Tungsten Carbide Coatings: Applied by the High Velocity Thermal Spray Processes
Here at ASB Industries, the most frequently applied wear resistant coating is tungsten. Using our different HVOF systems allows consistent production by choosing powdered feedstock best for your application. Our spray rooms are designed to handle different components, utilizing large turning capabilities with equipment from robots and X-Y gun manipulators to overhead cranes; and specialty-built fixtures for handling repetitive production and complex masking fixtures to protect uncoated areas.
In the continuous-combustion high-velocity oxyfuel HVOF thermal spray process, a fuel gas and oxygen are combusted in a high-pressure chamber, reaching temperatures of 4500 to 5600°F. The hot, high-pressure gas is ejected through a small-diameter nozzle and accelerated down a long barrel at supersonic speeds. Powder, such as Tungsten Carbide is also injected into the nozzle, where the particles mix with the speeding gases and reach velocities of 2500 ft/s to more than 3000 ft/s.
The high speeds impart tremendous amounts of kinetic energy to the particles. Remember that kinetic energy equals half the mass of the particle times the square of its velocity (KE= 1/2 mv2). When these highly energetic particles strike the substrate, the velocity goes to zero and the kinetic energy is absorbed by the particle, causing it to melt in a millisecond. Subsequent particles arrive almost simultaneously, rapidly building up the coating. The result is a very dense adhesive/cohesive coating. It has comparatively very high bond strength, low residual stress, low porosity (typically less than 0.5%), and high wear resistance.
Here at ASB Industries, the most frequently applied powder is tungsten carbide with a cobalt binder. Tungsten carbide melts at 5200°F, and is extremely hard, with Vickers hardness number 2242. On the other hand, cobalt has a melting point of 2460°F, and Vickers hardness number is 1043. Coating properties such as hardness, wear resistance, and strength depend primarily on the grain size and volume fraction of the tungsten carbide particles. Therefore, WC-Co coatings can be designed to provide the specific properties needed for an application by controlling the grain size of the tungsten carbide particles and their volume relative to cobalt. In general, cobalt content ranges from 5 to 30 wt%, and WC grain sizes range from one to eight microns, although for some applications grain size may reach 30 microns.
ASB Industries’ on-site and in-house capabilities in paper mills allow a long lasting carbide grip surface applied to roll surfaces for different processing stages during paper production. ASB will adapt carbide spraying parameters using our flame spray equipment to work best with the paper quality and thickness.
Erosion, abrasion and corrosion are considerations for choosing different chemistries and binder materials. Tungsten Carbide is typically used for extreme wear conditions in almost every industry.
In steel and metals production, tungsten carbide coatings, along with tungsten weld coatings, are widely used from ore production through finished product. A multitude of accepted applications show dramatic maintenance cost reductions and improved production quality.
In power generation where coal is the fuel source, components are required to be protected from extreme abrasion under demanding production seasonal schedules. ASB Industries has a wide variety of solutions incorporated in many critical components.
If your application requires a specific finish, then ASB Industries in most cases will be able to complete your carbide coated surface to varying surfaces finishes or Ra. From large to small components, ASB Industries will most likely be able to finish your project with our diamond grinding and diamond super finishing equipment.