Yet the tiniest void in components can compromise the performance of these critical components. Gareth Ridge, operations manager at Ultraseal International - Slough, explains how porosity sealing can help keep teams focussed on the prize.
Carbon fibre is one of the modern age’s great inventions. Strong yet light, carbon-fibre reinforced polymers are the composite components found in industries from oil & gas to aerospace to sports equipment.
One of the biggest beneficiaries in carbon fibre manufacturing has been in F1. The use of composite materials has been instrumental to the technological strides made in the development of Formula One cars over the past half century, where the lightness of the material helps to avoid loss of speed, while its rigidity and robustness protect drivers during collisions.
Achieving this balance of weight and strength depends on absolute precision, yet by their nature, the weaving together of separate fibres means that microscopic gaps can appear during manufacturing. This tendency towards porosity must be counteracted, to avoid air or fluid leaking from components or moisture ingress into components and compromising their effectiveness.
Consider the gearboxes used in F1. These gearboxes cannot be porous - this would severely impact performance and damage other critical components. And these aren’t inexpensive items, sometimes these gearboxes are worth tens of thousands of pounds. Gearboxes can be over 1m in length. Other components such as fuel pipes, oil sumps, air pipes, fuel tanks which must not leak too, as porosity in such components can lead to a race car retirement.
Based at Ultraseal’s Slough facility, the Impregnation Service Centre is used extensively to seal carbon fibre components. Components as critical as those found in F1 cars are impregnated twice to ensure that they are completely sealed. Generally, the double impregnation process consists of the following sequence of steps:
Components are packed in a basket and protected using Netlon to prevent damage
- The basket is placed into autoclave, where initial impregnation takes place
- Excess sealant is drained
- The component undergoes a manual hand wash to remove excess sealant
- The component then goes through a hot cure process at 95 degrees Celsius which polymerises the Ultraseal sealant.
- The cycle is repeated.
The cold wash is important because of the geometry of components. A pipe could easily become blocked with sealant; therefore it must be washed out thoroughly. This is generally done manually to ensure no blockage remains; a more labour-intensive process but having a trained operator gives customers the peace of mind that it is quality-assured.
Curing takes place either in hot water – the typical choice – or in ovens. As Rohacell, a honeycomb structure designed to improve the component’s internal strength, expands in hot water, risking damaging the component, if Rohacell is present, an alternative oven-based curing method is used.
Another factor to consider is the lightness of carbon fibre components, which must be packed carefully to avoid damage during impregnation. In Slough’s two top-loading machines, each component is packed with Netlon, a malleable plastic netting that keeps components separated.
Physically, each impregnation cycle takes about an hour for hot water cured components, with a cool-down period between cycles. Oven curing takes longer: around 3-4 hours for components containing Rohacell. Even so, this means that a component can be sealed and returned to the team the same day.
Any component that benefits from balancing maximum strength with minimum weight, will likely be manufactured using carbon fibre components – and that means the question of porosity sealing must be answered if they are to achieve peak performance.
