Thermal Spray Tips - Swinburne University of Technology

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Compiled by Jo Ann Gan, Edited and advised by Christopher C. Berndt Swinburne University of Technology Thermal Spray Group (SwinTS) Please contact Prof. Christopher Berndt at cberndt @swin.edu.au for further enquiries 4.2. Alumina Blasting Abrasives Aluminium oxide (Al2O3) particles. 130x. (a) 240 mesh (b) 150 mesh Alumina (Al2O3) grit works very well in blasting cabinets. The specific gravity of alumina is just over half that of chilled iron, so that this type of abrasive is readily picked up by the suction feed and is effectively accelerated through the blasting nozzle. The rate of breakdown is not excessive, except when very high air pressures are used to blast hardened steel or other very hard substrate materials. Alumina, fused and pure, is extremely hard (>9 on the Mohs scale), and when properly crushed has sharp cutting edges. There are two grades: C (coarse) and F (fine). A good all-purpose grit for general use in a blasting cabinet would be to start with a 50/50 mixture of C and F, with periodic small additions of the C grade to maintain a balanced grit range of the mix. If the -50 mesh fraction is occasionally removed by screening, it can be set aside and used where a fine, light grit blast is needed. Source: From Coating Processing, Frank N. Longo, Longo Associates, as published in Handbook of Thermal Spray Technology, J.R. Davis (Ed.), ASM International, 2005, p 114. Information and data acquired from ASM International Thermal Spray Society website at http://asmcommunity.asminternational.org/portal/site/tss/SprayTips/ 44 Back to TOC Back to Overview
Compiled by Jo Ann Gan, Edited and advised by Christopher C. Berndt Swinburne University of Technology Thermal Spray Group (SwinTS) Please contact Prof. Christopher Berndt at cberndt @swin.edu.au for further enquiries 4.3. Machining and Macroroughening Comparison of thermal spray coatings deposited on macroroughened and smooth surfaces. (a) Sprayed metal over grooves; shrinkage constrained by grooves (b) Sprayed metal on smooth surface; effect of shear stress on bond due to shrinkage Macroroughening is usually accomplished by machining grooves or threads into the surface to be sprayed. Typically, rough machined surfaces are also grit blasted prior to spraying. Surfaces roughened to this magnitude are often used for thick coatings to restrict shrinkage stresses and to disrupt the lamellar pattern of particle deposition in order to break up the shear stresses parallel to the substrate surface. Groove threads should be considered for coatings used on machine-element repairs for thicknesses greater than 1.3 mm (0.050 in.) on the radius, for high shrinkage coatings, and for coatings that may be subject to high shear stresses (i.e., loads parallel to the interface). Source: From Coating Processing, Frank N. Longo, Longo Associates, adapted from H.S. Ingham and A.P. Shepard, Eds. Metallizing Handbook, 7th ed., Metallizing Engineering Co. Inc., (Metco), p-A 10, 1959, as published in Handbook of Thermal Spray Technology, J.R. Davis (Ed.), ASM International, 2005, p 115. Information and data acquired from ASM International Thermal Spray Society website at http://asmcommunity.asminternational.org/portal/site/tss/SprayTips/ 45 Back to TOC Back to Overview
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Thermal Spray Tips - Swinburne University of Technology

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