ALTANA Temp-Chart - Handbuch (Seite 144)

temp-gard Hardware temp-chart Software
67
The Equivalent Holding Time
In his article on the use of the equivalence method for the evaluation of variable
temperature gradients, Äquivalenzmethode zur Bewertung variabler
Temperaturverläufe published in the JOT 1998/5, Dipl.-Ing-Eide Wilckens of the Dr.-
Ing.H.c.F. Porsche AG in Stuttgart describes a method for evaluating the effects of
temperature gradients on the crosslinking of paints. However, this method can also be
applied to a variety of similar problems.
The fundamental question is, how do the temperature gradients effect the crosslinking
behavior of paints. Normally, the answer to this question will also indicate whether or
not a reference temperature keeps the preset holding time when a temperature-time
gradient is given.
If the preset holding time is kept, the bordering temperature ranges can be regarded as
“reserves”, since the crosslinking should be sufficient. From an economic point of view,
however, it is also interesting to know if too much energy was wasted.
However, if the holding time for a preset temperature is not kept, it is questionable whether
the crosslinking might still be sufficient, since it is well-known that the crosslinking process
starts before the reference temperature is reached, and will be accelerated by higher
temperatures within certain limits.
The equivalence method tries to evaluate the entire temperature gradient in order to
furnish a measure for the equivalent holding time of this gradient.
First, the Equivalence factor for each time section of the temperature gradient is
calculated. This value indicates the time required by the reference temperature to reach
the same crosslinking degree as the effective temperature.
Then, the equivalence factor is multiplied with the length of the time section resulting in the
equivalent heating time of this section. The equivalent time of the entire gradient is the
sum of all sectional heating times.
For calculating the equivalence factor according to the Law of Equivalence, you need to
know the activation energy of the material.
This information is usually given by the supplier. If not, it can easily be determined with the
help of two pairs of reference temperature and preset holding time:
In general, your supplier will give you the required holding time for three reference
temperatures, for example:
Holding Time For a Reference Temperature of:
12 min
at 165 °C
10 min at 170 °C
8 min at 175 °C
This corresponds exactly to the data you have entered in the critical values page in the
setup notebook.