Carbon Bonnet Build

[Jaime Ward]

Thought I'd make a little post about the carbon bonnets that I have made over the previous weeks.

 

First of all I had to have a mould made, I didn't have the time to make the mould myself and didn't fancy stinking the neighbourhood out with the smell of styrene for a week, so had some mates that I used to work with help produce the mould. 

 

My bonnet wasn't in the best shape, and was a bit twisted so needed to be straightened up on the car. Did this by making small adjustments to the positioning, and then making a frame on the outside of the bonnet while in position. 

 

 

Then the bonnet was taken off, flipped over and an internal frame made, then prepared to have a splash made.

 

 

Because of the scoop we decided on a 2 piece mould so if we had any issues with releasing the part we could separate the mould halves. 

 

 

Finished mould :-

 

 

 

Now for the bonnet itself I wasn't sure of what layup would be best so decided I would do a resin infusion with a layer of 0/90 RC and +/-45 on either side of a layer of 2mm coremat, with some twill weave on the scoop for decoration.

 

Mould prepped with flanges :-

 

 

Laying up the layers of fabric :-

 

 

Vacuumed down ready to infuse :-

 

 

And the part popped out of the mould :-

 

 

Infusions can be tricky, lots of variables and doesn't take much for things to go wrong. I had a couple issues, first of which was bridging along the corners. I had trouble getting the cloth to stay in place, so used spray glue to keep things where I wanted. I used too much glue in the end, which stopped the layers of cloth from moving around the corners, and even under vaccum they remained suspended, causing some bridging.

 

The next issue I had was with my vaccum line to the pump. I used a goretex type material as a barrier, but when my part was fully saturated with resin this goretex line blocked itself off stopping the pull from th pump. Bad time to lose vac, but managed to rig up an alternative vac line.

 

I was trying a new method, and my overall setup wasn't quite right. I know how to get around this on my next infusion.

 

 

 

Now I wasn't very happy with this bonnet, it was a bit heavy (4.4kgs) due to the coremat core sucking up a lot of resin, and was also extremely stiff, a bit over the top for the car. And while the cosmetics could be fixed, it would always bother me, so I decided to go again.

 

I work with composites a fair bit, usually doing wet lamination under vac, so decided on this for my next attempt. Bit dirtier, and harder to get a visually decent job, but decided to have a go.

 

Target weight 1.5kgs.

 

Two layers of woven, with strips of +/-45 between where I wanted some extra thickness, and decorative twill down the centreline and on the sides. 

 

Decorative twill :-

 

 

RC layers :-

 

 

Of course unlike infusion, for this method you wet the layers of cloth out on a table and then lay them up on the job. Not the easiest, but if you stabilise the cloth with some plastic sheet and peel it off afterwards (similar to prepreg, think of it as poor preg!) you can end up with some decent edges and not too much wandering of the weave. 

 

Finished product :-

 

 

This second bonnet weighed in at 1.4kgs pre-trimming, so pretty happy with the result. Some porosity in the top layer, would need to heat the job while it's curing to allow the resin to flow better and let entrapped air out, but don't have the kit to safely do so and leave overnight at the moment, but nothing some sanding and clear coating can't fix!

 

Next step will be to fit it to the car, going to add a foam sandwich on the rear edge where it sits on the scuttle which will make it very stiff, and some mounts for the chassis bars. Going to put a spring catch or similar on, rather than going for on of the aero catches. 

 

 

Fun project in the end, eventually planning on having a full caron body made by me so more to come!