by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

O-Rings for Semiconductor Manufacturing

O-rings are a circular seal that is seated within a groove and compressed between two or more parts during assembly to form a seal at the interface. While they may look simple, their importance cannot be overstated–especially when it comes to o-rings for semiconductor manufacturing applications.

Semiconductor Operating Environments

In the semiconductor manufacturing industry, it can be difficult to find an o-ring solution that can handle the harsh operating conditions that can involve factors such as aggressive media, extreme temperatures, and vacuum pressures. Chemicals such as bases, acids, solvents, amine-based strippers, and chlorinated gases may be involved depending on the application. Extended exposure to oxygen and fluorine plasmas are common

The performance requirements of o-rings for semiconductor manufacturing are challenging to meet as well, often requiring thermal, dimensional, and chemical stability at high temperatures as well as low outgassing and high purity. Requirements may also include extremely low levels of anionic and cationic impurities, low levels of TOC (Total Organic Carbon), reduced IR (Infrared Absorption), and low permeation rates.

What to Look for in an O-Ring for Semiconductor Applications

The key properties of an o-ring material for the semiconductor industry vary with the type of application involved. For example, track and lithography equipment and processes often require an o-ring that is very resistant to solvents, while CVD (Chemical Vapor Deposition) needs thermal stability and excellent performance in the presence of vacuum pressures. 

Other applications, such as CMP (Chemical Mechanical Polishing), must have o-rings made from a material that is both abrasion resistant and resistant to high pH chemical exposure. Wet etch demands an o-ring made from a high purity material that will cause no elemental contamination (i.e., low particle generation) and dry etch requires that the material be resistant to plasma. Resist stripping not only requires general chemical resistance but outstanding performance in the presence of ozone. 

O-ring materials may have to meet other requirements as well, such as resistance to poisonous doping agents and reactive fluids, low outgassing, and low trace metal content. Almost all semiconductor o-rings involve a low compression set, excellent dimensional stability, and a wide range of operating temperatures.

Is there a material that can handle the operating environments just described? Yes, there is: FFKM, which provides the resiliency and sealing force of an elastomer with the thermal stability and chemical compatibility of PTFE (trade name Teflon).

Read more

by Jackie Johnson Jackie Johnson No Comments

Spring-Energized Seals for Spaceflight

With the success of commercial spaceflight companies such as SpaceX, Blue Origin, and Virgin Galactic, there is an increasing demand for high performance, dependable seals. Rockets are one of the areas where harsh environment seals are needed, but also pose extremely challenging issues for success. Spring energized seals are one solution, but why?

What Makes a Modern Rocket

Successful spaceflight involves rockets, and the primary sections of a modern two-stage rocket are the first stage engine bay, first stage, second stage engine bay, second stage, and, last of all, the payload. This constitutes the most common configuration for today’s NewSpace companies. 

Such a configuration features an expendable or reusable first stage that contains 4 to 9 engines (the number of engines varies based on company design) and an expendable second stage that typically contains a single vacuum-optimized engine. The goal of the first and second stages is to produce enough thrust to achieve a targeted orbital velocity–usually around 17,500 mph– for the payload that sits on top of the rocket.

Propellants and Pressurants

Most rockets use either solid or liquid propellant. In this blog post, the focus will be on bi-propellant rockets, which are most commonly being used or developed in the United States commercial market. Bi-propellant rockets, as the name implies, use a combination of propellants. Common propellant configurations include:

  • RP-1 (Highly refined kerosene)/Liquid Oxygen (LOX) (aka, Kero-Lox)
  • Liquid Methane/LOX (aka, Metha-Lox or Lox-meth)
  • Liquid Hydrogen/LOX (Hydro-Lox)

Pressurants and support fluids include:

  • GN2 (Gaseous Nitrogen)
  • Helium (He)
  • GOX (Gaseous Oxygen)
  • GCH4 (Gaseous Methane)

How Modern Rocket Propulsion Systems Work

For a pump-fed system, the propellants are fed from low pressure tanks into a turbopump assembly (TPA). This significantly raises the pressures to be injected into the main combustion chamber (MCC). In most cases, a small portion of the propellants are scavenged from the high-pressure side to feed a separate small combustion chamber known as a gas-generator or pre-burner and used to drive the turbine. These fuel or oxygen rich gases can then either be vented to the atmosphere or re-injected into the MCC.

Operating Conditions of a Rocket Propulsion System

Consideration of the operating conditions within a rocket propulsion system provides insight into the challenges faced by the seals.

  • State 1 – Tank to Turbopump Assembly (TPA) inlet: propellants (oxygen + methane) are usually around 50 -150 psi and RP1 will be between 20 F and 80 F while the cryogenics will be between -450 F to -260 F.
  • State 2 – TPA outlet: depending on the engine, pumps will raise these pressures to somewhere between 1,500 and 16,000 PSI.
  • State 3 – Pre-burner: pressure will have dropped across the lines and injector – usually 8-15%, however temperatures will be between 800 -1,500 F.
  • State 4: depending on the engine cycle, propellants may be in a liquid-liquid state, gas-liquid state, or gas-gas state at an array of temperatures and pressures before mixing in the MC; note that in most cases the fluids will be supercritical.
  • State 5: once across the injector, the remaining propellants will combust at temperatures higher than 4000 F while pressure in the MCC may be between 50-20% of State 2 depending on system losses; note that this pressure drops quickly as the gases are pushed toward the atmosphere.

Depending upon which stage is involved, seal requirements vary greatly but high pressures and extreme temperatures will always be involved. 

Rocket Engine Seals

Rocket engine seals must perform in some of the most harsh environments imaginable and may involve wide operating temperature ranges (including cryogenic), extreme pressures, wide thermal cycling, and chemical compatibility with fuels, propellants, and pressurants. Most importantly, they must be extremely reliable. As an example, consider the just a rocket turbopump.

The image shown is a Hydro-Lox turbopump with a geared coupling used in the Aerojet Rocketdyne RL10 engine. Where it is labeled with a 1 indicates flange locations that likely use spring-energized face seals. Downstream of the outlets  will be the main valves, and they too will most likely have additional flange connections that will require seals. Areas labeled with 2 indicate other flange locations that depend on face seals of unknown makeup but likely involve hot gas connections.

Spring Energized Seals: A Rocket Sealing Solution

One of the most reliable, harsh environment sealing solutions is the spring energized seal. Unlike conventional seals, a spring energized seal includes an energizer that enables the seal lip to stay in contact with the mating surface through extreme variations in pressure and temperature,and  dimensional changes, as well as out of roundness, eccentricity, hardware misalignment, and some degree of wear. Vibration, cryogenic temperatures, and high temperatures are also an area where spring-energized seals offer outstanding performance.

They are highly durable in operating environments where other seals simply cannot survive. In fact, the performance of such seals has been well established in aviation and aerospace, including both NASA and commercial rockets. 

A wide variety of jacket materials are available, with some of the most widely used aerospace options being PTFE (trade name Teflon) and Hytrel. Materials such as Teflon and Hytrel can handle extreme temperatures, are chemically compatible with media involved, are heat resilient, provide low friction, have excellent wear characteristics, and are typically self lubricating. In addition, both materials are available in grades that provide key characteristics such as improved wear, lower friction, additional stiffness, better strength, etc.

And the same is true for spring energizers, which vary in both geometry and material used. For example, vacuum pressure and cryogenic applications often utilize V-springs (also known as V ribbon springs), high pressure environments may use coil springs, and vacuum pressure operating conditions with medium speeds may utilize helical springs. Various materials can be used for the spring, which will be enclosed within the seal jacket; because of this, the spring material will be protected from whatever media is being sealed.

Conclusion

If you are in need of spring energized seals for space applications, allow the seal specialists at Advanced EMC help you. We have a long history of providing our customers with the seals they need, including custom engineered and manufactured solutions that not only meet their specifications but also the rigorous standards that may be involved. Advanced EMC has the design, manufacturing, and testing capabilities you need to make your design a success. Contact us today to learn more.

by Jackie Johnson Jackie Johnson No Comments

Benefits of PTFE For Sealing Applications

PTFE (Polytetrafluoroethylene), also known by its trade name Teflon, is a polymer material commonly used in sealing applications that offers unparalleled stability and sealing characteristics across an extremely wide range of temperatures, from the extreme heat of a space shuttle engine to the cryogenically cold temperatures used to preserve

In this article, we will discuss how and why PTFE is one of the best materials to use for seals in a wide variety of applications.

Low Friction

PTFE has the highest melting point and lowest friction, and is the most inert of all the fluoropolymers. It has a continuous service temperature rating of 500 degrees Fahrenheit. Molding powders are excellent, fine cut granular resins, well suited for a variety of demanding chemical, mechanical, electrical and non-stick surface applications.

Such applications include:

  • Cookware
  • Outdoor Rain Gear
  • Medical Devices
  • And more!

Cryogenic Applications

Cryogenic seals are used with super-cooled media, like liquid hydrogen or compressed natural gas, at temperatures below -238°F and down to -460°F (absolute zero). Cold temperatures like this are rough on a seal because at these temperatures most materials begin to exhibit highly brittle behavior and lubricants typically cannot be used because they will freeze. PTFE seals, however, can handle temperatures all the way down to -450°F and are capable of dry running because of their extremely low friction. PTFE cryogenic seals are used in industries like oil & gas, pharmaceuticals, and aerospace.

High Temperature Applications

PTFE seals work well at the other end of the spectrum, too. They can continue to function in extreme temperatures up to 600°F, and continuous operating temperatures up to 600°F. Note that a filler may be required to enable the PTFE to dissipate heat more quickly. It’s not uncommon to see PTFE seals in petroleum or steam applications where temperatures greatly exceed 200°F.

PTFE is also non-flammable, making it ideal for use in applications such as jet propulsion engines. Where other materials would simply melt under the pressure of constant exposure to high temperature flames, PTFE is built to withstand even the hottest of environments.

The use of seals for high temperature applications include oil and gas industry and aerospace, to name a few.

Chemical Applications

The chemical resistance of PTFE is some of the best on the market. It is stable in most aggressive and corrosive media, including:

  • Acetone
  • Chloroform
  • Citric Acid
  • Hydrochloric Acid
  • Sulfuric Acid
  • Tallow
  • Sodium Peroxide
  • And more!

However, it should be pointed that that PTFE is not chemically resistive to liquid or dissolved alkali metals, fluorines and other extremely potent oxidizers, as well as fluorine gas and similar compounds. Outside of those, PTFE is an excellent choice for applications involving chemicals.

Oil and Gas Industry

Seals are critical for the safe and reliable operation of oil rigs across the globe. Not only do seals need to be able to withstand a wide variety of extreme temperatures, but they need to be able to handle extreme pressures as well. For well drilling, for example, seals need to handle pressures from 345 to 2070 bar (5000 to 30000 psi).

For those reasons, PTFE is an incredibly popular material to make oil and gas seals out of. Because of it’s resistance to heat, cold and high pressure, PTFE can withstand the rigors of oil and gas unlike any other material.

Spring-energized Seals

In order to retain sealing power under extreme temperatures, many engineers and designers go with spring-energized PTFE seals. The spring provides optimal sealing by forcing the lip of the seal against the mating surface and helps to account for dimensional changes as a result of temperature fluctuations.

A highly efficient seal is created as the system pressure increases enough to take over from the spring and engage the shaft or bore. The spring or energized seal assembly provides permanent resilience to the seal jacket and compensates for jacket wear, hardware misalignment and eccentricity. The jacket material is critical in design to assure proper seal performance.

Rotary Shaft Seals

Using PTFE in rotary shaft seals allows them to be able to run at higher pressures and velocities when compared to other materials. They are also able to have tighter sealing, often exceeding 35 BAR and can run at far more extreme temperatures ranging from -64 degrees Fahrenheit (-53 degrees Celsius) to 450 degrees Fahrenheit (232 degrees Celsius).

On top of that, they are:

  • Inert to most chemicals
  • Can withstand speeds up to 35 m/s
  • Compatible with most lubricants
  • Come in a wide range of sizes
  • And more!

Conclusion

PTFE is an ideal sealing material for both extremely high temperature applications and demanding cryogenic applications. It retains its key sealing properties: stiffness, strength, dimensional stability (may require spring energizer), low friction, and chemical compatibility- even in the most aggressive operating conditions.

Need PTFE sealing solutions? Advanced EMC Technologies is the leading provider of PTFE spring energized and rotary shaft seals in the US. Contact us today!

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

O-Rings in Spaceflight

Since the Challenger disaster, o-rings have come under close scrutiny in spaceflight designs and applications and they continue to play a vital role in modern spaceflight, including modern commercial spaceflight ventures such as SpaceX, Virgin Galactic, and Blue Origin.

In this week’s blog post, we will discuss o-rings in spaceflight, including problems that arise, the best materials, and more.

O-Ring Failures in Modern Spaceflight

Few would argue the importance of seals and o-rings in space shuttles and rockets. From rocket engines to the International Space Station, the ability to retain media and prevent its contamination is of vital importance. This importance was first brought to public attention through the Challenger disaster where a stiff o-ring cost multiple lives. However, o-ring issues did not end there.

In 2005, orbiter tests prior to the space shuttle Discovery’s return to flight revealed a failure that traced back to Nitrile/Buna N o-rings. Six of nine flow control valve o-rings had suffered radial cracks, with one o-ring developing problematic leak paths as a result. The cause of the o-ring issue was found to be ozone attack of Nitrile/Buna N, which is one of its susceptibilities.

Back in 2016 a Blue Origin launch was delayed by o-ring issues. Jeff Bezos reported that the rubber o-rings in the New Shephard rocket’s nitrogen gas pressurization system were leaking and had to be replaced before the launch could continue. New Shephard is the same rocket used to take Star Trek legend William Shatner on his first real space flight.

Virgin Galactic, owned by Richard Branson, discovered a very dangerous issue with the flight vehicle SpaceShipTwo when it was returned to the hangar in 2019. A critical seal running along a stabilizer on one of the wings had “come undone.” While not an o-ring, this does reinforce the importance of seals on modern spacecraft.

Operating Environment Complications for O-Rings in Spaceflight

O-rings face a very hostile environment in space, including …

  • Extreme temperatures, ranging from cryogenic to high
  • Wide temperature variation
  • Extremely high pressures and vacuum pressures
  • Vibration during launch
  • Risk of permeation depending on the media involved
  • Chemical attack from media such as fuels and lubricants
  • Potential exposure to ozone, ultraviolet, and radiation

There are other potential issues as well. For rockets in particular, one of the challenges faced when specifying o-rings involves their ability to expand fast enough to maintain a seal even when joints (a common area of use for o-rings) move away from each other. Swelling when exposed to hydrocarbon-based greases used to protect components against corrosion can be problematic as well. 

O-Ring Materials in Spaceflight

O-rings are manufactured from a diverse group of materials, including EPDM, FEPM, FFKM, FKM, Fluorosilicone, HNBR, Hytrel, NBR, Neoprene, Polyurethane, and Silicone.

Any material used in spaceflight applications, however, would need to fall within the categories of high temperature service and/or chemical service, reducing the list to materials such as …

  • FEPM (trade name Aflas)
  • FFKM (trade names Kalrez, Chemraz, Markez, and Simriz)
  • FKM (trade names Viton, Technoflon, and Fluorel)
  • Silicone. 

Keep in mind, however, that other materials may be suitable that are not included in this list and the suitability of these materials is highly dependent on the application.

FEPM O-Rings

FEPM, perhaps better known by the trade name Aflas, is a copolymer of tetrafluoroethylene and propylene and often represented as TFE/P. In addition to chemical compatibility and a degree of high temperature performance, it offers excellent ozone resistance. It is known for providing excellent performance where traditional fluoroelastomers are known to fail.

FFKM O-Rings

FFKM, often referred to by trade names such as Kalrez or Chemraz, is an excellent option for applications that involve extreme pressures, extreme temperatures, and aggressive chemicals. FFKM, which is a perfluoro elastomer material, is available in various grades that offer key properties such as low permeation, low compression set, resistance to temperature cycling, and wide ranging chemical compatibility as well as resistance to explosive decompression and plasma resistance. 

FKM O-Rings

Fluoroelastomers such as FKM, known to most people as Viton, can provide excellent resistance to fuels, lubricants, and oils. Another key characteristic of is extremely permeability when exposed to a range of substances that include oxygenated aircraft fuels. They also offer reliable performance at extremely high temperatures where non-fluorinated elastomeric materials will start to degrade.

In addition, FKM comes in various grades focusing on features such as low temperature resistance, fuel resistance without sacrificing necessary elasticity, and chemical resistance that is unaffected by extremely high temperatures. Such features combined have already made them a common choice in aerospace applications, including o-rings.

Silicone O-Rings

Silicone rubber o-rings have been used extensively by NASA and remain a popular choice for o-rings used in spaceflight applications. In fact, here’s a direct quote from NASA that dates back to 2010:

“Silicone rubber is the only class of space flight-qualified elastomeric seal material that functions across the expected temperature range.”

It is considered by many to be the best in-class elastomer choice for extremely harsh environments involving high temperatures and among its key properties is its ability to maintain critical mechanical properties in the presence of extreme heat. A potential issue related to the use of silicone for o-rings lies in its gas permeability.

Conclusion

O-rings are just as important to modern spaceflight as ever, and so is the importance of choosing the right type of o-ring. A failed o-ring, no matter how tiny it may seem, can lead to serious disaster and potential loss of life. 

If you are looking for a reliable o-ring solution for an aerospace or spaceflight application, contact the sealing group here at Advanced EMC. Our team will work with you to explore all possible solutions, including materials beyond those discussed here. Give us a call today and let our team put their expertise to work for you.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

FEP Encapsulated O-Rings

FEP encapsulated o-rings can survive corrosive chemicals and retain their sealing power in extreme temperatures, which is the main reason more and more engineers are choosing them for harsh environment applications. But what makes these particular o-rings special and what options are available for them?

What Makes Encapsulated O-Rings Different?

Unlike traditional o-rings, encapsulated o-rings contain a solid or hollow core that is typically made from a very elastomeric material. The exterior of the encapsulated o-ring is able to protect the encased elastomer from corrosive media that would adversely affect its performance. Together, the core and encapsulating polymer are able to provide a highly reliable seal even in extremely harsh conditions that may involve aggressive chemicals, extreme temperatures, and high pressures.

Encapsulated o-rings can be used in a wide variety of applications, including flanges, swivels, joints, valve stems, pumps, and even rocket engines. They serve as an excellent replacement for solid PTFE o-rings that are just not flexible enough for sealing in the long term. 

Characteristics of FEP

One of the most popular materials for the jacket of an encapsulated o-ring is FEP (fluorinated ethylene propylene), which has several trade names including Teflon FEP, Neoflon FEP, and Dyneon FEP. It is well known for its resistance to chemical attack, low friction, and a wide operating temperature range of -420°F through 400°F.  FEP remains flexible even at cryogenic temperatures, as well. One of its key characteristics is a very low compression set, allowing it to return to its original shape after deformation. FEP is also non-flammable and easy to lubricate.

While FEP is often compared to PTFE (Teflon), there are several key differences to keep in mind. For example, it does have a low coefficient of friction but it is higher than PTFE; at the same time, it still possesses very low friction with minimal stick-slip behavior. In addition, FEP does exhibit better vapor and gas permeability, which could be key for some applications. It is also melt processable, which means it can be vacuum formed, injection molded, and extruded. And, like PTFE, it is easy to clean even viscous liquids from.

FEP is available in FDA-approved grades, is considered a high purity material, and is less expensive than PFA, another commonly used jacket material. Note that FEP is commonly used in applications such as pump housings, medical components, food processing, fluid handling, and chemical processing.

Recommended Cores for FEP

FEP encapsulated o-rings work especially well with FKM and silicone cores, but there are other options available. FKM, which is a fluro-elastomer, has rubber-elastic properties which allow it to reassume its original shape and form after deformation. This results in excellent properties related to compression set. Silicone cores are not as stiff or hard as FKM cores and exhibit very good flexibility, even in cold temperatures. When combined with a hollow core geometry, this additional flexibility means that less energy is needed to achieve a tight seal. They work best for applications that involve low compressive forces.

Cores made from stainless steel, such as SS 301 or 302, exhibit excellent performance at both cryogenic and high temperatures, ranging from -420°F to 500°F. These cores usually take the form of a spiral spring (not unlike spring-energized seals) and exhibit minimum compression set and good resilience. They are not commonly used with FEP, however. EPDM, which stands for ethylene propylene diene monomer, is a synthetic rubber that performs well in temperatures ranging from -58°F to 300°F. Again, this particular core material is not recommended for use with FEP.

Selecting an FEP Encapsulated O-Ring

First, there are limitations associated with FEP encapsulated o-rings. They should not be used with liquid alkali metals and some fluorine  compounds, and should not be exposed to abrasive media such as slurries and some powders. 

They are not suitable for applications that involve high pressures and are limited to static or slow moving applications. In addition, they are not recommended for applications where the o-ring will be highly elongated and end-users should be aware that installation forces will be higher for FEP encapsulated o-rings.

However, experts agree that chemical attack and swelling are among the most common causes of o-ring failure, and the use of FEP encapsulated o-rings can solve both of these issues. FEP with an FKM core is a standard solution with a low compression set, recommended for operating temperature ranges not exceeding -4°F to 401°F. 

Use of a solid silicone core results in better low temperature performance, with an operating temperature range of -46°F to 401°F. A hollow core, on the other hand, involves lower contact pressures and is ideal for sensitive or fragile equipment. 

Conclusion

FEP encapsulated o-rings involve several key advantages, starting with their excellent chemical resistance, which allows them to be used with corrosive chemicals. These o-rings can handle pressures up to 3,000 psi and provide both an excellent service life and reliable sealing, all at a cost effective price. Their reliability and durability also translate to less downtime and better M&O costs. If corrosive media or extreme temperatures are destroying your o-rings, it may be time to consider an FEP encapsulated solution.

Advanced-EMC will work with you to find the encapsulated o-ring solution your application needs, from FDA-approved solutions for use with food processing equipment or a reliable, cryogenically compatible solution for a rocket. Contact us today to learn more.

by Jackie Johnson Jackie Johnson No Comments

All About Thermoplastics

Thermoplastic elastomers, also known as thermoplastic rubbers, or simply TPEs, are some of the best materials for when your product needs to have more flexibility. In this week’s blog post, we will go over the different types of thermoplastics, a brief history, and the benefits compared to other materials.

Different Types of Thermoplastics

According to ISO 18064, commercial TPEs come in six different classes, each with slightly different properties that make it suited for certain tasks and applications.

Styrenic block copolymers, TPS (TPE-s)

TPS are tri-block copolymers containing an elastomeric midblock and a polystyrene endblock. They are non-toxic, odorless and resistant to many different chemicals and conditions. This makes them highly suitable to outdoor conditions.

Thermoplastic polyolefinelastomers, TPO (TPE-o)

TPOs are based on a polyethylene backbone. They offer low-density and high flexibility and are commonly used as additives to PE and PP compounds to make them more flexible.

Thermoplastic Vulcanizates, TPV (TPE-v or TPV)

TPVs are produced by dynamic vulcanization or cross-linking of a rubber during blending and melt-processing with a thermoplastic at elevated temperature. TPVs are inexpensive and can be produced in high-volume, making them a good alternative to cheaper elastomers.

Thermoplastic polyurethanes, TPU (TPU)

TPUs are a linear segmented block copolymer composed of both hard and soft segments. TPUs, like other elastomers, are flexible, but also offer additional sturdiness, high resilience and a good compression set, making the incredibly versatile.

Thermoplastic copolyester, TPC (TPE-E)

TPCs combine the flexibility and strength of thermoset rubber with the processing ease of engineered plastics. They are high performance and high temperature elastomers suitable for extreme conditions.

Thermoplastic polyamides, TPA (TPE-A)

TPAs are light-weight thermoplastic elastomers based on polyester-amide (PEA), polyether-esteramide (PEEA), or polyether-amide (PEBA) block copolymers. They have incredibly low temperature flexibility, making them suited for chemical environments.

Not classified thermoplastic elastomers, TPZ

TPZs are thermoplastic elastomers that do not fall in any of the above categories.

History of Thermoplastics

While the origins of TPEs date back to the 30s with the invention of poly vinyl chloride by DuPont, TPEs became readily available with the advent of thermoplastic polyurethane polymers in the 1950s.

The 1960s saw styrene block copolymer become available, and by the 1970s there were a ride range of TPE materials available commercially.

Benefits of Thermoplastics

TPEs have many benefits compared to other materials such as PTFE or silicone.

  • More Eco-Friendly than PTFE
  • More Cost Effective than Silicone
  • Consistent
  • Medical and Food Safe
  • Incredibly Versatile compared to other materials

If you need a material that is flexible, versatile, cost effective and eco-friendly, consider using thermoplastic elastomers!

If you need TPE seals, bearings or other industrial solutions, contact us at Advanced EMC Technologies today!

by Sara McCaslin, PhD Sara McCaslin, PhD 1 Comment

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.