Finite Element Simulation of the Pinch Off of a Six Layer Co-Extruded Blow Molded Gas Tank

This paper demonstrates the use of Finite Element Analysis (FEA) to improve the pinch off characteristics in a multi-layered blow molded polyethylene gas tank. The layers include virgin high density polyethylene (HDPE), a barrier layer of ethylene vinyl alcohol (EVOH), and a layer of reground tank trimmings and scrap. The position of each layer at failure is of importance to pinch off design. Controlling the final position of the “barrier” layer in the pinch off is of particular interest in meeting future emission standards. For an existing production mold, FEA simulates the pinch off to provide insight for design improvement.

Each layer follows a deformation path at a rate proportional to several factors: pinch speed, layer position, thickness, and material characteristics. FEA details the mechanical deformation of the layers, taking those factors into account. Analyzing each design provides insight for further improvement or evidence a prototype is likely to produce the desired effect.

FEA results guide and critique design changes prior to building a mold for testing. The insights and trends provided by FEA create confidence in expensive design modifications.