De-mystifying carbon fibre
The material we call carbon fibre is actually a composite of different types of carbon filaments held together by a resin. Just as there are different alloys of aluminium and steel, so there are numerous types of carbon fibre filaments. All SwiftCarbon bikes use a combination of T700, 800 and 1000 filaments, to deliver the superior ride quality of every bike. These different kinds of filament can be combined in different ways. Uni-directional (UD) carbon fibre has all the strands running the same way - it's very strong in one direction, less so in others. Woven carbon has interwoven strands at 90 degrees to one another, making it strong in both directions. Which is used where depends on the desired characteristics of the frame. Keeping a tight range means that we can invest the time needed to get each frame as good as it can be. For us, the quality of the product is paramount - get that right, and people will buy it.
The development of every SwiftCarbon product starts with a vision of what the product has to do. Our unique design process spans continents. Having identified the desired attributes, sketches and concepts are swapped between our designer in Europe and our engineer in South Africa. Bicycle design is a balancing act, juggling often conflicting requirements. A frame needs to handle accurately and be stiff under power, but also deliver a comfortable ride. lt needs to be strong, yet light. And it must look good, too. Drawings become plans and computer models, which become prototypes to be tested in real action and in laboratory.
Finite Element Modelling
One of the unique benefits at different types of fibre can be placed in varying orientations within a frame, putting strength exactly where it's needed. Using Finite Element Modelling (FEM) to visualise the loads on frames on computer, we can experiment with different materials, lay-ups and structures without having to build numerous physical prototypes.
With FEM, we can simulate the loads from riding and see exactly how those loads will affect a frame design. This step is essentially Finite Element Analysis (FEA), which not long ago was state of the art. FEM goes further, though, allowing us to add, remove or change material and refine the design virtually, testing as we go along. Once a frame design is performing as we want it in FEM, we know it's worth making a physical prototype for real-world testing.
EPS Moulding System
Making a carbon fibre frame involves compressing layers of carbon weave and epoxy resin into a mould to get the desired shape. Traditionally, inflatable bladders are used inside the frame to force the material into the mould, but because the shape of a bladder can't be finely controlled there can sometimes be wrinkles or inconsistent thickness in the finished frame. To avoid this, we use expanded polystyrene - essentially the same stuff that cycling helmets are made from.
We can make EPS formers to the exact shape we want before laminating carbon fibre around them and placing the whole lot in a mould. When heated, the individual beads in the EPS formers swell. Out in the open they'd reach 40 times their original size, but constrained by the mould they exert pressure on the inside of the carbon fibre, pushing it into exactly the desired shape with consistent thickness and no wrinkles.
But carbon fibre isn't just carbon fibre: woven carbon filaments by themselves aren't very useful. What turns carbon fibre from loopy sheets to stiff, resilient frames is epoxy resin. The resin binds the layers of carbon fibre together to form a composite structure. We use Carbon Nano Tech (CNT) reinforcement in the resin for our frames. These molecular-level cylindrical structures can strengthen a product significantly, but success relies on careful manufacturing.
These molecular-level cylindrical structures can strengthen a product significantly, but success relies on careful manufacturing. lt's easy for the tubes to clump together, leading to inconsistencies. Our construction technology gives us precise control of the distribution of resin in the carbon layers, ensuring that the nanotubes can do their job - giving a stiffer and more durable frame.