I have a fully operational autoclave in the Washington DC area looking for a good home. It is 34 feet long and 8 inches inside diameter - perfect for beach cat masts and many other composite parts. It has a flanged joint in the middle so it can be transported in two 17 foot sections. It operates at 350 Deg F and as high a pressure as you want. Although it has a penetration for insturmentation you will have to provide your own thermocouples. Uses about 3kw of power to full temperature - electric strip heaters.
The picture shows a mast sitting on top of the autoclave looking as the power end. This will be available in mid june. I have made four masts and lots of other parts using aerospace surplus prepreg carbon. Does a great job. My wife would greatly appreciate having her backyard returned.

Kevin

That is a great offer! To bad I dont have room for it and that shipping abroad would be murderous.

PS: Picture did not work. It would be very interesting to see how it looks. If you have more pictures, I would be interested in seeing them. One never knows when the knowlegde on how you did it comes in handy.

Anyone know how to insert a picture on the same page as text for this forum? I tried normal cut and paste routine - didn't seem to work. I confess to being a klutz with these things.
Kevin

Any clearer, or worse?

Kevin-
I am interested and in the process of building a 40 x 54' building so would house it fairly easily. My problem is I am in Little Rock- any idea what the weight is and dimensions of the two pieces? I could not see photo-
I actually have a cat trailer of mine at a friend's in Chattanooga, TN that might hold it- Any chance you could meet me somewhere inbetween or deliver to Chatanooga if I covered your costs? Or??

Thanks!

Kirt

Hey Kirt,
This rig is made of two 17 foot pieces of 8 inch carbon steel pipe with flanges welded on each end. The two sections are bolted together and there are blind flanges bolted to each end with penetrators for power/pressure/insturmentation. So you have two 17 foot long pieces about 300 lbs each. You would need to put it together at your site and re-insulate the outside of the pipes. The electric strip heaters inside worked last time I used it (about a year ago). You will to buy need a temp controller and a 220V relay (cheap on e-Bay). Sorry but I've got a busy schedule until September.

Kevin

Kevin,

do you have any pictures of how you made and used your autoclave? If you are unable to post them here, you can send them to me on e-mail and I'll resize and post here: rolf.nilsen at gmail.com

I might have access to high quality steel pipes of a suitable size. Just need to source flanges, penetrators etc. and have some welding done. Being able to study your creation would help greatly. That is, if we decide to do this.

One thing I dont understand with autoclaves. Why will the pressure consolidate the laminate. Is there some kind of bag going over the part with an outlet through the autoclave wall?

PS: Have anybody inherited the autoclave yet? :-)

Autoclave processing is the most common method used for curing thermoset prepregs. The curing of thermoset composites involves both mechanical and chemical processes. Mechanically, pressure is applied to remove trapped air and volatiles, and to consolidate the individual plies and fibers. Chemically, a crosslinking reaction must be initiated and taken to completion to form a rigid matrix. Crosslinking is most commonly initiated through the application of heat, though it also may be initiated by exposure to ultraviolet light, microwaves, or high-energy electrons (e-beam curing). In the autoclave process, high pressure and heat are applied to the part through the autoclave atmosphere, with a vacuum bag used to apply additional pressure and protect the laminate from the autoclave gases. The cure cycle for a specific application is usually determined empirically and, as a result, several cure cycles may be developed for a single material system, to account for differences in laminate thickness or to optimize particular properties in the cured part.

The typical autoclave cure cycle is a two-step process. First, vacuum and pressure are applied while the temperature is ramped up to an intermediate level and held there for a short period of time. The heat reduces the resin viscosity, allowing it to flow and making it easier for trapped air and volatiles to escape. The resin also begins wetting the fibers at this stage. In the second ramp up, the temperature is raised to the final cure temperature and held for a sufficient length of time to complete the cure reaction. During this step, the viscosity continues to drop, but preset temperature ramp rates and hold times then stabilize viscosity at a level that permits adequate consolidation and fiber wetting, while avoiding excessive flow and subsequent resin starvation. These control factors also slow the reaction rate, which prevents excessive heat generation from the exothermic polymerization process.

Yeees, thank you But how is the laminate consolidated without something physical pressing on it? Like it is in vacuum bagging.

Still hope Kevin (or others) have pics of parts ready for 'cooking' in the 'clave.

Rolf, the parts are in a vacuum bag inside the 'clave. using the 'clave lets you achieve more than 1 atmosphere of pressure.

Rolf,
You deserve some pictures and I will get you some. This rig is not hard to make if you know someone that can do the welding. I made penetrations out of 1/4 inch pipe nipples that threaded into drilled and tapped holes in the ends (blind flanges) of the steel pipe. Basically, you need one for power to the strip heaters, one for thermocouples, one for pressure inlet, one for a pressure gage,and one for a vacuum/vent line.

Sorry that was me.

Thanks for all the replies!
I am looking to scrounge parts as good steel is quite expensive. Might find most or all of in the scrapheap at work as high quality tubing goes in and out of the plant here all the time.

What kind of bags can be used when heating? Regular polyethylene would probably melt?
I am also curious how you set up the bags with the venting valve?? One pic probably say more than a thousand words at this stage.

How much pressure can you use if doing a wet layup? More than 2 bars and I was told the part would be resin starved.

I am not saying we are going to do this, but the idea is ricocheting around the inside my skull. I am a bit wary about having a homebuilt pressurized autoclave in my basement, but as long as my wife dont know..

Carefull Rolf! Sounds like you are close to jumping into it. The process materials you need (bagging film, breather cloth, release film, sealant tape) can be bought from AirTech International or SP Systems. AirTech has a store at their website for people buying small quantities.
The aerospace industry has pretty much standardized on 350 deg. cure material. So, if you make everything to operate at this temperature you can allow yourself access to cheap and plntiful surplus aerospace Prepreg material. I made the 42 foot mast for my tri out of material originally purchased for a contract to make helicopter rotor blades. It was two years out of date and cost $5.00 per pound (retail $30). It worked great - as long as it is properly stored at 0 degrees, it will last for manny years.
Material normally comes with a datasheet showing recommended cure cycle. I do not use pressure over 40 PSIG since this provided excellant quality laminate. Too high of a pressure can actually cause the fibers to break where they are woven over each other in cloth material. If I were to do it over, I would try to find 10 inch or 12 inch pipe instead of the 8 inch pipe I used. There are a lot more things you can make besides masts and a littile bigger size would give you much more flexibility.

Kevin

Kevin,
what are the advantages of using the autoclave with wet layup and not prepregs ?
Faster cure for sure but is it worth it for wet layup ?

Florin,
It is probably not worth going to this effort for using wet layup techniques. I think vacuum bagging is more appropriate. You can significantly boost physical properties of a wet layup part by post cure baking but you don't need to do this under pressure.
You need the Autoclave to process PrePreg which has advanteges over wet layup:
1. Precisely controlled low resin content (high physical properties)
2. High heat resistance of the finished part.
3. Accurate orientation of fibers - especially important for unidirectional reinforcement.
4. Ease of layup - the prepreg can be cut very accurately with a razor blade and stuck onto the mold or mandrel.
5. 30 days to complete the layup at room temperature before curing it.

By the way, you can cure prepreg in a regular vacuum bag placed in a "hot box" and get good results.

I agree with Kevin, you don't need an autoclave for wet laminates. If you want to get fancy with these try resin infusion.

Suitable bagging materials for pre-preg work should be available from who-ever you buy the pre-preg off. Typically the bagging film is green and quite crisp. In my experiance Aerospace autoclaves operate at about 7 atmospheres, but this will be unnecessary for your projects. Aerospace 'claves are also pressurised with inert gases to minimise the chance of them turning into bombs, however this might be a bit complicated for a home build.

Rolf,
After reading Srarecrow's post and thinking, you might want to get a few pounds of prepreg material to experiment with first. Before I built the autoclave, I made rudderheads and small parts in the kitchen oven or an insulated box using a regular vacuum bag set up. You need the high remperature bagging film and a teflon tube to use for the vacuum line. But, you can make useful small parts this way. If you go the oven route recommend waiting until your wife is out of towm a few days! Scarecrow also mentioned explosion hazard and he is right about the big production autoclaves - given the volumes, temp, and pressures we are talking about there is almost no risk. For the giant airplane size setups there is significant risk.

With my scare for epoxy sensitivity, I think the kitchen stove is out of the question. Will begin to look for a source of pre-pregs though. This adds a new dimension to homebuilding.