B&B Precision provide cermet coatings for high wear, high corrosion and high temperature applications, but what are cermet powders, how are they made and what materials can we spray?
What are Cermets?
Cermet is a combination of ceramic and metal. This combination allows these materials to function at higher temperatures and makes them more resistance to attack from chemical corrosion and oxidation. This term covers a wide range of composite materials and are found in extreme environments such as air-plane jet engines.
What is HVOF?
High Velocity Oxygen Fuel is one of four thermal spray processes in which powdered material is heated up and fired out at high velocity, impacting the component and forming a very hard and dense coating. This is the process of choice when you wish to coat using carbide materials as the high velocities involved (which are faster than a jumbo jet) mean the carbide phases are less likely to degrade during the coating process.
Although there is a wide variety of different material combinations the main ‘ingredients’ of these coatings is Tungsten Carbide or Chromium Carbide. There is a wide variety of commercially available coatings all with different combinations and amounts of Cobalt, Nickel Chromium. The different brand names and numbers are often confusing to customers, some of the most popular are woka, metco, amdry, but if you come across a spec/brand name you are unsure of please get in touch and B&B will point you in the right direction.
Powder Production Process?
There are two main processes in the actual production of carbide powders: Sinter and Crushing and Agglomeration and Sintering. In the first process blended raw materials are pressed into either bricks or cylinders, sintered (heated up and pressurised) and then crushed into powder. In the agglomeration process the raw materials are first dispersed in water and a binder and atomised into a powder, before being sintered and crushed. Generally speaking the Agglomeration process produces coatings with better corrosion resistance but is more expensive as a result. The powder production process influences the properties of the deposited coating and so there are many different factors that have to be controlled including, carbide grain size, density and shape. (Agglomeration produces a more spherical grain shape for instance)
HVOF Coating requires specialist equipment and B&B have invested heavily with a CO ² controlled spray booth, KUKA robotic arm which carries out 100% of our coatings and our own metallurgical laboratory for quality assurance. We are not tied down to one powder supplier and can advise customers on the best option for their application.