GENERAL INFORMATION
HOT AIR VS INFRARED WHAT MAKES TEMPEST® WORK
AlthoughthetechnologybehindtheTempest® dryerwassignificant enough to be awarded the GATF Intertech Award, it is by no means new. In fact, thermistors have been in use for many years. They were originally used in motors and other devices as a heat controller andlater usedin refrigeration toturn compressors on and off. It is only in the last 10 years or so that thermistors have been used as a heater.
Heat is generated by the thermistor because of the difficulty of electricity travelling through it when it is a conductor. The thermistor acts as a conductor until it reaches its set temperature and then it becomes a resistor. A thermistor is basically a coated semiconductor designed to switch from a conductor to a resistor at an established temperature.
When a current is applied to the thermistor it initially uses a large amount of electricity and heats up very quickly until it reaches its maximum set temperature. At this point it should not use any more electricity. However, air that is passed through the holes in the thermistor causes it to cool. This activates the thermistor to start using more power again so that can get back to its set temperature. The thermistor is constantly regenerating itself to stay at a constant temperature. This process is called autostabilization.
Thermistors are also the key element that makes the Tempest® dryer safe. Because the set temperature of the thermistor is lower than the flash point of paper, you can place even the most easily burned substrate (such as tissue paper) on top of the thermistor element without causing a fire. The tissue won't even char, let alone ignite. If you were to do the same with an IR element, a fire could start in a matter of seconds. This is particularly important if a jam occurs in the delivery.
The objective of any drying system is to raise the pile temperature to accelerate the drying of the ink. However, heating the paper too muchcanaggravateproblemssuchasblocking,setoff,mottle,loss of gloss, and loss of halftone definition. Too much heat can also cause the paper to shrink which can cause register problems in multiple pass work. The Tempest® dryer can keep the pile at a lower temperature than IR and still effectively set the ink film.
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