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| Reference: Ref. Reference information: See if this helps. http://www.geo.tum.de/people/thuro/pubs/2002_iaeg_durban_pli... See pages numbered 2231 and 2232: The occurrence of thermic wear (BB-T) of button bits depends on the effectiveness of the flushing system. Under normal circumstances button bits are cooled very effectively by their water flushing system so that tool temperatures normally don't exceed 40 oC. If no or insufficient flushing is available (i.e. insufficient air flushing, water-mist-drilling) thermal wear may occur. Wear types equal those of abrasive wear and wear due to material failures since high tool temperatures only increase those wear mechanisms. ***** When heated above 200 oC specific temper colours (Table 1) may show on the steel body and can be used diagnostically to estimate the maximum tool temperature. Table 1. Temper colours for tool steel (Steinmüller, 1991: Taf. 2.). ****** Colour detailed colour description temperature yellow light yellow - yellow - gold 200-230 oC brown/red yellow brown - reddish brown - red - purple red 240-270 oC violet/blue violet - dark blue - blue - light blue 280-320 oC grey blue grey - grey 340-360 oC At present there are two special wear types listed in the classification: Total wear down and widening of flushing holes. These types occur mostly independent from the geological circumstances: |
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