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In cryogenic temperatures, most O-rings become brittle and fail. Many times cryogenic applications can also involve media that is not chemically compatible with traditional elastomeric materials. However, for axial sealing applications, there is an effective, dependable solution: encapsulated O-rings. 

What is an Encapsulated O-Ring?

In short, encapsulated o-rings combine the chemical resistance and extreme-temperature performance of FEP or PFA with the elasticity and resilience of silicone, FKM, or stainless steel energizers. Stainless steel springs or rugged elastomers are encapsulated within a durable, chemically resistant jacket made from FEP (fluorinated ethylene propylene) orPFA (perfluoro alkoxy copolymer). These o-rings are used with valve stems, flanges, joints, swivels, pumps, turbo expanders, and waterless fracking.

Materials Used With Encapsulated O-Rings

For the outside of the O-ring, the most popular materials currently in use are FEP, PFA, and PTFE. FEP is highly resistant to chemical attack, offers a low compression set, and has a low coefficient of friction. Its operating temperature range is -420°F through 400°F and is less expensive than PFA. In addition, FEP is available in FDA-approved grades. 

PFA is resistant to a wide range of corrosive chemicals, including naphtha, acid, aromatic solvents, petroleum, and alcohol. It has a wider operating temperature range than FEP, from -420°F through 500°F. It also possesses a low compression set and resistance to cracking and stress in addition to a higher overall mechanical strength when compared to FEP. It is also available in grades that have the following approvals: USP IV, FDA-compliant, EU Reg. 1935/2004, ADI-free, and 3-A Sanitary Standards.

The materials used for the interior energizer of encapsulated o-rings include 302 stainless steel for spring energized as well as silicone, FKM (trade name Viton), or EPDM. Whether its a spring-energized approach or a core of silicone, FKM, or EPDM, the interior of the encapsulated o-ring provides the additional resiliency that makes these o-rings so effective for cryogenic applications. Note that silicone and FKM ensure an even pretensioning at the sealing point.

Silicone provides a softer core than FKM and offers very good cold flexibility. Using FKM as the core material means that the o-ring will be able assume its original shape very quickly after installation/deformation due to its outstanding compression set characteristics. It is not, however, as temperature resistant as silicone. While EPDM can be used as a core material, it is not recommended because of how it reacts to the heat involved in manufacturing the encapsulated o-rings.

Solid-Core vs Hollow-Core Encapsulated O-Rings

The two basic types of encapsulated O-rings are solid core and hollow core. Solid core o-rings have an energizer made from either silicone or FKM (fluoroelastomer, trade name Viton). Both types of cores provide good elasticity and low compression set, but when used in cryogenic applications silicone is usually the better choice because it remains more flexible at lower temperatures. Hollow-core encapsulated o-rings, on the other hand, are used when there is a need for extreme elasticity or for fragile applications. 

Advantages of Encapsulated O-Rings

There are several advantages to using encapsulated O-ring, besides the fact that they  can outperform traditional seals in harsh environments that can include extreme temperatures and corrosive media. These o-rings are …

• Chemically resistant
• Available in non-contaminating and FDA-approved materials
• Low coefficient of friction that prevents issues with stick-slip behavior
• Low permeation
• Excellent corrosion resistance
• Low compression set
• Excellent service life
• Reliable sealing
• Cost effective

Encapsulated O-Rings for Cryogenic Operating Environments

For cryogenic environments, the best approach to encapsulated O-rings is the use of FEP or PFA exterior with a steel flat wound ribbon spring at the core. This configuration can handle cryogenic temperatures all the way down to -420°F and pressures up to 3000 psi as long as vented holes are placed in the FEP jacket to prevent dangerous blowouts. These encapsulated o-rings work best in static and slow dynamic applications and are ideal for applications that involve cryogenic media such as liquid oxygen, liquid nitrogen, hydrogen. These encapsulated o-rings are readily available in both metric and US cross-sections and a wide range of diameters.

Conclusion

For cryogenic applications where traditional o-rings have failed, encapsulated o-rings with an FEP/PFA exterior and a 302 stainless flat wound ribbon at the core is an excellent option. It has already been successfully used by NASA in not one but several successful rocket launches and has been incorporated into designs by Lockheed and Boeing.

Injection molding is one of the most popular methods of mass producing identical plastic products. It is fast, highly efficient, with the ability to produce an incredible amounts of parts per hour.

It has many benefits compared to other manufacturing processes. For example, once the initial costs have been met, the price per unit is actually extremely low compared to processes like CNC machining. This is in part because it is easier to mass produce products with injection molding, as well as reduced waste. Injection molding is also incredibly fast, almost entirely automated, and highly reliable.

In this week’s blog post, we will go over the many benefits of injection molding, and why it might be the manufacturing process your business needs!

How it Works

Injection molding works by using a screw-type plunger to heat and inject molten plastic material under pressure into a closed metal mold.

With thermoplastics, pelletized raw material is fed through a hopper into a heated barrel with a reciprocating screw. This melts the pellets into molten plastic, which is then poured into the mold.

When the material is cooled, it is removed from the mold, where it can be cleaned and inspected.

Benefits of Injection Molding

Fast Production

Injection molding is one of the fastest means of production out there, especially when compared to other methods. This makes the process highly efficient and cost-effective. While speed depends on the complexity and size of the mold, there are typically 15-120 second pass between each cycle time.

Furthermore, automation, see Low Labor Costs below, allows for making incredibly precise and accurate injection molds. Computer aided design (CAD) and computer aided manufacturing (CAM) allow close tolerances during the making of the molds, which in turn also enable fast production of products.

Complex Part Design

Another benefit of injection molding is that it can handle extremely complex parts. In addition, it can create large quantities of uniform parts, virtually indistinguishable from each other.

In order to achieve that level of uniformity, however, the mold must

High Precision

A huge benefit of injection molding is its ability to create complex part designs requiring tight tolerances. In fact, with injection molding, the designs can be as accurate to within +/- .005” or even closer depending on part design.

This is particularly important for industries such as the medical device industry, where parts need to be as accurate as possible to function properly.

Stronger Products

Thanks to the process used, injection molding can create incredibly strong products. With the molding, it is possible to use fillers in the material, which reduces the density of the plastic while it is being molded and adds greater strength to the completed part that other processes do not offer.

Flexibility

Since the molds are subjected to extremely high presser, the plastic is pressed harder and allows for a larger amount of detail than other methods of manufacturing. Injection molding can be used for complex or intricate shapes.

And with choosing fluoropolymers, there are a lot of materials to choose from. It is easy to find the material to suit your needs.

Low Labor Costs

Because injection molding is an automated process, with the majority of the process being performed by machines and robotics that can be controlled and managed by a single operator, the overhead cost is greatly reduced. With a lower overhead, the manufacturing is significantly lowered.

Product Consistency

As stated above, the process of injection molding enables manufacturers to mass produce identical products. With an accuracy rate of a 100^th of a millimeter, injection molding is a great choice if you need to mass produce products.

Ability to Use Multiple Plastics at Once

The ability to use different types of plastic simultaneously is another benefit of injection molding. This can be done with the help of co-injection molding, a process in which a second component (core) is injected into the first component (skin).

This can save costs by filling a material with a cheaper material such as regranulate, and it can also enhance the quality of a component by giving it a more reinforced core.

Reduced Waste

Since part repeatability is so high with injection molding, there is very little plastic waste involved. Compared to traditional manufacturing processes like CNC machining, which cuts away substantial percentages of material, injection molding produces very low scrap rates, and what excess material is left over can be re-used.

This makes the process a good choice for companies wanting to reduce their environmental impact.

Some Considerations for Injection Molding

• Design Considerations
  1. Design the part with injection molding in mind. While injection molding can make complex parts, simplifying 3D geometry early on will save time and money in the long run. Other things to keep in mind:
     • Keep walls thin, typically between 132” and 110”
     • To strengthen parts, use additional structures such as ribs instead of thicker walls
     • Round corners and edges whenever possible
     • If possible, add a slight taper to the sides to allow for easy release of the part from the mold.
• Production Considerations
  1. Try to minimize cycle time as much as possible. Using machines with hot runner technology will help.
  2. To keep production fast and easy, try designing your part specifically to minimize assembly. This can save on overhead!
• Financial Considerations
  1. While injection molding will save you money in the long run, preparing a product requires a significant initial investment.
  2. Be sure to determine the number of parts you need to produce to be the most cost effective beforehand.

In Conclusion

Injection molding is one of the best manufacturing processes for producing high quality products on a massive scale. With its high accuracy and repeatability, as well as it’s reduced waste, it can save manufacturers money. It is also great for producing stronger products with more complex designs, perfect for complex parts for complex machines.

If you are looking for injection molded polymer parts, contact Advanced EMC Technologies today and we will be happy to help you!