Surface finish, standards

A variety of thermosetting resins are used in SMC. Polyesters represent the most volume and are available in systems that provide low shrinkage and low surface profile by means of special additives. Class A automotive surface requirements have resulted in the development of sophisticated systems that commercially produce auto body panels that can be taken direcdy from the mold and processed through standard automotive painting systems, without additional surface finishing. Vinyl ester and epoxy resins (qv) are also used in SMC for more stmcturaHy demanding appHcations. 

A third important factor in the economies of machining is the material of the cutting tool. This largely determines the rates of metal removal, the standards of surface finish and the frequency at which the tool needs to be reground - all of which are interrelated. These can be broadly grouped in three categories, each separated by a factor of 10 in terms of performance. 

These standards also outline requirements for surface finish, grain size, heat treatment, metallurgical cleanness, absence of delta ferrite and alloy segregation to ensure that besides having a well balanced chemistry the alloys shall be in the proper metallurgical condition to yield optimum mechanical and corrosion resistant properties. 

There are three standards controlling surface finish in common use. They are issued by the Steel Structures Painting Council (USA), the Swedish Standards Organisation and the British Standards Institution. They are roughly equivalent. 

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. 

The interior surface finish, to comply with EEC and other health standards, must be rustproof, cleanable, and free from any crevices which can hold dirt. Bare timber in any form is not permitted. Most liners are now aluminium or galvanized steel sheet, finished white with a synthetic enamel or plastic coating. GRP liners are also in use. Floors are of hard concrete or tiles. Very heavy working floors may have metal grids let into the concrete surface. Floor concrete is coved up at the base of the walls to form a protective curb. 

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... 

Standards to which flanges are manufactured (e.g., ASME B16.1, ASME B16.5, ASME B16.47) typically specify a standard surface finish... 

Zaki, Nabil. 1989. "Complying with Air Quality Standards with New Trivalent Chromium Plating Technology." 10th AESF/EPA Conference on Environmental Control for the Metal Finishing Industry. American Electroplaters and Surface Finishers Society, Inc., Orlando, Florida. 

A near white surface finish corresponds to Swedish standard Sa 2-1/2 or BS4232 second quality. This finish is defined as one from which is removed all oil, grease, dirt, mill scale, rust, corrosion products, oxides remaining coatings, except for a very light shadows of light streak discolouration. At least 95% of the surface shall have the appearance of a white metal surface finish and the remainder shall be limited to light discolouration. 

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... 

In rubber testing, the surface finish of metals is of importance, for example on mould surfaces and compression set plates. There are a number of standards in the ISO Geometric Product Specification series but the most relevant is ISO 428729 which covers terms, definitions and surface texture parameters relating to the profile method of measuring surface finish. There are apparently over 1000 different parameters to characterize surface finish30 but only a few are generally encountered. The most commonly found is Ra (previously called CLA) which is the mean deviation of the surface profile above and below the center line, followed by Rz, a measure of the peak to valley height. For example, the arithmetic mean deviation (Ra) of the compression plates for compression set tests must be better than 0.2 m. 

Silicon is a widely investigated substrate because it has a relatively high thermal conductivity and a perfect CTE match to silicon die. In addition, silicon wafers have a high-quality surface finish and are widely available in standard sizes that are adaptable to IC process equipment. However, silicon has a low modulus and a poor CTE match to polyimides, and thus, very thick substrates will be required to prevent excessive warpage. A final advantage of silicon substrates is that active devices such as driver circuits may be fabricated in the substrate. 

SRV seats must be lapped to a micro finish using special compounds. Prior to super finishing, the valve seats should be lapped flat and to a fine surface finish in accordance with the standard practice as described above A 3- i,m-size diamond lapping compound should be used as described in the following procedure... 

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... 

ASTM E 1317 Standard Test Method for Flammability of Marine Surface Finishes. Annual Book of Standards, Vol. 04.07, ASTM International, West Conshohocken, PA. 

For the pharmaceutical and food industries, surface finish is very important to enable effective cleaning and sterilization or sanitization. Equipment should be specified with a polished internal finish, possibly with electropolishing for critical applications, and designed with a minimum of crevices or dead spaces where dirt can collect. Welds must be finished to the same standard as the plates and ground flush with the internal surface and must be pinhole and crevice free. External surface finish may also be important for visual reasons and to enable cleaning down for surface decontamination in clean room locations. 

Tooling surfaces such as mold cavities and die openings require meeting certain surface finishes. Rather than identifying the required finish as dull, vapor-honed satin, shiny, etc., there are standards such as a diamond polishing compound, SPI (originally SPI/SPE) Mold Standard Finish, and American Association s standard B46.1 Surface Texture (extremely accurate surface measurements a near-perfect system) that are used. This ASA B46.1 corresponds to the Canadian standard CSA B 95 and British standard BS 1134. 

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