Surface speed |
11-01-2006, 11:38 AM
Post: #1
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Surface speed
Hello, Forum!
Sorry for my English!!! I have question. Influence surface speed during HVOF, APS and Flame Spray on quality coatings (bond strength, porosity, residual stresses...). How choose surface speed for each technique? Thank you. | |||
11-01-2006, 12:31 PM
Post: #2
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RE: Surface speed
Panf,
We have APS and air spray system, we are using about 250 surface feet/min speed. | |||
11-01-2006, 08:16 PM
Post: #3
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RE: Surface speed
Hi Panf
![]() Quote:Posted by Panf - Today 10:38 AMThis is a good question Quote:Posted by derek - Today 11:31 AMThis is roughly the sort of surface speed required, particularly for plasma and HVOF processes. It also tends to be maximum capability of most gun traversing equipment. The most notable advantage of the thermal spray process over most other surface engineering coating processes is that it is a "cold process" in respect to the substrate. May people when first introduced to thermal spray are usually very surprised and find it hard to understand how this is a cold process. The process may use plasma at 15000 degree C and spray molten high temperature materials, how can that be cold? The process is normally used in a manner where very thin layers of coating are rapidly deposited in stages, so that substrate heating can be controlled and kept very low. Analogous to passing ones hand through a hot flame, the quicker the hand moves, the less likely you will be burnt. This allows for temperature sensitive substrate to be coated with materials that have a very much higher melting point (ceramics on aluminium or plastics). Sorry for rambling on, I just wanted to highlight the importance of surface speed. The relative surface speed between the gun and substrate and the speed or step distance in the transverse direction are very important parameters. Along with powder feed rate, these parameters dictate the thickness of material deposited and exposure to hot gases on the surface per pass of the gun. With most thermal spray processes, the main heat input is from the deposited coating rather than the hot gas stream (possible exception being HVOF). So when setting surface speed and traverse speed or step distance we need to account for coating material properties and deposit rates. The shape, size and mass of the substrate, along with thermal conductivity and effects of any auxiliary cooling processes also need consideration. Usually my first consideration when selecting suitable surface speeds and other parameters, is the thickness of coating material to deposit per pass of the spray gun. Generally, flame and arc spray processes tend to be a little less critical than plasma or HVOF with around 0.001" to 0.004" (25 to 100 microns) thickness per pass giving good results. Plasma and HVOF, particularly when ceramic or cermet (WC/Co) type coatings are being sprayed, should always be kept below 0.001" (25 microns) per pass and ideally much lower. I select surface speeds that give me the desired thickness per pass (trial and error or from experience) and allows me control over coating/substrate temperature during spraying, rather than just accepting a general recommended surface speed, which may not take account of the many variable factors involved. The effects of excessive low surface speed and high thickness per pass on coating integrity is mainly heat and stress related and can result in cracking, layering faults and delamination. Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
11-02-2006, 08:47 AM
(This post was last modified: 11-03-2006 01:45 PM by Panf.)
Post: #4
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RE: Surface speed
Dear Gordon!
I glad that you understand me. Thanks for you reply. Few question more: 1. thickness of metall coatings (NiCrBSi or FeCrNi...) must be <25 micron per pass too? 2. what you recomended for surface cooling (air, water or what)? 3. Efficiency during spraying with high surface speed decreased or not? Thank you. | |||
11-04-2006, 10:39 PM
Post: #5
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RE: Surface speed
Hi Panf
1. I assume you are referring to HVOF metal coatings. Generally, these tend not to be as critical as cermets and would choose around 25 microns per pass. 2. Should additional cooling be required first consider air. If air blast cooling is not sufficient, then consider carbon dioxide cooling systems. I have used water spray mists, and in certain conditions it can be very effective. Water is very risky to use though, and generally best avoided. 3. I have thought that at very high surface speeds you might expect drop off in deposit efficiency, but I have found no noticeable evidence of this effect. Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
11-07-2006, 12:48 PM
Post: #6
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RE: Surface speed
Thank you very much, Gordon.
I hope you advices help me. | |||
11-08-2006, 06:42 PM
Post: #7
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RE: Surface speed
Panf Wrote:Hello, Forum! Hallo Panf, my experiences with HVOF is: surface speed 30-40 m/s ![]() | |||
11-09-2006, 07:04 AM
Post: #8
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RE: Surface speed
Really???
surface speed 30...40 m/s it's 1800...2400 m/min!!! for detail ?100mm W=7600 RPM....... - unreal!!! correct me if I wrong... | |||
11-09-2006, 02:00 PM
Post: #9
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RE: Surface speed
Panf Wrote:Really??? Sorry!!! 30-40m/min. | |||
11-09-2006, 02:08 PM
Post: #10
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RE: Surface speed
The highest surface speed I think I've ever used was around 10 m/s ("single pass" plasma spray r&d). That certainly stretched the capabilities of the handling equipment and gave concerns regarding health and safety. Imagine a solid lump of steel 500 mm by 300 mm diameter revolving at 600 rpm, thats a lot of energy stored, potentially very hazardous if it becomes unbalanced or set free.
![]() Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
11-09-2006, 02:20 PM
Post: #11
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RE: Surface speed
Hi Vladimir
Your last post just beat me to it ![]() Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
11-09-2006, 03:55 PM
Post: #12
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RE: Surface speed
Gordon Wrote:Hi Vladimir Hi Gordon I corrected my first mistake (30-40m/s - its wrong, I know),but 30-40m/min its 0,5-0,66m/s - and this is OK for HVOF. In accordance to Technical TAFA Bulletin: "RECOMMENDED FEEDS AND SPEEDS FOR SPRAYING WITH THE JP-5000 Note: these are recommended minimum feeds and speeds - some substrates or coatings may require different settings. Some operators may feel more comfortable with their own settings. This does not guarantee coating quality or the lack of substrate overheating. In general, a good average substrate surface velocity is: 100 ? 150 SFPM (31 ? 46 m/min)" Vladimir | |||
11-09-2006, 05:37 PM
Post: #13
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RE: Surface speed
Hi Vladimir
My ![]() Those sort of speeds are very often given as general guidance, but in my experience many applications are best done with much higher speeds. Spraying of carbides and ceramics or coating substrates with a limited heat sink or are heat sensitive are good examples. I've seen far too many problems where unsuitable speeds and feeds have been used (many using so called recommended settings). "Let's think out of the box," could be applicable here (sorry for using management-speak buzzwords). Usually, though we are limited by the capability of our handling equipment and have to compromise. Sometimes lowering powder feed rates (deposition rates) can be a useful trick, if the desired speeds can not be achieved. Please read my first post in this thread for the reasoning. ![]() Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
12-25-2006, 04:45 AM
Post: #14
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RE: Surface speed
Dear Friends.
We made a engineering diploma work on the influence of surface speed (actually passing speed). If one consider the difference in the actual passing velocity between various methods, the outcome is that the work peace surface velocity is minor compared to the particle velocity for any method. Of course one can imagine that spray methods with "low" particle velocity, can tolerate lower passing speeds, OK. The diploma work showed that the HVOF-process can take at least up to 300 m/min of surface speed without any quality problems, in the contrary the coatings where much cleaner than on lower speeds. I remember, in my beginning in this business, 10 to 30 m/min was considered the accurate values. My feeling is that more important are factors like (for rotating objects): - the right feed (rotation and pitch) to get the optimum lap and impact point. - to be aware that the spray impact point temperature is OK. - to have the optimum feed/revolution, 50 to 60 % overlapping. - to have a optimized ventilation or local directed suction. bhe | |||
12-30-2006, 04:22 PM
Post: #15
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RE: Surface speed
Panf Wrote:Hello, Forum!of course you have to calculate your speed owing the diameter you coat and rotation speed | |||
01-05-2007, 02:56 AM
Post: #16
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RE: Surface speed
bhellman Wrote:Dear Friends. Still read by comments on this subject. Even if not absorbing the way of thinking, please consider its validity. br bhe | |||
01-05-2007, 07:58 PM
Post: #17
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RE: Surface speed
bhellman Wrote:bhellman Wrote:Dear Friends. hello everybody before start working in spray coating ,I worked in several posts of mechanical fabrication,when I started coating we had lot of problems because we haven t the right speed and the right rotation.we only could coat succefuly one diameter .then i realize if i can use the diferent conditions(rotation,speed)owing diameters and calculate the speed coating conditions ,may be we can solve the problem.since then we are working and have no problem.I hope my english will be understood and happy new year to all of you we can coat all diameters with diferent speed and we have no problems | |||
07-16-2007, 05:32 PM
Post: #18
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RE: Surface speed + WC-Co16 coating problem
More info related to this thread here
with a copy below. Howied Wrote:Hi all, Gordon Wrote:Hi Howied fhyuan Wrote:I also think it is right the thickness per pass of the spray gun is the deposit rate. Gordon Wrote:Hi fhyuan Fergus Wrote:Hi fhyuan Wrote:Fergus, I think Gordon has given the above answer for your question. First test to have the foot print width, then calculate the relationship between the traver rate and the surface speed (RPM). Gordon Wrote:Hi Fergus, Howied and all, Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
05-25-2009, 02:17 PM
Post: #19
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RE: Surface speed + WC-Co16 coating problem
Dear,
Can you give the reference of above formula? | |||
05-27-2009, 04:52 PM
Post: #20
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RE: Surface speed
Hi ahmadsahid
![]() (05-25-2009 02:17 PM)ahmadsahid Wrote: Dear, Not sure what you mean, but if it is data like powder required, coverage, density, coating weight etc., then you will need reference to the specific material/process technical data sheets or contact your supplier. Failing that you will need to conduct your own actual deposition tests (which would be the more accurate way). One point that may not have been made clearly in above posts, is that any over-spraying (times when gun is not actually spraying on intended area to be coated) must also be considered in calculations. Regards Gordon www.gordonengland.co.uk www.surfaceengineer.co.uk Photography Obsession | |||
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