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Posted: Feb 19, 2009 10:19 PM	irregular spray pattern Hello fellow foamers. I have been spraying foam for 5 years now, so I am not a noobie. With that being said, I am trying to perfect my spray technique to get as flat and uniform a pattern as possible. Recently I have encountered a recurring, irregular pattern...a T-bone pattern if you will. I suspect this is due to my spray temperature being too hot. My foam specs call for around 120-125 degrees (btw I have a glascraft MH III w/ P-2 gun .01 mixing champer and tip). I have resorted to dropping my temps down to 108-100 degree range and a spray pressure of around 800-1000. I feel my temperature readings are off because at the lower temperatures I lose that damn T-bone pattern and it sprays relatively well The lower pressure helps me get close to my spraying surface without blowing foam everywhere. I see liquid for less than a second and it starts its reaction. When I try and boost the temp up, the A & B react too quick resulting in spraying foam that has already begun to react. MY mixing chamber then gets fouled up within a matter of a couple of hours. Have you guys encountered similar problems and if so, what has been your solution? What temps and pressure have you found the most conducive to good spraying. Thanks in advance for the input.
mason Posted: Feb 20, 2009 07:18 AM	Air purge guns must have sufficient air flow through the mixing chamber to clean out the residual foam build up on the tip. But, as you have seen, too much air blows away the foam if you go back too soon over the same area. Then you lower your air pressure to the spraygun and the tip gets fouled by reacting foam. Higher temperatures make the foam set up quicker but they also make the foam build up more on the tip. Cooler temperatures lesson the build up on the tip but make the foam set up longer. I have to admit, that for this reason, I typically like using a mechanical purge gun when doing detail or close in work. One spray technique to try is to take the spraygun back a few more inches from the substrate. Don't worry about getting overspray on the studs, it can be cleaned off fairly easily with a long handled scraper. This will give you less air pressure on the foam and minimize the foam blow off. This way you can increase the air pressure to the nozzle to prevent build up. Or just go to a mechanical purge gun. I would be careful about adjusting the temperatures and pressures too low. While many suppliers recommend higher pressures and temperatures than are needed to make good foam, you should be careful about adjusting the temperatures and pressures too low. Cell structure and physical properties can be negatively affected with improper mixing caused by low temperatures and/or pressure. You can check out the foam by spraying some samples at various temperature and pressure. Look for uniform cell structure, color and compressive strength. Talk to your supplier and let them know what you are doing. Send them samples of the foam so they can test it for optimum properties. If they say the foam is good then you have demonstrated the lower temperature and pressure can be used with their foam.
SprayFoamSupply.com Posted: Feb 20, 2009 07:24 AM	Hi trouble, One thing that you have to remember with the GC MH3 is that the hose thermocouple where it senses the hose temp is only 12 feet from the machine in the B hose. It is measuring the temp of the hose close to the machine and not close to the gun. So let's say you have the B preheater set at 120 and the hose set at 125, the material flowing by the hose thermocouple will be < 125. This will make your hose heat stay on all the time. It sounds to me like the material is too hot and it is clogging the insert faster. What is your climate? Do you notice that the gun gets hot while you are spraying? Shoot it with an IR thermometer or put a thermometer in the whip hose to try and get a handle as to what is happening. Have you asked your foam supplier for their advice? What did they say? George

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Posted: Feb 19, 2009 10:19 PM

irregular spray pattern

Hello fellow foamers. I have been spraying foam for 5 years now, so I am not a noobie. With that being said, I am trying to perfect my spray technique to get as flat and uniform a pattern as possible. Recently I have encountered a recurring, irregular pattern...a T-bone pattern if you will. I suspect this is due to my spray temperature being too hot. My foam specs call for around 120-125 degrees (btw I have a glascraft MH III w/ P-2 gun .01 mixing champer and tip). I have resorted to dropping my temps down to 108-100 degree range and a spray pressure of around 800-1000.

I feel my temperature readings are off because at the lower temperatures I lose that damn T-bone pattern and it sprays relatively well The lower pressure helps me get close to my spraying surface without blowing foam everywhere. I see liquid for less than a second and it starts its reaction. When I try and boost the temp up, the A & B react too quick resulting in spraying foam that has already begun to react. MY mixing chamber then gets fouled up within a matter of a couple of hours.

Have you guys encountered similar problems and if so, what has been your solution? What temps and pressure have you found the most conducive to good spraying. Thanks in advance for the input.

mason

Posted: Feb 20, 2009 07:18 AM

Air purge guns must have sufficient air flow through the mixing chamber to clean out the residual foam build up on the tip. But, as you have seen, too much air blows away the foam if you go back too soon over the same area. Then you lower your air pressure to the spraygun and the tip gets fouled by reacting foam. Higher temperatures make the foam set up quicker but they also make the foam build up more on the tip. Cooler temperatures lesson the build up on the tip but make the foam set up longer.

I have to admit, that for this reason, I typically like using a mechanical purge gun when doing detail or close in work.

One spray technique to try is to take the spraygun back a few more inches from the substrate. Don't worry about getting overspray on the studs, it can be cleaned off fairly easily with a long handled scraper. This will give you less air pressure on the foam and minimize the foam blow off. This way you can increase the air pressure to the nozzle to prevent build up. Or just go to a mechanical purge gun.

I would be careful about adjusting the temperatures and pressures too low. While many suppliers recommend higher pressures and temperatures than are needed to make good foam, you should be careful about adjusting the temperatures and pressures too low. Cell structure and physical properties can be negatively affected with improper mixing caused by low temperatures and/or pressure. You can check out the foam by spraying some samples at various temperature and pressure. Look for uniform cell structure, color and compressive strength. Talk to your supplier and let them know what you are doing. Send them samples of the foam so they can test it for optimum properties. If they say the foam is good then you have demonstrated the lower temperature and pressure can be used with their foam.

SprayFoamSupply.com

Posted: Feb 20, 2009 07:24 AM

Hi trouble,

One thing that you have to remember with the GC MH3 is that the hose thermocouple where it senses the hose temp is only 12 feet from the machine in the B hose. It is measuring the temp of the hose close to the machine and not close to the gun. So let's say you have the B preheater set at 120 and the hose set at 125, the material flowing by the hose thermocouple will be < 125. This will make your hose heat stay on all the time. It sounds to me like the material is too hot and it is clogging the insert faster. What is your climate? Do you notice that the gun gets hot while you are spraying? Shoot it with an IR thermometer or put a thermometer in the whip hose to try and get a handle as to what is happening. Have you asked your foam supplier for their advice? What did they say?

George

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