Arcspray reclamation of ships propeller shafts

Reason for use: To repair the worn bearing areas on a ships propeller shaft
INTRODUCTION 
Due to the constant rotation of a ships propeller shaft in a harsh marine environment, the bearing areas are very susceptible to wear, consequently giving rise to the inclusion of sand, salt water and other debris, leading to bearing seizure and loss of propulsion. By using the Metallisation Arcspray process it is possible to apply a coating of 316 stainless steel onto the worn bearing areas of the propeller shaft; bringing them back up to the original size at a fraction of their replacement cost.
On manganese bronze type propeller shafts it has been found that bearing areas reclaimed by applying a layer of Arcsprayed Metallisation 316 Stainless Steel using the same procedure will give up to double the life of original materials and in turn, reducing the total maintenance costs.
EQUIPMENT 
Metallisation Arcspray 528E, 340 or 140E Pistol
MATERIALS 
Bond Coat
Metallisation 75E Nickel Aluminium
Arcspray Bonding Wire exotherms during spraying which produces very high bond strength coatings.
Main Deposit 
Metallisation 84E – 316 Stainless Steel Wire provides a dense, corrosion resistant deposit. Excellent for coastal and offshore environments.
Cleaning 
(a) Steam clean if equipment available
(b) Degrease by solvent vapour if equipment available
(c) Inspect for longitudinal distortion, cracks or faults taking the shaft below the manufacturers recommended operating tolerances.
 
NOTE: Metalsprayed deposits do not impart any strength to base materials. 
Pre-Machining 
Rough turn or grind areas being reclaimed to a depth of 1.25mm (0.050”), machining their length the width of the bearings plus an allowance of 25mm (1”) either side.

Cleaning 
(a) Degrease by solvent vapour process if equipment available.
(b) Check that all surfaces are free from contamination and debris.
Preparation 
(a) Mask all machined surfaces adjacent to area requiring treatment with a heavy duty masking tape.
(b) Thoroughly inspect for contamination prior to blasting.
(c) Thoroughly blast with clean n° 30-36 grade aluminium oxide grit, the standard of surface cleanliness required is as Swedish Standard SA3.
(d) Ensure that areas to be treated are thoroughly blasted, paying particular attention to edges of machined areas.
Application of Sprayed Coating 
Masking 
 
(a) Apply sprayshield masking fluid using a small brush to all areas adjacent to the area being sprayed. Ensure fluid is not applied to area being metalsprayed. (Small amounts of masking fluid on area to be sprayed can be removed with emery cloth)
(b) Check thoroughly that area to be sprayed is free from contamination
(c) IMPORTANT Areas to be sprayed should not come into contact with chains, rope slings, hands or any other form of contamination. Delays between blasting and spraying should not exceed 20 minutes.
Bonding 
(a) The Arcspray Equipment should be set up in accordance with the Metallisation Manual for spraying of 75E Nickel Aluminium Arc Wire.
(b) The area to be sprayed should be cleaned with a vacuum cleaner or clean air blast to remove any loose particles of grit
(c) Apply 75E Bond Coat to a depth of 75-100μm (0.003”-0.004”) using multiple passes.
(d) The propeller shaft should be rotated to give a minimum surface speed of 18 metres/minute.
(e) The Arcspray Pistol should be set so that the spray stream is at 90° to the surface being coated and traversed at an even speed, giving a uniform coating.
(f) Spraying Parameters Bond Coat:
(i) Range: 100mm (4”)
 (ii) Nozzle Air Pressure: 3.7 Bar (55 psi)
 (iii) Voltage before spraying: 38V
 (iv) Voltage during spraying: 34V
 (v) Amperage: 200A
Note: Parameters may differ in accordance with type and length of power cables and hoses 
being used.
84E Deposit (To be applied immediately after bond coat) 
(a) The Arcspray Equipment should be set up in accordance with the Metallisation Manual for spraying 84E (316 Stainless Steel) Wire.
(b) Apply 84E final deposit to the specified thickness including grinding allowance i.e. finished ground dimension plus: 0.375mm – 0.50mm (0.015”-0.020”) grinding allowance
(c) The propeller shaft should be rotated to give a minimum surface speed of 18 metres/minute..
(d) The Arcspray Pistol should be set so that the spray stream is at 90° to the surface being coated and traversed at an even speed to give a deposit of not more than 0.13mm per pass.
(e) Using pre-set callipers, check final sprayed deposit thickness to ensure there are no areas below finished sprayed diameter.
(f) Remove loose particles on surface with wire brush or clean air blast.
(g) Allow to cool thoroughly, preferably whilst rotating.
(h) Spraying Parameters: Main Deposit 84E
 (i) Range: 15cm (6”)
 (ii) Nozzle Air: 4.3-4.6 bar (65-70 psi)
 (iii) Volts before spraying: 38V
(iv) Volts during spraying: 35V
 (v) Amperage: 250
Note: Parameters may differ in accordance with type and length of power cables and hoses 
being used. 
Sealing 
(a) Apply Sprayseal “M” in accordance with Metallisation Sprayseal “M” instructions. Keep surface wet by re-application for a period of approximately one hour.
(b) Allow to dry thoroughly
(c) Remove uncured sealer from surface with clean, disposable cloths or paper towels.
De-masking 
(a) Remove all masking tape
(b) Remove all overspray thoroughly taking care to prevent coating damage
(c) Remove all traces of sprayshield with solvent
Finish Grinding 
 
(a) Grinding Wheel Type N° 46 Grit Blue V Grade
(b) Wet grind to final diameter taking light cuts using feeds and speeds in accordance with grinding machine manufacturer’s instructions.
Inspection 
(a) Check dimensions
(b) Check for cracks, defects in sprayed coating, i.e. large pores or protrusions and loose particles
(c) Clean to remove all traces of grinding abrasive and loose particles
Finish Clean 
(a) Clean to remove any traces of grinding abrasive and loose particles
(b) Wash with petroleum spirit/paraffin
(c) Dry the surface with clean, disposable cloths or paper towels.
REFERENCE TECHNICAL BULLETIN N°S
SEE ALSO