Hi Fergus, Howied and all,

Fergus Wrote:Hi

Setting up speeds and feeds this way sounds logical, but where do we start . Is there a way of working this out or a formula to give us a starting point.

thanks

Fergus

I think most would start from a point from past experience, but you can theoretically calculate this using information supplied by powder/equipment supplier/manufacturer.

This only covers rotating cylindrical work pieces. For other types you will need to modify method.

1. Calculate

coating area (3.14DL)

2. Use

COVERAGE (sqft/hr/0.001" or sqm/hr/0.1mm) found hopefully in powder/equipment bulletin/manuals for your particular coating to calculate

SPRAY TIME
3. Divide desired

coating thickness by the

thickness per pass (for carbides and ceramics I would aim for ~ 0.0002" or 5 micrometres per pass) to get

number of passes required
4.

Part length x

No. of passes divided by the

spray time will give you

TRAVERSE SPEED
5.

Traverse speed divided by

traverse distance per revolution (this distance should be slightly smaller than your spray footprint) to get

rotational frequency RPM.
The theoretical calculations do not always work exactly in practise, but should give a good starting point for fine tuning.

Example: 6" diameter x 12" long cylinder coated with Metco 73F-NS-2 (P73F-10 spec) to 0.10" thick.

1. 3.14 x 6 x 12 = 226 sqin or 1.57 sqft coating area

2. Coverage from Metco 73F-NS-2 tech bulletin says 135 sqft/hr for 0.001" coating thickness.

for 0.010" coating thickness thats 13,5 sqft/hr

for 1.57 sqft thats (1.57/13.5) gives us 0.116 hrs or 7 minutes spray time.

3. 0.010/0.0002 = 50 passes

4. 12" x 50/7 mins = 86"/min or 7.17 ft/min traverse speed

5. Lets say 0.16" traverse per rev 86/0.16 = 537 RPM

6. So that gives us a starting point of 537 RPM (850 SFPM) and a traverse rate of 86"/min using 50 passes and spray time around 7 minutes.

There is a point particularly with high spray rate/high deposit efficient materials on smaller diameters where the part revolution frequency RPM becomes difficult to manage. We can only compromise in these situations, by excepting higher deposits per pass or reducing spray rates. In many situations carbide and ceramic coatings are applied much thicker per pass than I personally would like, but have proved adequate for purpose (I just know they are not as good as they could be

).

Beware my maths may not be that good