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screen printing => Equipment => Topic started by: GraphicDisorder on May 01, 2011, 02:57:50 PM
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Are most of you using donut probes or something else? If so what brand and where to buy it and such?
We are using a laser temp gun which is not exactly the best way but also do a stretch test and such. But want to get a more dialed in reading.
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Google Atkins or Atkins Donut Probe. The probe and readout unit are often sold separate, and I am thinking that the probe could be used with some other digital thermometers.
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Same as you, off-contact thermometer and a stretch test.
For someone like me with a pretty basic conveyor dryer (and no room for an upgrade) I find it necessary to test during the first half hour of printing to really get it to settle down, and that's after a half hour of initial warm-up and so-so stabilization. Aside from my inbred Scots thrift (what others call being too cheap), I'm not sure how much the purchase of a donut probe would help me, other than it's relative dead-on accuracy, but a temperature in a range, coupled with sufficient dwell, has done the job so far.
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X2
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Are you guys checking each time you fire up?
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To be honest no.
I can pretty much tell by the feel of the shirt on exit.
The way my dryer sits even on a windy open door day.
It is ok.
My Cinnie dryer has three cow rods and I can look inside to see if they are working or not.
My first few dryers were IR's and digital. Themos going out and burning wire ends off and god forbid replacing a digital controller.
For me a precentage hot rod dryer is just better with less to go wrong.
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I've used both the donut probe and the non-contact gun. While a gentleman & I got into a lengthy back & forth "discussion" on one of the boards once about the accuracy of non-contact temperature guns, the non-contact gun IS accurate when close to the object being tested.
I would reach inside the dryer (a fore-arms length) and take the temp of the ink (the gun had a laser "pointer" feature so I knew where it was pointed) with the gun an inch or two from the shirt. The reason I reached in was on my dryer (Hix) there was an area at the end of the heat chamber that was isolated from the heat. It was about 6 or 8 inches long. If I had waited for the shirt to exit the dryer before taking its temperature, it would have already been cooling off for a period of time and given me a lower than expected reading. I would then have increased the temp (unnessisarily) to compensate.
I also found the donut probe to be slow in responding. My primary ink/supplies merchant told me that it had been his experience that the donut probes don't work well with short dryers (which is what I had), but they did well in long dryers.
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I have a little more time now to respond more completely.
I, too rely on my settings (a combination of panel distance, temp setting, and belt speed) learned from experience, a draft free environment, and a non-contact thermometer.
However as we all know, the readings of a non-contact thermometer are only accurate relative to other things we have learned. They are only accurate as a surface reading, and then, as Nick pointed out, more accurate the closer one is. While one may learn, that a surface reading of 390 just before exit translates to the entire ink layer having reached 310, or 325, or whatever one has found, these readings and translations even change from shirt color and ink layer differences.
The donut probe, a weighted sensor, actually sitting in a film of ink has to be more accurate.
Also, the best test is, and always has been multiple launderings.
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It also feels good to just have a puff of smoke right at exit. For me anyway. :o
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Temperature guns can be VERY deceptive. Because the gun "sees" the heat, shiny things can reflect the IR light. So where you think you are measuring the ink, you are actually getting a martial reading from what the light being reflected via the ink. For a flash dryer, it is easy to get readings of 500+ degrees and still not cure the shirt, this is because the the heating elements of the dryer are being recorded.
I use the "pope" method to determine when a shirt is cured. When i see the white smoke, i know the job is done. When the shirts come out of the dryer, a short benediction (pull test) is performed to confirm the event.
(http://farm1.static.flickr.com/16/22665641_3b6d09e56d.jpg)
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It also feels good to just have a puff of smoke right at exit. For me anyway. :o
If any of your past posts are an indication, you have a lot of exits. ;D
I recommend waiting until the very last shirt of the day exits.
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I feel like we are way to hot. But I could be wrong. I had 2 pullers the other day and we where running about 60dz and hour and they both had blisters in no time flat from pulling the shirts.
Temp gun has been dropped a few times and I think its also reading "low" now. It's shows we are low, but the shirts are way hotter than they used to be when we used our little dryer, I know that has to do with the length the garment is being heated and such but I still think we are high.
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crazy logic question: Does a long chambered gas dryer "saturate" the whole shirt with heat, vs. a short electric dryer just hits the top?
I can barely touch the shirts --that is not normal, right? i think im having a weird transition from electric to gas and getting my feel for "done" considering the ink deposits are now thinner with the auto vs. manual so they come out soft and im not used to that either. i have a hard time in my head with soft does not equal still wet.
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We have a donut probe and it's great to have, especially since we are relatively new to discharge and water base. Plastisol is time tested for us, so we don't always need it because we know where we have to be on dryer settings, but with a big variable like a discharge under base I wouldn't want to be without it.
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It also feels good to just have a puff of smoke right at exit. For me anyway. :o
If any of your past posts are an indication, you have a lot of exits. ;D
I recommend waiting until the very last shirt of the day exits.
OK
Maybe I've become so simply its turned simplyminded.
I choose my friends for their good looks, my acquaintances for their good characters, and my enemies for their intellects. A man cannot be too careful in the choice of his enemies.
Oscar Wilde
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Get onto your knees and watch for the smoke. The smoke is a signal which indicated when the ink is hot enough to smoke, which "coincidentally" is the same temperature needed to cure.
I have a 4 foot dryer, the first 3 feet have heating elements and the 4th is blank. Looking into my dryer, the shirt needs to be smoking during the 3rd heating chamber. If there is smoke on the first, the dryer is too hot. Considerable smoking at the second is still hotter than needed. If its smoking before the forth, it is too late.
On my dryer, the shirt is already cooling in the 4th foot, so it is all but finished smoking when it comes out of the dryer. The dryer exhaust contains the vast majority of the smoke. For dryers without a cooldown section, i'd have the shirts come out smoking.
heat can be controlled either by dryer temperature or speed. If the smoke is hitting too early, you can either turn up the speed to increase production or turn down the dryer temperature to save energy costs.
My dryer is a brown, which come with (pc style) cooling fans on the exit path of the dryer. We use a pole fan following the flash dryer.
The issue might just be you have sensitive hands. They make cooking gloves which allow working at oven temperatures. There is no shame in using the protective equipment. The shirts coming out of the dryer will be hot.
The cool new Chef's Planet Oven Glove is a heat and flame resistant five-fingered glove that makes it much easier to grip and handle pans going in and out of the oven, compared to a traditional oven mitt. This seamless glove features a DuPont Nomex outer lining that can withstand temperatures up to 500? F (260? C), has a comfortable double knit cotton inner lining and fits great on both righties and lefties. Best of all, they kind of look like big old cartoon gloves!
http://www.amazon.com/gp/product/B000A3J4IQ?ie=UTF8&tag=201022-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B000A3J4IQ
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OK heres my take.....yes donut probes are the most accurate but yes really intended for longer dryers 10 to 12 ft. They will "tell the story" as to what is really happening in the dryer and can identify cool spots if they are present. Some gas dryers have IR "bump" panels in the front and (less frequently) in the rear exit section. Often on older dryers this is one of the first elements to go.....the donut probe will identify this problem. Also for discharge and density printing the are quite helpful. Density gels for example can melt and
"fall" if overheated.
Can't find a picture but in SC I had a bunch of dryers with short outfeeds and had the "blistering" problem.
Had my maintenance man hang two box fans from the ceiling; securing the base of the fans to the top of the dryer with the fans angling away from the exit chamber. Worked perfect and disperses discharge and poly fumes as a bonus. They still use them today I believe.
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I have a Boomerang, it does have a short exit chamber.
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Andy's correct in that the same donut can be used with any thermometer with the correct
(K-type I think) thermocouple input. Unfortunately the donuts are unique to screen printing
and priced as such.
Also, though I'm relatively new to the gas dryer world, I agree with the person that thinks
that a long gas dryer "saturates" the garments with heat. That's been my impression as well.
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I too do the pull test but I do it the next day... Have pulled them especially white after they cool and not tears but the next morning and it may pull apart. Have you ever tested some of the Wal Mart shirts???? I wonder sometimes if we do not go overboard but I see shirts I have printed 5 years ago still walking around town and looking good. I use test strips on my dryer and it is a monster ( electric 220 3-phase ) I guess it is 12' of heating and about 5' wide ( Pheonix Turbo ). I have re-wired some of the elements and turned off the temp adj. it stays on. I adjust the speed of the belt for the prints that need less heat. I check it every morning....Fuses do go out :(
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crazy logic question: Does a long chambered gas dryer "saturate" the whole shirt with heat, vs. a short electric dryer just hits the top?
Yes.
The Boomerang is nailing the entire shirt with super-heated air, and the tunnel is 10', and the heat is convective top to bottom, where as an IR panel dryer is radiating infra-red energy onto the top of the shirt only.
You won't really know exactly where in that 10' chamber that the ink is hitting the correct temp for a proper cure without a donut probe. You can measure at the exit but that only tells you what the temp is at the exit. A gas dryer can bring the temp to where it needs to be and hold it there, while not scorching the shirt. It's a gentler, more even heat than running it under IR panels.
So it's totally possible you are hitting the correct temp within the ink film by the first 5' of the dryer and the rest of the trip through is just baking the shirt until it's too hot to handle.
Just tell Brandt to shove is arm wayyyyy in there with the temp gun...
;)
We used to run into this at the shop I worked at running wb and plastisol prints at the same time. The wb prints needed the dwell time, so all of the shirts came out the end of the dryer at max temp. (15' tunnel gas dryer) The catchers wouldn't "catch" as much as let the shirts pile up in bins and stagger the stacking as they cooled a bit.
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Forced air gas dryers use a burner chamber, blower motor, and a series of baffles to circulate the hot air at an accelerated rate. Some of the better models even re-circulate exhaust air. And many have an optional IR bump panel in the front to speed up the process allowing the belt to run a bit faster. Important when running multiple autos or manuals and only one dryer. Forced air electric tries to replicate this but is never quite as efficient. Downside is gas dryers are typically much larger and more expensive but if you have the room a used one is an excellent consideration.
tp