Medical ventilator
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

How Canted Coils Springs are Used in Medical Applications

Canted Coil Springs

There are several distinct benefits to be had from using canted coil springs in place of more traditional springs. Because of this, it should come as no surprise that these springs are used extensively in medical applications. 

Canted Coil Springs Are Effective Electrical Connectors and Contacts

Canted coil springs are being used more and more for electrical contacts and connectors. Canted coil connectors make it easier to replace leads and lead segments without harming the patient, and lead interface solutions based on canted coil springs can significantly reduce risk to the patient. In some applications, the procedure time and the patient’s recovery time can be reduced through the wise application of canted coil springs. Canted coil springs also provide high contact power density with a minimal amount of temperature rise. In many instances, they can also reduce the size of the medical device and provide multi-channel connections.

Canted Coil Springs Can Provide EMI and RF Shielding

Another benefit of canted coil springs is their ability to provide shielding from harmful EMI and RFI interference in applications such as ultrasound equipment and vital signs monitors. Many times the medical data being transmitted cannot afford a compromise in its integrity of the disruption of the data flow. Canted coil springs can actually be tuned to meet specific impedance specifications so that medical equipment and devices can be protected from dangerous crosstalk interference.

Canted Coil Springs Can Be Used in Spring-Energized Seals

Canted coil springs can be used in spring-energized seals in medical equipment and external devices as well as implantable devices. Spring-energized seals are often used to maintain a seal when there are problems with hardware gaps, runout, eccentric contact surfaces, and vacuum pressures. In short, spring-energized seals can provide an effective seal where other seals would fail, and when canted coil springs are used then a far more consistent spring force can be applied. 

Canted Coil Springs Serve as Reliable Mechanical Connectors

 

Canted coil springs can provide a reliable connector in three specific ways: 

  • Holding and retaining two parts in alignment with customized forces, often used for surgical instrumentation
  • Securely fastening two parts together while allowing them to still be unlatched (where the latching force can be customized), which is also being used with surgical instrumentation
  • Permanently locking two parts together, including use during orthopedic implant surgery

Unlike most mechanical connector solutions, canted coil springs can achieve these connections with strength, reliability, and incredibly high precision. In addition, when canted coil springs are used as mechanical connectors, there is an option to customize the forces for insertion and breakaway. 

Medical ventilator

Medical Applications of Canted Coil Springs

There are a host of specific medical applications where canted coil springs have proven invaluable. The following is just a sampling:

  • Cochlear implants
  • Implantable medication pumps
  • Insulin delivery systems
  • Orthopedic instruments
  • High-speed surgical power tools
  • Neurostimulators
  • Ultrasound equipment
  • Pain management devices
  • Vital signs monitors
  • Hemodialysis equipment
  • Defibrillators
  • Cardiac rhythm management devices

Conclusion

Canted coil springs are used in connection with everything from neurostimulators to orthopedic implant surgery. Their ability to serve as electrical connectors/contacts, shield from EMI and RF interferences, serve as the energizer in spring-energized seals, and provide tailored mechanical connections make them ideal solutions for many different medical devices and implantables.

 

Back-Up Rings
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

The 3 Leading Materials for Effective Back-up Rings

There are three leading materials used for most back-up ring (BUR) applications: PTFE, Nylon, and PEEK. Each of these materials has specific benefits that it can bring to your application, starting with their stiffness and compressive strength.

Why Back-up Rings Are Important

Seal extrusion is one of the most common causes of polymer seal failure. Whether the cause of extrusion is a large gap between the mating surfaces, high temperatures, or extreme pressures, back-up rings can help. The right choice of a BUR can prevent seal extrusion, lengthen the useful life of the seal, and reduce the chances of a catastrophic failure.

PTFE Back-Up Rings

PTFE is well-known for its extremely low friction, dry running capabilities, and outstanding chemical resistance. Filled PTFE (either glass, carbon, graphite, or bronze filled) can handle operating pressures up to 5,800 psi, making it an excellent choice for both medium and high-pressure applications. Virgin PTFE has a much lower maximum operating temperature (around 3,600 psi) and is limited to low-pressure situations. PTFE also has a maximum operating temperature of 575°F, and that combined with chemical compatibility and the high-pressure capabilities of filled PTFE mean that it is an excellent option for harsh condition environments.

Nylon Back-Up Rings

Nylon 6,6 (sometimes written Nylon 6/6 or Nylon 66) is a polyamide material commonly used for back-up rings. It can handle high pressure very well but is limited to temperatures below 186°F. It possesses excellent rigidity, good compressive strength, and thermal stability, all of which are key to effective backup rings.

When used for back-up rings, Nylon is typically filled with Molybdenum Disulfide (MoS2) to achieve an even lower coefficient of friction. It is not recommended for use in wet or humid environments because it does absorb water unless fillers such as glass are added to offset the absorption effects. 

PEEK Back-Up Rings

Another commonly used back-up ring material is PEEK, which can handle temperatures of up to 500°F and pressures up to 20,000 psi. Like PTFE, it is low friction, dry running, and resistant to a wide variety of aggressive chemicals. It is also available with fillers to enhance properties such as compressive strength and stiffness. However, PEEK is much harder than PTFE: PTFE has a Shore hardness of D50 while PEEK has a significantly greater hardness of D85. For these reasons, PEEK back-up rings are often used in aggressive environments, such as those found in the oil and gas industry. 

Conclusion

If you are having issues with extrusion-related seal failure, polymer back-up rings are a cost-effective solution that can extend the life of your seals. When it comes to polymer back-up ring materials, the top three choices are PTFE, Nylon, and PEEK. While each has its own pros and cons, they are excellent options for solving the problem of seal extrusion. PEEK works best for high pressure, high temperature environments that can involve exposure to corrosive materials. PTFE can also handle high temperatures and corrosive environments, but its maximum operating pressure is lower than that of PEEK. Nylon is also an excellent choice with excellent hardness and thermal stability, with its main limitations being high temperatures and exposure to humidity and moisture.