When dealing with a sealed keypad assembly, there is one important factor that is often overlooked. Does any of the material used within that assembly outgas? Outgassing is the name of gas releasing that was dissolved, evaporated, trapped or frozen from a material. Often this occurs once a material reaches a certain temperature level, but can also occur due to chemical reactions between two materials.
One of the main culprits of outgassing in a sealed keypad assembly is RTV. Room Temperature Vulcanization Silicone is a type of silicone rubber that cures at room temperature. One of the main types of RTV is peroxide based, which is one of the highest types of outgassing RTV’s. Depending on the design of your keypad assembly, and the operating temperatures the keypad will see, side effects of using an outgassing RTV may occur. One of the main side effects a keypad assembly can see is ballooning. This occurs when pressures build within the keypad assembly. A simple way to prevent this from happening is to inquire with your RTV provider on a low-outgassing RTV to use.
Another culprit, is the silicone rubber itself. Typically at high temperatures and low pressures, silicone rubber will outgas. One of the main ways to prevent this from happening is introducing the silicone rubber component or keypad to a post-cure. After silicone is molded and initially cured, some by-products are left within the silicone rubber as a product of the chemical reaction that occurred. In order to remove these by-products, the silicone must be placed inside an oven at approximately 400 Deg F for up to 4 hours. The removal of these by-products introduces an additional level of shrink % to the silicone rubber, meaning after the process the part will be smaller. So remember that if your silicone rubber component or keypad requires post-curing, to plan for it in the design of the original mold and shrink calculations.
Heat curing the components used within a keypad assembly is one of the easiest ways to prevent outgassing from occurring. To do this, the components must be heated past the temperature in which they will be operated in to ensure no outgassing will occur at the lower temperature. Once the components have been fully outgassed, they should be safe to assemble within the assembly.
Keypad assembly is a value added service we provide here at SiTECH for ensuring the best quality product is delivered to our customer. If you would like to speak with one of our Engineering staff about incorporating a custom assembly into your RFQ, or simply would like to speak about a silicone keypad or component, please call us at: 757-887-8488 or use our Request for Quote form today.