Full Version: Heat press temperatures
From: Harvey only (HARVEY-ONLY) [#1]
27 Oct 2005
To: ALL
Heat press temperatures are critical. I measured my heat press temp with a contact digital thermometer and came up with it reading 15*F higher than the setting. Reducing the setting by this amount helped all transfers.
There was a special in Harbor Freight's flier for $60 for the laser thermometer so I broke down and bought one.
Surprise! It really was 28*F, (+_-2%) off. Now I will see how it goes with this more accurate reading.
The laser thermometer might have paid for itself instantly. No to check out the other press that said it was within 2*.
From: John (JOHNRMONTG) [#2]
29 Oct 2005
To: Harvey only (HARVEY-ONLY) [#1] 29 Oct 2005
Hi Harvey ... good to check things like that occaisionally ... I bought a non-contacting thermometer a couple of weeks ago and I had a slew of different readings from what was shown on the digital readout. I called the manufacturer and the rep felt that the thermometer might be giving poor readings due to, i believe (or remember) the emissivity of the surface on the platen.
Since you are an engineer, not sure your backround on thermodynamics however, what would your thoughts be? I have had a bit of exposure to basic thermodynamics especially as regards to heat transfer and theries and a bit on infrared thermography but I wasn't sure how to respond to their ideas.
From: Harvey only (HARVEY-ONLY) [#3]
29 Oct 2005
To: John (JOHNRMONTG) [#2] 30 Oct 2005
Put a piece of masking tape on the platen. Take the temperature of the tape. If you re getting various readings on an untaped surface, it is the emissivity of the surface, very common on metal. I tested my IR thermometer that way, many unstable readings of the same spot on the buff metal. The same reading each time from the masking tape.
I just posted in another thread that with a new controller in one press I used the IR thermometer and found that that press was really 25* too hot. [Black surface, with or without masking tape the readings were the same. Not so on metal surfaces.]
From: Michael [#4]
29 Oct 2005
To: Harvey only (HARVEY-ONLY) [#1] 30 Oct 2005
Hi, Harvey, long time since we've bandied about technical issues! :P
I use a Fluke digital multimeter with a K type thermocouple fexible probe. A bit more expensive than IR, but there are no concerns about bogus readings; if the temperature is there, it tells you, if the temp is high or low, it tells you.
Close the press on the probe, then read it. This can be done with or without a substrate in the press, but I wouldn't recommend it with a transfer in place.
From: Harvey only (HARVEY-ONLY) [#5]
30 Oct 2005
To: Michael [#4] 30 Oct 2005
From: Ken D. (KDEVORY) [#6]
30 Oct 2005
To: Harvey only (HARVEY-ONLY) [#5] 30 Oct 2005
Harvey,
I don't do dye sub, but wouldn't "the drain of the foam pad", be a more realistic representation of actual use conditions? When you do a transfer, which is more important. Temp at initial contact, or temp during the press?
From: John (JOHNRMONTG) [#7]
30 Oct 2005
To: Harvey only (HARVEY-ONLY) [#3] 30 Oct 2005
From: Harvey only (HARVEY-ONLY) [#8]
30 Oct 2005
To: Ken D. (KDEVORY) [#6] 31 Oct 2005
While it might seem more realistic, in actuality it is not for one reason. When specs are given for the dye-sub process they are created with a platen temperature reference.
That tends to make presses with more thermal mass seem to overcook the substrate, and presses with a low thermal mass, or large drain from the lower platen seem undercooked.
Once you get familiar with your press you make some adjustments from recommendation for good results. This is far easier when you start with the accurate platen temperature. One less variable.
Subbing is certainly an art form. This is one of the reasons.
From: Michael [#9]
30 Oct 2005
To: Harvey only (HARVEY-ONLY) [#5] 31 Oct 2005
Yup, heat migration from hot to cold will explain the difference. :-)
There are also some substrates that need a little "extra" by preheating the bottom pad or extending the press time to prevent migration of heat away from the substrate & transfer.
These tests are run for 10 minutes even though temps stabilize in about 2 minutes or less. The bottom pad heats up relatively quickly and it releases the heat at about the same rate once the press is opened. The real purpose of the test, for me, is to see that temps stay within an acceptable range during the pressing period, not when the press is sitting open/idle.
I've done this for all heat presses when new, whenever I change ink brands, or if there is any reason for questioning the temp (such as bad images when the image looks ok on paper). The oven used for mugs has also been tested. Also, sometimes I'm just bored and want to see what is happening on the substrate temperature-wise; hard for me to get a good ir reading when the press is closed doing it's work.
All that said, I'm a very firm believer & practitioner;