2. Evaluation of the efficiency of the base powder coating gun-nozzle

   The design work implemented in this paper makes use of reverse engineering to modify the existing gun nozzle design in order to design new efficient nozzles that are capable of achieving increased powder deposition efficiency. Figure 3 presents the 3D model and the Computer Aided Design (CAD) drawing of the existing nozzle, while in figure 4 the spray pattern of the existing gun nozzle is presented. The powder deposition test conducted was conducted on a flat plate with constant gun pressure and voltage.         

3. Design of Virtual Prototype Powder Coating Nozzle and CFD Validation

 

     In sections 3.1 and 3.2 brief description of the CAD design of a new prototype nozzle and it validation using CFD code, Fluent, are presented respectively. The results of the CFD simulation of the spray process of the prototype nozzle under different inlet and static pressures are also presented.

 

  

3.2.1 Simulation of Inlet Gun-Nozzle Pressure

The pressure of outlet powder feed from the fluidising bed and venturi pipe plays critical roles in deciding the powder flow rate of the inlet fluidised powder to the powder gun coating. Fluidised powder travelled from the fluidised bed through the venturi pipe to the gun nozzle. The venturi pipe ensures that fluidised powder is supplied to the powder feed-hose at a consistent rate. In order to monitor the flow condition in the, the outlet pressure was simulated using Fluent. Figure 6 presents the CFD model of the venturi pipe with the air and powder inlets and the powder feed outlet area.

  

  Fig.6: CFD model of venturi pipe and atomising inlet air

    

 Fig.12: Path lines from powder particles with inlet pressure At 1000 Pa

The simulation result of the prototype nozzle

 indicated that increased transfer efficiency is

 achieved when the inlet pressure is set at

 1000Pa with more than 90% of sprayed charged

 powder particles deposited on the target surface.

6.0 Conclusions

In this paper, a methodology for increasing powder deposition efficiency in corona applications has been presented. The methodology demonstrated an approach to nozzle design with a view of reducing over spray. A computational fluid dynamic code, Fluent, was used to simulate inlet pressure into gun nozzle from the venturi pipe. The CFD simulation offered an opportunity to investigate wide range of nozzle parameters with a view of finding an optimal candidate nozzle design for the powder application process. Experimental results of the candidate gun-nozzle indicated that powder deposition efficiency improved significantly.