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Seals for Space Vehicle Propulsion Systems

In addition to the growing market for commercial applications, Statista estimates that 80 countries will have their own space program by 2025. And a critical factor in the success of any space venture is the type of seals used, including those for space vehicle propulsion systems.

However, finding the optimum sealing solution that provides highly dependable performance can be formidable for several reasons, including extreme pressures and temperatures, chemical compatibility, SWaP, and outgassing, not to mention vendor requirements involving seal size manufacturing.

Extreme Pressures

Depending on the applications, the pressures faced by seals can involve not only high pressures in the range of 100 bar but ultra-high vacuum conditions as well. For example, consider a typical hypergolic rocket propulsion system where pressures can reach between 1,500 and 16,000 psi during Stage 2. To further complicate matters, pressure fluctuations make it much more challenging to retain a reliable seal. 

Extreme Temperatures

One of the challenges involved in designing seals for propulsion systems often involves wide temperature ranges from cryogenic to extreme heat. For example, the fuel tanks on many modern rockets must provide sealing at cryogenic level temperatures at which many polymeric and elastomeric materials become brittle and unreliable. And when temperatures fluctuate, traditional seal solutions can experience significant dimensional changes, leading to leaks.

Material Compatibility

Seals for vehicle propulsion systems must be compatible with the fuels involved. For example, cryogenic hyperbolic bipropellants often require seals resistant to oxidizers. Also, keep in mind that, according to a NASA Lesson Learned on Static Cryogenic Seals for Launch Vehicle Applications, seal materials must also be compatible with any anticipated purge or cleaning material that they may come into contact with.

SWaP

SWaP (Size, Weight, and Power) is a significant factor in both space vehicle engineering and aerospace in general. Designs must fall within tight constraints for weight to minimize fuel requirements and size to reduce the overall volume of the space vehicle. In addition, seals, including those for the propulsion systems, must also be optimized to meet SWaP requirements.

Outgassing

Vacuum conditions make outgassing, the release of gasses from solid materials, a serious problem. This phenomenon not only introduces new chemicals to what may already be a volatile environment but can also lead to the deposition of chemicals on critical surfaces. Therefore, NASA makes available spacecraft material outgassing data to aid in selecting safe materials.

Size

Large fuel tanks necessitate large seals. For example, some of the seals for NASA’s SLS (Space Launch System) are over 6’ in diameter, and other fuel tanks have similar requirements. Such seals are challenging to both manufacture and test. Such large seals must usually be custom manufactured with small production runs, making it difficult to balance cost and performance. In addition, not all seal vendors have the manufacturing capabilities required for creating seals of this size at the proper levels of accuracy and precision.

Spring-Energized Seals

Image from NASA

Spring-energized seals, widely used in aerospace, are a practical solution for space vehicle propulsion systems. They can retain seal integrity even when subject to extreme pressure and temperatures due to the energizer. In addition, these seals can account for misalignment, eccentricity, thermal expansion and contraction, wear issues, and other dimensional changes. And they provide a consistent force over a wide deformation range.

The most commonly used materials for spring-energized seals in space environments include PTFE, FFKM, and Hytrel. However, when outgassing is a concern, materials such as PEEK, PAI, PI, Acetal, PCTFE, and antistatic PTFE can be considered. And many of these materials are also available with fillers to enhance their properties.

There are also a variety of choices regarding the spring energizer used. For example, cryogenic and vacuum pressure environments most often implement V ribbon springs (also known as V-springs),  helical springs work exceptionally well for static cryogenic applications, and high-pressure conditions usually employ coil seals. And remember that canted coil springs can be highly customized to produce consistent forces.

Advanced EMC: Your Source for Space Vehicle Seals

When it comes to vendor concerns, Advanced EMC has the equipment and experience required to manufacture large seals accurately. Our sealing solutions team has the knowledge and understanding needed to help you at every step of selecting propulsion system seals for everything from small LEO satellites to passenger-laden space vehicles. Contact us today!

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Canted Coil Springs for Latching, Holding, and Locking

Many associate canted coil springs with spring-energized seals, but they can be used for much more. For example, canted coil springs provide a lightweight, easy-to-install alternative to traditional mechanical fasteners. 

Canted Coil Springs Fasteners

Canted coil springs can perform three different fastening tasks:

  • Latch: fastens two parts together
  • Lock: permanently fastens two parts together
  • Hold: holds and aligns two parts together

Note that both holding and latching allow for the parts to be disconnected and reconnected. However, if two pieces are locked together, they cannot be separated without either damaging the canted coil spring or the connected parts. Also, note that canted coil springs can be used for quick-release locking, which allows the lock to be bypassed for a quick, simple release. And in all fastening applications, the force required to latch, lock, or hold can be specified by the engineer and accomplished by varying the coil space, wire diameter, spring width, and height.

Advantages of Using Canted Coil Springs as Fasteners

There are several benefits to using canted coil springs instead of more traditional mechanical fasteners. For example, they are easy to install and require no special tools, shortening assembly time. They are also highly reliable and provide dependable performance over thousands of insertion/removal cycles.

Canted coil spring fasteners experience almost no compression set and provide precise, predictable forces even when subject to a wide range of temperatures. Furthermore, the individual coils compensate for mating surface irregularities, misalignment, and dimensional variations. 

Their lightweight, compact nature makes them ideal for use in applications where weight and available space are at a premium, and they can also reduce the complexity of assemblies. Finally, and perhaps most importantly, they can serve other functions besides fastening, such as grounding, service as multi-point conductors, and providing tunable EMI/RFI shielding.

Applications of Canted Coil Fasteners 

In the medical industry, canted coil springs are used for both latching and holding in various applications, including implantable and non-implantable devices and surgical devices, such as customized tools for use by specific surgeons. An example of an implantable device would be joint replacements that require highly reliable locking. 

The oil and gas industry depends on canted coil springs’ highly reliable mechanical fastening capabilities for advanced downhole tools where insertion and breakaway forces must be controllable. In the renewable energy market, canted coil springs work well as connectors within the highly confined environment of turbine nacelles. 

The automotive and aerospace industries find them an ideal approach to fastening in applications where SWaP (Size, Weight, and Power) is critical. In addition, canted coil springs are regularly used in the defense industry, where specific applications include aircraft system connectors and optoelectronics connectors. Finally, canted coil springs also work well for underwater, fluidic, and satellite/orbital connectors.

Conclusion

Canted coil springs are a simple, reliable, multi-use alternative to traditional mechanical fasteners. Benefits include the ability to compensate for dimensional changes, lightweight and compact nature, and their ability to reduce the complexity of systems. They can also serve as not only fasteners but EMI shields and multi-point conductors. And keep in mind that their use ranges from medically implantable devices where their ability to respond to particular insertion/removal forces is critical as well as the harsh and dangerous world of downhole tools in the oil and gas industry. 

FlexForce Canted Coil Springs

Advanced EMC’s FlexForce Canted Coil Springs are available in 300 Series Stainless Steel, Hastelloy, and copper alloys with gold, silver, or nickel plating. In addition to light, medium, and heavy load spring forces, the forces can be customized. Our FlexForce canted coil springs are available in wire diameters between 0.25 mm (0.010 inch) and 1.50 mm (0.059 inch) and coil widths between 1.5 mm (0.039 inch) and 15 mm (0.591 inch). However, other materials, finishes, and dimensions may be available.

 

Contact us at bvardeman@gmail.com or call us at (918)-994-7776 to learn more about the FlexForce canted coil springs and how they can benefit your designs.

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Canted Coil Springs For Conduction

Flexforce Canted coil springs, can be used as effective electrical conductors. They can provide reliable current conduction despite challenges such as vibration, dynamic conditions, and shock loadings where other conductor solutions would fail.

Situations That Pose a Challenge for Conduction

Certain operating conditions can make it challenging to achieve a solid connection for conduction. For example, vibration and shock loadings, such as those experienced in downhole tools for the petrochemical industry, can cause more traditional electrical connections to eventually work loose and risk the integrity of signal and power transfer. 

Any time there is a high probability of motion, such as EV/HEV battery pack connections, there is also a risk that the integrity of the electrical connection could be compromised. In the power industry, issues can arise with heat and reliability for high-current applications that perform conduction, grounding, and isolation.

Rotating parts, high temperatures, and variations in loadings are also challenging for maintaining electrical connections and common to wind energy applications involving turbines. In addition, rotating parts in robotic end grippers and similar automation equipment pose similar issues. 

Implantable devices, such as neurotransmitters and pacemakers, require electrical connections that must also be highly reliable, lightweight, and compact. In addition, lightweight design approaches are critical for many applications, including unmanned vehicles that must be lightweight to maximize their battery-constrained range. 

And some applications, such as semiconductor fabrication, need to take advantage of solutions that can perform multiple purposes, such as conduction combined with latching/holding/locking or EMI shielding.

Canted Coil Springs

Our Canted coil springs, also known as slanted or slanting coil springs, are often used as electrical conducting springs to achieve high integrity connections for applications such as those just described. However, several factors make these springs different, starting with their ability to maintain consistent force over a wide range of deflection. 

The Individual coils that make up these springs maintain contact with the mating surface despite surface irregularities, misalignment, tolerance variations, and dimensional changes. In addition, they experience little to no compression set and are ideal for oddly shaped cross-sections.

When used as electrical conducting springs, the individual coils serve as multiple contact points for electrical conduction and grounding; essentially, each coil is a contact point. As long as one coil remains in contact with the surface, then the electrical connection is maintained.

Benefits of Canted Coil Springs for Conducting

There are numerous advantages over more traditional approaches when canted coil springs are used for electrical conduction. For example, canted coil springs can be designed to meet specific electrical requirements in addition to being manufactured from materials with high conductivity. Varying parameters such as spring diameter, wire diameter, coil height, canted angle, and the number of turns make it possible to tune amperage and electrical resistance for optimized solutions. In addition, platings such as gold or silver can be used to achieve ultra-low impedance.

Because of the extensive surface area of canted coil springs, they can transmit high power levels while generating less heat than traditional solutions. As a result, they provide outstanding heat-to-current carrying capacity even in extremely high temperatures. This same aspect is also essential in implantable devices where heat generation must be minimized for patient safety. In addition to their conducting capabilities, canted coil springs can serve as excellent EMI/RF shields for applications such as downhole tooling in oil exploration.

Canted coil springs support SWaP (space, weight, and power) requirements while reducing system complexity. This system simplification is often seen when they are used for mechanical fastening (latch, lock, or hold) in addition to electrical conduction. They make it possible to achieve far greater contact densities in smaller spaces than equivalent conductivity solutions. And one of the outstanding features of canted coil springs, as alluded to earlier, is their ability to provide specific force levels for fastening that include low force insertion.

As discussed in the previous section, these springs are able to maintain contact with surfaces despite factors such as impact and shock loadings, angular misalignment vibration, dimensional changes, and mating surface irregularities. In addition, they maintain performance in other harsh conditions by using materials and platings that are corrosion resistant. And canted coil springs, when designed and installed correctly, can reduce the possibility of conductor fatigue failure in relation to multiple insertion/removal cycles. Their minimal compression set also contributes to their extensive operational life.

Finally, canted coil springs are easy to clean and sanitize if needed for medical, pharmaceutical, food, and beverage applications. 

Conclusion

Canted coil springs are used as highly reliable electrical conductors in industries such as medicine, transportation, aerospace, semiconductor fabrication, industrial, energy, and defense. From surgical bones saws to guided weaponry, canted coil springs have provided dependable, effective conductivity solutions. 

 

Advanced EMC FlexForce Canted Coil Springs

For economical, reliable, SWaP-friendly conductivity solutions, Advanced EMC FlexForce canted coil springs may be the answer. The experts here at Advanced EMC can help you determine if a canted coil spring conductor will meet your design specifications and constraints. And if it does prove to be what you need, they will be there every step of the way until you have the conductor your design requires.

To learn more, you can also read 7 Things to Know About FlexForce Canted Coil Springs.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Canted Coil Springs for EMI/RF Shielding

Canted coil springs are an effective, reliable solution for some of the toughest EMI/RF shielding challenges. But what makes them different from other options, like wire mesh over polymer and finger springs?

 

What Are Canted Coil Springs?

Sensitive electronics need protection against EMI (Electromagnetic Interference) , RF (Radio Frequency), and crosstalk, and they need to avoid interfering with other electronics. Among the EMI/RF shields on the market are canted coil springs. These springs get their name from the angle at which the individual coils are set. This allows them to achieve a consistent, highly predictable force once installed, which makes them ideal for latching, locking, and holding as well as spring-energized seals. As just mentioned, they also provide highly reliable EMI/RF shielding made possible in part because each coil serves as a contact point for conduction or grounding. 

Where Canted Coil Springs Are Used for EMI/RF Shielding

Canted coil springs are used in a variety of applications where they provide shielding for data and signal transfer, including 

  • Antenna bases
  • Power management systems
  • Electronic enclosures
  • Waveguide flanges
  • Cabling
  • Connect/disconnect assemblies
  • Coaxial and electrical connectors

Whenever EMI/RF shielding is involved, there are critical national and international standards that must be complied with. These standards come from several different organizations, including the following:

  • CISPR (Comité International Spécial des Perturbations Radio), dealing with emission and immunity as well as test methods and the equipment used for testing
  • IEC 61000 (International Electrotechnical Commission) focusing on EMC (Electromagnetic Compatibility)
  • ISO (International Organization for Standardization) standards specifically for automotive EMC concerns and covers road vehicles, earthmoving equipment, and forestry and agricultural machines
  • SAE (Society of Automotive Engineers) EMC Standards Committee
  • EN (European Norm) standards concerning unwanted electrical emissions and immunity to unwanted electrical emissions
  • FCC Part 15 (Federal Communications Commission) for unlicensed radio-frequency transmissions
  • MIL-STD 461, 464, and 469 (Military Standard)

For a product to be sold on either the national or international market, it must be in compliance with relevant standards. To learn more about canted coils, click this link to read the most common questions about canted coil springs.

 

Benefits of Canted Coil Springs for EMI/RF Shielding

There are several advantages to using canted coil springs for EMI/EF shielding, starting with their ability to serve two or more different purposes in a single design. 

Multipurpose Mechanical and Electrical Solution

Canted coil springs can be used for multiple purposes in a single application: they also perform latching, holding, and locking functions. They do so with highly predictable forces and almost no compression set. When they are designed correctly, these springs can provide precise insertion and breakaway forces. Canted coil springs perform these mechanical functions without the use of tools and can significantly simplify a design when used as a multipurpose solution (i.e., latching and EMI shielding).

Lightweight and Flexible

Canted coil springs are extremely lightweight and compact, which can make them an excellent option for SWaP (Size, Weight, and Power) constrained applications. Their flexibility allows them to be used with many geometries other than circular that would be otherwise challenging to shield. 

Geometric Options

Standard spring wire is available in wire diameters from 0.25 mm (0.010 inches) to 1.50 mm (0.059 inches). Standard coil widths range from 1.5 mm (0.039 inches) to 15 mm (0.591 inches). However, there are custom options available for wire diameter and coil width. The angle at which the coils are oriented can also be specified. Finally, the coil pitch can be varied, and is usually quite dense for EMI/RF applications.

Material and Plating Options

There are several different material and plating combinations available for canted coil springs. The most commonly used spring materials include …

  • Stainless steel
  • Beryllium copper
  • Zirconium copper
  • Inconel
  • Hastelloy
  • Platinum iridium.

These materials can be combined with platings such as nickel, silver, gold, and tin. Platings are especially useful when the springs may be exposed to corrosive environmental conditions.

Impedance Tuning

While canted coil springs already work across a very broad spectrum of EMI interference, they can also be tuned to very specific impedance specifications. This can aid not only in device performance but in achieving compatibility with the appropriate EMC/RF standards.

Reliability

Because canted coil springs can provide a near-constant force, they will remain in contact with surfaces extremely well. This is true even when subject to vibration, shock, and impact loads as well as dimensional changes due to temperature fluctuations. Canted coil springs do an excellent job of compensating for hardware variations, surface irregularities, and angular misalignment, leading to highly reliable performance even in difficult operating conditions.

Conclusion

If you are looking for an economical, effective, and reliable EMI/RF shielding solution, consider the use of canted coil springs. And the experts here at Advanced EMC can help you choose the right spring options, tune it to the impedance you need, and ensure that your design will comply with the right standards. Contact us today to learn more about our Flex-Force canted coil springs.

Auto Molding PTFE Seals and Seats
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Auto Molding PTFE Seals and Seats: Advantages for High-Volume Production Runs

Auto molding PTFE seals and seats offer a wide variety of benefits, especially for high-volume production runs. In this blog post, we cover some background on both PTFE and auto molding (also known as compression molding) and discuss why this particular manufacturing process is often preferred by engineers for both seals and ball valve seats.

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Low-Temperature O-ring solution
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Low Temperature O-Ring Solutions

Finding the right low-temperature o-ring solution can be critical to both the success and safety of a design — and FEP encapsulated o-rings are an excellent solution.

Low Temperature and Cryogenic Applications

Cryogenic refers to temperatures below freezing and extending to absolute zero (-460°F / -273°C), while low-temperature environments are typically defined as below -25°F. Common chemicals that are stored or transported at cryogenic temperature include 

  • Liquid Oxygen (LOX), -297°F
  • Liquid Natural Gas (LNG), −265°F
  • Liquid Hydrogen (LH2), -423°F
  • Liquid Nitrogen (LN2), –130°F 
  • Liquid Helium, -452°F 

The industries that involve low temperatures include aerospace, energy, electronics, chemical processing, food, pharmaceutical, and medicine. Quantum computing, rockets, and MRI machines are just a few specific examples where cryogenic o-rings are needed. 

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thermoplastic-polymer-seals-nuclear-industry
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Polymer Seals for Nuclear Applications

In general, thermoplastics are known for being corrosion resistant, robust, and usually easy to fabricate. However, the operating environment makes it challenging to find good polymer seals for nuclear applications. In this blog post, the focus will be on thermoplastic polymer sealing solutions as an alternative to elastomeric seals.

Nuclear Sealing Solutions

There are many different applications where seals are necessary for the nuclear industry, including transport flasks and port seals, waste containment packages, ventilation systems, repair systems, valve seats, robotics, manipulators, and hydraulic rams. Reliable seals are especially crucial to reactor coolant pumps (RCP) and self-actuated abeyance systems.

Harsh Environments for Nuclear Seals

One of the most challenging environments for nuclear sealing applications is a combination of halogenated material issues and high gamma radiation exposure levels.

Halogenated Material Complications

In many nuclear plant applications, the use of halogenated materials (particularly those containing fluorine or chlorine) is strictly prohibited because these materials can potentially leach aggressive chemicals such as halides. Halides in aqueous streams, for example, can cause such problems as stress corrosion cracking in stainless steel. This means that while a seal made from a halogenated material may perform well, it can cause severe damage downstream. In addition, halogenated materials may also release corrosive gasses resulting in serious safety issues.

Gamma Radiation

Gamma radiation can cause polymers to degrade and lose critical properties rapidly. This degradation typically takes the form of chain scission and cross-linking, which leads to brittleness and fractures. This has proven to be a severe problem for commonly used seal polymers such as PTFE, PFA, PA, and UHMW PE. And even though seals may not be directly exposed to gamma radiation, this type of radiation can penetrate materials and lead to indirect exposure.

In addition, free radicals can also be trapped within the polymeric structure when exposed to radiation, leading to continued degradation after exposure in a phenomenon known as post-irradiation degradation. High gamma radiation dose rates can also generate heat to complicate matters further.

Other Issues

Nuclear applications can also involve very high temperatures and pressures and wide pressure variation. Exposure to corrosive chemicals can also be problematic. And for a sealing solution to be effective, there are vital considerations such as qualified life and ability to withstand station black-out (SBO) conditions. Therefore, the importance of reliable seals cannot be overestimated.

Polymer Seal Materials for Nuclear Environments

For harsh nuclear environments, three particular polymers can be used as a seal jacket (depending on the application and relevant operating conditions). These are PEEK, FEP, and ETFE.

PEEK (Polyetheretherketone)

Polyetheretherketone is often known by brand names such as Fluorolon by Advanced EMC Technologies,  PEEK by Victrex, Ketron by Mitsubishi, and TECAPEEK by Ensinger. Of thermoplastic polymers suitable for nuclear applications, PEEK is the most commonly used material for rotary shaft seals. Among the key properties of PEEK are:

  • Excellent performance at high temperatures up to 500°F
  • Excellent chemical compatibility
  • Self-lubricating
  • Very low friction
  • Excellent resistance to high-energy radiation on the order of 109 rads

PEEK is, however, sensitive to certain acids, carbon sulfides, fluorine, and chlorine.

FEP (Fluorinated Ethylene Propylene)

Fluorinated Ethylene Propylene is often recognized by brand names such as Teflon FEP by Dupont, Neoflon FEP by Daikin, and Dyneon FEP from Dyneon/3M. Critical properties of FEP include:

  • Excellent performance at high temperatures up to 400°F
  • Very low friction
  • Excellent chemical compatibility
  • Self-lubricating
  • Good resistance to high-energy radiation on the order of 105 rads

In addition, FEP is melt-processable and therefore reasonably easy to use in the manufacture of seals. However, FEP’s limitations for nuclear applications are primarily its susceptibility to attack by acids.

ETFE (Ethylene Tetrafluoroethylene)

Ethylene Tetrafluoroethylene, or ETFE, is often referred to by trade names such as Tefzel by DuPont, Neoflon ETFE by Daikin, and Texlon by Vector Foiltec. Important properties of ETFE include …

  • High melting temperature
  • Excellent chemical compatibility
  • Very low friction
  • Non-stick and self-lubricating
  • Self-cleaning 
  • Excellent resistance to high-energy radiation on the order of 107 rads

Its limitations in nuclear applications include the fact that it is rated to only 300°F and is susceptible to attack by esters and aromatics. In addition, it is often cost-prohibitive.

Conclusion

Seals are a critical component in the nuclear industry. While elastomeric seals may be commonly used, there are high-performance polymer alternatives such as PEEK, FEP, and ETFE that provide fundamental properties needed. In addition, such materials can provide the required performance even when subject to gamma radiation, intense heat, and extreme pressures. 

If you are investigating polymer seals for nuclear applications, contact the sealing solution experts at Advanced EMC. We understand the specific challenges of the nuclear industry and will share our comprehensive knowledge of polymers to help you find the ideal sealing solution. 

Tail view of a commercial aircraft
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

PTFE Aerospace Seals

Finding the right sealing solution for aerospace applications involves a host of considerations, especially when it comes to the jacket material. However, there is one high-performance solution that rises to the top over and over: PTFE aerospace seals. 

Aerospace Seal Challenges

Aerospace sealing solutions can face a wide range of harsh environments that can include exposure to extreme temperatures, high pressures, and corrosive chemicals such as de-icing liquids and aviation fuels. There is also the ever-present demand for energy-efficient solutions,  critical requirements related to safety, and compliance with industry standards. 

In addition, aerospace seals must often perform in potentially explosive or flammable environments. There are other constraints in aerospace applications as well, such as the need to minimize weight and promote energy efficiency. And looking to the future, there will also be demand for more environmentally friendly, sustainable solutions.

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PVDF is used extensively in pumps, valves, fittings, and pipes
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

The Basics of PVDF

Kynar PVDF (property of Arkema) is a high purity polymer that combines extreme-temperature performance, easy manufacturability, and durability in some of the harshest environments. 

What is PVDF?

PVDF (polyvinylidene difluoride or polyvinyl fluoride) is a fluorinated thermoplastic resin that is classified as a specialty polymer whose brand names include Kynar (Arkema), KF (Kureha), and Solef or Hylar (Solvay). This engineering polymer can often be found in environments that involve high purity, hot acid, extremely high temperatures, and/or radiation. 

Where is PVDF Used?

PVDF is used extensively in a wide range of industries. Semiconductor manufacturing makes use of PVDF’s ultra-pure status and its ability to perform in harsh environments that may involve extreme temperatures and aggressive chemicals. Electronics and electricity applications depend on PVDF’s outstanding low smoke emission and fire-resistant properties along with electrical properties for use as wiring insulation.

PVDF’s ability to handle radiation makes it an excellent choice for nuclear waste handling, and its high-temperature performance and chemical compatibility lends itself readily to the oil and gas industry. Because PVDF has excellent high-temperature performance, high purity, and low permeability, excellent strength, and chemical compatibility, it is used extensively in chemical processing.

Purity and FDA approval have made it a popular choice in food and beverage packaging and processing as well as pharmaceutical processing. It is often used in connection with water and wastewater management for similar reasons. PVDF is also used extensively in the medical market and healthcare industry where it is used as a biomaterial for medical textiles, such as hernia meshes, as well as for medical sutures.

The transportation and energy market has begun using PVDF as a binder for cathodes and anodes in HEV/EVs (Hybrid Electric Vehicle/Electric Vehicle). Its chemical compatibility and anti-corrosion properties make it useful as a barrier liner for fuel lines and tanker trailer lines. Aviation also makes ample use of PVDF for wiring harnesses and general coatings

How is PVDF Used?

PVDF is commonly used for several specific types of applications across industries:

  • Pump assemblies
  • Heat exchangers
  • Tanks and vessels
  • Nozzles
  • Sensors and actuators
  • Fittings, pipes, tubing, and valves
  • Membranes, including microfiltration membranes
  • Filters and filter housings
  • Liners and films
  • Cable jacketing and harnessing
  • Biocompatible materials

Key Properties of PVDF

As alluded to in previous sections, PVDF possesses several features of interest to engineers:

  • Extremely high purity with low permeability
  • FDA compliant and non-toxic
  • Excellent heat resistance and thermal stability 
  • Good mechanical properties
  • Resistant to a wide range of aggressive chemicals
  • Resistant to UV exposure, ozone oxidation reactions, and radiation
  • Resistant to the growth of microorganisms
  • Excellent burn characteristics 
  • Good manufacturability
  • One of the lowest melting points of commercial fluoropolymers
  • Excellent electrical properties
  • Excellent abrasion resistance
  • Low density (1.78 gm/cm3)
  • Recyclable

In addition, PVDF offers excellent abrasion resistance, is lightweight, and can be recycled. Also, note that there are additives available for PVDF to enhance its properties and its melt processability.

Purity and FDA Compliance

In addition to being an extremely high purity polymer, PVDF is both FDA compliant and non-toxic while exhibiting very low gas and liquid permeability.

Heat Resistant and Thermal Stability

One of the outstanding features of PVDF lies in its excellent performance, chemical stability, and dimensional stability in high-temperature environments with a service temperature rating of up to 300 F.

Mechanical Properties

Among the outstanding mechanical properties possessed by PVDF are good deflection, tension, compression, and torsion when compared to other fluorinated polymers. In addition, its low rate of water absorption (0.4%) means that it will remain dimensionally stable (not swell) when in a moisture-rich environment. In addition, PVDF has excellent impact strength.

Chemical Compatibility

PVDF is known for its excellent chemical compatibility that includes weak and strong acids (including mineral and organic); alcohols; aromatic and aliphatic solvents; weak bases; hydrocarbons; halogenated compounds; ionic and salt solutions; and oxidants. Its primary weaknesses are caustics, esters, strong bases, and ketones. 

Microorganism Growth

The surface of PVDF is highly resistant to the growth of microorganisms, including bacteria, fungi, and mold. It is also resistant to weathering, grime, and even graffiti (which is why it is often used in the architectural industry).

Burn Characteristics

PVDF has excellent flame and smoke properties, including UL 94 V-0 rating indicating it is both non-flammable and self-extinguishing along, or more specifically “Burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.” In addition, certain grades of PVDF also possess an excellent flame spread/smoke developed rating of 25/50 (when tested in accordance with ASTM E 84).

Manufacturability

PVDF is also highly manufacturable and melt-processable, lending itself to precision machining, rotomolding, compression molding, injection molding, and extrusion as well as subsequent welding and fabrication. Its ability to be used in molding is primarily due to its low melting point of 352 F, compared to PTFE at 621 F or FEP at 517 F.

Electrical Properties

In addition to electrochemical stability, PVDF also possesses a very high dielectric constant (280 volts per meter) and a high piezoelectric constant. In fact, it possesses both piezoelectric and pyroelectric properties.

Conclusion

One of the polymers we work with here at Advanced EMC is PVDF Kynar made by Arkema. If you are interested in Kynar, have questions about its usage and processing, or need a quote, feel free to contact us and we will have one of our experts respond right away.

Semiconductor circuit board
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).

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