Hard Chrome Plating vs. HVOF Process

Why the Technology?

• Used for fluid power hydraulic repairs in cylinders and corner groups
• Provides long-term robust repair for hydraulic and fluid power components
• Cutting edge environmentally friendly technology
• Provides a safe working environment for associates to do repairs

Hard Chrome Plating

• Chrome Discovered 1798, first successful electrolytic plating 1856, commercial utilization late 1920’s
   
• Advantages
  • Resists most chemicals, oxygen, and moisture in air
  • Does not tend to seize, gall, or cold weld
  • Hard surface typical 69 Rc, 0.003-0.015” typical thickness
  • Simple technology
  • Excellent wear resistance
  • Historically relatively inexpensive 

• Issues with hard chrome plating
  • The process produces large amounts of hydrogen gas in the gas bubbles burst throwing hexavalent chrome solution into the air as fine mist. Hexavalent chrome is a know carcinogen.
  • The process produces large volumes of toxic waste.
  • EPA and OSHA have mandated more stringent stack emission levels and lowering of permissible exposure limits for workers.
  • This results in increased costs and business risks.

 Alternatives to Hard Chrome Plating Sought

• The Hard Chrome Alternatives Team (HCAT) formed during the 1990’s
• HCAT is a bi-national team comprised of Dept of Defense, US airlines, Canadian military and airline industries, support manufacturers
• Methods evaluated were Arc Spraying, Plasma Spraying, Flame Spraying, and High Velocity Oxy-Fuel (HVOF)

The Best Alternative

• The best clean alternative method determined by HCAT was HVOF thermal spray for Hydraulic
  Actuators (Cylinder Rods)
• The HVOF process utilizes a material in powder form injected into a flame of supersonic gas
• The material softens in the flame and forms a dense coating on the substrate.

HVOF

• The fuel for the flame is a gas such as hydrogen, acetylene, propylene, or a liquid such as kerosene
• The coating material is usually a metal alloy such as chrome carbide
• Typical deposit coating layers range from 0.003-0.015” in thickness

HVOF Spray Gun Cutaway

HVOF

• The two primary companies that make the HVOF spray equipment are Sulzer-Metcoand Praxair/TAFA
   

 HVOF

• The part to be coated must have chrome removed by stripping electrolytically or grinding
• If the surface has been previously HVOF coated, the surface must be ground to remove any
• imperfections
• Any area not to be coated must be masked off
• The surface to be coated must be thoroughly grit blasted using aluminum oxide material-36 grit-the prepared
  surface must be kept clean from this point on
• The work piece is put into the HVOF thermal spray cabinet.
• During the spray process the work piece rotates at 300 surface feet per minute
• Each pass applies 0.001”of coating
• The work piece temperature is not allowed to exceed 350 F, the spray process can be stopped and started to
  limit this temperature HVOF
• Final surface finishing requires use of either diamond belts or diamond grinding wheels
• It is necessary to not only grind but also
  superfinish
• The finished surface is measured and documented
• The bond strength is >10,000 PSI

Comparison of Hard Chrome Plating to HVOF 

Comparison of Hard Chrome Plating to HVOF

• At the bottom of each photo is the substrate material that is being coated. 

 Benefits of HVOF Coatings

• High density, low porosity
• Improved corrosion barrier
• Higher hardness ratings
• Improved wear resistance
• High bond strength
• Thick coatings
• Smoother as-sprayed surfaces

Summation

• Hard chrome has the advantage that it is a single material and deposition method that can be used for a wide variety of applications
• HVOF is a single technology, with a wide variety of materials that can be used to achieve the right combination of properties for many purposes.

Hazardous Environment Changes

• Provides a safer work environment for our people
• 80% reduction in hazardous waste
• Waste produced is considerably less hazardous than Hard Chrome Plating

HVOF Spray Booth with Stage Being Sprayed - Pre-heat Pass
 

HVOF Spray Booth with Stage Being Sprayed. Actual Spray Pattern
 

Grinder/Super Finisher