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MECHANICAL
FACE SEALS
Mechanical Face Seals
Mechanical Face Seals are designed to be employed in most exhaustive working conditions, accepted worldwide to use in extremely harsh environments under enormous stresses, sand, dirt, mud dust and earth material. Sealing technology for static or dynamic applications is mainly concerned with providing sealing solutions for machinery and applications in which conventional seals fail or lack the necessary durability.
What to expect from Mechanical Face Seals
The static as well as dynamic leakage prevention must be guaranteed. The heat generated at sealing faces die to friction must be dissipated with adequate oil flow in the sealing system. The pressure spikes in the application must be handled by the sealing system.
Mechanical Face Seals must withstand to circumferential speed of up to 10 m/sec.
The sealing faces must be continuously lubricated to prevent any cold welding due to excessive heat generated rubbing.
The sealing faces should be in contact all the time to prevent leakage. Same is about elastomer contact with the sealing system.
Sealing Function
The mechanical face seals are designed in such a way that they open out from the seal faces towards the centre axis, forming a cone-shaped gap which has following benefits:
due to capillary action in the gap and centrifugal force, lubricant admits easily into the seal faces, potential cold welding of the seal faces is avoided since adequate lubrication and cooling is assured, as wear goes on, sealing band increases and it can virtually only end when the seal collar gets completely worn out. This sealing system retains a continuous oil film in the sealing surfaces
The alloy cast iron seal rings are preloaded by Torric rings or O-Rings. As a result, the axial load closes the gap between the seal faces, which leads to the sealing function. The relative movement in circumferential direction is only taking place between the seal faces.Significance of elastomer O-Rings in seal assembly: axial load experienced by sealing faces is due to O-Ring pressure, friction torque is transmitted through O-ring and housing components, static sealing between each seal and housing is ensured by O-Ring
Lubrication Requirements
Oil Lubrication:
The use of oil lubrication considerably increases seal life on account of higher heat dissipation properties of the oil. It is however selected considering the field of application, arrangement available in the system for oil circulation and peripheral speed., Normally higher RPM applications prefer oil lubrication.
As as standard, transmission oil of grades SAE80 and SEA90 are found to be suitable for typical mechanical face seal operation.
The oil level after filling should be 2/3 of the available volume of oil housing and above the seal axis. When filled to the correct level normally it is sufficient for the lifetime if the seal. Hence the seal faces require no additional maintenance
Grease Lubrication:
When the applications are with low sliding speeds, to an extent of 1 m/s, grease lubrication is the right consideration as a permanent lubrication to the sealing system. Seal face gap is important design view in this selection. The maintenance care needs to be taken while filling grease is that, if the gun pressure is increased chances of dislodging the elastomeric torric rings.
Mechanical Face Seal DO-Type
The DO-Type mechanical face seal consist of two identical metal face seals and two rubber O_Rings placed on the ramp profile of the metal seal. SAPPARTS Seals come in twi material versions – Alloy cast iron and Alloy Forged Steel grades. The O-ring materials however are of a variety of types based on the application requirements.
In cast oran alloys, SAPPARTS propose twi proprietary compositions, selection of which is based on applications requirements.
At Seal assembly the O-Rings are compressed between the tapered contact surfaces of the seal ring and housing. The O-Rings undergo a calculated compression as per SAPPARTS standards it is around 25% volumetric compression, which is critical fore proper operation of the sealing system. Also the overall system cleanliness of the O-Rings and housing free of oil and dirt is of primary importance. Lubrication of the O-Rings with oil or grease is not permitted during the installation process.
Mechanical Face Seal DF-Type
The mechanical face seal of DF Type consists of two metallic angular seal rings with identical geometrical profiles. The seal rings are assembled with trapezoid rubber rings which are placed in the particular housing bore. The geometry of the housing profile is comparatively easier to produce and the seal installation requires a simple installation tool. As compared to the DO – type Mechanical face seals, the resilience of the trapezoid rubber ring is normally stiffer. This limits the permitted axial movement and tolerance.
Historically numerous mechanical face seal designs were developed based on a variety of application needs. SAPPARTS has few unique designs extremely suitable for demanding applications and adverse operating condition. The design of one of the seal in the group is inverted to the other seal. This provides considerable advantage in the manufacturing process of the sealing systems mating components.
