how to increase TBC deposit speed?

[derek]

I spraied TBC bond coat and top coat using SG-100. The bond coat was no problem but the ceramic coat's deposit speed was too low.
The parameter is:
Ar:87 SCFH(primary gas)
He:43 SCFH(secondary gas)
Ar: 18 SCFH(carrier gas)

36V and 600A with 3 inch spray distance and CPW388 powder.
After 20 passes, only build up 0.003inch.

Any help will be appreciated.

[Gordon]

Hi Derek

Have you done any deposit efficiency tests with this material?

[bhellman]

Gordon Wrote:Hi Derek

Have you done any deposit efficiency tests with this material?

Derek, even after decades in the TS business I have never seen a satisfying explanation on why oxide ceramic filler materials sometimes refuse to build up.
I don't know if it has something to do with that the powder is manufactured on the wrong side of the globe, due to static electricity or that the oxides are very effective blasting media, meaning that blast polishing is occurring while spraying. The best result we found to solve this problem was by experimenting with passing speeds and overlap per pass to find the right "hot spot" temp .
br bhe

[derek]

For Gordon:
I did not do any deposit efficiency tests. Do you have any idea to increase the deposit speed?

Thanks for your help,Bhellamn.

[Gordon]

Hi Derek

To increase deposit speed you will need to increase powder feed rate or possibly increase the deposit efficiency if that is lower than normal. Increasing powder feed rate without making any other changes will at some level begin to effect the quality of the coating (increase in porosity, unmelts etc.). If the changes in coating quality are not acceptable then changes in other parameters may need to be made.

If you think your deposit build-up speed is not right for your parameter settings, then I suggest doing deposit efficiency tests to see if your getting normal results. If your deposit efficiency is very low, increasing powder feed rate will not be very productive. bhellman post is essentially about deposit efficiency.

[bhellman]

Gordon Wrote:Hi Derek

To increase deposit speed you will need to increase powder feed rate or possibly increase the deposit efficiency if that is lower than normal. Increasing powder feed rate without making any other changes will at some level begin to effect the quality of the coating (increase in porosity, unmelts etc.). If the changes in coating quality are not acceptable then changes in other parameters may need to be made.

If you think your deposit build-up speed is not right for your parameter settings, then I suggest doing deposit efficiency tests to see if your getting normal results. If your deposit efficiency is very low, increasing powder feed rate will not be very productive. bhellman post is essentially about deposit efficiency.

As Gordon expressed, I was kind of talking about deposit efficiencies. But not totally of it. Picture the situation that you have to coat a large paper machinery cylinder with alumuminium oxide, t = 0,4 mm).
After two passes you find out that the coating doesn't build up anymore?
Before that all parameters have been locked and considered optimal.
Whatever you do, the coating just collects as debris on the spray booth floor.

I don't agree totally with the advancement in thinking that checking the deposit efficiency would solve the problem. Comment in between.; most thermal spray companies are handling quite small objects. That on the other hand makes it impossible to recognize larger problems in the total coating procedure.
Please, any arguments or comments are willingly accepted.

br bhe

[bhellman]

bhellman Wrote:

Gordon Wrote:Hi Derek

To increase deposit speed you will need to increase powder feed rate or possibly increase the deposit efficiency if that is lower than normal. Increasing powder feed rate without making any other changes will at some level begin to effect the quality of the coating (increase in porosity, unmelts etc.). If the changes in coating quality are not acceptable then changes in other parameters may need to be made.

If you think your deposit build-up speed is not right for your parameter settings, then I suggest doing deposit efficiency tests to see if your getting normal results. If your deposit efficiency is very low, increasing powder feed rate will not be very productive. bhellman post is essentially about deposit efficiency.

As Gordon expressed, I was kind of talking about deposit efficiencies. But not totally of it. Picture the situation that you have to coat a large paper machinery cylinder with alumuminium oxide, t = 0,4 mm).
After two passes you find out that the coating doesn't build up anymore?
Before that all parameters have been locked and considered optimal.
Whatever you do, the coating just collects as debris on the spray booth floor.

I don't agree totally with the advancement in thinking that checking the deposit efficiency would solve the problem. Comment in between.; most thermal spray companies are handling quite small objects. That on the other hand makes it impossible to recognize larger problems in the total coating procedure.
Please, any arguments or comments are willingly accepted.

br bhe

[Gordon]

Hi derek and bhellman

Some important points raised by bhellman.

Quote:I don't agree totally with the advancement in thinking that checking the deposit efficiency would solve the problem

I agree doing deposit efficiency tests will not solve any problem, but it is useful for identifying if a problem exists. I don't particularly like the methodology of the typical deposit efficiency test, where a small plate is sprayed for 30 or 60 seconds being weighed before and after and DE calculated from supposed spray rate. Testing in this manner is prone to significant errors, apart from the fact that it will not represent the job that you want to spray. May be OK to just check manufacturers claimed DE, but not necessarily what you will get in real life. My preferred method is to weigh powder before and after spraying and weigh work piece before an after spraying. The work piece ideally being the actual component or test piece that will simulate your actual working conditions. Obviously, if your part is more than a few kilograms in weight you will have to scale it down to suit your weighing instrument. The more powder you spray the more accurate your result. Measurement of time is not necessary, you just need the weight of powder sprayed at part and weight of coating deposited to calculate DE. Alternatively, you could estimate the DE from actual production conditions, by recording; powder weight sprayed, total spray time, spray time on job, accurate assessment of average coating thickness and knowledge of typical coating density and coating area. I leave the maths to you.

Quote:As Gordon expressed, I was kind of talking about deposit efficiencies. But not totally of it. Picture the situation that you have to coat a large paper machinery cylinder with alumuminium oxide, t = 0,4 mm).
After two passes you find out that the coating doesn't build up anymore?
Before that all parameters have been locked and considered optimal.
Whatever you do, the coating just collects as debris on the spray booth floor.

On a few occasions I have experience this effect with plasma sprayed chromium oxide and HVOF WC/co. I believe this phenomenon is due to an equilibrium between that of coating deposit build-up and grit blast effect. I have not observed this effect with thermal barrier coatings though (always a first time though:rolleyes

Other effects that you should be aware of is, measurement of the thickness for the first coating pass should not be taken too seriously, as this invariably gives you an inflated view of thickness per pass (measurement of localised peaks distorts view of average thickness). I see this often, for example your first pass measures 0.001?, you then spray another 9 passes to achieve 0.010?. On final measurement you find you have only got 0.004?. Recalculation gives 0.0004? per pass, so another 15 passes usually does the trick.

Quote:For Gordon:
I did not do any deposit efficiency tests. Do you have any idea to increase the deposit speed?

Though interesting, we may be getting a little side tracked, as derek may not be suffering from any deposit efficiency problems and just wants to speed up production. In which case he will need to develop high spray rate parameters or use more than one gun.

[derek]

Thanks for help,gordon and bhellman.
I decrease the primary gas and secondary gas flow and increase the amperagy. It works well. It is built up 0.005 inch in 10 pass.

[Gordon]

Hi Derek

Glad to see you making progress. Did you manage that 3 fold plus increase in deposition speed just by changing those parameters with no increase in powder feed rate? Sounds like your original parameters were in need of some serious optimisation. Did you also get any improvement in coating quality?

[derek]

Hi Gordon,
I didn't change the powder feed rate but some parameters and the coating quality has not be improved.

[hvofhamid]

hi everybody
10 pass are too much
could you please tell us the diametre you are coating?AND how many/100 lost powder ,i m afraid you fusion powder temperature is not correct,tell us please wich materiels and wich parameter you are using in orther to know ,how to help you?THANKS