Specialised Engineering Products

MANUFACTURING IN RUBBER
 Specialised Engineering Products

I N T R O D U C T I O N

Specialised Engineering Products Limited was established in 1976 and is a quality assured

company to industry approved standards.

The company is recognised throughout most industries as being a supplier of high quality

sealing devices for the majority of fluid sealing applications. As such, our development in

rubber technology has remained progressive, with rubber lending itself so readily to so many

sealing duties.

Our foundations are firmly established as a service company, where our ability to respond

quickly, through close technical co-operation, to quotation and despatch, has built SEP an

enviable reputation. Our vision and ongoing philosophy is to maintain these high levels of

service as a significant manufacturing company and develop these far beyond those of just

the fluid sealing sector. It is our ultimate intention to offer the widest range of quality,

competitively priced products manufactured in rubber.

Our commitment to continuous improvement has taught us, if there is one outstanding

lesson, it is that the earlier a designer involves the rubber engineer, the greater the benefits

in terms of cost, design effectiveness and ease of production.

This brochure has been designed to give designers and end users of rubber products

easy-to-use technical information, the result of which will assist successful working

partnerships in producing high quality, cost effective, trouble free components.

SEP continues to meet the growing demands of modern industry, setting our standards for

the future even higher than those of today. As such, the products we manufacture and

supply offer only the very best quality and reliability, minimising equipment down time and

increasing safety.

ANDREW SMITH
Managing Director

TWO
 Specialised Engineering Products

C O N T E N T S

FOUR

BENEFITS OF RUBBER
WHERE RUBBER CAN BE USED

FIVE

SELECTION AND COSTING OF RUBBER

WHAT IS REQUIRED

SIX/SEVEN

RUBBER DIRECTORY
DESCRIPTION AND SUITABLE USES OF VARYING RUBBER TYPES

EIGHT/NINE

DATA CHART
AT A GLANCE SELECTION

TEN/ELEVEN

PRECISION RUBBER MOULDING

T W E LV E

EXTRUSION, HOT VULCANISING AND FABRICATION

THIRTEEN

RUBBER GASKETS AND SHEETING

FOURTEEN/FIFTEEN

INFLATABLE RUBBER SEALS

THREE
 Specialised Engineering Products

B E N E F I T S O F R U B B E R

Rubber has found itself used in many industrial applications because it provides and maintains elastic properties across a

wide range of temperatures. Engineers and designers choose rubber because of its wide range of properties, available

in such a varied source of manufacturing processes, including sheeting, die or machine cut shapes/gaskets, moulded

components, and extruded lengths – which can be joined to form endless rings or shapes.

Some of the properties include: • The surface can be smooth and clean to assist
• Temperatures ranging from -60OC to +300OC hygienic applications
• Wide range of colours • It can be used in direct contact with foodstuffs
• Wide range of hardness when processed appropriately
• Resistance to extremes of weather and outdoor • It can be bonded effectively to metals, plastics,
environments indefinitely engineering materials and other substrates
• Electrically insulating, conductive or anti-static • It can be inflated and pressurised
• Resistance to fuels, oils and chemicals while

retaining its properties

• Flame retardent and self extinguishing types

• Maintain tension and compression forces as in

seals – even in hostile environments

• Accommodates movement, shock, thermal

changes, tolerance and rough surfaces

• Absorbs vibration, noise and can insulate

• Gas and fluid seal capability

• With a low thermal conductivity it can reduce

heat transfer

• With conductive fillers it can aid heat transfer

• It has friction properties and is comfortable to grip

Whilst no single material has all the desired properties,

indeed some properties may only exist in one type of

rubber, by understanding the application involved, the

desired properties can often be achieved with careful

selection and suitable compounding.

FOUR
 Specialised Engineering Products

S E L E C T I O N A N D C O S T I N G O F R U B B E R

Whether the requirement is for a new part, or replacements for existing parts that do not meet your expectation in

quality, cost, performance or availability, the same set of general rules apply. Good communication is vital if parts are to

be supplied to customer satisfaction at the right price. An existing sample or basic drawing is a good start, but questions

answered now will prevent surprises and difficulties later.

We strongly recommend that a specification is produced • Is there a specific surface finish required?
to consider and record the following points: • What colour?
• Is it a new part or potential replacement of • What are the tolerances?
existing part? • If the component is moulded, what amount and
• What is the expected usage – either batch position of flash is allowable?
or annually?

• Are there price constraints on parts or tooling?

• How is the component to be used?

• Will there be movement, vibration or compression?

• What is the highest service temperature?

• What is the continuous service temperature?

• What is the lowest temperature the part must

remain operable?

• What products (including cleaning agents) will

be encountered?

• Is product contact continuous or intermittent?

• Is long term weather or ozone resistance important?

As mentioned earlier, no one rubber type may have all

the required properties. However by understanding the

requirements through efficient communication, a cost

effective material and manufacturing process will evolve.

FIVE
 Specialised Engineering Products

R U B B E R D I R E C T O R Y

Natural Rubber
Isoprene
The original natural material which has been in commercial
use since the turn of the last century. A widely developed
rubber with a large range of low cost compounds.
PROPERTIES:
• High resilience
• Wide range of hardnesses
• Good compression set
• Very strong - tear & abrasion resistant
LIMITATIONS:
• Lack of resistance to oil and organic fluids
• Poor resistance to ozone, weather & oxidation –
tendency to perish in open air
• Low working maximum temperature
TYPICAL APPLICATIONS:
• Duties requiring good tensile strength & wear
resistance
• Shock absorption
• Dynamic components working inside equipment that
are protected from constant air changes Neoprene
Chloroprene
SBR One of the first synthetic rubbers developed in the search
Styrene Butadiene Rubber for oil resistant compounds. Extensively used due to its wide
One of the cheaper synthetic rubbers which is easy range of useful properties and comparatively low price.
to process in large quantities. PROPERTIES:
PROPERTIES: • Resistant to oils & chemicals
• Good physical strength • Flame retardant (self extinguishing)
• Good tear & abrasion resistance • Water & weather resistant
LIMITATIONS: LIMITATIONS:
• Poor resistance to oils or fuels • Not suitable for contact with fuels
TYPICAL APPLICATIONS: • Tendency to tear once initially damaged
• Widely used in the Footwear (shoe sales) and TYPICAL APPLICATIONS:
Tyre industries • Most general engineering & mechanical applications,
other than those in contact with fuel
EPDM
Ethylene Propylene Diene Monomer Hypalon
Another low cost synthetic rubber, originally developed in Chlorosulphonated Polyethylene
the 1950s for use within the tyre manufacturing industry. Another rubber developed around the 1950s. A combination of
It became more widely used because of its outstanding similarities between both EPDM & Neoprene, with some
resistance to ozone, weathering and water. improved characteristics.
PROPERTIES: PROPERTIES:
• Excellent water resistance, even at elevated • Resistant to oils and chemicals, especially at
temperatures elevated temperatures
• Good stability over long periods of time • Outstanding ozone & weathering resistance - stable
• Resistant to many water based chemicals over long periods of time
• Excellent weathering resistance • Water resistant
LIMITATIONS: LIMITATIONS:
• Will not resist oil or oil based products • Not suitable for contact with fuels
TYPICAL APPLICATIONS: • Not particularly resilient
• Potable water duties (WRC approved) TYPICAL APPLICATIONS:
• ‘O’ Rings, Seals & Gaskets • Heavy weather conditions
• General engineering not exposed to oil • Where there is exposure to hot liquids

SIX
 Specialised Engineering Products

R U B B E R D I R E C T O R Y

Nitrile Viton
Acrylonitrilebutadiene Fluorocarbon
A good quality oil resistant rubber with reasonable Suited to the petrochemical industry, this synthetic rubber
performance in contact with fuels. There are rubbers with offers the best all round resistance to hostile chemicals and
higher degrees of resistance, but these are much more oils particularly at elevated temperatures.
expensive. PROPERTIES:
PROPERTIES: • Good resistance to petroleum based fluids
• Good resistance to Petroleum based fluids - even at • Excellent chemical resistance
elevated temperatures • Strong with good tear and abrasion resistance
• Very low level of permeability to gases • Excellent upper temperature capabilities
LIMITATIONS: • Good resistance to water
• Flammable and burns with toxic fumes • Outstanding oxidation, ozone and weather resistance
• Comparatively low resistance to ozone and weathering LIMITATIONS:
• Poor electrical strength • Limited use at lower temperatures
TYPICAL APPLICATIONS: • Very expensive compared to nearly all other rubbers
• Seals, Gaskets, ‘O’ Rings etc., in contact with petroleum TYPICAL APPLICATIONS:
based fluids • Fluid sealing duties at elevated temperatures in
• Sealing against gases contact with aggresive chemicals and petroleum
products
Therban
HNBR Fluorosilicone
Hydrogenated Nitrile generally bridges the gap in relation to Fluorinated Polysiloxane
performance and cost between Nitrile and Viton. Best suited where conditions of low temperature are
PROPERTIES: present especially in contact with hostile chemicals, oil
• Good physical strength with very good tear and and fuel.
abrasion resistance PROPERTIES:
• Good dynamic behaviour with flex cracking resistance • Outstanding ozone and weather resistance
• Outstanding resistance to steam and hot water • Resistant to fuels at lower temperatures
• Resists ozone and weathering • Excellent electrical strength
• Maintains many of its properties at elevated • Very wide temperature range from -60 to 200 centigrade
temperatures LIMITATIONS:
LIMITATIONS: • Not particularly strong with relatively poor tear and
• Like Nitrile it has poor electrical and flame resistance abrasion resistance
TYPICAL APPLICATIONS: • Extremely expensive
• Seals in vehicle engines TYPICAL APPLICATIONS:
• Diaphragms requiring good heat ageing properties and • Normally special applications where performance in
resistance to oils and chemicals extremes of temperature are required – Aerospace,
petrochemical
Silicone
Polysiloxane
This rubber is generally characterised by its clean, smooth
appearance with good flexibility. It has an excellent range of
working temperatures and outstanding resistance to
weathering.
PROPERTIES:
• Wide temperature range
• Outstanding resistance to ozone & weathering
• Good resistance to oils
• Excellent electrical strength
• Low level of toxicity
LIMITATIONS:
• Not particularly strong, however
careful compounding can improve this
• Not suitable for contact with fuels
• Expensive compared to most other rubbers
TYPICAL APPLICATIONS:
• Situations involving extremes of high & low
temperatures - Aerospace
• Electrical applications
• Contact with food stuffs (FDA)

SEVEN
 Specialised Engineering Products

D A T A C H A R T

COMMON NAME NATURAL SBR EPDM BUTYL NEOPRENE

CHEMICAL NAME Isoprene Styrene Terpolymer of Isobutene Chloroprene

Butadiene Ethelene Propylene -Isoprene
Copolymer & a Diene

ABBREVIATION NR SBR EPDM IIR CR

COST FACTOR 1 1 1 2 2

o c c
HARDNESS RANGE 30-95 o
40-95 20-85 30-85 30-90o

COLOURS Full Range Full Range Full Range Limited Range Limited Range

HEAT RESISTANCE
maximum continuous 75oC 85oC 130oC 130oC 95oC
maximum intermittent 105oC 115oC 150oC 150oC 125oC

LOW TEMPERATURE
-40oC -40oC -40oC -40oC -40oC
RESISTANCE

RESISTANCE
oxidation Fair Fair Excellent Excellent Very Good
ozone & weather Poor Poor Outstanding Outstanding Very Good

PHYSICAL STRENGTH Excellent Good Good Good Good

COMPRESSION SET Good Good Good Good Fair to Good

TEAR RESISTANCE Very Good Fair Good Good Good

ABRASION RESISTANCE Excellent V. Good/Excellent Good Good Good

ADHESIVE PROPERTIES Good Good Fair Fair Good

RESILIENCE
hot Excellent Good Very Good Fair Very Good
cold Excellent Good Very Good Good Very Good

PERMEABILITY TO GASES Fair Fairly Low Fairly Low Excellent Low

DIELECTRIC STRENGTH Excellent Excellent Excellent Excellent Good

FLAME RESISTANCE Poor Poor Poor Poor Self-extinguishing

WATER RESISTANCE Very Good Good Excellent Excellent Fair

(ABSORBTION)

CHEMICAL RESISTANCE
acids Fair Fair Good Good Good
bases Good Good Good Good Fair

o
SOLVENT RESISTANCE (20 C)
alcohol Good Good Good Good Good
acetone Fair Fair Good Good Fair
benzene Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory

FUEL RESISTANCE
Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Poor
*ASTM FUEL B @ 40oC

OIL RESISTANCE
*ASTM OIL NO.1 @ 20oC Poor Poor Poor Poor Excellent
@ 100oC Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Good
*ASTM OIL NO.3 @ 20oC Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Good
@ 100oC Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Fair

The data provided within this literature is intended as a general guide to a material’s general properties and behaviour. They should be read
in conjunction with the appropriate standards and legislation relating to the properties and safe application of rubber. Customers must
assure themselves that the parts supplied are safe in use and have been tested under actual service conditions.

EIGHT
 Specialised Engineering Products

D A T A C H A R T

HYPALON* NITRILE SILICONE THERBAN† VITON* FLUOROSILICONE

Chlorosulphonated Acrylonitrile Polysiloxane Hydrogenated Fluorinated Fluorinated

Polyethylene Butadiene Acrylonitrile- Hydrocarbon Polysiloxane
Copolymer Butadiene Rubber

CSM NBR Si HNBR FPM FSi

3 2 6 8 15 40

o o o o o
45-85 40-100 20-80 50-95 50-95 40-80o

Limited Range Limited Range Full Range Full Range Limited Range Limited Range

130oC 100oC 205oC 140oC 205oC 180oC

160oC 130oC 300oC 165oC 260oC 200oC

-25oC -20oC -60oC -20oC -20oC -60oC

(special grades -80oC)

Excellent Good Excellent Excellent Outstanding Excellent

Outstanding Fair Outstanding Very Good Outstanding Outstanding

Good Good Poor Good Good Poor

Fair Good Good Good Good Good

Good Good Poor Very Good Good Poor

Fair Good Poor Very Good Good Poor

Fair Good Fair to Good Good Good Poor

Fair Good Good Fair Fair Fair

Fair Good Good Fair Fair Fair

Low Low Fairly Low Good Very Low Fairly Low

Good Poor Good Poor Good Excellent

Self-extinguishing Poor Good Poor Self-extinguishing Self-extinguishing

Very Good Good Good Very Good Good Good

Very Good Good Fair Good Excellent Good

Good Fair Fair Good Fair Fair

Good Good Good Excellent Good Good

Fair Unsatisfactory Fair Good Unsuitable Unsuitable
Unsatisfactory Unsatisfactory Unsatisfactory Fair Good Good

Poor Fair Unsuitable Good Excellent Fair

(good at low temperatures)

Excellent Excellent Excellent Excellent Excellent Excellent

Good Good Good Excellent 150oC Excellent 150oC Excellent
Excellent Excellent Good Excellent Excellent Excellent
Fair Good Fair Excellent 150oC Excellent 150oC Excellent

†
*Du Pont Registered Trade Mark Bayer Registered Trade Mark

NINE
 Specialised Engineering Products

P R E C I S I O N R U B B E R M O U L D I N G

As detailed earlier in the brochure an enquiry for rubber mouldings can be raised for many reasons. Our wealth

of experience, manufacturing for all industries, will assist in either new design or replacement of existing parts

that do not meet your expectation in quality, cost or performance.

The scope of mouldings we are able to offer has developed largely on our customers requirements.

The products we supply vary in size, material, quantity and tolerance, resulting in the development of our

considerable flexibility.

Our comprehensive range of moulding presses are built to our own modular specification, offering full interchangeable

tool loading to any press, thus giving SEP unparalleled ability in responding to urgent requirements. Suited to small batch

work as well as high volume production, the same presses give our customers the impression they expect – cleanliness,

innovation and quality.

Typical products

• Specification moulded sheets

• All types of seals

• Special application gaskets

• Diaphragms (plain, fabric reinforced, PTFE backed)

• Bellows

• Bottle fillers

• Bushes/Coupling Rubbers

• Rubber vulcanise bonding to PTFE/PFA

• Rubber vulcanise bonding to metal

• Covering and Recovering of Rollers

Industries

• Commercial engineering

• Marine

• Food processing and pharmaceutical (FDA compliant work)

• Petrochemical

• Aerospace

References and approved status available on request

TEN
 Specialised Engineering Products

P R E C I S I O N R U B B E R M O U L D I N G

Enquiries can be raised from the customers specification, drawings, samples (new or old),

or merely a bright idea in the back of a designer’s mind. Once a mutual understanding of the part exists

(reference to our Selection and Costing of Rubber will be useful – see page 5), development prototypes

through to full production manufacturing can proceed.

Our in-house design office and toolroom is capable of creating precision mould tools as well as quick turnaround

temporary tools for one off small quantity batches. Full 2D and 3D capability being available to produce single cavity

compression tools, through to multi-cavity injection moulds.

TOLERANCES

Hardness is measured in degrees, Shore A or IRHD (International Rubber Hardness Degrees) and is based on a

defined indentation into the rubber under a set load. User variation can be as great as +/-2.5O and +/-1.5O respectively,

and differences between the two types of readings can be significant. The general acceptable tolerance of rubber

hardness is +/-5O, with improved capability of +/-2O on harder rubbers if requested.

Dimensional tolerances in rubber are generally less critical as the material deforms

readily and accommodates variations. Tighter limits can be achieved with careful

tool design and rigorous procedural control, but restricted production rates

often have a commercial cost.

Unless specified ISO 3302 generally applies.

Tolerances for moulded products

to ISO 3302 1995 (BS 3734)
Table classes M1 (Precision) and M2 (Commercial)
Values in mm
F = Fixed dimensions C = Closure dimensions

Nominal Dimension Class M1 Class M2

Above Up to +/– F +/– C +/– F +/– C

0.00 2.50 0.08 0.08 0.10 0.15

2.50 4.00 0.08 0.10 0.10 0.15
4.00 6.30 0.10 0.10 0.15 0.20
6.30 10.00 0.10 0.15 0.20 0.25
10.00 16.00 0.15 0.20 0.25 0.30
16.00 25.00 0.20 0.25 0.25 0.35
25.00 40.00 0.20 0.25 0.35 0.45
40.00 63.00 0.25 0.35 0.40 0.50
63.00 100.00 0.35 0.40 0.50 0.65
100.00 160.00 0.40 0.50 0.70 0.90

ELEVEN
 Specialised Engineering Products

E X T R U S I O N , H O T V U L C A N I S I N G
A N D F A B R I C A T I O N

Particular attention to detail plays a vital role in the manufacture of extruded sections and profiles, with

various applications demanding different tolerance control. SEP takes a keen interest in the intended

use of products to ensure that they are always suitable in terms of dimensional stability, hardness,

colour matching where required, and that the most reliable rubber is used.

An almost infinite range of sections can be produced in most grades of rubber i.e. food grades (FDA),

high and low temperature capabilities and compounds resistant to known medium.

Whilst most rubbers can be joined using a comprehensive range of modern adhesives, the most successful method

of joining two pieces of cured rubber together permanently is by hot vulcanising. This process can offer virtual

equivalence in strength, flexibility and resistance to product or atmospheric attack and maintain the clean lines of an

endless moulded product.

This process is normally utilised for manufacturing products that are impractical to mould in one piece, offering

significant savings in tool charges with quicker deliveries.

Virtually any shape, hardness or rubber type can be joined.

Typical products
• Large section or diameter ‘O’ Rings

• Hollow section seals (tube, etc.)

• Large segmented gaskets (exceeding available

sheet sizes)
• Large segmented gaskets with profiled section

• Sleeves and ducting

• All profiled extrusion

• Inflatable seals (up to 12 bar rated) see pages 14/15

Hot Vulcanised ‘Extrusion’ to

‘Corner Mouldings’, producing
1867mm x 1257mm
steriliser door seals

T W E LV E
 Specialised Engineering Products

R U B B E R G A S K E T S
A N D S H E E T I N G

SEP process and/or supply full or part rolls of sheeting,

from a comprehensive stock in both commercial and

specification grade elastomers.

The list below being the most frequently requested.

Natural

White food quality Natural

Natural insertion

Neoprene Gaskets, strip or virtually any

EPDM (WRC approved) die-cut shape can be produced

Nitrile utilising the same stock from a

White food quality Nitrile variety of cutting and fabrication

Silicone (FDA) processes.

Fluoroelastomer (Viton®)

Cream DTD 5531 grade Silicone

0.5mm thick.
Ultrasonically cleaned for
oxygen service within
the Aerospace Industry

Special application requests show our ultimate flexibility. Where a

requirement exists for a specification grade of rubber, thickness,

hardness and colour, we have the ability to mould the material in an

economic sheet size and cut the gasket within the same factory –

sometimes on the same day.

Similar operations exist where gaskets are cut from moulded rings

to reduce waste and cost associated with the more

Viton Gaskets
expensive sheet materials.
596mm od x 572mm id x 4mm thick

THIRTEEN
 Specialised Engineering Products

I N F L A T A B L E R U B B E R S E A L S

The inflatable seals manufactured by SEP are designed to provide a clean, time saving solution to hermetic

sealing against, powders, granules, gases, liquids and dust.

These seals are most useful to seal fabricated pieces of equipment where:

• the sealing gap may vary

• fast efficient assembly and disassembly is required

• hygienic procedures exist (FDA applications)

Generally working from within a given groove size the seals can operate axially, radially inward or radially outward.

All seals are supplied with a suitable inflation connector, selected to accommodate any restrictions

associated with the equipment or customer preference.

Most requirements are for the FDA approved Silicone Rubber in either white or red iron oxide colours. Other rubbers

and colours are available. Using pre-extruded profiles held in stock, SEP utilise a high pressure ‘Shot Moulding

technique, which injects an identical compound at the join forming a high strength bond, with a clean smooth line finish.

No additives or adhesives form part of the bond. This process provides the seal with an ability to work under higher

pressures than most if not all other similar type seals in the market.

The same ‘Shot Moulding’ technique is used to bond most types of inflation connectors to the seals. This procedure

bonds the connector to the parent seal during the vulcanisation of the injected compound, the strength of which far

exceeds any mechanical fixing or adhesive bond, associated with this type of seal.

FOURTEEN
 Specialised Engineering Products

I N F L A T A B L E R U B B E R S E A L S

All seals manufactured by SEP are independently pressure tested and supplied with a supporting ‘Test Certificate’.

These tests on free standing, unsupported seals vary from 1 bar to 4 bar pressure, dependent on the profile type

and/or customer specification.

With the aid of purpose designed test rigs, which enclose the seal, our production techniques are tested (and supported

with proven case history) on some profiles to perform at up to 12 bar pressure.

The profiles shown are the most frequent extrusions utilised by SEP in the manufacture of FDA approved silicone rubber

inflatable seals. Other profiles are available and others can be manufactured to virtually any customer design or requirement.

The inflated dimensions shown are guides only, as unsupported surface area (closure dimension), can restrict
working pressures on some seal profiles. Customers should verify specific profile suitability with our
technical sales department.

Seal Description

Example: 1150 / SEP1A / 3 / a / 1234 / R

Developed length (mm); Type of extrusion profile;

Seal face orientation (1 = radially outwards, 2 = radially inwards, 3 = axially up or down);

Inflation connector orientation (a = opposite seal face, b = side wall adjacent to seal face);

Valve connector type and parts; Colour (R = red, W = white).

FIFTEEN
 C O M P A N Y I N F O R M A T I O N

This document contains Specialised Engineering Product’s information and is given in good
faith based on available sources at the time of issuing. However, because conditions and methods
of use of our products are beyond our control, this information shall not be used in substitution for
customer’s tests to ensure that our products are fully satisfactory for your specific applications
and compliant with all applicable laws thereof. Specialised Engineering Products disclaims any
express or implied warranty of fitness for a particular purpose and any liability for incidental or
consequential damages.

Specialised Engineering Products

C2-C7 Premier Centre, Abbey Park Industrial Estate, Romsey, Hampshire SO51 9DG
Telephone: (01794) 830757 Facsimile: (01794) 830736
E-mail: sales@specialisedengineering.co.uk Web: www.specialisedengineering.co.uk