What are the advantages of thin-walled composites tubes?

When it comes to thin-wall tubes for applications where stiffness and robustness requirements have generally favoured the use of metals because of their high stiffness and relatively low price. Traditionally, composites have not been able to replace metals in these applications because glass fibre composites, while lighter, lack the necessary stiffness. Alternatively, carbon fibre composites, while being mechanically suitable, may be considered too expensive. Patrick Loock explains why manufacturers should reconsider using composites thanks to advances in customised hybrid composites

Generally, thin-wall composites are anything with a thickness between 0.9mm and 2mm and are used for a variety of applications across many different industry sectors, including camera tripods, window cleaning poles, IMR equipment, telescope poles, and camouflage support poles.

Traditionally, metals such as aluminium and steel are used in these applications. Sustainability trends and light-weighting are pushing manufacturers to improve operational efficiencies by reducing weight without sacrificing mechanical properties. Typically, we see this is when composites are considered, and we are always asked how could composites replace metals in these applications?

Tunable mechanical properties

For thin-wall tubes in industrial applications, stiffness is a key consideration. Aluminium, which has been the traditional material of choice for many, has a stiffness of 70 gigapascals (GPa). Glass fibre, which is often the first choice for composite solutions because of its relatively low price, provides the desired weight savings compared to aluminium for tubes of equal dimensions but only has a stiffness of 35 GPa. Therefore, to match the stiffness of aluminium, usually thicker tubes are needed, impacting existing design specifications and reducing weight savings.

Carbon fibre composites tick all the boxes in terms of mechanical properties. They are much lighter than metals and boast much higher stiffnesses, with basic carbon fibre tube having a stiffness of 120 GPa and high-modulus carbon fibre tube having stiffness up to 210 GPa. However, carbon fibre composites are also more expensive than metals, with solutions costing around five times as much. This is where hybrid composites come in, providing the best of both worlds.

Hybrid composites, a combination of both glass and carbon fibres, allow manufacturers to tailor mechanical properties for any given application without changing the specified dimensions of the tubes or poles by adjusting the ratio of glass fibre to carbon fibre in the structure. For example, for window cleaning poles, a customer might require a pole predominantly made from glass fibre for cleaning two-story buildings but need something with a higher ratio of carbon fibre, providing extra stiffness, for poles intended for cleaning five-story buildings. This is a simple task for an experienced composites partner to produce composites tailored for your specific application.

Benefits of volume pull-winding manufacturing

For high volume cost-competitive composite production, continuous manufacturing processes, such as pultrusion and pullwinding, are advantageous because they ensure consistent high-quality production and high levels of repeatability. Pullwinding is particularly useful for manufacturing hybrid composites because it allows for cross-directional control of mechanical properties and selective reinforcement of the thin-wall composite tubes, meaning there is no wasted material and costs are kept as low as possible.

It does this by combining the unidirectional alignment of fibres with the helical winding of reinforcements, resulting in the ability to control unidirectional fibres and helical winds, from a few degrees up to 90 degrees. 

Manufacturing thin-wall composite tubes is possible using other manufacturing techniques, such as filament winding, however, these require more manual steps and are more suited for thick tubes with large diameters. Furthermore, because they involve more manual steps and smaller manufacturing volumes, it is often the case that thin-wall composite tubes manufactured using filament winding are more expensive.

By working with an experienced and knowledgeable composites partner who understands your application’s requirements and operational challenges, you can ensure you get the optimal solution for any given application.

Patrick Loock is segment business owner for products and applications at composites tubes manufacturer Exel Composites.