Some of the first loading dock seals — those fabric-wrapped foam pads surrounding dock door openings — were installed in 1959 to help prevent the infiltration of outside elements into a facility while trailers were loaded and unloaded. They quickly became popular throughout the world as a relatively low cost way to save energy and gain environmental control at the dock. There was one problem, however.
By nature of their function and design (repeatedly impacted and compressed by semi-trailers) dock seals were subject to damage. Wear and tear can come quickly on a dock with heavy trailer traffic, resulting in diminished sealing effectiveness, tattered appearance, and high repair and replacement costs.
Today, however, advances in materials and engineering have led to “new age” dock seals that withstand the abuses of today's trailers and dock conditions. The result is greater sustainable durability and performance.
Controlling the Elements
Foam dock seals form a snug gasket-type seal around the sides and tops of a trailer as it is backed into the loading dock. The tightly compressed seal helps keep heated or cooled air inside the building when the dock door is open and goods are being loaded or unloaded. Studies show that companies can reduce their energy costs by hundreds of dollars per year per dock position, simply by installing an effective seal that is sized and applied to match the variety of trailers being serviced. Seals also help keep outside elements from entering the facility, which protects products from damage, keeps employees safe and comfortable, and reduces infiltration of bugs, dust and other contaminants.
Dock seals typically perform well the first few years after installation, but they soon begin to wear out due to the pressure and friction inflicted by constant contact. Throughout the years, dock seal damage has been accepted as a costly but inevitable reality. Companies simply became accustomed to the ongoing costs of seal maintenance and replacement, or the shabby appearance and diminishing effectiveness of seals that weren't regularly repaired or replaced. Yet continually rising energy costs, the ongoing need for improved profit margins, and increased attention to safety and regulatory issues dictated the need for significant improvements in dock seal technology.
The sources of dock seal damage
Dock seals are severely compressed against the building wall every time an 80,000 lb. trailer backs into the dock. Besides compression, most of the damage has to do with how the trailers and seals interact and “fight” each other while in use.
The following findings from research and development in dock seals over the years have guided the industry's product improvement efforts:
Dock seal corners wear out first. Sharp projections in trailer corners dig, cut and chew into the foam and vinyl cover fabric. Dock seal manufacturers began reinforcing this area with additional layers of fabric, called wear pleats, in 1962. Pleats are helpful and provide some protection, yet this still remains the most damage-prone area of dock seals today.
Trailer motion causes extreme friction. As trailers “bounce” up and down during loading and unloading, dock seals - under great pressure of the backed-in trailer - are constantly abraded. Wear pleats were added to dock seal side pads early on to help resist this friction, but the advent of air-ride trailers in the 1980s and ‘90s exacerbated the problem. Tougher and more wear-resistant fabrics have also been introduced over the years, yet despite the improvements, the immense pressure and friction from trailer motion continue to destroy dock seal components.
On docks that use yard jockeys (also known as yard mules or shunt trucks), which shuttle trailers between dock positions, dock seals are subject to some unique sources of damage. When trailers are raised while parked at the dock, extreme inward and downward pressure is exerted against the dock seal head pad. The severe tugging motion can cause the foam of the head pad to separate from its backer and twist or sag as a result. Also, when a raised trailer is shuttled to a dock position and then lowered into place, the rear of the trailer frequently becomes caught beneath the head pad, and simply pries it off the wall. This problem, often referred to as “head pad pop-off,” creates a costly maintenance headache.
Head pads burn from compressed trailer marker lights. The frequency of fires at the loading dock originating in dock seal head pads has been well documented since the late 1990s, when the National Highway Traffic Safety Administration (NHTSA) began requiring all over-the-road trailers to be equipped with identifying marker lights at the top rear of the rigs. When the lights are compressed into foam seals at the dock, the heat from the lights begins to build, gradually reaching dangerously high temperatures. Foam begins to smolder, and if a trailer is in place long enough (as little as 20-30 minutes), the head pad can burn.
These costly damage issues had plagued the industry for years, and grown in significance as companies struggled to reduce costs yet maintain the effectiveness of the critical environmental control at their docks. In response, dock seal manufacturers have taken advantage of emerging technologies in materials and design to address each of these issues.
Solving seal problems
Armed with a solid understanding of how and why dock seals were being damaged, industry engineers began seeking ways to design dock seal features that would resist damage by reducing or eliminating the source. Some of the more recent improvements include:
Technically advanced materials - Some modern, high-wear dock seal fabrics have a rough or pebble-grained surface. These friction-resistant fabrics create a “slippery” surface that trailers slide against when in motion at the dock, thus better protecting the fabric from wear.
Pads without pleats - With new fabrics comes the ability to do away with traditional sewn-on wear pleats. Replacing pleats on seal corners and side pads with single-surface, friction-resistant reinforcing components, allows manufacturers to remove sew lines and fabric catch points. The result is less chance for tearing and snagging and greater overall resistance to damage and wear over time.
Reinforced wear points - Upper corners and insides of the side pads are now frequently reinforced with multiple layers of materials to resist damage in these high-wear areas. High molecular-weight polyethylene (HMWPE) sheeting and friction-resistant fabrics have become popular materials in reinforcing high-impact, damage-prone areas of the seals.
Replaceable wear components - Parts of the dock seal that wear out fastest (such as the upper corners) have become easy to remove and replace in some dock seals, reducing maintenance costs and minimizing the need for larger, more costly repairs.
Impactable, movable headers - To help prevent dock seal head pads from sagging and keep them sturdy under impact, some are designed with internal reinforcing panels imbedded in the foam. Other protective measures include eliminating the steel or wood backer so the head pad can “float” with trailer movement, reducing friction and wear. This pivoting action also prevents head pads from being pried off the wall when encountering yard jockeys. Similarly, dock seals with head curtains (for larger door openings) have traditionally been built with rigid framing that can be damaged by trailers backing in off center and higher than expected (such as over packed snow). Newer designs are made from impactable materials such as HMWPE and can sustain trailer impact without damage.
Heat-dissipating materials - When dock seal fires became prevalent in the early 2000s, dock seal manufacturers quickly explored ways to combat the danger. Fire-retardant foam and fabric were found to be ineffective in preventing the heat build-up that lead to these fires, so heat-dissipating layered foil technology was added to in the early 2000s to protect against the damage and danger of burning headers.
In conclusion, advanced materials and designs have added years to the productive life of dock seals, keeping them performing better and longer, and reducing repair and replacement costs in the process.
Mary Blaser is director of marketing for Frommelt Products Corporation, a Rite-Hite Company.