I saw a new How It’s Made last night, carbon racing shell. Again with no gloves and handling/using prepregs. UGH! How. Can. They. Do. That.
Companies should be fined for things like that.
[ame=“http://www.youtube.com/watch?v=tckwLt5aze0”]How It’s Made Rowboat Racing Shells - YouTube[/ame]
Ive worked for 3 different rowing shell companies in the past, not this one though. Our molds and process were much better. That spray adhesive used to hold down the core scares me, and is not needed.
Looks like they use Freekote. @ 40 sec. you can see masking tape on the side of the mold with the last Frekote date on it. Gosh I don’t know HOW boat manufactures can get away without it. I mean waxing a mold that big. :eek:
They trim the prepreg with a cutter on the mold surface (ok my srew driver action was not better:rolleyes:), use prepregs without an autoclave (yes it works but it is not perfect), fix the honeycomb with spray adhesive on a prepreg, they don’t use gloves but wear a mask…
Do they know what they are doing there? May be they want to build submarines 
I watched the video, a few things struck me as odd but nothing horrible. Then i read the comments to the video. All i can say is you guys have alot to learn about composites still.
Try to work like them in the video in an aerospace company, or a company wich manufactures race cars.
May be they have a special 1k Epoxy wich is used as a spray adhesive and cures at higher temperatures, but normal you do not need a spray adhesive to fix a core on a prepreg because it is tacky.
And you always have to use gloves when working with fibre material.
If you use a prepreg out of autoclav you have a lot of air in the laminate because you need the presure of the autoclave to remove ans compress the air between the prerpeg layers. With an infusion you will get a better laminate quality in this case.
Could you elaborate?
Please…
Lets start with my background…9 yrs of composite experience mostly in the aerospace sector.
6 of those yrs i worked for a Composite material manufacture in the r-d area, travelled to big and small shops building, fixing, testing and protyping there parts or molds for them. We were called when they couldn’t figure it out themselves or didn’t have the capability to do so.
I have built alot of things that range from going under water to going into space.
First gloves—is it wise to use? In my opnion yes. But you can also use something called Durashield. It’s like a mosturizing creme, that acts as a barrier between your skin and the material. Doesn’t last long but when messing with certian phenolics and epoxy resin systems in prepreg where touching it with a glove would tear the glove off your hand and leaving small glove pieces in the part. Remember i said some Not ALL epoxy systems.
Now onto the honey comb issue (Not all prepreg is sticky) DDcompound–not sure but my guess is that the company that supplies you your prepeg is the only company you dealt with. I could be wrong though just a guess. My personal preference is to apply to honey comb or any type of core without the use of adhesive of a spray adhesive. But with some companies materials, you have to use a spray adhesive, mainly the one sided materials where 80 percent of the resin is on the surface side and the backside is usually dry.
Now autoclave vs oven. Man running a autoclave is expensive, even more if you fill it with pure nitrogen for every run. Alot of companies, mainly small can not offord to do this. Yes your correct a autoclave will allow for a better product, but there are resin systems out there that you can use to get the same results as you would if you used a clave but using a oven instead. You get the same strength and void content. I know this to be true cause i worked on the system that i am talking about. Other compainies were developing a system that could be out of autovclave also just not sure if they completed it or not.
So in saying that working with composites is a very diverse field. I have learned over time from visiting and working for different companies that everyone does it there own way, I know some that still pefer to use a technololgy from the 60’s and 70’s to build there parts, and some use the most state of the art technology they can and embrace anything new. I’ve seen trash bags used as vacumme bags and parts cooked on the tarmack, i"ve seen other place age material past their out time cause it gave them a better finish. So just becouse you have been doing it one way for some many yrs doesn’t mean that the only way of doing it.
You are right, there are a lot of prepregs. Some are tacky and some not. In most times you use an epoxi/adhesive film between the Prepreg and the core. If not you can heat your Prepreg with a hair dryer and than it will become tacky. But using a honeycomb you need a little overfeed with epoxi.
Working with a creme is an absolute no go. You wear the glove so that no fat from you hand or even creme will contaminate the fibre. Fat or creme has the same effect than a release agent! With nitril gloves you have no problem with any kind of epoxi. If you have problems with an epoxi prerpeg with this gloves it must be a prepreg made by dissolvent, and than there is dissolvent in the prepreg so that you can not use it.
Using a spray adhesive is ok if it is a hot temperature curing 1k epoxi. A normal spray adhesive will make a lot of problems in combination with hot curing prepegs.
Our business is consulting, so i have seen a lot of companies, from airbus to a small messy company.
Most companies (all I know) use their autoclave with normal air, not with nitrogen. I dont think that you will get the same void content than an autoclave laminate. How do you want to get the air out? Than you have to put vacuum to the part after every layer.
Producing a formula one monocoque the put every two layers vacuum on the part (working in a clean room with gloves), and they cure in an autoclave.
Amines and arsenic are two of the most deadly materials I can think of involved in composites that are readily introduced through the derma.
Did u guys know one of the biggest esh mishaps happened as a result of misuse and ignorant composite materials handling and effective disposal. The former president clinton had to enact a law ti protect the government from it’s effects on the parties and companies present.
These companies will soon find out how costly it is to not provide proper ppe and training here shortly. There will be a move to bust mom and pop operations that are able to make parts at cheaper price because they operate in this fashion.
I worked for a company that literally threw uncooked prepregs in their dumpster and poured hexavalent chromium into the drain. They had a 50 gallon hazmat drum… That was specifically not to be used. I never took part but witnessed gross negligence that takes part in our industry. It is up to the EPA to take notice and properly identify these problems proactively an perform routine inspections. It is peoples lives and families at risk right now.
If your familiar with formula one then you know the company that i used to work for since 98% of the formula one teams used Advanced composites material to build there car. At least thats what it was 3 yrs ago. not all composites need to go into the autoclave…case in point–space ship one, the x-prize winner did not use a autoclave on alot of there craft when it was sent into space. The edge 540 aerobatic plane, that you will see raced in the redbull air races going around the pylons. The whole plane minus the minus the airframe is carbon. They do not use a autoclave and cook all the parts below 180F, then post cure them to 350F, the wings can withstand 23g’s of force before they will crack and fail. I do agree with alot that you said, but the durashield was desinged to be used with composites, i know airbus, northrop, nordam and spirit allow there employes to use it. I was not found of it since it made me break out. Yeh most companies do use normal air but some companies use nitrogen to help eliminate any fires that can happen when curing some epoxy systems. One thing that i do know of is that alot of the stuff you use in europe we can’t get in the states. Trust me there is some stuff that i would love to have used here in the states when i went to england but our import/export laws did not allow use to bring it over.
“out-of-autoclave prepreg” have come a long ways, and can produce a very high quality low void content part. However what it cant do is apply high pressures to produce a very high fiber volume laminate compared to that of an autoclave. I will agree that running cost are costly, too much for these boats(retail 25K-35K fully outfitted). However autoclaves can be run on oxygen with lower temp curing prepregs there for not requiring the nitrogen. But does require a very large investment for the autclave which for these boats needs to be 70 feet long!
As for the honeycomb, theres no need to use that spray adhesive in this applications, regardless if its epoxy curing version or 3m spray77. They cook the honeycomb to the skin layer first. pre-cutting the core and placing a caul plate along the flange and cooking would be a more effective approach. The spray adhesive for a simple curve as these boats is not worth it and makes no sense.
Prepreg tack is selected through the manufacturer, most have 2-3 tack levels to choose.
like i said, i agreed with some of the video an disagreed with other parts. But like i said in my 2nd post, everybody does it differently. There are alot of ways to get the job done, it all depends on what you want the end product to be.
Durashield ore other creme should be used in combination with gloves! And only with nitril gloves. The armine goes through a Latex glove within 30 secons, through vinyl after a few minutes and through nitril after about 30 min. So you should change your gloves after 30 min of work with epoxi if you had contact with the epoxy.
Low presure prepreg works, and it is not really diffrent to an autoclave prepreg. But it is like hojo said, you can not reach the fibre to volume ratio then an autoclave prepreg and the void content is not as good than in infusion ore autoclave.
And a laminate only starts burning if something goes wrong. The most prepregs i know immediatly stop curing if the temperature is cooled down, they need the heat to cure because the exothermic reaction is not enough.
“There are alot of ways to get the job done, it all depends on what you want the end product to be.”
Thats absolut correct.
Uni directional is not always tacky enough to hold a core, let alone itself down. As long as the spray is rated for what they are doing, might as well. That is one heck of a surface to keep put with uni prepreg.
Also, you do not always need an autoclave. There are many out-of autoclave prepregs, and normal ones with extra resin. You can’t infuse with a core, so you need pre-preg. I have made many parts in the oven with honeycomb and prepreg…they are bloody strong.
No gloves bother me on MANY levels…the resin, the fibers, and leave your body oil in between the layers!!
You can´t work with honeycomb in infusion. But you can work with a perforated foam.
But working with a honeycomb you normal cure the first layer and then fix the honeycomb with an epoxy adhesive film and the inner layers. In most times it is a 3step process to make a honeycomb laminate, not a one step. And in this video it seems to be one step.
If you put the honeycomb direct on the 1 layer there is no presure working in the comb, there is vacuum which is contraproductive to the laminate.
in the video you can see that they bag just the honeycomb and cook it off then follow with the B-side laminate. Common practice with these boats is: 0 drop, debulk. remaining laminate, debulk over night, film adhesive if required(sometimes debulked), core placement. bag and cook. remaining laminate, bagged and cooked.
Other variants are a-side laminate cooked, then adhesive and core placement then cooked, then remaining laminate and cooked
. This is the more expensive method but is better quality. Usually it is not practiced since profit margins are tight with these boats.
I’ve done: most of skin layer 1, cook, one more ply, honeycomb, cook, remaining layers, cook. Various debulks in there as well.
I miss making parts. flat panels just get boring after a few years.
you can laminate and debulk a-side laminate, then apply core, and do B-side laminate and cook all in one shot. However it is the least desired method since theres lots more trapped air in a-side. Really depends on the quality level your going for.