Carbon Fiber Aquarium Overflow Box: Gurus, please advise!

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#1

Im looking for an alternative to glass and acrylic to construct an overflow box for an aquarium. Due to the fragile nature and weight of both of these materials, especially in the thickness required for any sort of water pressure, Im looking at other options. Carbon Fiber and Kevlar, or a mixture thereof, seems like the most ideal solution thus far.

Couple questions regarding foam and/or cloth: The box( essentially just an “L” ),needs to remain rigid, function as a weir, and not bow under the pressure of a sheet of water flowing over it.
To achieve a stronger design,would it be advisable to use multiple layers of cloth glassed together to form a single plank? Or would a foam core provide a little more girth without that added cost of a dozen layers of cloth, yet still retain a rigid, flex resistant plank?

Please refer to the CAD. The black L shaped box attached to the interior of the tank is the structure in question.

Any advice or tips from those in the know are much appreciated:cool:

Shores

#2

Basicly just an L-shaped part, I see? Probably glued into the tank using an MS Polymer, a silicone, or something more high-tech, like an MMA, a PU or an epoxy. (some of these bond well to glass)

Forget aramides, like twaron or kevlar. They bring nothing for your situation. Either think in carbon, or in glass, or a smart mixture of the 2. (I say smart, as in many cases it does not make sense to mix the 2, will explain later)

If cost was not a problem, you could use carbon throughout, up to the desired stiffness/thickness.
You could do the same with glass, in which case you will need to be slightly thicker, to reach the same stiffness. You will also be slightly heavier, as a good glass laminate is heavier than a good carbon laminate (the fibers are heavier)
It is mostly the outer fibers that take the bulk of the load. So if cost is a problem, you could use carbon outer layers, and glass inner layers. In this case the glass is basicly a core material. Keep in mind though that the carbon is taking all the load (due to their higher stiffness), so in calculations, do calculate more like a sandwich structure than a monolithic laminate.
Also possible is to use a core material of some sort. In which case you add thickness cheaply. The skins take the load, and the core is subjected to shear forces. And in your case the core should be very water resistant as well.

I might probably use carbon for the outer skins, for stiffness, use some glass as a core for the bottom part, and some high density foam as a core for the side wall (which is unsupported on the top) I would construct between 2 aluminium L-profiles. Use clamps to apply pressure. After cleaning up a bit, route the foam away on the edge, fill with epoxy, and do a final cleanup.

However, I doubt that things are beneficial. If stiffness is a problem, I would probably add some baffles to the folded acrylic part…

#3

Herman, thanks for the feedback. Yes, basically just an L shaped floor & wall. I will focus on carbon and glass and ditch the Kevlar.
Cost isn’t too much of an issue: basically whatever it takes( within reason) to reach the end goal.
In regards to the core materials; you mentioned glass and possibly a high density foam. Would a polystyrene core skinned in carbon for both the floor and wall of the “L” be recommended?
After routing the edges, exposing the core, I assume a strip of carbon should be epoxied to cover the exposure?
Good call on the baffles, it was something I was debating. The baffles would have to non restrictive to the overall flow of water. Perhaps just some triangles secured into the apex of the " L" would suffice?

Thanks again.

Shores

#4

I would not call styrofoam high density. The stiffness of the bottom is less of a concern, but you could core it also. I would use something like PVC foam (80-200 kg/m3, 5-12 lb/ft3) or anything similar. (cork sheet, balsa).

The exposed edge indeed needs to be capped carefully, and it needs to be straight, to ensure a nice waterfall effect.

On the baffles, I would probably use triangles indeed. Keep as much as possible open area.

#5

Thanks, I will look into PVC and possibly balsa.
How would one go about capping the edges? Just on assumption ,but would I route the edge off, adhere a thin strip just over the exposure, allow resin to dry, then sand?
How many skins of carbon would do use in this app Herman?
Thanks again

#6

Just from intuition if the unsupported length is 2ft, I would use 2x5.7oz on each side of 1/4" balsa or 3/8" foam.

I might even cut the top in an angle, and glue a carbon or glass sheet on, angled 45Degrees downwards, to create that nice waterfall effect.

I might even have some aluminium company custom bend a mould with a nice rounded top, which might help create an equal water flow. In that case I would probably laminate from 2x5.7oz carbon (or slightly heavier) and some 1/8" glass or slightly less (3/32" or so) in the middle. In that case the shape would add to the stiffness greatly, and it would be stiff enough. It would also have a design that is hard to make in other materials, which would look neat.

Speaking of waterflow, if you feed water every 2’, so in every reservoir seperated from the baffle, the hole in the baffle would only need to be there to equalise water level, and be much less critical.

#7

Solid suggestions, thanks. Love the rounded edge idea.
This’ll be my first project of this nature, and I’d very much prefer that the end product isn’t obviously my first project of this nature… I’ve looked around a bit at the stickys etc but can’t seem to find a basic breakdown of the carbon process and materials needed. From what i gather, Ill likely just be making solid panes, router, seal, then secure and epoxy/ clamp in the “L” orientation that I’m after? ( Aside from some of the custom work such as the rounded or 45 edge idea)
Outstanding forum btw.

#8

No, you are not on the right path. What you do is have someone fold an aluminium sheet in the shape you want. (L shaped with rounded top)

After applying release wax (or applying self adhesive teflon), you can laminate your carbon part over that mould. You WILL run into some problems, but that is the basic principle.

As for the problems: You will probably want both sides smooth, which is a bit difficult in this design. I think it can be done the following way:

-have 2 moulds made, with a 1/8" offset between them. So when you mate the bottom and top mould, you have a 1/8" cavity between them.

-release wax or teflon application

-laminate a carbon sheet on both moulds.

-use an RTMlight mat (Rovicore or similar) and soak that in black pigmented epoxy, on one of the moulds.

-mate both moulds and press to the desired thickness. Excess epoxy will drip from the sides.

-after cure, clean up and you have your part. Carbon outsides, glass inside.

#9

Well I just learnt something there about mixing glass & carbon. Thanks for the post!

#10

Look at it this way: when carbon and glass are mixed in the same fiber ply, they both get to bear the same load.

Now carbon can be compared to steel, and glass can be compared with rubber band. (in this comparison).

Now imagine a 2000 lbs object, being lifted by a crane. The lifting rope is side by side a rubber band which can hold 1000 lbs, and a steel cable which can hold 1000 lbs. The crane starts pulling. What happens…

The steel cable snaps, then the rubber band snaps.

Conclusion:
The carbon will take all the load, and the glass is just sitting for the ride. So you need to have a darn good reason to include the glass.

Which is why I think fabrics like these are quite hilarious:

#11

Thanks for breaking it down for me Herman. Its becoming clear now
I think I’ve found a local metal shop that will bend the parts for me. Will be ordering my aluminum sheeting soon. Just a couple questions in that regard. How thick would you go on the aluminum moulds? Will 1/8" suffice? Also, I’m having trouble understanding the 1/8" offset between the moulds. How would I achieve this cavity?
Also, I will hopefully be applying this concept to another tank of mine, but the design of that overflow would require the “L” to have sides, forming more of a box. I’m assuming the same rule applies for the bent mould/ sandwich method, and then to fabricate a seperate sheet so I can cut out and epoxy in the sides of the box?

If there is a Herman Beer Fund, I’d be more than happy to donate to it. :wink:

#12

For your last sentence: That will be a problem for 2 reasons:

-1. There is no Herman Beer fund (although my last name is the Dutch equivalent for “brewer”.

-2. Do not drink alcohol. Had some bad experience. (involving 3 cars and a wall)

As for the mould: 1/8" should do the job.

Cavity: If you want the product to be smooth on both sides, you need a mould on both sides. Assuming your part will be 1/8", you will need 2 moulds which when mated together have a 1/8" cavity. How to achieve this: accurate metal shaping.

On the other project: More like a square box shape, with one corner gone. That is a more complicated shape, composite wise.

#13

One other thing: do you know the company ATM in Vegas?

#14

Lol fair enough.

ATM as in acrylic tank manufacturing? I’ve heard of them. Why do you ask?

Ok I will make the moulds 1/8". In regards to the 1/8" cavity: since both of the bent pieces of aluminum are flat surfaced, and the 90 angle on both will be the same, then I guess my question is, what will prevent them from mating completely flush?
3/8" on the rovicore since I won’t be using the balsa core?
Forming the “L” and installing corners to form a box via epoxy isn’t an option?

Thanks , much appreciated.

#15

On the cavity: If you skip the “waterfall” part, then the moulds will be flush. In that case your moulds could be just L-shape aluminium profile. Check them for straightness before you buy.

You can create a cavity by adding some spacers, which could be anything, like nuts, self adhesive silicone profile, or even mixing sticks (sacrificial)

For a complete box shape, you could glue 2 L shaped parts together, although the glue line is a bit flimsy. But it could work.

#16

Copy that. Regarding the glue line. Forgive me, are we talking an actual adhesive or epoxy for the corners?

#17

Epoxy adhesive, (Araldite 2000 series for instance) or an MMA glue.

Will answer your mail tonight.

#18

Herman, nothing is cut and dry in the world of composites, you know that. A hybrid fabric is not just for everyday use, or all applications either. They are for specific things. Take armor for example. Most common is glass. What if you want to make a structure armor. You want high stiffness, and have the elasticity and impact resistance of glass. Same thing for a non-ballistic application, where you have a VERY large structure. You need the glass for structure and ridgity, but the carbon is there to gain higher strength due to size. Don’t forget that sometimes these fabrics are held together by even another fiber.
Don’t discount hybrids, because they are very valuable to have for specific uses.

#19

Can’t seem to find Araldite avail here in the U.S.
Any thoughts on MMA Ext350 or 500? http://www.extremeadhesives.com/acrylics.php

#20

Ask these people:

http://www.huntsman.com/advanced_materials/a/Customer%20Service/Americas

But the MMAs in the link look OK to me as well. I would prefer a black or dark grey glue, but you can mix MMA glue with black epoxy pigment. (on a piece of card). It gets a bit messy, but it works.