Doug Sharpe President of Elasto Proxy
Dual-Durometer Rubber Bulb Trim Seals
Bulb trim seals are dual durometer rubber seals with bulb and retainer sections. Typically, the bulb is made of a medium-density foam or sponge rubber such as EPDM. The retainer or trim portion is often made of another rubber material, such as PVC. Because of their design and materials of construction, bulb seals and trim seals offer resistance to water, ozone, sunlight, and a range of service temperatures.
How to Select Rubber Trim for Indoor and Outdoor Applications
Buyers of bulb trim seals need to consider specifications such as seal dimensions and weight, durometer and shape, and rubber compound. Depending upon the application and industry, parameters such as temperature range, flammability, and code compliance may be also important to consider. Although most bulb seals and trim seals are black, rubber parts with different colors are available.
Bulb trim seals typically have A, B, C, D, and E measurements. Durometer, a measure of hardness, is given in duro. Bulb trim seals vary in terms of shape, and may feature the bulb portion of the seal in different locations. Bulbs also vary in size and have an inch-based inner diameter (ID) and outer diameter (OD). Weatherstripping and window rubber may have additional parameters.
EPDM, TPR, PVC, and TPE Bulb Trim Seals
Although some bulbs use 80-duro rubber, most feature medium-density EPDM. A synthetic rubber, EPDM is a closed-cell sponge material that resists moisture and withstands temperature extremes. This versatile, reliable compound also provides a relatively high degree of electrical insulation. Unlike many elastomers, EPDM also exhibits superior UV resistance, making it a good choice for outdoor applications.
Bulb trim seals are available in various types of thermoplastic rubber (TPR). Weather-resistant, reusable, and often recyclable, TPRs will repeatedly soften when heated and stiffen when cooled. Thermoplastic elastomers (TPE), which are sometimes referred to as thermoplastic rubbers, are polymers that have both thermoplastic and rubber-like (elastomeric) properties.
Thermoplastic rubbers are more expensive than other compounds, but offer advantages over popular plastics such as polyvinyl chloride (PVC) Flexible and pliable, TPE is less likely to break, especially in cold temperatures. Thermoplastic elastomers also offer good shape memory and lower thermal conductivity, an important consideration in some applications.
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