The Reclamation Of Crankshafts By Arcspraying

Reason for use:

Repair of worn, mis-machined or obsolete crankshafts

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Further Reading

The reclamation of crankshafts (and many other components) by electric arcspraying can produce considerable savings over replacement costs. 50% savings are common, and on large components, as much as 90% may be saved.

The need for reclamation may be to correct manufacturing errors, to repair an obsolete part or a part that has worn excessively in service.

Wherever used, crankshafts can be reclaimed using Metallisation arcspray equipment.

Equipment

Metallisation Arcspray 528E, 340 or 140E Pistol.

Materials

Bond Coat

Metallisation 75E Nickel Aluminium

Specially formulated Arcspray Bonding Wire, which exotherms during spraying, producing a very high bond strength coating.

Main Deposit

Metallisation 60E Chrome Steel Arc Wire.

The general purpose material for reclamation or O.E.M. work, giving hard, low shrinkage coatings that exhibit work hardening properties and provide good corrosion resistance.

Inspection

  • Check for cracks by ultrasonic or magnetic crack detection method.
  • Check for longitudinal distortion.
  • Check dimensions accurately for wear, uniformity of wear and particularly depth of grooves.
  • Check for signs of overheating.
  • Check for signs of nitriding.
  • Check technical data for the specific crankshaft with particular reference type of bearings in which it is to run.

Note: Crankshafts having the following defects are not recommended for treatment by arcspray:

  • Cracks, distortion, wear below final re-grind tolerance. All traces of nitriding should be removed during pre-machining refer to a) and b).
  • It is reported that crankshafts running in aluminium tin bearings have exhibited ‘pick up’, therefore caution should be exercised when this type of bearing is being utilised.

Cleaning

  • Steam clean if equipment available.
  • Degrease by solvent vapour if equipment available.
  • Pay particular attention to oilways and ensure removal of all contaminants during (a) and (b).
  • Carry out final inspection.

Pre-machining

  • Grinding wheel type N° 46 Grit Blue V Grade
  • The grinding wheel corners should be dressed to a radius that matches the radius of the crankshaft fillet.
  • Dry grind to remove the minimum amount of original metal ensuring that you maintain manufacturer’s minimum recommended diameter.
  • Shallow grooves not exceeding 0.1mm (0.004”) in depth are acceptable in the pre-machined surface, provided that the area can be properly gritblasted.
  • Whilst bond coatings will adhere to carburised or induction hardened surfaces, they will not bond to nitrided layers. ALL nitriding must be removed before spraying.

Cleaning

  • Degrease by solvent vapour process if equipment available.
  • All particles of abrasive and ground metal retained on ground surface should be removed by careful brushing or momentarily applying adhesive tape.
  • Check that all oilways are free from contamination and debris.

Preparation

  • Mask all machined surfaces adjacent to the area requiring treatment with a heavy duty masking tape.
  • Plug oilways with tapered, heat resistant, rubber plugs. This plug should protrude equal to finished ground deposit thickness.
  • Thoroughly inspect for contamination prior to blasting.
  • Thoroughly blast with clean N° 30-36 grade aluminium oxide grit. The standard of surface cleanliness required is as Swedish Standard SA3.
  • Ensure that radius at each end of bearing surfaces are thoroughly blasted.

Application of Sprayed Coating

  • Apply sprayshield masking fluid using a small brush to all areas adjacent to the area being sprayed. Ensure fluid is not applied to the area being metalsprayed. Small amounts of masking fluid on the area to be sprayed can be removed with an emery cloth.
  • Check thoroughly that the area to be sprayed is free from contamination
  • Important: The areas to be sprayed should not come into contact with oil, grease, hands or any other form of contamination. Delays between blasting and spraying must not exceed 20 minutes.

Bonding

  • The Arcspray Equipment should be set up in accordance with the Metallisation manual for spraying 75E Wire.
  • The area to be sprayed should be cleaned with a vacuum cleaner or clean air blast to remove any loose particles of grit.
  • Apply 75E Bond Coat to a depth of 75-100μm (0.003”-0.004”) using multiple passes. Ensure radii are evenly coated.
  • Spraying Parameters:
  • Range: 10cm (4”)
  • Nozzle Air Pressure: 3.7 bar (55 psi)
  • Voltage before spraying: 38V
  • Voltage during spraying: 34V
  • Amperage: 200A

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

60E Deposit (To Be Applied Immediately After Bond Coat)

  • The arcspray equipment should be set up in accordance with the Metallisation manual for spraying 60E Wire.
  • Apply 60E final deposit to the specified thickness including grinding allowance i.e. finished ground dimension plus: 0.40-0.50μm (0.0016”-0.002”) grinding allowance.
  • The crankshaft should be rotated to give a minimum surface speed of 18m/min (60 ft/min).
  • The arcspray pistol should be traversed by hand to give an even coverage ensuring that the radii are also evenly covered.
  • Using pre-set callipers check final sprayed deposit thickness to ensure there are no areas below finished sprayed diameter.
  • Remove loose particles on surface with wire brush or clean air blast.
  • Allow to cool thoroughly preferably whilst rotating.
  • Spraying Parameters:
  • Range: 15cm (6”)
  • Nozzle Air Pressure: 4.3-4.6 bar (65-70 psi)
  • Voltage before spraying: 38V
  • Voltage during spraying: 35V
  • Amperage: 250A

Sealing

  • Apply Sprayseal “M” in accordance with Metallisation Sprayseal “M” instructions. Keep surface wet by re-application for a period of approximately one hour.
  • Allow to dry thoroughly.
  • Remove uncured sealer from surface with clean, disposable cloths or paper towels.

De-masking

  • Remove all masking tape.
  • Remove all overspray thoroughly taking care to prevent coating damage.
  • Remove all traces of sprayshield with solvent.

Finish Grinding

  • Grinding wheel type N° 46 Grit Blue V Grade.
  • Dress grinding wheel to match radius of crankshaft fillet.
  • Wet grind to final diameter taking light cuts using feeds and speeds in accordance with grinding machine manufacturer’s instructions.
  • Remove rubber plug from oilway and chamfer hole by hand grinding with profiled stone or rotary file.

Inspection

  • Check dimensions.
  • Check for cracks or defects in sprayed coating, i.e. large pores or protrusions and loose particles.
  • Clean to remove all traces of grinding abrasive and loose particles.

Polishing

  • Set the crankshaft in a lathe to rotate in the same direction that it will rotate when assembled in an engine.
  • Polish finished ground area until the shaft is highly polished.

Finish Cleaning

  • Clean the crankshaft thoroughly to remove all contamination, including any grinding debris retained on bearing surfaces
  • Check all oilways are clear
  • Wash with petroleum spirit/paraffin
  • Dry all bearing surfaces with clean, disposable cloths or paper towels.
  • Final inspection prior to packing
  • Wrap in clean polythene sheet
  • Pack and despatch

Note: Prior to installation in engine, repeat procedure – ‘Finish Cleaning’ a)-d). Immerse crankshaft in clean engine oil to fill any remaining porosity.

Reference Technical Bulletins

See Also:

Further Reading