Thin membranes have always been sought for use in pressure detection devices. Because the membranes are thin, they are sensitive and can detect a change in pressure. The thinner the membrane, the more it will be able to react to the slightest change
Pressure-sensitive diaphragms and other thin membranes serve as important safety devices in applications such as the following:
Pressure Switches: A pressure switch in a furnace is located near the draft inducer motor in gas forced-air furnaces. Its function is to sense the negative pressure created by the draft inducer motor during the furnace startup, and to shut down the furnace ignition if the air pressure is inadequate.
Gas Control Valves: Thin gaskets, diaphragms and valves serve a crucial function in gas control valves used in gas water heaters and other gas appliances. The gas control valve controls the pilot light and water temperature. When the pilot is lit a current is sent opening the safety valves and allowing gas to flow.
Reliable performance is essential for gaskets, membranes and diaphragms used in these types of applications. There are several key requirements that ensure reliable performance:
Delicate: The part geometry must be as thin as possible to detect the slightest change in pressure.
Durable: The membranes must perform and return to their original shape after repeated uses.
Temperatures: Pressurized gas and pressure-sensitive devices are used in a wide range of products. Pressurized gas appliances and equipment can be located indoors or outdoors, and operate in a vast array of environments and temperatures.
Longevity: Membranes must have a long life span and be resistant to the constant fatigue it will undergo.
Some materials used for thin diaphragms are made out of natural rubber and TPEs (Thermoplastic elastomers). Although these materials provide the elasticity required for the application, the average operating temperature range of natural rubbers is only around 150 degrees Celsius (~300 degrees F). This lower operating temperature range limits the applications where natural rubber membranes can be used. Additionally, both natural rubbers and TPEs become brittle over time. The aging of the material will cause improper function and premature failure such as unresponsiveness and even cracking.
Mold flow is another characteristic where natural rubber and TPEs do not offer the flow in the mold that’s needed to form thin walls, a common characteristic in many gaskets and other membranes. With inadequate material flow the membrane may either be inconsistent, create pinholes, or not fully form which would cause a critical error in operation.
Liquid Silicone Rubber (LSR) is a preferred material selection for thin membranes because it does not have the shortcomings of TPEs and natural rubber, such as a limited range of operating temperatures, brittle lifespan, and mold cavity flow. Silicone has an operating temperature threshold well into 250 degrees Celsius (~480 degrees F) and is still able to perform at sub-zero degrees Celsius and Fahrenheit temperatures while maintaining its properties. Unlike its counterparts, silicone will not become brittle over time and will not degrade with constant cycling.
Finally, because LSR has a respectably lower viscosity, it will flow more easily in the mold and have a more consistent thickness. LSRs are available in a broad range of durometers (soft to firm), diaphragms typically use LSR material grades with durometers ranging from 30 to 50 Shore A. Another key factor why LSR is selected for thin membranes is that it offers design engineers greater design flexibility facilitating complex part geometries and thin thicknesses across an extended length, consistently. For example, a silicone diaphragm with a 50mm outer diameter can be 0.1mm thick while holding a ±0.02mm tolerance.
Contact a SIMTEC Expert
To discuss your thin membrane applications, contact a SIMTEC expert. We have over 20 years of knowledge and experience in LSR, LSR overmolding, and LSR multi-shot injection molding allowing us to offer our customers extraordinary solutions.