Often we get requests asking if we can hard-face internal diameters and bores using HVOF. What are the process limitations of doing this and what would we recommend as an alternative where we can’t coat?
In our HVOF process, coatings are sprayed on using a gun attached to a KUKA robotic arm. This gives us maximum control over the application process but does limit what we can spray. In terms of internal diameters we need enough space to be able to rotate the gun itself inside the bore. We would recommend that internal diameters would need to be a minimum of 25cm in order for us to apply a coating. The other factor is the depth of the sprayed area. We can only reach about 30cm deep on the inside, but may be able to coat a deeper bore if there is a step included or could coat it from two sides.
Vs Other Processes
As the HVOF process is applied directionally it doesn’t surround a component in the same way that electroplating might for example. Where you require an internal diameter hardfaced that would be too narrow or deep for our process then we would recommend either you add some sort of sleeve to protect the part or you electroplate instead. Electroless Nickel is able to form evenly on an uneven surface and can be heat treated to gain additional hardness near the level of Hard Chrome. It would still be possible for us to thermally spray the outside area afterwards.
B&B Precision have dedicated Internal Grinding machines which allows us to grind intricate internal work including multi-diameter and tapered bores. We have in house capability to manufacture special jigs enabling us to hold items which would otherwise be difficult to hold in a chuck or on a permanent magnet. Bores from 10mm up to 500mm in diameter can be ground up to 1500mm deep. Internal Grinding ensures that the ground bores run true to the component face.
If you have an internal diameter or bore that you would like to hardface then get in touch with B&B today to see if we can help you with your application