AAA Spraying help needed please

[mlarm]

Hi
I would be grateful for any help/ advice.

I have just set up a spray booth to spray the joinery we make.
I am spraying morrells omnia with a graco 45:1

The spray equiptment supplier recommended:
Fluid pressure of 40psi
Gun pressure of 20psi

The paint supplier morrells have recommended:
Fluid pressure of 30psi
Gun pressure of 22 psi

So I an a bit confused as to which is correct.

The main problem I seem to be having is runs and sagging of paint on the edges.

Does this mean I am holding the gun too close ?

I would appreciate any advice I have sprayed with a conventional gun during my apprenticeship but this is a different kettle of fish.

Many Thanks
Matt

 

[thick_mike]

Sagging can have a Number of causes, you could be building the primer too thick, you could be putting the gun to close (as you said), you could beat you Might not be atomising the primer enough, your primer might be too viscous and so on...

Things that will reduce sagging are:

increasing the distance of the gun from the part.
Increasing atomising air pressure (at the gun).
Reducing the rate of paint delivery to the gun.
Decreasing the viscosity of your paint slightly (if the cause is poor atomisation)

It's important to only trigger on/off the gun when you are off the edge of the part. If you have the gun on the part when you trigger the paint the first bit won't atomise as well and you can get runs.

Also, when spraying waterborne paint, the humidity of your booth will have an effect. You will get a wetter application if it is humid in your booth.

 

[mlarm]

Thanks for your reply I really appreciate it.
I am off to the workshop now to try what you suggest.

I have been using 30psi fluid and 20psi atomising pressure.
Do you think this is ok?

I primed a few pieces Friday evening before I left and they looked pretty bad when wet, however when I came in on Saturday I was pleasantly suprised the coating seemed to have flattened out alot over time.
It was just the heavy build up on the edges and some corners that spoiled it.
Would it be advisable to turn the fluid pressure down and do an extra coat untill I get used to it ?

Many Thanks
Matt

 

[RobinBHM]

The setting for the fluid pressure depends on the pump ratio.

For eg a 45 to 1 pump will have 45 x the pressure at the tip, whilst a 30 to 1 will have 30 x.

Having said that altering pump pressure wont have a huge influence if you are in approx the correct range. Increasing pressure will increase the flow rate and may be compensated by gun speed.

I would do some sprayouts on a flat board (i use off cuts of melamine faced chipboard as the smooth surface shows the finish really well).Start with low pressure, say about 25 to 30 with no air, and see if you get an even oval pattern with the right weight of coat, increase pressure as needed until you are happy with finish. Without air you will have a tail at top and bottom of the pattern. Turn on air just enough for the tails to clear. Keep fluid and air pressures only high enough to achieve the finish quality required, any more will increase overspray, hence reason for starting low.

If the coat is orange peel, this cant be corrected by pressure, you may have to add a few % water. Temperature and humidity also influence flow out of finish

What tip size do you have? Typically a 4 - 11 tip is used for exterior joinery coatings. This is an 11thou x 40 degree size, giving about 8" wide spray with gun at about 8" away.

Are you using a grace g40 gun? These can alter spray width somewhat by altering air pattern at nozzle, although as soon as the air holes are a bit blocked this feature wont work. For narrow work swap to a 3- 11 tip.

Most exterior coatings are sprayed at about 150 to 180 micron wet film thickness, drying to about 60. You can get a wet film gauge to check. A lot of these type coatings will still hold up at up to 300 microns before runs appear.

Are you spraying frames, doors, sashes, beading?

I assume you are following conventional routine for sashes. IE inside rebate/edges, starting at top centre, then outside edges, then faces. Faces are done by starting the fan pattern coming in at the corner at 45 degrees, running along then turning 45 degrees at other corner. Hence spraying as though drawing the outline of a mitred picture frame. It avoids double coating corners.

In joinery edges should really have a 2.5 to 3mm radius so paint film stays at correct thickness at the corner -externally, 1.00mm internally.

I assume it is opaque finish you are doing -as you mention primer. Transluscent coatings are different as they have stain basecoat, possibly a mid coat, then high build top.

 

[mlarm]

Thanks for your time Robin.

After studying every sash and frame I have sprayed the place I am getting the run/ sagging is always on the face on the rebate side. I am guessing that when I am coating inside the rebate I am hitting the face with coating aswell, so when I spray the face it has got a coating on the edge nearest the rebate and it is building up too thick.
Is there a way to avoid this maybe holding the gun more upright against the rebate?

I am using a Graco g40 yes with a 4 11 tip.
I have just got some melamine board to test on from the workshop.
I am following the method you describe, apart from mitring at the corners. If sure this will help where I am getting a build up on the corners.
I think maybe I am applying too thick a coat I will order thickness gauge.

Once again thank you for your reply

Matt

 

[RobinBHM]

Its best when spraying the inside, to stand at 90 degrees to the sash. If you are right handed, stand so you are facing left. Gun starts facing the ceiling, trigger with fan pattern in front of sash, then start moving gun anti clockwise and turn pattern into inside face. You should be able to rotate wrist all the way around ending back up at the top, overlapping where you came in.

This method allows the gun to be facing the inside edges and avoids the coat you are getting on the face

If you spray the inside of the sash, facing straight towards it, you wont be able to rotate your wrist all the way around.

Morrells might give you a wet film gauge, i expect they have some. It isnt that vital to use one, but it does help initially to get a feel for film thickness.

The G40 is a great gun, you will very soon be getting a fantastic finish. Be aware of recoating too soon otherwise you will have jobs going out which arent cured and at this time of year could remain uncured for weeks. Resulting in bubbling up or peeling. A simple test is to lay a soaking wet tissue on a test piece done with your batch of joinery. Leave it on for half a hour and see if you get any bubbling, if not it should be cured. Darker pigmented paints cure more slowly.

 

[mlarm]

Hi Robin
Thanks so much for your advice Its so helpful.
I assume you spray yourself?
I was worried I had done the wrong thing in taking on a seperate workshop to finish the joinery we make.
But I guess it's just practice.
I was just so frustrated with the finish we were getting when out sourcing our spraying. All the company's we used only seem to use a conventional spray system and water the coating down. we always got products back that looked like the coating was so thin.

Great tip for testing if the pain has cured, thankyou

Many Thanks
Matt

 

[RobinBHM]

I run a joinery with a paint shop, weve been spraying AAA for many years.

Conventional spray set ups wont spray joinery finishes, they wont atomise. The best is a SATA 1000 gun with a large tip set up 2.0mm or 2.5mm, very useful for painting colour samples or the odd trim.

Once youve got the hang of using the gun, you will find it dead easy set up to use.

I think there is some useful advice about 'winter paint curing problem' on the Teknos site, it can be a serious problem. I would suggest looking at Teknos and Remmers exterior joinery paints as options and their websites for info. If you pm me I can give you contact details for a technical rep that could provide all the spraying advise you may need, as well as on site training -if you wanted to use their products.

You wont regret bringing the finishing in house.

 

[thick_mike]

Here is a video that explains how to set the fan pattern for your primer...

http://youtu.be/O9ZujbVODNY

 

[mlarm]

Thanks Mike, really useful video.

Does anyone have any advice for spraying into grooves in mdf using a conventional gun, the finish seems to bounce out or miss the sides of the grooves.?

 

[thick_mike]

Bounce back from concave surfaces is a real problem ( I used to design coatings for the insides of drinks cans, so I know what I'm talking about!). HVLP guns can improve the situation as can narrowing the fan pattern or turning the gun sideways. You have to be very careful though as any adjustment can flood other parts of the object.

 

[thick_mike]

This shows the difference between HVLP and conventional guns...

https://m.youtube.com/watch?v=rKDHkMRKeUU

 

[mlarm]

Thanks Mike

I'll give these methods a try.
What about spraying beading for joinery, I have loads of it to spray and need to spray all edges.
Is it best to try suspend it? Or lay it all out flat?

Thanks
Matt

 

[thick_mike]

You could tape it to a board, that way you can spray multiple pieces at once. (I'm guessing that there is a face that doesn't need painting). Whether you paint them horizontal (more chance of dust, less chance of sags), or vertical (less chance of dust, more chance of sags) is up to your preference (and space considerations.

In fact, if you have some chicken wire (or similar) to attach them to, you will get fewer problems with bounce back.

 

[mlarm]

Thanks for all your help mike.
I'm guessing you spray yourself?

Would you attach the beads to the chicken wire somehow?
Would the chicken wire be suspended between 2 tressles?

Once again thanks so much for your help.

Matt