Bexxon Global

Kermetico HVAF Thermal Spray Equipment and Wear Resistant Coatings for Mud Motor Rotors

Wear resistance of the mud rotor surface is one of the key factors of an oil well directional drilling cost. 

Kermetico HVAF technology and equipment provide a way to protect mud motor rotors with gas-tight, 1,350-1600+ HV300 hard and ductile tungsten carbide coatings.  Other mud motor components, such as flow restrictors and drive shafts, also benefit from our coatings. And we produce  Convertible HVAF + HVOF equipment for companies that still need to spray conventional HVOF coatings for conservative clients.

HVAF HVOF tungsten carbide coating mud pump
tungsten carbide mud pump rotors

The Kermetico HVAF System Spraying a WCCoCr Coating onto a Mud Motor Rotor

Numerous researchers have found that Kermetico HVAF WCCoCr coatings provide wear resistance several times longer than HVOF or electrolytic hard chrome.

Let’s find out why.

The Wear of Mud Rotors

Downhole drilling motors, or positive displacement motors (PDM), consist of a helically shaped metallic rotor rotating within a molded stationary elastomer lined stator.

The heart of the mud motor is the rotor-stator pair. The circulation of the rotor transforms the pressure of hydraulic energy of drilling mud into the mechanical energy causing the motion of the drill.

Mud-rotors have been plagued with excess wear, corrosion, erosion and coating delamination resulting in small drilling times. Most mud rotors had historically been chrome plated or nickel plated, but frequent coating failures have forced the industry search for other solutions.

Drilling mud is contaminated with chlorides that permeate the microcracks and pores of traditional chrome plating and corrode the underlying steel.

The appropriate coating should increase drilling times, reduce wear, increase corrosion resistance and minimize repair times.  The coating must be capable of sustaining horizontal and vertical flexing and needs to be impact resistant.

For performance in the harsh conditions the coating should:

  • have very low residual stresses
  • be as ductile as possible
  • have very high cohesive and adhesive strength


Kermetico HVAF Coating Features,  Kermetico High Velocity Air Fuel (HVAF) has been shown to be very competitive for mud rotors’ protection.

HVAF carbide coatings are superior to HVOF Tungsten carbide for both wear protection and HVAF lower production cost. The high velocity of the particles (greater than 1,000 m/s) in our Kermetico HVAF process enables the production of very dense coatings with high bond strength.

Kermetico HVAF low spraying temperature 1,960-2,010°C  and the gentle particle heating lead to minimal feedstock phase transformation and almost nonexistent elemental depletion/decomposition of the in-flight particles.

The Kermetico HVAF process significantly reduces the oxide content in the coatings, and produce high-performance coatings.

A Comparison of Main Features of HVAF and HVOF Tungsten Carbide Coatings for Mud Rotors HVAF vs. HVOF for Mud Motor Rotors Coating

WC-10Co-4Cr HVAF coatings in compared to the best HVOF coatings, in 2011 Schlumberger UK data, Hunan University (Changshu, Hunan, China) and the data from the Central Power Research Institute (CPRI, Bangalore, India).

The improvement of our HVAF coatings versus the best HVOF coatings of similar chemistry:
abrasive wear: 35-50% slurry erosion (jet) at 90° attack angle: g3-4-fold (Schlumberger and Hunan, different powders manufacturers, different shops)

cavitation resistance:
5-fold for a 1,320 HV300 hardness HVAF coating,
10-fold for a 1,450 HV300 HVAF coating
15-fold for a 1,550 HV300 HVAF coating (CPRI India).

diamond belt grinding pump rotor

HVAF Equipment Mud Motor Rotors

High Quality Tungsten Carbide