Bulb Trim SealsBulb trim seals provide sealing and insulation for doors, hatches, and enclosures. These industrial rubber products have bulb and retainer sections that are made of different materials. The bulb section provides sealing and insulation under compressive force. The trim or retainer presses onto a flange or substrate.  Each section of the seal also has a different durometer or hardness to support proper compression.

This technical article from Elasto Proxy is designed to help you choose the right bulb trim seals for your application. In addition to compound selection and part dimensions, product designers and technical buyers need to consider color, texture, internal supports, and exterior finishes. Your application may also require flame-resistant compounds or rubber that meets specific industry standards.

Compound Selection

Selecting the right bulb trim seal for your application involves proper compound selection for both the bulb and retainer (trim) sections. Otherwise, the bulb trim seal may admit wind or water, fail to withstand ozone or ultraviolet light (UV), or become unable to resist permanent deformation after compressive force is removed – a condition known as compression set.

The bulb portion of a bulb trim seal is usually made of EPDM sponge rubber or a thermoplastic elastomer (TPE). EPDM provides excellent resistance to weather, ozone, aging, water, and steam. This durable synthetic rubber also remains flexible at low temperatures and is color stable. TPEs are also weather-resistant, but are reusable and typically recyclable.

The retainer or trim portion of a bulb trim seal is usually made of PVC, a plastic that maintains its flexibility at lower temperatures and that resists kinking. PVC plastics also offer excellent impact resistance along with good abrasion resistance, tensile strength, and resilience. Like EPDM and TPEs, PVC is a good choice for outdoor applications.

Part Dimensions

Bulb Trim Seals from Elasto ProxIn addition to bulb and trim materials, buyers and designers need to specify these part dimensions when choosing bulb trim seals.

  • Bulb size
  • Gap or edge thickness
  • Minimum bend radius

To determine the required bulb size, measure the distance between the door and the jam when the door is closed. As a rule of thumb, add between 25% and 50% to this measurement to account for compression. Over-compressing the bulb will not create a better seal. In fact, over-compression can reduce seal life and cause compression set.

Next, specify the gap or edge thickness for the retainer section. This measurement is the distance between the two “legs” or straight sections of the retainer. As a rule, choose a bulb trim seal where the gap equals the flange or substrate. In other words, select a bulb trim seal with a gap of 1/2” for a flange or substrate that’s 1/2”. Specifying a larger or smaller gap may result in leakage.

The PVC that’s used in bulb trim seals can avoid kinking, but only if the angle isn’t too great (i.e., less than 90°). If the bend radius is too large, recesses or valleys may form and allow the passage of water. The results can range from leaky doors in vehicles interiors to drafty exterior doors on enclosures. To avoid these problems, specify a minimum bend radius that’s appropriate for your application.

Color, Texture, Internal Supports, and Exterior Finishes

Most industrial rubber products are black, but bulb trim seals are used in a variety of product designs.  That’s why Elasto Proxy also offers sealing solutions that come in colors such as white, off-white, beige, tan, and gray. We can also source bulb trim seals with specific textures. Many industrial rubber products are flat and smooth, but bulb trim seals with coarse, pebbly, or ribbed finishes are available.

Finally, note that the retainer section of a bulb trim seal can include an internal clip that’s made of aluminum or steel. This metal clip promotes permanent gripping under application conditions such as the opening and closing of doors. The retainer portion of the seal may also support the use of a hot-melt adhesive for fastening, and may have an outer coating made of vinyl to impart a textured finish.

Find the Bulb Trim Seals You Need

Do you need bulb trim seals for doors, hatches, or enclosures? Elasto Proxy is ready to help. Contact us for more information.

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