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Composite curing DIY oven

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mpitfield

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I am looking to expand my carbon fiber experience with prepreg and or post curing of composite components and sub assemblies. Specifically I am looking to try rolling tubes, creating plate, and creating fincan assemblies.

However as some of you know this requires an oven that can be reasonably controlled with temperatures including ramp ups, hold temps and ramp down. A commercial oven is not affordable therefore I am looking to build my own. I know others have done this and have used a variety of materials and methods. To control the temps and set a schedule I have been looking at PID temp controllers, which are readily available at a reasonable price range.

My initial thoughts were to build an inexpensive wooden box and insulate it. However I would like to look into making something out of metal, possibly stainless. I was envisioning a fan that continually moves the air from the top to the bottom in a vertically standing chimney design, which also works well based on my work and storage space. Ideally I am hoping for a design that has a reasonable amount of flexibility and life.

Safety has to be the number one requirement for any design to be considered. Beyond safety the box should physically accommodate assemblies up to 6’ in length and 24” in diameter. I am not sure of the temperature ranges that I might want in the future but I currently have some low-medium prepreg that has a target temp of at most 310F for 1 hour, with a ramp up and down cycle. The ramp up rate should be no more than 5°F per minute until the target temperature is attained. Then I need to maintain the target temperature throughout the cure cycle and ramp down at a rate of less than 5° F per minute to at least 150°F (66°C) before removing from the oven.

I am looking for some practical guidance on a design, materials, etc., as well as realistic expectations on a DIY project like this.
 

cherokeej

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On the hobby level, I built an oven using 2" thick foam insulation panels bought from the Homer's De-Pot. Draw the design, cut the pieces, assemble using aluminum tape. Thermostat, pancake fan, and a 500 watt halogen light for heat. Works great for curing a wrapped a/f.

But doubt it would work on the scale you're seeking. 24"? You've got a big hobby room...
 

mpitfield

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On the hobby level, I built an oven using 2" thick foam insulation panels bought from the Homer's De-Pot. Draw the design, cut the pieces, assemble using aluminum tape. Thermostat, pancake fan, and a 500 watt halogen light for heat. Works great for curing a wrapped a/f.

But doubt it would work on the scale you're seeking. 24"? You've got a big hobby room...
Your plans sound like what I have reviewed in the past and seem to be good enough for the job, but I am looking for something a bit more robust.

I actually have two spaces I can work from. My basement hobby room "rocket lab" which is about 15' x 20'. This is where I do most of my work, however I just purchased a CNC router and 3D printer so I am now considering moving some of the fabricating tools to my office. At the office I have a space in the back that is not being utilized, except the guys keep loading it up with junk, that is about 25' x 30'. Also the landlord just installed 600 amps of 3 phase power and is looking for it to be used.

You may find something of interest in this link:
https://forum.ausrocketry.com/viewtopic.php?f=10&t=5659

Should scale to the size that you need quite well.
Thanks, there is a lot to go through in that thread, I will have to pick it over. Fortunately one of my clients has 20 or so mechanical and electrical engineers on staff so I will try to solicit an opinion before I finalize a design from a safety perspective.
 

prfesser

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My latest build, for (whisper it!) curing propellant at 55-65C started with thin cement backerboard used under bathroom tile, lots cheaper than metal and pretty much fireproof, I hope (does concrete burn?). Made a box of the size I wanted, which was about 12*15*36 stupid-'murican-units with a top that lifted off. Covered in two layers of 1" blue extruded styrene foam. Do not use white "beadboard" unless you want thousands of tiny foam beads following you about all day, getting in the morning coffee and elsewhere. Assembly was with urethane-type caulking, which is only so-so for cement backerboard but works okay for the most part. Since I was only interested in hitting and staying at one temperature I used a $25 controller from fleaBay:

Undoubtedly you could find a more complex controller.

Heat source was an incandescent bulb. If memory serves a 60W bulb would bring the temp to about 75-80C. Add a little computer fan to spread the heat about and Bob's your uncle.

Best -- Terry
 

Sooner Boomer

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I've built a wide range of ovens, from 50 C to 800 C. For what you need, a simple home heating blanket might work fine. Two important things to be aware of; 1) uniformity of heat, 2) an overtemp shutoff not part of the controller (and keep a fire extinguisher next to curing oven). I'm away from the house now, but when I get back, I can PM or email you more details.
 

JLebow

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I'm in process of building a composite curing oven myself. I'm trying design for 350 deg F maximum. My ramp soak controller is an arduino uno, with a touch screen LCD display and a thermocouple. I wrote a program that can store different cure profiles, and uses PID control to switch a solid state relay on and off. I also plots the profile and actual temperature during the cure cycle.

I did some calculations to convince myself that 500 watts would be enough to hold my oven at 350 degrees (and have enough reserve power to raise the temp 2 degrees F/ min) if I could get R12 worth of insulation. Power requirement depends on your oven surface area, and how cold it is outside of the oven. I'm thinking of using a single burner portable electric cooking stove for the heat source (1200-1500 watts).

For the oven liner I bought a used sports locker that is 78"x18"x12". It was the cheapest way I could find to get enough sheet metal for the job. The plan is to wrap the locker with mineral wool insulation (rated at 2000 deg F) and make a plywood box for the external enclosure. I have a small blower for air circulation (not sure if 20 CFM will be enough), that I'm modifying to try to keep the motor away from the heat.

For safety, I'm putting a ceramic terminal block into the oven, to mount a thermal cutoff fuse. The fuse is in series with the heater element. This should kill power to my heater element if my controller code has a bug, or the solid state relay fails closed (as they are known to do).
 

dhbarr

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If you're grabbing kaowool, get some satanite as well to stiffen it up between the layers.
 

SpaceManMat

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I'm in process of building a composite curing oven myself. I'm trying design for 350 deg F maximum. My ramp soak controller is an arduino uno, with a touch screen LCD display and a thermocouple. I wrote a program that can store different cure profiles, and uses PID control to switch a solid state relay on and off. I also plots the profile and actual temperature during the cure cycle.

I did some calculations to convince myself that 500 watts would be enough to hold my oven at 350 degrees (and have enough reserve power to raise the temp 2 degrees F/ min) if I could get R12 worth of insulation. Power requirement depends on your oven surface area, and how cold it is outside of the oven. I'm thinking of using a single burner portable electric cooking stove for the heat source (1200-1500 watts).

For the oven liner I bought a used sports locker that is 78"x18"x12". It was the cheapest way I could find to get enough sheet metal for the job. The plan is to wrap the locker with mineral wool insulation (rated at 2000 deg F) and make a plywood box for the external enclosure. I have a small blower for air circulation (not sure if 20 CFM will be enough), that I'm modifying to try to keep the motor away from the heat.

For safety, I'm putting a ceramic terminal block into the oven, to mount a thermal cutoff fuse. The fuse is in series with the heater element. This should kill power to my heater element if my controller code has a bug, or the solid state relay fails closed (as they are known to do).
Sounds similar to what I was planning. I ran into issues with the touch screen not working. Would be interested in what you did.
 

JLebow

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Sounds similar to what I was planning. I ran into issues with the touch screen not working. Would be interested in what you did.
I'm using one of these without issue: tft with touch screen. A bit expensive, but they have a library and tutorial to learn how to use and calibrate the touch input. I will start a new build thread for my oven soon. Just wanted to chime in with some of the design considerations mpitfield originally asked about.
 

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