Material in PPL’s head restraint has a tensile strength of 40,000 psi (276 MPa) and flexural modulus of 5.4 x 106 psi (37,233 MPa), meeting the stiffness and creep resistance requirements for a titanium replacement while optimizing fiber loadings for better flow during manufacturing.

A material incompatibility problem in a surgical head restraint led designers to swap a PEEK-based material for costly titanium. Performance Plastics Ltd. (PPL), Cincinnati, (performanceplastics.com) shaped the restraints with a PEEK (polyetheretherketone) compound from RTP Company, Winona, Minn., (rtpcompany.com) because it was structurally sound and nonmagnetic.

Making such a swap, however, can lead to incompatibility problems. For instance, the wrong material can distort magnetic resonance brain scans, and computer tomography images become unrecognizable if magnetic components are used. Even titanium, although non-magnetic, can generate excessive heat, and designs calling for it can miss cost targets.

Size limitations and high loads during surgery required a high strength-to-weight ratio. In addition, they need a material that can withstand the high temperatures of sterilization. “A big hurdle with this application was that we needed a compound that was modified more than the supplier's standard PEEK grades because the restraint is made of large parts with long flow lengths,” says PPL Engineering Manager Ken Kelly. “We asked the RTP engineers to optimize the fiber loadings.” They succeeded in customizing a PEEK version to handle extreme temperatures and harsh conditions of autoclave and gamma radiation sterilization.