The spring soon became the answer to manufacturers’ device fastening difficulties, shortly after it was invented.
The canted coil spring, invented over 50 years ago consists of wire that has been coiled with precision and resistance welded to a specific diameter. The popularity of the canted coil spring has sprung up due to its versatility. This specific coil spring can be designed to lock two pieces together, permanently, and it can even act as a holding function, providing a certain amount of friction between the two components. Another benefit, is that it can perform electromagnetic interference shielding and grounding functions, or serve as an electrical contact between two pieces.
A great number of medical grade canted coil springs are used in latching applications in which two components are fastened with one another on a device, conforming with the force requirements specified by the designer.
A surgical instrumentation design is gravitating towards custom products for certain surgeons and what the spring does, is make it easier for engineers, because it enables them to tailor the instrument to the surgeon’s needs.
Acquiring a locking component has advantages for orthopaedic implants. The spring can lock any two pieces together during surgery using minimal force, which eliminates the use of hammers and other surgical tooling equipment and gives the surgeon free hands to administer the surgery more efficiently and effectively.
Holding canted coil springs are usually designed into surgical instrumentation.
Drill guides, sleeves or any other sliding components that need a certain amount of sliding force, will be able to incorporate a spring.
The drag force can e specified within the design process, as it requires consideration of the housing dimensions, tolerances and surface finishes.
Electrical contact/EMI shielding and grounding
For many years, medical device manufacturers have been pressurised to reduce their package sizing, while improving performance and reliability.
Device manufacturers have embraced the spring as an effective component to connect and conduct electricity – it can be used to provide electrical contact to sensors and other devices. It performs exceptionally in grounding and/or shielding applications for long periods inside or outside of the body.
Importance of the wire
The wire is the basic foundation for a canted coil spring, as it deters how well or badly the performance of the component is in an application.
The wire size, diameter and materials are used to address a wide range of design criteria.
Springs used in medical applications require a specific gas welding process, which eliminates any black carbon deposits.
The life of the spring’s performance varies, depending on the force ratios.
Smaller medical device applications will typically have a maximum 1:4 force ratio.
Generally, the higher the force ratio, the less number of cycles.
On the larger end of the scale, of industrial applications, they can range as high as 10:1 force ratio, with limited cycle life; the insertion and breakaway force are always tailored to the specific application.
A solution to consider
The canted coil spring will not be the go-to answer to every medical device design challenges you face, although, for engineers who want to advance their technology and obtain an added level of customisation and performance from their design, the spring offers an excellent alternative.