Blasted surface finish

A commercial blasted surface finish corresponds to Swedish Standard Sa2 third quality. The finish is defined as one from which oil, grease, dirt, rust-scale and foreign matter have been completely removed from the surface, except for slight shadows, streaks or... 

Surface finish is increasingly referred to as surface cleanliness . This can be misleading because the standards refer to the appearance of the blasted steel and do not deal with chemical contamination. Site tests for assessing the level of soluble salts on freshly blast-cleaned surfaces, and which allow the semi-quantitative determination of the chlorides, soluble sulphates and soluble iron salts, are urgently needed. 

In BS 4232, Surface Finish of Blast Cleaned Steel for Painting, first quality corresponds to SA3,2nd to SA2-5 and 3rd toSA2of the much more extensive Swedish Standards Commission s SIS 055 900-1962, RusI Grades for Steel Surfaces and Preparation Grades Prior to Protective Coaling, Stockholm (1962) see also BS 7079 Part A1 (1989)... 

The inspector s working standard for the surface finish of blast-cleaned steel is now the new British Standard . In the special circumstances where absolute freedom from soluble contaminants such as ferrous sulphate is necessary, the specification should include reference to a test for removal of such residual salts, e.g. the potassium ferricyanide test . The area to be sampled should be wetted with a fine spray of distilled water and the paper held against it. The development of blue spots on the paper indicates the presence of ferrous salts on the surface. 

It should be recognized that surface finish can be more than just a cosmetic standard. It also affects product quality, mold or die cost, and delivery time of tools and/or products. The surface can be used not only to enhance clarity for the sake of appearance but to hide surface defects such as sink and parting marks. The Society of Plastics Engi-neers/Society of Plastics Industries standards range from a No. 1 mirror finish to a No. 6 grit blast finish. A mold finish comparison kit consisting of six hardened tool steel pieces and... 

Surfaces destined for reuse Surfaces destined for smelting NACE Visual Standard No. 2, Near White Blast Cleaned Surface Finish NACE Visual Standard No. 3, Commercial Blast Cleaned Surface Finish... 

As the compressed air required for blasting is generated in compressors, the presence of small quantities of oil cannot be excluded, which remain on the surface after blasting. For this reason, ensuing degreasing is essential, with the additional advantage that possibly existing shot residues in the surface finish will also be removed. 

BS4232, Surface finish of blast-cleaned steel for painting, British Standards Institution, 1967. 

Sweep blast n. See NACE No. 4 brush-off blast cleaned surface finish. 

The pipe surface is cleaned by means of an automatic shot-blasting machine to minimum SA 2 /4 surface finish as per Swedish standard SIS... 

The service life of the blasting media should be established for efficiency and quality of surface finish. Grit in use should be cleaned of dust resulting from removed oxide scale and its own degradation products and be downgraded or discarded if it becomes too worn. 

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