Hvof VS Hvaf

[JAKDL]

Hi All,

Need some help deducing what major coatings do better with Hvaf and which major coatings perform better with Hvof. If anyone could include WC and Cr3C2 this would also be greatly appreciated.

Thankya now,

JakDl

[Gordon]

Hi JakDl

HVAF (High Velocity Air Fuel) process with its lower temperature flame may show benefits with the tungsten carbide based coatings. HVOF on the other hand maybe a better all rounder particularly with the higher melting point materials.

Comments from any body running HVAF and HVOF systems side by side would be very interesting.

[JAKDL]

Thanks Gordon,

I am having a hard time finding unbiased information comparing the two systems. Any help there as well?

[Intel55]

Thanks Gordon,

I am having a hard time finding unbiased information comparing the two systems. Any help there as well?

Hard to find comparisons in the US. I can only think of about 4 places that use it. Kermetico, Heany, Solid Spray and the other name is escaping me. As Gordon stated, HVOF seems to be a better all around solution. Open for debate I guess, but overall, many many many more people use HVOF.

The people you would want to contact are David Jewell (Solid Spray/aka Unique Coat) and Andrew Verstack (Kermetico). They are the ones with extensive dealings with HVAF.

[JAKDL]

Hi JakDl

HVAF (High Velocity Air Fuel) process with its lower temperature flame may show benefits with the tungsten carbide based coatings. HVOF on the other hand maybe a better all rounder particularly with the higher melting point materials.

Comments from any body running HVAF and HVOF systems side by side would be very interesting.

Thanks Gordon for this information, you have been really helpful. You mentioned above about Hvaf being good for Carbide based coatings, can you let me know what types of coatings those would be? You also mentioned that Hvof might be better with higher melting point materials. What would those materials be?

Thankya now,
JakDl

[Intel55]

Hi JakDl

HVAF (High Velocity Air Fuel) process with its lower temperature flame may show benefits with the tungsten carbide based coatings. HVOF on the other hand maybe a better all rounder particularly with the higher melting point materials.

Comments from any body running HVAF and HVOF systems side by side would be very interesting.

Thanks Gordon for this information, you have been really helpful. You mentioned above about Hvaf being good for Carbide based coatings, can you let me know what types of coatings those would be? You also mentioned that Hvof might be better with higher melting point materials. What would those materials be?

Thankya now,
JakDl

HVOF can spray ceramics. Al2O3 and Cr2O3. In fact HVOF ceramics are harder and tougher than APS.
I do not know if HVAF can spray ceramics.

[Gordon]

Hi JakDl

Really, I tend to consider HVAF and HVOF to be very similar and would group them as "high velocity combustion spray processes" difference being air and oxygen. HVOF is a more mature process, when you look at the wide range of different equipment, fuels used and capabilities, it makes it difficult to make generic comparison between HVAF and HVOF. To make a choice between specific pieces of equipment, you need to establish clearly what type of coating work you need. If it is general coating work, I would consider some of the HVOF systems (or even some of the other thermal spray processes ), simply because it is a more mature process, wider range of suitable spray materials, proven track record etc.. If on the other hand you are going to specialise, say in spraying tungsten carbide/cobalt chromium coatings for say hard chromium plating replacement coatings, then I would seriously consider some of the HVAF systems with a proven track record.

When you know what coatings you need to produce, I would get the equipment suppliers to demonstrate their capabilities and hopefully you will make a wise choice based on your needs.

If you look at this thread select-a-twin-arc-spray-system-t-564.html you will see opinions differ greatly on which system is best Probably none are right nor wrong, just different.

These threads on HVAF may be of interest:

hvaf-t-473.html

hvaf-development-t-326.html

[djewell]

Thanks Gordon for this information, you have been really helpful. You mentioned above about Hvaf being good for Carbide based coatings, can you let me know what types of coatings those would be? You also mentioned that Hvof might be better with higher melting point materials. What would those materials be?

Thankya now,
JakDl

HVAF sprays commercially available tungsten carbide and chrome carbide powders. Your current powder vendors can supply powders for use in an HVAF system.

HVOF can spray ceramics. Al2O3 and Cr2O3. In fact HVOF ceramics are harder and tougher than APS.
I do not know if HVAF can spray ceramics.

HVAF cannot spray ceramics. On the other hand, metal coatings have properties similar to cold sprayed coating.

[k09]

Hi Everyone!

Well..after i came across HVAF, in one of the posts made by Djewel..Me and my colleague decided to get all the info related to it....and whatever we could find was in favour of HVAF (well...most of it)

Advantages with HVAF in comparison to HVOF (Purely based on what i could find over the net and the websites of various HVAF manufacturers)

- Does not require a seperate cooling unit. So you save on energy + you donot have to worry about the considerable space that it consumes

- Controls very user friendy and the system is compact, again a space saver.

- Compatible with a vide range of fuels

- Higher spray rates and slightly higher thickness limits. As the process is comparatively less heat intensive to HVOF, stresses induced are lower

- Does not require seperate oxygen input so you save a lot of time replacing the empty oxygen cylinders (which is very frustrating especially if you donot have a manifold system) and this again reduces your cost.

- Not sure about the coating quality in terms of hardness and bond strength but it seems to have lesser porosity (<0.5%)

Disadvantage of HVAF

- Does require a larger compressor. Requires 150-200 SCFM flow rate.

- Although the concept has been thorougly tested and validated, it is still at its infant stage.

And lets face it... people and even organizations usually tend to ignore a concept unless it is validated by well known player in the field... Tomorrow if Praxair or Sulzer Metco comes up with an HVAF system, this forum wud be litreally buzzing with this topic and boasting what an amazing feat they have achieved!!

I personally feel that HVAF holds great prospects and the exisitng manufacturers, be it Unique-coat or Kermitco, should capitalize on the first mover advantage that they have...

Regards

K09

[Intel55]

Hi Everyone!

Well..after i came across HVAF, in one of the posts made by Djewel..Me and my colleague decided to get all the info related to it....and whatever we could find was in favour of HVAF (well...most of it)

Advantages with HVAF in comparison to HVOF (Purely based on what i could find over the net and the websites of various HVAF manufacturers)

- Does not require a seperate cooling unit. So you save on energy + you donot have to worry about the considerable space that it consumes

- Controls very user friendy and the system is compact, again a space saver.

- Compatible with a vide range of fuels

- Higher spray rates and slightly higher thickness limits. As the process is comparatively less heat intensive to HVOF, stresses induced are lower

- Does not require seperate oxygen input so you save a lot of time replacing the empty oxygen cylinders (which is very frustrating especially if you donot have a manifold system) and this again reduces your cost.

- Not sure about the coating quality in terms of hardness and bond strength but it seems to have lesser porosity (<0.5%)

Disadvantage of HVAF

- Does require a larger compressor. Requires 150-200 SCFM flow rate.

- Although the concept has been thorougly tested and validated, it is still at its infant stage.

And lets face it... people and even organizations usually tend to ignore a concept unless it is validated by well known player in the field... Tomorrow if Praxair or Sulzer Metco comes up with an HVAF system, this forum wud be litreally buzzing with this topic and boasting what an amazing feat they have achieved!!

I personally feel that HVAF holds great prospects and the exisitng manufacturers, be it Unique-coat or Kermitco, should capitalize on the first mover advantage that they have...

Regards

K09

Prax did some testing in HVAF years ago and let it go. The HVAF torch is a carbide torch. Huge spray rates, but lil in the way of parameters yet, more trials are underway from some end users. HVAF has been around for awhile, but really has never taken off. That might change in the future, but alot of people are still in the wait and see mode.
I am curious to see how many systems are operating in the US. I think Hayden has one.

[djewell]

Prax did some testing in HVAF years ago and let it go. The HVAF torch is a carbide torch. Huge spray rates, but lil in the way of parameters yet, more trials are underway from some end users. HVAF has been around for awhile, but really has never taken off. That might change in the future, but alot of people are still in the wait and see mode.
I am curious to see how many systems are operating in the US. I think Hayden has one.

Praxair bought the original HVAF patent. The second generation of HVAF made tremendous improvements in the process such as reducing the size of the gun, increasing deposit efficiency, and decreasing air consumption. Now, the third generation of HVAF produces even better coatings. In the case of tungsten carbide, the coatings are harder, denser, and more wear resistant. The coatings passed non-permeability testing at 15,000 psi without sealing.

[bfpapa6]

I would be VERY interested in learning what kind of HVOF equipment can spray ceramics - particularly Chrome Oxide! Do you have any actual data on this?

Hi JakDl

HVAF (High Velocity Air Fuel) process with its lower temperature flame may show benefits with the tungsten carbide based coatings. HVOF on the other hand maybe a better all rounder particularly with the higher melting point materials.

Comments from any body running HVAF and HVOF systems side by side would be very interesting.

Thanks Gordon for this information, you have been really helpful. You mentioned above about Hvaf being good for Carbide based coatings, can you let me know what types of coatings those would be? You also mentioned that Hvof might be better with higher melting point materials. What would those materials be?

Thankya now,
JakDl

HVOF can spray ceramics. Al2O3 and Cr2O3. In fact HVOF ceramics are harder and tougher than APS.
I do not know if HVAF can spray ceramics.

[Stephen Booth]

Top Gun, FX1, or MK2000 type gun with acetylene as fuel gas can spray chrome oxide according to my sources, but I have not tried myself

[jensputzier]

From my experience the Uniquecoat HVAF system produces coatings that are comparable to JP5000 or GTV K2 WC coatings rather than e.g. TOPGUN coatings. The HVAF system has a thermal energy that ranges between HVOF and coldspraying, so that is some kind of niche.

I have just yesterday looked a Uniquecoat system and it has strong points as far as the installation is concerned. You do not need an qxygen tank and you do not need kerosine for fuel. Furthermore first tests have shown that nozzle clogging rarely occurs, only when you push hydrogen levels you will experience that.

You can spray ceramics with HVOF systems, but you cannot generally say that they are better. They have different electric and corrosion resistant properties compared to APS coatings, so you need to check you application and coose the spraying process from that.

As of today, HVAF coatings will not deliver the same oxygen level in metal coatings as coldspraying does.

Regars
Jens

[Gordon]

Hi Jens

to the Surface Engineering Forum.

Thanks for your input.

[Jaydev]

Dear Jakdal, i read all the replies against your query and more or less i do agree with gordon, but i want to add few more things, HVAF & HVOF both are high velocity systems the only difference between these is only composition of fuel used. we use oxygen along with any liquid/gaseous fuel because oxygen acts as a catalyst in combustion it provide more intensity while fuel get burn. now if we use AIR in place of oxygen, as we know air composed of mostly Nitrogen (78%) which doesn't take part in combustion at all just opposite to the characteristics of oxygen.

so hence we can say that if you need a high velocity coating on a substrate which may undergo a high temperature then it would be good to do with HVOF system, and if a substrate need a high velocity coating but too sensitive in slight high temperature then it would be worthwhile to go for HVAF system. i think except few applications HVAF system would be suitable for those components where HVOF system cant be viable option we need to find out some more opportunities in scope of thermal spray coating which need a coating with good characteristics but are very much sensitive in slight high temperature. i think some components in glass industry would be option to apply HVAF coating.

[pulaunias]

Just curious to know if there are any hybrid between HVOF and HVAF?

For example, we have a Sulzer DJ 2700 HVOF in out lab. This machine consumes 307 normal litter/min of oxygen, and 439 normal litter/min of air. Is this considered something between?

[Gordon]

Hi Pulaunias

Just curious to know if there are any hybrid between HVOF and HVAF?

For example, we have a Sulzer DJ 2700 HVOF in out lab. This machine consumes 307 normal litter/min of oxygen, and 439 normal litter/min of air. Is this considered something between?

Well, I suppose it depends on which way you look at it. The fact that air is used you could say yes, but with the Sulzer Metco Diamond Jet systems the air does not take any significant part in the combustion process, its there to shape, cool and accelerate. The DJ system is a burner nozzle and air cap, basically just a big advancement on some of the older flame spray guns. HVOF systems not using air are basically a combustion chamber and barrel.

[Stephen Booth]

In reply to an old post:

Kermetico Convertible Thermal Spraying Equipment Working in HVOF or HVAF Mode

http://kermetico.com/convertible