Castings Technology International (Cti) has developed “tactile comparators” that will help casting buyers specify and assess surface quality and surface texture more accurately and definitively. They provide a practical and functional alternative to photographic representation of casting surfaces in standards like MSS SP-55-2001.
Cti, in Rotherham, England, is a member-based, ISO 9001-accredited organization with over 90 multi-disciplinary personnel providing R&D, consultancy and technical services to casting producers and users around the world. Contact Cti’s CEO Mike Ashton for more details.
More than 1,000 of 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 preferred way for metalcasters to reach agreement with buyers on the required surface quality of a finished product. They also provide the basis for acceptance of the castings after the order has been placed.
Cti’s 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 surface roughness, surface inclusions, laps and cold shuts, surface finish after thermal and mechanical dressing, etc.
A larger set of 48 comparators applies to ISO 11971:2008 Steel and Iron Castings – Visual examination of surface quality; BS EN 1370:1997 Founding – Surface roughness inspection by visual tactile comparators; BS EN 12454:1998 Founding — Visual examination of surface discontinuities, Steel sand castings.
According to Cti, foundries that already have the ‘short’ ASTM A802 set can upgrade to the larger set by purchasing the 17 additional comparator plates.
A third set of 14 comparators, the basis of BS 7900:1998 Specification for examination of the surface texture of precision steel castings, is applicable for buying steel castings manufactured by precision casting techniques, such as resin-shell molding, lost wax, Shaw process, etc.