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.
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.
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
- 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)
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.
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.
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.
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).
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).
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.
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.
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.
Expanded PTFE (or ePTFE), like regular PTFE, is an incredibly versatile and rugged material. And like PTFE, ePTFE began as an accident. Before we can get to that, however, we should start at the beginning.
What is the history of ePTFE? When his ideas for expanding the use of PTFE was turned down by his employers at DuPont, chemist Wilbert “Bill” Gore left the company to start his own. And in 1958 Gore and his wife Genevive “Vive” Gore founded W.L. Gore and Associates out of the basement of their Delaware home. During this time, Gore’s company began to serve the burgeoning computer industry by using PTFE to insulate multiple copper conductors and fashion them into ribbon cable resulting in a product known as MULTI-TET.
Learn More About the History of ePTFE
As the years went on it became clear to Gore that trends in computer technologies meant that computers were becoming smaller and smaller, resulting in the need for less cables for circuitry. In 1968, Gore tasked his son, Robert “Bob” Gore, to come up with a solution. One night in October 1969, Bob Gore was researching a new process for stretching extruded PTFE into pipe-thread tape when he discovered that the polymer could be “expanded.”
After several failed experiments in which Bob tried to slowly expand the material even further, he became frustrated and yanked the material. As it turned out, this was the exact conditions PTFE needed to become expanded. This sudden yank resulted in the transformation of solid PTFE into a microporous structure that was about 70% air. This material would later become known as ePTFE, or Gore-Tex.
Today, ePTFE is used in a wide variety of applications. These applications include:
- And much more
Interested in learning more about ePTFE and how Advanced EMC Technologies can offer you premiere sealing solutions? Contact us today!
There are certain polymers out there that can be classified as millable or machinable. When millable plastics are needed for the aggressive environments encountered by oil and gas equipment, the challenge to find a suitable polymer becomes even harder.
As you know, polymers behave very differently from metals. One aspect of that behavior involves the glass transition temperature. In this blog post, we are going to focus on the glass transition temperature of thermoplastics.
This blog post represents the second installment in a series of posts on thermal analysis techniques for polymers. In part 1 we discussed differential thermal analysis, thermomechanical analysis, and dynamic mechanical analysis.
In this blog post, we are going to start a discussion about the most common thermal analysis techniques used to investigate the properties of polymers. In part 1 of this series, our focus will be on:
- differential thermal analysis
- thermomechanical analysis; and
- dynamic mechanical analysis
This discussion will include how these tests are performed and what kind of properties can be determined from the resulting data.
Polyimide, typically abbreviated as PI or referred to tradenames such as Vespel, Plavis and Duratron-PI, is the second most powerful high temperature engineering polymer on the market today, right behind Celazole. In this blog post, we are going to discuss the characteristics and uses of this powerful high-performance polymer.
Extreme polymers are known for their performance at high temperatures that other polymers just cant handle. In this blog post, we’ll take a look at PBI the highest performing thermoplastic on the market today.