Carbolite STF Series - Manual (Page 7)

STF 14-16
LMF08 – 1.13
7
slowly to ensure that large temperature differences do not arise.
Poor thermal contact should be encouraged between the workpiece and the tube; crucibles or boats
should be of low thermal mass and should have feet to reduce the contact with the tube (fig. 4).
Do not set too high a heating rate. Large diameter tubes are more susceptible to thermal shock than
smaller. A general rule for maximum heating rate is 400/internal diameter (°C/min); for 75mm i/d
tubes this comes to 5°C per minute. The controller can be set to limit the heating rate.
3.5 Pressure
Work tubes are not able to accept high internal pressure. When gas seals or similar fittings are in
use, the gas pressure should be restricted to a maximum of 0.2 bar (3 psi). A pressure of about half
of that should normally be sufficient to achieve the desired flow rate. The customer must ensure
that the exhaust path from the tube is not blocked, so that excess pressure does not occur.