Process Temperature Control Rings
A PTCR is a ceramic device that registers the total amount of heat transferred to it. Because of the advanced technique and materials applied and used for this product, it gives a fair representation of the real heating process taking place in a kiln at the location of the ring. PTCR helps to achieve a reliable, outstanding and regular quality level.
The actual set temperature of a kiln during a firing process, as measured by thermocouples, does not give any guarantee of the repeatability of process conditions which of course will harm the quality of the products. A thermocouple merely gives a specific spot temperature, which is not the same temperature as the one at the position of the product. The ultimate temperature of the product is determined by the total transferred heat. This is not measured by the thermocouple. Besides, the same set temperature in different kilns or kiln layouts does not guarantee the same heat treatment.
The PTCR measures the total heat transferred to the ring, by means of conduction, convection and radiation. It takes into account different firing conditions that may occur in a kiln such as heat sinks, temperature gradients, gasflow, heat transfer coefficient, time, kiln setting, etc. Because of total heat measurement, the repeatability of the process is assured and thus so quality level of the product.
How Does PTCR Work?
The PTCR is a ceramic ring which shrinks if it is exposed to heat. The degree of shrinkage depends on the actual temperature in the kiln, the heat transfer properties of the kiln and the time it is exposed to the heat treatment.
The measured shrinkage is converted by means of a chart into a Ring Temperature (RT) which is an effective temperature that describes the total amount of heat absorbed by the ring and also by the products. The observed Ring Temperature is an effective temperature for the total firing cycle, which has no direct relation to the absolute temperature in degrees Celsius, Fahrenheit or Kelvin nor any direct relation with the set temperature. The PTCR temperature reading is further influenced by the top temperature hold time (soak time).
At a constant temperature, the PTCR will continue to shrink, leading to a higher RT reading. There is a maximum to the hold time, during which the ring will continue to shrink. The maximum hold time, which is typically between 0.5 and 10 hours, depends on the type of ring used and the actual temperature compared to the temperature range of the ring under consideration. Using the PTCR beyond this maximum hold time may lead to erroneous results because the PTCR ceases to shrink further on a certain moment.
The PTCR has been developed to give a better representation of the firing processes, to allow a tight control of the real amount of heat transferred, taking into account the above described influences.