HVOF Small-ID Spraying

[ykang]

Dear All:

My company is trying to do some small-ID (<2") spraying by HVOF DJ Gun process, but we have no experience with such spraying. Anyone could advice what should I take note with it?

For sure I need to do it with off-angle spray, but other than that how should I proceed it?

Thank You
Ykang

[Gordon]

Hi Ykang

Could you describe part to be sprayed in more detail?

[a.termika]

ATTN: Technical and production managers.



Dear Sirs,

The firm A.Termika Ltd tenders you the portable installation"Termika-3"

of a mean power for gas-thermal deposition of coatings by HVOF method

As has shown long-term experience it differs from existing today in the

market by ease in exploitation, compactness and reliability.

All complete set of the installation places in one portable suitcase (photo).

It is possible to deposit different powders with the size of grains up to 50 microns.

The output on an operational mode implements turn of one handle.

The opening-up and start of the �Termika-3� takes up to 15 min.

The characteristics of received coatings correspond to HVOF technology.





Best Regards

Dr.Boris A.Eizner

Director

A.Termika Ltd.

Israel

boris_iz@zahav.net.il

Tel.:+972-4-8211301

Fax.:+972-057-7973430

Skype address:a.termika

[ykang]

Hi Gordon:

The area to be sprayed is around 1.5"~2" ID diameter and about 1" in length. The requirement is WC-Co coating with 0.006" thickness. Since it is so small, the DJ2600 gun couldn't access into it with pristine condition spraying (90Deg). So I am thinking to spray it with off-angle, but other than that, I wish to know what things to take note in order to spray the component with minimum post-spraying machining job.

[a.termika]

Hi Ykang

Our equipment for this purpases is Termika-3

Rgrds
A.Termika Ltd.

[k09]

In my opinion, Spraying at any angle other than perpendicular would cause two things. First, Drop in coating deposition efficiency and second, increase in porosity due to shadow porosity effect.

But in your case, as you mentioned the lenght is 1" and the ID is 1.5" you only have to tilt the gun axis by 15-20 degrees and approach half the lenght from one end and other half from the other end.

This will ensure minimum porosity (in comparison to tilt angles greater than 20 degrees)... but this will also cause a coating overlap at the centre; which you might have to grind off if you have very close tolerances.

I have never tried ID coatings on HVOF before..But if you HAVE to do with HVOF then this probably is a good way to do it..

If you do manage to do it..do let us know the results..good luck!! )

[Gordon]

Hi Ykang

Agree to some extent with comments by k09. Not so sure of spraying from both ends (assuming both ends are open), while spray angle problem is much improved, coating overlap in middle, probable need for re-blasting prep to second stage, fiddle factor and not being ideal for finishing will be problematical.

Spraying from one side will probably need a spray angle around 45 degrees to clear bottom before top edges start to mask spray. Please appreciate the coating quality will be compromised compared to normal exterior spraying. A few tips:

* Rotate part as fast as possible.
* Grit blast in same direction as spraying direction - avoid opposing direction.
* Get as much cleaning/cooling air through flow as possible (again assuming open ended and mounted to allow free flow) complimenting spraying direction to cool and vent dust and debris.
* If possible spray in one direction only against air flow (dirty to clean direction) - bottom to top avoiding spraying on return stroke.
* Take care with coating and part temperature and any required masking.

Good luck

[ykang]

Hi Gordon:

Thanks for the reply. Got some info for internet mentioned about the overheating of small components spraying. So I am wondering if I need to adjust my WC-Co coating process parameter to suit such small ID spraying to avoid too much overspray and overheating? Currently process parameter is recommended by OEM.

I am thinking to make the flame thinner in size by reducing O2H2 and feedrate. How would you say?

Thanks
ykang

[k09]

Hi Gordon, Ykang..

Ya, I did assume that the part is open from both ends. Gordon, what you said is completely true about coating from both sides. But on the other hand inclination of 45 degrees from the perpendicular will drop deposition efficiency drastically and will surely increase porosity levels.. Please correct me if im wrong..Also, If you have any experience of spraying at such inclination, Please do share with us..

And, I belive small tweaks in the parameters is OK...but not beyond a certain limit...it would be very hard to predict how other factors (coating quality, deposition efficiency) will be affected. The hardware is designed and parameters are set in order to give best quality coatings and tweaking them unless you have a good technical support from the manufacturer is not advisable...

[Gordon]

Hi Ykang and k09

k09, looking at my post again it does sound a little dismissive of your ideas, that was not my intention . While in fact I think I would experiment with both approaches to see which works best. At the end of the day it does not matter how much we theorize on this type of application, the proof will only come with practical spraying trials.

Changing the gun spray parameters and reducing spray rate may help little. But if you are not prepared for some hard work with coating and process development or job is just not worth the added investment cost of this development work, then I would stick with the OEM parameters.

[k09]

...no no...I really dint mean to point it out in that sense..

If it sounded as if i was complaining, Plz ignore it .. i would never dare to question your expertise in this field..

I was only curious to know what was best solution for the problem at hand..