TPi April 2010

Developing and implementing new technology • Change to “greener” process chemicals • Change from “wet” processes to “dry” processes • Develop nanotechnology Shot blasting highlights Shot blasting made using low carbon steel shots Shot blasting is a commonly used method to prepare steel surfaces for painting applications. Due to recent developments and future aspects in “shot” materials and “shot” manufacturing processes, the conventional polishing routine made by using specific machinery and common abrasives may be substituted by some convenient shot blasting applications. One of the key points may be the selection of low carbon steel shot – instead of high carbon – to yield a longer service life, also providing a more effective and faster cleaning cycle. Due to bainitic microstructure, low carbon steel shots have crack-free grains and higher impact absorbing capacity. The impact is distributed evenly over the surface of the shot. Unlike high carbon shots, no surface cracks are observed on low carbon shots. Cracks shorten the use of shots considerably. Following few operational cycles in shot blasting machines, low carbon steel shots harden up to 46–49 HRC and their active cleaning effects increase. The ideal surface finish can be reached using the convenient shot dimension, which may be as tiny as 0.07mm (0.029") corresponding to SAE mesh no 200 to 2.8mm (0.111") corresponding to SAE mesh number 7.

Raw material conformity, limitation and uniform distribution of surface roughness, geometrical and dimensional stability, weld integrity, proper inside weld beam removal are the critical requirements. Under these circumstances, “quality” should be the basic criteria to make a decision for the most convenient tubular product selection, rather than price.

References

• Paul D Chalmer, The Future of Finishing, January 1, 2008

• Henry B Linford, Edward B Saubestre, Cleaning and Preparation of Metals for Electroplating, AES, 1950

• RA Lula, Stainless Steel, American Society for Metals, 1986

• Malkin S (Stephen), Grinding Technology: theory and application of machining with abrasives/Stephen Malkin and Changsheng Guo [2 nd ed.], 2008 • ISO 8501 “Preparation of steel substrates before application of paints and related products – visual assessment of surface cleanliness”

Another technical development in blasting is achieved by using spherical shots made of glass.

The above and such special process designs may make shot blasting become a preferred surface finishing method even for electroplating applications.

Conclusions It is vital to select the right quality of steel tubes for either electroplating or decorative painting application. Surface treatment (finishing) operations applied for the purpose of preparing the metal surface for electroplating are too costly due to intensive utilisation of labour, machinery, equipment and consumables. The surface conditions required to be provided by chrome plating are directly related to surface quality and conformity of raw material used in the production of the tubes to be plated.

By Murat Ergin, Borusan Mannesmann Boru – Istanbul, Turkey Fax: +90 212 293 69 60 Website: www.borusanmannesmann.com Email: musteriiliskileridepartmani@borusan.com

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Tube Products International April 2010

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