HVLP spraygun setup/paint defects

[eng622]

Have used a HVLP gun with 2K and cellulose without getting the finish I expected. Firstly the gun max fan out is quoted to be 150/200 mm but in reality is no more than 100 mm which makes for more passes/accurate overlap. I've tried a spray pattern and the droplets do not give complete coverage even around the centre. This is with the pressure control at min. (the spec states 10psi cap pressure but there are no setting instructions and I have no means of measuring this pressure) but if I increase the pressure the result is better. Am I right in thinking it is an atomisation problem which may be the answer to the defect in the finish I am getting. I have had the odd solvent entrapment problem but the worst is the dusty appearance to the finish when rubbed down (like numerous random displaced microscopic dots much smaller than solvent pops). I've read what I can and think this may be air entrapment due to holding the gun too close. I have had some success with holding the gun further from the panel but am not pleased with the overall finish due to the varying degrees of orange peel which I think may be connected with poor atomisation. I've experimented with the volume control and tried thinning the celle paint but to no avail. Any help appreciated.

[wizzbilly]

it may help to stick a pic up of what problems mate pepole can understand easy then .

what compresor are you using ?

and where abouts you are actualy trying to spray the veicele ?

[eng622]

The defects are too small to show in a picture, much smaller than solvent pops. The compressor is 2hp 8cfm and the gun says it requires 7.5 cfm. Most panels have been removed from the vehicle and sprayed on a workmate. I've done a test today and thinned the celle 2 thinners to 1 paint and with the air pressure slightly above the min setting the result is acceptable.

[Wheelrepairit]

What makes the spray gun.(do you know tip size)

Also 2-1 mix for the paint sounds way too much. (60-40 mix is better)

[V8covin]

Firstly if you're planning on spraying more than the odd panel your compressor won't be up to the job.You need at least a 3hp/14cfm compressor.
Secondly,have you got hvlp fittings on your airline ? These are larger bore than standard fittings.If not then your gun will not be working as hvlp as it wont be getting enough air....that would explain your atomisation problems.

[eng622]

The gun has nothing marked on it but the box states AS1006 but no name. It came with 3 setups, 1.4, 1.8 and 2.2, I'm using the 1.4. The needles are SS and the caps brass, all looks well made. Regarding the compressor and gun, it has Euro snap on fittings so not sure what the bore is. I take the point that the compressor is probably inadequate for large jobs or continuous spraying but surley with a tank full of air the initial volume shoud be adequate and enough for good atomisation, which the test pattern suggests I am not getting. Would I be better off buying one of the HVLP electric type of sprayers because don't really want another compressor, or should I right the gun I have off and buy another one, but then it may not work any better.

[7even]

A couple of things spring to mind:-

a/ being a smallish compressor I take it you have no water trap on it, so could be a moisture problem.

b/ Could be reminents of silicon either in the air or on the panel, or the workbench or even in the vicinity

c/ As you have already mentioned could be a reaction to what ever primer you have used (or even filler) solvent pop holes can vary in size

d/ Atomisation of the gun, if its not correct and you trap wet coats under "drier" coats this too could cause solvent trap, effects more 2pac as opposed to celly, but can happen. The only way to get round this is practice with the equipment you have.

All the best

Edited by 7even on Wednesday 10th September 22:37

Edited by 7even on Wednesday 10th September 22:39

[Wheelrepairit]

Some good pointers there.

1.4 does seem a tad big, we use hvlp guns for solvent and use a 0.8 tip size for the paint and 1.0 for the lacquer.

With waterbase you will need a bigger tip size, perhaps your gun is set up for waterbased paint.

[V8covin]

Wheelrepairit said:

Some good pointers there.

1.4 does seem a tad big, we use hvlp guns for solvent and use a 0.8 tip size for the paint and 1.0 for the lacquer.

With waterbase you will need a bigger tip size, perhaps your gun is set up for waterbased paint.

Unless you're using a gun setup for smart repairs,1.3 or 1.4 is the ideal size for 2k or basecoat
If you've just bought a cheap gun of ebay or somewhere you could have any size needle/cap,I've seen as big as 2.2.

[Wheelrepairit]

2.2, now that would scare me

We do mostly paint wheels but i have done car/van bodywork with 0.8 and 1.0 tips with no problems at all.

[eng622]

Maybe the gun is not up to the job but the three setups were separately packaged each with cap and needle. Informed that the 1.8 was suitable for primer and the 2.2 for more heavy coatings. I've used the 1.4 for both primer and top coat. Maybe I'm getting the defects in the primer as well but as yet I've not noticed any. Now when I flat the top coat then I see the defects. I think I can see the difference between solvent pops and fisheye (had this on a greasy inner panel I failed to clean properly). I can only think that this dusty appearance which is really random white dots, some in clusters but not always all over a panel, sometimes just confined to a small to medium area. Thinking it is poor atomisation and as the coats build there are pin holes down to the primer where the droplets of paint have not overlapped. As said a single shot spray yields a pattern of droplets that do not show a dense central mass which is only improved if I up the pressure.

[V8covin]

Poor atomisation can sometimes take on the appearance of fisheyes.
I'd try upping the pressure and have another go