Coating Small interrupted surfaces
10-24-2013, 06:06 PM,
Coating Small interrupted surfaces
Good day all,

This is my first time using an Hvof process and i am having some issues.
i am applying a tungsten carbide coating about .007 inches thick on one cutting edge of a saw blade. it is quite aggressive and used for cutting hay bails.

the problem i am having is that that while the surface is small, due to the large widely spaced teeth, i am achieving about 20% inefficiency in my coating on the blade. meaning that 80% of the powder is ending up on the floor.

does anybody know of a way to focus the jet or otherwise channel the flow so that the coverage area is smaller? i considered perhaps making an adapter for the nozzle out of copper, or some kind of jig that i could spray into to limit the over flow.

the size of the blade is about 5.625" x 2.9" and about 3 mm thick.
you can see the shape here

10-24-2013, 11:00 PM,
RE: Coating Small interrupted surfaces
Which HVOF System are you using ?

With the JP5000 you can convert it to the ST attachment (Small Target) which concentrates the spray stream slightly

Other than that there aint really much you could do due to the nature of the application. Coat more than 1 at a time ? make a jig up or something ?
10-25-2013, 11:21 AM,
RE: Coating Small interrupted surfaces
Hi Fat Dragon

Sign0016 to the Surface Engineering Forum.

I would try stacking maybe 8 parts on top of one another then off-setting each one to reveal the surface to be sprayed, so that the parts themselves become the masks to those below. I would then consider mounting more than one of these assemblies along the line of spraying. This would make a huge difference in target efficiency and thus much less powder used per component and probably speed up production. Another benefit would be larger surface area and mass making temperature control a little easier.
10-25-2013, 05:57 PM,
RE: Coating Small interrupted surfaces
Thank you for your replies.

KevGarty, i am using a Chinese knockoff of what i assume is your jp 5000 model. it is called the sx-5000 i will contact the company that makes it and see if they do an ST nozzle . if not from what i have read i can make one out of polished electrolytic copper.

Gordon, i agree with you and had come to a similar conclusion , unfortunately the shape of the teeth does not permit me to stagger them and still have full coverage, but the overlapping idea should work. here are some pictures of what i have so far. this is just rough sketch but i should have something more final soon.

does anyone know of any material or coating i could use on the jig that would prevent the tungsten over spray from adhering to the jig?
or perhaps a way to remove it?
10-27-2013, 10:31 PM,
RE: Coating Small interrupted surfaces
Hi Fat Dragon
You could use antibond products, both as paint or high temperature adesive tapes.
Best regards

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