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Tuesday, 19 December 2017
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Machining Print E-mail
Baked carbon can be machined wet or dry with ordinary machine tools. Changes between wet and dry working on the same machine are best avoided. The different steps are as follows:
Dust extraction
Individual extraction arrangements are essential on all machines when dry machining is carried out. Centralized extraction equipment is not worth installing except in large graphite machine shops. Where workshops are predominantly engaged in metal machining it is enough to install industrial vacuum cleaners on individual machines (vacuum 300mm head of water or air velocity of about 18 m/sec).
Cutting
Carbon is cut with bronze-matrix diamond cutting wheels, grain size 200-300 microns, at a peripheral speed of 50-60 m/sec. The cutting speed is 300-600 m/min.
Drilling
For drilling carbon, hard metal or diamond coated drills are used. To avoid chipping at the drilling exit the point angle should be 70-100°and the clearance angle 10-15°.
Turning
The work piece is best held in a spring collector with an expanding ring and the clamping pressure spread over as large an area as possible in view of the ceramic nature of graphite. Where close tolerances are needed it is advisable to use diamond tools. By applying radii or chamfers to the edges of the tools chipping of the work piece is reduced.
Milling
This is carried out with hard metal or diamond tools. The clearance angle should not be less than 10°. Cutting speed can be increased up to 50% by using diamond tools.

 
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