by Jackie Johnson Jackie Johnson No Comments

Rocket Engine Seals For Use With Cryogenic Hypergolic Bipropellants

The use of hypergolic bipropellants such as RP1/LOX have proven to be an efficient approach to seals for rocket engine propellant. However, they require highly reliable, leak proof seals to keep them separate before actual launch, in part because the bi-propellants will ignite when they come into contact with each other. 

Critical Factors for Rocket Engine Seals

There are four critical factors for rocket engine seals that apply regardless of the type of propellant used: safety, weight, cost, and cost per kilogram of payload. 

Regardless of whether space flight is privately or federally funded, safety remains the main priority. The seals used in rockets and rocket engines must be highly reliable with predictable behavior for every possible environment in which they will be operational, including the temperatures, pressures, and media involved. Seals in general have been problematic for rockets in the past, and accidents with hypergolic bipropellants are certainly not unheard of, with spills having occurred at Johnson Space Center, White Sands Test Facility, and Edwards Air Force Base. 

Weight has been a major concern in aeronautics and space flight for decades. The weight of the rocket is directly related to the fuel required for launch, and the combined weight and fuel reduces the payload that can be carried.Payload is a determining factor for the commercial viability of the rocket. Lightweight seal materials with high specific stiffness and/or specific strength are in high demand.

Cost is another major factor, and some approaches to sealing within rocket propulsion systems are more expensive with determining factors including the type of seal (e.g., spring energized vs traditional seals) and the material involved (PTFE, Torlon, Silicone) . For custom solutions, the size, manufacturing method, and production run are also key. 

Also, keep in mind that the commercial viability of a rocket is often determined by cost per kilogram of payload. Striking a balance between reliability, weight, and cost to achieve a lost cost per kilogram of payload is a challenging aspect of specifying rocket seals.

Hypergolic Bipropellants

Bipropellants use a mixture of two propellants, a fuel and an oxidizer, and fall into one of two categories: hypergolic and non-hypergolic. Hypergolic bipropellants will  ignite when the oxidizer and fuel come into contact with each other, while non-hypergolic propellants require a separate ignition source.

For example, the last several iterations of Blue Origin (which recently took actor William Shatner into space) rocket engines have been using the follow the following bipropellants:

  • BE – 2: Kerosene + Peroxide
  • BE – 3PM: Hydro-LOX (Liquid Hydrogen + Liquid Oxygen)
  • BE – 3U: Hydro-LOX
  • BE – 4: LNG-LOX (Liquified Natural Gas + Liquid Oxygen)
  • BE – 7: Hydro-LOX

Bipropellants that include liquified oxygen, hydrogen, or natural gas are considered cryogenic because of the extremely low temperatures required to keep these materials in liquid form.

Cryogenic Hypergolic Bipropellant Seal Challenges 

When cryogenic hypergolic bipropellants are used, the cryogenic portion must be stored at extremely low temperatures (e.g., storing LOX before it is fed into the MCC). More conventional sealing materials such as traditional elastomers and uncoated metals do not provide the necessary performance at the cryogenic temperatures involved, in part due to the brittle behavior exhibited at extremely cold temperatures.

To further complicate matters, these cryogenic bipropellants will come into contact with seals as they travel through the various stages of a rocket, including compressors, pumps, ducts, joints, manifolds, and valves. And after ignition, extremely hot temperatures are involved. 

Specifying and Designing Rocket Engine Seals

In the context of cryogenic hypergolic fuels, there are some specifications that must be carefully considered, in addition to typical seal characteristics. These include …

  • Wide Operating Temperature Range
  • Lower Temperature Limit
  • Thermal Cycling
  • Cleanliness
  • Chemical compatibility
  • Wear
  • Low Friction
  • Surface Finish of Glands and Grooves

Seals that come into contact with oxidizers need to be resistant to the aggressive effects of oxidizing liquids, including long-term exposure. In addition, for seals exposed to either extreme heat or cold, their change in dimensions must also be accounted for during the design phase.

Rocket Engine Seal Solutions

One of the most popular options for rocket engine seals are spring-energized seals, which include a spring-energizer that keeps the seal jacket in contact with the sealing surface in a wide range of environments where traditional seals would fail. 

Another potential seal option would be encapsulated o-rings, which have proven themselves in a wide variety of cryogenic applications. These o-rings have a stainless steel, FKM, or silicone energizer encased within a durable, chemically compatible material. 

As to the most commonly used materials with spring-energized seals and encapsulated o-rings, both FFKM and PTFE provide excellent mechanical and chemical characteristics that suit the harsh operating environment of rocket engine seals in general, and cryogenic hypergolic bipropellant fueled rock engines in particular. Traditional elastomers often do not have the needed performance at cryogenic temperatures, which is why polymer or perfluoroelastomer materials are often preferred. 

FFKM, trade name Kalrez or Viton, is a perfluoroelastomer that offers excellent performance in the extremely harsh environments of rocket engine seals. It is highly resistant to the effects of oxidizers and has very good chemical compatibility. Another commonly used material for hyperbolic bipropellant sealing solutions is PTFE, better known by the trade name Teflon. It provides outstanding chemical compatibility, extremely low friction, and the necessary mechanical and thermal characteristics to provide reliable sealing in extreme environments.

Conclusion

When hypergolic cryogenic bipropellants are used in rocket applications, factors such as safety, weight, cost, and cost per kilogram of payload must be balanced with the various challenges involved with designing and specifying reliable seals. Two potential solutions to the issues related to rocket seal design are spring-energized seals and encapsulated o-rings, both with jackets of FFKM or PTFE.

If you are looking for a rocket sealing solution, let the engineers and experts in the Advanced EMC seal group lend their knowledge and expertise. They will work with you from the early design phase onward to find the seal type, geometry, and materials you need for a successful design. Contact them today!

by Jackie Johnson Jackie Johnson No Comments

Fluoropolymers in the Food Industry

High-performance fluoropolymers are incredibly vital for use in food and drink manufacturing industries. Setting them apart from general-purpose plastic such as PVC and PE, fluoroplastics enjoy a range of unique properties:

  • Thermal: Resistant to very low and very high working temperatures
  • Chemical: Total resistance to chemicals and solvents
  • Mechanical: Low friction, non-stick characteristics and tensile strength
  • Environmental: Resistant to weather, UV light and corrosion
  • Health: Non-toxic and high purity

Fluoropolymers such as PTFE (Polytetrafluoroethylene), FEP (Fluorinated Ethylene Propylene) and PFA (Perfluoroalkoxy Alkane) bring an abundance of benefits to the food and drink production, from cooking equipment to food coverings, conveyor belt rollers, UV lamp coatings, temperature sensor casing and non-stick surface covers. Because of this, fluoropolymers have kept products uncontaminated, workers safe and production running smoothly for years now.

In this week’s blog post, we will discuss the various ways the fluoropolymers are used in the food industry.

Beverage Dispensing

The requirement for a biologically harmless tubing product coupled with intermittent high temperatures over a long period of time present a challenge for hot beverage dispensing machines. Fluoropolymers such as PTFE and FEP are used as a tried and tested, FDA, NSF and EU compliant solution. Build of residue is greatly reduced due to the smooth internal surfaces provided by fluoropolymer materials. Not only are they FDA compliant, but they are low maintenance as well!

Food Packaging

In packaging and processing food, it is extremely important that the materials used are safe. As such, fluoropolymers such as PVDF, or Polyvinylidene Fluoride Fluoropolymer, are highly regarded in the food packaging industry for a variety of reasons. First, they are incredibly stable materials, and highly resistant to most chemicals, mineral acids, organic acids and other food preservatives. In addition, they are non-toxic and resistant to bacterial and fungi growth.

PVDF is particularly useful in food processing industry due to its unique chemical resistance when temperatures go as high as 300 degrees Fahrenheit (or around 149 degrees Celsius).

PTFE Coatings

With the invention of PTFE, also known as Teflon, non-stick and low friction coatings have played a vital role across the food industry.

For years, PTFE has been used as a coating for cooking applications where particularly sticky or abrasive products are used, such as commercial waffle irons, bread pans, mixers and beaters, hoppers, dough rollers and blades. This allows them to function much more effectively, and the use of oils or other release agents can be substantially reduced or even eliminated.

With ease of use also comes ease of cleaning, and PTFE coating can reduce the intensity and frequency of the cleaning process. It also acts as a hygienic barrier between the food and the surface of the component. These combined save significant employee time and effort, which ultimately reduces labor costs, saving both time AND money.

Belt Conveyors

In the cooking and food processing industries, belts and conveyers made with PTFE coatings are used for mass-produced foods such as bacon, chicken, hamburgers and eggs.

Because of its nonstick properties, the PTFE coating allows food to easily come off, with little mess. This facilitates a high volume of production for commercial food processors.

Industrial Bakeware

Fluoropolymer coatings assure high-quality coating solutions for bakeware used by industrial bakeries. This helps bakeries not only drive efficiency, but also improve the hygiene and safety of their operations. It also improves the quality of the final baked product, with less waste and less butter and/or grease used to keep the product from sticking to the pan.

Home Cookware Manufacturing

We have talked about how fluoropolymers are across the commercial industry, but they are just as equally prevalent in our homes as well.

The use of nonstick pans has been popular in homes since the 1950s, when a French engineer begun coating his fishing gear with Teflon to prevent tangles. His wife then suggested using the same method to coat her cooking pans. In 1956 the Tefal company was formed and began manufacturing non-stick pans.

And nonstick cookware is popular to manufacture as they can be machined and coated relatively easily.

Other Uses

As discussed, fluoropolymers have many uses in the food industry, and many more that we did not cover. Some of these include

  • Shatterproof Coatings for Heat Lamps
  • Encapsulated Temperature Sensors
  • FEP Roll Covers
  • Laser Marked and Printed Tubes for Identification
  • And more!

In Conclusion

With the strength and versatility of fluoropolymers, it is no wonder that it is such a popular material within the food and drink industries.

Because of its high temperature and chemical resistance, nonstick and non-toxic surface, many health organizations have recognized it’s inherit value and, as such, have made fluoropolymers the gold standard within the food industry.

To learn more about fluoropolymers, visit our page by clicking the link here. And if you need PTFE sealing solutions, contact us today!

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Benefits of Labyrinth Seals

The term “labyrinth” conjures up images of elaborate mazes, and in the context of seals that really isn’t far from the truth. They are a fascinating use of fluid dynamics to prevent contaminant intrusion in an extremely effective manner. And these seals are used in everything from basic machine spindles to cryogenic turbopumps for rockets. There are many benefits of labyrinth seals. 

A labyrinth seal is a specific type of dynamic mechanical clearance seal that utilizes a maze-like cross section to create areas of turbulence to prevent contaminants from making their way in and fluids from making their way out. They also reduce the clearance that is available for particles to enter. Labyrinth seals are most typically used to isolate an area of high pressure from an area of low pressure, but they work well in other applications as well. 

In this week’s blog post, we will discuss the many benefits of labyrinth seals, their applications, and more!

How Labyrinth Seals Work

Labyrinth seals consist of two pieces referred to as the rotor and the stator. The stator attaches to the machine in which the shaft resides and remains stationary; the rotor, on the other hand, attaches to the shaft and rotates with it. The rotor and stator then interlock once installed to provide the seal. In fact, this design makes it relatively easy to install. 

Any type of contaminant (e.g., particle, moisture) that tries to make its way past the seal must go through a maze-like combination of angles and turns that have been designed to generate enough turbulence to make ingression almost impossible. To cross the seal barrier, media and contamination must overcome significant flow friction and turbulence. 

Non-Contact Seal

Even though labyrinth seals are a type of mechanical seal, they are non-contact because the two opposing seal faces (the rotor and the stator) do not come into contact with each other but rather a seperated by an extremely small gap. This effectively eliminates wear issues associated with traditional seals, which also means that labyrinth seals have a longer useful life and require less maintenance. In addition, the non-contact feature of these seals also means they are resistant to galling as well as generated contamination from seal erosion and wear. 

Frictionless Seal

And because they are non-contact they are also frictionless, which means there are no special concerns with lubrication. The fact they are frictionless also leads to elimination of stick-slip and starting torque. Perhaps even more importantly is the fact that they will enhance the efficiency of the systems in which they are used by reducing frictional losses. In addition, thermal effects will be minimal because of the elimination of heat generation from friction.

Highly Effective Sealing

Labyrinth seals can prevent media from leaking out while preventing ingression, which can be a serious challenge even for traditional seals with excluders. And labyrinth seals not only exclude particle contamination but moisture ingression as well, and can do so even when exposed to water sprays. These characteristics, combined with the non-contact nature of these seals, makes them extremely reliable compared to more traditional lip seal solutions.

Polymer Labyrinth Seals

When polymers, as opposed to elastomers, are used, there are additional benefits. For example, the right choice of polymer means a seal that is highly resistant to corrosion and chemical attack. Polymer labyrinth seals can be manufactured from a variety of materials, including PEEK (polyetheretherketone), Torlon PAI (polyamide-imide), Vespel PI (polyimide), and Fluorosint (enhanced PTFE).

PEEK offers excellent performance and is extremely resistant to chemical attack. PEEK labyrinth seals are available as a special type referred to as fix tooth labyrinth seals or rub tolerant seals. They make it possible to achieve an even more reduced clearance. When there is contact made between the seal and the shaft (i.e., rubbing), the fixed teeth are able to deflect to prevent both wear and damage to the rotor.

Torlon labyrinth seals offer superior mechanical properties under extended high temperatures and can be either compression or injection molded.  They can be also configured as fixed-tooth seals and work the same way as the PEEK seals just described. In addition, Torlon meets several key requirements such as FAA requirements for smoke density, toxic gas emissions, and flammability, as well as UL approval with regard to vertical flammability. 

Abradable labyrinth seals are designed with the seal and rotor are reversed such that the seal wears away and not the teeth if they come into contact. This makes it possible to design the seals with only enough clearance for installation. Abradable labyrinth seals work extremely well when either the stationary and rotating elements are extremely close to each other or in cases where the rotating element grows axially or radially toward the stationary element. The most popular material for abradable labyrinth seals is modified PTFE. In particular, low LCTE (coefficient of thermal expansion) modified PTFE (often called Fluorosint) is used as a base for the seal, providing a wide operating temperature range, outstanding chemical resistance, and extremely low friction.  

Conclusion

Labyrinth seals are an excellent option for separating areas of low pressure from those of high pressure, as well as applications that demand a sealing solution with extremely small clearances. The benefits of labyrinth seals include excellent reliability, long operating life, low friction, improved efficiency, and easy installation when compared to their traditional counterparts. When engineer polymers are used, sealing solutions are possible that can withstand corrosive media and offer superior mechanical properties even in the presence of continuous high temperatures.

If you are looking for a sealing solution where traditional options have failed, contact Advanced EMC today to find out how a polymer labyrinth seal can benefit your application. 

by Jackie Johnson Jackie Johnson No Comments

Why Geckos Can’t Cling to PTFE

It may come as a surprise to some but geckos are not, in fact sticky! Gecko’s can cling to glass and climb up walls, but geckos are not inherently adhesive. In fact, there are certain surfaces geckos can not cling to at all- mainly PTFE.

In this week’s blog post we will go over exactly how the gecko gets its Spiderman like abilities, and why exactly they can not seem to climb on PTFE.

A Sticky Situation

With certain types of geckos, their feet contain thousands of tiny, hair-like, hierarchical fibrils called setae, that end in even more, microscopic hair-like structures, so tiny they are not much larger than the wavelength of visible light.

These setae are also ultra-flexible, so when a gecko jumps to another surface, they are able to absorb an incredible amount of energy and redirect it, allowing the gecko to quickly cling from surface to surface.

There are two prevailing theories as to how this process works. One is known as van der Waals forces, or molecular attractions that operate over very small distances. The other, proposed by Yale research Hadi Izadi is that geckos use static electricity which allows them to cling to most surfaces.

Most surfaces except, it seems, Teflon.

Teflon – The Bane of Geckos?

Did you know that PTFE was engineering specifically to resist adhesion by van der Waals forces?  PTFE is composed of carbon and fluorine atoms.  Of all the elements known to date, fluorine has the highest electronegativity.  This causes PTFE to repel other atoms that come near it.  More specifically, it works against van der Waals forces.

Furthermore, the molecular structure of Teflon is such that the fluorine atoms surround the carbon atoms.  It repels any atoms that try to come near the carbon atoms, giving PTFE its outstanding chemical inertness.

Researchers at the University of Akron, in an effort to further understand, and hopefully replicate, gecko stickability, decided to see what kind of surfaces geckos can cling to, and Teflon was one of the materials tested.

The answer?

Because of its ability to resist adhesion by van der Waals forces- geckos, who potentially use van der Waal forces to cling to other materials, cannot cling to dry PTFE surfaces.

In Conclusion

So, it would seem that the very mechanisms that prevent geckos from walking up dry PTFE provide its most attractive characteristics: extremely low friction and high chemical resistivity.  So, when you are looking for a low-friction option for a bearing or seal, don’t forget the bane of gecko’s everywhere: PTFE.

by Jackie Johnson Jackie Johnson No Comments

Amcor Partners with Michigan State University

Michigan State University’s School of Packaging is getting an upgrade thanks to global packaging leader Amcor Ltd. Thanks to Amcor, the school is receiving more than 10 million in US dollars to go towards funding a packaging sustainability professorship at the school, as well as upgrading the programs building, which has not been upgraded since 1987. And as Amcor partners with Michigan State University, both the school and the company hope to create a more sustainable plastics packaging industry.

In this week’s blog post, we will discuss the various upgrades the school is getting, the professorship and the building renovation.

Packaging Beginnings

The program at MSU was started in the fall of 1952 as a discipline in the Department of Forest Products, with the first Bachelors of Science degree in Packaging awarded in March 1955. In 1957, the MSU Board of Trustees separated the Packaging curriculum from Forest Products and, with industry assistance and advice, established an independent School of Packaging.

By the late 1960s enrollment in the program. had risen to about 300 students. With that many students, new facilities needed to be built, and in 1964 the original Packaging Building was completed with funds from corporate and private donors. Major additions to the building were completed in 1986 after student enrollment peaked at a whopping 1000 students.

Today, the School has earned a world-wide reputation for leading the charge in packaging design, innovation and sustainability.

Amcor’s Transformative Gift

In August, plastic packaging company Amcor made a $10.8 million dollar donation to MSU’s School of Packaging. The reason, according to Amcor, is manyfold.

“Today, we have over 100 MSU graduates working at Amcor already.” Said David Clark, vice president of sustainability for Amcor. “We see this as an opportunity to make a long-term commitment toward developing a stream of talent, not just for our company but also the industry.”

Amcor also has the benefit of close proximity to MSU. Amcor Rigid Packaging is based in Ann Arbor, MI, while Amcor Flexibles North America is based near Chicago, IL, both mere hours away.

“The ability to have somebody close by who is advancing the thinking about more sustainable packaging and more sustainable packaging systems is something we’re really excited about,” Clark said.

Transforming the Packaging Program

With the money, MSU plans to bring on board an endowed chair, a professorship paid for by the endowment provided by Amcor, for sustainable packing.

“The endowment for a faculty position for sustainability and the circular economy,” said Matt Daum, director of the MSU School of Packaging, “represents Amcor’s shared commitment with MSU to excellence and innovation in the future of packaging.”

While half of the money will be going to the endowed chair, the other half will go to upgrade the school’s existing building on the MSU campus.

The building, which, as stated earlier, was last renovated in 1986, is due for an upgrade. Teaching methods have changed drastically since the 80s, and a portion of the money is set to renovate the building’s main classroom, that seats a mere 100 in a slightly outdated auditorium/stage setting.

According to Daum, MSU plans to transform it into a flexible learning area, with a level floor, movable furniture and the ability to use a variety of technologies including laptops, smartphones and smartboards.

The construction will also focus on other building renovations such as more office space for faculty, more laboratories and, eventually, more classroom spaces.

“…we want it (the building) to be inspirational”, said Daum, “to be a hub where this becomes the place to draw the best minds for packaging and business leadership to come and think though and innovate in the packaging sustainability area.”

Planning for a Bright Future

The partnership between Amcor and MSU is certainly exciting. With the collaboration, both Amcor and MSU hope to lead the way to creating solutions that effectively manage used plastics. Clark is particularly enthusiastic about the partnership and what it means for the future.

“We hope it inspires other companies to make similar contributions to both academics and other collaborations that are going to help our industry move forward with solutions,” he said.

With nearly 10,000 MSU packaging school alumni around the world, Daum also hopes that school alumni will learn of the upgrades and contribute to the future of the program.

And as more and more students graduate, Amcor is excited for the innovation and ground-breaking advancements they will bring, creating a more sustainable industry as a whole.

For more plastics industry news, visit our blog HERE. For polymer seals, bearings and more, contact us today.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Benefits of Spring-Energized Seals for Wind Turbines

According to Statista, installed wind power worldwide reached a cumulative capacity of almost 743 GW (gigawatts) in 2020 and is expected to reach almost 841 GW by 2022. As it remains a competitive source of renewable energy, engineers are looking for ways to enhance the efficiency and reliability of wind farms and the turbines that comprise them. One design aspect under consideration is the seals that are used in these turbines. This week, we will discuss the various benefits of spring-energized seals for wind turbines. 

Sealing Challenges in Wind Energy

Wind turbine seals face many challenges during their lifetime:

  • Wide range of temperatures and temperature variations
  • Abrasive materials that can wear down a seal jacket and damage the sealing surface over time
  • Complications arising from below freezing temperatures
  • Regular exposure to moisture and rain
  • Constant exposure to UV that can degrade the seal jacket material

In addition, there are issues related to seal failure: maintenance and repair, a potential domino-effect of damage to internal components (e..g, gear box, electronics),efficiency errors, downtime, and technician safety.

One potential sealing solution for wind energy applications is the spring-energized seal. Spring-energized seals are commonly used in renewable and green energy applications, and wind energy is no exception.

What Are Spring-Energized Seals

Unlike traditional seals, spring-energized seals have an energizer (usually in the form of a spring or rubber) that enables the seal lip to maintain contact with the sealing surface. As with traditional lip seals, they are available in a wide variety of configurations. And there are different types of spring energizers to choose from, allowing for a fairly customized sealing solution for various renewable energy applications.

Benefits of Spring-Energized Seals

The resiliency made possible by the energizing spring enables the seals to provide very reliable performance in high pressures as well as wide environmental pressure variations. In fact, when configured correctly they provide an almost leak-proof seal, which can be critical not just for the wind turbine as a whole but for the precision components inside. 

Spring-energized seals can continue to provide an effective seal even in cases of hardware misalignment, out of rounders, eccentricity, and some degree of jacket wear and changes in sealing surface condition due to wear  (often caused by abrasive materials in the environment). They can also account for dimensional changes that result from wide temperature differentials such as those experienced by wind turbines, as well as extreme heat and cryogenic environmental conditions that can range between 140°F and -65°F.

Implementing spring-energized seals results in several benefits. More reliable seals reduce overall maintenance requirements for a wind turbine, and this can have a very positive financial impact for wind farms with multiple wind turbines at work. Effective, durable seals also lead to significantly less downtime and associated costs as well as more continuous electricity output. In fact, investing in spring-energized seals as opposed to more traditional seals will undoubtedly save money over time and extend the useful life of the wind turbines.

When a polymer material such as PTFE, PEEK, and UHMW PE is used for the seal jacket, there are no complications due to lubricants because these materials are self-lubricating. They have extremely low friction, do not exhibit stick-slip behavior, and have an extremely low starting torque and prevent the seal from freezing to the sealing surface. In addition, PTFE and PEEK exhibit excellent chemical compatibility with the various lubricants they may come into contact with. 

They also possess good UV resistance, which can be critical for seals that are constantly exposed to sunlight. Because wind turbines are often exposed to abrasive materials such as sand, dust, and saltwater, their wear properties are a definite benefit. The low levels of moisture absorption exhibited by these materials means that they will not change shape when exposed to humidity, moisture, and water.

Both materials also work well in the presence of extreme temperatures (including cryogenic) and exposure to moisture, humidity, and rain. In addition, PTFE and PEEK are available in high PV (Pressure-Velocity) grades that are ideal for dynamic sealing solutions. When combined with the proven performance of a spring-energized seal, they lead to more efficient wind turbines.

Finally, the use of spring-energized seals also has a positive effect on technicians’ safety by reducing the maintenance and repairs that must be performed at dangerous heights.

Conclusion

The use of spring-energized seals for wind energy should be considered as an option to 

increase efficiency and useful life while reducing downtime and maintenance costs. These seals along with a polymer jacket can provide an almost leak-proof solution that can withstand the many challenges of seals in the aggressive environments where wind turbines are found.

by Jackie Johnson Jackie Johnson No Comments

Fluoropolymers for Injection Molding: Challenges and Solutions

Fluoropolymers are used in many different industries and applications, ranging from medical devices to oil and gas. Engineers often assume that just because a part is to be manufactured from a fluoropolymer that it cannot be injection molded, but that is not correct. Fluoropolymers are not just limited to manufacturing processes such as machining, compression molding, or sintering. 

What Are Fluoropolymers?

A fluoropolymer, as the name implies, is a fluorocarbon-based polymer with multiple carbon–fluorine bonds. Fluoropolymers are known for certain characteristics such as …

  • Very low friction
  • Non-stick
  • Excellent performance in high temperatures
  • High purity and non-toxic
  • Aging is minimal
  • Easy to sterilize
  • Excellent resistance to acids, bases, and solvents
  • Also resistant to microbiological and enzyme attack
  • Good electrical insulating properties

Commonly Used Fluoropolymers

The most commonly used fluoropolymers include …

  • ECTFE (ethylene chlorotrifluoroethylene), trade name Halar
  • ETFE (ethylene tetrafluoroethylene), trade names FluonETFE, Neoflon, and Tefzel
  • FEP (fluorinated ethylene propylene), trade names Dyneon FEP, Neoflon FEP,  and Teflon FEP
  • FPM/FKM (fluoroelastomer), trade names Viton, Tecnoflon FKM, DAI-EL, and Fluonox
  • PFA (perfluoroalkoxy alkane), trade name Chemfluor, Hostaflon PFA, and Teflon PFA
  • PTFE (polytetrafluoroethylene), trade name Teflon
  • PVDF (polyvinylidene fluoride), trade names Hyldar, KF, Kynar, and Solef
  • PVF (perfluoroalkoxy), trade names Teflon PVF, Fluon PVF, and Dyneon PVF

Only some of these fluoropolymers have the properties that allow them to be injection molded. What makes the difference is whether they are melt processable.

Melt Processable Fluoropolymers

For a fluoropolymer to be injection molded, it must be melt processable. And while some materials like PVF may offer excellent properties, they cannot be injection molded. . However, PFA, FEP, PVDF, ETFE, ECTFE, and PCTFE are melt processable and can be injection molded. PTFE can also be injection molded, but it takes an extremely high level of skill and specialized equipment. In fact, just because a fluoropolymer can be injection molded does not mean there are not major challenges.

Common Issues With Injection Molding Fluoropolymers 

Injection molding offers a host of benefits in manufacturing and is a popular choice for a wide variety of components. However, there are certain problems that must be addressed for fluoropolymer injection molding, including high melt temperature, high melt viscosity, high shear sensitivity, and fluorine outgassing.

High Melt Temperature

A very high melt temperature is required to work with fluoropolymers, and the injection molding equipment and molds may reach temperatures up to 800°F. Hot runner systems are also needed, and careful attention goes into the design of runners and gates to encourage even flow of the material. However, the temperatures must remain controlled to avoid degrading the fluoropolymers.

High Melt Viscosity

Another complication lies in the fact that fluoropolymers such as PFA have a high melt viscosity, which is related to how flexible the polymer chains are as well as their degree of entanglement. Polymers that have a high melt viscosity flow very slowly even in their melted form and the melt can actually fracture if it encounters sharp edges or gates and runners that are too small.

High Shear Sensitivity

Another challenging aspect of injection molding a fluoropolymer is their high shear sensitivity. A material that exhibits shear sensitivity changes its viscosity when subject to stress or pressure, which is a problem. The viscosity of the polymer melt will vary significantly as it goes through the various stages of injection molding.

Fluorine Outgassing

Fluorine outgassing occurs when these polymers are melted, presenting another issue because of the corrosive effects of fluorine gas on barrels, screws, nozzles, runner systems, and molds. To make matters more complicated, fluorine gas is also highly toxic. 

Solutions for Injection Molding Fluoropolymers

Solutions have been developed to address the challenges involved with fluoropolymer injection molding, starting with thermal management. 

Thermal Management

Managing the temperature of the polymer melt as it passes through the various stages in the injection molding is vital to keeping the polymer flowing predictably. It also helps to ensure the integrity of the final part by preventing degradation of the polymer melt. The different zones and points have specific temperatures at which they should be kept and this requires highly precise thermal management. 

Gate, Runner, and Mold Design

While any injection molded part requires careful design of the gate, runner, and mold, this is especially important in the context of fluoropolymers. Depending on the fluoropolymer being processed, there are certain key dimensions for gates, hot runner systems, and the mold cavity. There also exist recommendations for the gating systems, such as whether tunnel, sprue, or fan gating should be used. In addition, careful design is needed to prevent issues with melt fracture.

Corrosion Resistant Materials

Barrels, screws, nozzles, runner systems, and molds must be made from materials that are corrosion resistant. The materials for these components have to possess excellent high-temperature material properties including hardness and wear resistance. Ther barrel, screw, and nozzle must be manufactured from special materials. 

For example, barrel material options include IDM 260, Xaloy 309, and Wexco B022 often work well. Effective screw materials are usually certain grades of  Inconel and Hastelloy as well as Haynes 242 alloy. For the nozzle tip there are Hastelloy grades that provide the needed properties.For the molds, materials such as plated tool steel or nickel alloys possess the needed corrosion resistance, thermal performance, and wear properties. 

Venting

Fluorine outgasses can be managed with proper venting, but the materials for the vent must be extremely corrosion resistant. Furthermore, the vents must be kept very clean. In addition to the danger of outgassing, gas trapped within the mold must also be addressed in order to avoid part defects and reduce the maintenance required to keep the molds ready to use.

Conclusion

There are certain fluoropolymers that can be injection molded, but certain issues must be addressed to successfully manufacture parts of the quality and integrity needed. And while there are many companies that are good at injection molding parts, not all of them have the equipment and experience to injection mold fluoropolymers. 

Here at Advanced EMC, we have the equipment and skill to successfully manufacture fluoropolymer parts through injection molding. In fact, we offer engineering assistance to help you select the best type and grade of material and configure your parts to make them as manufacturable as possible. Our injection molding machines range from 75 to 500 ton and we have a Class 100,000 clean room if needed. Contact us today for all your fluoropolymer needs. 

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring Energized Seals in the Food and Dairy Industries

The food and dairy industries are tough on seals, whether its extreme pressures and temperatures or the limitations posed by using only FDA-approved materials. Spring-energized seals, however, can prove an excellent solution for the challenges posed by these industries. In this week’s blog post, we will discuss spring energized seals in the food and dairy industries.

Issues for Spring Energized Seals in the Food and Dairy Industries

There are several key issues involving seals for the food and dairy industries. The most obvious is FDA approval, but these seals are also exposed to both extreme temperatures and high pressures. Sanitation procedures are extremely harsh, often involving steam, hot water, and aggressive chemicals to achieve hygienic conditions. In addition, the seals will often be exposed to water for extended periods of time, which could be absorbed by the seal material and result in compromising dimensional changes. Lubrication can also be an issue, which means seals may have to be self-lubricating. Finally, the seals must be reliable, able to perform in less than ideal circumstances.

Spring-Energized Seals

Unlike traditional seals, spring-energized seals include an energized seal provides permanent resilience to the seal jacket. The energizer compensates for hardware misalignment, jacket eccentricity, and wear. These seals are typically made of strong, corrosion-resistant stainless steel with a polymer jacket.

FDA Approved Materials

FDA CFR 177, contained in Title 21 of the Code of Federal Regulations, deals with indirect food additives (i.e., substances that inadvertently make their way into food) in the form of polymers. In addition to FDA regulations, there are other standards in place that apply, including (EU) 1935/2004, NSF/ANSI standard 61 for drinking water systems, and 3A Dairy sanitary standards 18-03 and 20-27.

Spring-energized seals are available in materials that are FDA approved. These materials include UHMW PE (Ultra High Molecular Weight Polyethylene) and PTFE (both virgin and certain grades of mineral-filled) and are both known for low friction, chemical inertness, and the ability to handle rugged sterilization and cleaning procedures that can involve steam, hot water, and aggressive chemicals. Other polymers that might be considered  dependent on the application are certain grades of PEEK and Acetal. In addition, UHMW PE, PTFE, and Acetal are also 3A-Dairy and USDA compliant.

Extreme Temperatures and Extreme Pressures

Food and dairy seals must provide reliable performance in extreme pressures and temperatures. Spring-energized seals are able to maintain a tight seal in temperatures and pressures that would cause more traditional seals to fail. This is primarily due to the spring-energizer that keeps the seal lip intact regardless of dimensional changes due to temperature variation as well as pressure fluctuations. Spring-energized seals are well known for their sealing ability at extreme pressures, including vacuum pressures. In addition, they work extremely well in cryogenic temperatures.

Sanitation Procedures for the Food and Dairy Industries

Food and dairy applications almost invariably involve harsh sanitation procedures that can compromise the performance of typical seals. For example, steam and hot water can cause a significant temperature difference, but the spring-energizer is able to maintain a positive seal even if the seal lip changes dimensions. The right choice of an FDA-approved material can ensure that the seal jacket will remain undamaged in the presence of any aggressive chemicals used.

Hygroscopic Effects

When seals are exposed to moisture, water, or humidity for extended times, the seal jacket material may absorb that moisture. This can lead to dimensional changes that compromise the performance of the seal. However, with a spring-energized seal, the energizer allows the seal to maintain contact regardless of those dimensional changes. And with a material such as PTFE or UHMW PE for the seal jacket, the possibility of moisture absorption and associated hygroscopic effects is further reduced.

Lubrication

In food and dairy applications, it may not be possible to lubricate seals because of the possibility of contamination. Choosing the right FDA-approved material for a spring-energized seal can eliminate the need for a lubricant because both UHMW-PE and PTFE are dry running, self-lubricating materials.

Reliable Performance

Seals are critical in food and dairy processing: a failed seal can contaminate goods and, if undetected, can put consumers in danger. Spring-energized seals are extremely reliable, both for the reasons already discussed as well as their ability to compensate for issues such as wear, out-of-roundness, eccentricity, and issues with the surface of the shaft. These seals can perform where traditional seals would fail, again thanks to the spring-energizer that keeps the lip of the seal in contact with the shaft.

Additional Benefits of Spring-Energized Seals

Spring-energized seals can also be used as direct replacements for traditional seals that have failed, even for failures. Because of their durability and resistance to corrosion and contamination, spring-energized seals last longer which in turn leads to reduced downtime and repair costs.

Conclusion

Spring-energized seals are needed in various applications related to the food and dairy

Industry, including blenders, homogenizers, mixers, process vessels, and hygienic piping systems. For reliable, durable, high performing seals for the food and dairy industries, consider the use of spring-energized seals.

by Sara McCaslin, PhD Sara McCaslin, PhD 1 Comment

Most Common Questions about Canted Coil Springs

Here are answers to seven of the most common questions asked about canted coil springs.

Where Are Canted Coil Springs Used?

Canted coil springs can be used in many different ways, but many are not aware of exactly how versatile they are. In the medical industry, they are used to shield equipment from crosstalk that could compromise the integrity of data. The automotive industry depends on canted coil springs to achieve solid mechanical and electrical connections while reducing weight and minimizing the complexity of assemblies. 

In the oil and gas industry, they are used to achieve both electrical and mechanical connections in the rugged environment of downhole tools. Canted coil springs protect sensitive equipment from lightning strikes in the aerospace industry. And those are just a few examples of how they can be used.

What is a Canted Coil Spring?

Traditional springs have all the coils perpendicular to their longitudinal axis. Canted coil springs, on the other hand, have the individual coils parallel to each other and at an angle to the longitudinal axis. Because of how the coils are oriented, these springs can effectively serve a wide range of uses that traditional springs cannot.

Are There Any Other Names for a Canted Coil Spring?

Yes, as a matter of face there are. Canted coil springs are also called slant coil springs and cant coil springs, both in reference to the angle (or cant) at which the coils are parallel to each other.

What Makes a Canted Coil Spring Special?

Because of the cant of the coils, these springs have a flat load curve when compressed–which is rather unusual for a spring. This means that the load generated as these springs are compressed is predictable through their wide deflection range. 

What Can Canted Coil Springs be Used For?

Canted coil springs have four specific areas of application in which they excel: energizers for spring-energized seals, mechanical connectors, multi-point electrical connectors, and EMI/RF shielding.

Spring-Energized Seals

Canted coil springs are one of the options when specifying a spring-energized seal. Spring-energized seals provide outstanding performance in spite of issues such as uneven mating surface,  hardware gaps, runout, eccentricity, out of roundness, and seal lip wear. 

In that context of spring-energized seals, canted coil springs generate a flat load curve that in turn keeps friction at a predictable, constant level. This is extremely important in sealing applications for which friction and torque are critical to the functionality of a seal. In addition, canted coils do not experience compression set. Canted coil spring energizers work best when there are moderate to high speeds involved and are ideal for situations where friction needs to be highly controlled.

Mechanical Connectors

First, canted coil springs work well for latching, or fastening two parts together so they can still be disconnected when needed. They also work extremely well at locking, where two parts are permanently “locked” together. Holding is another task for which canted coil springs excel: two parts can be aligned and retained, but with sliding possible. Sliding is highly controlled by spring force generated when the canted coil spring is deformed.

In this type of application, canted coil springs can be fine tuned to achieve highly specific insertion and removal forces. This is made possible by the nearly constant spring force that these springs generate over their deformation range.

EMI/RF Shielding

One of the more interesting applications of canted coil springs is their ability to provide EMI/RF shielding.  Their electrical properties can be adjusted to meet specific impedance requirements to achieve optimal shielding for certain ranges of interference, including both conductive and radiated. And they work extremely well at shielding from crosstalk.

These springs can easily adapt to even the most uneven and irregular shapes, allowing them to provide a consistent level of shielding, and can be used with connect/disconnect assemblies, waveguide flanges, rectangular electronics enclosures, and both radial and coax connectors.

Multi-point Electrical Conductors

Canted coil springs can also serve as multi-point electrical conductors. Because surface area provided by the canted coils, they provide a cooler operating temperature which can be critical in certain designs, including those where space is highly limited. Canted coil springs can serve as both conductors and grounds, in both static and dynamic applications. Their multi-point contact system means they can keep electrical contact even in extremely harsh conditions, including those where vibration and shock are common. 

What Kind of Materials Are Canted Coil Springs Available In?

The three most common materials for canted coil springs are:

  • Hastelloy
  • Inconel
  • Elgiloy
  • 300 Series Stainless Steel (e.g., 316, 316L, 302)
  • Copper alloys

In addition, they can be nickel, silver, or gold plated if needed. 

If there is going to be extremely high temperatures and/or exposure to corrosive media, Elgiloy is typically recommended. For shielding or use as a multi-point conductor, stainless steel and copper alloys work extremely well.

What Kind of Options Are Available for Canted Coil Springs?

The basic options for canted coil springs outside of those related to materials are …

  • Wire diameter
  • Coil size (width and height) 
  • Coil cant angle 
  • Number of independent coils
  • Inner and outer diameter of the spring

By adjusting these parameters and material selection, specific performance goals can be achieved.

Conclusion

Canted coil springs are useful in so many different applications, and their performance is fully proven in the field. Whether you need highly reliable spring-energized seals for use in vacuum conditions, locking components for orthopedic implants, a way to protect rectangular electronics enclosure from a specific range of interference, or a multipoint conductor that also serves as a latching connector, canted coil springs are an excellent option.

And remember that Advanced EMC offers FlexForceTM canted coil springs. Our engineers can work with you to find the right combination of characteristics and properties to meet the needs of your application. Contact us today!

 

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring-Energized Seals for the Medical Industry

Spring-energized seals, when designed correctly, provide a highly-reliable sealing solution for medical applications where failure can be fatal. Selecting the right seal jacket material and energizer is critical, but also complex. In this week’s blog post, we will discuss spring-energized seals in the medical industry, the best materials, how they are used, and more!

Spring-Energized Seals in the Medical Industry

Spring-energized seals are regularly used in equipment that involves rotary motion, including a variety of surgical instruments such as high- and low-speed handpieces, surgical saws, bone shavers, oscillating saws, and bone drills.  They are also seen in rotary catheter systems, centrifuges, and both small motors and small pumps. 

Reciprocating equipment also may require spring-energized energized seals, with typical applications including respirators, oxygen compressors, dialysis machines, syringe pumps, and blood analysis equipment. In addition, spring-energized seals work exceptionally well in cryogenic applications.

How Spring-Energized Seals Work

A spring-energized seal makes use of an energizer, most often in the form of a spring, to enable the seal lip to stay in contact with the mating surface. For high pressure applications, the pressure of the media is usually able to keep the seal lip in contact with the mating surface and the springer-energizer then takes over for high pressures. On the other hand, when used in applications involving low pressures, the spring-energizer is responsible for keeping the seal lip in contact with the sealing surface at all times. 

Seal Jacket Materials

There is a wide variety of seal jacket materials that can be used, but the choices are significantly limited for medical applications. The materials used must be FDA, USP Class VI, and ISO 10993-5 compliant. This significantly limits what materials can be used for the polymer jacket. The three most common choices are these: UHMW PE, PTFE, and PEEK.

UHMW PE

UHMW PE (Ultra High Molecular Weight Polyethylene) is a high-performance engineering polymer that possess the following characteristics:

  • Low coefficient of friction
  • Good chemical compatibility
  • Low moisture absorption
  • Good dimensional stability
  • Good operating temperature range up to 180°F
  • Can withstand extended exposure to hot water and steam
  • Self-lubricating

In addition, it exhibits excellent wear and abrasion resistance. UHMW PE is also known for its high purity and is also commonly used in orthopedic implants, in part because of its strength and toughness.

PTFE

PTFE (Polytetrafluoroethylene), often referred to as Teflon, has the following properties:

  • Extremely low coefficient of friction
  • Excellent chemical compatibility
  • Good dimensional stability
  • No moisture absorption
  • Excellent operating temperature range up to 450°F
  • Self-lubricating
  • Can withstand extended exposure to hot water and steam
  • Low cost

The primary weakness of virgin PTFE is its wear resistance, making it best adapted to light-service duty applications. However, wear resistance can be significantly improved through mineral additives.

PEEK

PEEK (polyether ether ketone) offers these properties:

  • Extremely low coefficient of friction
  • Excellent chemical compatibility
  • Moderate moisture absorption
  • Good dimensional stability
  • Wide operating temperature range up to 480°F
  • Self-lubricating
  • Can withstand extended exposure to hot water and steam

It is also extremely tough, abrasion resistant, and known for its outstanding heat resistance. In addition, PEEK is also used quite often in medical implants because of its biocompatibility, stiffness, strength, and toughness. 

Spring Energizers

Spring energizer materials are either metal or elastomeric, with metal being the most common. For medical applications, the three most commonly used metals for the spring energizers are stainless steel, Elgiloy, and Hastelloy.

Metal energizers are ideal for several reasons, with the first being their natural stiffness. They also work well in applications that involve autoclaving because of their thermal characteristics and contribution to maintaining the shape of the seal jacket. In addition, a metal spring helps to dissipate heat, reducing the potential effects of thermal deformation in the seal jacket. 

In the medical industry, the energizing spring will fall into one of these categories: canted coil, helical, or cantilever. Because spring loads can be customized, canted coil springs (also known as slanted coil springs) can serve in a variety of operating conditions. Heavy force canted coil springs perform extremely well in high pressure applications but may experience more wear than other configurations. Springs designed to provide more of a light force are ideal for high-speed applications but should not be used in cryogenic environments or with vacuum pressures.

In general, helical springs for medical applications involving cryogenic temperatures, vacuum pressures, and high pressures with only moderate wear, but are not recommended for high speed applications. Helical springs work extremely well on seals interacting with lightweight gases or fluids.

Cantilever springs offer excellent performance in vacuum pressure conditions but, as with helical springs, should not be used in high speed applications. However, a high degree of wear is to be expected. And, because the energizing force will be concentrated at the very front of the seal, they work extremely well for scraping and exclusion applications. 

Choosing the Right Spring-Energized Seal 

Dynamic sealing solutions for medical applications can prove extremely tricky for several reasons. For example, seals can be exposed to a variety of fluids and media, which can include bodily fluids and materials such as adipose, hemoglobin, proteins, carbohydrates, and general bioburden. For such applications, PTFE with its natural hydrophobic properties is an excellent option.

For seals which may be exposed to abrasive materials such as bone shavings, wear and abrasion resistant polymers such as UHMW PE and PEEK work very well, although there are FDA-approved fillers for PTFE that can enhance its wear properties. 

Cleaning, sterilization, and disinfection are critical factors in deciding on an appropriate sealing solution. Sterilization in particular is the most aggressive of the tree, and may involve the use of autoclaves (also known as steam sterilizers) that require elevated temperatures and pressures. There are other methods, such as dry heat, plasma gas, VHP (Vaporized Hydrogen Peroxide), and chemical sterilization. 

Chemical sterilization may use bleach, ozone, hydrogen peroxide, or EtO (ethylene oxide). While all three materials have good chemical neutrality and handle heat quite well, warpage may occur due to residual stresses and should be considered when developing the seal jacket molding process. 

There may also be issues with the use of lubricants, therefore many medical sealing applications require the use of a self-lubricating material of which PTFE, UHMW PE, and PEEK all qualify. However, for the lowest coefficient of friction and least slip-stick behavior or startup torque, PTFE is optimal.

Conclusion

Many different factors go into choosing the right spring-energized seal for a mission-critical medical application, and engineers must consider factors such as pressure, sterilization methods, lubricants, chemical compatibility, wear, and other. There are, however, proven sealing solutions for medical industry applications.

If you need a reliable seal for  the complex environment of a medical application, contact the sealing group at Advanced EMC. We can put our years of experience in polymers, spring energizers, and mission critical sealing solutions to work for you. Contact us today!