Redesign of a test environment for an elastic mechanism for usage as pressure sensor element

When dealing with plastics producing techniques such as injection molding and extrusion control of pressure is a decisive parameter influencing the quality and reproducibility of plastics products. Different types of pressure sensors are commonly used which most often transform mechanical deformation into electrical signals and these in turn are converted into the value of pressure. In some cases separate pressure chambers might be necessary, often the pressure range is limited, and usage of electrical components lead to constraints concerning temperature range. This in turn means extensive effort for installation and insulation of the pressure sensors for example when you want to control the pressure at any desired area of the injection system. This work is based on an approach of using a flexible element and determining the pressure solely by its deformation. This eliminates thermal insulation and electromagnetic shielding. But concurrently this demands some knowledge concerning the mechanical behavior of the flexible element. To determine the mechanical behavior of the flexible element especially its stiffness different approaches have been taken into account. First one is to regard the flexible element as Kirchhoff plate. This analytic approach implies a constant bending stiffness which means a linear dependency between working pressure and resulting deflection. This could be confirmed evaluating measurement data that has been taken using a test rig specially designed for that task. In the test rig as substitution of the pressure a variable but defined load can be applied. When carrying out some measurements with one certain flexible element the influence of assembling and disassembling the test rig was obvious. Only when not changing the assembled test rig measurements have been reproducible. Main reason was the radial variance of applied load and the center of the flexible element. In order to solve that a test rig was redesigned including a centering device to guarantee load transmission happening always at the same point. Additionally influence of certain linkages in the test rig has been investigated. Combination of both leads to a more reliable and better test rig with higher reproducibility.