Salvaging procedures for defective casting include mechanical smoothing procedures that erase surface defects usually limited in depth to less than 50 μm. Information on inspection and salvage procedures was developed during research programs administered by the International Lead Zinc Research Organization, Inc.
Mechanical Smoothing
Parting lines are smoothed by:
- Mechanical polishing with abrasive-coated wheels or belts.
- Tumbling with abrasive media, or.
- Vibration with wheel or continuous cloth belts that run over flexible backup wheels are usually used for mechanical polishing.
Tumbling in horizontal barrels loaded with abrasive stones such as preformed and fused aluminum oxide, granite or flint, and a lubricated such as soap solution removes parting line burrs from die castings in 4 to 12 hr. The barrels may be rotated at 5 rpm, but higher speeds reduce the time cycle and costs. The weight ratio of abrasive stones to zinc die casting is approximately 2.25:1.0.
Vibration in a bed of abrasive ceramic media usually removes parting line burrs in 3 hr or less. Frequencies range from 700 to 3000 cycles/min and amplitudes from 0.8 to 6.4 mm. A vibrating tub with capacity of 0.5 m3 can be loaded with about 900 kg of abrasive media and 180 kg of zinc die casting.
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