Mechanical Face Seals

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  • Description
  • Properties
  • Technical data
  • Dimensions

Description

Mechanical Face Seals consist of two metal seals and two elastomeric components, which are mounted into two separate housings. The elastomeric parts, as a secondary seal, take over the function of the elastic force of the spring, the static sealing between the sliding ring and the housing as well as the torque transmission. The perfectly lapped contact surfaces of both metal sealing rings are pressed and axially slide on each other.

 

An essential functional feature of the Mechanical Face Seal is a robust construction form combined with very long lifecycles. The selection of the most suitable materials for the sliding ring and elastomeric part ensure high wear resistance. Mechanical Face Seals guarantee a fully adequate corrosion protection, as well as optimal lubricant and temperature resistance. O-rings’ materials assure minimal power loss over the life of the drive seal. Thus, this seal typology is technically superior to other types of construction.

 

Mechanical Face Seals are especially used for rotary shafts in severe and dirty environments. Due to their outstanding technical features Mechanical Face Seals have achieved worldwide distribution.

 

Different geometric designs and material types of metal and rubber parts can be found depending on the application and construction of the sealed units. The standard seal (FS1) usually consists of two metal rings and two O-rings assembled into a set, inserted into particularly shaped, conical cavities. Another type of design is called “Square Bore Seals” (FS2), which fit in cylindrical cavities using a diamond-shaped rubber part instead of the O-ring.

 

Depending on application, design characteristics and operating conditions, the selection of the most appropriate sealing system is implemented.

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Properties

As a result of permanent operations in adverse and dirty environments the sealed units and vehicles are exposed to extreme and constant strain. In all “outdoor” applications such as coal-mining, open-cast mining, construction industry, agricultural- and forestry applications, chemistry, waste disposal and removal industries, water treatment, wind craft energy, offshore drilling etc. the following abrasive and corrosive media have to be taken into account: 


• sand, loam, mud, earth, stone, lime sandstone, granite, basalt;
• concrete, lime, potash, rubble, grit, slag, glass, asphalt, bitumen;
• chemicals, liquids, salts, lye, acids;
• sewage water, rainwater, harbor water, dirty water, sea water.


Additionally, in combination to extreme weather conditions such as -55 [°C] / -131 [°F] to +200 [°C] / +392 [°F] and corrosive surroundings, e.g. maritime climate, the Mechanical Face Seal solutions proved to be highly reliable and functional in a wide range of applications.

 

Mechanical Face Seals distinguish themselves in many application due to three outstanding advantages:

 

• prevention of entry of abrasive dirt, contamination and media into the sealing space;
• avoidance of leakage (oil or grease) from the sealing space;
• extremely high wear resistance according to application.

 

Selection of appropriate Mechanical Face Seal

Cast Iron and Steel

 

As a result of very high requirements for the wear resistance of Mechanical Face Seals DICHTA® uses cast iron (15Cr3Mo) or steel (GCr15/100Cr6) with a hardness range from 58 to 68 HRC. The extremely high wear resistance is reached thanks to a carbidic-martensite structure of the material and a selection of the alloy elements as well as their concentration. Cast iron ring are suitable for extreme operating conditions: thanks to its material structure and its high hardness values cast iron can operate at pressures up to 0.3 [MPa] and rotating speed up to 2 [m/s], ensuring a lifetime up to 5000 hours. For lower speeds (≤2 [m/s]) and lower pressure values (≤0.15 [MPa]) bearing steel GCr15 (100Cr6) can be a good alternative.

 

Individual Material Recipes

 

Depending on the media that has to be sealed off, it is possible to tailor individual material recipes for a special high alloy cast in order to substantially increase life span and wear resistance of the Mechanical Face Seal. Individual recipes of high alloy cast for sealing solutions in biogas fermentation plants or harrowing machinery with chemical exposure to slurry show substantial improvements with respect to life cycles, wear resistance and corrosion resistance.

Selection of appropriate o-ring material

High thermal resistance and a low compression set are the essential criteria for the elastomeric material in demanding applications. The normal NBR compound meets these requirements. For higher thermal stresses the O-rings are made of HNBR, VMQ or FPM. The oil compatibility of several elastomers has to be assessed. The elastomeric materials listed are offered in various degrees of hardness, so that the O-ring can adequately perform its function of generating a permanent and consistent contact pressure within the sealing system.