O-Ring Cord NBR FKM EPDM VMQ - Sealing Cord for Custom O-Rings
O-ring cord is a continuous elastomeric profile with a round cross-section, used primarily to manufacture custom-size or large-diameter sealing rings. The cord can be cut to the required length and its ends appropriately joined to create a closed sealing ring for a specific groove or application. O-ring cord is available in materials such as NBR, FKM/FPM, EPDM and VMQ/MVQ silicone, allowing the material to be selected according to oil exposure, water, temperature, weathering and other operating conditions.
What Is O-Ring Cord?
O-ring cord, also known as O-ring cord stock, round sealing cord or rubber O-ring cord, is supplied as a continuous elastomeric profile rather than as a finished molded ring.
Its primary dimensional parameter is the cross-sectional diameter.
For example:
O-Ring Cord 2 mm
means a round elastomer profile with a nominal cross-section of 2 mm.
Unlike a molded O-ring, cord stock does not have a predefined inside diameter.
It can be cut to a selected length and joined to create a sealing ring with the required circumference.
What Is O-Ring Cord Used For?
O-ring cord is particularly useful when:
- a required O-ring diameter is non-standard
- a very large sealing ring is needed
- the correct molded O-ring is difficult to source
- machinery must be repaired quickly
- maintenance teams require dimensional flexibility
- a custom sealing groove is used
- a prototype or one-off seal is required
- large housings or covers must be sealed
One cord cross-section can therefore be used to produce many different ring diameters.
O-Ring Cord vs Molded O-Ring
O-ring cord and a conventional molded O-ring are not identical solutions.
A molded O-ring is manufactured as a continuous closed ring without a joined section.
O-ring cord must be cut and its ends joined.
The principal advantage of cord stock is the ability to produce custom and very large diameters.
A molded O-ring is generally preferable when the required standard size is available and the application benefits from a continuous, joint-free ring.
O-Ring Cord by the Metre
O-ring cord can be used to manufacture seals with a length adapted to the actual requirement.
This makes it particularly useful for:
- maintenance departments
- MRO
- machine service companies
- industrial workshops
- machine builders
- production facilities
- prototype departments
- technical spare parts warehouses
Keeping several commonly used cord cross-sections in stock can reduce the need to hold every possible molded O-ring diameter.
How to Select O-Ring Cord Diameter
The main dimensional parameter is the diameter of the round cross-section.
Typical designations may include:
1.5 mm O-ring cord
2 mm O-ring cord
2.5 mm O-ring cord
3 mm O-ring cord
4 mm O-ring cord
5 mm O-ring cord
as well as many other sizes.
The cross-section should correspond to the sealing groove geometry and required compression.
A cord diameter should not be selected solely from the approximate diameter of an old seal.
How to Make an O-Ring from Cord
A typical procedure includes:
- selecting the correct material and cross-section
- determining the required cord length
- cutting the cord accurately
- preparing the cut ends
- joining the ends using a suitable method
- allowing the joint to cure or stabilize as required
- checking the finished ring geometry
Cutting accuracy and joint quality are critical.
Misaligned ends or uneven cuts can create a local discontinuity in the sealing surface.
Joining O-Ring Cord
One common method of producing a closed ring is bonding the prepared cord ends.
The adhesive or joining system must be compatible with the specific elastomer.
One bonding product should not automatically be assumed suitable for:
- NBR
- FKM
- EPDM
- VMQ silicone
Joint performance depends on:
- elastomer type
- cutting accuracy
- surface preparation
- adhesive chemistry
- curing time
- operating temperature
- final mechanical load
The bonded area may have different mechanical properties from the continuous molded elastomer.
Can O-Ring Cord Replace a Molded O-Ring?
In many static sealing applications, it can provide a practical solution, but it is not always a direct equivalent to a molded O-ring.
Extra evaluation is required for:
- high-pressure systems
- reciprocating applications
- rotary applications
- high-speed movement
- pressure pulsation
- safety-critical systems
- aggressive chemical media
- applications requiring specific approvals
The joined section is an additional feature of the finished seal and should be considered when evaluating performance.
O-Ring Cord for Static Sealing
One of the most natural uses of O-ring cord is in large or non-standard static sealing applications.
Potential applications include:
- machine covers
- housings
- flanges
- tanks
- access covers
- large enclosures
- industrial equipment
- service covers
In a static arrangement, the bonded joint is not continuously exposed to relative motion against the mating surface.
This generally makes static service more suitable for cord-made sealing rings than demanding dynamic operation.
NBR O-Ring Cord
NBR, or Nitrile Butadiene Rubber, is one of the most common sealing elastomers.
NBR O-ring cord is particularly useful for many applications involving:
- mineral oils
- lubricating greases
- machinery
- compatible hydraulic fluids
- industrial maintenance
- mechanical equipment
- general MRO applications
For many standard NBR compounds, a typical reference temperature range is approximately -30°C to +100°C.
Actual limits depend on the compound and operating medium.
FKM FPM O-Ring Cord
FKM/FPM is a fluoroelastomer used in more demanding thermal and chemical environments.
FKM cord may be selected for many applications involving:
- oils
- fuels
- hydrocarbons
- elevated temperatures
- selected chemicals
- process equipment
- industrial machinery
For many standard FKM compounds, a typical reference range is approximately -20°C to +200°C.
Exact resistance depends on the formulation.
FKM vs Viton
FKM and Viton should not automatically be treated as identical product names.
FKM describes a family of fluoroelastomers.
Viton is a trademarked material name.
For this reason, technical product descriptions should normally use FKM/FPM, unless the specific cord is confirmed as being made from Viton-branded material.
EPDM O-Ring Cord
EPDM is particularly useful in water-based and outdoor applications.
Typical properties include:
- very good water resistance
- excellent ozone resistance
- excellent UV resistance
- strong weathering resistance
- compatibility with many water-based fluids
- good low-temperature flexibility
For many technical EPDM compounds, a typical temperature reference range is approximately -40°C to +120°C.
Is EPDM O-Ring Cord Oil Resistant?
Generally, EPDM is not selected for mineral oils or hydrocarbon fuels.
If the application involves mineral oil, NBR or FKM is often more appropriate, depending on temperature and the specific fluid.
This is one of the key differences between EPDM and NBR.
VMQ Silicone O-Ring Cord
VMQ/MVQ silicone cord is valued primarily for broad temperature capability and resistance to ozone, UV radiation and weathering.
It can be useful in appropriately designed:
- heating equipment
- electronics
- instrumentation
- technical housings
- static sealing systems
- temperature-sensitive assemblies
For many technical silicone compounds, a typical reference range is approximately -50/-60°C to +200°C.
Special compounds may offer different limits.
Is Silicone O-Ring Cord Oil Resistant?
Standard VMQ should not be treated as universally resistant to mineral oils and fuels.
Where mineral oil is the primary medium, NBR or FKM may be more suitable.
Where silicone-like thermal properties are required together with better resistance to certain fuels or hydrocarbons, specialized elastomers such as FVMQ fluorosilicone may be considered.
HNBR O-Ring Cord
HNBR, or Hydrogenated Nitrile Butadiene Rubber, is a modified nitrile elastomer.
Compared with conventional NBR, suitable HNBR compounds can provide improved resistance to:
- higher temperatures
- ozone
- ageing
- selected oils and technical fluids
The exact properties depend on the specific HNBR compound.
If HNBR is not actually available within the category, it should not be emphasized in the H1 or Meta Title.
NBR vs FKM vs EPDM vs VMQ O-Ring Cord
The most important selection criteria are operating medium and temperature.
| Operating Condition | NBR | FKM/FPM | EPDM | VMQ/MVQ |
|---|---|---|---|---|
| Mineral oils | Often suitable | Very often suitable | Generally not | Requires verification |
| Fuels | Depends on fuel | Often suitable | Generally not | Generally not preferred |
| Water | Depends on conditions | Requires verification | Very good choice | Depends on conditions |
| High temperature | Limited | Very good | Good depending on compound | Very good |
| Low temperature | Good depending on compound | Compound dependent | Very good | Very good |
| Ozone and UV | Limited | Very good | Excellent | Excellent |
| Outdoor weathering | Limited | Good | Excellent | Excellent |
This table is a general material guide and does not replace verification of the specific compound.
O-Ring Cord for Large Diameter Seals
This is one of the most important advantages of cord stock.
Manufacturing or stocking very large molded O-rings can be impractical.
O-ring cord allows a sealing ring with the required circumference to be produced from the selected cross-section.
This is particularly useful for:
- large housings
- machine covers
- tanks
- large flanges
- industrial equipment
- older machinery
- custom machine designs
- one-off repairs
O-Ring Cord for MRO and Maintenance
O-ring cord is a practical component for MRO and maintenance inventory.
Instead of storing a very large number of different molded O-ring diameters, maintenance teams can keep commonly used cord cross-sections in stock.
This may support:
- emergency repairs
- planned maintenance
- machine overhauls
- service work
- custom seal production
- prototyping
- reduction of spare-part SKUs
However, a bonded cord ring should not automatically be considered suitable for every sealing application.
O-Ring Cord for OEM Production
In OEM production, cord stock may be used where large or unusual static sealing rings are required.
Before introducing cord-made seals into serial production, the specification should define:
- material
- cross-section
- dimensional tolerance
- cord length
- joining method
- operating medium
- temperature
- pressure
- groove design
This supports repeatability and consistent finished seal geometry.
O-Ring Cord for Hydraulic Applications
NBR or another compatible O-ring cord may be used in hydraulic equipment, but cord stock should not be promoted as a universal solution for high-pressure hydraulic sealing.
In high-pressure applications, the joined section can become important to sealing reliability.
A molded O-ring may be preferable for critical pressure systems, depending on the machine design.
O-Ring Cord for Pneumatic Applications
The same principle applies to pneumatic systems.
Cord stock can be useful for large static housings and appropriately designed sealing joints.
In dynamic cylinders, valves or high-cycle applications, however, joint integrity, friction and wear require careful evaluation.
Is O-Ring Cord Food Grade?
Not automatically.
The material family alone does not confirm food-contact approval.
Not every EPDM, silicone, FKM or NBR compound is food grade.
Where food-contact compliance is required, the documentation for the specific material and supplied product must be verified.
Is Silicone Cord Medical Grade?
Not every silicone cord is suitable for medical applications.
Medical use can require:
- specific material grades
- biocompatibility testing
- controlled manufacturing
- cleanliness requirements
- appropriate documentation
The designation VMQ/MVQ alone does not confirm medical suitability.
How to Calculate O-Ring Cord Length
If the required finished ring geometry is known, the cord length can be estimated from the required circumference.
The basic geometric relationship is:
L = pi x D
However, it is essential to define what diameter D represents.
The calculation may also need to account for:
- installation stretch
- groove geometry
- target ring dimensions
- joining method
- dimensional tolerance
For this reason, simply measuring an outside groove diameter and multiplying it by pi may not produce the correct cord length.
Why Groove Design Matters
Like molded O-rings, cord-made seals work through controlled compression of the cross-section.
Important parameters include:
- groove depth
- groove width
- cord cross-section
- compression
- groove filling
- temperature
- pressure
- operating medium
An incorrectly designed groove can cause leakage even when the material and cord diameter are otherwise correct.
Installing an O-Ring Made from Cord
Before installation, check:
- quality of the bonded joint
- alignment of the cord ends
- absence of excess adhesive
- groove cleanliness
- mating surface condition
- absence of sharp edges
- uniform seating around the entire circumference
The joint area deserves particular attention because it distinguishes a cord-made ring from a molded O-ring.
Storage of O-Ring Cord
Elastomeric cord should be stored in conditions that help minimize ageing and permanent deformation.
Avoid:
- direct sunlight
- excessive heat
- ozone
- aggressive chemicals
- permanent stretching
- sharp bending
- mechanical damage
In technical warehouses, each cord should be clearly identified by material and cross-section, because visually similar cords can have very different chemical resistance.
Advantages of O-Ring Cord
Custom Diameters: allows sealing rings to be produced in non-standard sizes.
Large Diameter Seals: practical for large covers, housings and industrial equipment.
MRO Flexibility: useful for maintenance, repair and emergency service.
Reduced Inventory Complexity: one cord cross-section can produce multiple ring diameters.
Multiple Elastomers: NBR, FKM, EPDM and VMQ allow material selection according to operating conditions.
Prototype Applications: useful for quickly producing a sealing ring for custom equipment.
FAQ - O-Ring Cord
What is O-ring cord?
O-ring cord is a continuous elastomer profile with a round cross-section, used to produce sealing rings with custom or non-standard diameters.
What is the difference between O-ring cord and a molded O-ring?
A molded O-ring is manufactured as a continuous closed ring. O-ring cord must be cut to length and the ends joined.
Which O-ring cord materials are available?
Common materials include NBR, FKM/FPM, EPDM and VMQ/MVQ silicone. Actual availability depends on size and product range.
What is NBR O-ring cord used for?
NBR is commonly selected for many applications involving mineral oils, greases and general industrial machinery.
When should FKM O-ring cord be selected?
FKM is particularly relevant for elevated temperatures and many applications involving oils, fuels, hydrocarbons and demanding chemical media.
When is EPDM O-ring cord used?
EPDM is commonly used in water-based systems and where ozone, UV and weathering resistance are important.
What is silicone VMQ cord used for?
VMQ is useful where broad temperature capability, low-temperature flexibility and ozone/UV resistance are important.
Can any O-ring size be made from cord?
Many custom diameters can be produced, but suitability depends on groove design, medium, temperature, pressure and type of operation.
Can O-ring cord be glued?
Yes, suitable elastomer cords can be bonded using a joining system compatible with the specific material.
Is O-ring cord suitable for high pressure?
Not automatically. In critical pressure applications, the joint may be a limiting factor and a molded O-ring may be preferred.
Frequently Asked Questions by Engineers
Does a bonded O-ring have the same properties as a molded O-ring?
Not necessarily. The joint can have different mechanical properties from the continuous molded elastomer.
Which is more important when selecting cord, material or diameter?
Both are critical. Cross-section must match the groove, while the elastomer must be compatible with the medium and temperature.
Can the same adhesive be used for NBR, FKM, EPDM and silicone?
No. The joining technology must be compatible with the specific elastomer.
Is O-ring cord a good solution for very large diameters?
Yes. Producing large and non-standard static sealing rings is one of the main advantages of cord stock.
Can EPDM cord replace NBR cord?
Not automatically. EPDM and NBR have very different chemical compatibility, especially with mineral oils.
Is silicone cord automatically food grade?
No. Food-contact suitability must be confirmed by documentation for the specific compound.
Should cord diameter match the cross-section of the original O-ring?
It is an important reference point when reproducing an existing seal, but groove geometry and required compression should also be checked.
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O-Ring Cord - Warehouse and Store in Lublin
Warehouse and Store: Lublin
Address: ul. Smoluchowskiego 1, building 4
Delivery: 24h
We supply customers throughout Poland and the European Union, including industrial companies, OEM manufacturers, maintenance departments, MRO organizations, service workshops, technical buyers, distributors and B2B customers.
AI OVERVIEW
O-ring cord is a continuous elastomeric round profile used primarily to manufacture custom-size and large-diameter sealing rings. It can be cut to the required length and its ends appropriately joined to create a closed seal. Materials such as NBR, FKM/FPM, EPDM and VMQ/MVQ allow selection according to oils, water, temperature and environmental conditions. A bonded cord ring should not automatically be considered equivalent to a molded O-ring in every application, especially in demanding dynamic or high-pressure systems.
