Silicone connectors are molded rubber parts that connect the intake pipes and tubes in diesel-powered vehicles and equipment. These engine components resist high temperatures while providing strength and flexibility. Typically, silicone connectors are used in mobile equipment such as generator sets (gensets), ships and boats, and on-road and off-road equipment for forestry, mining, construction, and agriculture. Continue reading
How is silicone rubber used for sealing and insulation? Silicones have valuable properties, but engineers need rubber that meets specific requirements. If you’re wondering whether silicone seals, gaskets, or insulation are the right choice for your application, consider some of the uses for this versatile polymer. The examples you’ll read about aren’t the only uses for silicone, but they’re representative. Continue reading
When is silicone rubber the right choice for sealing and insulation? Silicones have many desirable properties, but can cost more than other polymers. That’s why some engineers avoid them – even though silicone prices have fallen. At the same time, newer materials such as thermoplastic elastomers (TPE) are interesting but even more expensive.
If you’re wondering whether silicone rubber is the right choice for your application, Elasto Proxy invites you to take a fresh look at these synthetic elastomers. In Part 1 of this two-part series, we’ll examine the advantages of silicone rubber, cover some basic chemistry, and then focus on silicone gasket materials. Next, we’ll categorize silicones in different ways so that you’ll be ready to understand the applications. Continue reading
John Rye Branch Manager at Elasto Proxy
Food grade silicones are used in food processing facilities and industrial kitchens to help keep food items from coming into contact with equipment surfaces. Products include non-stick baking molds, pads, and trays; sanitary door seals for refrigerators, freezers, mixers, and ovens; and protective rubber profiles for the sharp edges on stainless steel surfaces such as food prep tables.
A type of synthetic rubber, silicone is an inert compound that will not react with food products or food ingredients. This flexible, durable synthetic material doesn’t off-gas fumes either. Suitable for high and low service temperatures, silicone seals can be used with both ovens and freezers. Applications for silicone extend beyond the food equipment industry, so suppliers use the term food grade silicones.
Not all food grade silicones contain the same ingredients, however, and silicone sponge and solid silicone have different material properties. There’s also the matter of meeting standards such as those from the National Sanitary Foundation (NSF) and the Food and Drug Administration (FDA). Although the FDA’s regulatory jurisdiction is limited to the United States, FDA standards are used worldwide.
Food Grade, FDA Compliant, or FDA Approved?
Many suppliers offer food grade silicones, but some describe their materials as “FDA compliant” or “FDA approved”. Typically, these compounds comply with only the FDA’s extraction requirement, or contain only a subset of ingredients that are FDA approved. In other words, these silicones are food grade, but they’re not fully FDA compliant – and they’re not fully FDA approved.
What does this matter? In an article entitled Is It Really FDA Approved?, the agency explains how and what it approves. Materials such as silicone, which were once known as indirect food additives, are now called food contact substances (FCS) instead. If an FCS contains multiple additives (as compounds do), then all of the additives must be approved in order for the FCS to be fully-approved.
Technical buyers also need to understand the FDA’s extraction limit. CFR 21.177.2600 specifies multiple extraction test limits for rubber that comes into contact with food. Using distilled water and n-hexane, suppliers must prove that their rubber does not exceed allowable extractive amounts. Yet meeting this standard alone doesn’t make a food grade silicone fully FDA approved.
A Silicone Sponge That Fills the Gap
As an experienced custom fabricator with expertise in compound selection, Elasto Proxy offers sealing solutions that are made from fully FDA approved silicone sponge. The sheets, rolls, and extrusions that we convert are made from a special silicone compound that meets the FDA’s extraction test, and also contains only FDA-approved additives.
Food and beverage equipment manufacturers, the pharmaceutical industry, and medical manufacturers now have a new option for meeting application requirements. Moreover, because this fully FDA approved silicone is a sponge, its features include excellent compression set and recovery. This is important not just for door seals, but also with baking mats where food products fall onto a packing line.
How Can We Help You?
Do you need help sourcing silicones for sanitary applications? For 25 years, Elasto Proxy has been working with partners in a variety of industries to solve sealing challenges. By listening to all of your requirements and analyzing all of your needs, our solutions providers can recommend silicone seals that are right for your application.
Please contact us for more information, or join the conversation on our social media channels. Look for a post with a link to this blog entry on LinkedIn, Facebook, Google+, and Twitter. Elasto Proxy has a YouTube channel, too. Finally, please subscribe to our free e-newsletters. They’re a great source of information delivered right to your email inbox, and they provide links to blog entries like this one.
Doug Sharpe President of Elasto Proxy
Do people say that you look like your father? How about your mother? Maybe you resemble both of your parents, but in different ways. Human genetics can be complex, but so can polymer chemistry. Like DNA strands, long-chain polymeric molecules consist of base units (monomers) and groups. The double-helix structure of DNA is well-known, but the tangled configurations of polymer molecules are difficult to describe. That’s not the hard part, however. The real challenge is creating a plastic alloy from them.
Because of their complex structures, many polymers do not lend themselves to blends. Human history includes a Bronze Age and an Iron Age, but have you read any books that call our current era the Age of Long-Chain Polymer Blends? Through advances in material science, however, mixers are able to create compounds from rubbers such as silicone and EPDM. Blending these long-chain polymers is challenging, but imparting the best characteristics from each is essential.
Let’s look at the advantages – and disadvantages – of silicone and EPDM. Next, we’ll learn how mixers make silicone/EPDM blends, and how creating a blend for an application means getting the recipe for rubber just right.
Silicone resists ozone, sunlight, oxidation, and weathering while providing excellent electrical insulation and flexibility at low temperatures. Although silicone is valued for its low compression set and superior color stability, this synthetic rubber is best known for its usefulness at high or low service temperatures. Silicone is more expensive than EPDM, but silicone seals generally last longer.
Silicone isn’t ideal for all applications, however. Because of its chemical properties, this type of rubber isn’t recommended for use with acids, alkalis, solvents, oil, or gasoline. Silicone lacks strong resistance to abrasion and tearing, too. Although many excellent silicone compounds are available, pure silicone isn’t the right choice for applications that require high tensile strength.
EPDM also has its strengths and weaknesses. A popular polymer, this synthetic rubber is used in belts, hoses, and O-rings for the automotive and mass transit industries. With its excellent resistance to aging, ozone, and weathering, EPDM also provides strong resistance to acids, alkalis, and some solvents. EPDM parts are color stable, remain flexible at low temperatures, and resist both water and steam.
EPDM isn’t perfect however. In fact, this synthetic rubber is no match for mineral oils or aromatic hydrocarbons. EPDM compounds aren’t recommended for applications involving petroleum derivatives then. Though suitable for use as a high voltage insulation material, EPDM can conduct electricity if carbon black is added to improve weathering.
Silicone EPDM Blend
To produce blends with the best properties of silicone and EPDM, compounders add the two rubbers in proportions such as 50:50 or 70:30 to a two-roll mixing mill. Typically, dicumyl peroxide is used as the vulcanizing agent. After the materials are compression-molded into sheets and cured, the mixers test the blends and measure properties such as dielectric strength, tensile strength, and percentage elongation at break.
According to test results published by the IEEE, increasing the proportion of silicone improves a blend’s electrical insulation. By increasing the weight percentage of EPDM, mixers can boost mechanical strength instead. As with other compounds, there are tradeoffs. For example, silicone-modified EPDM blends can withstand higher temperatures than EPDM alone, but provide less temperature resistance than pure silicone. EPDM/silicone blends are tougher than silicone, but not as tough as EPDM alone.
Expansion, Resistance – and Conversation
Do you need to source expansion joint systems for bridges and highways? How about electrically insulating materials for outdoor environments with solid airborne particles? Let’s talk about how a silicone EPDM blend might meet your application requirements. For over 20 years, Elasto Proxy has been solving challenges and providing solutions. Join the conversation today.
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