THE EGG: DIRECT FIXATION FASTENER

The Egg is a vibration-attenuating track fastener, appropriate for direct fixation environments - at grade, aerial structures and tunnels. In service in the U.S. since 1983, the Egg owes its excellent acoustical performance and superior maintenance records to its unique design. Vertical forces are cushioned as rubber is placed in shear when the Egg deflects under load from passing trains. The Egg can now be found in installations across the U.S.

The Egg track fastener is specifically designed to reduce ground-borne vibration, the cause of secondary noise in buildings neighboring transit tracks. The Egg name is derived from its characteristic oval shape.

Egg-type fasteners consist of two metal components, the Top Plate and Frame, bonded together with elastomer. Ductile iron was selected as the best suited for all metal components for reasons of strength, endurance, corrosion resistance and economics. Except under unusual conditions, rubber is the elastomer of choice due to its superior spring performance and enduring life-time characteristics (i.e. dynamic stiffness).

The rail rests on the Top Plate which is oval. Its side surface is angled with respect to the vertical. There is a corresponding angled oval surface built into the outer containment Frame which supports the Top Plate and also houses the anchor bolt holes. The Top Plate is suspended on a belt of elastomer, bonding it to the mating angled surface of the Frame. This allows the Top Plate to “float” and geometry dictates that vertical forces be transmitted largely in shear and only partially in compression. This is perhaps the single most significant feature explaining the unique acoustical effectiveness of the Egg-type design.

Equally important, the geometry also provides “fail-safe” maintenance of track gauge. Thus, the Egg-type design creates the vital combination of lateral integrity and vertical softness. Reacting to overload, or the unlikely event of elastomer failure, the Top Plate sinks further and further into the “nest” provided by the Frame. As it does, lateral stability is not only maintained, but is increased - a huge safety benefit, particularly on curves.

The belt of elastomer separating the two metal components, not only dampens rail forces, but also provides excellent electrical isolation.

Vertical stiffness can be adjusted to customer preference by altering elastomer thickness and/or varying hardness. Typical static stiffnesses are in the range of 50,000 and 75,000 pounds per inch. Stiffness range is approximate. Contact us for more details.