O-rings are a tried and trusted method of sealing two component parts in a wide range of industries that have been relied upon for well over a century. However, just because they are an excellent solution to a universal challenge, that doesn’t mean that they aren’t susceptible to failure on occasion.

There are many different reasons why an O-ring might become damaged and the seal it is protecting become compromised. Here is a quick rundown of the five most common contributing factors to an O-ring failure, as well as advice on how to determine which problem is responsible and how to rectify it.

Abrasion

• Symptoms: O-rings which suffer from abrasion might have a rough or disfigured surface, while in extreme cases there may be ruptures or lacerations in the outer ring.
• Cause: One of the most common forms of O-ring failure, abrasion is caused by too much contact between the O-ring surface and the surrounding architecture. This can happen when not enough lubricant is used or when alien substances infiltrate the gland.
• Solution: Correct use of appropriate lubricant normally solves the problem, while the use of scraper rings may be necessary to prevent contaminants from entering the gland.

Chemical corruption

• Symptoms: Blisters, discolouration, lacerations and swelling can all be indicative that the O-ring has become exposed to chemicals with which it is not compatible.
• Cause: Exposure to certain chemicals can result in reactions with some type of elastomers. Depending on the O-ring material and the chemical in question, this can lead to reduced flexibility, strength and cross-link density, while swelling often incurs extrusion and seal failure.
• Solution: It’s essential that the right type of O-ring material is used for the right application. Many substances boast high resistance to chemicals; be sure to choose one of these if exposure is a concern.

Compression set

• Symptoms: Once removed from the gland, an O-ring should return to its original O-ring shape. However, those which have taken on a “set” will retain characteristics of the gland even after use, including flattened surfaces instead of circular ones.
• Cause: O-rings can lose their resilience and ability to return to their original form after exposure to extreme temperatures, through prolonged use or being fitted in incorrect groove geometry.
• Solution: Selecting an O-ring material with a low compression set or a high tolerance to extreme temperatures should ensure that the O-ring has a longer life. Ensuring the correct amount of pressure is being exerted on the O-ring, by using correct groove dimensions, is also key to avoiding compression set.

Extrusion/nibbling

• Symptoms: The surface edges of the O-ring have a chipped or frilly appearance and it may seem to be peeling away from the material underneath.
• Cause: Prolonged exposure to high amounts of pressure or repeated bursts of intense pressure can force an O-ring into the clearance gap between the two mating surfaces. In dynamic applications, the movement can then erode the O-ring’s surface, resulting in extrusion and nibbling.
• Solution: Using the correct size of O-ring is the most important precaution when avoiding extrusion and nibbling, but minimising the appearance and size of clearance gaps and selecting a hardier material for the O-ring can also help.

Thermal damage

• Symptoms: Two types of thermal damage can afflict O-rings: degradation and extrusion. The former will exhibit cracks and fissures on the O-ring’s surface, as well as a shinier aspect on occasion. The latter will result in the same symptoms outlined for extrusion and nibbling above.
• Cause: Both thermal degradation and thermal extrusion are caused by elevated temperatures. The former comes about when the temperature exceeds the O-ring elastomer’s upper threshold, while the latter occurs when the O-ring’s tolerance level is higher than the surrounding materials.
• Solution: The gland should be developed to withstand the same temperatures as the O-ring, while selecting the right material for the O-ring itself is also key to circumventing this problem.

The the most common seal used in a multitude of industries is O-rings. From aerospace to chemical processing, food and pharmaceutical industries, O-rings come in a variety of robust materials that offer high-quality and reliable seals for many different fields. Whether it’s heavy plant or agricultural machinery, these donut-shaped rings are suitable for the most demanding of jobs.

As O-rings are used regularly in a number of applications, sometimes you may not even realise they are there until one starts to crack and then leak. One of the reasons this can happen is due to ozone exposure. In manufacturing this can cause aggravation, but out in the field ozone damage can be detrimental and if left unchecked, it can lead to serious injury or even death. This is why it’s important to know how ozone damage can occur and what you can do to prevent it.

Why ozone causes O-ring cracks  

O-ring failure can be attributed to a combination of causes, but it’s mainly exposure to oxygen atoms that causes cracks in rubber O-rings. Exposure to oxygen is inevitable as it’s in the air we breathe, but typically oxygen atoms join up in pairs to form dioxygen which is the majority of the oxygen in the atmosphere. Occasionally, oxygen atoms will join in groups of three and this creates the ozone substance.

In the stratosphere, ozone is extremely useful and protects us from the sun’s harmful rays. However, up-close it can cause health problems and even in tiny concentrations it can cause cracking in rubber O-rings. Ozone concentration in the stratosphere is somewhere between two and eight parts per million but in the troposphere concentrations are above 75 parts (per billion).

Most rubbers are polymers which consist of individual units that are bonded together in a long chain. If the polymer chain develops a weak spot because of exposure to ozone, the O-rings can crack and and over time will get bigger until the damage can be seen by the naked eye.

Preventing ozone damage to O-rings

As expert manufacturers and distributors in the UK, NES are a great resource when it comes to knowing how to ensure O-rings have a long life. In industry applications, the main drivers of ozone exposure are electrical arcing, ultraviolet light and electromagnetic fields (the main reason for higher ozone levels in the upper layer). In order to prevent ozone damage, it’s vital to store and install O-rings correctly.

Firstly, inspect your storage area for any ozone-generating equipment that could cause damage to the O-rings. Ensure O-rings are not stored within range of an electric motor, or other potential sources of electrical arcs. O-rings should be stored in a dark room, away from florescent bulbs and direct sunlight. These forms of ultraviolet light can cause damage to the rubber and lead them to crack before they’ve even been used. Try not to store O-rings in a stretched state – ozone damage will typically only occur to stretched O-rings. If you have to store O-rings in a stretched state, keep them in an airtight bag until ready to use.

It’s recommended to install O-rings into the mating part within 24 hours of installing the O-ring fitting. When installing, wet the O-rings with a grease to protect from them from ozone. In applications where long-term exposure is likely, use O-rings made from ozone-resistant materials such as EPDM or fluorocarbon. EPDM O-rings are used for sealing in many industries because of the material’s excellent resistance to ozone and UV as well as heat, steam, mild acidic and oxygenated solvents.

Northern Engineering (Sheffield) Ltd are a leading O-ring suppliers and manufacturers who distribute a range of engineered, elastomeric products across the globe. From food and beverage industry to the pharmaceutical industry we are reputable O-ring suppliers for a variety of businesses across all industry sectors.

NES offers an extensive range of O-rings that can be used for both domestic and more demanding applications. We supply O-rings that are developed to withstand extreme temperatures, are oil and ozone resistant, and even those that can be used for bio-technology and hygiene equipment.

Our vulcanised O-rings are used in many markets across diverse applications due to profile and material versatility. Manufactured in materials such as Silicone, Nitrile, EPDM and Viton™, they are developed to best suit your individual application. We also offer a range of FEP and PFA encapsulated o-rings to suit your applications requirements

For more technical information and to learn more about the O-rings we manufacture and the industries we supply to, you can explore our full product range on our website. Need a sealing solution for your project? Get in touch with us and we’ll tell you more about how we can provide you with O-rings to best suit your needs.

Different types of O-ring applications

One of the most crucial components of modern industry, the humble O-ring is as versatile as it is reliable. Despite having been first patented in 1896 by Swedish inventor J O Lundberg, the basic design of the O-ring has changed very little in the intervening century. Neither has the function it performs or the valuable service it provides, facilitating an airtight or watertight seal in any number of different applications and industries.

Of course, the materials used to construct O-rings have been developed and improved over the years, meaning that there are now a wide variety of elastomers used in O-ring manufacturing to meet the needs of a range of applications. From O-rings resistant to extreme temperatures to those impervious to chemical damage, there’s sure to be an O-ring to suit your specific situation. However, it’s imperative that before making a purchase, you consider which material would be satisfy your circumstances, since using an O-ring that is too large, too small or made of the wrong material could lead to its failure and potentially jeopardise the equipment it services.

In order to make an educated decision on which O-ring is right for you, this handy guide intends to provide some background on how O-rings work, how they’re made and how they lend themselves to a variety of different applications.

How does an O-ring work?

As the name suggests, O-rings are circular, donut-shaped mountings which are compressed between two different components to form a better, tighter seal. In essence, they are very similar to a standard form of gasket, with the difference being that O-rings are specifically developed for industrial use in applications where they will be subjected to extreme temperatures, pressures or substances. In these cases, a standard gasket made of rubber, cork or metal would not withstand the tension exerted upon it, which is why O-rings are such a simple but effective solution to an age-old problem spanning many industries.

By contrast, O-rings are constructed of more durable elastomers which are capable of withstanding the extreme conditions to which they are subjected. They work by being placed in the channel or groove (known in industrial terms as a gland) between two different parts of machinery, which can be either static or dynamic. When the two components are compressed together, the O-ring is developed so that its shape will mould to fit the unique dimensions of the surfaces pressing against it, thus creating an impermeable seal which won’t allow either water or air to enter. The greater the amount of pressure exerted on the O-ring, the tighter the seal it will create – up to a point. However, it’s essential to ensure that not too much pressure is applied to the O-ring or it will become damaged and the seal itself will become compromised.

Another attractive selling point of O-rings is that once the two compressed parts of the machinery are detached and the pressure being exerted on the O-ring is relaxed, it will return to its original donut shape. While this does mean that O-rings can be reused for several different purposes, it should be remembered that it cannot be recycled indefinitely. Eventually, the pressures exerted upon it will negatively impact the consistency and resiliency of the O-ring and it must be replaced with a fresh one if an adequate seal is to be maintained.

How is an O-ring made?

Due to the fact that the design of O-rings has remained largely unchanged since their inception over a hundred years ago, the manufacturing process also remains relatively simple. The rings can be created through the use of a number of different techniques, including compression moulding,  injection moulding, transfer moulding or vulcanisation. Nowadays, modern advances in scientific and technology understanding mean that O-rings can be constructed from a wide variety of materials, including nitrile, silicone and fluorocarbons (among many others). The type of material used will be dependent on the specific purpose and circumstances of the O-ring in question.

Different types of O-ring applications

Whether it’s for use in an industrial power plant, as part of heavy-duty agricultural machinery, underwater in a marine environment or amongst the cogs and pistons of the automotive industry, there’s sure to be an O-ring that’s perfect for every purpose. But with so many materials available to choose from, it can be difficult to know which one is right for you.

Here’s a breakdown of the various kinds of O-ring available, as well as the advantages of each and the possible applications to which they may be suited.

• Nitrile O-rings

Widely regarded as a general-purpose type of O-ring, Nitrile elastomers (also known as Buna-N or NBR) offer a respectable temperature range of between -50°C and 120°C, with excellent resistance to tears and abrasive treatment. Nitrile also enjoys decent resistance to water, oils and some hydraulic liquids, although it is susceptible to damage from automotive brake fluid, halogenated hydrocarbons, ketones, nitro hydrocarbons or phosphate ester. As such, it’s suitable for use in select purposes in agriculture, the automotive industry, dairy, mining, plumbing and railways.

• Silicone O-rings

With one of the widest temperature ranges of any O-ring material, silicone O-rings can withstand temperatures of between -100°C and 300°C. Indeed, this hardy material has even be known to tolerate greater extremes (-115°C to 315°C) for a limited time, making it an ideal choice for applications where very high or low temperatures are a factor. It offers great flexibility and performs brilliantly alongside water, steam or petroleum, but is prone to damage from abrasion and tearing. As a result, it’s better suited to static applications rather than dynamic ones.

• Viton™ O-rings

Also known as FKM O-rings, Viton™ O-rings are made from fluorocarbons and boast resistance to temperatures from -40°C up to 250°C, low gas permeability, superb mechanical characteristics and a low compression set. They are highly suitable for use with acids, halogenated hydrocarbons, petroleum and silicone fluids or gases. However, they should not be used in conjunction with amines, esters, ethers with a low molecular weight, hot hydrofluoric acids or Skydrol. Their incredible versatility makes them popular in a wide range of industries, including the automotive sector, aviation, chemical processing and mechanical engineering plants.

• FEP O-rings

FEP O-rings pair a silicone or fluorocarbon core with a coating of fluorinated ethylene propylene (FEP), which offers users several distinct advantages over a standard PTFE O-ring. Firstly, they are capable of handling temperatures of between -60°C and 260°C for silicone cores and -20°C and 204°C for fluorocarbon cores. Secondly, they also provide superb elasticity and low friction levels in comparison to their PTFE counterparts. Although they are best suited to static applications, they can also be adaptable to dynamic ones where the movement is slow and short. This makes them popular in the chemical, food, petrochemical and pharmaceutical industries.

• PFA O-rings

O-rings which are encapsulated with perfluoroalkoxy (PFA) are an attractive alternative to PTFE or FEP O-rings which offer several advantages over their competitors. In comparison to PTFE, PFA O-rings are a more cost-effective option, while the substance has greater resistance when dealing with temperatures of above 250°C than FEP does. Similarly, it is also better equipped to keep a variety of chemicals from permeating its seal, making it ideal for use within the chemical and petrochemical industries, the food sector and with pharmaceutical organisations.

• USP Class VI O-rings

In this context, USP stands for United States Pharmacopeia and the rubber compounds which have achieved a Class VI certification definitely offer a unique selling point, too. All of the elastomers which receive this accreditation are subjected to rigorous testing procedures, which assess their consistency, purity, quality and strength to ensure they are safe for use in situations where human life is at stake. As such, USP Class VI O-rings are in high demand among the medical and pharmaceutical industries.

• Vulc O-rings

While all of the O-rings listed above are created through moulding techniques, Vulcanised O-rings (or Vulc O-rings) are made by treating the parent material with sulphur at very high temperatures and splicing its ends together to create the donut shape. This allows for a much faster creation of the production on a more cost-effective scale, with an average of 90% of the joint strength of the equivalent moulded part. As such, Vulc O-rings are an attractive alternative whose versatility and low compression values make them suitable for a range of industries where the end user wants to avoid the higher tooling costs of moulded O-rings.

• Large O-rings

As well as the economic advantages of vulcanisation opposed to moulding, the unique method of manufacturing O-rings means that there is no limit on the size to which they can be created. Standard larger O-rings range up to 25.4mm in size, though it is a fairly simple process to manufacture a bespoke O-ring to any specifications required. As with standard Vulc O-rings, dispensing with the need for moulds and expensive tooling equipment not only slashes the cost incurred, but also greatly reduces lead times, making them ideal for applications of all kinds.

Expert advice from the professionals

Still unsure as to which type of O-ring would suit your situation best? Not to worry. Our extensive range of O-rings is guaranteed to have a product that will satisfy your unique circumstances and our friendly team is on hand to provide any guidance you might need in making your choice. Simply fill out our online form, give us a call on +44 1909 560 203 or drop us an email at sales@nes-ips.com and we’ll be happy to help. We’re waiting to hear from you.

Encapsulated O-rings are specially developed seals which solve a common problem in many industries. Sometimes you need the chemical and temperature resistance of PTFE, but a PTFE O-ring wouldn’t have the flexibility you need for compressive fluid sealing. Or perhaps you want a flexible elastomer but can’t rely on the material to resist the chemicals you are dealing with.

An encapsulated O-ring brings the best of both worlds together. The outer jacket is made from Teflon, giving the seal high thermal stability and resistance to corrosion, while the rubber inner ore provides compressional and elasticity.

Types of encapsulated O-rings

Encapsulated O-rings can have two different types of core, which enables them to be suitable for different applications. The two types are:

• Solid core: These are standard encapsulated O-rings which have either a silicone energiser ore or a core made from FKM, also known as Viton. FKM cores have excellent elasticity and a good compression set. Silicone has very much the same benefits, but because it is softer it has a higher standard of heat resistance. For very cold temperatures, a silicone core would be recommended as they remain flexible to a lower temperature too.
• Hollow core: For applications where extreme elasticity is required, no core at all outperforms both FKM and silicone cores. This may come with a compromise in terms of compression set and recovery, but for fragile applications a hollow core encapsulated O-ring will perform well.

As well as having various options for the elastomeric core, the outer jacket of the encapsulated O-ring can be made in a choice of materials too. Most commonly, we make them with either PFA or FEP outer jackets.

• PFA: To give it its full title, perfluoroalkoxycopolymer is excellent at resisting a range of corrosive chemicals. These include alcohol, naphtha, acid, petroleum and aromatic solvents. Compression set is low, and their operating temperatures range from -60°C to +260° Compared to FEP, they have higher mechanical strength and improved resistance to cracking and stress.
• FEP: Fluorinated ethylene propylene jackets for encapsulated O-rings have very similar qualities to those of PFA. They resist chemicals, have low coefficient of friction and a low compression set. However, they are slightly weaker mechanically and have a narrower operating temperature range, of -60°C up to +205° Their service life is slightly shorter, but they are FDA approved and are generally lower cost too.

For advice on the right construction of encapsulated O-rings for your application, talk to the expert team at NES.

The Advantages of Encapsulated O-rings

As you can see from the description of the materials, encapsulated O-rings have excellent resistance to almost all types of media. They work in a wide temperature range and an be made from FDA approved materials to suit food and drugs processing applications.

Their non-contaminating material makes them ideal for use where hygiene is required. The chemical resistance of the materials also means they are a good solution for chemical and petrochemical industries.

The combination of the elastomer-like flexibility with the PTFE-like chemical resistance brings unique advantages to encapsulated O-rings over other types of seals.

Limitations of encapsulated O-rings

In general, encapsulated O-rings have many properties which make them a top choice for strenuous processes. However, there are some situations where they are not the best choice.

The thin outer jacket means they are susceptible to scratching, so should not be used in applications containing abrasive slurries or powders.

We find that encapsulated O-rings are generally best suited to static applications, or at best in slow moving rotary applications. Highly dynamic systems may not be best suited to the use of encapsulated O-rings.

Overall, the success of an encapsulated O-ring will depend on the right product being selected for the job. NES can help you choose the best product for your needs, whether that’s an encapsulated O-ring or something else. We can manufacture custom sizes and profiles to suit your application too; just talk to our team for further information.