Closed Mold Infusion

General Composites Discussions Engineering Talk
#1

Hi,
I am trying to build a constant chord wind turbine blade (no twist or taper) from fibreglass using a female mold and a male core mold. I have a diagram but I am not allowed upload attachments for some reason so I will explain in words.

The female mold is in two halves, the top airfoil section and the bottom airfoil section, when the halves are clamped together the resulting void is the shape of my blade. The length of the blade is 2.5m and it’s 165mm wide.
The male core or mandrel will be made solid from casted resin in the same profile as the airfoil except reduced by a scale so that when placed inside the female mold there will be a 6mm gap all the way around between the male mandrel and the female mold.

What I intend to do is wrap the mandrel with my dry fibreglass and build up the required thickness with multiple wraps, place the mandrel ontop of the bottom female mold, place the top female mold on top and clamp. At one end of the mold I will attach resin inlet feeds and at the other end attach a vacuum line. The mold will be sealed so that there are no leaks.

I have not worked with infusion before so I’m asking if this process will work?
The reason I want to do it this way is so that the blade is one structure meaning that there are no flanges that could introduce weakness. I know I could just do two halves and join them once cured.
I want to be able to remove the mandrel afterwards which is where I am a little concerned, I know I need to prepare it someway. I was thinking of using a release wax, then a plastic barrier, then a flow media and then the layers of fibreglass, maybe I need
a peel ply, unfortunately I’ve no experience with the use of these materials so not sure if this idea will work?

I can use hydraulic pullers if necessary. I know it would be better to have a tapered mandrel but this would be very difficult for me to make and I thought I would try the easier straight mandrel first. Is the pulling power needed absolutely huge and in danger of ripping the thing to pieces if the mandrel is not tapered?

My concerns that I would like advice on:
Will the resin flow the 2.5m and fill the 6mm gap assuming I have a good vacuum pump and no leaks? (low viscosity resin)
Will I be able to remove the mandrel?
Am I missing something very obvious?

I have read about other ideas such as bladders, diagionally split mandrel, freezing the mandrel so it shrinks and a few more.
These all seem to solve the problem but involve more work. Not saying that I’m not prepared to do the work, BUT if I can use a simpler method that works then thats where I want to try first.
Thank you for any help.
ruairihev

#2

can you just use a lightwweight polyeurathane foam mandrel/core and just leave it in there? It will not effect the structural properties of the blade, but will keep it rigid.

Resin will flow the 2.5m to fill the 6mm gap, but you will probably need a glass makeup with a flow media inbetween layers to assist resin flow.

As for infusing, it can be done several ways;

The common way would be to have a resin chanel running right around the perimeter of the mold cavity, allowing resin to flow from the outside to the catchpot in the centre. unfortunately, this is difficult as your part is incredibly long, and narrow.

The other way would be to infuse from one end of the mold, and have the resin get drawn through to the other end. you can also have multiple injection ports along the length of the mold.

You may also want to have several outlets along the length of the mold, and shutting them off one at a time, as the resin reaches them. This is worth a thought due to the length of your part.

FYI, if you do use a removable mandrel, you should have some sort of taper. removing anything from fibreglass, no matter how good the release agent used is, will be difficult with no taper at all.
However, if you decide to make a lightweight non removable foam mandrel/core, you can make a mold for that, and just cast it yourself

#3

Removing a non tapered mandrel is impossible. It will rip the part to pieces.

Either taper the mandrel, or use a foam part. The foam part can have grooves for resin flow, in which case 2 meters should be no problem infusing from one end to the other. (I would suggest putting the whole structure upright, so gravity helps avoiding dry spots).

As youare in ireland, I suggest looking into a product called “Polymat” made by Scott&Fyfe in Scotland. Using tis as a first layer will create enough permeability to infuse the part.

Your challenge might lay in getting the 2 moulds closed airtight. For the rest I see no problems.

#4

Hi Ruairi,

tried to pm you there with what I reckon will be pretty useful for you, however, your profile doesnt seem to accept pms, so drop me your email or mobile and ill give you a shout

#5

Thanks to all for replying. The foam mandrel could be an idea, I was trying to avoid this as I thought that if water gets in the foam will soak up the water and cause an imbalance in the blades as they spin. I would need to make the blades water tight to avoid this issue, after the blade is made I need to drill holes in the root so that I can fix the blade in place using bolts, the seal would need to be water tight here. I would prefer to have hollow blades but if needs be then the foam core is the route I will go.
Thanks for the Polymat reference, never heard of it but it looks like the stuff I need.
Findhan, as a new user I have very limited access to the site, must be to do with avoiding spam, I’m sure as I reach a certain number of posts the settings will allow me more access. Thanks for your offer to help me, here is my email: ruairi hev at g mail dot moc
I have made it a little cryptic to avoid spam picking it up but I’m sure you will figure it out. All one word, no spaces. moc = com.
Regards
ruairihev

#6

composite grade foam is closed cell and will not uptake water or resin. Only at the surface cells that are cut open by cutting/drilling/etc…You should have no worries about it.

#7

I’m tired so please forgive me if i misread something.

You should use flow medium or a core and cloth that flows resin made for infusion.

without infusion materials the resin will only travel about 8 inches or so.

also use a resin with a long gel time.

#8

it is entirely possible to make a mandrel with complex shapes that is not designed to slide out. is simply dissolves…

building salt tooling… thats right salt. it simply dissolves when sprayed with a hot pressure washer or hot water bath.

its widely used in aerospace FYI.

salt pour setups are expensive. but if you are already paying for metal tooling might as well do it easy and fast.

there are foams that dissolve with chemicals but this process is not recommended.

#9

also with salt tools you can use vacuum and hydraulic assisted injection of the resin. the tools are very strong. they are poured at about 650*F and can be autoclaved. they reach temperature fast as well.

if flow media is not designed i would recommend hydraulic injection of the resin. most of the time the ram and piston are “home made”.

#10

Ehhhh…i’ve done worse. 20" non-crimped carbon, with core and caul plate…no distro.

#11

if your mould is designed properly and closed tight, you will have no air gaps for water. we use polyeurathane foam as a core in some parts we make. you need to make sure the foam core is precise or you WILL get air trapped in there. i would work off having a 3mm cavity right around the core and use a proper RTM glass with a resin flow media already in it. this will be the easiest solution.
if you have and questions, just pm or email me at ryan.oldfield@live.com. we do this sort of thing every day and it is pretty straight forward once you get your head around it.

#12

Thanks everyone for all the comments, they have been very helpful and informative. I hope to start this project very soon, I just need to cost all the options now and weigh up which method gives the desired result with an acceptable setup cost, and where I can source my materials.
1968falconxt, thank you for offering your email, I expect that I will be making use of it soon.
I’ll keep this thread updated with progress for any one that is interested. Hopefully I’ll be able to post pictures if my account will allow me.
Should I push the resin using a hydraulic pump or pull the resin using a vacuum pump, would one be better than the other for this application?

Edit
dallasb84, I just re-read your post and you have answered my question, if no flow media then push it with hydraulics.
Thanks

#13

Exactly but you would have to make a cylinder and piston setup with hydraulic lines and fittings to the tools. Also would need a solid mandrel like a salt pour. It would essentially be a resin injection rather than infusion. This setup would be very expensive. It would on the other hand be very fast and would make parts that are identical. Plus fundamentally it is a bit simpler.

On the other hand to infuse you will have to incorporate design changes to allow flow media at a much lower initial cost.

Without taking into account start ups the salt pour injection makes a much more profitable process for a large scale manufacturing. Infusion on the short run of things.

The hydraulic setup is simply a hydraulic pump with a pressure gauge and valve online to a two way ram that pushes and pulls a custom piston inside a custom cylinder. Pressurized resin feed lines can be strategically placed throughout the tooling to allow faster resin saturation.

Cost and size of run are the biggest factors. Also part design plays a big part too.

If you have a machine shop this is no biggie and would be much more feasible.

#14

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#15

These machines are called RTM machines.

Magnun Venus Plastech and Composite Integration are the 2 brands that spring into my mind.

I have a Plastech machine which I am about to throw away (renovation costs about 1500 euro) if it is not already thrown away.

#16

yep but most people think of lite rtm and what im describing is not. so i did not want to confuse lite rtm with a full rtm system. plus in most singular applications a group of engineers will usually make a system over adapting one to the process. as much as i have seen anyway.

shelve the components. they are valuable. do a quick search of companies that use the same machines. often they will buy the stuff you got!!! makes for a nice vacation or a free bonus to go around to your employees. much better than just tossing the system. ya know. or you could send it to me!!!

#17

you can buy an injector, or make one. If you are in mass production, this will be the way to go.

however, if you are not making very many parts, you can simply use a funnel to pour resin in, and use vacuum to draw it through. This works very well on parts that are not huge. controlling resin flow through a mould is easier just using a controlled vacuum, rather than trying to push it through with a pump. Keep in mind that if you are trying to force resin in with a pump, your seals have to be extremely good as the back pressure will be very high.

#18

Do you know the Plastech Hypaject? It is one of those. I just learnt it was given to a customer that still has one other.