Cryogenic Seals for Low Temperature Situations
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Meeting the Challenges of Cryogenic Seals

The term “cryogenic” typically refers to temperatures that are below freezing, extending to absolute zero (-460° F / -273° C). At these extreme temperatures, cryogenic seal design and specification becomes especially challenging–but far from impossible.

Where Cryogenic Seals Are Used

In general, cryogenic temperatures are often required for food preservation, transporting gases, cryosurgery, and cryoelectronics. Such low temperatures are needed in connection with some types of food storage, cooling superconductors, recycling, and storing blood and tissue samples. In fact, there are many different critical applications that require seals that can handle media stored at cryogenic temperatures, such as loading arms for transporting LNG, infrared telescopes, dilution refrigerator units, and sealing the liquid helium used formagnetic resonance imaging. 

Reliability

The first priority for a cryogenic seal is that it be reliable. While any seal failure is a problem, cryogenic seal failures can be especially dangerous. Aside from obvious issues such as environmental impact and toxicity, there can be an explosion that results from the rapid expansion of the cryogenic materials as well as potential asphyxiation and the effects of sudden exposure to extreme cold on employees and equipment.

Fluids Near Their Boiling Point

If fluid being stored at cryogenic temperatures is near its boiling point, then there is a strong possibility that it could flash into a gas if there is a sudden change in either pressure or temperature. This, in turn, would lead to a catastrophic (and possibly very dangerous) seal failure. 

Dimensional Stability

The installation temperature and service temperature of a cryogenic seal are going to be vastly different, which means that dimensional changes due to temperature are unavoidable. When designing or specifying a cryogenic seal, it is very important to account for these dimensional changes and adjust critical size and clearance parameters accordingly. In fact, it is vital to remember that the seal material be chosen for its properties at the expected operating temperature, not at room temperature.

Elasticity

Another challenge in sealing cryogenic fluids lies in the elasticity of the seal material itself. At extremely low temperatures, both elastomers and metals can reach a temperature where they transition from being an elastic material to a brittle one. This is another example of why cryogenic seals need to be selected based on their material properties — including stiffness and strength — at the cryogenic temperature of the application.

Lubrication

Lubrication is another major problem for cryogenic seals: at such extremely low temperatures, traditional lubricants simply will not function or will freeze and the fluids being sealed within cannot provide lubrication. If there is any moisture present in the lubrication, this can lead to freezing and a shattered seal. Cryogenic applications require seal materials that are dry running and/or self-lubricating, such as PTFE or TFM.

Meeting the Challenges

For many cryogenic sealing applications, spring-energized seals work extremely well. For seal jacket materials, polymers are an excellent choice and available options include PTFE, modified PTFE (also referred to as TFM), and UHMW PE. These materials are ….

  • Corrosion-resistant
  • Self-lubricating
  • Durable
  • Posses excellent thermal insulation properties
  • Retain elasticity and strength at low temperatures
  • Exhibit good wear properties
  • Are compatible with a wide variety of chemicals

Not that in some cases, especially those where flash boiling is an issue, polymer labyrinth seals may be a better choice than a spring-energized seals.

Conclusion

While there are a host of challenges involved in designing effective seals for cryogenic applications, there are effective solutions available. These include polymer spring-energized seals and labyrinth seals.

3D Printing
by Jackie Johnson Jackie Johnson No Comments

History of 3D Printing

3D Printing, or additive manufacturing, is older than most people think. In fact, it has been around since the 1980s! Today we will go over this technology’s exciting history, from its earliest prototypes to today’s use. In this blog post, we will go over the history of 3D printing, from it’s earliest prototype to today!

While the concept of 3D printing has been around since the 70s, the first experiments began in 1981, when Dr. Kodama began research into a rapid prototyping technique. He was the first person to describe the layer-by-layer development that 3D Printing is famous for. Dr. Kodama used SLA (Stereolithography), which is a photosensitive resin that he then polymerized with a UV light. While it is clear that Dr. Kodama was the first to describe, he, unfortunately, did not file the patent in time.

In 1986, an engineer by the name of Charles Hull submitted the first patent for SLA. Two years later he founded the 3D Systems Corporation and released the SLA-1, the first, official, 3D printer.

1988 was a big year for 3D printing technology! That year, along with the founding of 3D Systems Corp, the University of Texas was also dabbling in the fledgling technology. Carl Deckard developed a patent for selective laser sintering (SLS) which is a 3D printing technique in which powder grains are fused together by a laser. At the same time, Stratasys Inc. filed a patent for fused deposition modeling (or FDM).

The 90s had its share of 3D printing innovations. But it wasn’t until the 2000s when 3D printing as we know it really gained traction, especially in the media. 2000 saw the world’s first 3D printed kidney, which put the spotlight on the technology. In 2004, home printers started to become more readily accessible, leading to a boom in the maker community that is still going strong today.

2008 saw the world’s first 3D printed prosthetic limb, 2010 the first 3D printed car. There seemed to be no limit to what this technology could do. And in 2013, then-President Barak Obama included it as a major issue in his State of the Union speech.

3D Printing is continuing to grow and expand, with sights focused on the ability to print in more materials. Today printers can use industrial-strength materials such as PEEK, PTFE, nylon, and even metals. There are also several types of research being done on the subject of 3D Bioprinting, which could completely change the medical industry. There truly is no limit to what this technology can do. We are just beginning to scratch the surface of what 3D printing can do.