8.3.1.1 The average temperature of the furnace
as derived from the furnace thermocouples specified in 7.2 should be monitored and controlled
such that it follows the relationship (i.e. the standard heating curve)
where:
|
T
|
= |
is the average furnace
temperature (°C) |
|
t
|
= |
is the time (minutes) |
8.3.1.2 The following points are defined by the
above relationship:
| -
|
at the
end of the first 5 min
|
576°C
|
| -
|
at the
end of the first 10 min
|
679°C
|
| -
|
at the
end of the first 15 min
|
738°C
|
| -
|
at the
end of the first 30 min
|
841°C
|
| -
|
at the
end of the first 60 min
|
945°C
|
8.3.1.3 The per cent deviation 'd'
in the area of the curve of the average temperature recorded by the
specified furnace thermocouples versus time from the area of the standard
heating curve should be within:
| ±
15%
|
from
t = 0 to t = 10
|
(i)
|
| ± 15 -
0.5(t-10)%
|
from 10
< t ≤ 30
|
(ii)
|
| ± 5 -
0.083(t-30)%
|
from 30
< t ≤ 60
|
(iii)
|
| ±
2.5%
|
from
t = 60 and above
|
(iv)
|
where:
|
d
|
= |
(A - A
s) x 1/A
s x
100, and
|
|
A
|
= |
is the area under the
actual average furnace time-temperature curve |
|
A
s
|
= |
is the
area under the standard time-temperature curve |
All areas should be computed by the same method, i.e. by
the summation of areas at intervals not exceeding 1 min for (i), 2
min for (ii), and 5 min for (iii) and (iv).
8.3.1.4 At any time after the first 10 min of
test, the temperature recorded by any thermocouple should not differ
from the corresponding temperature of the standard time-temperature
curve by more than ± 100°C.