Hood construction

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#1

I have noticed on some carbon fiber car hoods the weave looks sort of distorted in pictures… almost like there are waves under the carbon fiber. What is the best way to lay up a hood so the weave and finish is perfect looking?

Also does anyone know of what mold release to use with epoxy surface coats? I am using TR104 and the epoxy likes to bead up and is sort of rejected by the mold release. I let the epoxy stay beaded up for about 15 minutes then went back with a brush and it seemed to help elimnate the beading, but not 100%. So i’m thinking there must be a better mold release for this?

#2

Do it right!
:slight_smile:

#3

I wonder if some look slightly wavy because they were not vacuum bagged?

Yep, I prefer to work the right way :slight_smile:

I have 3 hood ( make model) I want to make molds for. Money being the big factor for molds since I have to use epoxy tooling and buy the oem hoods.

How would you layer the mold laminate as far as this cloth first, this one second, and so on? How thick should I build the mold? I do want to egg-crate the backside with wood or steel frame.

#4

it usually has to do with the worker that places the carbon in the mold. if the hood was a wetlayup-vacuum bag process and too much resin was used on the first layere it tends to float and slightly distort the carbon. take your time doing it right and keep your RC down, youll have no problems. also a clear surface coat/gelcoat thats not very flat can also cause distortion.

I always recommend semi-permanent release agents with any mold personally. its a industry standard. many different companies available. call them up tell them your application, there hundereds of different semi-releases ment for different applications/processes. dont forget the sealer! a very important step that tends to be forgotten. keep the caps closed and tight all the time! Also do a tape test before each layup.

#5

Depends on what your going to do with the mold. if its high temp mold you should make it from solid carbon fiber(depends on the part but 5-6mm thick is common), high temp surface coat and epoxy laminatin resin. a very balanced laminate. vacuum bagged or infused. with a carbon structure. post cured correctly.

a non-high temp mold would be similiar but you do no need to worry as much since it doesnt see heat cycles. you can use fiberglass cloth just fine for mold and structure.

#6

Thanks Hojo,

The molds will be room temp cure using fiberglass.

I guess with the part itself… i am going to use epoxy surface coat applied with a roller or brush.

Yeah i was kind of surprised to see a name brand $1100. hood have distorted weave.

With non-prepreg carbon fiber can i spray glue 4oz fiberglass cloth to the underside of the carbon fiber so it does not loose it’s weave alignment? Since this is a large part and I would be using 6oz carbon twill.

I emailed the resin supplier to ask what mold release I should use with their surface coat.

#7

In my opinion you shouldnt have a problem getting a straight weave on a hood. just dont man handle the material. always cut on a nice table when your ready to make the part, tape where your going to cut with masking tape. attach to poles if the piece is big. carefully place in and look at a low angle to make sure your carbon is straight in both directions.

ofcourse spraying 77 then placing a light glass down on the carbon will hold the carbon together much more. but its best not too since the 77 is a contaminant. the method is good if you need to have multiple pieces of carbon on one surface and you want to have hard cut lines.

Look in to Axel release agents.

#8

plus if you use a glass backing there’s a chance you will be able to see it through some of the pinholes in the carbon…

#9

If you use a slightly heavier cloth you will have no problem.use a 250 - 280g as apposed to the commonly used 200g.Weave is much tighter than on the lighter cloths and still easy to work with round curves.Tends to stay together better and not distort as easily

#10

or just use a glass scrim on the carbon…but I think the idea was to make the carbon weave in place, not use one layer of CF and one layer of GF, and that’s all :slight_smile:

And Deetech…even with a heavy cloth, you can still get weaving imperfections and see through it.

#11

i agree with deetech however i believe its down to the quality of each fabric too. the 240gr twill i used last time was so much better than the 200, tightly woven and not fraying so easily. they both come from the same company too.

btw,even if you have some pinholes in the carbon,the glass is gonna turn transparent when its wetted out anyway…and in the end, you re gonna paint in black from the inside anyway…

#12

true enough I guess…

#13

Quote: “Also does anyone know of what mold release to use with epoxy surface coats? I am using TR104 and the epoxy likes to bead up and is sort of rejected by the mold release. I let the epoxy stay beaded up for about 15 minutes then went back with a brush and it seemed to help elimnate the beading, but not 100%. So i’m thinking there must be a better mold release for this?”

Yes, I’ve found this ,too. The only option I know of is using pva. The resin won’t bead up or fisheye on the surface. TR104 is a great release, but I’m told it contains silicone which gives it it’s high temperature properties, but causes the beading. I usually use Frekote 770(I think that’s the number) but this ,of course, causes the beading up as well. However, there are many different types of Frekote, does anyone use one that has low-slip properties that allow resin to be used as a surface coat?