The next area and probably the most important section to install infrared temperature devices, is at the oven portion. Here the temperature is critical and the only information provided to the machine is from thermocouple inputs from the heater elements or inside the oven walls.

This does not accurately represent the temperature of the plastic sheet itself.

There are two different methods used for the plastic sheet at this point.

The first method is that the company has a timer set so that the sheet heats for a certain amount of time and then is shifted out into the cooling and molding zone automatically.

The second method is that an operator watches the plastic and when the plastic sags the operator manually hits a lever to move the plastic to the next section.

Obviously in both methods the room for error is enormous and thus can lead to poor quality material, overheated plastic, or plastic that is too cold to be molded. In any of these scenarios it could cause the company to scrap the plastic and in turn lose money.

The appropriate solution is the use of a couple of infrared pyrometers over the top of the plastic and oven.

Imaging cannot be used at this point because typically the oven top and bottom comes down and covers the plastic from the sight of view. However sight tubes can be installed and allow the use of a pyrometer with the correct optics to gauge the temperature of the plastic.

It is recommended to install an air purging and cooling jacket onto any pyrometer because of its close proximity to the heaters and ovens. Although, sometimes outside of the oven is not that warm and cooling may not be required. Just be cognizant to the fact that the ambient can be out of the range of the typical specifications for the pyrometer.

An important thing to recognize is the spectral response of the pyrometer must be correct. Not all of the plastics can be seen in the 8-14um spectral response some might require different detectors. A sample of the plastic should be analyzed and the correct instrument can then be selected based on spectral response.

The pyrometers in turn can be used in a process control loop to control the heaters. They can
be integrated via RS-232 or 4-20mA analog output into an automation or process control system.

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This entry was posted on Thursday, April 10th, 2008 at 12:03 am and is filed under Equipment Vendor, Infrared Thermography, Infrared Thermometry. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.