Technical Information - Composite Sealing Systems Division | Parker US
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Find performance data, leak rates, installation guides, specifications and more to help fine tune your metal seal design.

PERFORMANCE DATA

All metal seals, except for metal wire rings, are designed to undergo both plastic and elastic deformation when installed. (Wire rings are essentially limited to plastic deformation only.)

Plastic deformation of the jacket, or O-ring tubing, enlarges the contact area, or "footprint," to bridge across surface imperfections or tool marks in the mating surfaces. It also creates a reduced gradient in the load/deflection curve to permit a wide tolerance in the working height, resulting in a robust sealing process. High integrity sealing is ensured by the ductile outer layer or coating which, being inelastic and of low compressive yield strength, flows into and fills the mating surface crevices.

Elastic deformation provides elastic recovery or "springback" to maintain good sealing, despite separation of the mating surfaces due to the effects of thermal cycling, flange rotation, applied mechanical or hydrostatic loads or creep.

Download the PDF below to learn more about the terminology.

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LEAK RATE INFORMATION


The graph herein shows typical ranges of leakage rates that may be expected with various types of seals. 

The widths of the horizontal bars indicate the spread of leakage values that may be expected depending on the specific plating selection and surface condition.

As a service to our customers, we are pleased to offer specific seal performance testing and analysis for unusually challenging and “mission critical” applications. Testing can be set up to reproduce the actual conditions expected in service. Please contact your local Parker representative. 

Download the Leak Rate Information PDF below.

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FATIGUE AND STRESS RELAXATION

Fatigue is the main failure mechanism in a material that is subjected to fluctuating loads. Under cyclic loading, localized slip bands can form in regions of high localized stresses. As fluctuating loading continues, these bands increase in number and small microscopic cracks form. Given enough time and stress amplitude, the cracks will grow and propagate through the wall of the seal resulting in a fatigue failure and leakage.

Stress Relaxation
Any highly stressed component, held at high temperatures, is subject to a form of permanent deformation known as stress relaxation. Unlike creep, stress relaxation occurs in a relatively short period of time, typically in as little as 100 hours of exposure time. This is an important design consideration in any critical sealing application at elevated temperature. Stress relaxationcompromises both the sealing load and springback properties of the seal, impacting its ability to maintain sealing integrity under both static and dynamic conditions.

Parker Hannifin has extensive experience designing and testing seals to mitigate the negative effects of stress relaxation. Seals can be designed to optimize resistance to stress relaxation through careful consideration of geometry, materials and appropriate heat treatment.

Download the Fatigue and Stress Relaxation Data PDF below.

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INSTALLATION GUIDELINES

In addition to the required cavity dimensions provided under Material Selection, there are other important cavity design issues which affect seal performance including the roughness and waviness of the mating surfaces.

Surface Roughness Recommendations
The roughness of the mating surfaces directly affects the leak rate when using unplated seals. Selecting high load eals with appropriate plating can substantially offset the ffects of rough finishes; however, the guidelines in the able, left should be followed whenever possible. We also recommend a turned finish with a circular lay.

Surface Flatness Recommendations
Metal seals can accommodate some degree of waviness,or lack of flatness of the mating surfaces. Spring energized seals offer the greatest amount of compliance since each coil of the spring acts as an independent force to assist the jacket in conforming to the mating surface. (download PDF for more details)

Surface Hardness Recommendations
Many metal seals are designed to produce high seating loads against the mating surfaces to meet ultra low leakage requirements. To withstand these high compressive stresses, without damage to the sealing surfaces, requires these surfaces to have a hardness of at least 35 Rc. This is particularly important when the seal seating load exceeds 200 lb/inch (35 N/mm) of circumference. 

Download the Installation Guidelines PDF below.

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BOLT LOAD & TIGHTENING TORQUE GUIDELINES

Download the Bolt Load & Tightening Torque Guidelines PDF below.

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SEAL SHAPING REQUIREMENTS FOR NON-CIRCULAR SEALS

All standard metal seals can be formed into various shapes. The illustration below shows some of the many shapes in which metal seals can be made. For applications as varied as fuel nozzle mounting flanges on aircraft gas turbine engines, or dies for extrusion of plastic film, the availability of specially shaped metal seals offers the greatest design flexibility.

Download our table which provides the minimum outer corner radius for the various cross sections of metal C-rings, O-rings, spring energized C-rings, wire rings, E-rings and U-rings. All shaped seals are custom designed by our engineers.

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METAL SEAL MANUFACTURING SPECIFICATIONS


The table herein provides the allowable roundness and flatness for standard metal seals: C-rings, E-rings, O-rings, U-rings, spring energized C-rings, and spring energized O-rings in an unrestrained state. When restrained, the seal diameter shall be within the limits specified in Section C for axial seals, roundness and flatness allowances. Note: Values are reference only.

Definition of Roundness
Difference between the largest measured reading and the lowest measured reading.

Definition of Flatness
The greatest distance between a theoretically flat surface and an unrestrained seal when placed on that surface.

Metal Seal Surface Finish
All unplated and plated metal seals are produced with a 16 μ inch Ra surface finish.


Metal O-Ring Weld Finishing
The Metal O-Ring weld process results in a weld fillet which is finished and smoothed to the adjacent surfaces. The surface at the blend area shall not be more than 0.002 inch below the adjacent surfaces.

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REFERENCE TABLES

Tolerance Reference & Conversion Tables

Download these tables consistent with the American National Standard Tolerances (ANSI B4.1) and the British Standard for Metric ISO Limits and Fits (BS 4500).
 

Tolerance Reference & Conversion Tables

 

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