HVOF (HIGH VELOCITY OXY-FUEL)
The Process: HVOF is a thermal spray system utilizing the combustion of gases, such as Hydrogen or a liquid fuel such as kerosene. Fuel and oxygen mix and atomize within the combustion area under conditions that monitor the correct combustion mode and pressure. The process creates a very high velocity which is used to propel the particles at near supersonic speeds before impact onto the substrate. One of the basic rules of spraying is that high combustion pressure = high gas velocity, high particle velocity and resulting high coating quality. One of the key benefits of this system’s high velocity is the extremely high coating density and low oxide content. The low oxides are due partly to the speed of the particles spending less time within the heat source and partly due to the lower flame temperature (around 3,000 °C) of the heat source compared with alternative processes.
HVOF is best recommended for Carbide matrix coatings. Carbide coatings sprayed by HVOF renders good hardness, wear resistance and abrasion resistance characteristics. HVOF Sprayed Carbide coatings have a perfect alternative for Hard Chrome plating.
Widely used Carbide Coatings Sprayed by HVOF Process:
- Tungsten Carbide: Excellent Wear and Abrasion Resistance
- Chrome Carbide: Excellent Corrosion Resistance
Features:
- High density (Low Porosity <1%), High bond strength (>10000 psi)
- Coating thickness, Smooth sprayed Surface (3-5µmRa)
- Optimum hardness and corrosion resistance
- Improved toughness and excellent wear resistance
- Beneficial residual stress and fine surface finishes
- Reduce oxide content than plasma coating.
- Improved performance, life and efficiency
Application:
- Francis and Pelton Turbine Runner, Guide Vane Blade, Impeller ID fan etc..
- Landing gear, Calender rolls, Kaplan blades, sleeves, plungers, piston etc..
Extend hydro turbine runner service life, increase efficiency of Francis and Pelton turbine runner components:
The situation/condition/problem:
Apart from popular alternative energy resources like wind or solar, hydropower is one of the most efficient and environmentally friendly electric power sources available. The successful operation and economic viability of a hydropower facility depends on high-quality equipment and a long life cycle. In the long run, these two factors assure the operator’s return on investment (ROI) and profitability.
Erosion and Abrasion
Many hydro turbines operate with high pressure water laden with abrasive minerals. If not properly controlled, these sharp, abrasive particles can cause Pelton and Francis turbines to suffer premature equipment failure from erosion and abrasion. More significant is the high risk of catastrophic mechanical failure if preventative steps are not taken.
Cavitations Effect
In addition, wear-induced changes in runner geometry can result in cavitation – the formation and rapid collapse of bubbles in the water. These collapsing bubbles produce very high, localized, hammer-like loads.
Over time, wear caused by cavitations can weaken the Pelton cup, leading to fatigue-induced failure with dangerous consequences. Wear can cause Francis turbines to lose efficiency as a result of labyrinth seal and wicket gate erosion. Kaplan turbines face wear and erosion of discharge runners and guide vanes.
Our solution:
To help our customers increase the sustainability of their hydro Turbines and turbine runners. This high-quality, extremely wear resistant coating family protects hydro turbine vanes, turbine runner and other wetted parts against erosion, abrasion and cavitations.
HVOF system with tungsten carbide coating has been designed specifically to enhance the performance and extend the service life of turbine components in contact with water.
These coating we recommended for application to both new equipment and used components to provide superior performance and extend life – especially where water is laden with silt and sand. When needed on-site coating refurbishment is feasible.
Benefits:
Component Safety: Unlike other methods of producing a hard, tough coating on turbine parts, such as heat treating, HVOF process ensures that components do not overheat during the coating application. No heat distortion means that the component substrate physical properties remain unchanged.
- Used for all turbine components to protect against hydro abrasion
- Coating material based on carbide alloys
- Hardness up to 1250 HV0.3
- As-sprayed surface of Ra 4–8μm (160 — 320 μm)