by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

When to Use a PTFE Rotary Shaft Seal

Rotary shaft seals are used in a host of applications, including many that involve harsh environments or strict compliance with FDA standards. But when should PTFE be used?

Industries Where Rotary Shaft Seals Are Used

A good place to start would be looking at some of the industries that depend on the reliable performance of PTFE rotary shaft seals:

Certain characteristics become apparent from this list, such as exposure to corrosive and aggressive chemicals, low friction, reliability, extreme temperatures, and high purity. 

When to Consider a PTFE Rotary Shaft Seal

There are certain circumstances under which PTFE is the material of choice for a rotary shaft seal:

  • When there is aggressive media involved
  • When low friction or dry running is needed
  • When applications involve high speeds
  • When thermal stability is critical
  • When FDA/USDA compliance is necessary
  • When high temperatures are involved
When there is aggressive media involved

PTFE is the most chemically compatible seal lip material on the market, with the main exceptions being rare fluorinated compounds and certain alkali metals. In addition, some halogenated and organic solvents can be absorbed by PTFE and cause temporary (and minor) changes in dimension. On the other hand, it is compatible with chemicals such as acetone, hydrochloric acid, sulfuric acid, citric acid, tallow, and sodium peroxide.

When low friction or dry running is needed

The coefficient of friction for PTFE ranges from 0.04 for virgin PTFE(the lowest for any material currently in existence) to 0.19 for 15% Glass / 5% MoS2. In addition, PTFE is self-lubrication, low coefficient of friction, and lack of stick-slip behavior results in significantly reduced breakout torque.

When applications involve high speeds

PTFE rotary shaft seals perform extremely well in high-speed applications with shaft surface speeds up to 35 m/s. PTFE also has the lowest coefficient of friction of both polymers and elastomers, making it perfect for seals that must have an extremely low coefficient of friction. This can be a critical factor in high-speed rotary shaft seal applications where significant heat can be generated between the rotating shaft and the seal lip. 

When thermal stability is critical

The maximum service temperature for PTFE is around 500°F and it has the highest melting point of all fluoropolymers, which is why it is used extensively in the oil and gas industry. However, it is often a material of choice for cryogenic applications down to -64°F because of its ability to maintain both its strength and elasticity at low temperatures.

PTFE also possesses a low coefficient of thermal expansion, ranging from 3.8×105 for 25% glass-reinforced PTFE to 5.5×105 for virgin PTFE. Because of this, seals made from PTFE are able to maintain their dimensional stability in operating conditions that can involve significant temperature changes.

When FDA/USDA compliance is necessary

PTFE is available in several different grades that are compliant with strict standards related to food, dairy, and water:

  • FDA 21 CFR 177.1550 for fluoropolymers
  • (EU) 1935/2004
  • 3-A sanitary standards 18-03 and 20-27
  • NSF/ANSI standard 61 for drinking water systems

PTFE also holds up extremely well to the intense cleaning and sanitation procedures that such seals may undergo, including hot water, steam, and aggressive cleaning compounds. In addition, PTFE is also hydrophilic, which can prevent water and moisture from being trapped around the seal during cleaning.

PTFE Grades for Rotary Shaft Seals

The most common PTFE grades used for rotary shaft seal applications are:

  • Virgin, which works well for slow rotary light duty
  • Glass-filled, which enhances strength and wear resistance but should only be used on shafts with high hardness 
  • Glass MoS2-filled, which increases wear resistance and strength without the abrasiveness of glass-filled
  • MoS2-filled, which increases wear resistance and life but should not be used on shafts with low hardness
  • Carbon-filled, which will increase wear resistance with less impact on the coefficient of friction
  • Carbon and MoS2-filled, which increases wear resistance, enhances high-temperature performance, and maintains the capability of dry running

Other Benefits of PTFE Rotary Shaft Seals

There are other benefits to using PTFE for rotary shaft seals, such as their wider temperature ranges and longer life span when compared to elastomeric seals. They also have low outgassing, good electrical insulation properties,  They are also inert to most chemicals and not only compatible with most lubricants but also self-lubricating).

If you are considering a PTFE rotary shaft seal, contact Advanced EMC today. Our team of experienced seal experts will work with you to determine is PTFE is the right material for your application.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Underlip Temperatures and Rotary Shaft Seals

Many engineers do not realize the impact that underlip temperatures can have on seal performance and service life, especially when elastomeric materials are used. Learn why underlip temperature is so important and what you can do to reduce its impact.

What is Underlip Temperature?

Before we can define underlip temperature, we should start out with sump temperature, which refers to the temperature of the oil/lubricant. The lip of an oil seal moves across a very thin meniscus of oil. Some friction exists between the seal lip and the shaft which can generate enough heat to increase the temperature under the lip of the seal. This temperature at the point where the seal lip and shaft make contact is referred to as the underlip temperature and it can be higher than the sump temperature, especially for higher shaft speeds.

Why Underlip Temperature is Important

If the seal lip material does not possess good thermal conductivity, the heat generated can raise the underlip temperature high enough to exceed the operating temperature limits of the seal. This will result in accelerated wear and eventual seal failure. Signs of such a problem might be a seal lip that is …

  • Cracked
  • Blistered
  • Hardened

That is why it is important to use the estimated underlip temperature, as opposed to the sump temperature, as the expected operating temperature for a seal.

Estimating the Underlip Temperature

The underlip temperature is related to the friction between the seal and the shaft as well as the shaft speed. One way to estimate the increase in underlip temperature (in degrees Fahrenheit) based on shaft speed is to take the square root of the shaft seal speed in feet per minute.

Change in Underlip Formula | Advanced EMC Technologies

Before we look at an example, remember that …

Example 1

Suppose you need to estimate the increase in underlip temperature for a shaft rotating at 2500 fpm. The associated increase in underlip temperature would be ….

Example 2

If a 3” shaft is rotating at 2500 rpm and the sump temperature is 150°F, what would the underlip temperature be?

If the sump temperature is 150°F, then the underlip temperature is the sump temperature + the change in underlip temperature …

150°F + 44°F = 194°F

Faster Estimate

There is a faster way to estimate the underlip temperature, but it is not nearly as accurate: add 20°F for every 1000 rpm of shaft speed. However, the applicability of this estimate is limited to sump temperatures less than 210°F.

What Influences an Increased Underlip Temperatures

The underlip temperature is a function of several different characteristics. These include …

  • Shaft speed
  • Shaft size
  • Surface condition of the shaft
  • Friction between the shaft and seal
  • Thermal conductivity of the seal lip material
  • Oil level

In the chart below, you can see how the underlip temperature increases as the rotational shaft speed increase for a 1” diameter shaft. Even for a relatively small shaft, the increase in underlip temperature is significant.

Sump Temperatures vs Underlip Temperatures | Advanced EMC Technologies

In this next chart, it is evident how the change in underlip temperatures varies significantly as a function of shaft speed and diameter. In particular, notice that the upper limit for a 5-inch shaft rotating at 5000 rpm can lead to a 90°F increase in underlip temperature.

Change in Underlip Temperatures

When specifying a seal for a specific application, the engineer has control over the surface condition of the shaft, the friction between the shaft and the seal, and the thermal conductivity of the seal lip material. 

Reducing the Change in Underlip Temperatures

A smoother shaft combined with a low-friction seal lip material reduces the amount of heat generated at the point of contact, which can help reduce the increase in underlip temperature. 

Furthermore, a material with high thermal conductivity will be more likely to conduct generated heat away from the seal lip, further reducing the increase in underlip temperature.

Conclusion

Polymer seal lip materials such as PTFE and PEEK provide reduced friction, higher thermal conductivity, and better performance at high temperatures than their elastomeric counterparts when used in rotary shaft seals. When elastomeric seals are exhibiting signs of failure due to high underlip temperatures (i.e., cracking, blistering, hardening), then it may be time to consider a change in seal lip material.

At Advanced EMC, our rotary shaft seal experts can help you troubleshoot the cause of premature seal failure and advise you on the best choice of material for your application. Contact us today for more information.

 

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Rotary Shaft Seals for Automobiles

Even the simplest automobile requires a wide variety of seals, including rotary shaft seals. In this blog post, you will learn the basics of these seals within the context of the automotive industry, including the materials commonly used and why PTFE is so often recommended.

Rotary Shaft Seals

The goal of a rotary shaft seal is to prevent the leakage of oil, grease, and other fluids (e.g., transmission fluid, brake fluid, air conditioning refrigerant) while also keeping environmental contaminants out. These seals, sometimes called oil or grease seals, are used with bearings to keep lubricants within the bearing and environmental contamination out (i.e., lubrication retention). The term rotary refers to their ability to perform in the presence of both rotary and swiveling movements.

Where Rotary Shaft Seals Are Used in the Automotive Industry

Rotary shaft seals are a necessary part of many components and systems within cars, trucks, buses, high performance vehicles, and motorsports. And seals are needed for EVs (electric vehicles) and HEV (Hybrid Electric Vehicles) as well. These seals are also used with ATV (All Terrain Vehicles).  Some of the most common areas of application in automotive transportation are:

  • Air conditioning compressors
  • Braking systems
  • Pumps
  • Gearboxes
  • Power transmissions
  • Steering wheels

In most of these applications, the failure of a seal can lead to serious repercussions that include bodily injury, damage to the vehicle, and danger to those around the vehicle. Because of this, finding the right high quality seal for your application is extremely important.

Automotive Seal Operating Conditions

While the conditions for automotive rotary shaft seals do vary depending on their specific applications, the most common operating environments include …

  • Extreme temperatures
  • Environmental elements
  • Vibration and shock loadings
  • High contamination exposure
  • Chemical compatibility
  • Low friction
  • Wear resistance
  • Compliance with automotive standards

Environmental elements include exposure to sunlight, ozone, UV, and oxidation, all of which can accelerate the degradation of a seal. Contamination can include water, dirt, grease, and other debris, while the seals are likely to be exposed to materials such as diesel, hydraulic fluid, brake fluids, coolants, and chemical solvents. 

Materials Used in Rotary Shaft Seals

The basic components of a spring energized seal include a flexible inner seal lip that is bonded to a rigid outer component. In addition, some of these seals may include a spring energizer to keep the lip in contact with the sealing surface (note that spring-energized seals are most commonly used for oil retention as opposed to grease retention). Furthermore, some applications may require a seal with two lips where one serves as a wiper seal or dust lip to further prevent the ingression of contaminants.

The outer material for a rotary shaft seal is responsible for seal positioning and retention in the seal housing. This part of the seal is typically made from stainless steel, aluminum, or a rigid non-metallic composite material. 

The seal lip itself is made from either an elastomer or a polymer, with high performance PTFE being one of the most commonly used polymers. PTFE meets all the requirements for an effective, dependable seal lip, including the ability to handle high pressures, wide ranging chemical compatibility, extremely low friction, and excellent wear resistance. PTFE can also include additives such as carbon or MoS2 that can enhance properties such as strength, stiffness, wear resistance, and low friction.

Nitrile rubber (NBR, Buna-N) and polyacrylate rubber (ACM) are both widely used elastomeric materials for automotive rotary shaft seals. Another often used elastomer category is fluoroelastomers commonly referred to as FKM, Viton, and FPM. These offer superior performance compared to nitrile and polyacrylate, but they do cost more. 

PTFE Rotary Shaft Seals

At Advanced-EMC, we highly recommend the use of PTFE rotary shaft seals in the automotive industry where possible. They provide excellent performance in the harsh conditions often involved and are the most chemically compatible and low friction polymer on the market today. They can outperform elastomeric materials and are quickly replacing their use in many applications.

There are several grades of PTFE to choose from, including …

  • Virgin PTFE: light-duty service with slow speeds
  • 25% Glass-filled PTFE: wear and extrusion resistant but abrasive to shafts with a hardness less than 62C
  • 23% Carbon / 2% Graphite-filled PTFE: general purpose service where extrusion and deformation resistance are necessary
  • 15% Glass / 5% MoS2 filled PTFE: excellent wear resistance makes it well adapted to higher speed applications
  • Polyimide-filled PTFE: because of its low abrasion, works well with soft materials such as 300 SS and Aluminum
  • Modified PTFE: higher mechanical strength and better wear resistance

Conclusion

Rotary shaft seals can be found everywhere from the air conditioning to the power transmission system on a vehicle. Finding the right sealing solution that can handle the extremely harsh operating conditions and high temperature environments can be challenging, but PTFE has become one of the most popular choices for the seal lip material. 

If you are interested in an effective, reliable sealing solution for your automotive application, contact the knowledgeable team at Advanced-EMC today. Our engineers can work with you to find the right seal, made from the right materials, for even your most challenging designs.

 

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

All About Automolding

PTFE is an excellent material for many different applications and operating environments. Its low friction, chemical compatibility, and ability to maintain key properties at extreme temperatures has made it ideal for everything from seals in sterile food handling equipment to sleeve bearings in the harsh world of oil and gas

And there are several different options when it comes to manufacturing PTFE components, but not all methods are the same. In this blog post, we will be discussing auto molding in the context of manufacturing PTFE components.

What is Auto Molding?

Auto molding, as known as compression molding, is a popular manufacturing technique for making thermoset and thermoplastic parts–and one of the oldest plastic forming methods still in use. In short, auto molding uses compression and dies to form a near net shape polymer part. 

Where is Auto Molding Used?

There are numerous industries that depend on auto molded parts, such as aerospace, chemical processing, and the manufacture of semiconductors.

Auto molding is used to manufacture a wide range of parts, as well. These include …

  • Bearings
  • Bushings
  • Piston rings
  • Sleeves
  • Seals
  • Gaskets
  • Valves
  • Valve Seats
  • Diaphragms
  • Bellows
  • Electrical components

When compression molding of a PTFE part is done correctly, then you can depend on key aspects such as specific density, strength, elongation, and flex life as well as permeation resistance.

How Auto Molding Works

In the auto molding process, the raw materials are in the form of molding compounds. These molding compounds may be preforms (which is already shaped somewhat like the final part), granules, or putty-like masses. 

The basic design for the mold is usually generated from a 3D CAD file, and the tool and die maker will then base the mold design on that file. However, the mold designer must account for shrinkage, molding compound flow, size and positioning of channels to carry away excess material, and achieving uniform curing temperatures for the part. It is also important to ensure that the part can be removed from the mold, and there may be a need for ejector pins to achieve this. Needless to say, the mold is the most expensive aspect of auto molding.

Once the mold design is complete, it is manufactured out of steel using a CAD/CAM (Computer-Aided Design / Computer Aided Manufacturing) system and a CNC (Computer Numeric Control) milling machine. Additional features and surface finishes may require post-processing of the mold.

Once the mold is ready to go, the amount of compound needed for the part is carefully measured out and placed in the pre-heated open mold cavity. Once in place, the other side of the mold closes over the mold cavity and pressure is applied (most often by a hydraulic ram) in one direction to force the raw materials to fill up all cavities within the mold. Any excess material is carried away from the mold via overflow grooves.

Heat and pressure are both maintained until the polymer has completely cured. Once the part has cured and cooled, it is removed from the mold, and this part of the process may require the use of part ejection pins to completely free the newly cured part from the mold. After the part is removed, any flash can be easily trimmed away and precision machining can be used to ensure the part meets necessary tolerances.

Auto Molding PTFE

There are certain key aspects to auto molding PTFE compounds, including …

  • Pressure (usually between 3,000 and 4,500 psi)
  • Sintering temperature (in the range of 685°F – 720°F)
  • Dwell time (how long the part is held at the sintering temperature)

Pressure and dwell time are dependent on the volume and geometry of the part, as well as the machine being used.

Benefits of Auto Molding 

Auto molding PTFE has numerous benefits:

  • Range of geometries and shapes are possible
  • Can produce larger parts than possible with extrusion
  • Minimal waste material
  • Very cost-effective when compared to injection molding
  • Good surface finish
  • Close tolerances
  • Avoids defects associated with machining a polymer (e.g., internal stresses, warping)

In addition, auto molding can be used with both virgin and filled PTFE. Fillers can include both those that enhance structural and material properties (e.g., carbon fiber, molybdenum disulfide MoS2) and colors. Depending on the size and geometry of the part, it may be possible to compression mold multiple parts simultaneously. In such cases, a multi-cavity die would be used.

Disadvantages of Auto Molding

However, there are pros and cons to every PTFE manufacturing process. In the case of auto molded PTFE, the production speed is slower compared to injection molding (due to longer cycle times). Flash will always form and needs to be removed before the part can be considered finished, and this can also add a bit to the production time. While compression molding can be used to manufacture complex parts, there can be issues, such as underfilling in certain areas and the inability to achieve undercuts.

Auto Molding Costs

The most expensive aspect of auto molding, aside from the machinery needed, is the compression molds. Mold cost depends in part on the size of the component, but is more heavily influenced by the complexity of the die. The more complex the geometry of a part, the more expensive the die will be. However, the cost of a compression molding die is significantly less than that of an injection molding die. This is mostly due to the fact that compression molds do not require a complicated system of gates and runners that are necessary in injection molds.

Conclusion

Auto molding works well for manufacturing PTFE components that are not overly complex, have no undercuts, and involve a medium to large production run. In addition, the auto molding process is generally far more cost effective than injection molding. However, for PTFE parts to be high quality and durable, you need a company that is familiar with the process.

At Advanced EMC, we have the knowledge and experience to assist you with auto molding PTFE parts for your applications. Contact us today if you have any questions or are interested in obtaining a quote.

by Jackie Johnson Jackie Johnson No Comments

The Mexican Plastics Industry During COVID-19

With COVID-19 spreading across the globe, one company in Mexico City has created a rotomolded solution to help curb the infection in one of the world’s largest food markets. In fact, Mexico’s plastics industry has played a large part in COVID-19 relief.

The Mexican plastics industry is a relatively young one. However, it has quickly become one of the fastest developing sectors in the country. In 2016, the country was the tenth largest worldwide plastic producer, with a market of $33 billion.

Because it is so new, the Mexican plastics industry has the unique advantage of having new machinery that is on par with, and even superior to, those in Europe, where equipment could be 50 years old. Which means there are fewer problems to contend with which in turn allows for rapid production and innovation when the country needs it most.

So, in this week’s blog post, we will cover how the Mexican plastics industry has combated COVID-19.

Hospitals and Hand Washing Stations

The Mexico City based company Grupo Rotoplas SAB de CV has teamed up with toilet cleaning brand Harpic as well as the Mexican Red Cross to install a field hospital at the Central de Abastos, an open-air food market in the borough of Iztapalapa in central Mexico City, which was considered in the early days of the pandemic to be one of the main sources of contagion in the city. The hospital has been able to provide tests and care for sufferers of COVID-19.

Developed in the 1970s, Iztapalapa is one of Mexico City’s sixteen municipalities, and with a population of 1.8 million it is the most populous. The borough is heavily working class, and the people of Iztapalapa have been still working on the streets even while the threat of the Corona virus looms. When COVID hit the Central de Abastos, it spread rapidly, with one testing center testing 15,000 people with 1,347 testing positive.

In response, in addition to the field hospital, Rotoplas has installed multiple hand washing stations across the market, which covers 800 acres, as well as hanging banners offering advice on preventative action. Because of this it is estimated that 12,000 people have benefited from the new sanitary measures.

Rotoplas is best known for manufacturing large water tanks. They have a 27 product lines operate a score of manufacturing facilities across North and Central America and employs about 3,000 people.

From Coca-Cola to Face Masks

Like most of the world, Mexico has had a hard time procuring masks for hospitals and other medical facilities. One company, food-grade PET recycler PetStar SAPI de CV, stepped up to the plate by donating around 212,000 20-calibre face shields made from 1-million plastic bottles, which in turn were donated by Arca Continental, a company that is part of the Mexican Coca-Cola industry.

The process of recycling plastics is a labor intensive one. The plastic must first be washed to remove impurities that could impede operation. Then the plastic is fed into shredders which break down the plastic into much smaller pieces. These smaller pieces can be processed into the next stages for reuse. Before that, they must be checked again for any remaining impurities and given a second wash. After the plastic is further tested and identified by class and quality, they are melted down and crushed together to form pellets. These pellets can then be molded to form items such as face shields.

Recycling plastic bottles not only helped provide more masks to frontline workers, it also kept plastic bottles out of landfills and the ocean, where they could linger for generations. Not only did PetStar provide life-saving face masks, they also helped reduce plastic waste by recycling bottles.

Much Needed Protection

Dow Inc. contributed 25,000 protective gowns to the health sector of Mexico. For healthcare professionals battling COVID-19, isolation gowns are among the most used personal protective equipment right behind masks. And like masks there has been a shortage. In response, DOW, Inc. collaborated with nine key partners across a multitude of industries to develop donate 100,000 isolation gowns to frontline workers in Texas, Louisiana, and of course, Mexico.

Michelle Boven of Dow, Inc. had this to say on the subject:

“Many companies have shown tremendous ingenuity and speed in changing over production to meet the needs for respirators, masks, face shields, hand sanitizer and other products critical to fighting this pandemic,” said Boven from Dow. “With the accelerated product development, testing and certification of these medical gowns, Dow is proud to be among these innovators and we will continue to look for ways to use our vast material science expertise to address the needs of frontline workers around the world.”

Other Examples

  • Chemical manufacturer Alpek SAB de CV donating 500 gallons of hand sanitizing gel to public hospitals.
  • Polyethylene maker Braskem Idesa S.A.P.I. donated 12 metric tons of PE for the production of one million bottles of disinfectant.

In Conclusion

Mexico’s plastic industry is relatively young, but still booming despite the pandemic. It has expanded rapidly to become a $33 billion industry. With the increase in growth the Mexican plastic industry has been in the unique position to help the people of Mexico withstand the deadly pandemic.

Whether it’s providing lifesaving protective equipment or simply placing banners with tips on how to stay safe, the plastics industry has stepped up to help during these uncertain times.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

The Basics of Ball Valve Seat Materials

Ball valves play a critical role in controlling the flow of fluid and pressure within a pipeline, but their effectiveness and safety is only as good as the seat material used. In this blog post, we are going to review the basics of five commonly used ball valve seat materials.

Ball Valves

Whether found in a petrochemical application where a leak could be environmentally devastating, or in a pharmaceutical laboratory where cleanliness and sanitation are critical, ball valve seats must be reliable and robust. A ball valve consists of the body of the valve, the body cap, the stem, the hollow ball, and the round ball valve seat. 

The ball valve seat is responsible for sealing the fluid inside and uniformly distributing the seating stress. In soft seat ball valve designs, either an elastomer or polymer is used as the seal and are inserted into a metallic seat ring. This approach, as opposed to hard seat ball valves, is popular because it provides good sealing action, is lighter weight, and more cost effective. 

Key Properties of Ball Valve Seat Materials

When choosing a polymer material for a ball valve seat, there are numerous factors that are involved. Key material properties include …

  • Sufficient ductility to provide a reliable seal
  • Dimensional stability to ensure the ball valve seat retains its shape for reliable sealing and performance
  • Very low friction to keep stem torque at a minimum
  • Low coefficient of thermal expansion so that the ball valve seat retains its shape when temperature changes occur
  • Excellent wear resistance for a long service life
  • Chemical compatibility with all media involved 

In some operating environments, it is also important that ball valve seat materials exhibit these properties:

  • Low moisture absorption to prevent dimensional changes in the presence of water or high humidity
  • Maintain performance with repeated sterilization that can include hot water, steam, and harsh cleaning chemicals
  • Good performance in the presence of sudden decompression (i.e., pressure drops over 650 psi)

Recommended Materials for Ball Valve Seats

There are several materials that work well as ball valve seats, including acetal, PEEK, PTFE, TFM, and UHMW-PE.

Acetal Ball Valve Seats

When aggressive environments are involved, Acetal (also known as Delrin) is often used. Acetal provides excellent wear resistance, is very rigid, has good toughness, and is resistant to cold flow. Although its operating temperature range is not very wide (-70°F to 180°F), it can handle pressures up to 5,000 psi. Acetal also works well in radioactive environments  but should not be used with oxygen flow.

PEEK Ball Valve Seats

PEEK offers excellent chemical resistance, very low friction, self-lubrication, and is flame retardant while also possessing a wide operating temperature range (from -70°F to 550°F). It can handle very aggressive applications and works well when there is a need for hot water and steam exposure–but does not do well in the presence of sulfuric acid.

In addition, PEEK is very well adapted to nuclear applications and is available in FDA-approved grades as well as filled grades with improved wear properties and better thermal conductivity. Note that PEEK is usually chosen for ball valve seats when the operating temperature range is outside that of PTFE.

PTFE Ball Valve Seats

PTFE (also known by its trade name, Teflon) has many of the same properties as PEEK, but involves even lower friction, dry running capabilities, and more extensive chemical compatibility. Like PEEK, it is available in FDA-approved grades and can handle cryogenic temperatures down to -50°F and high temperatures up to 550°F as well as pressures up to 5,000 psi.  \

Also like PEEK, PTFE can continue to perform even when repeatedly exposed to hot water and steam. Keep in mind, however, that PTFE does not perform well in the presence of fluorine or alkalies. PTFE is also very easy to clean and available in glass or carbon-reinforced grades that can provide improved wear characteristics, less propensity to cold creep, and lower thermal conductivity. 

TFM Ball Valve Seats

TFM (sometimes referred to by the brand name Dyneon) is a second-generation PTFE material that combines the best properties of PTFE (low friction, chemical resistance, high-temperature performance) with better stress recovery and the ability to handle higher pressures. It is also more elastic and resilient than PTFE. The operating temperature of TFM ranges from -100°F to 450°F and it is well adapted to applications involving steam and thermal fluids.

UHMW-PE Ball Valve Seals

UHMW-PE, which stands for Ultra-High Molecular Weight Polyethylene, has a low coefficient of friction, an operating temperature ranging from -70° F to 200°F, good chemical resistance, good dimensional stability, and good abrasion resistance. In general ball valve seats made from UHMW-PE can handle pressures up to 1,500 psi and can handle low to medium levels of radiation exposure.

Conclusion

Ball valve seals are used in many different industries, including chemical processing plants, oil and gas operations, manufacturing facilities, food preparation, and even residential use. As a leak-proof means of pressure and flow control, their smooth and reliable operation is critical–which is why polymer materials work extremely well for ball valve seats. If you are in the market for a ball valve seat material, contact the experts at Advanced EMC. We can put our years of experience to work for you, helping you select the right material for your project.

 

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

7 Things to Know About FlexForce Canted Coil Springs

FlexForce canted coil springs have special characteristics that make them useful in a variety of applications, ranging from locking components together in an orthopaedic implant to providing an energizer for mission critical aerospace applicants. In this blog post, we will introduce seven key facts about FlexForce canted coil springs that you need to know.

Are a Specific Design for Springs

Canted coil springs, also known as slant coil or cant coil springs, are springs that have the individual coils set at an angle to each other, rather than having them all parallel. This coil configuration significantly impacts the performance of these springs and makes them ideal for a wide range of uses.

What makes canted coil springs different from other types is the fact that they have a flat load curve when they are compressed. Because of this, canted coil springs generate predictable loads throughout their wide deflection range.

Can be Used as Mechanical Connectors

Canted coil springs are ideal for applications that involve latching, locking, or holding to connect two components (also known as detent mechanisms). Latching involves fastening two parts together so that they can still be disconnected when needed. Locking creates a permanent connection that can only be broken by damaging the sea. Holding, on the other hand, both retains and aligns parts and makes sliding possible via the controlled spring force. 

Canted coils are commonly used to connect two mating surfaces in a highly predictable, repeatable fashion thanks to the flat load curve. When canted coil springs are used, the insertion/removal force can be engineered to a high degree of accuracy.  And when used as a latching, locking, or holding connector, FlexForce canted coil springs provide a lightweight, high strength option that can be used for practically an infinite number of cycles.

Can Provide Exceptional EMI/RF Shielding

One of the common uses of canted coil springs is their ability to effectively provide EMI/RF shielding. Furthermore, the electrical properties of these springs can be customized to provide more optimal shielding against certain ranges of conductive and radiated interference.  

Add to this the fact that they can adapt to irregular and uneven shapes to provide consistent shielding, and it is easy to see why they are a common choice for applications that need to be protected from harmful electromagnetic and radio frequency crosstalk interference.

Can Act as a Multiple Point Electrical Conductor

Some designs depend on multiple electrical contact points, which a canted coil can provide. Using a canted coil spring for electrical connections results in a reliable connection that results in a cooler operation temperature. It allows engineers to manage more power in compact spaces and provides both conducting and grounding capabilities in both static and dynamic applications. In addition, canted coil springs as electrical conductors can perform in some of the harshest operating environments that may involve vibration and shock. It should come as no surprise that canted coil conductors are often used in medical applications inside the human body.

Can be Used with Spring Energized Seals

Canted coil springs work extremely well as the energizer in spring-energized seals. Because of the energizer, spring energized seals are able to maintain contact with the sealing surface, even if issues such as out of roundness, uneven mating surface, runout, hardware gaps, eccentricity, or seal lip wear are present. 

The flat load curve of these springs also means that friction stays fairly consistent in dynamic sealing applications. This makes them ideal for sealing situations that involve critical friction and torque specifications. In addition, canted coil springs are very unlikely to experience compression set. 

Available With a Range of Options

There are several options for canted coil springs. They are available in varying levels of spring force: light, medium, and heavy. And canted coil springs come in both standard and custom sizes. As to the spring wire itself, they are available in wire diameters between 0.25 mm (0.010 inches) and 1.50 mm (0.059 inches). As to the coil width, they come in sizes ranging from 1.5 mm (0.039 inches) and 15 mm (0.591 inches). However, designs can be highly customized if needed.

Finally, the three most common wire materials are Hastelloy, stainless steel (usually 300 series), and copper alloys. For use as a conductor or EMI/RF shielding, stainless steel is recommended. For applications that involve high heat and corrosive media, Hastelloy and Elgiloy may be recommended. Also keep in mind that these canted coil springs can be obtained with nickel, silver, or gold plating.

Used in a Wide Range of Industries and Applications

Canted coil springs are being used in a diverse group of industries and applications, including oil & gas, renewable energy, aerospace, defense, fluid power, transportation, semiconductor manufacturing, and medical devices

  • As a mechanical connector, canted coil springs are often used to lock together frame assembly of a ventilator cart or to hold components together in wind turbines.
  • As a multiple contact point conductor, canted coil spring assemblies are often used in active implantables such as pacemakers or neurotransmitters. 
  • As EMI/RF shielding, canted coil springs can be found in electrical enclosures or used with data transmission cables.
  • As a part of a spring energized seal, canted coil springs are used in critical aerospace applications and dangerous petrochemical environments involving extreme heat and corrosive materials.

Conclusion

FlexForce canted coil springs can be used as detent mechanisms, EMI/RF shields, multipoint electrical conductors, and energizing springs in seals. They are available in a number of options and can be fully customized to meet user needs. In addition, their reliable performance has already been proven in number industries and applications. If you are interested in FlexForce canted coil springs, contact us at Advanced EMC today.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Benefits of Hytrel for Sealing Applications

Hytrel (property of the Dupont Company) is gaining in popularity as a material for seals, and there a number of reasons for this. In this blog post, we are going to talk about the general characteristics of Hytrel as well as the specific grades used for sealing applications.

What is Hytrel?

Hytrel is a TPC-ET thermoplastic polyester elastomer made by Dupont. Hytrel can be found in applications that seem to vary significantly in requirements and environmental challenges, such as off-road transportation equipment, oil and gas, hydraulic power, food handling, and medical devices. It is also used in electronics, automobiles, healthcare equipment, power tools, sporting goods, appliances, and cables.

Characteristics of Hytrel

Hytrel has a long list of excellent characteristics, including impact resistance, toughness, and resistance to chemical attack (including hydrocarbon solvents and fuels). In terms of sealing applicants, it offers:

  • Flex fatigue resistance
  • Spring-like properties
  • Creep resistance
  • Inherent flexibility
  • The ability to flex in multiple directions
  • Wide operating temperature range (cryogenic to +315°F)

In addition, Hytrel retains mechanical properties even at high temperatures and remains flexible at low temperatures. Hytrel also lends itself to a variety of manufacturing methods, including extrusion, blow molding, injection molding, and rotational molding. However, it is sensitive to water and phosphate fluids above 175°F.

Grades and Blends of Hytrel

Hytrel is available in various grades and blends, including seven specific grades that are well-adapted for seals. In addition to the grades discussed below, there are also renewable sourced options. Note that stabilizing additives can be combined with these grades to improve Hytrel’s resistance to heat aging and UV light.

Hytrel 4056

Hytrel 4056 is the most flexible grade, offering both toughness and strength over a considerably wide temperature range. It works extremely well for low-temperature applications because of its ability to retain flexibility. In addition, its low modulus allows it to be formed using extrusion and has a low melting point.

Hytrel 4068 and Hytrel 4069

Both Hytrel 4068 and 4069 provide flex-fatigue and creep resistance along with outstanding low-temperature properties. These grades can be formed using molding or extrusion and possess a higher melting point than Hytrel 4056 and a lower modulus. In addition, there is a food-grade available: Hytrel 4068FG.

Hytrel 4556

Hytrel 4556 is very similar to 4068 and 4069, with a low-to-medium modulus and can be manufactured using both extrusion and molding. This grade works extremely well for seals and gaskets.

Hytrel 5526 and Hytrel 5556

In terms of general properties, Hytrel 5526 provides a good balance. Its flow properties, however, primarily limit it to injection molding. Hytrel 5556 also offers a balance of properties with a medium modulus. It works well with extrusion but does not have the same high-flow properties available with Hytrel 5526. 

Hytrel 6356

Hytrel 6356 offers an excellent balance of properties such as toughness, flexibility strength, thermal resistance, and creep resistance. This high modulus grade is well adapted both to molding and extrusion processes.

Hytrel 4053FG NC010

When food contact grade seals are needed, Hytrel 4053FG NC010 may be an option. This is a low modulus extrusion grade whose properties include creep resistance, good low-temperature properties, and flex-fatigue resistance. 

Hytrel 5553FG NC010

This is a medium modulus molding and extrusion grade of Hytrel that provides a good balance of properties. It is intended for applications involving food contact.

Hytrel 6359FG NC010

Another good grade option of Hytrel, this material provides a good balance of properties including strength, toughness, flexibility, creep resistance, and thermal resistance. It is a medium to high modulus grade that works well with both molding and extrusion processes.

Benefits of Using Hytrel

When used in sealing applications, Hytrel offers a number of distinct benefits. For example, Hytrel can be used to replace multi-piece assemblies (including those composed of various materials) with a single component.

Because Hytrel has excellent creep and recovery properties, seals using Hytrel will be more resistant to dimensional changes and less likely to be permanently deformed. This is critical in many sealing applications, including those where there are extreme pressure and temperature changes. And because it can flex in multiple directions for far more cycles than a traditional elastomer such as rubber.

Unlike some seal materials, Hytrel grades vary according to modulus, which makes Hytrel a very versatile material choice. The differences in modulus are important: low modulus options can be used where little force should be needed to stretch the material, while high modulus grades work well for situations where significant force should be required to result in stretching. In addition, Hytrel is available in Shore D hardness ranging from 30 to 82.

As mentioned earlier, Hytrel has excellent properties when it comes to chemical compatibility and resistance to chemical attack. More specifically, it is resistant to mineral oils, greases, water-based hydraulic fluids, dilute acids, dilute bases, glycol, and hydrocarbon fuels. There are also grades of Hytrel that offer excellent resistance to the degrading effects of radiation. 

Hytrel is available in food grades that conform to both FDA and  European Food Contact regulations.  There are also grades in compliance with regulatory requirements that make them suitable for use in medical devices and other healthcare applications.

Conclusion

Hytrel combines the strength of engineering plastics with the flexibility of elastomers and the ease of processing provided by thermoplastics. Its combination of properties and flexibility in terms of manufacturing processes make it an excellent option for sealing applications

by Jackie Johnson Jackie Johnson No Comments

Polymer Seals and How They Are Used in Space

Today more and more countries are entering the space industry. According to the Space Foundation, the global market for space exploration was a whopping $383.5 billion worldwide in 2017, with a 100% increase in the total number of spacecrafts deployed. It is expected to grow to $1.1 trillion by 2040.

As the space market opens up, so does the need for technology that assists with cost, sustainability, efficiency and safety- such as seals.

In fact, polymer seals have been used in a variety of functions for spacecrafts such as:

  • Propulsion
  • Payload Systems
  • Ground Support Equipment
  • Regulators
  • Main Fuel and Oxygen Valves
  • Regulators
  • And more!

In today’s blog post, we will explore the use of polymer seals in the space industry.

A Changing Landscape

Since the first expedition into space in 1961 by Russian cosmonaut Yuri Gagarin, there has been a surge in emerging countries and private sectors entering the space race.

In 2002 Elon Musk founded SpaceX, a private company whose goal is to manufacture and launch advanced rockets and spacecrafts with the goal of enabling commercial trips into space. In 2010 it became the first private company to return a spacecraft from low Earth orbit in 2010 and the first commercial spacecraft to deliver cargo to and from the International Space Station in 2012.

In India, the Indian Space Research Organization (or ISRO) has developed a massive and ambitious space program. In 2014 they launched their Mars orbiter, becoming the fourth space agency and the first in Asia to reach the red planet. In 2017, it launched 104 satellites in a single rocket, tripling Russia’s record.

With so many new players entering the scene, the space industry has never looked more exciting. This also requires an increase in demand for high quality parts, such as polymer seals.

Space is Cold and Engines are Hot

Polymer spring energized seals are commonly used in a variety of space applications because of their durability and ability to withstand extreme temperatures.

With temperatures in space reaching cryogenic (-238*F or -150*C) it is important that the seals used can withstand the extreme temperatures. The outer polymer lip of a spring energized seal for example allows the seal to be used in temperatures of -423*F (-253*C) to 302*F (150*C).

On top of having seals that can be used in the cold, dark vacuum of space, seals are also used in conjunction with things like thrusters, combustion chambers, and other parts of the shuttle where temperatures can reach a whopping 6,000*F (3,315*C).

Aggressive Chemicals

Many seals face frequent exposure to liquid oxygen and liquid hydrogen, the latter of which must be below 20K (-423*F or -253*C) in order to reach a liquid state. This puts an incredible amount of strain on the seal. One way around this is to make seals out of high-quality polymers such as PTFE, Torlon and more.

Increase of Pressure

In outer space, the pressure is 1.322 x 10-11 Pa. For those keeping track at home, this is essentially zero. However, the act of leaving the Earth’s atmosphere causes such a huge fluctuation in pressure that there is a potential for metal and other hardware to open, which in tern could potentially impact the seal.

As such it is critical that seals used can hold up to the extreme fluctuation of pressure, and continue to run, to keep the shuttle and its crew safe.

Teflon, or PTFE, is a popular material used because of its ability to not only handle extreme temperatures, but extreme pressure fluctuations as well.

Cost Efficiency

As of 2012 it is estimated that the average launch cost of a NASA space shuttle is around $576 million. That cost does not factor in the price to build the craft, which values at a whopping $3.5 billion. As such, it behooves space programs to find ways to not only be cost efficient, but to be sustainable as well.

Luckily, with seals, making them out of polymer materials solves both problems!

Because of it’s ability to be produced at high volumes, making seals out of polymers can greatly reduce overhead cost. And because the plastic can be melted down and reused, they are highly sustainable as well!

In Conclusion

With more and more people interested in space exploration, it is becoming more and more critical to have high quality parts to perform critical functions.

Polymer seals are the best choice for companies looking to have a high quality, cost efficient, and sustainable part that will withstand the rigors of space travel.

For more information, or to learn how Advanced EMC Technologies can help your spaceship blast off, contact us today!