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Creating the Hamster Wheel of Death

Spinal cord injuries can drastically alter the way of life of those that suffer them and investment in technology to aid research in the area is vital.

Carter Manufacturing was approached by a customer to help create a new technology, now known affectionately as the Hamster Wheel of Death by the scientists and engineers who worked on the project. The aim to assist in stem cell research in the area of spinal injuries, which would make use of electro spinning.

Using a well established technique in a revolutionary manner to produce nanofibres for a variety of natural and synthetic polymers. A polymer is injected at a constant rate through a nozzle of needle which is charged to a high voltage.

The applied voltage induces a charge on the surface of the liquid droplet and when this is sufficiently high, the hemispherical surface of the fluid elongates and what is known as a Taylor cone is established. On increasing the applied voltage further, a charged liquid jet is ejected from the Taylor cone and attracted to the earthed collector, which is positioned at a fixed distance from the needle. During this process the solvent evaporates from the polymer solution, leaving dry polymer fibres on the collector.

Fibre flow path

In order to accurately capture the fibres for use and analysis an innovative and unique drum system had to be manufactured, which is where Carter Manufacturing stepped in. As well as manufacturing the highly complex drum component, there was an additional challenge of keeping the device rotating at a controlled speed so the flow of the fibres were not impacted.

The requirements for the application were beyond the standard bearing capability as it required full non-magnetic bearings able to run completely dry under high speeds of up to 13 000 Rpm under loads of 150 Newton’s. The drum was initially intended to be a lightweight solution but the design quickly leaned towards a hollowed out and tunnel bored solution of 360mm diameter and dodecagon (12 sided) shape. This presented some challenges as it significantly increased the loading on the bearings which meant it was critical to have a perfectly balanced assembly

Hamster Wheel of Death

The Nano Fibre Collector / Hamster Wheel of Death was designed and supplied by Carter Manufacturing, which supported bearing assemblies that met the strict non-magnetic and non-conductive requirements. Silicon nitride Abec 5 precision fully ceramic bearings were selected for the final production model.

Ceramic races and rolling elements were selected and manufactured from silicon nitride to meet the criteria of being a self lubricating material as well as being completely non-magnetic. The bearings were arranged as angular contact bearing pairs and were manufactured with a lightweight and non-magnetic polyetheretherketone (PEEK) cage.

The cage material was selected as it could withstand the aggressive chemicals used in the cleaning of the rig while having the combination of extremely robust, lightweight and thermally stable properties with the additional benefit of high speed capability.

Ultimately, the complex and detailed project concluded and a successful collection of woven fibre was collected from the drum assembly.

The assembly is now being utilised to further enhance the revolutionary spinal research, for which this project was designed, and could open a world of new development which could change the life of millions. In addition to the original uses many other possibilities have also been realised ranging from body armour, artificial joints and light weight sails for racing yachts

Author: Martin Wakelin, Carter Manufacturing Limited

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