Demanding customer application
A German manufacturer of a waterproof and submersible prosthesis knee and foot system, WEIGEL+ medical, required a strong fastener that had excellent corrosion resistance to ensure it could cope with being submerged in seawater.
The ‘All Terrain Knee’ and the ‘Niagara Foot’ can be used in aquatic environments as they purely work mechanically. However, this requires that all components are resistant to saltwater, including the screws.
The BUMAX solution
WEIGEL+ began using BUMAX® SDX (Super Duplex) 109 screws. Super duplex stainless steel fasteners are unique as they combine super high strength with excellent corrosion resistance compared with alloy steel fasteners, which would have corrosion issues if exposed to seawater.
“We tried a variety of stainless steel screws when developing the waterproof knee joint, but BUMAX® SDX 109 was the only screw that provided both the strength and corrosion resistance we required,” explains Jochen Weigel, owner of WEIGEL+ medical and co-owner of DOI ortho-innovativ.
Duplex Stainless Steel is a family of stainless steel that has a two-phase microstructure containing Ferrite and Austenite. BUMAX® Duplex grades achieve their high strength from cold working such as cold heading and thread rolling.
“BUMAX® SDX 109 is from our high strength Super Duplex fastener range and provides excellent mechanical properties, and exceptional resistance to general crevice, pitting and stress corrosion,” says Klaus Vogt, Business Development Manager at BUMAX. “Due to their high levels of chromium and molybdenum, super duplex grades provide even greater corrosion resistance than duplex grades.”
Corrosion Resistance
Super Duplex stainless steel offers very good resistance to general and pitting corrosion due to its high Pitting Resistance Equivalent (PRE) number. The higher the PRE number, the more resistant the steel against pitting corrosion is in seawater and chloride induced corrosion. Super Duplex grades are also well known to possess excellent stress corrosion (SCC) resistance in chloride environments, even in its high strength strain hardened condition.
A simple and durable prostheses system for use around the world
The ‘Niagara Foot’ was designed by Prosthetist Rob Gabourie and the ‘All Terrain Knee’ knee joint was developed by a team with the scientist Jan Andrysek and Brandon Burke, who lost his leg himself at the age of 18. Together with the Fraunhofer Institute, WEIGEL+ medical and DOI ortho-innovative brought the foot and knee joint to series production.
WEIGEL+ medical (development and manufacturing) and DOI ortho-innovativ (distribution and education) works with the German international aid agency ‘Ein Herz für Kinder’ and is committed to simple prostheses for use in all climatic conditions. The fact that the prosthetic knee is purely mechanical and foot is durable in any environment makes it the perfect solution for the developing world. In this sense, BUMAX® SDX 109 screws contribute to providing prosthesis solutions to people all around the world.
