Water cooled vs air cooled

[Met.Eng.]

Hi

I have a question about gun cooling. I have a Hipojet 2700 water Cooled Hybrid gun,

Today I check the DE about the CRC-NICR and WC/Co. At my experiment results DE is too low about 35-40 ,

We dont have any spray paremeter document like metco DJ2700, couse the supplier gives only one parameter for all powders
250 O2 , 60 LPG , 12 N and 200 mm distance,
We try lats of parameters

When I check the dj parameters they gives different parameters and hardwares. I saw at document air cooled deposition higher than water cooled , I don’t understand about that couse gas velocity and density is highest when use water cooled hardware.You can see this when operation, flame diameter and flame length is higher when use hybrid gun. But why DE is lower than air cooled?



Is any one have an experience about hipojet hybrid ?

Good day

[Lemster68]

Sorry, I don't have any experience with those torches. But, I hypothesize that with air cooling you will have less heat loss to cooling and therefore more heat for heating the powder.

[Vadim Verlotski]

Hi Met.Eng.,

Answer by Lemster68 is completely correct. Water cooling takes significantly more heat from the flame than air cooling, and at the same conditions flame gets colder. But that's not all. Water-cooled burners allow a higher gas velocity than air-cooled burners and this also leads to a lower particle temperature.
It can generally be said that with the same burner power, air-cooled burners "spit out" hotter but slower particles than water-cooled burners.

In order to get an increase in particle velocity and particle temperature at the same time, burner power has to be increased (you can see it in modern burners that have over 300 kW of power). There is also another way to do it: using fine-grained powder in combination with shortened spray distance.

Conclusion:
if you do not want to change powder, then for burners with approximately the same power, you can either raise the particle temperature, but reduce the particle velocity, or the other way round: increase particle velocity at the expense of the particle temperature. An increase in particle temperature improves DE, and an increase in particle velocity improves coating quality; You can choose what is more important to you.

[Met.Eng.]

Thank u for ur answers.Is there any way to Increase particul tem with water cooled for change the parameters? for ex increase the oxygene for hot flame, or decrease the carrier gas for hottest particul tem , ect...

[Vadim Verlotski]

I do not know your burner, but basically the following rules apply to parameter variation:

1. The shorter the nozzle the hotter and slower the spray particles (for maximum particle temperature, choose the shortest nozzle).
2. The larger the nozzle diameter, the hotter and slower the particles (for maximum particle temperature, choose the nozzle with the largest diameter).
3. Maximum particle temperature is achieved at lower spray distances than the maximum particle velocity. This means that a shorter spray distance provides better DE with poorer coating quality.
4. Use of high-carbon fuels (ethene, acetylene, kerosene, etc.) instead of LPG or propane increases the particle temperature.
5. Use of smaller particle sizes increases as well the particle temperature as also particle velocity.
6. Reducing of carrier gas increases the particle temperature.

[vcduramais]

Hi

I have a question about gun cooling. I have a Hipojet 2700 water Cooled Hybrid gun,

Today I check the DE about the CRC-NICR and WC/Co. At my experiment results DE is too low about 35-40 ,

We dont have any spray paremeter document like metco DJ2700, couse the supplier gives only one parameter for all powders
250 O2 , 60 LPG , 12 N and 200 mm distance,
We try lats of parameters

When I check the dj parameters they gives different parameters and hardwares. I saw at document air cooled deposition higher than water cooled , I don’t understand about that couse gas velocity and density is highest when use water cooled hardware.You can see this when operation, flame diameter and flame length is higher when use hybrid gun. But why DE is lower than air cooled?



Is any one have an experience about hipojet hybrid ?

Good day

Dear Met. Eng.

If you want to increase DE a simple thing to do is to work with higher part temperature.

Starting the spray process when the part temperature is about 100°C can increase DE to something about 50%.

I don't know what DE you are trying to get but this make really big difference. I use it and almost every coating company I know use it too.

Best Regards.