Inhaltsverzeichnis; What Is A Ptcr; How Does A Ptcr Work - schupp PTCR Handbuch

PTCR
Technique & Application
In this manual we want to provide useful hints and application advice
for the use of Process Temperature Control Rings PTCR.
Index
1. What is a PTCR?..................................................................................Page 1
2. How does a PTCR work?..................................................................Page 1
3. Which PTCR types are available? ..................................................Page 1
4. When to apply PTCR?......................................................................Page 2
5. Application..........................................................................................Page 2
5.1 General application advice..................................................Page 2
5.2 First time usage.......................................................................Page 3
5.3 The PTCR Micrometer.........................................................Page 3
5.4 The temperature conversion table...................................Page 3
5.5 Interpretation of the ring temperature.............................Page 3
5.6 Different atmospheres..........................................................Page 3
5.7 Pre-treatment of PTCR.........................................................Page 4
6. FAQ........................................................................................................Page 4

1. What is a PTCR?

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 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.
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, gas flow, 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.
Rev. 4_26.01.2018

2. How does a 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 amount of contraction - the amount by
which the ring diameter has shrunk - is measured with a numerical or
digital micrometer.
For ease and for comparison, this shrinkage - and therefore the total
absorbed heat quantity - is translated into a single, fictitious
conversion parameter the so-called „ring temperature "(RT). Basically,
this is not a „temperature", but a parameter that depends on time and
temperature. The RT does for example not reflect the maximum
temperature of the firing process, and does not correspond to the
real kiln temperature, because the PTCR accumulates the absorbed
heat quantity over time.
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 neither 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. The max. hold
time for ZTH rings is 2 hours. Using the PTCR beyond this maximum
hold time may lead to erroneous results, because the PTCR ceases to
shrink further on a certain moment.
3. Which types of PTCR are available?
There are seven different ring types, each in 3.5 mm (named L) and 7
mm thickness (named H) with an outer diameter of 20 mm and an
inner diameter of 10 mm. They cover a temperature range from
560°C to 1750°C. The ring types are colour coded, with batch
number and type embossed.
PTCR type
ZTH
UTH
ETH
LTH
STH
MTH
HTH
Select a PTCR type whose central temperature spread is nearest to
the kiln's peak firing temperature. PTCR are most sensitive to
temperature changes in the central temperature range rather than at
the extreme ends. If the maximum temperature is within the limit
range of two ring types, the selection falls according to the holding
Page 1 of 6
Temperature range (from - to)
560°C - 660°C
660°C - 900°C
850°C - 1100°C
970°C - 1250°C
1130°C - 1400°C
1340°C - 1520°C
1450°C - 1750°C
M.E. SCHUPP Industriekeramik GmbH & Co. KG
Neuhausstraße 4-10, 52078 Aachen/Germany
Tel.: +49 (0) 241 -93677-0 Fax: +49 (0) 241 -93677-15
www.schupp-ceramics.com info@schupp-ceramics.com