Method of Research Approach for Structural Analysis of Automotive Plastic Fans: Analytical and Experimental Investigation

In this paper a method of research approach adopted by USUI International Corporation (UIC) for structural analysis of automotive plastic fan is described. The fan material used and perfected by UIC for engine-driven fans is polypropylene. The analysis is carried out by finite element method and complemented by experiments in some cases. Structural analysis procedure specific to automobile engine-driven fan is described. Polypropylene fan offers several advantages over other plastic/metal fan. Polypropylene is lightest of all plastics having specific gravity of 0.9. However plastic fans pose certain challenging structural problems. Plastic properties such as modulus of elasticity are temperature dependent and properties detoriate with increase in temperature. Also continuous or repetitive loading of plastic fan over the period of life of fan results in creep of plastic material at high stress areas on the hub of fan. In actual practice plastic fan with molded-in steel insert is used. Steel insert is used to maintain the structural rigidity and integrity of the fan. Hub and blades are made of plastic. Such fans are also subjected to thermal stresses due to differences in thermal expansion coefficients between steel and plastic. Further, plastic fans are usually manufactured by injection molding process. This gives rise to weld lines on hub of fan. Weld lines are weak compared to other portions of hub.

There are not many papers in the literature on structural analysis of plastic fans. Very few papers have compared analytical results with experiments. In this paper we report general procedure adopted for structural analysis of plastic fan with steel insert. The results of a typical experimental polypropylene fan for our analysis are reported. Finite element procedure is used for the analysis. The analysis procedure used and results obtained for polypropylene fan subjected to centrifugal loading, air pressure loading, combined air pressure and centrifugal loadings and thermal loadings are given. The effect of creep of high stress regions and effect of weld lines on distribution and magnitude of stresses for different loading conditions are studied. Practical and powerful procedures are developed for the consideration of creep and weld lines. Some experimental verification is also presented.