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Simulation Helps Develop Spray Gun with 50% Larger Pattern in Significantly Less Time

Graco engineers used FloEFD computational fluid dynamics (CFD) software from the Mechanical Analysis group of Mentor Graphics Corporation to optimize the design of a new plural component spray gun in 1/3 the time that would have been required to produce an acceptable but not optimized design using the trial and error method. “The use of software prototypes made it possible to explore a much wider design space than would have been possible with physical prototypes, said Rick Anderson, Senior Project Engineer at Graco. “It’s important to note that I achieved these results despite the fact that I am a design engineer without any training in CFD.”

Graco provides systems, products and technology for a wide range of fluid handling applications including spray finishing and paint circulation, lubrication, sealants and adhesives, processing and power application equipment for the contracting industry. Graco plural component spray guns are designed to apply products that need to be mixed just prior to spraying such as polyurethane foam insulation. The performance of these guns depends upon thoroughly mixing the two polyurethane foam components – the resin and the catalyst. It’s also important to control the motion of the spray as it leaves the gun in order to provide the desired pattern shape on the surface to which it is applied. In the past, the company used a long and expensive trial and error process to design these guns.

More recently, Graco has begun using computational fluid dynamics (CFD) to simulate the flow of resin and catalyst inside the gun. The CFD software originally used by the company was expensive, difficult to use and took a considerable amount of time to analyze each design. Then the only engineer who knew the software left the company. Graco evaluated alternative CFD software and discovered one product – FloEFD from Mentor Graphics Corporation – that is tightly integrated into the computer-aided design (CAD) software used by the company’s design engineers. This software substantially reduces the amount of skill and time required to simulate fluid flow through its use of native 3D CAD data, automatic gridding of the flow space, and managing of flow parameters as object-based features.

Graco engineers have used the new software to improve the performance of its spray guns to industry-leading levels. For example, Graco used CFD to develop one model of its Graco Fusion plural-component spray gun that provides a 50% larger spray pattern than traditional guns, thus substantially improving the productivity of the contractors that apply the foam insulation. Anderson embarked upon an interactive process that involved parametrically changing key design variables such as the length, diameter and amount of offset of the impingement ports and the diameter of the exit hole.

For each design iteration, he checked how thoroughly the two components mixed in the chamber and the size and shape of the resulting output pattern. “During this process, I was able to achieve the required level of mixing and round shape while substantially increasing the size of the spray pattern,” Anderson said. “As a result, we are confident that this design is the best that can be achieved within the constraints of the project.” Based on this and other successes, Graco has expanded its use of FloEFD software to the point that the company now has licenses in use at three different divisions.

Graco uses FloEFD from Mentor Graphics Corporation to develop spray guns significantly faster than traditional methods.

 
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