Heat treatment - Graphitisation

Castner furnace/longitudinal graphitisation

Lengthwise graphitisation (longitudinal array) was first described by Castner, and is characterised by the direct connection of the stock one to another in a row without a resistor material in between. The artifacts are clamped between the head electrodes of the furnace and heated by passing the current directly through the load. The contact area of the material to be graphitised has to fit well and therefore requires plane-parallel machining and an adjustable clamping device in order to secure a constant, tight electrical contact for a low-contact resistance. The insulation against oxidation and high heat loosses is the same as for Acheson furnaces. This graphitising method has the advantage of shorter heating periods, less power consumption and smaller furnace dimensions.

GRAPH LengthWiseGraphitisation furnace

LWG vs. Acheson

Advantages of LWG over the Acheson furnace:

• Lower energy

• Reduced cycle time

• Better control of process for electrode

Production – Inductively heated

Inductively heated furnaces

Inductively heated furnaces are normally used for parts, which need to be graphitised with a very well controlled temperature profile. Indirectly heated furnaces consist of a horizontal or vertical graphite tube of rectangular or cylindrical cross-section. The outside of these tubes is insulated with carbon black surrounded by a carbon felt jacket. The material is passed through the furnace, either continuously or at intervals. It is protected from oxidation by using water-cooled seals at the ends of the furnace and by applying a stream of inert gas. The main advantage of such furnaces is very close temperature control.