Bonded seals are composed of a round or square metallic washer that is adhered to a seal similar to an o-ring; they are found in both hydraulic and pneumatic connections that are exposed to extreme pressure. They are bonded together inside the diameter to provide low to high-pressure sealing, but they are used mostly in high-pressure applications.
Bonded seals are lightweight, thermally conductive and have good corrosion resistance, ductility and strength. Originally used to replace copper washers in high pressure systems, bonded seals are used to seal bolted connections, mounted elements, pipe connections and couplings. The metal washer component can be made of carbon steel, zinc-plated stainless steel, aluminum, brass, bronze and copper, while the elastomeric part is usually a rubber material with ductility and elasticity; it can be made of ethylene or nitrile butadiene because of their resistance to oil, moisture, extreme temperatures and many different abrasive chemicals. Bonded seals are a unique type of seal because they are made of a metal washer, while other types are solely an elastomeric ring. The metallic component resists pressure caused from bursting forces and helps to prevent deformation of the rubber component, which resists over-compression and extrusion.
The bonded seal begins as two separate pieces - the metal washer and elastomeric o-ring. In order to form a strong, adherent bond between the two different materials, the rubber to metal bonding process is used. Each rubber seal is adhered to the metal part using a bonding agent made of polymer-solvent solutions that are applied in two layers - first a phenolic resin, then a topcoat of polymer. While the metal part is often plated or galvanized with zinc to improve its strength and oxidation resisting properties, the metal has a surface finish of cadmium plating, chromic anodizing, clear passivating, zinc plating and gold passivating. The rubber part is always vulcanized, a process that converts the rubber or polymer material into a more durable substance by adding sulfur or other curatives. The material becomes less sticky and exhibits improved mechanical properties. All bonded seals are available in a wide variety of sizes and dimensions. They are usually manufactured quickly, inexpensively and in very high volumes. Compared to other types of seals, they are very durable, have high tensile strength and last for long periods of time.
