A critical investigation into the spray-drying of hydroxyapatite powder for thermal spray applications

This work examines the investigation of the spray drying process of Hydroxyapatite powder (HA) used as a thermal spray deposit in the application of orthopaedic femoral implants. In this research, the Niro- Minor™ mixed spray dryer was used for both modelling and experimental studies. The process parameters investigated included HA slurry viscosity, temperature, and air flowrate. Computational Fluid Dynamic (CFD) modelling and validation of the spray drying of HA powder was performed. An analysis of the spray drying of the HA slurry, was performed using the UMETRI AB, MODDE 7 software. For the CFD analysis, the Spray dryer was divided into the three parts; two-fluid nozzle, the drying chamber, and atomisation. The Standard K-e, Reliable K-e and Reynolds Stress Model models were used to predict velocity profiles of the air, feed pipe of the two external nozzle and temperature profile for the drying chamber. Different model results were compared, studied and compared with experimental results. The standard K-e method is found to have good agreement with the experiment data in predicting the air and feed nozzle velocities, and the Reliable K-e simulated the temperature profile of the drying chamber. These results were also used to predict atomisation modelling. The models hence have proved to be an innovative method of understanding the dynamics of the spray drying technique. In the statistical analysis of the spray drying process, factors such as temperature and flowrate of the inlet hot air in the spray dryer, viscosity of feed/ HA and responses (chamber powder size, cyclone powder size, deposition of powder on the wall of spray dryer and overall thermal efficiency) were determined using a Multiple Linear Regression (MLR) method and the statistical analysis of main and interaction effects were quantified using the ANOVA test. For the chamber particle size, the statistical analysis showed that the viscosity of the HA slurry is most significant and for the cyclone particle size, the main affects are temperature, viscosity and flow rate, and also the interaction effect of temperature and viscosity were significant. Wall deposition is influenced by temperature and the interaction of both temperature and viscosity. The spray dried HA powders were also studied in terms of morphology. The two main shapes observed are a doughnut and solid sphere shape as a result of the different input parameters. A solid sphere of HA spray dried powder with pores was observed when a viscosity of 75 mPa.s was applied to all three levels of drying temperature. Doughnut shaped particles were observed when a slurry viscosity of 50 mPa.s was utilised. This doughnut phenomenon was more pronounced with an increase in the spray drying air temperature (461K) in the chamber powders. While a viscosity of 50 mPa.s and temperature of 461K yielded the ideal particle size and range, in terms of HA morphology, where a mix of solid and doughnut shape powder was produced. This is beneficial for HA thermal spray coatings as they require porous coatings to help the growth of the cells inside the coating to provide a strong bioactive bond between the implant and bone. This research provides a deeper understanding into the spray drying of hydroxyapatite powders providing data to improve its application in the use of HA deposits to anatomically join femoral implants to human tissue

Electrochemo-magneto abrasive flow machine setup fabrication and experimental investigation of the process alongwith mathematical modeling and optimization

In abrasive flow machining, there are two sets of piston-cylinder arrangements, i.e. machine and media. the machine ram pushes the media piston two and fro so that media filled inside it flows past the inner wall of workpiece and the material is removed. The extrusion pressure is the main mechanism of material removal. Various authors have made the process more effective in terms of material removal and surface roughness by providing rotational and magnetic force

Techniques for the Fabrication of Super-Hydrophobic Surfaces and Their Heat Transfer Applications

Super-hydrophobic surfaces are surfaces that have extreme water-repellent properties and show contact angle greater than 150° and sliding angle less than 5°. These surfaces play a significant role in different processes like icing delay, anti-frosting, boiling, condensation, drag reduction, self-cleaning, etc. The present study comprises of different techniques for the fabrication of super-hydrophobic surfaces. These techniques include chemical etching, solution immersion, laser electrodeposition, template deposition, spray coating, various others. Important characteristics of super-hydrophobic surfaces like durability, storability, corrosion resistance, etc. are achieved differently by different methods. Also, some methods are simple, rapid, cost-effective and versatile. Moreover, various heat transfer applications of super-hydrophobic surfaces like boiling, condensation, icing delay, drag reduction, etc. have also been discussed in this chapter

An experimental and simulation validation of residual stress measurement for manufacturing of friction stir processing tool

Residual stresses have been considered to be an important parameter when friction stir processing (FSP) tool is to be manufactured. FSP has often been used for surface modification and fabrication of surface composites. Involuntary residual stress in a designed tool may cause it to fail before due time. Because of this, the knowledge about the stresses on the tool probe after its machining has been considered to be desirable. The present research has focused on the analysis of the residual stresses on the tip and periphery of the FSP tool probe which has been manufactured using H13 tool steel material during the turning processes on a CNC lathe machine. The experiments have been performed on two different types of tool probes, namely circular, tapered circular probes. ABAQUS/CAE simulation has been performed for circular and tapered circular probe, as the provision of a sustainable, simple and reasonable model to analyze the machining processes (using ABAQUS/CAE software) has been the primary objective of this research. The results have been found to be within a close range of the experimental observations. The same model can thus be applied to other geometries

An experimental and simulation validation of residual stress measurement for manufacturing of friction stir processing tool

826-836Residual stresses have been considered to be an important parameter when friction stir processing (FSP) tool is to be manufactured. FSP has often been used for surface modification and fabrication of surface composites. Involuntary residual stress in a designed tool may cause it to fail before due time. Because of this, the knowledge about the stresses on the tool probe after its machining has been considered to be desirable. The present research has focused on the analysis of the residual stresses on the tip and periphery of the FSP tool probe which has been manufactured using H13 tool steel material during the turning processes on a CNC lathe machine. The experiments have been performed on two different types of tool probes, namely circular, tapered circular probes. ABAQUS/CAE simulation has been performed for circular and tapered circular probe, as the provision of a sustainable, simple and reasonable model to analyze the machining processes (using ABAQUS/CAE software) has been the primary objective of this research. The results have been found to be within a close range of the experimental observations. The same model can thus be applied to other geometries

Optimization using genetic algorithm of tribological behaviour of WC tool material

In this investigation we have used a heuristic approach to optimize the process parameters in terms of tool wear rate. We have used the L8 orthogonal array design of experiments with three input parameters set at two levels. We have carried out the experimentation on two different processes viz. dry sliding and dry turning processes. An attempt has been made to achieve and validate the results obtained from these processes to check the repeatability of values in the same experimental environment. The tool material chosen for tool insert is Tungsten Carbide which is used in the manufacturing industries. We have optimised the results obtained on tribometer under the dry sliding process through a modern optimization technique i.e. genetic algorithm. The response surface methodology model (L8 orthogonal array) formed the basis for the development of genetic algorithm model through which we have defined the conditions. We have used the conditions of minimum tool wear for turning process, minimum coefficient of friction and minimum surface roughness for sliding process on a pin-on-disc test rig. It has been inferred that the sliding and turning processes under the conditions of no lubrication yielded analogous results. We have verified the same results practically by performing confirmation experiments on lathe machine for turning operation under the same experimental conditions

Optimization using genetic algorithm of tribological behaviour of WC tool material

889-896In this investigation we have used a heuristic approach to optimize the process parameters in terms of tool wear rate. We have used the L8 orthogonal array design of experiments with three input parameters set at two levels. We have carried out the experimentation on two different processes viz. dry sliding and dry turning processes. An attempt has been made to achieve and validate the results obtained from these processes to check the repeatability of values in the same experimental environment. The tool material chosen for tool insert is Tungsten Carbide which is used in the manufacturing industries. We have optimised the results obtained on tribometer under the dry sliding process through a modern optimization technique i.e. genetic algorithm. The response surface methodology model (L8 orthogonal array) formed the basis for the development of genetic algorithm model through which we have defined the conditions. We have used the conditions of minimum tool wear for turning process, minimum coefficient of friction and minimum surface roughness for sliding process on a pin-on-disc test rig. It has been inferred that the sliding and turning processes under the conditions of no lubrication yielded analogous results. We have verified the same results practically by performing confirmation experiments on lathe machine for turning operation under the same experimental conditions

Synthesis and Wear Behaviour Analysis of SiC- and Rice Husk Ash-Based Aluminium Metal Matrix Composites

Research efforts seek to develop aluminium alloy composites to enhance the poor tribological performance of aluminium alloy base matrix. In this research, a hybrid metal matrix composite (HMMC) was developed by reinforcing an aluminium alloy (AA8011) with SiC and rice husk ash (RHA) using a stir casting technique. RHA was prepared by the cracking of rice husk, which is abundantly available in the Indian subcontinent. The samples were cast by keeping the amount of RHA constant at 2.5 wt.% and varying the amount of SiC from 0.0 wt.% to 8 wt.%. The samples were machined to manufacture pins for wear tests (at ambient temperature, 100 °C, and 200 °C) and hardness measurement. The microstructures of the cast samples were analysed using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM), along with energy-dispersive X-ray spectroscopy (EDS). It was observed that the composites with greater reinforcement of SiC exhibited improved hardness and wear resistance, but the coefficient of friction increased with the addition of RHA and SiC, and the wear performance deteriorated with an increase in the operating temperature. The contribution of RHA alone to the improvement in wear performance was marginal compared to the pure alloy. It was also confirmed that the reinforced composites could be a better option for automotive applications to replace aluminium alloys

Characterization of finished surface through thermal additive centrifugal abrasive flow machining for better surface integrity

29-44Abrasive Flow Machining (AFM) process has been a useful technique for deburring and polishing of the surface and edges through the abrasive laden media. The surface material has been removed in form of micro chips due to abrasion action of sharp cutting edges abrasive particles. A large amount of force and energy has been lost due to frictional forces between the surface and abrasive particles in AFM process. A new hybrid form of AFM process named as thermal additive centrifugal abrasive flow machining (TACAFM) has been discussed in the present investigation, which utilized the spark energy to melt the surface material. A lesser amount of force has been required by the abrasive particles to remove the molten material from the surface and also minimized the energy loss. In the present investigation central composite design response surface methodology has been used to plan and conduct the experiments using Design Expert® 11 software. Experiments have been performed to analyze the effect of input process variables such as current intensity, duty cycle, abrasive concentration, rotational speed of the electrode and extrusion pressure on scatter of surface roughness, micro hardness and % improvement in Ra of the workpiece. Also the finished surface of the brass work piece has been characterized for the microstructure study using SEM and XRD analysis. From the experimental results it has been found that duty cycle has the most significant effect towards Scatter of surface roughness with a contribution of 17.5 % while current has been contributed largest as 85.17 % towards micro hardness. Also it has been observed that current has contributed largest as 21.88% against the % improvement in Ra. The optimum scatter of surface roughness, micro hardness and % improvement in Ra has been observed as 0.15 μm, 345.95 HV and 39.52 % respectively