What is a “pyrometer”?
In my last blog post I mentioned using a pyrometer to verify the displayed temperature of your heat press. In this article, I want to expand on this device and how to use it, and why I think it is the single most underrated yet vitally important tool you can have in your shop.
Simply put, a pyrometer is a device to accurately measure temperature. In the context of heat presses, and with the addition of a surface probe, it allows you to verify that your heat press is actually at the temperature you think it is.
If you’re thinking “yeah, right, it probably costs a lot…” No, it really doesn’t. And what it does cost, it can save you, the first time you need it.
Why buy a pyrometer?
I’ve lost count of the number of phone calls I’ve received regarding sublimation image quality. While most of these could be traced to simple issues (more on those in a future post), there have been a handful that were directly related to the heat press the customer was using. In almost all of those cases, if the customer simply had an inexpensive pyrometer, they could have saved themselves days of aggravation, phone calls, ruined products, and a significant amount of time and money.
Here’s the thing – unless you are very lucky, or the press was calibrated precisely in the factory, the temperature it shows on the display, dial, or gauge is not what the actual temperature is. As a press ages, that variance will also change. Digital gauges are the most accurate, but they still have to be calibrated periodically. Dials or gauges that insert into the platen are notoriously inaccurate.
Ultimately it boils down to one main fact – if you don’t have an accurate method of double-checking your press temperature and you have any issues with the products you are pressing, you simply cannot determine whether the problem is with your heat press or the product itself.
What kind of pyrometer should you get?
There are two popular types of pyrometers. You may have even seen the first type, a hand held gun-like device using an infra-red sensor, typically with a laser pointer built in. Some people think that the laser is the sensor, but it isn’t – it’s only there as a pointer (or to play with your cats).
Those are usually the least expensive, but the problem is that they only work well on things that have no reflectivity, like walls, carpet, ceilings, or dark/matte surfaces. Since many heat press platens are aluminum (which is somewhat reflective), it will give you a false reading. Even if you have a coated platen with a dark matte surface that it will work with, it won’t always remain so, and will develop blemishes over time that will alter the readings.
The second type, which is what I recommend, is a hand held unit that looks much like a multi-meter, with the addition of a plug-in surface probe. In this case, you place the end of the probe against the surface of the heat platen for a few seconds to obtain a direct reading of the temperature. Because the temperature is measured with a sensitive probe and direct contact with the platen, any color, reflectivity, or blemishes simply don’t matter.
What’s the best way to use a pyrometer?
Heat up your press to whatever operating temperature you need, including setting the pressure and timer. Draw a tic-tac-toe grid on a piece of paper, and use the surface probe to measure 9 spots on the platen in the same tic-tac-toe pattern. Hold the probe against the platen several seconds, until the temperature on the display stabilizes. Write those temperatures down in the corresponding squares of the grid you drew.
Now, run a complete pressing cycle as if you were producing the product of your choice. As soon as it is finished, take a new set of 9 temperature readings and record those below the first set of numbers.
The difference between the first and second numbers will give you the likely drop in the press temperature during operation, and the differences between the 9 different locations on the platen will point out any hot or cold spots. You’ll also be able to instantly see if your press has a problem. Any significant variances (more than 20 degrees F) between the highest and lowest numbers can be a problem, depending on the tolerance the products you are pressing allows.
To set the press to provide your ideal temperature, average the first set of numbers together, then average the second set. Pick a temp between the two averages, but closer to the higher number. That should match the temperature recommended for the product you are pressing. If it does not, then adjust your press so that it does. You may have to repeat the measurement process above a few times to get it dialed in just right, but once you do it, you should only have to check it periodically.
If your press has a feature that allows it, once you dial in the temp, you can calibrate the temperature display to show that exact temperature.
What’s the purpose of all that?
No press is going to maintain the exact set temperature 100% of the time, since heat energy leaves the platen and goes into your product when you are pressing it, and the press then has to switch on and heat the platen back up.
By using your pyrometer, in addition to knowing exactly what temperature your press is, you are able to set any good quality heat press to compensate for those swings in temperature, and even minimize the variance on less expensive presses. You also have the added benefit of diagnosing any problems that may be occurring related to heat.
Different manufacturers of presses handle the temperature in different ways, and some of those methods can cause delays between when the platen reaches its set temperature, and when the press turns off the heat, resulting in over-shooting the temperature. The same thing can also occur on the low end before the press turns back on. This and other reasons cause variances in temperature.
Good quality presses minimize this variance with various technologies that allow for continuous press operation and even heating, whereas lower quality inexpensive presses are typically made to meet a low price point and usually have temperature swings that can be wide enough to cause you to have to wait between pressings for the temperature to recover along with cold spots in the platen.
This will ultimately improve the quality of your products and save you time and money if you ever have an issue with your heat press, because it will let you pinpoint whether the problem is related to the temperature of the press or not. Even if the problem isn’t the press – you’ve now eliminated it as an issue, which is something you can tell your product tech support when calling to explain that you aren’t getting the results you should be. That will save you both some time, helping you get back up and running again quickly.