High-end electronics with specialized o-rings pose a number of challenges that conventional seal applications do not. While most conventional seal applications focus on media compatibility, physical properties, and longevity, high-end electronics are generally require more emphasis on cleanliness, repeatable processing, dielectric properties, and ease of assembly. Many electronic components rely on a high purity media to conduct energy. These media can take several different forms, but the purity of the media can be paramount in the performance of the component. Liquid media, for example, depends on the purity of media to maintain performance. Media such as acenitrile depends on the purity to store and transmit charges in application. If the material of rubber o-rings, for instance, has any ingredients (waxes, plasticizers, process aids) or ancillary residual material (mold releases, residual cleaning media) which could leech out of the rubber and into the fluid, it could compromise the effectiveness of the electrical component.
Studies have shown that performance of specialty seals can be altered as much as 12% from fugitive chemicals that are released from rubber and/or plastic parts that are exposed to the media. The raw material choices and processing characteristics for materials which will be exposed to medial in applications of this nature should go through extraction testing, which is the process of testing the actual fluid before and after exposure to the intended application media. Real Seal can help in determining acceptable levels of fugitive extractable material, which is normally measured in ppm.
Due to the exacting nature of electronics, most manufacturers expect and demand the highest degree of repeatability in processing. This can create issues with thermosetting rubber materials, as the process is highly labor intensive, and the mixing of material is performed in lots which are a fraction of the size of thermoplastics. Ironically, the very things that create the best physical properties in the vulcanized rubber material of specialty o-rings are the same things that make processing more of a challenge. For example, the less plasticizer and process aids that are included in a rubber recipe, the better the properties of the finished, molded product, and the lesser the chance of extraction into the media meant to be sealed.
There is a delicate balance to be struck between process economy and efficiency, and the properties of the finished molded part. The geometry of the seal plays an important part in the decision making process as well. The more challenging the geometry of the part, the more difficult it is to engineer a process that nets the most consistent result. Processing techniques such as rubber injection molding, LIM systems, and vacuum press systems should be considered in the choice of material and processing, including the tooling for each method, as the cost can vary widely.
Other electrical applications such as hydrogen fuel cell technology may require many of these features, and depending on the engineering requirements, dielectric properties may also need to be considered. The rubber material chosen for a seal application may be required to insulate or regulate electrical energy, while providing a positive seal at the same time. The science of measuring dielectric properties, or the amount of electrical energy transmitted through the rubber material, can therefore be very important in creating a balanced and efficient system of energy distribution. Using the seal for both purposes can create a very nice engineering result, as the elastomer can help to make up for dimensional variance in the other components with its flexible properties. A precision molded part can achieve many desired engineering objectives, providing greater economies for the other components.
Rubber and plastics can be molded with a number of different techniques, and the latest technologies can provide for consistent and repeatable results. The design of these parts should include a generous radius in place of sharp edges, draft angles to enhance both molding and location/assembly of the part, and a general geometry that will pay dividends in both processing and tool cost. A generous radius will allow the part to be tooled for more easily, as conventional cutters can be used to cut the cavity and core in the mold. Sharp edges are a natural air trap mechanism during the molding process, so the radius will normally increase the molding yield by avoiding air trap issues. If the part design is symmetrical, it will pay dividends in yield and assembly, and any design should avoid undercut geometry for ease of molding. The closer to the middle of the part you can plan the parting line for molding, the more it will tend to favor a positive result in processing, particularly in thermoplastic molding. All of these features should be considered, and taken advantage of in order to maximize the repeatability of processing, and consequently reduce the bell curve results as much as possible.
Although many do not consider rubber and plastics to be as critical as metal, chemical, or electrical engineering of a product, rubber and plastics can find their way into being one of the most critical and economically impactful components in the design. Real Seal regularly engages in design support services, and can offer insight of this nature in a wide variety of applications. For more information, visit http://www.real-seal.com/ for a consultation.
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