The point of this thread is to discuss and share info on building an oven for curing composites. I will be updating with progress of upgrading the oven built here. I will try and take as many pictures as possible to show any progress and hopefully anyone else thinking of building an oven may find the info and pictures useful.

I only have a basic understand of ovens and electronics. So if any mistake is made in my terminology or what i am doing please let me know!


Okay so first off i have already built an oven! This first part is written in hindsight so will include suggestions that may have not been considered/ known about when it was built. By the way now it is time to upgrade the oven to something more sustainable and useful but i thought i would post the main build for anyone interested in seeing some piccys.

Part 1:

Some sources to build an oven:

• This guy built his oven out of house insulation board and then used a room heater for his heating element seems to work reasonably well http://www.privatedata.com/byb/rocketry/composites/ovens/Airframe%20Composite%20Curing%20and%20Post%20Curing%20Oven.html
• Same guy http://www.privatedata.com/byb/rocketry/composites/ovens/Propellant%20and%20Composite%20Post%20Cure%20Oven.html
  

• This super quick clip from the TV show How its Made, They are curing carbon fiber cellos in what looks like a similar design to the first link. jump to 2:44
  

• A boat building forum, mainly focused on building some kind of huge boat oven however some interesting ideas http://www.boatdesign.net/forums/fiberglass-composite-boat-building/building-oven-25398-2.html

• links submitted in this forum:

• Sheet metal oven with a link that shows construction incl wiring diagram http://www.powdercoatoven.4t.com/Index.html

• Stuart321's space saving oven http://www.talkcomposites.com/Attachment444.aspx http://www.talkcomposites.com/Attachment445.aspx

Structure:

A good/efficient oven is one that can insulate the heat so that the heating element only needs to be on for a minority of the curing time. A professional/ industrial oven would probably be looking at 20% of the overall time with the heating element powered on.

So with those and a few other sources that i can't find/remember at the moment i decided to go with a similar design to the first 2 but something that was a little more sturdy. The basic idea is a wooden frame with ply wood/mdf boards as walls and then on the inside a layer of house insulation board.

A tip i heard about mounting the oven:

Don't mount it directly on a concrete floor because it will suck up all the heat. Suggestions to remedy this were to mount it on batons of wood or the solution i went with, mount it on castors. (Not 100% sure about this as i have heard from other people that having it mounted from the floor can insulate it better so who knows...)


Heating elements:

• Room Heater fan assisted
• Room heater Infra Red
• Hot Lamps (Not sure of their proper name)
• Duct Heater (This is probably what i will upgrade to with my V.2 of zee oven)
• Electric Blanket
  

The Basic idea is that you want a heating element that will produce heat and then a fan that will circulate the hot/cold air in a cycle that passes the heating element to give you an even temperature gradient across your oven. So with the heating elements that are not fan assisted you will need to also have a fan mounted in the oven somewhere. I decided to go for a fan assisted room heater as i felt it was a good all in one combo that didn't require any effort.

It is also highly recommended that you make sure there is a thermostat device that can shut off your heating element in the event that something goes wrong and the element starts to increase its temperature more than desired.

I also do not recommend leaving your oven unattended whilst it is running, most of these heating elements need to be monitored constantly whilst powered on and cooling down. It is probably not a bad idea to have a fire extinguisher lying around as a safety precaution.

The Build V.1.

So here comes the build of Oven V.1. Sorry for the lack of pictures of the frame but i did this like 8 months ago with out the intention of this thread.


Supplies from the timber yard (much cheaper than your avg diy store!) A few 4x8ft sheets of plywood/MDF and then two 3m long 2.5x2.5inch "bits of wood?" maybe  i will call then Bars of Wood or batons


I didn't take a proper picture but i also got 6 castors from machine mart to make it portable... Definitely worth it with something this size/shape/weight. Proably can get them cheaper elsewhere.


Some house insulation from local DIY store, IMO it is fairly expensive.


Using the jigsaw to cut the boards in half (using the straight edge of another one for the jigsaw to follow)


Structure finished with one piece of insulation put in. Also you will notice the two latches i forgot to mention for keeping the "door" secured. As you can see i decided to not go with a door that was the length of the oven like in the examples at the beginning. Due to its size i felt it could be a pain to open and close often. For a smaller oven a door being a whole side is probably better.


Picture of the inside.In this picture i had started to line the wooden structure with Tesla aluminum foil tape ( good quality and thick). Not sure how necessary this was, my reasoning was that the corners of the bars didn't have any insulation over them and so i wasn't too comfortable leaving them bare.



Picture of the inside fully insulated and been used a few times.




My heating element: A Clarke 6kw Space heater. Glove box is there to give you an idea of size. This picture is after a lot of use and as you can see the dial snapped.

Conclusion to Part 1:

The oven works okay. I can get it up to a sort of constant temperature of 50 degrees C however it is a bit of work as i have to monitor that room heater and adjust the temperature dial to keep it constant. If it is left  unadjusted the temperature will bounce around from 20C to 80C which is where the thermostat in the room heater kicks in and turns it off. I was hoping the thermostat in the heater would manage the temperature better. A solution would be to wire up a PID controller to it. At the time i didn't know how to do that aannd still don't .

The structure does not hold heat amazingly. I think this is mainly due to the terrible job of the doors i did, i'm sure most of the heat is leaking out there because when it is on, the outside of the oven does not feel very hot. Due to my application i needed a reasonably long oven however i think for most people doing smaller parts something half the length would be really nice and neat.

Overall i was pleased as it did i wanted it to do: It cured parts at an elevated temperature which greatly reduced curing time and increased the parts glass transition temperature by tens of degrees. It is now a case of heavy upgrading/tweaking to make it more efficient and precise.

Part 2:

I will begin this part over the weekend. Here's a quick explanation of it

I have had the oven for around 8 months and it has had a fair bit of use but now it is time to upgrade and kit it out so that it is more of an oven and less of a leaky wooden box with a room heater in it! I had a chat with Paul from EC who gave me some great ideas that i will be going into in part 2. A quick summary of what i want to improve: (i will discuss the ideas in detail and show some CAD drawings on the weekend hopefully and get your ideas/criticisms.)

Upgrades:

Heating element - Thinking about switching to a ducted system that runs outside the oven from one end to the other and houses a duct heater from a central heating style unit and a duct fan. Ducting will be made from stainless or something. Will also look into adding PID, SSR and a temp cut off sensor.

Insulation - I will most likely swap the current insulation with roc wool and add cement board as an inside wall. Will also be looking into a different way of fastening the door and a way of sealing it so that less heat will escape.


Thanks for reading, i will be looking forward to your ideas on the weekend.
 
Dave.

P.S. i apologize if i have used different tenses whilst writing, it has been screwing with my head trying to write about something i built 8 months ago but still use now.

What about using an old chest freezer for the housing?

Any updates of your oven?

 



 


    A $1000 electronic device will always protect a 10 cents fuse

None yet! Unfortunately lots of things have come up in the last week and so i haven't had time, i'm going to be redesigning it in the next few days hopefully.

The chest freezer idea is interesting! However finding one that has a large enough internal capacity could be hard to find.

Dave

This thread is really useful - thanks for posting your experiences to date!
Although I found an electric blanket worked well to elevate temps for curing/post-curing in the summer its nowhere near warm enough in my garage now so I'm planning an oven that sounds very much like your v2.

Ducting from opposite end to fan heater for air circulation and minimise temp variation, Digital PID temperature controller with thermocouple, output to a solid state relay to drive the fan heater element.  Safety cut-out at 85 degC to turn the whole lot off.
Oven construction will be foil backed foam sheets, chipboard base with an extra layer of rockwool (loft insulation) as that is so cheap in the UK.
Fan, controller, relay is £40-50, ducting, foam sheets & chipboard I already have, rockwool insulation probably £15 so should be pretty cost effective and will let me cure parts properly in the garage all year round.

I'm thinking a 2kw fan heater should provide plenty of capacity for the planned size of 1.25m3 (assuming that the oven is pretty leak-proof) but any other views appreciated (I noted you were using a 6kw space heater but surely that must have been on a very low setting or not recycling the air)?

I'll update as I have more to share.
Stuart

if you live in sunny climates the sun can help kick it off. but if you do it too soon it can cause air bubbles so not the best idea. i suppose if it were 2nd
day and your part is still a bit soft the sun would likely be ok but be careful and monitor the part.
the automotive refinishing industry has many infra red heat lamps, from 150.00 dollars to 4000.00.
i suggest if you use heatlamp keep it 3 feet away. once the resins are warmed they will go off and
as it's exotherm happens it generates it's own heat and finish on its own.
so if you can warm it up and help it along, cool. i am sure like auto paint the whole chemical process
stops at low temps and will finish off once the temps come back up.
  so if you leave the part in the shop leave the heat on.
also ambient air temps are usually 15 degrees more cold than your part temps which will effect your cure times.
so you MAY be in the range for your hardener and catalyst type and quantity based on ambient air temps, but the parts
and mold temps will be lower so be aware of your work area temps.

so in all our learning something as simple as shop temps and resin selection and catalyst are very important.
i have a sample of epoxy incompletely mixed for 10 months and it is dry to touch, but soft and flexy. temps and
complete mixing is very important.

CarbonFiberCreations

I have found that the oven I built from an old metal storage cupboard works very well. I took an old 1.8m tall storage cupboard and clad the exterior with 50mm Celotex building insulation including the doors and then fitted the heating element, fan and thermostat / temp controller from an old domestic fan oven. I have found that it easily holds 100 degrees + or - 4 degrees and I monitor it with an RS components temperature probe to keep it just right.

Aaaah, good old box ovens lol

Awesome when they work, catastrophic when they set on fire :/

@CarbonMike - Have you had an oven catch on fire on you? I would be interested to know what you think went wrong and any tips on how to avoid would helpful too!

Nice job.

I pulled the guts out of old kitchen ovens for my heating oven and my autoclave. Its the thermostat bulb and control I needed. I have this control activate a relay that controls the power to my heating eliment in the autoclave. My heat box has a 2000 watt space heater in it. Works great.

Fred