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Purchasers of castings can specify and assess surface quality and surface texture more accurately and definitively using tactile comparators developed by Castings Technology International (Cti). These provide a practical and functional alternative to photographic representation of casting surfaces in standards such as MSS SP-55-2001.
These sets of comparators are used around the world by multi-national companies and by small enterprises. The durable plastic comparator plates, actual replicas of relevant characteristics of surface finish, have proved to be a more attractive way of reaching agreement with casting suppliers on the required surface quality during contract negotiations. They also provide a basis for acceptance of the castings after order placement.
The comparators form the basis of ASTM A802/A802M – 95 (2006) Standard Practice for Steel Castings, Surface Acceptance Standards, Visual Examination. This standard comprises 31 comparators that define features such as:
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Surface Roughness (A)
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Surface Inclusions (B)
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Gas Porosity (C)
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Laps and Cold Shuts (D)
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Scabs (E)
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Chaplets (F)
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Surface Finish – Thermal Dressing (G)
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Surface Finish – Mechanical Dressing (H)
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Welds (J)
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Hot Tears
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Mechanical Dressing - Chipping