the forming stage follows upon kneading and is reached by means of hot extrusion of the semi-finished electrode. Other processes used for forming graphite products (such as blocks) are explained in later articles.
Extrusion forming of graphite electrodes
After kneading, the paste must be brought into the characteristic electrode cylinder form. Standard sizes range from dia. 200mm to 700mm (8″ – 26″) and lengths from 1500 mm to 2700mm (60″ – 110″). The extrusion process is depicted in diagam 1.
Diagram 1: Schematic of the direct, hot extrusion process. McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.
- The paste is loaded into a thick wall container
- The paste is forced through an extrusion die secured in a holder. The extrusion force is applied by a ram with a reusable intermediate dummy block. Pressure is produced hydrostatically.
- the paste flow from the extrusion die is in the same direction as the forward motion of the ram.
- the extruded paste will be undergoing synchronous cutting
Extrusion force is related to
- friction between billet length and container
- cross sectional area (=diameter) of the final product
The size of the die is generally slightly bigger than that of the final product. The longer the semi finished electrode, the longer needs to be the die. After the material is cut to the desired size, it is cooled at a temperature of 100°C.
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