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41 CHAPTER 4 CONCLUSIONS AND SUGGESTED RESEARCH CONCLUSIONS provided higher tensile adhesion than low RPC and high RQ values. Further work is recommended to The results of the laboratory testing indicate the conclu- determine the optimum values of RPC and RQ. sions listed below. 3.2. Until the critical values of RPC and RQ can be defined, angularity should be defined by a surface compara- 1. The Effect of Sealers tor chart such as the chart showing abrasive grit shapes that was published in the Journal of Protec- 1.1. The use of sealers has no detrimental effect on TSMCs tive Coatings and Linings in 1994 (38). Acceptable and might actually improve the adhesion properties grit shapes, as determined under 25-power magnifi- as measured by the tensile adhesion, U-bend, and cation and the standard chart, should be "very angu- impact tests. lar," "angular," and "subangular." 1.2. Sealers appear to improve the performance of zinc TSMC, but do not appear to improve the performance 4. Application Parameters of aluminum TSMC in the corrosion tests to date. 1.3. Based on the falling weight impact tests, the use of a 4.1. Increased gun-to-surface distance decreases the adhe- sealer improves the impact resistance of the TSMC. sion of aluminum, but does not affect the adhesion of the zinc or zinc/aluminum coatings. The angle of 2. The Effect of Abrasive Mixes the gun to the work surface did not affect the adhe- sion of any of the TSMCs tested at the angles used 2.1. Based on tensile adhesion and disbondment tests, in this study. 100-percent grit abrasive results in significantly 4.2. The corrosion tests indicate that aluminum TSMC is better adhesion than does 100-percent shot. Also, insensitive to the application parameters tested in 100-percent grit provides better adhesion than do this study. either of the two shot/grit mixtures tested in this 4.3. The corrosion tests indicate that the zinc TSMC is study; however, the shot/grit ratios used might pro- sensitive to the gun-to-workpiece angle, showing vide acceptable performance based on the corrosion lower performance at an angle of 45 degrees. tests completed to date. At this point, the TSMC Guide should specify the use of 100-percent grit as the optimum surface preparation finish. 5. Steel Hardness 2.2. The zinc TSMC showed better corrosion perfor- mance with 100-percent grit and the 70-/30-percent 5.1. Similar surface profiles (as measured by depth) and shot/grit mixture than with 100-percent shot or the adhesion values for aluminum and zinc TSMCs were 33-/67-percent shot/grit mixture. observed on the A36 and Grade 50 steel panels. 2.3. The aluminum TSMC appeared to be insensitive to 5.2. Both zinc and aluminum thermally sprayed coatings the abrasive mixes tested in this study based on the applied to the A36 and Grade 50 steels are perform- 12-month corrosion tests. ing similarly to date. 3. Angularity Measurements 6. Carbon Steel and HSLA Steel 3.1. A simple field-friendly measurement technique for Aluminum, zinc, and zinc/aluminum thermally sprayed coat- angularity was found in this study. Measurements ings applied over carbon steel and HSLA steel showed no using a surface profile gauge that measures RPC and RQ differences in performance in previously conducted studies showed that high values of RPC and low values of RQ and in galvanic studies conducted in this research.