HVAF development

[djewell]

HVAF has some big advantages over the D-gun. First, HVAF guns are simpler. Combustion is continuous, unlike the D-gun which has multiple moving parts to create waves of explosions. Second, I have seen test data that show that HVAF spray 86WC10Co4Cr coatings have lower wear rates than D-gun sprayed coatings. Third, HVAF guns are smaller and easier to use then D-guns. Fourth, HVAF uses air, (as opposed to oxygen), so there is no need to maintain cylinders or a liquid bulk tank.

Does anyone know the spray rate with a D-gun? HVAF guns can spray up to 30 kg/hr of tungsten carbide powders.

[rofon]

I would like to read about the differences between HVOF and HVAF if anyone have a paper/article/book that can suggest it would be really appreciated.
tanks !

[djewell]

Rofon,

Here is a link to a document that discuss the differences between HVAF and HVOF. HVAF can apply the same materials as HVOF but for less cost, at a faster rate, and can achieve the same or better coating quality.

(link dead)

This a white paper I prepared a few years ago. The operating cost numbers are old, but the technical discussion is still the same.

I have other information I can share with you about the advantages of HVAF over HVOF, but I do not want to post them here. If you contact me off line, I will send them to you.

[Stephen Booth]

Very interesting discussion!

This is one or the benefits of the forum, thx Gordon.

[Nesher]

Hi, ycwbycwb, as far as I know the selling point of HVAF is cost saving, as it does not use Oxygen, however, I got to prepare a high capacity 380v electrical power for this machine as it needs a big air compressor. You know we only use such high power for APS. This limits its cost advantage. Also, it needs extra fine powder for better melting.

We need a compressor with a capacity of about 7,000 liters / min. It is very expensive

[Vig]

Hi, ycwbycwb, as far as I know the selling point of HVAF is cost saving, as it does not use Oxygen, however, I got to prepare a high capacity 380v electrical power for this machine as it needs a big air compressor. You know we only use such high power for APS. This limits its cost advantage. Also, it needs extra fine powder for better melting.

We need a compressor with a capacity of about 7,000 liters / min. It is very expensive

Hi, Nesher

You are on the right way to improve your coating processes. Do not fear to invest.

A compressor is a one-time investment, not an expense. The expenses of a thermal spray shop consist mainly of the cost of powder and workforce. Having higher deposit efficiency, higher spray rate and lower cost of spare parts, the Kermetico HVAF system pays back spraying a second metric ton of tungsten carbide. Can prove it with your shop data.

The HVAF process is less expensive than HVOF because there is no need to extract oxygen from the air (you just use air), no need to water cool the gun (you cool it with the same air you combust later, preheating it first) and no need to cool down most of the parts (the HVAF process induces less heat). It is more efficient, meaning less expensive.

7000 l/min compressor is needed for the largest gun,AK7, with a spray rate of 550 g/min.
Imagine, how expensive will be using 6 HVOF guns to reach this throughput.
And if you do not need this power - use universal AK5 which can spray into 200 mm internal diameter and needs much less air to spray at 250 g/min rate.

4.Lower combustion temperature means less tungsten carbide decomposition and less metal oxidation -> fewer coating quality issues.

I have 11 years experience using Kermetico HVAF equipment and can consult you how to choose and use it the best.

Best Regards,
Vig

[Nesher]

I only know the following two:
kermetico
uniquecoat

Actually these two are one company before 2006. Then for some reason the founders separated apart. The technology is based on the same patent. Spraying coatings with the equipment can be seen at youtube, one has been posted by Gordon, I add another):

https://www.youtube.com/watch?v=FglI2CfZxV4
https://www.youtube.com/watch?v=HQAdQvDrSl0

Large paper machinery company Metso has been using this equipment to spray WC coating onto large paper rolls.
Good things:
1. No pure oxygen source is needed.
2. Longer spare parts service time.
3. Better WC coating performance confirmed by many reports(wear, toughness, fatigue)

Bad things:
1. Large air compressor: at least 10m3 per min. (but don't forget large cooling need for many HVOF)
2. Manufactures are small companies.
3. Fine powders, -30+5 microns WC, for better DE, 45%. ( However Kermetico claims to add little H2 to the powder feeder gas, so fine powders has DE over 60% and coarse powder for HVOF has DE over 40%)

Powders with particle sizes -30 are comparatively very expensive. Therefore, the process with 45% is doubtful in its effectiveness. And the use of hydrogen in general deprives him of any attractiveness in terms of safety.

---

Hi, ycwbycwb, as far as I know the selling point of HVAF is cost saving, as it does not use Oxygen, however, I got to prepare a high capacity 380v electrical power for this machine as it needs a big air compressor. You know we only use such high power for APS. This limits its cost advantage. Also, it needs extra fine powder for better melting.

We need a compressor with a capacity of about 7,000 liters / min. It is very expensive

Hi, Nesher

You are on the right way to improve your coating processes. Do not fear to invest.

A compressor is a one-time investment, not an expense. The expenses of a thermal spray shop consist mainly of the cost of powder and workforce. Having higher deposit efficiency, higher spray rate and lower cost of spare parts, the Kermetico HVAF system pays back spraying a second metric ton of tungsten carbide. Can prove it with your shop data.

The HVAF process is less expensive than HVOF because there is no need to extract oxygen from the air (you just use air), no need to water cool the gun (you cool it with the same air you combust later, preheating it first) and no need to cool down most of the parts (the HVAF process induces less heat). It is more efficient, meaning less expensive.

7000 l/min compressor is needed for the largest gun, AK7, with a spray rate of 550 g/min.
Imagine, how expensive will be using 6 HVOF guns to reach this throughput.
And if you do not need this power - use universal AK5 which can spray into 200 mm internal diameter and needs much less air to spray at 250 g/min rate.

4.Lower combustion temperature means less tungsten carbide decomposition and less metal oxidation -> fewer coating quality issues.

I have 11 years experience using Kermetico HVAF equipment and can consult you how to choose and use it the best.

Best Regards,
Vig

Dear Sir
To apply a ton of powder, you need to purchase two tons of powder (very expensive -30). This is with your use (DE) of 45%. During this time, your compressor will require expensive maintenance. And the introduction of hydrogen to raise use (DE) ... it's murder.
Life and practice put everything in its place. Your process has the right to life, but in a very narrow application.
Sincerely yours

[Vig]

Hi, Nesher

It is always a pleasure to read your messages.

AK7 in economy mode has DE 65% without any hydrogen and with the same quality as a good HVOF.

with 45% DE you will get Ultra mode (1500+ HV300, less than 0.3% porosity). Bulk-like ductile coating.

The WCCoCr coating could be used as a cutting tool. link
https://www.youtube.com/watch?v=RILM1bClWTQ

Quite far from whatever you have seen with HVOF.
Compressor cost is peanuts comparing to the cost of powder. You are correct.
But the cost of 10-30 is the same as 15-45 from all the major suppliers. Check yours.

King regards,
Vitaly

[Stephen Booth]

Just curious what others consider in comparison of a typical liquid fuel HVOF system vs HVAF concerning the peripherals:

in LF system in a warmer climate (summer time up to 40C) , seems we typically need a chiller of 90+KW, sometime even up to 130kw chiller.

While with the HVAF system (depending on the gun used) it can run with 75 KW of a compressor.

Seems to me, in a job shop having a large compressor probably a lower cost to operate and maintain compared to a chiller. Plus the compressor can be used for other functions like HVAF blasting, etc.

Just curious....

[Frantisek78]

I only know the following two:
Kermetico
Uniquecoat

Actually these two are one company before 2006. Then for some reason the founders separated apart. The technology is based on the same patent. Spraying coatings with the equipment can be seen at youtube, one has been posted by Gordon, I add another):

https://www.youtube.com/watch?v=FglI2CfZxV4
https://www.youtube.com/watch?v=HQAdQvDrSl0

Large paper machinery company Metso has been using this equipment to spray WC coating onto large paper rolls.
Good things:
1. No pure oxygen source is needed.
2. Longer spare parts service time.
3. Better WC coating performance confirmed by many reports(wear, toughness, fatigue)

Bad things:
1. Large air compressor: at least 10m3 per min. (but don't forget large cooling need for many HVOF)
2. Manufactures are small companies.
3. Fine powders, -30+5 microns WC, for better DE, 45%. ( However Kermetico claims to add little H2 to the powder feeder gas, so fine powders has DE over 60% and coarse powder for HVOF has DE over 40%)

[Stephen Booth]

The HVAF C in the HVOF mode (still using only 10% volume of O2 as standard HVOF) Kermetico C equipment works in HVOF mode at a particle temperature up to 1,700°C (3,100°F) and accelerates the particles sized at -45/+15 microns to 700-850 m/s (2,300-2,800 ft./sec.).

So it can use the standard 45-15 grade of HVOF powders.

https://kermetico.com/convertible

[Lyokha ibn Ivanovich]

only 10% volume of O2

Hello. Let me know. That is, you per 1m3 of air, mix 0.1m3 of oxygen? And this is enough to get a coating of powders -45 / +15 microns

[Stephen Booth]

only 10% volume of O2

Hello. Let me know. That is, you per 1m3 of air, mix 0.1m3 of oxygen? And this is enough to get a coating of powders -45 / +15 microns

Clarification, 10% of the volume of 02 as normally consumed by an typical JP5000 during operation.

[Lyokha ibn Ivanovich]

[/quote]
Clarification

[/quote]

Thanks