How does gas-shroud HVOF (warm spray) system work?
12-22-2014, 05:17 PM,
#1
Lightbulb  How does gas-shroud HVOF (warm spray) system work?
I was reading some scientific articles on warm spraying in which in-flight powder particles travel with high velocity and reduced surface temperature. There is an extra shroud with continuous supply of nitrogen is attached to the barrel of JP-5000 torch. Can someone explain me how the velocity of in-flight particles is increased by using a shroud. I can understand the effect of using nitrogen in the shroud which is to quench the flame and consequently reduction in particle temperature. Can we achieve the same condition by increasing the barrel length of jp5000 torch and supplying nitrogen from auxiliary port placed just after the de-laval nozzle or powder feeding port?
Reply
12-23-2014, 04:46 PM,
#2
RE: How does gas-shroud HVOF (warm spray) system work?
I don't see how a shroud gas could possibly impart any additional velocity to the particles. In order to accelerate the JP5000 gas stream, you must expand it after the choke. Introducing additional gas in the nozzle is going to compress the gas stream. Would you post the article to which you are referring?

Warm spray is a strange technological development, in my opinion. By quenching the flame with nitrogen, the operator is basically synthesizing air. In other words, they are turning a JP5000 into an HVAF gun. They get some nice looking coatings, of course, because they are synthesizing the HVAF spray conditions. However, in the process, they still have the same drawbacks of the JP, namely radial powder injection, water cooling, short nozzle life, etc. If the researchers would start with an HVAF gun, they could also take advantage of HVAF's lower operating cost, higher deposit efficiency, and longer component life.
Reply
12-24-2014, 10:36 AM, (This post was last modified: 12-24-2014, 10:38 AM by Lalit.)
#3
RE: How does gas-shroud HVOF (warm spray) system work?
Dear djewell, thanks for reply and I am convinced with your idea that they are presenting hvaf in different style. One thing I would like to know that if you can tell me why the barrel length is more in d-gun as compared to Jp5000. Because I think the shroud also work in the same way. You can read the papers of seiji kuroda and Watanabe, NIMS, JAPAN. In every paper they have written that shroud increases the particle velocity.
Few days back I attended 6th Asian thermal spray conference in India where professor Seiji kuroda delivered a lecture on warm spraying. He compared hvof and warm sprayed wc-co coating. Initially hvof coayings were superior than warm sprayed coating but I was surprised to know that he was claiming to get a high fracture toughness value (17 MPa.√m) of wc-co coatings which was very near to sintered wc-co material. He got this high value of warm sprayed coayings after conventional heat treatment (800 °c) whereas no improvement was shown by HVOF coating.
Reply
12-24-2014, 06:13 PM,
#4
RE: How does gas-shroud HVOF (warm spray) system work?
In normal operation, a liquid fueled HVOF gun typically consumes approximately 1,000 l/min. I found a presentation from Mr. Kuroda on the Swiss Federal Laboratories web site. He achieved the best looking coatings from his warm spray gun with 1,000 l/min nitrogen flow. His actual oxygen concentration in the flame is less than 50%. This is not much different than air (~21% oxygen content).

Regarding your original question, I did find that Mr. Kuroda injected the nitrogen shroud into the combustion chamber before the nozzle choke, which would increase the pressure and lower the flame temperature, which could increase the gas density. As the gas expanded, it could achieve a higher velocity. You would have to look at some combustion and gas flow equations to confirm this.
Reply
11-24-2022, 08:22 AM,
#5
RE: How does gas-shroud HVOF (warm spray) system work?
Gas-shroud HVOF systems use a high-velocity water stream to clean floors by mixing the correct pressure and velocity to remove all types of liquid, dust, and dirt. The system is simple to operate: turn it on and wait for the machine to do its job. It's also lightweight, so you can move it around quickly, which is great if your business has multiple locations.

Design Engineer at Testo India
Manufacturer Of Portable Combustion Efficiency Analyzers
https://www.testo.com/en-IN/
Reply
02-17-2023, 09:25 PM, (This post was last modified: 02-17-2023, 09:26 PM by J!m.)
#6
RE: How does gas-shroud HVOF (warm spray) system work?
(12-24-2014, 06:13 PM)djewell Wrote: Regarding your original question, I did find that Mr. Kuroda injected the nitrogen shroud into the combustion chamber before the nozzle choke, which would increase the pressure and lower the flame temperature, which could increase the gas density. As the gas expanded, it could achieve a higher velocity. You would have to look at some combustion and gas flow equations to confirm this.

This is interesting, and makes sense. Metco (Bill Rusch specifically) developed a new HVOF torch that never went to market. It operates on Methane, Oxygen and Nitrogen. Coatings are extremely dense, and also extremely compressive (which limited their usefulness). It never went to market, but I wanted to resurrect the technology while I was in equipment R&D at Metco, as the cold spray wave was gaining momentum. I am sure this torch could make "cold spray" coatings for far less than what cold spray costs...

Back on track, I agree with djewell in how the nitrogen is affecting things.
Spraying since '87. University of Metco alum (99-16)

Available for consultation services- please send a PM
Reply




Possibly Related Threads…
Thread Author Replies Views Last Post
  Twin Arc spray system ( request for your recommendation) demionkrishan 0 1,766 03-04-2019, 10:22 PM
Last Post: demionkrishan
  HVOF System Considerations Josgates 5 3,112 07-10-2018, 03:01 PM
Last Post: Stephen Booth
  The best HVOF system for MCrAlY DMack 12 10,522 01-21-2017, 04:54 AM
Last Post: david.wang
  Is it possible to spray powder established for gas based HVOF in Fluid HVOF system?? sreenuvundela 0 3,474 04-18-2016, 07:52 AM
Last Post: sreenuvundela
  INFO ON ROKIDE SPRAY SYSTEM ehasan 11 23,037 07-10-2015, 07:39 AM
Last Post: shantanu
  Miller Thermal Plasma spray system Vijay Deshpande 2 5,986 06-20-2015, 06:19 PM
Last Post: Johnny_Blaze
  Tangential velocity of work surface Airbin 7 8,033 03-13-2014, 09:43 AM
Last Post: sreenuvundela
  Water Plasma Spray System sreenuvundela 0 3,348 03-12-2014, 06:26 AM
Last Post: sreenuvundela
  how does sacrificial coating work? JNRT 1 2,768 10-14-2013, 12:06 PM
Last Post: Gordon
  HVOF: Gas fired system Vs liquid fired system shantanu 3 7,769 06-19-2012, 04:06 PM
Last Post: Pete_F
  Select a twin arc spray system Florin 27 38,547 02-20-2010, 03:42 PM
Last Post: Florin
Question upgradation of HVOF system. dibyendudhara 3 7,396 05-21-2008, 11:28 AM
Last Post: hvofhamid



Users browsing this thread: 1 Guest(s)





Surface Engineering Forum Sponsor - Alphatek Hyperformance Coatings Ltd