Flanges and fibreglass thickness question

General Composites Discussions Composites Talk
#1

Being a total newbie at this “fibreglass” thing I was always under the impression that whenever you make a mould you would always have to make some flanges on it (this was from after reading tutorials on this site and other forums/sites).

But then after searching a bit more, I see that people make moulds like the one pictured below for example without any flanges

So what my question is, when do you need to make flanges and when do you dont? Is flanges only required when working with cf for vacuum bagging and not fibreglassing or something?

Also another question I have is, what is the advantage of using multi-layers of fibreglass against one thick layer? For example I wanted to make a part that was equivalent to a thickness of 600csm. Now I can use 4 x 150csm layers or 2 x 300csm layers, what would be the adv/dis of both?

Im assuming the one with more thin layers would be more “hard”? while the one of less thick layers will be more flexible? Also how would this apply when using chopped strand and cloth?

Sorry for all the questions, Im just planning to make my first bumper mould and would like to make it in one go rather than wasting time and material and having to do it twice. For a bumper mould how “thick” would one recommend anyways? and for the actual item? I plan to add some flex additives in if possible.

#2

Ill take a stab at this one.

Flanges can work for … a couple of things

  1. multi flanged part means the part will never come out b/c of the shape. i always use the egg/ball/cyl. shape in this . If you have an egg, how do you mold it? you flange it by putting it right in the middle. and the part will come out

  2. yes sometimes just for vacumm bag/infusion, it helps put the bag on something instead of all the way around.

now in the thickness part, try putting a thick piece of carbboard on a 90degree corner, and then try putting a piece of paper on a 90 degree corner. which will bend better? :wink:

#3

The picture uses flanges…look at the end caps bolted to the rest of the mold.

No you dont need to use flanges…at all. you can simply make a mold over the part…but its alot harder to work with a mold that has jagged edges all over it and no real good placed to get at the part.

Mold thickness? 4 times the part thickness…you dont want to have your mold warp from the heat of the part curing.

Bumber material thickness? As the guy above me said…chopped strand matt in thickness is a royal bitch to work with.

I build my molds up in thickness with 3.5oz CSM and I have to peel it in half or it wont wet out easily or flex how I want it to.

Personaly I wouldnt make a part in chopped strand matt…that counter intuitive to making a nice part that doesnt take a chopper gun to make. You should use 2 or 3 layers of surfacing veil…and then build up some layers of 6-9oz plain weave and on each layer orient it a different direction so it gets the maximum strength possible.

The reason people hate on alot of kits is because people use crap or take little time to build parts…CHOPPED STRAND MATT is not a good material for thin parts of strength…or strength period.

the only thing I could see using chopped strand matt for is body tubs…and Id use a chopper gun at that…so I wansnt trying to build a car body for 8 months…

If you need any more explanation Im sure I or anyone here regularly can help you out.

#4

Better tell all the makers of GRP yachts that CSM has little strength…but would have thought they must have figured this by now!

Also know a laminator who has been making motorcycle parts (including fuel tanks) for nearly 30 years who also hasnt found out about the weaknesses of CSM…

Finally parts made using a chop gun will never be as strong as properly hand laminated items, but chop gun is fine for making things like fish ponds, or cosmetic car parts.

#5

Im not talking about 1/2 thick parts…like you see in big boats or car bodies.

The nature of chopped strand matt says that its not as strong as weave…nothing holding the small strands together but resin.

I wouldnt use it for anything that I could use plain weave on…the plain weave would be stronger and thinner and lighter in the end.

#6

Sorry if I didnt make my self clearer, but I’ll try another stab at this.

Yes I understand that the picture of the bumper mould I have above DOES have flanges and that can be seen at the end wheel well part. What I dont understand is that I was always under the impression that you needed to make the flange go around THE WHOLE PERIMETER of the object. Example of this is like this picture here:

Lusin: What I meant by the thickness part is this; Imagine I had two pieces of wood. One is just a piece which is plain and is 1 inch in thickness and the other one is made up of two pieces of seperate woods 1/2 inch thick each glued together to make a 1 inch piece. Out of the two which would be more strong and flexible?

Now apply this same theory to fibreglass, what is the adv/dis of using 1 thick layer of fibreglass compared to using 2 thiner layers which in reality gives the same thickness as the one layer one?

Now i understand plain weave cloth is better in strength due to the fact that its woven and the strands are continuous, but isnt this item more suitable for flatter surfaces? Since it is one larger piece isnt hard to use for something like a bumper which has heaps of curves?

What is the recommended thickness to make bumpers anwyays? 2 layers of 300gm csm? what about when using plain weave? Also would there be a different requirement when I use plain polyester resin and when I use something with a flex agent added?

Once again sorry for all the questions and thanks for taking your time reading this and giving your opninions.

#7

If you are using vacuum then you must have flanges. There is no need for flanges if you are laminating by hand.

In regard to strength of CSM parts the motorcycle tank/seat units we make use a lay up which is only 3mm thick in some places, and never had a single problem over 3 years.

#8

The image above is from my mold building tutorial ;). The flange around the perimeter is used for vacuum bagging or vacuum infusion. The bumper above doesn’t have a true “flange,” per se. The mold pieces that bolt on near the wheel wells really shouldn’t be considered flanges. The “wrap around” is an intergral part of the bumper. That picture is just a plain multi-piece mold, IMO.

#9

Depends on the situation. Along one axis, a single piece of would would be better. However, when load is introduced along another axis, 2 pieces glued together would be stronger (ie. plywood).

2 thinner layers will be better because you can orient the individual layers to have more strength along a certain axis. For example, a single ply of plain weave will provide strength along 0 and 90 degrees. A second ply can be oriented 45 degrees away from the first ply. This will provide more strength than a single ply.

Thicker cloths are usually better suited on flat surfaces. Lightweight cloths will conform to bumpers with ease. Different weaves (ie plain, twill, 4 harness) also affect conformability.

#10

Thanks alot guys and especially you perfeng702, most of my questions are pretty much answered by now.

Im guessing on the point about the multi-layers thing, it doesnt apply to csm does it? considering its already layed in different directions and multi-axial. I’ve never used plain weave before so I guess its time to experiment with it.

Only question that I still have left is how many layers of plain weave or csm (and what weight) are you guys using on your bumpers?

#11

I dont make anything less than 8 layers of 6 oz thick.

Im not striving for low weight…Im trying to make a good part.

#12

A heavy inflexible part is liable to crack rather then flex, and its never a good idea to make parts any thicker than required.

Eglass off road bike cosmetic parts made by a friend of mine are around 2mm thick, and according to a bike importer here in the UK, these are a lot better than the 3mm thick parts that they are currently getting from Spain.

#13

My parts consisting of 2 layers of tex and 6 layers of eglass are about 3mm thick…they flex and look good.

Im not interested in making any race body kits.

there are enough knucklheads doing that crap here in the states already…the prices are way too low to play with. I get way more for cosmetic cool guy parts that I cant afford to have so much flex that they turn into a liability.

I build parts for pretty…and they sell pretty well so far.

#14

Poorly made race parts are indeed crap, but I would say properly made lightweight parts that actually fulfil a function, rather than just look nice and are merely cosmetic, seem to me a little more satisfying to make than the cosmetic stuff.

Personally I quite enjoy making functional competition items, but dont know if I would feel the same about making things that didnt actually do anything much.

#15

You and I are from the same school of thought but I gotta tell you…I make my money from “looks pretty” so I can go racing with my own hand built “functional monster”

I cant stress enough about how tight the market is with racing composites in the US hell one of our members here (cheetah Jeremy) works with a company that I cant compete with. They have hundreds of molds and will furnish a complete racing body kit for 400 dollars US…sound kind of silly for me to go and make molds off of one or two bikes and try to nickel my way in the door.

I make some trinket parts for this or that and get way more money versus my time.

So you make what you make and Ill make what I make, so long as we both make it to the tracks we love I see no harm.