High-temp epoxy curing oven

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dixontj93060

dixontj93060

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Well, I have made progress on my Thunderstruck Mach Madness rocket and am to the point were I need to do some tip-to-tip and nosecone laminating. A while back I purchased some high-temp laminating epoxy from ACP Composites but to get the high-temp performance you need to do a stepwise cure cycle up to 350 degrees. Well, after considering using our kitchen oven for a few weeks, I figured the risk of collateral damage (including my spouse's relationship) could be too great. Thus I am building an oven. First step was to find a temperature controller.

After some searches and comparisons, I found this controller at Amazon for a decent price of $55.49. After taking a look at the features and the quality of the internals, I was impressed. Made in the USA too from a company out of Minnesota. It has two independent controls with set points and ranges that can be set up for heating and/or cooling.

014 (960x1280).jpg

Wiring was fairly straightforward with most connections done in the adjacent/attached dual-gang box.

015 (960x1280).jpg

Went through the programming sequence. Only thing that caught me a bit was the factory delay of 5-min pre-programmed so you don't short-cycle compressors in cooling operations. Once I cleared that setting, everything behaved as I expected. First (but secondary) application is temperature regulation for my home winemaking set up (fermentation happens in the mini-greenhouse you see behind the controller in operation).

018 (960x1280).jpg
 
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Can you set a ramp? In talking with PTM&W they told us the "increase temperature, dwell, increase temperature, dwell" formula for heat treatment is only necessary if you can't ramp slowly.
 
CarVac said:
Can you set a ramp? In talking with PTM&W they told us the "increase temperature, dwell, increase temperature, dwell" formula for heat treatment is only necessary if you can't ramp slowly.
Click to expand...

No, it doesn't have a programmable ramp (and the ACP expoxy doesn't require it at least the way their spec sheet is written). I expect that a controller with programmable time sequencing puts you in a whole other (higher) price range.
 
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dixontj93060 said:
No, it doesn't have a programmable ramp (and the ACP expoxy doesn't require it at least the way their spec sheet is written). I expect that a controller with programmable time sequencing puts you in a whole other (higher) price range.
Click to expand...

Or it perhaps could be done with a Raspberry Pi and 50 bucks of accessories.
 
CarVac said:
Or it perhaps could be done with a Raspberry Pi and 50 bucks of accessories.
Click to expand...

Well sure, if you are going to program it yourself then why do you care whether it has ramping or stepping functions--you can do anything you want.
 
Ramping up is more common in prepregs as it takes time for the resin to liquify throughout the part. Prepregs go around +5 degrees/min. That being said, I wouldn't just chuck a normal wet layup into an oven full blast.
What kind of insulation are you going for in the oven? You should look at mineral wool. Its cheap and can withstand temps as high as 1200 F.

-Tom
 
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StanO said:
I'm curious if you considered ShadowAero’s COMPOSITE CURING OVEN PLANS SET which includes the temp controller?

Also did you get the optional RTD sensor good for (0 to 600 degrees f) to get the cure cycle to 350 deg?

I'm looking at building an oven so your find is very useful information.

Thanks,
StanO
Click to expand...

No, I didn't purchase Dave's plan set. My assumption, although it may be wrong, is that it was designed for the Aeropoxy he sells which is only a 170 degree cure IIRC.

Yes, I have both the PTC and RTD sensors.
 
I bought the plans. I have not built it yet. I plant to build one with a different set of plans first.
 
dixontj93060 said:
Yes, board version of mineral wool material.
Click to expand...

Cool, it's very easy to work with. I like to cutting it with a razor blade.

I'm in the process of building one too. Aluminum flashing on the inside with AL tape covering the edges and holding the mineral wool to the flashing. The shell is wood. Going for ~300 F.
Temp controller is a DIY Arduino unit with a micro processor. I'm using a metal fan with a 1500 W heating element unit that I got from an old black and decker space heater. The goal is to have a nice slow ramp up to full temperature.

Keep us posted on the progress!
-Tom

image-1754742873.jpg

image-1640408761.jpg
 
Tominator 2 said:
Cool, it's very easy to work with. I like to cutting it with a razor blade.

I'm in the process of building one too. Aluminum flashing on the inside with AL tape covering the edges and holding the mineral wool to the flashing. The shell is wood. Going for ~300 F.
Temp controller is a DIY Arduino unit with a micro processor. I'm using a metal fan with a 1500 W heating element unit that I got from an old black and decker space heater. The goal is to have a nice slow ramp up to full temperature.

Keep us posted on the progress!
-Tom
Click to expand...

Yes, I started with a wood frame, but changed my mind. Also thought about tape use internally but couldn't find any rated > 150F. I'll post my oven materials and planned structure tomorrow.
 
Since there has been some interest, I will go ahead and post more detail than I was planning for this project. I guess the first place to start is a basic parts list. BBBUUUTTT, since this project is somewhat experimental in nature, I will wait until completed to provide that detail. Instead I will provide some insight into my current work plan and the materials. I caution anyone on going out and buying these things until I prove them in (and provide an official parts list) as I don't want you to waste money. I do believe it is worthwhile though to post this "in process," so to speak, to get some feedback.

First a DISCLAIMER... I am not a mechanical engineer and have had only cursory training in thermodynamics (but I did get an "A"), thus the approach here is not to do rigorous analysis of the solution (although I welcome others to do so if they would like), but instead to use readily available equipment to achieve a reasonably cost-effective solution, that may, hopefully meet my needs. OK, on to a lighter subject...

First, as was mentioned by StanO a while back, I did purchase an RTD sensor for use with the above mentioned controller so I could get the desired temp range control. This sensor was sourced on Amazon for $12. It has one bad review and I haven't tested it yet, so I will let you know how it works. If it doesn't work, I will go back and get the sensor recommended/sold by the company that supplies the controller.

016 (960x1280).jpg

Second is the oven itself. As mentioned in the comment back to Tominator2, I had considered a wood outer structure, but then abandoned it after considering both the weight and fairly poor insulating quality of ply and/or pressboard. Instead I am going with the medium density pink sheathing (2" in thickness gives me R-10 effectiveness) for the outer structure. The overall dimensions will be 52"x24"x24" which will provide an effective volume of 48"x20"x20" after the interior lining is installed. This sheathing was sourced from Menards @ $24/sheet (shown in link is tongue and groove version, I purchased square edge).

The outer structure will be glued together with foam adhesive and then the seams will be sealed and reinforced with Gorilla brand heavy duty duct tape. Both of these were sourced at Menards for about $9 total.

019 (960x1280).jpg

The inner lining as mentioned in an earlier post is a mineral wool material. This stuff is not generally found at a building supply store. You might find it in bigger metros at an audio store as it is used for sound dampening. I purchased mine from a local supplier, ATS Acoustics, to save on shipping. I purchased Roxul Rockboard 60 for $52 for six 2'x4' sheets. This is the lighter density board version, but still maintains R-8.3 insulating performance--more importantly it can withstand temperatures >1000F.

There are versions of the mineral wool board above that have foil lining. I could not find them locally, so I decided to foil line myself. To do so my plan is to use the heavy-duty (thick) aluminum foil and glue it to the inner face of the rockboard. The overlapping of the foil and adhesive bead will effectively seal the internals of the oven without a need for tape. The aluminum foil and high-temp adhesive (1380F) were purchased at Menards for about $8 total.

018 (960x1280).jpg

Next up is the heating element. I know many people have used lamps/light bulbs to do the heating in a homemade oven. In these applications it seemed like the temperature they were trying to achieve was fairly low (<250F). I felt that a radiant heater (and fan combination for heat distribution) would work better for higher temperatures (we'll see). I chose the heater below that I sourced from Northern Tool for $15 (I purchased two, as one will be installed in each end of the oven). This heater was selected for two reasons, 1) size/shape fits comfortably in oven ends with some spacing to walls and, 2) it was cheap as I plan to de-construct the heater to get it to work in this application.

017 (960x1280).jpg

Finally the distribution fan for use with the above is a simple computer box fan. I ordered this 4-pack from Amazon for ~$12. I ordered the 12V version as I have an extra 12V supply in my workshop, but you may want to use a 120VAC if it fits your application better. BTW, I expect to only use two of these in the oven.

OK, that is about it on the major components. Next up will be construction of the oven and de-construction of the heaters.
 
Last edited by a moderator:
dixontj93060 said:
Since there has been some interest, I will go ahead and post more detail than I was planning for this project. I guess the first place to start is a basic parts list. BBBUUUTTT, since this project is somewhat experimental in nature, I will wait until completed to provide that detail. Instead I will provide some insight into my current work plan and the materials. I caution anyone on going out and buying these things until I prove them in (and provide an official parts list) as I don't want you to waste money. I do believe it is worthwhile though to post this "in process," so to speak, to get some feedback.

First a DISCLAIMER... I am not a mechanical engineer and have had only cursory training in thermodynamics (but I did get an "A"), thus the approach here is not to do rigorous analysis of the solution (although I welcome others to do so if they would like), but instead to use readily available equipment to achieve a reasonably cost-effective solution, that may, hopefully meet my needs. OK, on to a lighter subject...

First, as was mentioned by StanO a while back, I did purchase an RTD sensor for use with the above mentioned controller so I could get the desired temp range control. This sensor was sourced on Amazon for $12. It has one bad review and I haven't tested it yet, so I will let you know how it works. If it doesn't work, I will go back and get the sensor recommended/sold by the company that supplies the controller.

View attachment 115681

Second is the oven itself. As mentioned in the comment back to Tominator2, I had considered a wood outer structure, but then abandoned it after considering both the weight and fairly poor insulating quality of ply and/or pressboard. Instead I am going with the medium density pink sheathing (2" in thickness gives me R-10 effectiveness) for the outer structure. The overall dimensions will be 52"x24"x24" which will provide an effective volume of 48"x20"x20" after the interior lining is installed. This sheathing was sourced from Menards @ $24/sheet (shown in link is tongue and groove version, I purchased square edge).

The outer structure will be glued together with foam adhesive and then the seams will be sealed and reinforced with Gorilla brand heavy duty duct tape. Both of these were sourced at Menards for about $9 total.

View attachment 115692

The inner lining as mentioned in an earlier post is a mineral wool material. This stuff is not generally found at a building supply store. You might find it in bigger metros at an audio store as it is used for sound dampening. I purchased mine from a local supplier, ATS Acoustics, to save on shipping. I purchased Roxul Rockboard 60 for $52 for six 2'x4' sheets. This is the lighter density board version, but still maintains R-8.3 insulating performance--more importantly it can withstand temperatures >1000F.

There are versions of the mineral wool board above that have foil lining. I could not find them locally, so I decided to foil line myself. To do so my plan is to use the heavy-duty (thick) aluminum foil and glue it to the inner face of the rockboard. The overlapping of the foil and adhesive bead will effectively seal the internals of the oven without a need for tape. The aluminum foil and high-temp adhesive (1380F) were purchased at Menards for about $8 total.

View attachment 115691

Next up is the heating element. I know many people have used lamps/light bulbs to do the heating in a homemade oven. In these applications it seemed like the temperature they were trying to achieve was fairly low (<250F). I felt that a radiant heater (and fan combination for heat distribution) would work better for higher temperatures (we'll see). I chose the heater below that I sourced from Northern Tool for $15 (I purchased two, as one will be installed in each end of the oven). This heater was selected for two reasons, 1) size/shape fits comfortably in oven ends with some spacing to walls and, 2) it was cheap as I plan to de-construct the heater to get it to work in this application.

View attachment 115694

Finally the distribution fan for use with the above is a simple computer box fan. I ordered this 4-pack from Amazon for ~$12. I ordered the 12V version as I have an extra 12V supply in my workshop, but you may want to use a 120VAC if it fits your application better. BTW, I expect to only use two of these in the oven.

OK, that is about it on the major components. Next up will be construction of the oven and de-construction of the heaters.
Click to expand...

I will say that the sleeve-bearing fans will fail with great haste. The lubricant will evaporate very very fast. Theoretically, if you took the fan apart, you could replace it with an appropriate grease (krytox?), but I simply wouldn't stick a computer fan in a 400F oven anyway.
 
Last edited by a moderator:
CarVac said:
I will say that the sleeve-bearing fans will fail with great haste. The lubricant will evaporate very very fast. Theoretically, if you took the fan apart, you could replace it with an appropriate grease (krytox?), but I simply wouldn't stick a computer fan in a 400F oven anyway.
Click to expand...

OK, thanks. The fans may be the least critical component, but I do need them to work. When I get them I will take a look and see if I can disassemble and re-grease. I do have some Krytox for hybrid motor use. Probably overkill in this application--I have other high-temp bearing grease that should work.
 
dixontj93060 said:
OK, thanks. The fans may be the least critical component, but I do need them to work. When I get them I will take a look and see if I can disassemble and re-grease. I do have some Krytox for hybrid motor use. Probably overkill in this application--I have other high-temp bearing grease that should work.
Click to expand...

Just mount the motor outside of the oven with a shaft extension and a metal blade.

-Tom
 
For my curing oven I mounted a motor externally and built a shaft extension that protrudes into the oven. Works great.
 
As probably expected, the outer structure is pretty straightforward. After measuring and cutting the six required pieces and testing the foamboard adhesive, I found I would needed a way to keep the seams stationary and tight. After some contemplation, I decided to simply build the structure and use the strong bond Gorilla tape to tighten down and tack everything in place until cure is complete. So I first just positioned everything and made tape hinges then spread the adhesive in the joint area. As the joint closed the tape held and tightened down nicely. Then added the tape strips on the upright corners. All of the seams look pretty good with the exception of about a 5" section at the bottom rear. I will probably come back in after the adhesive cures and add a bit of Gorilla glue that will expand and fill any slight gaps.

023 (960x1280).jpg 024 (960x1280).jpg
 
Burner said:
For my curing oven I mounted a motor externally and built a shaft extension that protrudes into the oven. Works great.
Click to expand...

Tom and James, thanks. Sounds fairly easy--do either of you have pictures of what you did?
 
OK, had a bit of time to work on the heaters. These were referenced before, but, as shown in the first picture below are simple, radiant heaters with two 400W elements. The switch on the side allows you to turn on one or both elements. There is also a safety "tip" switch on the bottom.

007 (1280x960).jpg

As is typical, all the space heaters sold today have a thermal cut-off safety switch. Once tripped you typically have to hit a manual reset switch or remove power to the heater and let it cool before it will work again. Of course, having the heating element switch off inside an oven as it is heating is problematic. So, at the very least this cut-off switch must be removed. So I began disassembling the heater. Looking below at the inside the power/select switch can be seen in the foreground, the thermal cut-off is the square element just to the right (and a ways behind) the power/select switch, and the "tip" switch is still mounted in the bottom of the frame and is partially hidden in the bottom right behind the power cord.

003 (1280x960).jpg

My original plan was just to jumper the thermal cut-off and button the whole thing back up. After disassembly though, I felt that I would get more heat radiated by removing the outer frame and having a circulating fan simply blowing from behind/around the heating element's concave "reflectors." Also, I then realized it is advantageous to have the control of the heating element outside the oven (duh!). So, I discarded all the heater frame (including tip switch) and am left with the power/heat select switch, its control knob, the heating element and its reflector, and the power cord. I will rewire the main switch and switched side of the heating element with longer wire and mount the switch on the outside of the oven. Internal to the oven I will mount the reflector on 1/2" conduit you see in the picture below to "hang" each element in open space at either end of the oven.

006 (1280x960).jpg
 
Swung up to Piper City, IL today (kinda in the middle of nowhere) to pick up my mineral wool panels. Was chatting with the company personnel and they tell me this stuff is made from spun lava rock and stable up to 2000F (Wow!).

033 (1280x960).jpg
 
Repurposed heater controls now combined with power feed and will be remote mounted on the outside of the oven.

003 (960x1280).jpg
 
Lookin good. Are you having trouble with your foil adhering to the mineral wool? I was having issues with it and aluminum tape. I'm curious to hear how that goes.

-Tom
 
Tominator 2 said:
Lookin good. Are you having trouble with your foil adhering to the mineral wool? I was having issues with it and aluminum tape. I'm curious to hear how that goes.

-Tom
Click to expand...

We'll see. Just installed it on the top and bottom panels. Significant tack to begin with, but I'll have to see when I check tomorrow morning.
 
Tominator 2 said:
Lookin good. Are you having trouble with your foil adhering to the mineral wool? I was having issues with it and aluminum tape. I'm curious to hear how that goes.

-Tom
Click to expand...

So Tom, just checked the high-temp caulk, and although not perfect, it is holding the aluminum foil well. By not perfect, I mean that you can, if you try, peel the aluminum foil off and away from the mineral wool, but you have to deliberately do it. It certainly isn't moving around and/or falling off under its own weight (and the top panel was checked).

The thing I was more worried about was the mineral wool adhering to the Fomular. This is also good. I was more worried here because the mineral wool panels are so heavy. The Loctite foam adhesive seems more than up to the task.
 

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