Views: 0 Author: Site Editor Publish Time: 2022-07-27 Origin: Site
Seals are parts that prevent the leakage of internal substances in mechanical equipment and the intrusion of external impurities into the interior. They are widely used in the industrial field and are indispensable. The performance of seals directly affects the performance of mechanical equipment. Due to the special working environment in the aerospace field, the performance requirements of seals are higher. Aerospace seals are high-end seal products with high technical barriers.
Due to the special working environment, aerospace seals have high requirements on materials. For example, fuel tank seals need to consider whether the material can resist fuel corrosion, as well as its high temperature resistance, pressure resistance, vibration resistance, service life and other characteristics. The main raw materials used in aerospace seals are rubber, such as fluororubber, perfluororubber, silicone rubber, fluorosilicone rubber, hydrogenated nitrile rubber, EPDM rubber, etc. The products made include O-rings, hydraulic seals parts, rotary seals, pneumatic seals, static seals, oil seals, etc.
Seals are mainly divided into three categories: seals, gaskets and oil scraper rings.
A seal may consist of more than one component, such as an O-ring and a back-up ring, or it may consist of an O-ring and two back-up rings. Hydraulic seals used inside sliding or moving components are often referred to as packings. The hydraulic seal used between the stationary joint and the boss is often called a gasket.
1. Sealing ring
a. V-ring seal
The V-shaped sealing ring is a one-way seal, and the open end of the V-shaped sealing ring always faces the pressure during installation. Once installed, the V-ring must have male and female connectors to hold it in place. The sealing cover must also be tightened to the specified torque value or it may not provide the desired sealing effect.
b. U-shaped seal
U-ring seals and U-cup seals are used for brake assemblies and brake main actuators. U-seals and U-cup seals are pressurized in only one direction. Therefore, the edge of the seal must face the pressure. U-ring seals are primarily used for low pressure sealing, with pressures less than 1000 psi.
c. O-ring seal
Most seals and gaskets used in aircraft are manufactured in the form of O-rings. The shape of the O-ring is circular with a small cross-section relative to its diameter. The cross-sections are true circles that have been shaped and trimmed to very close tolerances. O-ring seals provide an effective seal in both directions. This sealing is accomplished by elastic deformation of the extrusion of its material.
Advances in aircraft design have necessitated new O-ring configurations to meet changing conditions. Hydraulic O-rings were originally established to U.S. Air Force-Navy (AN) specification numbers 6227, 6230, and 6290 for use in fluids operating at temperatures between -65°F and +160°F. More chemicals were developed and refined as new designs raised the operating temperature to a possible +275 degrees Fahrenheit.
d. Support ring
Back-up rings, also known as Anti-extrusion rings, are used to prevent the seal from being extruded. Back-up rings made of PTFE will not deteriorate over time, are not affected by any system fluids or vapors, and can withstand temperatures exceeding those encountered in high pressure hydraulic systems. Inspection of the support ring should include ensuring that the surface has no irregularities, that the openings are clean and sharp, and that the opening cuts are parallel.
The gasket serves as a static (fixed) seal between two flat surfaces. Some of the more common gasket materials are asbestos, copper, cork, and rubber.
Wherever heat resistant gaskets are required, asbestos film is used, and it is widely used in exhaust system gaskets. Most asbestos air-entraining gaskets have a thin copper edge for extended life. Solid copper gaskets are used for ignition nozzle gaskets, in which there must be an incompressible semi-soft gasket.
Cork gaskets are used as oil seals between engine crankcases and accessories, and where gaskets are required, the gaskets are capable of taking up uneven or varying spaces due to rough surfaces or expansion and contraction.
Rubber gaskets can be used where a compressible gasket is required. But it should not be used anywhere where it may come into contact with gasoline or oil, as rubber deteriorates rapidly when exposed to these substances. Used in fluid systems around end covers of actuator cylinders, valves and other components. Gaskets commonly used for this purpose are O-rings, similar to O-rings.
3. Oil scraper
The wiper ring is used to clean and lubricate the exposed part of the piston shaft. They keep contaminants out of the system and help protect the piston shaft from scratches.
The wiper ring can be metal or felt. They are sometimes used together, with a felt wiper ring mounted behind the metal wiper ring.