Carbolite RHF 17/3 Installation, Operation & Maintenance Instructions Manual page 6

1700-1800° Chamber
3.3 Atmospheres & Corrosive Materials
In oxidising atmospheres, metal oxides react with the silica layer on the surface of the elements
and may lead to premature failure. Protect the elements from splashes of molten metal and dust
when charging the furnace, and from fumes developed when melting, especially from fluxes. Also
avoid compounds with a high alkali content.
The furnace is designed for use up to its maximum temperature in oxidising atmospheres, but can
be operated successfully in neutral or carburising atmospheres. It may be used with nitrogen,
argon or helium atmospheres to 1600°C. Reducing atmospheres are not recommended. Sulphur
dioxide in normal concentrations is not harmful, but chlorine, and more so fluorine, strongly
attack even oxidised elements and should be avoided.
The furnace is not recommended for burning off carbonaceous materials. Other Carbolite furnaces
are available for this application.
When an optional gas inlet is fitted there is a label near the inlet saying "INERT GAS ONLY". In
practice inert or oxidising gases may be used, but not combustible or toxic gases. Chamber
furnaces are not gas tight, so it should be understood that gas usage may be high, and that the
chamber is likely always to contain some air. Residual oxygen levels of 1 % are to be expected.
The hearth can be protected from abrasion, if required, by the provision of a secondary plate. This
consumable item can either be in light weight ceramic fibre or in dense, hard-wearing alumina
refractory.
3.4 Operator Safety
The furnace incorporates a safety switch which interrupts the heating element circuit when the
door is opened. This prevents the user touching a live heating element, but also prevents the
furnace from heating up if the door is left open.
Avoid burns. Carbolite can supply tongs, face masks, and heat resistant gloves. Before you
remove a hot object from the furnace make sure you have a safe place to put it down.
When the door of a hot furnace is opened there is considerable radiative heat. Do not keep any
inflammable objects near the furnace.
See also the warning about eye protection in section 5.6.
3.5 Note on Temperature Control
The furnace is designed for rapid heating and cooling applications The programmer enables the
furnace to heat or cool at slower rates as desired, and variable "hold" (dwell) periods can be
programmed as required.
The programmer is used in conjunction with a phase angle thyristor Eurocube, which incorporates
a current limit potentiometer preset by Carbolite. The models designed for 3-phase use have three
of these thyristors.
The elements are connected in series across the low voltage output of a transformer housed in the
furnace case. Molybdenum disilicide elements do not age, so if an element fails it is not necessary
to replace the complete set.
3.6
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