating.

Method - Cleaning

1. Steam clean if equipment available.
2. Degrease by solvent vapour process, if material available.
3. Check all surfaces are free from contamination and debris.

Preliminary Inspection

Check for cracks or surface imperfections taking hooks below the manufacturers recommended operating tolerances.

Preparation

1. Mask surfaces adjacent to area requiring treatment with a heavy duty masking tape.
2. Thoroughly inspect for contamination prior to blasting.
3. Thoroughly blast the area to be sprayed with clean chilled iron grit grade G24.
4. Ensure that areas to be treated are thoroughly blasted A surface profile of between 75μm-100μm should be achieved. It is important that the surface to be sprayed should not come into contact with hands, oil, grease or other contaminants which may cause bond failure after spraying. Delays between blasting and spraying should not exceed 20 minutes.

Application of Sprayed Coating

Bonding and Simultaneous Spraying of Phosphor Bronze.

1. The Arc spray Equipment should be set up in accordance with the MSSA Manual for the spraying of Phosphor Bronze.
2. The area to be sprayed should be cleaned with a vacuum cleaner or a clean, dry air blast to remove any loose particles of dust or grit.
3. The first 75μ-100μm should be applied at close range (typically 100mm) and at lower air pressure to achieve a higher bond strength.
4. The coating should be applied evenly by rotating the component in front of the Arc spray Pistol, keeping the spray-stream at as near as possible to 90° from the surface being treated.

Bond Coat

Spraying parameters for Bond Spraying Phosphor Bronze.

1. Range: 100mm
2. Nozzle Air Pressure: 3.7 bar (55 psi)
3. Volts Before Spraying: 32-34V
4. Volts During Spraying: 28-30V
5. Current: 200A

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

Main Deposit

1. Apply Phosphor Bronze final deposit to specified required thickness (typically 0.40-0.50mm).
2. The coating should be applied evenly by rotating the component in front of the Arc spray pistol, keeping the spray-stream at as near as possible 90° from the surface being treated.

Spraying parameters for Main Deposit Phosphor Bronze.

1. Range: 150mm
2. Nozzle Air Pressure: 4.3-4.6 bar (62-87 psi)
3. Volts Before Spraying: 32-34V
4. Volts During Spraying: 30-32V
5. Current: 250A

De-Masking

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

Inspection

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

Finishing

Under normal circumstances, it is possible to use the component in the as-sprayed condition without any problems but for cosmetic purposes, a light polish may be required.