Evaluation and Analysis of the Erosion Performance of Flame Spray-Coated Polyurethane Liners

• Author / Creator

  Ashrafizadeh, Sayed Hossein

• Polyurethane has excellent wear resistance and is an effective protective liner against erosion caused by the impact of solid particles. However, similar to most polymeric materials, polyurethane has low thermal and electrical conductivity, and this limits its applicability for use in environments where the operating temperatures are high or where electrical conductivity is required. One of the solutions to overcome such problems is metallization of polymeric materials by thermal spraying processes. Due to the thermal sensitivity of polymer materials and the high temperatures that are typical of thermal spraying processes, prediction of the temperature distribution in the polymer material substrate during spraying is considered to be a key factor in the selection of appropriate coating materials and control of spray process parameters. The first phase of this PhD project focused on deposition of metallic conductive coatings on polyurethane substrates. A mathematical model for determination of the temperature distribution within polymeric substrates during flame spraying was developed to allow for monitoring of the temperature during the spraying process. The effect of air pressure and the stand-off distance of the flame spray torch on the temperature distribution, characteristics of the deposited coatings and electrical resistance were also studied. An analytical heat transfer model based on Green’s functions was developed and validated with experimental data. It was found that the temperature distribution, coating porosity, and electrical resistance decreased by increasing the pressure of the air that was injected into the flame spray torch during deposition. The injection of air also allowed for a reduction of the stand off distance of the flame spray torch to deposit coatings with higher electrical conductivity. Dynamic mechanical analysis was performed to investigate the effect of the increase in temperature within the substrate on its dynamic mechanical properties. It was found that the spraying process did not significantly change the storage modulus of the polyurethane substrate material. The deposited coating may function: a) to distribute heat to avoid excessive local temperature increases in the polyurethane liner during practical applications that involve erosion and b) for use as a heating element. To that end, the second phase of this PhD thesis research focused on studying the effect of temperature on the wear resistance of polyurethane. A test assembly capable of conducting erosion testing at controlled temperatures was designed and developed. The temperature distribution within the samples during the erosion tests was determined by a three-dimensional finite element model and the velocity of the erodant particles was estimated by a mathematical model based on the principles of supersonic compressible fluid flow through a converging-diverging nozzle. The results that were obtained showed the effect of temperature on the erosion resistance of PU elastomers. The stress-strain behavior of the polyurethane elastomers was characterized at room and at elevated temperatures up to 100ºC by conducting tensile tests and cyclic loadings. Comparison of stress-strain behavior of the polyurethanes with their erosion resistance at controlled temperatures revealed that the residual strain as a result of plastic deformation, stress softening, ultimate failure stress and final elongation at break were the key parameters affecting the erosion resistance of polyurethane elastomers. Evaluation of the surface morphology of the worn samples confirmed the importance of the residual strain and elongation at break on the erosion resistance of polyurethane elastomers. In order to study the effect of temperature on the stresses and strains that were generated during the erosion testing, the impact of erodant particles on the elastomer surface was modeled by using the finite element technique. The model that was developed allowed for better understanding of the mechanism of material removal during solid particle erosion of PU elastomers. The results obtained by the finite element model showed that the ultimate strength and elongation at break have the most significant influence on the erosion rate at velocities higher than a critical value. Residual strain as a result of plastic deformation and stress softening caused by Mullins damage and PU softness were found as other parameters that can affect the erosion rate.

• Subjects / Keywords

  • Green's Functions
  • Polyurethane
  • Heat Transfer
  • Thermal Spraying
  • Finite elements
  • Wear

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3CR5NM34

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.