Carbolite CAF DIGITAL IMAGING - Manual (Page 22)

Caf Digital Imaging
page 22
MF36-3.21
5.0 M AINTENANCE & C ALIBRATION .
5.1 General Maintenance.
The outer surfaces may be cleaned with a damp cloth. Do not allow water to enter the interior of
the case, work tube or control box. Do not clean with organic solvents.
5.2 Element Ageing.
Silicon Carbide heating elements gradually increase in resistance with use and the power of the
furnace gradually declines until the furnace can no longer keep up with its program. To
maximise the element life it is advisable to follow the recommendations below:
a) Do not run the furnace at higher temperatures than you need. See section 4.5.1.
b) Do not select unnecessarily fast ramp rates. See section 4.5.2
There is a feature in the furnace controller which allows the power to the elements to be turned
down, this ‘power limit’ is pre-set at Carbolite. As the element performance declines the
available power can be increased to compensate. The maximum power figure available is 100
(%), if the furnace performance is still poor when the power is set to 100 (%) the elements must
be replaced.
To adjust the available power figure proceed as follows:
Press Page  until oP (output list) is displayed. Press Scroll  until OP.Hi (Output High) is
displayed. Press Down  or Up  once to display the value of OP.Hi (it is good practice to
write down the original value). Use the Up and Down buttons () increase the preset figure as
necessary to improve the furnace performance. The controller will return to its home page
automatically after a few seconds.
OP.Hi should not be set too high as this will result in poor control and short heating element or
furnace life. For standard values of the parameter (as factory set with new elements), see section
3.6.
5.3
Checking And Replacing The Door ‘O’ Ring Seal.
Wear neoprene gloves before handling the O ring seals – see section 1.5.
Regularly check the condition of the door ‘O’ ring seal, see fig 17. The ‘O’ ring seal is a push fit
into the groove in the door plug ring, carefully remove it by hand, do not use sharp tools as this
could damage the seal and the door plug ring.
Inspect the condition of the door ‘O’ ring seal, it must be uniform in shape and section, and free
from cuts, cracks dust and grit. If the seal is damaged replace it, a faulty seal can cause leakage
of carbon monoxide during testing. See section 1.2: Carbon Monoxide Warning.
Clean the seal faces of the door plug ring and work tube front seal assembly, these must be free
from dust, grit, chips and scratches. Any damage to these faces can cause leakage of carbon
monoxide during testing and must be rectified.
To re-fit the door ‘O’ ring seal simply push it into the groove in the door plug ring. A small
amount of high temperature grease smeared over the back face (groove side) of the ‘O’ ring will
help to retain it.
5.4 Cleaning The Viewing Window.
Clouding of the silica (fused quartz) viewing window may occur. It is not certain whether this is
caused by impurities in gases supplied into the furnace or by volatiles given off from the cones.
The effects of any volatiles in the cones can be minimised by allowing a couple of minutes for
the cones to burn off before closing the door after loading the furnace. A cloudy glass absorbs
more heat than a clear one and heat accelerates the corrosion of the surface, regular cleaning of
the glass before a test can avoid cumulative effects.
5.4.1 To remove the viewing window for cleaning or replacement: