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Mechanical Face Seals

Applications

Static and dynamic sealing technology is concerned with providing sealing solutions for machinery applications in which conventional seals lack the required durability.

The drive mechanisms for tracked vehicles and construction machinery, or the power transmission equipment for conveyor systems, sand conditioning plant, concrete and cement mixers, mining machinery and similar heavy plant are subjected to extreme abrasive stresses in the environment in which they work.

Failures can severely disrupt operations, and repairs are extremely cost-intensive.

Our metallic mechanical face seals have served well in such demanding conditions for years.

In a robust and efficient way they guarantee our customers high serviceability, long durability and maximum productivity of their equipment.

Operating Parameters

• Especially on tracked vehicles it is of vital importance to protect the bearing of the track rollers, carriers and idlers as well as the final drives or axle hubs effectively against abrasive media such as dust, sand, mud, stones or earth.
• Peripheral speeds of up to 10 m/sec can be handled.
• The friction heat generated at the contact faces between the static and dynamic components of the seal must be dissipated by ensuring an adequate supply of lubricant.
• The seal faces must be continuously lubricated in order to prevent cold welding.
• Friction loss must be minimized.
• Corrosion during stationary periods must be avoided.
• The adjustment forces within the sealing system must be tuned to the wear rate of contacting seal faces.
• The static leak-tightness towards the air side must be guaranteed.

Designs

Mechanical Face Seal Type 76.90H / 76.97H

There are no fundamental differences between types 76.90H and 76.97H, and both are fully interchangeable. Unlike 76.90H, however, the outer profile of type 76.97H is not ground, giving it the benefit of even better torque transmission.

Design
Mechanical face seal type 76.90H / 76.97H consists of two geometrically identical metallic seal rings, located against the respective housing bores by means of large-volume O-rings.

At installation, the O-rings lodged between the tapered contact faces of the seal ring and housing undergo a defined deformation which is crucial to permanent operation of the sealing system (dimension "A")

Mode of Operation
The resilience of the O-Rings acts in a number of ways:

• Exertion of axial load on the metallic sealing faces
• Transmission of the friction torque to the housing components
• Static sealing between each seal ring and its housing bore

The seal faces of the metallic rings are finely lapped to a radial width of about 2.5 mm. The rings 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 the following benefits:

• The lubricant is readily admitted to the seal faces by capillary action and centrifugal force.
• Adequate lubrication and cooling are assured and potential cold welding of the seal faces is avoided.
• As wear increases, the sealing face continuously shifts towards the centre axis.Therefore, the seal has considerable wear reserves which virtually only end when the inside diameter is reached.
• As a result of the system a slight oil film can appear on the outer sealing surface.

Adapter Rings - Type 76.91
In some sealing applications the use of the standard design 76.90H / 76.97H is more complicated because of functional, constructive or production related reasons. This is the case, for example, when the seal type 76.90H / 76.97H is fitted into cylindrical bores.

The adapter ring also facilitates a quick repairing possibility, e.g. for maintenance of coal mining machines direct on-site below ground. Therefore, a laborious disassembly and delivery of the parts to the workshop for refinishing is not necessary.

In many cases, such initial problems can be solved fairly easily by using adapter rings type 76.91, which afterwards enable the standard seal to be fitted.

The adapter rings are available in two forms, A and B, consisting of deep-drawn sheet metal casings sheathed in an oil-resistant elastomer material. The rubber-like, ribbed profile of the outer surface ensures static sealing and transmission of torque and protects from corrosion.

Further Information
For more infomation please contact Tony Snowdon at FTL Technology on 0113 252 1061 or e-mail tonys@ftltech.co.uk