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Is Silicone Heat Resistant?

All types of silicone are polymers and are made up of siloxane. Silioxane is a chain of alternating silicone atoms and oxygen atoms, often combined with carbon or hydrogen. Found in sand, Silicone is a naturally occurring element but the majority that you’ll come across day to day are synthetic products which have been manufactured from silica.

Silicone rubbers are elastomers, meaning they can stretch and return to their true form many times over. They are non-reactive, stable and resistant to extreme environments including extreme temperatures. This makes them a popular choice for products used in vehicles, aircraft, pharmaceutical production and much, much more.

What temperatures can silicone tolerate?

Silicone is incredibly popular due to its tolerance for extremes of temperature. Most silicones have an operating temperature from -60°C up to +230°C. However, the amount of time it spends exposed to such temperatures will define its ability to maintain integrity within application.

There are specialist types of silicone which can endure an even greater range of temperatures. High temperature silicone rubber can be exposed to temperatures as high as +300°C.

Why is silicone so heat resistant?

Silicone has a low thermal conductivity. This means it transfers heat at a much slower rate than some other materials, leading to excellent heat resistance. It can also be described as having good ‘thermal stability’ meaning it retains its structure and properties over a wide temperature range.

Its heat resistance is largely down to the highly stable chemical structure of the material. The backbone of siloxane is a stable formation which doesn’t allow the material to degrade in the presence of heat. With such outstanding characteristics, it’s no wonder that silicone has such a wide range of applications and uses.

For more information on what Silicone products NES can offer you, please click here or contact our expert Sales team!

The Best FDA Approved Rubber Materials

If you’re looking to purchase components which are likely to come into contact with food, it’s essential to use FDA approved products. The FDA defines products requiring approval as:

“any substance that is intended for use as a component of materials used in manufacturing, packing, packaging, transporting, or holding food.”

By assuring FDA compliance, you can be confident that the materials are safe for direct food content. This means they will not contaminate food products or cause a danger to the end consumer of the food items.

In general, this means that they will:

  • Be odourless, tasteless and resistant to bacteria
  • Be safe to use with food, beverage, meat, milk and certain food compliant chemicals
  • Non-toxic, non-marking and non-allergenic

In addition to ensuring the product you choose is FDA approved, other attributes must be suitable for the application. This means ensuring that the material is safe to use:

  • Within the temperature you plan to work
  • Safe for the type of food it is in contact with (fats, acidity etc.)
  • Robust enough for the environment in which it will be used

There are many types of FDA approved elastomer and rubber products. We’ve chosen four of the best ones for use in the food industry to help you narrow down your choices.

  1. Fluorocarbon

Known more commonly by its trade name of Viton™, fluorocarbons or FKM are high performance FDA approved silicone materials. They cope well with high temperatures, are chemically resistance and do not absorb water. The scope of their working temperature ranges from -20°C to 204°C, although compounds can be made which function from -45°C to 250°C.

  1. Silicone

The low toxicity and low chemical reactivity makes FDA approved silicone one of the best choices for food grade rubber. Silicone O-rings and silicone rubbers of food grade standard have one of the broadest operating scope ranges out there, of -60°C to 300°C. FDA approved silicone will not contaminate food and is one of the best materials for cooking tools, insulation, sealants and lubricants.

  1. Nitrile (NBR)

As a highly economical material to purchase, nitrile is one of the most widely used elastomers for seals in the food processing industry. It has excellent resistance to oils and fuels and is robust and abrasion resistant. Standard compounds have an operating temperature range of -40°C to 140°C.

  1. EPDM

For EPDM food grade products offer excellent flexibility and robustness. The EPDM food grade compounds are tasteless and odourless and are suitable for a wide range of uses within their temperature range. Normal operating temperatures for this material fall within -40°C to 140°C, making it a popular choice for food processing applications.

The Importance of Shore A Hardness

You’ll see us talk a lot about Shore A Hardness in our product descriptions, but what is it and why is it important for your design? Let’s find out.

What is Shore A hardness?

Shore Hardness is a measure of the resistance of a material to denting. The Shore A Hardness scale is one such unit of measurement, use to determine the hardness of flexible rubbers and elastomers. The scale ranges from extremely pliable to hard with almost no flexibility at all.

In general, the higher the Shore A Hardness, the harder a material will be. As an example, a rubber band would have a Shore A Hardness of around 25, whereas the hard wheels of a skateboard would have a Shore A Hardness of around 98.

In terms of O-ring selection, a Shore A Hardness of around 75 is the ideal measurement. This means the O-ring will offer enough flexibility to do its job properly, while also being rigid enough to maintain its shape.

Is Shore A Hardness really important?

In a nutshell, yes. The hardness of a rubber material under consideration for an O-ring can make the difference between a successful installation and a disaster. Understanding Shore A Hardness measurements will ensure you end up with the right material for the job.

For example, if you were looking to seal a high pressure fluid, you may need a harder material with a higher Shore A Hardness. However, if you were looking to use an O-ring on delicate hardware, or need to minimise insertion force for whatever reason, a more flexible rubber with low Shore A Hardness may be better.

For more information on understanding Shore A Hardness and selecting the right material for your O-ring, our team are on hand to help. Get in touch and we’ll be pleased to assist.

What Causes O-Ring Cracking?

Having an O-ring fail in an application is never a fun event. At best, it will mean some downtime and production delays, at worst it could lead to contamination of products requiring a major clean down to rectify.

One of the reasons O-rings can fail is because the material has cracked. If you’ve removed an O-ring from its application and have discovered multiple cracks, you need to understand what’s caused this issue so you can effectively prevent it from happening again.

Why do O-rings crack?

The most common cause of O-ring cracking is ozone cracking, also called ozonolysis. This mainly occurs in nitrile rubber O-rings, including Buna and Buna-N varieties.

Nitrile rubber is a polymer made up of units of carbon, hydrogen and nitrogen. The makeup of the nitrile molecules is such that there is an inherent ‘weak spot’ within the molecule. This spot can be susceptible to an oxygen atom being ‘donated’ from ozone, which breaks the chain and weakens the material.

Over time, these tiny cracks caused by ozonolysis get larger and more serious, until eventually they are large enough to be seen with the naked eye.

Preventing O-ring cracking

The molecules of oxygen which cause O-ring cracking are not from the general oxygen that we breathe. Breathable oxygen is O2, which is molecules joined in pairs. However, sometimes oxygen joins in threes, creating a substance known as ozone.

In the upper atmosphere, ozone is the layer that protects us from the harmful rays of the sun and gives the sky that beautiful blue colouration. In the lower atmosphere, the presence of ozone can cause health problems, breathing issues and, even in very small concentrations, O-ring cracking.

The best way to prevent O-ring cracking is to keep them away from sources of ozone production. These include UV light, electrical arcing and electromagnetic fields. To store your O-rings safely, you need to:

  • Keep them away from UV light, including sunlight and fluorescent light
  • Keep them away from electrical arcs such as electric motors
  • Store them in an un-stretched state

Nitrile O-rings should be assembled wet, using a grease to protect them from ozone. When fitting them, we recommend adding the mating part within 24 hours of installing them on the fitting itself. If you need to store them in a stretched state, use an airtight bag to protect them.

What Are Encapsulated O-rings and What Are They Good For?

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.

What is EPDM?

It might seem like a small detail,  but the choice of o ring material is incredibly important. Picking the wrong one could result in failure of the seal, causing machinery to become damaged and expensive downtime to be caused.

In terms of versatility, not much comes close to the popular and inexpensive material that is EPDM. This type of rubber is capable of coping with a range of difficult tasks, which makes it a popular choice for many applications.

If you’ve ever wondered what is EPDM and what should it be used for, our guide will help you better understand this adaptable material.

EPDM-O-ring

What is EPDM?

To give it its full title, ethylene-propylene diene monomer (EPDM for short) is a synthetic rubber which is suitable for use in a diverse array of applications. Its versatility and excellent durability make it a top choice for all sorts of tasks, from sealing against water ingress to providing insulation in freezer room seals.

Many rubbers are capable of coping with extremes of high temperature, but hardly any can withstand the cold in the way EPDM does. It can compress well and recover fully and is resistant to cuts and tears.

One of the most attractive things about this material is the low cost of EPDM meaning the cost of purchase and replacement is low. More expensive materials will be able to cope with more extremes, but unless you actually need to cover those issues, why spend more than you have to?

It might seem like a small detail,  but the choice of o ring material is incredibly important. Picking the wrong one could result in failure of the seal, causing machinery to become damaged and expensive downtime to be caused.

If you’ve ever wondered what is EPDM and what should it be used for, our guide will help you better understand this adaptable material.

What is EPDM?

To give it its full title, ethylene-propylene diene monomer (EPDM for short) is a synthetic rubber which is suitable for use in a diverse array of applications. Its versatility and excellent durability make it a top choice for all sorts of tasks, from sealing against water ingress to providing insulation in freezer room seals.

Many rubbers are capable of coping with extremes of high temperature, but hardly any can withstand the cold in the way EPDM does. It can compress well and recover fully and is resistant to cuts and tears.

Why use EPDM?

EPDM is a particularly good choice for applications which are outside. It’s resistance to weathering mean it will not degrade in the way some other material will under UV exposure. Its ability to withstand the cold makes it a great choice for applications involving freezing temperatures too.

Using the right material for your needs means a more reliable, more durable seal. This can reduce the risk of failure and unexpected downtime, and can increase the time between service intervals, saving you money on your maintenance costs.

EPDM is a good choice for sealing water but should not be used with more corrosive materials. Petro-chemical applications are more suited to a material like Viton™, but if you’re only looking to seal water then there’s no need to pay the premium price for such a specialist product.

EPDM rubber extrusion

What is EPDM good for?

EPDM has some unique characteristics which make it excellent for some particular tasks. When we’re thinking about what EPDM is good for, we should consider the properties of this material to see where it would be most useful. For example:

  • Large temperature range: The temperature range of EPDM goes from -51°C to 140°C, making it an ideal choice where extremes of temperature are involved.
  • Resistant to steam: As well as being suitable for high temperature applications, EPDM is resistant to steam and is proven to retain its integrity even during extended exposure.
  • Environmentally stable: Sunlight and UV does not affect EPDM negatively, so it’s a choice that will be appropriate in outdoor applications.
  • Resistant to some chemicals: EPDM will resist dilute acids, ketones and alkalis. However, it should not be used where it will come into contact with solvents or aromatic hydrocarbons.
  • Abrasion resistance: Its durability is one of the properties which sets EPDM apart. Both abrasion resistance and tear resistance are good to excellent, making it suitable for dynamic applications.

Some of the most common uses of EPDM include in solar panel heat collectors, as tubing, for electrical insulation and, of course, in o rings. We supply EPDM seals and o rings into a variety of applications, in industries as diverse as food and beverage, pharmaceutical, cold storage and vehicle manufacturing.

If you need more information on EPDM, or any of our other products, please don’t hesitate to get in touch. Our experts at NES are on hand to help you specify the exact components you need to ensure a great result.

Things You Need To Know About Rubber Shrinkage

One of the key factors in successful equipment design is the calculation of O ring squeeze. The amount the O ring will be squeezed by the surrounding hardware can have a bearing on the material selection, design and other key characteristics.

What exactly is O ring squeeze?

O ring squeeze is the amount that the ring will deform when pressure is applied. O rings only work as seals because of deformation, as they ‘flow’ to fill the gland, blocking any leakage from the assembly.

Virtually every gland has a tiny gap between the two mating surfaces, called a diametrical gap. This means that the O ring needs to be larger, in terms of cross sectional height, than the height of the gland. When the O ring is squeezed, it expands into the gap and forms a complete seal.

How much squeeze is enough?

To get the right amount of squeeze for the best seal, consideration has to be given to both the size of the O ring itself and the type of application being used. In a dynamic application, a lower squeeze is preferred as it will reduce friction and therefore wear on the seal.

With little or no squeeze applied, the natural elastometric characteristics of the O ring will prevent liquids from passing through. However, in situations where gasses need to be confined, a greater amount of squeeze is required to prevent passage through the hardware.

Increasing squeeze will tighten the seal, but should you always specify a high level of squeeze?

Is more better?

Some might say that the more an O ring is squeezed, the tighter the resultant seal will be. The greater the squeeze, the greater the force between the O ring and the mating hardware. This increase in force will do an even better job of preventing liquids, gasses and powders from escaping the seal. Or will it?

While a strong squeeze is desirable for a good seal, it’s not always a case of more is better. The more forcefully an O ring needs to be squeezed at installation, the higher the risk of creating a pinch, and therefore a pathway for leaks. Squeezing forces rise exponentially, so an increase in squeeze on the O ring could, in fact, lead to excessive stresses on the hardware and, potentially, to damage.

Higher squeeze also comes with a risk of greater friction and therefore faster wear. In short, squeeze is not something to be maximised, rather something that needs to be optimised.

Conclusion

There’s no hard and fast rule for the amount of squeeze you need in our O ring. In very general terms, a squeeze percentage of 13 – 27% is typical for hydraulic operations, and 10 – 24% for pneumatic.

However, these figures can change based on the materials in use and other factors such as temperature and environmental influences. If you’re unsure, the best option is to seek expert advice. Our team are always on hand to help; just get in touch to find out more.

MQ, VMQ, PMQ, FVMQ… What Does It All Mean?

The world of silicone rubber is full of confusing acronyms. To an outsider, the names of some compounds can seem like a foreign language, potentially leading to confusion and misinterpretation. However, there are standardised names for the materials we use, as defined by the ISO. As such, it’s key that you’re familiar with these names and the properties of such materials in order to use the right variant for the job.

What types of silicone are there?

Silicone is widely used in a variety of industries, from food and medical to aerospace and more. It has amazing flexibility, low toxicity and excellent resistance to UV, oxygen, ozone and microbial growth.

For O ring materials, silicone has one of the greatest ranges of operating temperatures available. Standard silicone O rings are capable of handling temperatures from -60°C to 230°C, whereas specialist compounds can be made to reach as low as -100°C and as high as +300°C.

We’re going to look at four of these compounds in more detail today. Specifically, we’ll consider MQ, VMQ, PMQ and FVMQ to see what they are and what benefits they can bring to components.

MQ silicone

To give it its full name, this is methyl silicone, and is the simplest form of silicone compound . At a molecular level, it contains repeating units of oxygen, which gives it excellent resistance to ozone, as well as UV and general damage from weathering.

We don’t often use this type of silicone in this format, as it doesn’t have the best elastomeric properties. However, it is sometimes used as a base and them processed to improve performance.

VMQ silicone

This silicone is vinyl methyl silicone. It is produced by processing MQ silicone into a format where the methyl groups of molecules are replaced with vinyl ones. The resulting material has an impressive temperature range and better compression set than MQ. However, its poor tensile strength means it’s not suitable for some O ring fabrication.

PMQ silicone

Also known as PVMQ, this is phenyl methyl silicone. With this compound, the methyl groups are replaced with phenyl groups, which dramatically improves the low operating temperatures of the material. In fact, PMQ silicones have almost a 100°C lower operating temperature than the equivalent MQ silicone, with a working temperature of -100°C.

FVMQ silicone

The final type has a more easily understood name: fluorosilicone. As with other fluorinated elastomers (FKM, FFKM etc.), adding fluorine at the molecular level results in stronger bonds. Stronger bonds mean fewer chemical reactions can take place, leaving us with a silicone with vastly better chemical resistance. Other properties of FVMQ silicone are similar to those seen in VMQ, although its hot air resistance is lower.

Clear as mud?

If you still feel confused about the types of silicone available for use, we’re here to help. Our friendly team are just a phone call away and can give you bespoke advice on the right material selection for your needs. Get in touch to find out more.

Choose Silicone: Five Situations Where This Is Your Perfect Material

Silicone is one of the best multipurpose polymers out there. Its widespread use, not just in the sealing industry, is testament to the amazing properties of this material. The molecular make up of silicone, with a backbone of alternating silicone and oxygen atoms, gives it some unique characteristics that make it a top choice for certain applications.

Here are just five examples of situations where silicone is a top choice of material for you.

  1. If you’re using it outdoors

Silicone is amazingly resistant to ozone, UV and weather, all key considerations if your assembly is going to be open to the elements. Although exposure to these factors can be mitigated to some degree in a lab, out in the open, there’s not much you can do.

Outdoor seals andgaskets which are exposed to sunlight can reach internal temperatures of as high as 60°C. At the opposite end of the spectrum, they can also experience freezing temperatures in the winter. In addition to this, UV and ozone can cause cracking and degradation in materials susceptible to them.

The high energy siloxane bonds in silicone means it maintains integrity in a range of challenging conditions. It’s one of the most weather resistant polymers available, and a great choice for use outdoors.

  1. If it’s going to get very, very hot

Silicone has one of the widest temperature ranges of any material, making it a top choice for applications involving extremes of heat. Normal silicone’s operating temperature can go as high as +230°C. However, specialist types of silicone can be manufactured to withstand even higher temperatures, as much as +300°C.

  1. If it’s going to get very, very cold

Standard silicone maintains integrity down to temperatures as low as -84°C. However, specialist compounds such as phenyl methyl silicone (PMQ) have been developed to perform even better. PMQ has a working temperature range which goes as low as -100°C although, again, prolonged exposure is not recommended.

  1. Where cost is a consideration

Although not the cheapest material out there, silicone is far from being an expensive choice. What you get in terms of heat resistance and other characteristics offers excellent value for money in comparison with other, similar performing compounds.

  1. In static applications

When we’re considering what silicone is good for, it’s a good idea to think about what it’s not good for too. Silicone, by its nature, has poor resistance to tears and abrasions. It also has weaker tensile strength, which means it sill suit some applications better than others.

Notably, it is more suited to static applications, rather than dynamic ones, where there are no moving parts and it won’t need to stretch or compress to extremes.

There are, of course, many other places where silicone is a great choice of elastomer. It’s odourless, tasteless nature and resistance to microbial growth make it a popular material for use in the pharma and food industries, to name just a few.

If you’d like to find out more about silicone and whether it’s right for your project, talk to NES for expert advice.

5 Tips From The Pros For Perfect Installation of Seals

Having a precision manufactured seal produced for your application is the first step to getting a reliable, competent part. However, faults which occur in the fitting of such seals could lead to failure, regardless of the quality of the seal itself.

For perfect installation of your seals every time, here are five tips from our experts to help you get it right.

  1. Clean the seal and installation tools

Working in a clean environment can help you give your seal the best chance of a reliable, long life. Dust and particulate that becomes trapped in the joint at the time of installation will affect performance massively. Ensure the seal itself is clean and clear of debris, using a lint free cloth to clean it. Ensure all tools being used in the installation and cleaned thoroughly too.

  1. Protect it from sharp edges

Being damaged during installation could lead to seal failure, so check the assembly for any sharp edges or imperfections. Remove any grease and grime from the surface too, again using a lint free cloth to do the job.

  1. Lubricate the seal and the sealing path

The majority of seals need to be fully lubricated prior to installation. There are a range of lubricants available, from petroleum based products to fluorocarbon fluid. The right lubricant for your seal will depend on the elastomer used for the seal itself. Talk to your expert at NES if you’re unsure what to use.

  1. Warm up the seal

Heating the seal slightly will improve elasticity and make installation much easier. This can be done by soaking the seal in warm lubricant but be sure to stay within the temperature tolerances for that material. Never put a seal in a microwave to warm it; just a few seconds can overheat an elastomer. Don’t heat it in a stretched state, as this could cause crosslinking and misshape the seal permanently. Once warm, don’t overstretch the seal while you are installing it.

  1. Use the right tools

Attempting to install a precision seal with the wrong tools can cause dents and damage to the seal itself. Any imperfections in the seal at this stage will be exacerbated once it’s under pressure, increasingly the risk of early seal failure. Use the appropriate tools for the job and take your time over installation to protect the seal’s integrity.

For more help on seal installation, as well as advice on custom made seals for your business, talk to the experts here at NES.