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Elasto Proxy's Sealing Solutions Blog

Elasto Proxy's Sealing Solutions Blog is the place for conversation and discussion about the design and custom fabrication of rubber and plastic components. For nearly 25 years, our family-owned company has provided high-quality, low-volume seals to a variety of industries. Doug Sharpe, Elasto Proxy's co-founder, is a former president of the International Sealing Distribution Association (ISD), a not-for-profit trade association that enhances member success through information, education, and interaction. By blogging for CR4 in this same supportive and collaborative spirit, Doug and other members of the Elasto Proxy team will share our experiences with you.

Commercial Grade Rubber vs. Specialty Rubber: Make the Right Choice

Posted January 15, 2018 2:16 PM by Doug Sharpe

Commercial grade rubber provides sealing and insulation for a wide variety of applications. Compounds such as commercial grade EPDM, silicone, and neoprene also cost less than specialty rubber materials that meet standards, approvals, or regulatory requirements from organizations such as ASTM International, Underwriters Laboratories (UL), and the U.S. Food and Drug Administration (FDA).

For engineers, choosing the right rubber means understanding when a specialty material is required, and when a commercial grade rubber is sufficient. Engineers want to make sure that the products they design meet application requirements, but over-specifying an elastomer can incur unnecessary costs. In addition to paying more per unit of material, you may have to buy greater minimum order quantities (MOQs).

In this article from Elasto Proxy, we’ll consider the differences between commercial grade rubber and specialty rubber in terms of some real-world examples. You’ll also learn about some best practices that can strengthen your seal designs.

Asking for ASTM Rubber

Sometimes, engineers ask for “ASTM rubber” or an elastomer that “meets ASTM D 2000”. There are several challenges here. First, there isn’t a single ASTM test standard for rubber materials. In fact, there are many different and specific testing standards. Do you need an elastomer that meets the thermal conductivity requirements of ASTM F433-02(2014)e1? Maybe you need a gasket material that meets the minimum liquid leakage requirements of ASTM F 37-06(2013) instead. If you don’t need a specialty rubber that meets an ASTM test standard, could you use a commercial grade compound that costs less?

ASTM D 2000 is a published specification that provides buyers and suppliers with a standard way to describe vulcanized elastomers. Asking for “ASTM D 2000 rubber” instead of “ASTM rubber” may seem more specific, but it’s not. ASTM D 2000 covers thousands of elastomers and uses a combination of letters and numbers to “call out” material properties. To use a food-related analogy, simply asking for “ASTM D 2000” rubber is like ordering a sandwich without specifying the bread, fillers, or condiments. Unless you’re incredibly lucky, the sandwich you receive probably won’t be the one you thought you’d ordered.

Asking for UL 50 Gaskets

UL 50 applies to enclosures for electrical equipment that will be installed and used in non-hazardous locations in accordance with national electrical codes in Canada, the United States, and Mexico. This standard applied to the entire enclosure, however, and not to individual components such as seals, gaskets, and insulation. In fact, UL 50 states that if an individual product has requirements that are at variance with UL 50, then the requirements for the individual product takes precedence.

Sometimes, however, engineers ask for “UL 50 gaskets” when a UL 50 approved material is not required. There are several challenges here. First, a well-designed enclosure may be able to meet UL 50’s requirements without the use of more expensive UL-approved gasket materials. Second, there is a separate UL standard (UL 50E) for the environmental construction of qualifying environmental enclosures. During the design process then, engineers may need to account for two separate but related standards. If the electrical enclosure is for an appliance, then UL 94 may apply to your gasket design instead.

Commercial Grade Rubber, Specialty Rubber, and Best Practices

Asking for a “rubber gasket” but including “UL 50 gasket” or “ASTM rubber” on your schematic is also problematic. Ultimately, your part drawing is your contract for gasket fabrication. That’s why Elasto Proxy helps you not just with material selection, but with seal design. If you use a CAD application such as SolidWorks®, we can send you DWG files of standard profiles that you can drop into your design. We can send you PDF versions of our standard profiles, too.

Are you wondering whether you need commercial grade rubber or specialty rubber? Do you have questions about seal design? Don’t wait until the end of your next project to ask for assistance. Otherwise, you may need to use specialty rubber because a commercial grade compound can’t support a design constraint. To learn more, contact Elasto Proxy.

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Bulb Trim Seals: Compounds, Colors, and Approvals

Posted December 18, 2017 10:10 AM by Doug Sharpe

Bulb trim seals don’t just come in EPDM rubber. They’re available in colors besides black, too. That’s good news if you need to use recyclable materials, or if you’re searching for colorful sealing solutions to complement distinctive product designs. Bulb trim seals that contain EPDM aren’t all the same either. Some meet specific industry or regulatory standards. Others are made of harder or softer rubber.

Do you need bulb trim seals for doors, hatches, or enclosures? In this week’s blog entry, Elasto Proxy’s last for 2017, we’ll finish the year with a flourish – and with a look at some of the compounds, colors, and approvals for bulb trim seals. Black EPDM gaskets are available if you need them, but procurement and engineering personnel may have more choices in compounds than they may realize.

Bulb Trim Compounds

As last week’s blog entry explained, bulb trim seals have separate bulb and retainer sections. The bulb compresses to form a seal when the door, hatch, or enclosure is closed. The trim or retainer section attaches to the flange or substrate. These sections can be made of the same or different materials, but typically have different durometers since the bulb needs to support compression.

Typically, the bulb section is made of EPDM, TPE, or silicone.

EPDM bulb trim seals provide excellent resistance to water, weather, ozone, aging, and steam. They also resist tearing, abrasion, and a range of outdoor temperatures. EPDM rubber doesn’t resist fuels and oils, and it’s not recyclable like thermoplastic elastomers (TPEs). Yet for applications like the door seals on mobile equipment, EPDM bulb trim seals are often the right choice.

TPE bulb trim seals cost more than EPDM, but thermoplastic elastomers (TPEs) are recyclable. That’s important for sustainability, or if you need to comply with the Restriction of Hazardous Substances (RoHS) directive. TPE profiles also have significantly tighter tolerances (2x) that most extruders can achieve with EPDM. TPE bulb trim seals are available in novel colors, too.

Silicone bulb trim seals are used in applications that require low toxicity, low chemical reactivity, and thermal stability over a wide temperature range. Silicone seals also repel water and resist oxygen, ozone, and ultraviolet (UV) light. Many different silicone compounds are available, but bulb trim seals that are made from these synthetic elastomers provide electrical insulation and won’t support microbial growth.

Some bulb trim seals contain a trim or retainer section that’s made of polyvinyl chloride (PVC), a smooth plastic that resists kinking and provides other desirable properties. For example, PVC is flexible and resistant to fracture. It’s also strong, lightweight, difficult to ignite, and resistant to abrasion. The trim section of a bulb trim seal can also include internal metal clips for improved gripping, too.


Most industrial rubber products are black, but bulb trim seals can come in other colors. This is especially important in industries (such as mobile equipment) where companies use distinctive colors to support larger product designs. Colors for bulb trim seals include black, white, off-white, beige, tan, gray, and silver. In the case of TPE bulb trim seals, profiles with translucent and metallic colors are available. Most bulb trim seals are smooth, but some have coarse, pebbled, or ribbed finishes.


Finally, the compounds that are used with bulb trim seals can meet specific regulatory requirements and industry approvals. Examples include:

In the mass transit industry, engineers and buyers can source Certified Transit Grade (CTG) bulb trim seals from Elasto Proxy that provide resistance to flame, smoke, and toxicity, (FST).

Find Bulb Trim Seals in 2018

We hope you’ve enjoyed this article from Elasto Proxy and wish you a happy holiday seasons. This is our final article for 2017, but we invite you to contact us if you’d like more information about bulb trim seals or other industrial rubber products. See you in 2018!

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Bulb Trim Seals: Three Measurements You Need to Know

Posted December 11, 2017 8:11 PM by Doug Sharpe
Pathfinder Tags: bulb trim seal measurements

Learn about bulb trim seal measurements from Elasto Proxy.

Bulb trim seals are industrial rubber products that are used to seal and insulate doors, hatches, and enclosures. They fit radiused corners and have separate bulb and retainer sections, each of which can have a different durometer (hardness) and use a different material. The bulb compresses to form a seal when the door, hatch, or enclosure is closed. The trim or retainer attaches to the flange or substrate.

There are many different types of bulb trim seals, and plenty to learn about these industrial rubber products. In this two-part series from Elasto Proxy, we’ll examine three bulb trim seal measurements that engineers need to specify: bulb size, bend radius, and flange thickness.

Bulb Size

Choose a bulb that’s large enough to fill the gap and that also supports the proper amount of compression. Determining this bulb size is a two-step process that’s represented by the following calculation.

Bulb Size = Average Jam Dimension + Compression Percentage

First, calculate the average jam dimension. An easy way to do this is to place some modeling clay in each corner and then close the door, hatch, or enclosure to compress the clay. Next, insert calipers into the clay and record the measurement for each corner. Now divide this number by four to get the average jam dimension or gap size.

Next, apply a percentage to this amount to account for compression. As a rule of thumb, apply between 25% and 50%. Do not apply more than 50% because over-compressing the bulb will not create a better seal. In fact, over-compression can reduce seal life and cause compression set, a permanent deformation that occurs when a force that was applied to a material is removed.

Bend Radius

Unlike some other industrial rubber products, bulb trim seals aren’t designed for 90-degree corners. To accommodate rounded or radiused corners, choose a bulb trim seal with a bend radius that will support flexing or bending and avoid kinking. To do this, determine the minimum distance from the center point to the edge (the radius) that the seal must bend.

Remember that a more flexible material can support a smaller bend radius. Yet if the radius is too tight, the corners can “pop” out. Conversely, if the bend radius is too large, recesses or valleys may form and allow the passage of water. The results can range from drafty doors on mobile equipment to leaky doors on electronic enclosures.

Note: Elasto Proxy's in-house laboratory can perform three separate tests to determine the maximum bend radius before kinking.

Flange Thickness

Finally, specify the thickness of the trim or retainer section. This gap or thickness is the distance between the two “legs” or straight sections. As a rule, this measurement should equal the thickness of the flange or substrate. For example, if a bulb trim seal has flange that’s 1/2” thick, choose a bulb trim seal with a gap of 1/2”. Specifying a larger or smaller gap may result in leakage.

Learn More About Bulb Trim Seal Measurements

Elasto Proxy supplies a wide variety of bulb trim seals and can custom-fabricate bulb trim for your specific application. We offer minimum order quantities (MOQs) as small as a coil, and keep plenty of standard profiles in stock. If you need expert fabrication, ask how we can splice seals into endless loops or create square or rectangular gaskets.

Next week, in our final blog entry for 2017, we’ll cover some bulb trim seal compounds (and colors) that can both strengthen and brighten your designs. Until then, and whenever you have questions about sealing and insulation, contact Elasto Proxy.

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EPDM Rubber for Sealing and Insulation

Posted November 27, 2017 10:15 AM by Doug Sharpe

When is EPDM rubber the right choice for sealing and insulation? EPDM seals and gaskets are used widely with vehicles and equipment, but this synthetic elastomer has unsatisfactory resistance to gasoline, diesel fuel, and motor oil. EPDM’s advantages are numerous, however, and this cost-effective compound is often a better choice than silicones – especially in outdoor environments.

If you’re wondering whether EPDM is the right choice for your sealing and insulation application, Elasto Proxy invites you to take a closer look at this M-class elastomer. The M in M-class indicates that EPDM is part of ASTM D1418, a common specification for characterizing rubber compounds. Often, design or product engineers use ASTM specs to designate the rubber material on a part drawing.

In this article, we’ll examine EPDM’s advantages and applications. We’ll also consider its disadvantages – and consider how EPDM rubber compares to some other materials. Finally, we’ll look at how EPDM is supplied and fabricated.

EPDM Advantages

Ethylene propylene diene monomer (EPDM) is a compound that resists sunlight, ozone, oxygen, aging, acids, alkalis, water, and severe weather conditions. This odor-free elastomer also provides excellent color stability and high heat resistance. Depending on the compound’s chemistry, service temperatures can range from -70° C to 250° C. All EPDM rubber isn’t the same, so differences in ethylene content and the dienes that are used can affect physical properties.

EPDM rubber also provides good-to-high tensile strength and elasticity. Tensile strength, the resistance of a material to breaking under tension, is often measured in pounds per square inch (PSI). Typical EPDM values are in the 1000 PSI range. Elasticity, a measure of a material’s ability to resume its normal shape after being stretched or compressed, is expressed as a percentage. With EPDM, this percentage is typically in the 300% range. Most EPDM rubber has a durometer, or hardness, of 40 to 90 (Shore A).

EPDM Applications

With its strong combination of thermal and mechanical properties, EPDM is a good choice for the door and window seals used with mobile equipment. These rubber gaskets seal out wind, water, dust, mud, and a range of outdoor temperatures. EPDM gaskets also provide a measure of acoustic insulation against road noise and equipment sounds. Additional vehicle applications include hood seals. EPDM’s strength and elasticity also make it a good choice for the vibration isolation mounts used with machinery.

For bus, subway, and rail manufacturers, certified-transit grade (CTG) seals made from a special EPDM rubber can meet specific flame, smoke, and toxicity (FST) requirements. Indoors, EPDM rubber is used for applications where there’s contact with hot and cold water or saturated steam. Examples include refrigerator and freezer gaskets, dust boots, and rubber pipe sleeves. With its resistance to vibration and support for thermal expansion and contraction, EPDM is also a good choice for HVAC gaskets.

EPDM Disadvantages

EPDM’s main disadvantage is its unsatisfactory resistance to certain categories of chemicals. In addition to gasoline, diesel fuel, and motor oil, EPDM is not recommended for use with synthetic diester oils, lubricants found in some types of industrial machinery. EPDM also provides unsatisfactory resistance to Freon, a category of fluorocarbons that are used as refrigerants. Before selecting an EPDM compound, it’s important to check for chemical compatibility.

EPDM Comparisons

EPDM is often used instead of silicones, nitrile, or thermoplastic elastomers (TPEs). Silicones can withstand lower and higher temperatures, but they lack EPDM’s resistance to abrasion, cutting, and tearing. EPDM also provides better tensile strength than silicone rubber. For applications that require resistance to fuels, greases, and oils, nitrile is a better choice than EPDM. For applications that require recyclable materials, engineers can choose TPEs.

EPDM and Custom Fabrication

EPDM sheets and profiles support custom fabrication via manufacturing methods such as water jet cutting, lamination, gasket taping, and parts marking. They are available in standard and special grades, and can be supplied as solid, sponge, and foam materials. Examples of specialty materials include EPDM that meets FDA, UL 94, or NSF standards.

To learn more about EPDM rubber and whether it’s the right choice for your sealing and insulation application, contact Elasto Proxy.

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How Silicone Rubber Is Used for Sealing and Insulation

Posted November 20, 2017 6:13 PM by Doug Sharpe

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.

Mobile Equipment

Mobile equipment manufacturers need sealing and insulation materials that can withstand demanding conditions such as engine heat, extreme outdoor temperatures, wind, water, and mud. Examples of silicone products for mobile equipment include shaft seals, spark plug caps, radiator heating hoses, O-rings, and roller gaskets.

Mobile equipment manufacturers also need floor mats, door and window seals, and thermal and acoustic insulation. Silicone rubber isn’t used for all these applications, but Elasto Proxy custom-fabricates engine bay insulation with a silicone-coated fiberglass facing and a layer of open cell silicone foam. This custom insulation is fire-resistant and withstands continuous temperatures up to 500° F.

Defense and Aerospace

Defense contractors need rubber for the hatch seals on military vehicles and for other demanding extreme environments. Sometimes, military-grade silicones are required. For example, MIL-DTL-83528 defines the requirements for elastomeric shielding gaskets. When a silicone base is filled with metal or metal-coated particles, the polymer can provide protection against electromagnetic interference (EMI).

The aerospace industry also needs silicone gaskets with specialized properties. For example, silicones that meet the requirements of the A-A-59588A specification provide strong flex-fatigue resistance – a measure of an elastomer’s ability to withstand repeated flexing or bending. Standard silicones can withstand a range of temperatures, but not all silicones resist higher levels of fatigue.

Stainless Steel and Food Equipment

Manufacturers of stainless steel and food equipment need rubber that can withstand high heat from commercial ovens and cold temperatures from freezers and refrigerators. Silicones handle these temperatures and can resist the frequent cleaning that’s required with food and beverage equipment. From baking mats to oven seals, silicone rubber also resists greases and oils.

Depending upon the specific application, manufacturers of stainless steel and food equipment may need to use rubber products made from FDA approved materials. FDA silicones are non-toxic, non-marking, and non-allergenic. They’re also tasteless, odorless, and resistant to the natural growth of bacteria. Not all food-grade silicones are FDA approved, however, so it’s important to choose compounds with care.


Infrastructure is a broad category of applications that includes building and construction projects, industrial machinery, electrical equipment, and enclosures. In residential and commercial construction, silicone rubber can be used in window seals and door seals. With other types of built structures, silicones are used in expansion joints because these elastomers allow for thermal expansion without distortion.

With their strong dielectric properties, silicones are used with cables and cable terminations, corona-resistant insulation tubing, keyboards, and contact mats. Particle-filled silicones that provide EMI shielding are used in conductive seals because metal or metal-coated particles also provide electrical conductivity. UL 94 silicones that resist the spread of fire are used in rubber gaskets for electrical enclosures.

Medical and Healthcare

Silicones for medical and healthcare applications are used in tubing for medical devices and equipment, bellows for artificial respirators, and EMI gaskets. As with food and beverage equipment, FDA approved rubber may be required. Yet not all silicones for healthcare environments require FDA approvals. Examples include the silicone door seals in walk-in bathtubs for hospital patients.

Silicones are also used with the handles for patient lifts. A metal tube can support a patient’s weight, but stainless steel is cold, hard, and sometimes slippery. Slip-on silicone foam handles support easier gripping for greater patient safety and comfort. To learn more about applications for custom-fabricated silicone products, contact Elasto Proxy.

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