Pressure Sensitive Thin Membrane – Assembly

Background

The heart of a pressure regulator is a sensitive, thin diaphragm that must hold and react with pressure changes. However, the diagram must also have a component hard enough to interact with other mechanical mechanisms. Requiring both a solid interaction platform, but at the same time provide an elastic feature that is able to reflect the pressure, requires two diverse materials to be attached. So LSR (liquid silicone rubber) can be used for the thin membrane so the part can have elastic characteristics. However, a PA (polyamide) is used for a core to provide the needed interaction. Furthermore, the diaphragm must be placed into a greater assembly with no deformation so it can perform correctly.

Problem

The first problem that is encountered during the molding of the parts is the bonding between the LSR and the PA. With manual assembly, the LSR and PA components could be improperly lined up. With an unaligned diaphragm, the component will perform inconsistently or even fail. To compensate for manual error, transfer molding could be used where the PA core is formed and then later put into a mold to have silicone injected over it. This process requires a primer to prep the material for silicone over molding which requires constant maintenance on the tool and an additional process that requires material. Even with the component properly assembled, putting the component into the greater device may cause problems as the thin diaphragm may distort or be contorted.

SIMTEC Solution

Increasing the bond strength between the LSR and PA true two shot molding is a viable option. In true two shot over molding, the substrate (PA) is molded in one half of the mold and then is transferred to the other half of the mold to have the silicone injected over the top of it. A better bond is formed since the PA is still hot, allowing more of the composition to settle in place with the silicone. Furthermore, the part was just molded, so there are no surface contaminants that would get in the way of the bond. With a quick transfer, the part does not require any pre-treatment that would add to the cycle time, maintenance, or operating costs.

To address the integration into the main component, design plays a large factor. To ensure the diaphragm is never distorted or wrinkled when placed into an assembly, a stabilizing feature should be in place. The stabilizing feature could be simple like a thicker silicone ring that will provide a lip to interact with. However, this will still require manipulation to properly place in an assembly. Another choice that would be coupled with two shot over molding is using a PA stabilizer ring as the outer diameter of the component. If true two shot is used, the part will provide great bond strength, and with a solid outer ring, the part can essentially just be dropped into place.