superior technical guide for precision moulded seals continuous, aggressive improvement in the...

Superior technical guideFor precision moulded seals

We have not designed it to be a catalogue,

but a reference to guide you through the

relevant selection and design processes.

It will become clear as you use the

guide that we are not in the business

of commodity production. Superior

manufactures precision components

from specialised high performance

rubber compounds.

As a result, we actively seek the most

demanding customers. We relish involvement at

the earliest point in their product development

cycle. It is the customer who benefits most:

more effective application of seals means

better product design – everyone wins.

To this end, we have committed to a culture

of continuous, aggressive improvement in the

design, manufacture and supply of precision

o-rings and special mouldings.

We like to exceed expectations. Innovation

and investment are the keys to this.

Natural curiosity and the desire to find better

processes and methodologies feed the

Superior promise to innovate.

Re-investment in state-of-the-art facilities

and valued, accountable people increases our

ability to convert ideas into production reality.

This guide is a part of that investment.

Use it with confidence. It is fully backed by

both our Engineering and Technical Service

teams who are on hand to offer advice and

support: we strongly recommend using this

service as part of your design development

process. You will find the contact number

at the foot of each page.*

Superior technical guide We believe that this latest edition of the guide will become an invaluable resource for anyone involved in the specification and application of elastomer seals.

*This service has been developed with you in mind. If you have any issues or comments arising from it, please contact us in the first instance.

Material Science Department +44 (0)1202 854300 | 1

Your guide

ContentsSuperior technical guide

Research, development and partnership A relevant approach to design for today’s manufacturing.01

01

Consultation 3

Testing

Optimising

Tooling

Staying ahead

02Temperature 4

Media compatibility rating 5

Approvals

Superior elastomer grades 6

Materials reference guide 7

Elastomer properties 8

Hardness

Compression set

Tensile strength

Elongation at break

Tear strength

Gas permeability

Abrasion 9

Colour

Ageing

Low temperature flexibility

Media table 10

Producing an order specification 12

03

Precision o-rings 13

O-ring size and compound

selection program

Groove layouts 14

General housing guidelines 15

Housing diametrical tolerances

Lead chamfers Z

Surface finish or texture

Coefficient of thermal expansion

Coefficient of friction

Static sealing – axial and triangular 16

Static axial face housing

Static triangular housing

Static/dynamic sealing – radial 17

O-ring stretch in piston sealing

Reduction of cross-section due to stretch

Guidelines

Gough-Joule effect

Typical compression range 18

Typical o-ring housing data for piston

and rod sealing applications

Pressure 19

04

Superior engineering 22

Seal integrity

Seal performance

Development of a seal profile

Precision mouldings / bespoke seals 23

Lip seals / U-seals / V-seals

Symmetrical seals

Quad rings

Moulded gaskets

Custom radial seals

Tolerances for moulded parts 24

A heritage of excellence 25

Our tool room

The service we offer to our customers

05

O-ring size range standards 26

Quality acceptance criteria ISO 3601-3 27

Quality control: documentation 28

Seal surface inspection levels

Special moulding tolerances

Certification

Environmental compliance

06

O-ring stretch during assembly 29

Fitting aids and sharp edges

Housing chamfers 30

Traversing cross drilled ports

Rolling

Cleanliness / cleaning materials

Storage 31

Light

Humidity

Contaminants

Stress

Temperature

Oxygen and ozone

Shelf life

Customer Service lies at the heart

of everything we do at Superior.

Our philosophy is based upon three

key constituents:

• Material science and technology

• Seal engineering

• State-of-the-art manufacturing

The combination of these three factors

provides the high integrity of our precision

o-rings and seals, and in turn, provides the

long term performance and high integrity in

our customers products. Our ‘fast response’

culture is applied to each individual factor to

help reduce our customers’ overall project

lead time.

ConsultationWe actively encourage and cultivate early

involvement in customer projects. This helps

to ensure that the seal element is optimised

within the environment demanded by the

customer. This ensures that our products are

reliable, fit for purpose, correctly specified with

all critical features identified, controlled and

costed at an appropriate and agreed level.

TestingWe work closely with our customers on

all aspects of seal testing and development

programs. All testing procedures are carried

out to international standards, BS ISO, DIN,

ASTM, or to customer specific requirements.

We offer a diverse range of compounds

to satisfy the majority of market needs.

If a customer has a specific need that

cannot be met within our existing elastomer

range, we will develop new compound

grades at our in-house laboratory.

We are able to conduct extensive test

programs to fully validate specific

elastomers to customer parameters

(e.g. temperature/media exposure

and mechanical property testing).

We will also validate to specific accreditation

standards (e.g. EN681, WRAS, DVGW, ACS,

KIWA, NSF, EN 549).

Optimising

Through the customer partnership exchange,

we can assist with optimised seal profile

design and application.

Tooling

Our Tooling Manufacture department designs

and machines precision prototype and

production moulds to exceed conventional

tolerancing. Pilot tooling can be provided

economically and rapidly to further expedite

customer test programs.

With our extensive tooling expertise, we can

optimise critical surface features to facilitate

reliable function with mating parts.

Staying aheadOur continuous capital investment program

allows us to remain at the leading edge of

our field.

We continually implement latest technology

systems, ensuring batch-to-batch consistency

throughout the manufacturing process.

With such broad customer support facilities,

Superior will always strive to provide added

value with our customer programs.

Indeed, we find that each new project

challenges our thinking and creates a

springboard to increasingly enlightened

manufacturing practices.

Research, development and partnershipSuperior technical guide

2 | www.superiorltd.com Material Science Department +44 (0)1202 854300 | 3

Research, development and partnership

Specifying compounds

Seal design Quality

Custom seal design

Assembly

Media compatibility ratingVirtually all elastomers exhibit a physical or

chemical change when exposed to working

media, whether gas or fluid.

The degree of change depends upon

media composition in combination with

the elastomer exposed. Aggressive media

become more active with subsequent

increase in temperature. Physical changes

become apparent in two ways and can

occur simultaneously;

• the elastomer absorbs the media

– creating a volume increase or swell

• a base constituent (such as plasticiser)

is extracted – creating a volume decrease

or shrinkage.

The degree of volume change is

dependant upon:

• the media type

• the elastomer chemical structure

• the geometric shape of the seal

(section thickness)

• the stressed condition of the seal

• temperature

• time.

A rubber will swell significantly less when

compressed in the working envelope than

in the free state (up to 50% less).

Chemical changes tend to affect the

cross-linking structure of the elastomer

(e.g. embrittlement).

Any application where the media can create

high shrinkage changes to the elastomer

should be avoided, due to squeeze reduction

and resultant leakage risk.

Approvals We are able to develop and provide

a comprehensive range of elastomers

specific for;

Water Industry:

WRAS, NSF, DVGW, KTW, ACS,

KIWA, UL

Gas Industry:

EN549, EN682 Compliance

Food and Beverage Industry:

FDA, AAA, NSF51

Pharmaceutical:

USP Class VI

Please consult our Technical Service

department for specific accreditations.

Specifying compoundsSuperior technical guide

Specifying compounds Important environmental parameters.02


Temperature At Superior we are able to develop and

manufacture the majority of elastomer

compounds used in most market sectors.

Awareness of specific limitations on each

elastomer is fundamental, in terms of both

mechanical and chemical characteristics.

The most relevant influential working

criteria should then be carefully matched

to elastomer parameters.

Only then is it possible to achieve accurate

selection of the most suitable elastomer

for any given environmental condition.

Please refer to the materials reference

guide on page 7.

Terms and environmental aspects related

to working with compounds are highlighted

in the following pages.

Each elastomer type has a specific

working temperature range, however this

will be influenced by many factors: media

compatability, dynamic or static operation

and seal design being several of these.

Many factors affect the service temperature

of elastomers. All dynamic and shock loads

should be avoided at temperatures below the

minus limit of a given compound. However,

elastomers stored in static conditions,

below the low temperature flexible range,

will recover full physical properties during the

warm-up period. At elevated temperatures,

consideration must be given to the long term

running limit and the short term peak limit of

each elastomer.

Elastomers exposed to the extreme limit

can suffer an accelerated loss of flexibility,

resulting in excessive compression set.

This can dramatically shorten effective sealing

life. Also there is an influence in volume swell

and age hardening at high temperatures,

dependent on compound type.

The temperature guide below is generic for

each elastomer type. We have developed

particular compounds which exhibit improved

upper or lower temperature performance.


department on +44 (0)1202 854300

NBR Nitrile rubber MN/HN

NBR Low temperature Nitrile rubber LN

IIR Butyl rubber BB

ECO Epichlorohydrin EC

ACM Polyacrylate rubber PA

EPDM Ethylene-Propylene-Diene rubber EP

HNBR Hydrogenated Nitrile rubber TH

AEM Ethylene Acrylate VA

FVMQ Fluorosilicone rubber FSIL

FPM Fluorocarbon rubber VF/VP

VMQ Silicone rubber SIL

FFPM Perfluorinated elastomer

°C -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300F -148 -112 -76 -40 -4 32 68 104 140 176 212 248 284 320 356 392 428 464 500 536 572S

uper

ior

des

igna

tion

Recommended temperature range: guide only Extended temperature range: guide only

Rating

••• Very Good

•• Good

• Fair

x Unsuitable

It should be noted that the parameters specified in this table illustrate the typical working band of commercially available elastomers. Material development is constant and we are able to assist for parameters outside of the stated values if required.

Specifying compoundsSuperior technical guide

Materials reference guideSuperior elastomer grades


Principal properties

EPDM: EP Ethylene Propylene Terpolymers

• outstanding resistance to water

and steam

• excellent weathering resistance

• general temperature use -40°C to +130°C

• can be designed to meet DW Approvals

and food approvals

• can be designed to give specific

chemical resistance (mineral acids

and phosphate esters)

• low compression set in water and air

• not suitable for use in mineral oils.

NBR: LN, MN, HN, WN, FN Acrylonitrile Butadiene (Nitrile)

• very good resistance to petroleum

based fluids

• good flexibility at low temps,

-50°C for LN grades

• upper temperature limit of 100°C

• can be designed to meet DW

approvals – WN grades

• can be designed to meet gas approvals.

HNBR: TH Hydrogenated Nitrile

• extend the temperature range

of NBR’s to 150°C

• excellent mechanical properties:

high strength and wear resistance

• good dynamic properties and

weathering resistance

• good resistance to many oil additives

• can be designed to meet gas approvals

• low temp -40°C to -20°C depending

on grade.

VMQ: SIL Silicone

• excellent low temperature properties,

capable to -60°C

• excellent high temperature performance

to 200°C

• good flexibility, tactile material

• can meet FDA, USP expectations

• poor mechanical properties

• poor resistance to fuels/oils

• high permeability.

FVMQ: FSIL Fluorosilicone

• excellent low temperature

dynamic performance

• increased resistance to fuels, particularly

useful for aerospace applications

• poor mechanical properties.

FKM: VF/VP Fluorocarbon

• excellent resistance to a wide spectrum

of chemicals: fuels, oils, biodiesel etc

• chemical resistance can be improved

by use of specific grades

• excellent resistance to heat

• can be designed to give high performance

in steam/water

• can be designed to offer excellent

compression set

• low permeability

• limited use at low temperarure, -20°C

(special grades are available to extend

this to -40°C)

• poor resistance to ketones,

amines and ethers.

Grades can be provided in a hardness range of 30 to 90 IRHD. Grades can be black or coloured (mineral filled). The choice of filler will however affect mechanical properties and approvals. Advice should be sought from the Technical Service department.

Material Nitrile Butyl Ethylene Propylene

Hydrogenated Nitrile

Fluorosilicone Silicone Fluorocarbon

Designation NBR IIR EPDM HNBR FVMQ VMQ FPM

Superior elastomer code MN, LN, HN, WN, FN

BB EP TH FSIL SIL VF, VP

Hardness range (IRHD) 40 – 90° 40 – 80° 40 – 90° 50 – 90° 40 – 80° 20 – 80° 55 – 85°

Colours Limited range Black Limited range Limited range Limited range Limited range Limited range

Heat resistance °C

Peak 120 130 160 170 230 230 250

Normal 100 110 130 150 200 200 200

Low temp °C -30 -50 low temp version

-50 -50 -40 -55 -60 -20 -35 low temp version

Resistances

Mineral oil (low aromatic) •• x x ••• ••• •• •••

Oxidisation •• ••• ••• ••• ••• ••• •••

Ozone x ••• / •• ••• •• ••• ••• •••

Weathering • ••• ••• •• ••• ••• •••

Radiation •• / • x ••• •• ••• ••• •••

Integrity

Tear strength •• •• •• ••• x x ••

Compression set •• • •• •• ••• ••• ••

Abrasion resistance •• •• / • •• ••• • • •• / •

Resilience •• / • • •• •• / • •• •• •

Gas permeability •• ••• •• •• x x •••

Electrical insulation • ••• ••• • ••• ••• Grade dependant

Inflammability x x x x ••• • •••

% Compression Set =original height – recovered height

original height – compressed height x 100

Superior technical guide

Hardness

The term hardness is the measure of a

material’s resistance to a set deforming force

exerted by a given standard indentation

implement over a defined length of time.

Hardness is measured in degree units of IRHD

(International Rubber Hardness Degrees).

It is generally the unit of measure on standard

dimensioned test pieces. It is also the unit

used for measuring the finished component

(e.g. o-ring cross section) by the Micro

Hardness Test.

Standard compounds are nominally 70 IRHD.

Superior can, however, provide compounds

from 20-90 IRHD range, depending upon

material type. Selection of hardness is

dependent upon specific application

requirements. For example:

Softer compounds

• deform more readily under load

(e.g. cover/housing assembly) conform

to surface irregularities

• lower stick/slip effect

• higher running friction.

Harder compounds

• higher extrusion resistance

• lower running friction

• higher stick/slip effect.

The hardness is usually expressed

and controlled as a nominal figure

with ± 5 points tolerance.

Compression set This is the measurement of a compound’s

loss of elastic memory. A standard cylindrical

test piece of rubber is subjected to a

defined pre-load at given temperature

and time parameters (e.g. 24hrs/100°C).

The test deformation is usually 25%

of the original height.

The measured recovery of the cross-section

is carried out at ambient temperature.

The end result is recorded as the height not

recovered, expressed as a percentage of the

amount by which the part was compressed.

Usually it can be stated that the better the

elastomeric memory, the lower the compression

set. This is regarded as an important feature

of any compound, as leakage will occur if high

set (and therefore loss of memory) occurs.

Tensile strength

This is the force necessary to rupture a

standard test piece at a given rate of

elongation and expressed as force per

unit area.

In practical terms, this property result does

not assist the end user to select a compound,

because a correctly assembled o-ring does

not rely on its tensile strength to achieve

effective sealing.

Elongation at break

Elongation at break is measured at the

moment of rupture of a test piece under

tensile load, expressed as a percentage.

This is a useful indication of a compound’s

suitability as a large percentage of stretch

may be necessary during assembly

(e.g. piston seal).

Tear strength

Resistance to tear propagation from

a point of initial damage, sustained

for example, during assembly.

Gas permeability Elastomers allow gas to enter into

the structure. They will diffuse or

permeate through and escape via

the low pressure side.

The rate of permeation is governed by

temperature, pressure, gas type and

elastomer type. This may be critical

for vacuum and gas containment.

To reduce permeability:

• use larger o-ring sections

• apply more compression

• optimise surface finish

• select high-density elastomers.

AbrasionAbrasion resistance is a general term

indicating wear resistance.

It can be noted, generally, that HNBR

compounds perform best.

NBR and EPDM have relatively good

abrasion resistance. FPM has a lower

abrasion resistance.

Abrasion resistance improves with hardness

(up to 80 IRHD). However, Silicone and

Fluorosilicone have poor properties

and should only be applied to static

environments.

Colour

Rubbers are usually formulated with the

addition of carbon black fillers. Hence, the

majority of compounds are black in colour.

Rubbers gain much of their strength and

heat resistance from the addition of carbon

black fillers.

However, at Superior we have the expertise

to formulate and produce colour pigmented

compounds for most of the elastomer

range. Colouring is mainly used as

a means of identification, allowing

differentiation of compound grades

in safety-critical applications.

In addition, colour can be used to separate

similar sizes on a customer’s production line.


department on +44 (0)1202 854300 for

application and colour range availability.

Ageing

Heat ageing tests are widely used to record

changes in property of an elastomer.

Usually hardness, tensile strength and

elongation are measured and compared

to original properties.

Air and relevant fluid ageing over standard

time/temperature durations are meaningful

to compare life expectancies of rubbers.

Standard test conditions are:

NBR 24/70 hrs @ 100°C

EPDM 24/70 hrs @ 120°C

FPM 24/70 hrs @ 200°C

VMQ 24/70 hrs @ 200°C

If elastomers are pushed beyond their

ageing resistance parameters, they will suffer

from cracking, splitting and/or hardening.

Low temperature flexibility

The TR test (low temperature retraction)

provides a measure of the rate of recovery

of an elastomeric material after it has been

subjected to low temperature.

The test, which is described in ISO 2921,

consists of stretching a test piece with an

effective length of 50 or 100mm and placing

it in a bath at -70°C.

The test piece is allowed to retract freely

whilst the temperature is raised at the

rate of 1°C per minute.

The percentage retraction of the test

piece is plotted against temperature.

Retraction values are calculated automatically

with TR10, TR30, TR50 and TR70

values being most commonly recorded.

TR10 and TR70 values are of particular interest.

Elastomer properties To fully specify and select a compound, the most relevant physical characteristics should be known, these are:



Recommended

Superior designation LN/MN HN EP TH FS SIL VF/VP compound

Maximum service temperature °C 100 100 150 150 200 200 230/2v00

Low service temperature °C -45/-30 -20 -50 -40 -55 -60 -20/-35

Water/steam resistance

Water/steam resistance <60°C ••• ••• ••• ••• ••• ••• ••• / ••• WN70/3

Water/steam resistance <80°C •• •• ••• ••• •• •• ••• / ••• EP1/1/5, WN12/7/1

Water/steam resistance <150°C x x •• •• x x *•• / • EP7/3/7, EP11/7/4

Water/steam resistance >150°C x x • x x x *•• / x VF12/99/3, EP11/7/4

Fluid resistance

Acids

Acetic 10% • • ••• •• x •• • / •••* EP10/00/2

Formic x x ••• x • •• • / •••* EP10/00/2

Hydrochloric 20% • • ••• • •• • •• / •••* EP10/00/2

Nitric 30% x x ••• x • • •• / ••• VF3/00/10

Phosphoric 20% • • ••• • •• •• ••• / ••• EP10/00/2

Sulphuric 30% x x •• x • x •• / ••• VF3/00/10, VP5/00/5

Alkalis

Baruim hydroxide •• •• ••• ••• •• •• ••• / ••• EP7/3/7, EP11/7/4

Calcium hydroxide •• •• ••• ••• •• •• ••• / ••• EP7/3/7, EP11/7/4

Sodium hydroxide •• •• ••• •• • • •• / ••• EP7/3/7, EP11/7/4

Alcohols

Butyl alcohol (Butanol) ••• ••• •• •• ••• •• ••• / ••• EP70, MN70

Ethyl alcohol (Ethanol) •• •• ••• ••• ••• ••• • / ••• EP70, MN70

Methyl alcohol (Methanol) •• ••• ••• •• •• •• x / ••• EP70, MN70

Amines

Ethylene diamine •• •• ••• •• x •• x / ••* EP7/3/7, EP11/7/4

Ammonia – cold gas ••• ••• ••• ••• x •• x / • EP7/3/7, EP11/7/4

Ammonia – hot gas x x •• • x •• x / x EP7/3/7, EP11/7/4

Chlorides

Ammonium chloride ••• ••• ••• ••• ••• ••• ••• / ••• EP7/3/7, EP11/7/4

Calcium chloride solution ••• ••• ••• ••• ••• ••• ••• / ••• EP7/3/7, MN70, EP11/7/4

Magnesium chloride ••• ••• ••• ••• ••• ••• ••• / ••• EP7/3/7, MN70, EP11/7/4

Zinc chloride ••• ••• ••• ••• ••• ••• ••• / ••• EP7/3/7, MN70, EP11/7/4

Recommended

Superior designation LN/MN HN EP TH FS SIL VF/VP compound

Fluids resistance (continued)

Gases

Butane •• ••• x ••• •• x ••• / ••• TH5/03/1, HN75

Carbon dioxide (dry) ••• ••• •• ••• •• •• ••• / ••• TH5/03/1

Chlorine (wet) x x • • •• x ••• / ••• VF75B

Freon 12 (R12) ••• ••• •• ••• • x •• / ••• HN75

Freon 22 (R22) x x ••• x x x x / x EP7/3/7, EP11/7/4

Freon 134a (R134a) o o ••• ••• x o x / x EP7/3/7, EP11/7/4

Natural gas •• ••• x ••• • •• ••• / ••• TH5/03/1, HN75

Methane •• ••• x ••• •• x ••• / ••• TH5/03/1, HN75

Propane •• ••• x ••• •• x ••• / ••• TH5/03/1, HN75

Oils and fuels

ASTM No 1 oil ••• ••• x ••• ••• •• ••• / ••• MN70

ASTM No 2 oil ••• ••• x •• ••• • ••• / ••• HN75

ASTM No 3 oil • ••• x • ••• x ••• / ••• HN75

ASTM fuel A •• ••• x ••• ••• x ••• / ••• HN75

ASTM fuel B • •• x x ••• x ••• / ••• VF75B

ASTM fuel C x • x x •• x ••• / ••• VF75B

Diesel oil •• ••• x ••• •• x ••• / ••• HN75

Diesel oil + RME (10%) x x x x • x ••• / ••• VF5/4/4, TH8/5/6

Mineral oil (low aromatic) ••• ••• x ••• ••• •• ••• / ••• MN70

Hydraulic oils (petroleum base) ••• ••• x ••• •• • ••• / ••• MN70

Lubricating oils ••• ••• x ••• ••• • ••• / ••• MN70

Paraffin ••• ••• x ••• ••• • ••• / ••• MN70

Petrol •• ••• x ••• ••• x ••• / ••• VF75B

Silicone oil / grease ••• ••• ••• ••• • • ••• / ••• EP7/3/7, EP11/7/4

Transformer oils ••• ••• x ••• ••• • ••• / ••• MN70

Vegetable oils ••• ••• • ••• ••• •• ••• / ••• FN70

Solvents

Acetone x x ••• x x • x / x EP7/3/7, EP11/7/4

Benzene x x x x •• x ••• / ••• VF75B

Carbon tetrachloride x • x • • x ••• / ••• VF75B

Dimethyl formamide • • •• • x •• x / •• EP7/3/7, EP11/7/4

Ethyl acetate x x •• • x • x / x EP7/3/7, EP11/7/4

Methyl ethyl ketone x x ••• x x x x / x EP7/3/7, EP11/7/4

Tetrachloroethylene x x x x •• x ••• / ••• VF75B

Toluene x x x x •• x ••• / ••• VF75B

Turpentine •• ••• x ••• • x ••• / ••• HN75

Xylene x x x x • x •• / ••• VF75B

Miscellaneous

Ethylene glycol ••• ••• ••• ••• ••• ••• ••• / ••• EP2/9/10

Detergents ••• ••• ••• ••• ••• ••• ••• / ••• EP7/3/7, EP11/7/4

Dioctyl phthalate x x •• x •• • x / •* EP7/3/7, EP11/7/4

Formaldehyde • • ••• • • •• x / x EP7/3/7, EP11/7/4

Hydrogen peroxide (90%) x x •• x •• •• •• / ••• VF3/00/10, VP5/00/5

Phosphate esters x x ••• • • • • / •• Consult

Potassium nitrate ••• ••• ••• ••• ••• ••• ••• / ••• MN70

Rating

••• Excellent – recommended (5-8% swell)

•• Good – minor to moderate effects (8-15% swell)

• Fair – moderate to severe effects (1-25% swell)

x Poor – not recommended (>25% swell)

o Insufficient data available

*Conditions apply Temperature or other limitation affecting polymer choice

The table above refers to room temperature tests.

For other conditions and additional media advice please refer to the Technical Service team for advice.

Please note that in some conditions a negative swell (shrinkage through extraction) may occur.


Media table



For dynamic applications it is recommended that a swell up to 8% maximum be adhered to (••• rated). For static seals a volume change up to 25% can be tolerated (••/• rated) as long as the groove volume accommodates any increase.

It is important to keep in mind that reliability,

standardisation and ease of manufacture

around mating parts is achieved through

consultation with our Engineering department

at the earliest possible stage of development.

Practicality demands that this is a concise

guide, as each application could present

infinite parameter variables compared with

previous examples. As a result, guidelines and

trends tend to focus in general areas, so we

always encourage additional direct contact

with our Engineering department to fine

tune and elaborate where conditions are

not covered specifically within this guide.

Precision o-rings

These are the most versatile and economical

form of sealing device available. O-rings

will conform most readily to general design

guideline recommendations, as they have the

most extensive record of service life in diverse

conditions. O-rings are mainly used in static

applications, sealing against liquids, gas and

general environments.

Our Engineering department is able to

assist in specifying for dynamic applications,

with special consideration given to individual

working conditions. O-rings are generally not

recommended for dynamic applications.

O-ring Size and Compound Selection Program

Superior has created a program to assist the

selection process for a specific o-ring. The

program allows the user to enter the criteria

required and media in which it will be used, as

well as the housing information if known, and

the program will select a number of options

available. There is also an option to contact

the sales department for a quotation based

on the information entered. Our O-ring Size

and Compound Selection Program can be

found on our website www.superiorltd.com.

Sealing types

The various configurations can be

defined according to the type of sealing,

as described below:

A correctly designed housing with the

appropriate sized seal is important. However,

this function is not solely responsible for an

effective seal: the compound used influences

the sealing performance.

In all applications, where possible the largest

o-ring cross section diameter d2 should

be specified for the application to overcome

tolerances and rolling.

The first part of this section considers

design criteria for o-rings.

Superior is able to select from an extensive

range of standard and non-standard

o-rings (see our Superior size list for

further details or download from our

website www.superiorltd.com).

We can also recommend and manufacture

bespoke sizes. We will then produce

precision moulds which exceed recognised

industrial standard tolerances – quickly and

efficiently, in-house.

d1 d2

Seal designSuperior technical guide

Producing an order specification

Seal design This section of the guide is intended to assist engineers when considering sealing criteria.


Unstretched O-ring

Stretched O-ring

Piston rod sealingType A

Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2

% stretch of inside diameter d1

2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Radial compression

Axial compression

To ease liaison with our Sales department

and ensure the correct compound and

size of seal is ordered, we advise that

you apply the following considerations

to your specification:

• Highest peak temperature/duration

• Highest operating temperature

• Lowest temperature at which components

are expected to still function

• Media contact on assembly and

during operation

• Approval for water, gas or other

legislative requirements

• Static or dynamic working condition

(cycle rates/duration)

• Weathering/ozone resistance required

• Likely material being considered: refer

to materials reference guide or provide

compound designation number (e.g. MN70)

• Specific physical property minimums

e.g. Tensile strength, elongation,

compression set

• System pressure

• Colour/hardness requirements

• Quality and documentation requirements

• Lead time plan

• Size of seal (in the case of o-rings,

inside diameter and cross section).

03

Letter symbolsb Seal housing width (b1 and b2 for anti-extrusion devices)

d1 O-ring inside diameter

d2 O-ring cross-section diameter

d3 Groove diameter

d4 Bore diameter

d5 Shaft diameter

d6 Groove diameter

d7 Outside diameter: axial application internal pressure

d8 Inside diameter: axial application external pressure

d9 Shaft diameter

d10 Bore diameter

g Radial clearance

h Seal housing depth: axial sealing

r1 Corner radius

r2 Edge radius (0.2mm)

t Seal housing depth: radial sealing

z Lead-in chamfer: piston and rod housing

Please note that Ød10H7 applies to dynamic application.

rounded, flash-free

(external pressure) (0.2mm max)

br1

g

t

r2z

d4

0° to 5°

d3d9

15° to 20°

B

AB

d7

d8b

B

0° to 5°

B A h

r2

r1

(internal pressure)

b

t

r10 - 5°

r2

Pressure direction

No back-up ringb

Pressure direction

One back-up ring

b1

Pressure direction

Two back-up rings

b2


Bore diameterShaft diameter

Axial – outside diameterAxial – inside diameter

d4/d10

d5/d9

d7

d8

H8

f7H11

H11

These tolerances are as specified in ISO/R286,ISO System for limits and fits – Part 1, generaltolerances and deviations.

d1 d2

0° to 5° r1z

g

A t

rounded, flash-free

r2

b

B

B

15° to 20°

d10 d6d5

rounded, flash-free


br1

g

t

r2z

d4

0° to 5°

d3d9

15° to 20°

B

AB

d7

d8b

B

0° to 5°

B A h

r2

r1

(internal pressure)

b

t

r10 - 5°

r2

Pressure direction

No back-up ringb

Pressure direction

One back-up ring

b1

Pressure direction

Two back-up rings

b2




d4/d10

d5/d9

d7

d8

H8

f7H11

H11


d1 d2

0° to 5° r1z

g

A t

rounded, flash-free

r2

b

B

B

15° to 20°

d10 d6d5

rounded, flash-free


br1

g

t

r2z

d4

0° to 5°

d3d9

15° to 20°

B

AB

d7

d8b

B

0° to 5°

B A h

r2

r1

(internal pressure)

b

t

r10 - 5°

r2

Pressure direction

No back-up ringb

Pressure direction

One back-up ring

b1

Pressure direction

Two back-up rings

b2




d4/d10

d5/d9

d7

d8

H8

f7H11

H11


d1 d2

0° to 5° r1z

g

A t

rounded, flash-free

r2

b

B

B

15° to 20°

d10 d6d5

Groove layouts

To identify each feature of the housing standard letter symbols can be applied in all cases.

Housing Dimensions – static axial (mm)

d2 h+0.10 b+0.20 r1 r2 Surface finish or texture

The above is for guidance only and covers the majority of the sealing applications. However, Superior should be consulted in areas of particular concern.

Letter

A

B

Surface

Housing sides

and static diameters

Mating surface in

contact with o-ring

e.g. cylinder bore for

piston seal

Application

Static

Dynamic

Static

Dynamic

Pressure

Non pulsating and

non alternating

Pulsating or alternating

All types

Non pulsating and

non alternating


All types

Surface roughness

Ra µm

1.6

0.8

0.8

0.8

0.4

0.4

Lead in chamfers Z (30° – 40° inclusive)

All edges to be rounded

d2

Z minimum

Up to 2mm

1.1mm

2.01 to 3mm

1.5mm

3.01 to 4.5mm

1.8mm

Above 6.01mm

3.6mm

4.51 to 6mm

2.7mm


d2 h+0.10 b+0.20 r1 r2 Surface finish or texture

The above is for guidance only and covers the majority of the sealing applications. However, Superior should be consulted in areas of particular concern.

Letter

A

B

Surface

Housing sides

and static diameters

Mating surface in

contact with o-ring

e.g. cylinder bore for

piston seal

Application

Static

Dynamic

Static

Dynamic

Pressure

Non pulsating and

non alternating


All types

Non pulsating and

non alternating


All types

Surface roughness

Ra µm

1.6

0.8

0.8

0.8

0.4

0.4

Lead in chamfers Z (30° – 40° inclusive)

All edges to be rounded

d2

Z minimum

Up to 2mm

1.1mm

2.01 to 3mm

1.5mm

3.01 to 4.5mm

1.8mm

Above 6.01mm

3.6mm

4.51 to 6mm

2.7mm

rounded, flash-free


br1

g

t

r2z

d4

0° to 5°

d3d9

15° to 20°

B

AB

d7

d8b

B

0° to 5°

B A h

r2

r1

(internal pressure)

b

t

r10 - 5°

r2

Pressure direction

No back-up ringb

Pressure direction

One back-up ring

b1

Pressure direction

Two back-up rings

b2




d4/d10

d5/d9

d7

d8

H8

f7H11

H11


d1 d2

0° to 5° r1z

g

A t

rounded, flash-free

r2

b

B

B

15° to 20°

d10 d6d5

Piston sealing (radial) type A

The inside diameter (d1) of an o-ring

should always be smaller than the housing

diameter (d3). The maximum stretch must

be limited to keep the resultant loss in cross

sectional diameter to an acceptable level and

keep the tensile stress to a minimum.

Rod sealing (radial) type B The ideal condition is for the o-ring outside

diameter to be equal to, or slightly greater

than, the housing diameter (d6). Too higher an

interference of the seal outside diameter (d6)

will result in distortion of the seal profile. This

is due to its inability to cater for the difference

in circumferential length.

A maximum outside diameter interference

of 3% is considered optimum but on small

diameters this could be up to 8%.

Face sealing (axial) type C & D This is the simplest use of o-rings, provided the

basic rules are remembered. Seal compression is

controlled by the depth of the groove and should

be between 15% to 30%.

For internal pressure, the o-ring should be

supported by the housing diameter (d7) whilst for

external pressure the inner diameter (d8) is used.

It is possible to remove the internal spigot, where

there is internal pressure, provided there is no

risk of cavitation.

Housing diametrical tolerances For radial sealing it is important to use tight tolerances as specified for the shaft and bore.

This reduces possible eccentricity and possible loss of compression.

For face sealing it is important to use a tight tolerance to reduce the range of stretch

or o-ring outside diameter as applicable.

Coefficient of thermal expansion When an unloaded rubber is heated it will expand inline with the coefficient of thermal expansion

for that particular rubber grade. Rubber compounds have much higher coefficients of thermal

expansion than steel or Aluminium (approx. ten times of steel), thermal expansion may cause an

already tight seal to swell and overfill the groove as temperature rises. Housings have been known

to rupture under the force exerted by an expanding seal. A seal design that provides minimal

compression in a low temperature environment cannot rely on thermal effects for help in tightening

the seal. It is therefore imperative that the seal has the correct compression and groove width

to allow for these situations.

Coefficient of frictionThe coefficient of friction for a rubber seal is influenced by many factors. These include compound

hardness, surface finish of mating components, speed of movement and lubrication. Breakout

friction is generally higher than running friction. To lower breakout and running friction, coatings

or lubrication can be applied.

Superior offer a wide range of solutions to help alleviate frictional forces. Superior dry coatings can also

aid assembly and increase efficiency on automatic assembly lines while reducing assembly efforts,

reduce risk of rolling during installation, and eliminate sticking of components after long storage.

Lead in chamfers Z (30° – 40° inclusive) To enable the o-ring to be fully assembled without undue risk of damage, the appropriate

lead in chamfer needs to be applied to the housing.

Surface finish or texture Sealing efficiency can be directly related to surface finish. The application must be considered

from a number of aspects to establish the most effective and economic surface finish.

General housing guidelines



Static axial face housingThe o-ring is compressed in the axial direction.

When the o-ring is subjected to a pressure

the o-ring will undergo a relative displacement.

Therefore it is important to correctly size the

o-ring to limit the movement when pressure

is applied. If the pressure is internal, then

the o-ring’s outside diameter should be in

contact with the housing outside diameter.

The circumferential interference should be

no more than 1%.

If the pressure is external then the o-ring’s

inside diameter should be in contact with

the housing. In this case the o-ring should

be stretched up to a maximum of 4%.


d2

1.50

1.78

2.00

2.50

2.62

3.00

3.53

4.00

5.00

5.33

6.00

6.99

8.00

9.00

10.00

12.00

h+0.10

1.10

1.30

1.50

2.00

2.10

2.30

2.80

3.25

4.00

4.35

5.00

5.75

6.80

7.70

8.70

10.60

b+0.20

1.90

2.40

2.60

3.20

3.60

3.90

4.80

5.20

6.50

7.20

7.80

9.60

10.40

11.70

13.00

15.60

r1

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.8 - 1.2

0.8 - 1.2

0.8 - 1.2

0.8 - 1.2

0.8 - 1.2

r2

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

pressurefrom inside

pressurefrom outside

r1

r2

h

b

d7

B

B

A

0° to 5°

0° to 5° d8

b

B

A

h

Br1

r2


d2

1.50

1.78

2.00

2.50

2.62

3.00

3.53

4.00

5.00

5.33

6.00

6.99

8.00

9.00

10.00

12.00

h+0.10

1.10

1.30

1.50

2.00

2.10

2.30

2.80

3.25

4.00

4.35

5.00

5.75

6.80

7.70

8.70

10.60

b+0.20

1.90

2.40

2.60

3.20

3.60

3.90

4.80

5.20

6.50

7.20

7.80

9.60

10.40

11.70

13.00

15.60

r1

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.4 - 0.8

0.8 - 1.2

0.8 - 1.2

0.8 - 1.2

0.8 - 1.2

0.8 - 1.2

r2

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

0.2 - 0.4

pressurefrom inside

pressurefrom outside

r1

r2

h

b

d7

B

B

A

0° to 5°

0° to 5° d8

b

B

A

h

Br1

r2


d2 h+0.10 b+0.20 r1 r2

Lead in chamfers z1 and z2 (30˚ – 40˚ inclusive)

d2 Up to 2mm 2.01 to 3mm 3.01 to 4.5mm 4.51 to 6mm Above 6.01mm

Z minimum 1.1mm 1.5mm 1.8mm 2.7mm 3.6mm

All edges to be rounded.

Surface finish or texture

Letter Surface Application Pressure Surface roughness

Ra µm

A Housing Sides Static Non pulsating and 1.6

and static diameters non alternating

Pulsating or alternating 0.8

Dynamic All types 0.8

B Mating surface in Static Non pulsating and 0.8

contact with ‘O’ Ring non alternating

e.g. cylinder bore for Pulsating or alternating 0.4

piston seal Dynamic All types 0.4

The above is for guidance only and covers the majority of the sealing applications. However, Superior Seals should be consulted in areas of particular concern.

1.50

1.60

1.78

2.00

2.40

2.50

2.62

3.00

3.50

3.53

4.00

5.00

5.34

5.70

6.99

8.40

1.00/1.05

1.20/1.25

1.24/1.37

1.35/1.45

1.70/1.80

1.78/1.88

1.90/2.03

2.20/2.30

2.60/2.70

2.54/2.80

3.00/3.10

3.80/3.90

4.19/4.45

4.40/4.50

5.60/5.85

6.60/6.70

2.25/2.55

2.36/2.66

2.54/2.84

2.89/3.19

3.45/3.75

3.38/3.68

3.60/3.90

4.00/4.30

4.50/4.80

4.80/5.10

5.10/5.40

6.23/6.53

7.10/7.40

7.00/7.30

8.90/9.20

10.00/10.30

2.08/2.20

2.20/2.32

2.41/2.54

2.76/2.88

3.30/3.42

3.44/3.56

3.68/3.81

4.20/4.32

4.81/4.93

4.95/5.08

5.51/5.63

6.86/6.98

7.50/7.63

7.80/7.92

10.03/10.16

11.50/11.62

3.80

4.00

4.80

4.60

5.00

5.25

6.35

6.00

6.80

8.00

7.40

8.90

11.00

10.00

15.00

14.00

0.2

0.2

0.5

0.5

0.5

0.5

0.9

1.0

1.0

0.9

1.0

1.0

0.9

1.0

0.9

1.0

0.75

0.80

0.76

1.10

1.30

1.40

1.02

2.00

1.90

1.52

2.20

2.70

2.20

3.00

2.54

4.00

O-ring housing data for axial and triangular sealing applications

d2 h b t sminimum

Triangularr1

maximum

Axialr1

maximumd2

Static axial face housingThe ‘O’ ring is compressed in the axial

direction. When the ‘O’ ring is subjected

to a pressure the ‘O’ ring will be subject

to a relative displacement. Therefore it is

important to correctly size the ‘O’ ring to

limit the movement when pressure is applied.

If the pressure is internal, then the ‘O’ ring’s

outside diameter should be in contact with the

housing outside diameter. The circumferential

interference should be no more than 1%.

If the pressure is external then the ‘O’ ring’s

inside diameter should be in contact with

the housing. In this case the ‘O’ ring should

be stretched up to a maximum of 4%.

Static triangular housingLocation grooves with a triangular shape

are sometimes used for screwed flanges

and caps. However, manufacturing these to

accurate sizes is difficult. Since the sealing

function of the ‘O’ ring depends on the exact

shape of the locating groove, the dimensions

and tolerances given in the following table

are to be strictly observed. Installation in

rectangular grooves is preferable.

15° to 20°

Piston assembly

Use of a fitting aid

Rod assembly

15° to 20°

Axial compression or face seal

Sq

ueez

e %

d2 (mm)static-axial

O-ring cross section d2 in mm

1 2 3 4 5 6 7 80

5

10

15

20

25

30

35

max.

min.

Recommended axial compression

Static sealing – axial and triangular

rounded, flash-free


br1

g

t

r2z

d4

0° to 5°

d3d9

15° to 20°

B

AB

d7

d8b

B

0° to 5°

B A h

r2

r1

(internal pressure)

b

t

r10 - 5°

r2

Pressure direction

No back-up ringb

Pressure direction

One back-up ring

b1

Pressure direction

Two back-up rings

b2




d4/d10

d5/d9

d7

d8

H8

f7H11

H11


d1 d2

0° to 5° r1z

g

A t

rounded, flash-free

r2

b

B

B

15° to 20°

d10 d6d5

rounded, flash-free


br1

g

t

r2z

d4

0° to 5°

d3d9

15° to 20°

B

AB

d7

d8b

B

0° to 5°

B A h

r2

r1

(internal pressure)

b

t

r10 - 5°

r2

Pressure direction

No back-up ringb

Pressure direction

One back-up ring

b1

Pressure direction

Two back-up rings

b2




d4/d10

d5/d9

d7

d8

H8

f7H11

H11


d1 d2

0° to 5° r1z

g

A t

rounded, flash-free

r2

b

B

B

15° to 20°

d10 d6d5

Piston sealing (radial)

Rod sealing (radial)

Static/dynamic sealing – radial

O-ring stretch in piston sealing When an o-ring’s internal diameter is less than 50mm, the maximum stretch should be less than

8%. When an o-ring’s internal diameter is greater than 50mm, the maximum stretch should be less

than 6%. The maximum stretch is derived from the largest groove diameter and smallest o-ring

internal diameter.

Reduction of cross-section due to stretchWhen an o-ring is stretched, the cross-section distorts to assume an oval form. The o-ring cross-

section reduces when subject to stretch. As rule of thumb, approximately half of the stretch

e.g. 5% stretch equals 2.5% reduction in cross-section.

This reduction in cross-section lowers the compression and thus the sealing stress.

Guidelines• Static o-rings are squeezed to higher percentages than dynamic, as friction

concerns are reduced.

• Surface finish requirements can be relaxed in comparison to dynamic

applications (except where pulsating pressure is present).

• Dynamic o-rings are exposed to lower squeeze percentages compared to static

to reduce friction and wear.

• Surface finish requirements are critical to reduce friction, seal wear and damage.

• The groove width will need to be increased for one/two back up rings, if system

pressures are exceeded beyond normal o-ring capability.

• Oscillating and rotating conditions are regarded as dynamic.

• Although suitable for dynamic work, o-rings are best applied to short stroke/small

diameter applications.

• The preferred o-ring hardness is 60 to 80 IRHD.

• Media compatibility and temperature are critical, as swell or shrinkage should

be minimised for reliable function.

• Compounds with the highest wear resistance should be selected.

• Pneumatic and hydraulic applications can be accommodated.

Superior does not generally recommend the use of o-rings as rotary seals.

Gough-Joule effectWhen a freely suspended, loaded rubber is stretched and heated, the rubber will contract,

attempting to regain a less stressful state. This occurs because of the rubber’s stressed structure.

This phenomenon is of particular importance in rotary applications, where the combination of

installed stretch and system heat can cause the o-ring to retract and seize the rotating shaft.

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13

Unstretched O-ring

Stretched O-ring


Type B

Type C & D

Piston sealing

Face sealing

% r

educ

tio

n o

f cr

oss

-sec

tio

n d

2


2 4 6 8 10 12 14 16 18 20 22 24 260

1

2

3

4

5

6

7

8

9

10

11

12

13



Static triangular housingLocation grooves with a triangular shape are

sometimes used for screwed flanges and caps.

However, manufacturing these to accurate sizes

is difficult. Since the sealing function of the o-ring

depends on the exact shape of the locating

groove, the dimensions and tolerances given

in the following table are to be strictly observed.

Installation in rectangular grooves is preferable. Housing Dimensions – static axial (mm)

d2 h+0.10 b+0.20 r1 r2

h

b

pressurefrom inside

Ø d70° to 5°

r2

r1

A

B

B

h

b pressurefrom outside

Ø d80° to 5°

r1

r2

A

B

B

b+0.2

rounded, flash-free

Ø d4Ø d3

t

Ø d9

r1

r2

0° to 5°

15° to 20°

z

B

B

Ag

Installation in atriangular groove

Ø h8

45°

t

s

O-Ring Rousing data for piston and piston rod sealing applications

Mode d2 t b t tb1 b2

Static

*Static

Static anddynamic

Pneumatic

Static anddynamic

Pneumatic

*Dynamic

*Static

Static anddynamic

Pneumatic

Static anddynamic

Pneumatic*Dynamic

Pneumatic

*Static

Static anddynamic

Static anddynamic

Static anddynamic

Pneumatic

Pneumatic

Static anddynamic

Static anddynamic

Pneumatic

*Dynamic

Pneumatic*Static

Static anddynamic

Pneumatic

*DynamicPneumatic

*Static

1.60

1.78

1.50

2.00

2.40

2.50

2.62

3.00

3.50

3.53

4.00

5.00

5.34

5.70

6.99

8.40

7.20/7.50

7.75/7.967.50/7.75

6.12/6.32

6.00/6.12

4.70/4.955.22/5.38

4.95/5.184.83/4.93

4.66/4.77

4.30/4.52

3.40/3.57

3.02/3.12

3.18/3.25

4.57/4.67

2.94/3.11

2.20/2.30

2.34/2.41

2.50/2.65

2.35/2.50

2.70/2.77

2.06/2.19

2.24/2.31

1.84/1.97

1.64/1.72

1.97/2.09

2.13/2.20

1.55/1.60

1.46/1.52

1.18/1.251.17/1.09

7.00/9.20

11.00/11.20

11.00/11.20

8.65/8.85

8.65/8.85

6.40/6.607.50/7.70

6.35/6.55

6.35/6.55

7.50/7.70

6.60/6.80

6.60/6.80

5.30/5.50

4.30/4.50

4.30/4.50

4.70/4.90

3.70/3.90

4.00/4.20

4.00/4.20

3.17/3.37

3.17/3.37

3.40/3.60

3.40/3.60

3.10/3.30

3.20/3.40

3.20/3.40

2.70/2.90

2.40/2.60

2.40/2.60

2.30/2.50

2.30/2.50

7.63/7.75

-

-

-

6.07/6.14

-

-

5.08/5.18

-

4.71/4.49

-

4.42/4.52

3.47/3.57

-

3.10/3.15

3.01/3.11

-

-

2.57/2.65-

2.26/2.31

-

2.12/2.19

-

-

2.01/2.09

1.68/1.72

-

1.47/1.52

-

-

13.20/13.40

--

10.05/10.18

-

--

9.30/9.50

-

7.60/7.73

-

8.40/8.60

-

6.70/6.90

5.50/5.63

-

6.10/6.30

-

5.40/5.60

-

4.60/4.73

-

4.80/5.00

-

-

4.60/4.80

-

4.10/4.30

-

4.10/4.23

-

7.63/7.75

--

-

6.07/6.14

--

5.08/5.18

-

4.71/4.79

-

4.42/4.52

3.47/3.57

-

3.10/3.15

3.01/3.11

-

-

2.57/2.65

-

2.26/2.30

-

2.12/2.19

-

-

2.01/2.09

-

1.68/1.72

1.47/1.52

-

-

15.40/15.60

-

-

-

13.50/13.63

-

-

11.10/11.30

-

10.20/10.33

-

10.20/10.40

-

8.10/8.30

7.40/7.53

-

7.50/7.70

-

6.80/7.00

-

6.50/6.63

-

-

-

6.20/6.40

6.00/6.20

5.50/5.70

-

6.10/6.23

-

-

1.00

0.90

1.00

0.90

1.00

1.00

1.00

0.90

1.00

0.80

0.80

0.50

0.50

0.50

0.500.50

0.40

0.40

0.40

0.40

0.40

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

Withanti-extrusionrings

Withoutanti-extrusionrings

r. maximum

Corner radiid2

d2

b b1 b2b2

tt

b1

t

b

(100 bar maximum)pressure

(100 bar +) (100 bar +)

alternating pressure

*BS 4518 recommendations NOTE: All dimensions in mm

15° to 20°

Piston assembly


Rod assembly

15° to 20°

0

5

10

15

20

25

30Hydraulics, dynamic

Pneumatics, dynamic

Sq

ueez

e %

Sq

ueez

e %


Hydraulics, pneumatics, static

Sq

ueez

e %

Sq

ueez

e %


max.

min.

1.8 2.65 3.55 5.3 7


1.8 2.65 3.55 5.3 7


1.8 2.65 3.55 5.3 7

d2 (mm)static-axial

0

5

10

15

20

25

30

0

5

10

15

20

25

30

max.

min.

max.

min.

max.

min.

0

5

10

15

20

25

30

35

1 2 3 654 7 8

15° to 20°

Piston assembly


Rod assembly

15° to 20°

0

5

10

15

20

25


Pneumatics, dynamic

Sq

ueez

e %

Sq

ueez

e %



Sq

ueez

e %

Sq

ueez

e %


max.

min.

1.8 2.65 3.55 5.3 7


1.8 2.65 3.55 5.3 7


1.8 2.65 3.55 5.3 7

d2 (mm)static-axial

0

5

10

15

20

25

30

0

5

10

15

20

25

30

max.

min.

max.

min.

max.

min.

0

5

10

15

20

25

30

35

1 2 3 654 7 8

15° to 20°

Piston assembly


Rod assembly

15° to 20°

0

5

10

15

20

25


Pneumatics, dynamic

Sq

ueez

e %

Sq

ueez

e %



Sq

ueez

e %

Sq

ueez

e %


max.

min.

1.8 2.65 3.55 5.3 7


1.8 2.65 3.55 5.3 7


1.8 2.65 3.55 5.3 7

d2 (mm)static-axial

0

5

10

15

20

25

30

0

5

10

15

20

25

30

max.

min.

max.

min.

max.

min.

0

5

10

15

20

25

30

35

1 2 3 654 7 8

Typical compression range

Typical o-ring housing data for piston and rod sealing applicationsWhilst the adjacent table is a guideline for o-ring compression, the following graphs display a more accurate representation.

Pressure

600

500

400

300

200

150

1009080706050403020100

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

70degrees of hardness 80 90 IRHD

diametrical play (mm)

wor

king

pre

ssur

e: b

ar

extrusio

n

no extrusio

n

mm

Pressure

Cle

aran

ce (r

adia

l)

70 80 90 rubber hardness (IRHD)

0 70 140 210 280 350 410 bar0

0,05

0,10

0,15

0,20

0,25

0,30

• Anti extrusion rings are required when

considering conditions to the right of

the hardness curve.

• For temperatures above 100°C use

the curve for the next hardness rubber.

A good quality 70 IRHD compound will resist

extrusion at room temperature up to 100 Bar.

However, extrusion resistance is influenced by:

• temperature

• pulsating pressure spikes

• seal cross section

• housing design (radii, draft angles).

Please consult our Engineering department

for detailed information regarding particular

working conditions.

Elastomers tend to act as a viscous fluid when under pressure, resulting in migration into the

‘extrusion gap’.

Therefore, under certain conditions, a supporting back-up ring is used in conjunction with

an o-ring to reduce the risk of extrusion. The back-up ring effectively bridges any gap due

to the clearance between the shaft and bore.

For axial face-sealing applications, extrusion gaps should be eliminated, ensuring that pulsating

pressures do not create ‘panting’ between mating faces.

When exceeding the recommended gap size (in accordance with the graph below)

an anti-extrusion device is required.

• Recommended extrusion gap is based upon radial clearance if eccentricity is zero,

or diametral clearance if concentricity of mating diameters cannot be assured.

• It should be noted that Silicone and Fluorosilicone (due to low tensile strength) should

only be applied in grooves with extrusion gaps at half the recommended radial clearance

for other compounds.

• If a selected radial clearance will not achieve a given pressure, then the next

hardness range should be considered.

• If a 90 IRHD rubber compound does not satisfy the given parameters, then a PTFE

or Thermoplastic back-up ring should be selected.

Zero pressure

Pressure

Extrusion

Zero pressure

Pressure

Extrusion

Zero pressure

Pressure

Extrusion



Our state of the art toolroom designs and manufactures precision prototype and production moulds to meet the engineering challenges of our customers.

Precision mouldings / custom seals

Where a specific moulding profile is required,

we apply our extensive experience to guide

the design evolution to achieve the most

reliable and cost effective solution.

Our broad design capabilities at Superior

enable us to supply unique profiles for

applications where traditional o-rings

are not suitable.

Our portfolio includes generic profiles

such as:

• diaphragms

• precision flat washers

• spherical balls.

Although there is an infinite number of different

seal profiles which can be used to suit

individual applications, there are a number

of more commonly used custom seal profiles.

Listed below are just a small number and their

advantages.

Lip seals / U-seals / V-seals

• Self energising when pressure acts

against the lips

• Lower assembly force than the

equivalent o-ring

• Lower dynamic running force than

the equivalent o-ring

• Require less space than the

equivalent o-ring

• Less creep in housing

• Able to cope with larger tolerances

• Able to cope with eccentric conditions

• Able to cope without flatness

(axial sealing).

Symmetrical seals • Lower assembly force than the

equivalent o-ring

• Greatly reduces the chance of spiralling

• Symmetrical design enables seal to be

assembled both ways

• Less volume than the equivalent o-ring

• Can cope with pressure from both sides.

Quad rings

• Two sealing beads in contact with both

the groove and bore

• Greatly reduces the chance of spiralling

• Symmetrical design enables seal to be

assembled both ways

• Lower friction for dynamic applications.

Moulded gaskets

• Low assembly force

• Tailored profile

• Able to cope with larger tolerances

• Able to cope without flatness

• Plastic housings

• Retention

• Axial (face) sealing

• Multiple sealing ports

• Customer information

• Location tags

• Stabilising features.

Custom radial seals

• Low dynamic force

• Eccentric conditions

• Tolerances

• Special conditions

• Profile.

Moulded Seals are homogenous rubber parts

which are components that operate within

static and dynamic applications.

Superior engineering Superior’s core strength is providing our

customers with optimal design and robust

sealing solutions. Superior has the ability to

assist in the design of sealing solutions which

exceed customer expectations. Support

and Technical Service are always on hand

to provide advice on component design,

compound selection and analysis.

When an o-ring is desired we can calculate

the ideal housing geometry and o-ring size

for given parameters. Where an o-ring cannot

be used, Superior can offer help and advice

to find a solution for you.

Seal integrity

We are focused on the fact that our precision

o-rings and special mouldings are a crucial

part ‘of the bigger picture’. The integrity and

quality of Superior products are fundamental

to the integrity of each end product, helping

to achieve outstanding product performance

and enhance our customers’ hard-won

reputations. The unique integrity of our

products is achieved through a combination

of 3 Key Elements; Compound, Design and

Manufacturing process.

Seal Integrity

Design Compound

Manufacturing Process

Custom seal designSuperior technical guide


04 Custom seal design and manufacture Using Superior custom designed seals can mean fast service and quality assurance to you.

Seal performanceThe performance of the seal is dependant

on 5 factors:

• system media

• hardware

• service conditions

• seal design

• seal compound.

Seal design assistanceGetting involved at the earliest possible stage of

development, our engineering department aims

to become an integral part of our customer’s

team, providing services such as:

• seal design

• housing recommendations

• design for manufacture and assembly

(DFMA)

• CAD

• problem solving

• advice.

All these services combined assist in reducing

project lead times.

Custom seal designSuperior technical guide


Tolerances for moulded partsMoulded seals are subject to changes

in their geometry during vulcanization.

These changes should be allowed for when

designing. The greater the degree of accuracy

demanded, the closer the control which must

be exercised during manufacture. When

particular physical properties are required

in the product, we advise consultation with

Superior’s Engineering department.

All rubber shows some shrinkage when

cooled after moulding, and allowance for this

is made in the mould design. The amount of

shrinkage is dependent on rubber type.

Moulds are made in various ways depending on

the type of product and accuracy demanded.

Superior recommend the use of ISO 3302-1

Class M2 tolerance for high-quality precision

mouldings (see table below).

In compression moulding more rubber is

used than is required to fill the cavity, and

the excess is flashed. This flash can prevent

the mould sections from fully closing and

thus affects the finished part dimensions.

However, for injection and transfer moulding

all dimensions can be considered as fixed.

A heritage of excellence

Since 1972 Superior has built a reputation

for engineering excellence. Our tool-making

expertise and capabilities ensure we

consistently meet the tightest tolerances,

not to mention budgets and deadlines,

every single time.

Our tool roomAs a full service facility we are able to manage

projects from prototyping right through to

production. We focus on providing engineers

and product designers with physical samples

in the shortest possible lead time.

The marketplace and our customers’ needs

are constantly changing. We are flexible

enough to react to changing demands

quickly, and can use off-line programming

to take new designs to machine as quickly

as possible.

We have complete control of the tool making

process, and are committed to expanding

our facility in line with client needs. In fact we

constantly invest in the latest, state-of-the-art

technology to ensure all tooling and products

are manufactured with 100% accuracy and

meet our customers’ tightest deadlines.

The service we offer to our customersOur success is based on our clients’ success.

That’s why we do everything we can to make

working with Superior benefit their business.

Our clients can expect to have samples

perfectly bagged, delivered on their desk

ready for practical trials. We are here to help

our customers win business and launch new

products in the most compressed time scales

and above all with confidence.

Above Up to and including

F ±

C ±

Nominal dimension Class M2

0 4.0 0.10 0.15

4.0 6.3 0.15 0.20

6.3 10 0.20 0.20

10 16 0.20 0.25

16 25 0.25 0.35

25 40 0.35 0.40

40 63 0.40 0.50

63 100 0.50 0.70

100 160 0.70 0.80

160 - 0.50% 0.70%

Dimensions in mm

F

F

F

C

C

C

lower half of mould

flash

upper half of mould

moulded part

Two types of tolerances, F and C are used.

Fixed dimension (F): Dimensions which are

not affected by influences like flash or lateral

movement of different mould parts.

Closure dimension (C): Dimensions which

can be altered by flash thickness or lateral

movement of different mould parts.

O-ring size range standardsAt Superior, we pride ourselves on our

precision o-ring range which exceeds the

cross-sectional tolerances for the following

dimensional standards;

ISO 3601-1

DIN 3771 Part 1

BS 4518

The benefit of close tolerances on an o-ring

cross section (d2), is the ability to reduce our

customer’s tolerance chain and improve the

overall performance of the customer’s product.

In the Superior o-ring size list, the internal

diameters conform to ISO 3601-1 tolerances

and the cross section diameter has a reduced

tolerance. These precision o-ring tolerances

apply to NBR 70 compounds. O-rings

manufactured in other compounds and

hardness’ are produced to conform

ISO 3601-1 tolerances, however

dimensions for the internal diameter

may be towards the lower end.

High shrinkage compounds may

require dedicated tooling to comply with

ISO 3601-1 dimensions and tolerances,

but will still allow for the principle of a more

accurate cross-section. Superior can also

supply o-rings to customer’s specifications.

A continually updated version of the Superior

o-ring size list can be downloaded from our

website www.superiorltd.com

d1 d2

Quality acceptance criteria ISO 3601-3

b+0.2

rounded, flash-free

Ø d4Ø d3

t

Ø d9

r1

r2

0° to 5°

15° to 20°

z

B

B

Ag Off-register

mismatch(offset)

Combinedflash

Backrind

Excessivetrimming

Flow marks

Foreignmaterial,non-fills andindentations(includingparting-lineindentations)

e

f

g

h 0.08

0.18

0.10

0.08 0.10

0.12

0.27

0.08 0.10

0.36

0.14

0.13 0.15

0.16

0.53

0.10 0.13

0.70

0.18

0.15

Grade N

O-ring section diameter d2

Size limitLimitingdimension

Surfaceimperfection

<2.25 >2.25<3.15

>3.15<4.50

>4.50<6.30

>6.30<8.00

e e e

f

f

g

h

n

j

k

m

l

l

Not less than o-ring section diameter on lower tolerance

n

j

k

l

m 0.08

0.60

0.08

1.50 * 1.50 *

0.08

0.80

0.08 0.10 0.10

1.00

0.08

6.50 * 6.50 * 6.50 *

0.08 0.08

1.30 1.70

0.13

* or 0.05 x o-ring internal diameter, whichever is greater but not exceeding 50 mm

Limits of size for surface imperfections for Grade N o-rings

QualitySuperior technical guide

Quality Standards compliance05


Quality is an integral part of the Superior customer service philosophy

Total control of all aspects of seal

manufacture ensures that we always

comply with recognised standards

applied by the industry.

With our expertise we can closely define

and control seal tolerances and surface

characteristics. Our continual investment

programs enable us to apply the latest

control and inspection techniques.

This section is designed to give guidance

to quality and design engineers.

We thoroughly recommend that all quality

and specification issues are addressed at

the earliest point in the development stage

of any new project. This ensures that all

customer-critical features and commercial

issues are identified from the outset.

Quality control: documentation

All documentation for despatch to the

customer conforms to the ISO 9001 standard.

The documentation issues and details are

continually being revised and updated

according to demands from individual

customers and the industry in general.

Please consult our Quality department

for specific requirements.

Seal surface inspection levels

All our o-rings are inspected to ISO 3601-3

DIN 3771 part 4. The standard level is Grade N.

For more information on inspection levels

please consult our Quality department.

Special moulding tolerances

Dimensional tolerances on special

mouldings will relate to ISO 3302-1

or customer specification.

Certification

Certification can be provided with the product,

but must be stated at point of order.

Environmental compliance

Superior is able to provide materials compliant

to current European and Worldwide legislative

requirements e.g. ROHS, REACH and IMDS.

AssemblySuperior technical guide

Assembly This section of the guide is intended to assist engineers when considering sealing criteria.06


Use of a Fitting Aid

An o-ring is a precision component requiring

care during installation and handling. Many

failures of o-rings can be directly related to

improper installation. Long-term, leak-free

o-rings can only be achieved when the

correct size for the housing is chosen.

O-ring stretch during assembly

During assembly an o-ring inside diameter

can be stretched up to 50% for most

compounds, however it is advisable to keep

below this value where possible to prevent

damage to the o-ring. Sometimes this value

may be unachievable, this is particularly

true with o-rings of small inside diameter

and large section.

It is essential to give the o-ring time to

recover, this is especially important during

automatic assembly.

Fitting aids and sharp edges

O-rings should not be drawn over sharp

edges, threads, slits, bores and splines

during fitting. The use of fitting aids during

assembly ensures the avoidance of sharp

edges and features.

Suitable assembly tools, as detailed,

aid location and avoid contact with sharp

edges. The aid should be manufactured

from materials which will not damage sealing

locations and surfaces (e.g. plastic or brass).

For manual assembly or removal of an

o-ring from a groove, a spatula-type tool

can be manufactured from a soft material.

All edges should be smooth, rounded

and free from burrs.

Rod sealing assembly aids

Piston sealing assembly aid

StorageSuperior technical guide


Housing chamfers To prevent damaging the o-ring section

during assembly, chamfers are necessary

on all leading edges, all other edges must be

free from burrs. Dimension X should always

be greater than dimension Y to ensure

trouble free assembly.

Traversing cross drilled ports An o-ring can be sheared when a

spool or a rod moves in a bore broken

by cross-drilled ports. The deformed

o-ring returns to its original round cross

section as it enters the port and is sheared

as it leaves the drilled area. To avoid this,

connection holes should be repositioned.

If repositioning is not feasible, an internal

chamfer is recommended.

Rolling O-rings are at risk from rolling when fitted

over a diameter. This risk can be accentuated

on large inside-diameter/ small section

o-rings. This can result in spiral failure and

leakage. To reduce the risk of rolling we

recommend that suitable lubrication be

applied to the o-ring prior to assembly.

Cleanliness / cleaning materials At Superior we rigorously control cleanliness

at all process stages, particularly during the

final post-deflashing cleaning cycle.

All seals are supplied to the customer free

from surface silicone film and surface particle

contamination (e.g. flash particles).

Foreign particle contamination on seals

can cause leakage after assembly.

If applying lubricants, the seal should be

assembled immediately into the housing,

or protected if placed in storage or transition.

All cleaning media must be compatible

with the elastomer.

Leading edge chamferX>Y

Y

X

15°to 20°

Leading edgechamfer and an ‘O’ ring beforedeformation.Dimension xshould always be greater thandimension y toensure trouble-free assembly

leading edge chamfer x > y

y

15° to 20°x

15° to 20°

15° to 20°

Piston assembly

Rod assembly


Fitted ‘O’ ring,rolled

Optimal solution is chamfering the full bore circumference, allowing the o-ring to return to a round cross-section before re-compression

Leading edgechamfer and an ‘O’ ring beforedeformation.Dimension xshould always be greater thandimension y toensure trouble-free assembly

leading edge chamfer x > y

y

15° to 20°x

15° to 20°

15° to 20°

Piston assembly

Rod assembly


Fitted ‘O’ ring,rolled

Optimal solution is chamfering the full bore circumference, allowing the o-ring to return to a round cross-section before re-compression

Recommended storage conditions for products based on Superior rubber compounds.

Optimum service is the primary objective

in the development of any compound

at Superior.

We give careful consideration to minimising

the compound factors that may adversely

affect seal performance. It is in the nature

of rubbers that changes can occur during

extended component storage and become

exacerbated by inappropriate conditions

and practices. Recommended conditions

should always be followed.

Light Sunlight and intense artificial light can cause

surface deterioration of rubber components.

In extreme cases, this is manifested as

shallow crazing.

We recommend that storage of such parts

should take place in dark or very low-intensity

artificial light conditions.

Humidity

You should avoid conditions where

condensation may occur prior to

assembly/installation.

Contaminants

Airborne contaminants deposited on the

surface of o-rings prior to installation can

promote surface attack. Examples include

cutting oil mists, powders and active

chemicals used in production processes.

In the case of particulates, such

contamination can create a leakage

path when in service.

As far as is possible, o-rings should be

kept in their sealed delivery bags until

required for installation.

Stress

Always store o-rings in their unstressed,

free state, avoiding distortion and the risk

of ozone attack. Large rings should never

be hung on pegs.

Temperature

Finished components should be stored

below 30°C and preferably below 25°C.

Extended exposure to higher temperatures in

air can accelerate ageing effects and cause

distortion, hardening, elongation loss and

impairment of low temperature flexibility.

If inadvertent freezing has occurred, the

apparent hardening effect can be reversed by

warming to normal ambient temperatures.

Oxygen and ozone Superior o-rings are supplied in sealed

polythene bags which prevent exposure to

circulating air and atmospheric impurities.

We recommend that o-rings are kept in these

bags until required – it is the combined effect

of atmospheric oxygen and temperature that

promotes the problems encountered above.

Ozone is present in low concentrations

in the atmosphere and at much higher levels

near some electrical equipment. It will attack

rubber components based upon particular

elastomers when they are stretched or

distorted. This appears as cracks at right

angles to the direction of distortion.

Of all common o-ring elastomers,

only nitrile (NBR) is significantly prone

to ozone attack.

Once again, storage in the original

sealed polythene bags in dark or very

low-intensity artificial light conditions

offers full protection.

Shelf life It is practically impossible to define a specific

maximum shelf life for finished elastomeric

products. To achieve the best results, always

rotate stock and store as recommended.

The following table of suggested

shelf life is for guidance only.

These storage times are more

conservative than those proposed in

BS ISO 2230:2002, ‘Controlled storage

and packaging of vulcanised rubber

and rubber products’.

Storage

3 years

Superior FN

Superior WN

5 years

Superior LN

Superior MN

Superior HN

7 years

Superior EP

Superior SIL

Superior PA

Superior TH

Superior VF/VP

We are fiercely proud of our place in the world of engineering.


We are also constantly aware of the continuous challenges that face us in order to maintain our position and ensure we continue to fulfil obligations to our customers.

By continually monitoring our performance, sharpening our technical expertise and tightening

response times, we are able to reinforce our added value. If you would like to learn more about

how Superior can contribute to your business’ success we would be pleased to answer your

questions and welcome you to meet our people, see our facility and discuss your requirements.

A warm welcome awaits you at Superior.

Superior Seals Limited

Nimrod Way

Ferndown Industrial Estate

Wimborne, Dorset BH21 7SH, UK

Tel: +44 (0)1202 854300

Fax: +44 (0)1202 854313

Email: [email protected]

Superior Specials Limited

Nimrod Way

Ferndown Industrial Estate

Wimborne, Dorset BH21 7SH, UK

Tel: +44 (0)1202 891180

Fax: +44 (0)1202 894468

Email: [email protected]

01.1

3.02

All technical information included in this document is provided free of charge for guideline purposes only and is based on

technical data which Superior believes to be reliable. This information is intended for use by suitably skilled and qualified

persons entirely at their own discretion and risk. As the end use of our product is beyond our control, we make no warranties

express or implied and no liability can be accepted in connection with the use of this information, which is subject to revision

without prior notice as additional knowledge and experience are gained. COPYRIGHT © 2013 Superior GROUP LIMITED

www.superiorltd.com

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