Seal Rounded Corners with Bulb Trim Seals Do you need to seal rounded corners against wind, water, dust, or dirt? Bulb trim seals are industrial rubber products that provide sealing and insulation for machine doors, vehicle hatches, and equipment enclosures. They’re designed to seal rounded corners and have separate bulb and retainer sections. Each of these sections can use a different material and have a different durometer or hardness.

With bulb trim, the bulb section compresses to form a seal when the door, hatch, or enclosure is closed. The trim or retainer section attaches to a flange or substrate. To choose bulb trim for your application, you need to specify the bulb size, bend radius, and flange thickness. By choosing the right bulb size, you can avoid over-compression. The right bend radius and flange thickness help to avoid kinking and leakage.

Bulb Size

Choose a bulb that’s large enough to fill the gap but that will compress to form a reliable, long-lasting seal. For example, a door seal needs to fill the gap between the edges of the door and a frame. When the door is closed, the seal compresses to prevent the entry of wind, water, dust, or dirt. If the seal works properly, the rubber will “rebound” when the door is open and then compress again when the door is closed.

Determining the bulb-size you need 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 compression percentage to this amount. As a rule of thumb, apply between 25% and 50%. Do not apply more than 50% because over-compressing the bulb won’t 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’s applied to a material is removed.

Bend Radius

Remember that unlike some other industrial rubber products, bulb trim seals aren’t designed for 90-degree corners. To accommodate rounded or radiused corners then, you need a bulb trim 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.

Keep these guidelines in mind, too. A more flexible material can support a smaller bend radius, but a radius that’s too tight can cause the corners to “pop” out. It’s also important to avoid using a bend radius that’s too large. Otherwise, recesses may form and allow the passage of wind, water, dust, or dirt. The results can range from drafty doors on mobile equipment to leaky doors on electronic enclosures.

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 a 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.

Seal Rounded Corners with Bulb Trim from Elasto Proxy

Do you need to seal rounded corners against wind, water, dust, or dirt? Elasto Proxy stocks standard bulb trim and can custom-fabricate the industrial rubber products that you need. As this video shows, our abrasive water jet cutting machine can make 45° cuts for bulb trim seals. Digital manufacturing is faster and more accurate than manual cutting, so it pays to learn more.

Would you like to some sample bulb trim for yourself ? Then let us know what you need.