Hexagons spread bolt head loads
A bolt head in which torque load is exceptionally well distributed
Problem: For fastening composites it is best to use screws made out of similar materials to those they are joining, with the similar strengths and thermal expansion coefficients.
However, while continuous fibre reinforced composites offer exceptional strengths and stiffnesses per unit weight, they can be damaged surprisingly easily, especially in regions where fibre is lacking. This is a particular problem with conventional hexagonal headed bolts and screws. Rounding the edges off the head is a problem with any bolt, but if the bolt is made of continuously reinforced fibre, it is unlikely that the fibres will extend right into the corners.
Solution: Swiss composite expert Icotec, has derived . This is achieved by using what it calls a ‘HexHex’ drive, which combines an inner hexalobular socket and an outer hexagon. The company offers them in carbon/PEEK or glass fibre/PEEK and says that they offer a weight reduction of 80% compared with steel.
Dry friction values are 0.075 and 0.1 respectively, continuous-use temperature is up to 260 degrees C and they have, according to the company, “excellent creep resistance” and “outstanding fatigue resistance”.
Corrosion resistance is inherent because of the materials used and the use of glass reinforcement enables thermal and electrical insulation.
Applications: Their use is seen in general engineering, marine, textile machinery and aeronautical applications.
Icotec screws are a standard in Formula 1 both for chassis and engine applications and DLR, the German Aero-space Centre, uses Icotec carbon/PEEK fasteners for its space robots. Reasons cited are their light weight combined with maximum strength and thermal stability. TS
