Automotive

Bioplastics are increasingly being used for components in industrial products across a variety of industries. However, adapted fasteners that can be processed reliably are required to screw biopolymers together, which is why ARNOLD Umformtechnik GmbH & Co KG has been investigating the suitability of its Remform II HS thread forming screw for use with bioplastics.

Remform II HS is characterised by an asymmetrical thread profile with a rounded flank tip and curved load flank. This geometry is adapted to the flow properties of plastic and enables gentle material displacement. The screw also has an optimised, enlarged thread core, which significantly increases both its breaking torque and tensile breaking force. This results in a more stable connection between the joining partners, but also allows a higher assembly torque to be applied to high strength plastics without the risk of the screw breaking. 

The combination of radius profile and steep load flank allows the plastic material to flow towards the load flank when screwing in, ensuring good flank coverage. By reducing the load flank angle to 10°, the radial stresses are also significantly reduced. Despite the high thread overlap, a low screw-in torque is generated and the risk of cracking in the plastic is reduced due to the lower radial expansion.

ARNOLD has been investigating the suitability of the Remform II HS for bolting Tepex^®, a registered trademark of the Lanxess Group. Tepex^® dynalite 813-F250 is a 100% bio-based composite material with a matrix of PLA (polylactic acid) reinforced with flax fibres. The fibres are obtained from the stalk of the flax plant and are grown locally. The Tepex^® material samples were provided as plates for the basic tests on suitability with regard to screwability, which were then cut into small samples for the screw tests. Due to the sample thickness of around 6mm, a Remform II HS with a diameter of 2.5mm was used as a fastener. 

The initial results of the screw-in and over tightening tests indicate that the Remform II HS can be used to form a nut thread with maximum load-bearing capacity in the bio-based material. The combination of Remform II HS and Tepex^® also scored highly in terms of process reliability. This means that, in future, customers can be supported even better in the design and conception of direct fastening with regard to bio-based composite materials.