Wet pregs

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
I used and like to make my own "wet pregs" on 90% of mold jobs. Its just dammn too easy to wet all fiber on flat table. But if you go to some bigger one sizes, you need more mens skilled in composites, or nice and big rollers.

This one here is maximum size which one could achieve as per size part / complexity.

And that one is kind of a dream of everyone who need to make composite in "calmer" way.

- machine sprays 12 streams of epoxy on foil at constant speed and pattern, and putting fabric on top of it. And another foil on the top if needed.

What is between of two of them ?

Put gravure roller

1637328394428.png

Into this one glue roller ?

1637328430233.png

1637328498912.png
 
Last edited:

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
7,149
Location
US
Looks attractive. Some of the things that work well with paints and glues would need modification to work with epoxy (e.g. might be difficult to get the epoxy cleaned out of that gravure roll).

Thanks for the ideas. Seems appropriate for one-off or a limited run where it's not worth the setup and trial/error to get a reliable infusion rig worked out.
 

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
Seems appropriate for one-off or a limited run where it's not worth the setup and trial/error to get a reliable infusion rig worked out.
Infusion for one-off is always trail and error. And for 200 gsm cf with some core is 70% of epoxy in trash due to flow mesh. Or soric with 710 or 1000 gsm of epoxy penalty..

Will wait for other ideas, but i think i have one, absolutely KISS.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
7,149
Location
US
It would be convenient if the resin and hardener were supplied separately and mixed very close to the spreading roller (to minimize waste and avoid exothermic runaway due to a large lump of mixed epoxy).
Maybe a ratio pump on the bench pushes the resin and hardener in the proper proportion through two separate tubes to a small combining/mixing plenum at the roller or squeegee.
Not very KISS, though. It would require some means to throttle the fluid flow.

Or, totally mechanical: The rotation of the application roller drives separate peristaltic ("roller") pumps for the resin and hardener. The mix gets applied to the application roller or flows through holes in it to fabric. The application roller and mixing chamber are disposable. (Okay, still not very simple. :) )

Do we need an application roller? If we have an electric mixture pump on the bench, a hardener and resin tube that just combine in a small mixing chamber right at the head/nozzle and the stuff gets dispensed across a squeegee blade. Pull the trigger switch to get more goo and just spread it out on the fabric with the squeegee. Then, work it further in with rollers and squeegee.
 
Last edited:

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
Do we need an application roller? If we have an electric mixture pump on the bench, a hardener and resin tube that just combine in a small mixing chamber right at the head/nozzle and the stuff gets dispensed across a squeegee blade. Pull the trigger switch to get more goo and just spread it out on the fabric with the squeegee. Then, work it further in with rollers and squeegee.
Problem that we need 40%-45% of resin per weight applied to each area of fabric. Not impregnation itself.. As in second video - 12 sprinklers cover foil.
 

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
10,045
Location
KWHP, Los Angeles CA, USA
Are we talking about making this easier for a garage homebuilder, or are we talking about production volume for production airplanes? Huge rollers and spray nozzles certainly are very clever solutions for large sheets (wing skins and such), but how much time and effort is saves for a production run of one or two airframes?

The big breakthrough AFAIC would be the development of lower viscosity resins that can wet out the cloth faster and easier. In my very limited experience with composite layups, wetting out the cloth was the most tiresome and potentially failure prone part of it. If it had been possible to just thin the epoxy resin way down with MEK, without having a negative effect on the strength or performance of the final cured resin, that would have made me a much more enthusiastic proponent and experimenter with composites.

But I was always told you can't do that without messing around with the performance of the resin matrix. If that were to change...
 

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
The big breakthrough AFAIC would be the development of lower viscosity resins that can wet out the cloth faster and easier.
Heat it with hot gun or fan for 15 seconds or so. But it have to be high viscosity to be ok to work with it later.

All this is for small shop. Not pro level.
 

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
KISS (not the most optimum. ):

You need this one (or other non-strech line)

1637428899471.png

Big syringe and some pulleys (or empty tube from glue).

1637429212571.png

And math is simple. For 200gsm of epoxy delivered.

We have 10 nozzles which covers 200mm width of our fabric. 200*0.2 = 40gsm. Epoxy density is 1.15. 40/1.15 = 36cc of epoxy per 1 meter of our impregnator travel.

Our dosing syringe bore is 50.4mm. Or its area is 20cm2. For 1 meter of travel we need an 36/20 = 1.8cm of piston stroke.
Or 100/1.8 = 55.5 mechanical advantage ratio. Or 56 pulleys in total. And for 5m2 of wing skin - we need 56 pulleys and 25 meter of Kevlar line. And 50cm of our syringe length. So it is a little bigger than caulking gun.

Maybe it is too clumsy, but its all depend on size of pulleys. But it will be light to operate - in this advantage ratio, you will not fill any tension from line.

So you impregnate one line longitudal, go back, mount you line onto next arbor positioned 200 mm and repeat.

For thicker laminas, you could change number of pulley, or just rotate you line of nozzles from 90 degree. At 45 degree it will give you 1.41 more resin..

Pure math. Ok for Medieval or Ancient time.

But ! we can change that system of pulleys to some ball-screw driver for our piston with gearbox.
 
Last edited:

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
Lets make it more compact. And easier. And ommit that gearbox.

Ballscrew 1610. We need to rotate it 1.8 times per 1 meter. Which gives us a puley with 17.69 cm. Simple and compact one. But not the most one :)
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
7,149
Location
US
Caveman approach:
If we just want to get the epoxy quickly spread evenly over a relatively large expanse of fabric, then maybe use a refillable caulk tube (10 oz = 296 ml), a spreader device (3" wide is commonly available for applying glue to floor coving/molding), and either a manual caulk gun ("4 squeezes per stripe") or a cordless caulk gun. Pretty simple, and with some practice and modifications, it might be very repeatable. Probably fairly rough on the hand/grip, but a battery powered caulk gun solves that problem and allows for an adjustable/repeatable flow rate. In this case, the "spreader" is just a way to dispense epoxy over a 3" wide strip through 11 nozzles, the spreader wouldn't need to touch the fabric (or, you could attach a roller behind it to spread the epoxy without pulling on the fabric). By your math in Post 8, 10 oz of epoxy should cover approx 1.9 M2 of impregnated cloth at a rate of 200g/m2.

- Refillable 11 oz caulk tubes (4 pack, $15.50)
- Caulk Spreader--11 holes, 3" wide (generally ($3-$7)
- Ryobi cordless caulk gun ($50. Has variable speed selector to adjust dispensing speed/flow rate. 200 tubes per battery charge).

More Involved:
If we want to do a lot of this, there may be some advantages to a device that holds the epoxy in a pool, dispenses the cloth vertically. Pull the cloth and both plastic skins out and lay it on the table with the plastic already on both sides. See attach. Adjust resin content via the roller pressure setting and the roller composition (metal, hard rubber, soft rubber, etc). Maybe relatively few air bubbles if the epoxy is thin enough and the fabric is advanced slowly?
Don't we risk having the epoxy cook off if we mix it and leave it in a lump/pool while we are waiting to get it onto the fabric in a thin layer?
 

Attachments

Last edited:

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
If we just want to get the epoxy quickly spread evenly over a relatively large expanse of fabric,
My goal is to spread it evently. For quick one we could bucket approach. But it will be far from being consistent. If we do it consistent - it is a win-win scenario. We get superb characteristics of composite at lowest weight possible. On three layered construction we do not need a perforation in our core to drain excess epoxy to our breather.. because we do not have excess epoxy.

And beeing a caweman - electricity is a no-go.
 
Last edited:

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
7,149
Location
US
I inserted the "NOT" below into your statement. Have I got that right?
On three layered construction we do [NOT] need a perforation in our core to drain excess epoxy to our breather.. because we do not have excess epoxy.
And beeing a caweman - electricity is a no-go.
I'm always looking for an excuse to buy another Ryobi cordless tool to add to my collection.

Three questions about this homemade prepreg:
1) Do you use perforated plastic and bleeder on one side to get trapped bubbles out of the layup?
2) Do you do an entire multisheet layup schedule between two pieces of film at once, or do you use peel-ply and do multiple cure sessions?
3) For curved panels (simple 2D or compound 3D with fabric suitably cut) against a female mold, do you leave the outer plastic film in place, or do you remove it and put release paste on your mold?

Thanks.
 

Hephaestus

Well-Known Member
Joined
Jun 25, 2014
Messages
2,363
Location
YMM
Might look at the x-winder feed mechanism- pair of rubber(?) rollers partly in the tray, material runs through the middle, then you drip as it climbs away. Might be able to squeegee / run through a second pair of rollers with squeegee to reduce that to a less wet mix.
 

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
I'm always looking for an excuse to buy another Ryobi cordless tool to add to my collection.
I change Ryobi for wedge rail. For 1250mm width fabric. As per earlier example - we need a a travel of piston in our dosing syringe 18 mm per 1000mm of travel. So - we just take an closed shaped aluminium box as a main rail, 1500mm length. Make 3 simple roller to ride on edges A, and make third (B) Extra rail (slot, angle iron.. etc). Where B one is inclined at 18mm per 1000mm. And our syringe with 10 nozzles rides on A edges, and B edge is used to power a piston via some roller. After each pull or push, we mount our main rail to another slot mounted on the wall or edge of our work table and repeat. And reset piston "pusher". Same as in caulk gun. We may want to have some extra leg in our main rail to make it square to our table.

But this primitive computer will deliver epoxy in +-5% tolerance per whole area of our fabric. Cover it with PE foil, roll it and all is nice as it should be. And if we made our B rail inclination variable - we can tailor our epoxy deliver for each fabric used.

1637521021933.png
 
Last edited:

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
1) Do you use perforated plastic and bleeder on one side to get trapped bubbles out of the layup?
2) Do you do an entire multisheet layup schedule between two pieces of film at once, or do you use peel-ply and do multiple cure sessions?
3) For curved panels (simple 2D or compound 3D with fabric suitably cut) against a female mold, do you leave the outer plastic film in place, or do you remove it and put release paste on your mold?
1. Yes, and to take all extra/excessive epoxy. Do not know, will bleeder be needed to take all bubbles. In pre-preg bleeder a not used as far as i know.
2. Yes, i try to design it to be able to do all layout in one shot. I have a lot of helper who want to help. But their experience may vary.
3. I will not make any "normal molds". I totally converted to film on foam as molds. Or cnc hot wire cutted or cnc milled.
 

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
Might look at the x-winder feed mechanism- pair of rubber(?) rollers partly in the tray, material runs through the middle, then you drip as it climbs away. Might be able to squeegee / run through a second pair of rollers with squeegee to reduce that to a less wet mix.
My number one task is consistency of epoxy amount per area delivered. You can't get below 50/50 with bucket and squeegee, because at 50/50 some places will have extra epoxy, some will starve.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
7,149
Location
US
Anybody: For projects like this (testing a device to rapidly and evenly spread epoxy) do we have a good simulant for mixed epoxy? Something with approximately the same viscosity (or that we can easily thin as needed to the viscosity of our chosen epoxy), is cheap, readily available, and easy to clean up? The first thing that occurs to me is honey or some type of syrup (cheap pancake syrup, molasses, etc). I suppose the right motor oil would work, but what a mess it would make. Water soluble would be best.
 

stanislavz

Well-Known Member
HBA Supporter
Joined
Aug 21, 2016
Messages
1,113
Location
Lt
I think you could use some water, sugar and starch or jelly mix. If any roller like spreader you will gave to add some coarse pigment ant test to its uniform cover. Like chalk for example.. in epoxy wayyou will have to cut your sample to small pieces equal size and measure it to find a distribution of glue to fiber ratio, and tailor you impregnator setup for it...

But ! If you go my way - dosing syringe and fixed number of nozzles you need only to calibrate each nozzle while stationary. Dosing itself is relied to you stroke per travel. Which is easy to make with that wedge rail.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
16,135
Location
Memphis, TN
Why not like an old style credit card receipt machine. Lay the cloth on bag material saturate, hold ends, have a roller tracked to the table and troughs to catch excess. Maybe two starting from the center so the cloth doesn’t bunch up.
 
Top