Blog

While the vast majority of people have never heard of fluoropolymers, they are everywhere in our lives. It is undeniable that because of their durability and versatility, this particular group of polymers is one of the most popular polymer materials to date. In this week’s blog post, we will explore this wonderful material, from its history to its uses.

What is a Fluoropolymer?

To start, let’s go over what a polymer is. A polymer is a material made of long, repeating chains of molecules. The materials have unique properties depending on the type of molecules being bonded.

A fluoropolymer is a fluorocarbon-based polymer with multiple carbon-fluorine bonds. It is characterized by high resistance to solvents, acids, and bases. The first, and best-known, fluoropolymer is polytetrafluoroethylene, also known as Teflon.

While Teflon is arguably the most famous fluoropolymer used today, it is certainly not the only one. Other popular fluoropolymers include:

• PTFE (Polytetrafluoroethylene)
• PFA (perfluoroalkoxy alkane)
• FEP (fluorinated ethylene propylene)
• ETFE (ethylene tetrafluoroethylene)
• PVDF (polyvinylidene fluoride)
• ECTFE (ethylene chlorotrifluoroethylene)

These may also be known by their brand names, including Excalibur, Algoflon, Xylan, Solef, and Fluon.

They also come in several different forms, making them well suited for several different applications. These forms include granulate, melt-processable, films, pastes, and dispersions.

Fluoropolymers are also used as a coating for products made of other materials. More on that later!

History of Fluoropolymers

While mineral fluorides were known as early as the 16^th century, modern fluoropolymers were not discovered until the early 20^th century. Fluoropolymers, as we know them, were first discovered in the form of polytetrafluoroethylene, better known by its brand name Teflon, or by its abbreviation PTFE.

It was discovered entirely by accident when in 1938, Roy J. Plunkett of Dupont accidentally froze a compressed sample of tetrafluoroethylene. This gaseous material became a white, waxy, and solid form that would, in 1945,  become marketed as Teflon.

Since than, of course, other fluoropolymers have been introduced, such as:

• FEP in 1960
• EFTE in 1970
• PFA in 1972

In 1985, Dr. Plunket was introduced into the National Inventors’ Hall of Fame, where he joined the ranks of distinguished scientists and innovators such as Louis Pasteur and the Wright Brothers.

Benefits of Fluoropolymers

Fluoropolymers are a unique group of materials with many benefits that make them well suited for a variety of applications.

Chemical Resistant

Fluoropolymers have a very high resistance to chemicals and solvents. This allows them to be used to seal or contain hazardous materials.

Electrical Resistant

With the ability to insulate up to 5,000 volts, Fluoropolymers make excellent insulators for things such as electrical wiring.

High-Temperature Resistance

The typical range of temperatures that fluoropolymers can cover ranges from -328 degrees Fahrenheit all the way to 500 degrees Fahrenheit. With such a vast range, fluoropolymers are a perfect material for extreme environments.

 Low Friction (AKA Non-Stick)

Because they shed a molecule every time something passes over them, fluoropolymers are incredibly smooth and thus incredibly non-stick. This property has made them popular with cookware manufacturers.

Non-Toxic

The smooth surfaces of fluoropolymers are non-microbial, which makes them suitable for use in the food, beverage, medical, and pharmaceutical industries.

Other benefits include:

• Durable
• Self-cleaning
• Corrosive Resistant
• Non-Flammable
• UV Resistant

Cons of Fluoropolymers

Price

Unfortunately, such a versatile material comes at a higher price point. Fluoropolymers are often more expensive to produce than other materials, and even other polymers, or plastics.

Production Sizes

Fluoropolymers are relatively more difficult to process and manufacture, and can not be as easily mass-produced as other materials.

Can Shape Under Pressure

Elevated pressures and temperatures can affect their surfaces and cause them to bend and bulk.

Extremely High Temperatures

While it can withstand high temperatures and is resistant to chemicals, it can melt at 680 degrees Fahrenheit, making fluoropolymers unsuitable for molten environments.

Other cons include:

• Cannot be Cemented
• Unweldable
• Decomposition Product Toxic

Uses of Fluoropolymers

Fluoropolymers are used in a wide variety of industries and applications, from the industrial to every day.

Industrial Applications

Because of their many benefits and versatility, fluoropolymers are frequently used in the industrial space.

The non-stick and chemical resistance makes them well suited for use in the processing of hazardous materials such as chemicals. This is particularly common within the oil and gas industry.

They are also popular materials with which to make machined parts. Because they are very durable on top of their aforementioned versatility, many manufacturers use fluoropolymers to make parts for machines, such as seals, backup rings, bushings, bearings, and canted coil springs.

Fluoropolymers are popular in the automotive industry, where fluoropolymer coatings help to prevent friction and corrosion in car parts. Another popular application is with the aerospace industry, where fluoropolymer coatings are applied to the wiring insulation.

Non-Industrial Applications

Fluoropolymers are also fantastic for the average consumer. Many everyday products are on the market today that use some form of fluoropolymer.

Teflon, or PTFE, is particularly popular. If you have a nonstick pan in your home, chances are it is made from Teflon. It is also used in waterproof clothing such as rain jackets and hiking shoes, self-cleaning ovens, microwave popcorn bags, pizza boxes, and more.

The demand for fluoropolymers is high. In fact, in 2011, it hit $7.25 billion. Thanks to innovative engineers, new uses and applications are constantly being developed.

In Conclusion

Fluoropolymers are one of the most versatile materials on the market. With high durability, high-temperature range, low-friction, and nontoxicity, fluoropolymers are often some of the best materials to choose for your project.

And if you need fluoropolymer products, Advanced EMC Technologies is the premiere one-stop solution. We provide many types of custom-made fluoropolymer products, including PTFE. We pride ourselves on being able to provide accurate, on-time solutions when you need them most.

Contact us today for more information!

Premature seal failure is a major problem that leads to expensive downtime as well as the potential for equipment damage, environmental impact, and even physical harm. When a seal does fail prematurely, it is important to track down the root cause of failure to prevent it from happening again with a new seal.

Normal Wear

All seals are going to experience normal wear and eventually reach the point where they need to be replaced. The signs of normal wear include an even, glossy circumferential pattern on the seal lip and on the hardware and a relatively small protrusion on the heel of the seal at the extrusion gap. 

When high pressures are involved, normal wear also entails circumferential wear patterns (which will be over a larger area) and a protrusion at the extrusion gap (which matt also be larger). In addition, grooving may be present on the sealing surface. While normal wear cannot be prevented, it can be minimized through proper installation and maintenance.

Shaft Surface Hardness

If the hardness of the contact surface of the shaft is not sufficient, excessive wear is likely to occur. In most cases, the shaft surface hardness should be at Rockwell 30C at minimum. In situations where there can be issues of the shaft being nicked or scratched prior to installation, operating speeds in excess of 15 fps, or the potential for abrasive contamination exist, then the minimum hardness should be 45C. In addition, the surface hardness should penetrate to a depth of 0.3 mm. If the shaft cannot be hardened enough, then a wear sleeve should be considered.

Signs of surface hardness issues include radial grooving with embedded metal filings and either axial or circumferential scratches on the dynamic surface. This type of damage can be prevented by ensuring that the shaft surface meets the appropriate hardness requirements for the application and seal jacket material.

Shaft Surface Finish

Another potential cause of premature shaft failure lies in the surface finish of the shaft because the sealing lip makes direct contact with the shaft. For most applications, the surface finish of the shaft should be between 10 and 25 𝝁in Ra but that is highly dependent on the seal material chosen and the shaft material. For example, PTFE is a dry-running material that needs a certain level of roughness on the shaft in order to create a low friction barrier between the materials and serves as an additional seal barrier.

In addition, there should be no machine lead (helical scoring or spiral lines). The presence of a lead can not only abrade the seal lip but can essentially act as a pump and lead to leaking. A lead essentially serves as a leak path, which is never a good thing.

The signs of having too rough a mating surface include radial grooving with metal filings embedded, axial nicks on the seal lip, and/or axial scratches on the dynamic surface. The appropriate surface finish and removal of the machine lead can both be accomplished through careful plunge grinding,

Chemical Compatibility

It is extremely important that the seal material chosen is compatible with the media it will be exposed to during operation. And when the media is changed, that can often necessitate a change in seals. Furthermore, media includes not just what is being sealed but the type of lubricant used with the seal. Signs of chemical incompatibility include cracks or holes in the seal jacket, pilling, corrosion, and/or circumferential grooving of the dynamic surface.

When issues with chemical compatibility arise, the best solution is to choose a seal jacket material that is chemically compatible with the media and the lubricant. While the base fluid may be compatible, lubricant additives may cause problems.  If lubricants are the problem, keep in mind that materials such as PTFE and PEEK are both highly chemically compatible and self-lubricating so that no lubricant is needed.

Compression Set

Compression set occurs when a seal has become less elastic, resulting in leaks even at low pressures. If this is a regular occurrence, it might be wise to choose a different polymer for the seal jacket. The primary sign of the compression set is a flat-sided seal cross-section where the flat side corresponds to contact with the mating surface.

High Pressures Extrusion

At high pressures, seals can be forced into the extrusion gap where the seal will experience excessive wear and may eventually be torn apart. The best approach to preventing damage resulting from high pressure is to use a thermoplastic seal in place of an elastomeric seal or to use a BUR (Back-Up Ring) to prevent extrusion.

Improper Installation

One of the most common causes of premature seal failure is improper installation. Using the right tools will help prevent common issues such as installing the seal backwards or damaging the seal during installation. 

Another common source of seal failure that is typically related to installation is misalignment and runout. This is caused when either the shaft or seal is out of alignment. In some cases, the alignment issues may not be apparent until the shaft is rotating. The signs of damage related to misalignment include an even pattern of wear on the seal lip with one part that is more heavily worn, heavy wear on one side of the seal, an offset wear pattern, or a combination of high and low wear spots.

The key to preventing failure associated with installation is quite straightforward:

• Follow any instruction provided by the manufacturer
• Use appropriate tools
• Verify that the seal is being installed in the right direction
• Check for any sharp areas that could damage the seal
• Ensure that the shaft and the seal are properly aligned

Conclusion

Premature seal failure does not have to be a repetitive cycle if the root cause is detected and addressed. However, just replacing a seal without tracking down the cause will simply mean high M&O costs and unnecessary downtime. By inspecting a failed seal, it is possible to narrow down what caused the failure and take steps to prevent it from happening again.