Failure is not an option when it comes to medical equipment. From critical or sensitive devices like lasers, MRI scanners, knee joints, and implantable pacemakers to instruments as straightforward as stethoscopes, when life or quality of life is at stake, medical equipment must be reliable.

In the medical field there's little room for the $15 billion per year spent by 25 of the largest US manufacturers on warranty claims; and little room for processing those claims that eat up 2.5% to 4.5% of revenues for companies across all industries. The industry has higher aims than other fields and customer satisfaction and warranty problems associated with fastener failure must be prevented or quickly and economically handled.

Due to medicine's working environment inside and outside the human body, fasteners such as C-clips and specialized retaining rings can prove too cumbersome and costly. Because repetitive loads, shock and vibrational loosening must be decisively handled, traditional fasteners susceptible to self-loosening rotational movement, stripping, and shearing are not always appropriate either. Testing, in fact, has found that the first two threads of traditional fasteners can carry as much as 80% of the load, permitting stripping or shearing, while subsequent male threads "float" within the female threads.

Medical equipment manufacturers are successfully attacking these problems with a variety of new technologies. One of the most interesting solutions is also the simplest - an innovative self-locking fastener called Spiralock. By its unique design, Spiralock is capable of resisting loosening even under loads and vibrations strong enough to break the fastener.

Protecting Medical Equipment from Shock, Vibration, and Warranty Issues

In a proactive design change to increase reliability in the field, the medical/aesthetic laser technology firm Lumenis recently sought to safeguard its precision critical laser alignments. These could potentially become misaligned during rough shipping or handling using standard thread forms, and traditional locking techniques were not well suited to the task.

"We wanted to increase the design's robustness to better withstand the shock and vibration of shipping, as well as carting from room to room in the field," said Peter Hines, a Lumenis R&D engineer responsible for laser design.

Hines ruled out chemical adhesives because of their tendency to emit gaseous material which could collect on sensitive optics, degrading their performance. He was less than satisfied with traditional techniques, such as locking washers, which add weight and complexity with less than desired locking ability. Lumenis chose Spiralock self-locking fasteners.

What makes Spiralock unique is a 30-degree "wedge" ramp cut at the root of the female thread (while traditional fasteners use 60-degree thread). Under clamp load, the crests of the threads on any standard male bolt are drawn tightly against Spiralock's wedge ramp. This not only eliminates sideways motion that causes vibrational loosening but also distributes the threaded joint's load throughout all engaged threads, a claim supported by a Massachusetts Institute of Technology research study. The load percentage on the first engaged thread is significantly lower than traditional thread forms, which further reduces possible bolt failure and improves product performance.

"We're using the Spiralock self-locking fastener to help alleviate our concerns regarding a system's critical precision alignment," says Hines. "With its shock and vibration resistance, we're preventing screws from backing out and preserving critical alignment for enhanced reliability."

Manufacturers of ultra-precision devices and instruments who face product reliability problems or whose components are used in larger OEM systems turn to Spiralock, whose self-locking fasteners are able to withstand micro-vibrations and restrict minor but noticeable torsional loads.

By using the Spiralock self-locking thread form, manufacturers can achieve increased productivity, durability, more cost-effective and repeatable manufacturing processes, as well as the ability to retro-manufacture thousands of inventory parts that could end up as very costly scrap.

Production changeovers to Spiralock fasteners are typically quick and seamless, usually requiring just an exchange of traditional nuts, wire inserts or simply drilling out and re-tapping existing parts stock that have unreliable standard tapped holes.

The Future of Medical Device Performance

As the reliability of medical equipment, devices, and implants becomes increasingly important and tolerances become stricter, innovative technologies like Spiralock's self-locking fasteners are becoming more widespread in medical applications.

Because of their vibration-resistant, reliable locking features Spiralock fasteners hold various components together in artificial limbs, heart pumps and MRI machines and are also being considered for cardiovascular devices such as pacemakers and implantable defibrillators, as well as for dental and orthopedic surgical instruments and CT scanning applications.

For more info on Spiralock Corp. technology and products, visit www.spiralock.com; email slinfo(at)spiralock.com; call (800) 521-2688; fax (248) 543-1403; or write to them at Madison Tech Center, PO Box 71629, Madison Heights, MI 48071