Resilient Metal Seals

Resilient metal seals from GFD have already proven themselves worldwide under the most diverse extreme operating conditions. They are used when conventional sealing products can no longer meet the parameters and requirements in new or existing applications.

For example, when the conventional seal is not suitable for the temperature range or the flat gasket cannot compensate for flange gaping or the required leakage rate cannot be achieved by the seal previously used.

Possible applications and advantages:

  • Seal for vacuum, gases and liquids under extreme operating conditions.
  • Applicable in pressure ranges from UHV up to 5000bar at service temperatures from -269°C to 750°C.
  • Resistant against radioactive radiation, chlorides, corrosion and other aggressive influences. No aging.
  • Can be optimally adjusted to parameters and requirements in the application through a variety of possible combinations
  • Achievement of lowest leakage rates through additional coating
  • Maintenance of tightness even when the flange is lifted off by elastic compensation behaviour of the seal
  • Resistant to explosive decompression
  • Simple force calculations, since ring works in force shunt.
Any questions? Contact us!

We are known as a problem solver in the field of resilient metal seals. Every application is tested and evaluated by our technical department on the basis of years of experience in order to provide the best possible solution for your application.

Resilient metal seals from GFD are available in a variety of different types, cross sections, wall thicknesses, materials, coatings, coating thicknesses and heat treatments.

Diameters can be defined by the customer starting with the minimum diameters, which depend on the seal type and cross section. Due to the resulting infinite combination possibilities, these sealing elements are manufactured by GFD order-related. For the selection of the most suitable sealing element for your application you are free to contact the technical support of GFD. Please let us know the relevant parameters, e.g. temperature, pressure, medium, surface quality, etc., as well as the requirements in the application, e.g. required leakage rate, load cycles, expected flange lift-off, etc.

By pressing the sealing element from the original cross section (A) to the required groove depth (C), the maximum press load (F max) is generated. In this process, the ring is not only deformed elastically (A-B) but also plastically (B-C). In the case of coated rings, the press load also causes the coating to flow. Microscopically small irregularities in the counter sealing surface of the groove are closed by this mechanism and the lowest possible leakage rates are ensured. Resilient metal seals have the ability to spring back in a defined manner (C-E) when relieved of load, this behavior is also known as Springback SB. The usable elastic springback (C-D) ensures that the tightness is maintained when flange lift-off occurs as a result of pressure and temperature application. In order to maintain the sealing performance, usually only a part of the total SB can be used, so that the sealing load F min SB is not undercut.

Typical applications / industries

  • Machine and plant constructions:
    Gas turbines, heat exchangers, plastic injection machines, pressure vessels, pump housings, internal combustion engines
  • Oil and gas industry:
    Fittings, valves, cryogenic applications
  • Chemical and process technology:
    High vacuum, heat exchangers, pressure vessels, fittings, valves, cryogenic applications
  • Sealing Technology
  • Laser and sensor technology
  • Aerospace industry:
    mechanics, modules, fuel system, engines



Notes on the design of the construction

With this recommendation, we would like to give all those responsible for the components advice on how to design the construction in order to implement a successful sealing solution. Appropriate dimensioning and material selection depending on the parameters and requirements contribute as much to the reliable functioning of the sealing solution as the sealing element itself.
Contrary to complex calculations, e.g. when using flat gaskets, in the case of resilient metal seals the press load of the seal must essentially be added to the operating forces of the application.
Especially for high-temperature applications, knowledge of the strength curve of the construction materials for the stiffness of flanges as well as the design and number of bolted connections is of great importance. If a flange gap can be expected from calculations on the behaviour of the construction, please provide us with exact numerical values. We are able to support you in the selection of a suitable GFD sealing element.

Furthermore the surface quality of the counter sealing surface is of elementary importance. The tightness is the result of the successful interaction between the sealing element and the surface quality of the counter sealing surface.

The necessity of a coating and, if necessary, the determination of the coating thickness depends on the desired leakage rate . Rougher surfaces can be compensated within limits by a higher coating thickness in order to meet the leakage requirement.

For rings in internal and external pressure applications:
The processing marks caused by machining must be concentric with the line of contact of the seal.
Avoid radial scoring and scratches.
Processing marks on the groove or flange surface must be free of dirt, grinding dust or other foreign matter.

The following applies to rings in axial pressure applications:
Processing marks caused by machining must be concentric with the line of contact of the seal.
Avoid axial scoring and scratches.
Processing marks on the inside and outside of the groove must be free of dirt, grinding dust or other foreign matter.

Permissible eccentricity:
- up to bore Ø 85mm = max. 0.015mm
- from bore Ø 85mm = max. 0.03mm
Surface hardness 60 HRC

The GFD seal

  • The seals should be kept in their original packaging until the time of installation to avoid damage.
  • When opening the packaging, make sure that the seal is not damaged by sharp objects, e.g. a knife or scissors, as even the smallest scratches can have a negative effect on the sealing performance.
  • After unpacking, check the seal for possible damage or other defects.
  • Use only suitable tools for assembly, if at all necessary.
  • Wear suitable gloves if required by the specification.
  • Handle the seal with the utmost care.

The customer design: groove and flange

  • The condition of the counter sealing surfaces plays a decisive role in the subsequent sealing effect. In addition to the points mentioned in the design recommendations, it must be ensured that grooves and flanges are free of dirt, foreign particles, scratches and other damage and deformation, as any of the above-mentioned conspicuous features can lead to leakage. Cleaning, e.g. with a dust-free cloth and acetone, immediately before installation is recommended.
  • Wear suitable gloves if required by the specification.
  • Carry out the above mentioned tests and cleaning with the utmost care.

Assembly

  • When installing the seal in the groove, make sure that no scratches or other damage is caused.
  • When using tools, if at all necessary, ensure that neither the seal nor the surrounding construction, especially the counter sealing surfaces, are damaged in any way.
  • Do not use any auxiliary materials such as oil, grease or other products
  • Wear suitable gloves if the specification requires it.
  • After placing the seal, carefully guide the adjacent structural parts towards each other. In the case of multiple fittings, gradually tighten the flanges crosswise to achieve even compression of the seal.
  • When installing MCA type seals, ensure excellent guidance of the components to be sealed to each other (see chapter Design Recommendations) to avoid damage, e.g. due to tilting. Assembly tools are available on request.
  • Work with the utmost care during assembly.

Note on reusability

GFD recommends not to reuse resilient metal seals after disassembly. Background: The rings are not only elastically but also plastically deformed during assembly. In addition, there is a risk of damage and contamination. In case of repeated use, this usually leads to a (significant) decrease in sealing performance and thus to the original specification not being met.

Ring and spring material

Various stainless steels and nickel alloys are available for the production of rings and springs. The selection of the most suitable material depends on the application and specification.


Heat treatment

It is possible to subject rings to different heat treatments depending on the materials and applications. A suitable heat treatment can positively influence the performance as well as the lifetime of the rings. The specification can be determined directly by the customer or by GFD if all essential parameters and requirements are present.


Coating materials

The tightness of metal rings can be significantly improved with a suitable coating: When the ring is pressed, the coating flows into the microscopic unevenness of the counter sealing surface and seals it. This mechanism allows excellent sealing qualities to be achieved. The tightness specified as the leakage rate in mbar l/s is the result of the successful interaction between the ring and the surface quality of the mating sealing surface (see also chapter "Design recommendations and assembly"). The necessity of a coating and, if necessary, the determination of the coating thickness is thus dependent on the desired leakage rate and is further determined by the surface quality of the groove and flange. When selecting the coating, it is important to ensure that it harmonizes with the pressing load of the ring, so that tiling takes place reliably. Thus, a comparatively hard nickel coating should only be used in combination with a ring with high pressing load. In contrast, tin or PTFE coatings should preferably be configured with rings of low pressing force. Silver covers the widest range of applications and is therefore considered the standard coating material. Furthermore, coatings such as PTFE or gold can also be used as protection to improve the resistance against aggressive media.

Metal O-Ring
normal
Metal O-Ring
self energizing
Metal O-Ring
pressure filled
Metal C-Ring Metal C-Ring
spring energized
Metal C-Ring
Highflex spring energized
Metal C-Ring
for axial pressure
Metal C-Ring
for axial pressure spring energized
Metal U-Ring
Internal pressure MOR NPType MOR
Design NP
MOR SIType MOR
Design SI
MOR PFType MOR
Design PF
MCIType MCI MCI-FType MCI-F MCI-HFType MCI-HF MUIType MUI
External pressure MOR NPType MOR
Design NP
MOR SOType MOR
Design SO
MOR PFType MOR
Design PF
MCOType MCO MCO-FType MCO-F MCO-HFType MCO-HF MUOType MUO
Axial pressure MCAType MCA MCA-FType MCA-F
Description for low to moderate pressure and vacuum conditions has a self energizing effect by a drilling hole at the ID or AD Pressure filling is effective from temperatures of approx. 425°C Metal C-rings have a higher elasticity than metal O-rings. The open side of the metal C-ring points in the direction of the higher pressure. It therefore has a self energizing effect. The spring reinforcement further improves the sealing effect and springback. has high springback with low pressing load
available as moulded seal x x x x x x
available as segment seal x x x x x
Metal O-Ring
normal
Internal pressure External pressure Axial pressure
MOR NPType MOR
Design NP
MOR NPType MOR
Design NP
available as moulded seal available as moulded seal
available as segment seal available as segment seal
for low to moderate pressure and vacuum conditions
Metal O-Ring
self energizing
Internal pressure External pressure Axial pressure
MOR SIType MOR
Design SI
MOR SOType MOR
Design SO
available as moulded seal available as moulded seal
available as segment seal available as segment seal
has a self energizing effect by a drilling hole at the ID or AD
Metal O-Ring
pressure filled
Internal pressure External pressure Axial pressure
MOR NPType MOR
Design NP
MOR NPType MOR
Design NP
available as moulded seal available as moulded seal
Pressure filling is effective from temperatures of approx. 425°C
Metal C-Ring
Internal pressure External pressure Axial pressure
MCIType MCI MCOType MCO
available as moulded seal available as moulded seal
available as segment seal available as segment seal
Metal C-rings have a higher elasticity than metal O-rings. The open side of the metal C-ring points in the direction of the higher pressure. It therefore has a self energizing effect. The spring reinforcement further improves the sealing effect and springback.
Metal C-Ring
spring energized
Internal pressure External pressure Axial pressure
MCI-FType MCI-F MCO-FType MCO-F
available as moulded seal available as moulded seal
available as segment seal available as segment seal
Metal C-rings have a higher elasticity than metal O-rings. The open side of the metal C-ring points in the direction of the higher pressure. It therefore has a self energizing effect. The spring reinforcement further improves the sealing effect and springback.
Metal C-Ring
Highflex spring energized
Internal pressure External pressure Axial pressure
MCI-HFType MCI-HF MCO-HFType MCO-HF
available as moulded seal available as moulded seal
available as segment seal available as segment seal
Metal C-rings have a higher elasticity than metal O-rings. The open side of the metal C-ring points in the direction of the higher pressure. It therefore has a self energizing effect. The spring reinforcement further improves the sealing effect and springback.
Metal C-Ring
for axial pressure
Internal pressure External pressure Axial pressure
MCAType MCA
Metal C-rings have a higher elasticity than metal O-rings. The open side of the metal C-ring points in the direction of the higher pressure. It therefore has a self energizing effect. The spring reinforcement further improves the sealing effect and springback.
Metal C-Ring
for axial pressure spring energized
Internal pressure External pressure Axial pressure
MCA-FType MCA-F
Metal C-rings have a higher elasticity than metal O-rings. The open side of the metal C-ring points in the direction of the higher pressure. It therefore has a self energizing effect. The spring reinforcement further improves the sealing effect and springback.
Metal U-Ring
Internal pressure External pressure Axial pressure
MUIType MUI MUOType MUO
has high springback with low pressing load

Achievable leakage rate

Force/stroke principle – Overview of different type

Metal O-Ring normal

Internal pressure

Type MOR
Design NP

External pressure

Type MOR
Design NP

Metal O-Ring self energizing

Internal pressure

Type MOR
Design SI

External pressure

Type MOR
Design SO

Metal O-Ring pressure filled

Internal pressure

Type MOR
Design PF

External pressure

Type MOR
Design PF

Internal pressure application

Internal pressure application

For internal pressure applications the outer diameter of the ring ODR is calculated as follows:

ODR = OD - Z

External pressure application

External pressure application

For external pressure applications the outer diameter of the ring ODR is calculated as follows:

ODR = ID + Z + 2*CSR + (4*Pt)

(4*Pt) only valid for rings with coating For the calculation, the largest value of the selected value range must be used.

CSR Nominal cross-section: cross-sectional dimension (without coating) e.g. similar to the cord thickness of elastomer O-rings
Code Performance Index: shows characteristics of the ring (e.g. pressing load, springback)
D Groove depth: axial design dimension to which the ring is pressed from the original cross-section CSR.
F Pressing load: the mentioned guide values refer to 1mm seal length. To obtain the total load of the seal for the design of the construction, this value must be multiplied by the circumferential length of the seal.
ID Inner diameter of the groove: reference dimension for external pressure applications.
OD Outside diameter of groove: reference dimension for internal pressure applications.
ODR min. Outside diameter of the ring: The outside diameter of the ring is freely selectable from the mentioned minimum dimension ODR min. and is at the same time the corresponding dimension to the outside or inside diameter of the groove.
Pt coating thickness
R Radius: Design dimension that improves the support of the ring under pressure
SB Springback: maximum possible measure by which the ring can spring back elastically overall. Important value in connection with possible flange gaps.
Wmin groove width: radial design minimum dimension. The specified minimum dimension Wmin. must not be undercut.
Wt Wall thickness: sheet thickness of the ring.
Z diametric clearance between ring and groove.

The following ordering example describes a metal O-ring in

5
Material Inconel X-750
2,39
Cross section 2,39 mm
s
with wall thickness 0,46 mm
0054,70
Ring outer diameter ODR 54.7mm incl. coating
(suitable for groove outer diameter OD 55.00mm)
SI
self energizing inside (internal pressure application)
S
Silver Coating
L
0.01 - 0.03mm thick
Metal O-Ring MOR Installation space Performance
Nominal
cross-section
Performance
index
Wall thickness Outer diameter
ring
diametrical
clearance
Groove depth Groove width Radius Pressing load
(Guide values)
Springback
(Guide values)
CSR
mm
Code Wt
mm
Ø ODR min.
mm
Z
mm
D +0,1
mm
W min.
mm
R max.
mm
F
ca. N/mm
SB
ca. mm
0,89 w 0,15 6 0,20 0,65* 1,4 0,25 70 0,01
1,57 w 0,25 15 0,25 1,15 2,3 0,35 110 0,03
1,57 s 0,36 15 0,25 1,15 2,3 0,35 230 0,03
2,39 w 0,25 25 0,30 1,9 3,2 0,5 60 0,05
2,39 s 0,46 25 0,30 1,9 3,2 0,5 210 0,03
3,18 w 0,25 45 0,40 2,55 4,2 0,75 40 0,07
3,18 s 0,51 45 0,40 2,55 4,2 0,75 170 0,04
3,96 w 0,51 70 0,60 3,2 5,2 1,25 115 0,08
3,96 s 0,64 70 0,60 3,2 5,2 1,25 195 0,06
4,78 w 0,51 100 0,70 3,85 6,4 1,3 95 0,10
4,78 s 0,64 100 0,70 3,85 6,4 1,3 160 0,08
6,35 w 0,64 160 0,75 5,1 8,5 1,5 110 0,15
6,35 s 0,81 160 0,75 5,1 8,5 1,5 190 0,10
9,53 w 0,97 300 1,00 8,3 12,7 1,5 170 0,15
9,53 s 1,24 300 1,00 8,3 12,7 1,5 290 0,12
12,7 w 1,27 800 1,25 11,1 16,5 1,5 200 0,20
12,7 s 1,65 800 1,25 11,1 16,5 1,5 370 0,18

*) D +0,05 plus coating thickness

Ring material

Ring material Code Material no.
SS321 3 1.4541
Inconel 600 4 2.4816
Inconel X-750 5 2.4669

Other materials on request.

Design

Design Code
normal NP
self-energizing inside SI
self-energizing outside SO
pressure filled PF

Coating

Coating Code max. temperature
Tin Z 200°C
PTFE P 290°C
Silver S 430°C (650°C*)
Copper C 930°C
Gold G 930°C
Nickel N 1200°C
without O

* Only valid for non-oxidizing media.
Other materials on request.

Coating thickness

Coating thickness Code
0,01 - 0,03 mm L
0,03 - 0,05 mm M
0,05 - 0,07 mm H

Other coating thicknesses on request.

Metal C-Ring

Internal pressure

Type MCI

More information

External pressure

Type MCO

More information

Axial pressure

Type MCA

More information

Metal C-Ring spring energized

Internal pressure

Type MCI-F

More information

External pressure

Type MCO-F

More information

Axial pressure

Type MCA-F

More information

Metal C-Ring Highflex spring energized

Internal pressure

Type MCI-HF

More information

External pressure

Type MCO-HF

More information

Metal U-Ring

Internal pressure

Type MUI

More information

External pressure

Type MUO

More information

In addition to the circular version, many of the seal types listed in the catalog are also available as shaped and segment seals for a wide variety of applications.

The minimum radii that can be implemented are based on the minimum diameters specified in the table for the respective type and are formed from ODRmin/2 for internal pressure applications, IDRmin/2 applies for external pressure applications.

A detailed representation of the groove contour incl. dimensioning and tol. with reference to internal or external pressure application is required for the assessment of feasibility.

Hot Runner seals

Metal O-rings in hot runner systems of plastic injection molding machines

Seals for hot runner systems are available from stock in many sizes, as the groove dimensions from different manufacturers are often identical.

The seals are used, for example, in the nozzles, connectors and component separations of HK systems.

The seal is a " one-time " item and is exchanged when the components are changed.

Space Limiter

The Space Limiter enables the use of resilient metal seals when there is no groove geometry between two flanges. It limits the compression of the gasket to the required height and supports the seal when pressurized.

The surface finish of the flange pairs in the area of the counter sealing surface should follow GFD recommendations.

Space Limiters can be designed, for example, with a bolt circle corresponding to that of the bolted connections of the flanges.

Space Limiter

If there is a shoulder in the flange connection, this can be used as a form fit.

Space Limiters can be manufactured for both internal and external pressure. A detailed flange drawing incl. dimensions and tol. with reference to internal or external pressure application is required for checking feasibility.

Space Limiter




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