New HVAF breakthrough?

[ycwbycwb]

Now Uniquecoat claims that its new M3 HVAF gun sprays with particle velocity over 1000m/s and DE over 50% for WC-CoCr, WC-Co and over 70% for Cr3C2-NiCr.
Do you believe it? It sounds like continuous detonation spraying.
Here is the link:
(links dead)

[LEN WOOD]

Amazing - Looks awesome!

[Alexangel1226]

What's the diff between HVAF vs the conventional HVOF in terms of process requirement and mechanism?

[Gordon]

DE over 50% for WC-CoCr, WC-Co and over 70% for Cr3C2-NiCr.

and hardness values from link I assume are relative to previous HVAF models, as they don't seem remarkable generally.

Amazing - Looks awesome!

It certainly does - but lets judge by eating the pudding rather then looking at the box

The particle velocity claims sound good and hopefully impact on coating quality, particularly the carbide based coatings. What particles were used in the measurement?

What's the diff between HVAF vs the conventional HVOF in terms of process requirement and mechanism?

Air instead of oxygen - sorry that's the obvious one.
Air cooled, no water cooling as in some HVOF
Cooler spraying conditions, advantage in some cases where process leans more to kinetic than thermal - better for tungsten carbide based coatings and coatings with less oxidation.

[djewell]

What's the diff between HVAF vs the conventional HVOF in terms of process requirement and mechanism?

HVAF is simpler to use than HVOF because it gets its oxygen from an air compressor instead of an oxygen storage tank. The operator has an unlimited supply of air available for use.

As Gordon pointed out, the HVAF flame temperature is lower than HVOF, so carbides are not decarbeurized. The same materials can be sprayed with both systems. HVAF coatings can be applied very thick - up to 13 mm of tungsten carbide have been applied. HVAF also allows the user to apply 50 um of coating thickness per pass, so the coating job can be completed faster.

There are quite a few other differences. Someone might accuse me of sales work if I continue too long with this discussion. If you contact me off-line, I will be happy to share them with you.

[Gordon]

Hi djewell

HVAF also allows the user to apply 50 um of coating thickness per pass, so the coating job can be completed faster.

This statement does not make sense to me. You can apply 5 um of coating thickness per pass and complete the job in a similar time, by just increasing speeds and feeds by about 10. The only way to complete job faster would be to spray at higher deposit rate. I guess that you really wanted to say that the system is capable of higher deposition rates (high spray rate, good deposit efficiencies)?

Though, I can imagine this HVAF system may be more tolerant with regard to deposit thickness per pass, I personally would still favour using ~5 um deposit per pass over ~50 um in the belief that coating/part temperature control and coating quality will be superior.

Never the less, this new system sounds impressive and hopefully a lot more than hype. I wish it luck in pushing progress towards filling that gap between thermal and kinetic (HVOF/HVAF and cold spray).

[djewell]

It is not always possible to increase speeds and feeds. Otherwise, a spiral pattern will appear on your cylindrical substrate surface. On a flat surface, traverse velocity can be increased to the maximum achievable by the arm holding the gun. HVAF can apply 50 um thick layers without cracking and without degrading coating quality or overheating the part, so a 250 um thick coating can be applied in 5 passes instead of 10 or more.

[Gordon]

Hi djewell

It is not always possible to increase speeds and feeds

Yes, I agree. Unfortunately we are bound by the capabilities of our mechanical handling equipment. So sometimes we can not achieve our ideal goal, but compromise and get as close as we can.

Otherwise, a spiral pattern will appear on your cylindrical substrate surface.

Yes, but only if you don't balance part rotation with gun traverse speed.

HVAF can apply 50 um thick layers without cracking and without degrading coating quality or overheating the part, so a 250 um thick coating can be applied in 5 passes instead of 10 or more.

I can't argue about what you have achieved in certain applications, but I do find it a bit of a sweeping statement. I can think of many situations where parts of low mass, thin section or high heat sensitivity would be seriously troubled by this approach. Don't get me wrong, I appreciate the point that HVAF is a cooler process than HVOF and will show benefit here.

My main point really was that deposit thickness per pass does not significantly effect production rate. In my experience (particularly carbides/ceramics coatings) using fewer passes to achieve a certain thickness is more detrimental to the coating/substrate than using more.

[ycwbycwb]

Hi djewell,

Please give us some information to prove that your gun can get almost 1000m/s particle velocity with so short nozzle.
It's well known that the high particle velocity depends on the long barrel for Detonation gun.

-------------------------------
Regards,
Ycwbycwb

[k09]

Hi everyone,

I had read somewhere that particle velocity in Detonation spray is around 3500m/s and that in HVOF is around 1200-1500m/s. are these statements correct?

secondly, since i have been using Detonation spray myself..the overall deposit efficiency is lesser or equal as compared to HVOF.. is this normal?

Also can somebody explain how can direct compressed air instead of bottled oxygen make the process/substrate temperature cooler?

There will be an inconsistent composition of air directly from the compressor(in spite of filters in place)..will this not cause the coating quality to vary?

sorry if i have missed something that is very obvious but i donot have much knowledge about HVAF...although it does seem very interesting..) can somebody recommend top 3 HVAF system manufacturers/models?

[Gordon]

Hi k09

I had read somewhere that particle velocity in Detonation spray is around 3500m/s and that in HVOF is around 1200-1500m/s. are these statements correct?

3500 m/s? more like ft/s and possibly gas velocity. Typically ~800m/s +or- 400 particle velocity for HVOF/HVAF/DGun, though I may be getting behind the times

Also can somebody explain how can direct compressed air instead of bottled oxygen make the process/substrate temperature cooler?

Flame temperature
oxygen/propane ~ 2820 C
air/propane ~ 1980 C
Air is only ~1/5 oxygen. The rest mainly nitrogen which dilutes and cools flame. Basically, you need 5 times as much air than pure oxygen for combustion.

There will be an inconsistent composition of air directly from the compressor(in spite of filters in place)..will this not cause the coating quality to vary?

I doubt this would be a problem with a good compressor and air composition should vary little, unless your drawing air from very close proximity to fossil fuel burning exhaust.

[djewell]

Hi djewell,

Please give us some information to prove that your gun can get almost 1000m/s particle velocity with so short nozzle.
It's well known that the high particle velocity depends on the long barrel for Detonation gun.

-------------------------------
Regards,
Ycwbycwb

We set up an Accuraspray device and measured the particle velocities with different powders. Velocities ranged from 1,000 to 1,200 m/s. I may be able to send you screen images if you would like.

[Intel55]

David,

Can you recommend a good air compressor (in the USA) to run with this gun? Cost?

[ycwbycwb]

Hi djewell,

Please give us some information to prove that your gun can get almost 1000m/s particle velocity with so short nozzle.
It's well known that the high particle velocity depends on the long barrel for Detonation gun.

-------------------------------
Regards,
Ycwbycwb

We set up an Accuraspray device and measured the particle velocities with different powders. Velocities ranged from 1,000 to 1,200 m/s. I may be able to send you screen images if you would like.

Dear David,

Please show us some of these pics. Thanks.

BR,
Ycwbycwb

[djewell]

Hi djewell,

Please give us some information to prove that your gun can get almost 1000m/s particle velocity with so short nozzle.
It's well known that the high particle velocity depends on the long barrel for Detonation gun.

-------------------------------
Regards,
Ycwbycwb

We set up an Accuraspray device and measured the particle velocities with different powders. Velocities ranged from 1,000 to 1,200 m/s. I may be able to send you screen images if you would like.

Dear David,

Please show us some of these pics. Thanks.

BR,
Ycwbycwb

Below are pictures of the M3 gun running and a screen shot of the Accuraspray measuring a velocity of 1,128 m/s. Notice that the nozzle has not turned red from the heat. The nozzle is air cooled and runs very cool.

   
   

[ycwbycwb]

[/quote]
Below are pictures of the M3 gun running and a screen shot of the Accuraspray measuring a velocity of 1,128 m/s. Notice that the nozzle has not turned red from the heat. The nozzle is air cooled and runs very cool.
[/quote]

Dear David,

I am sorry I can't see the velocity from your screen shot of the Accuraspray. You compressed the image too much.

BR,
ycwbycwb

[djewell]

Below are pictures of the M3 gun running and a screen shot of the Accuraspray measuring a velocity of 1,128 m/s. Notice that the nozzle has not turned red from the heat. The nozzle is air cooled and runs very cool.
[/quote]

Dear David,

I am sorry I can't see the velocity from your screen shot of the Accuraspray. You compressed the image too much.

BR,
ycwbycwb
[/quote]

Send me a PM with your e-mail address, and I will send you the original picture.

[yeldarb]

How does the HVAF system perform in regards to MCrAlY coatings vs. a standard HVOF system?

[djewell]

How does the HVAF system perform in regards to MCrAlY coatings vs. a standard HVOF system?

HVAF will spray MCrAly's and achieve an excellent coating quality. There is no reason why HVAF could not replace HVOF for this application. Doing so would give the user some big advantages and eliminate some problems from the spraying process.