DIY Autoclave

General Composites Discussions Equipment Talk
#1

Hi All,

In the process of building a small autoclave using a Binks 15 gallon pressure pot. I have a few questions regarding plumbing I hope someone can help me with.

(a) Vacuum line - I have 3/8 NPT access point in the front of the pot that I want to control the vacuum with i.e., pull vacuum and also release vacuum while under pressure. The question is what type of fitting do I need here ? as the main concern I have is if I have a leak, having 90 psi go backwards through these fittings.

(b) The next plumbing issue is going to be running the heater and themocouple into the pressure vessel; has anyone tried this type of thing ?

Thanks in Advance,
.adrian

#2

Hi Adrian,

I like the idea to turn a Binks 15 Gallon pressure pot into an autoclave. So much that I bought one (the stainless version) and a bunch of other parts 10 months ago :wink:
Now I finally have the time to start the project.

I haven’t looked into the vacuum plumbing and pressure control in detail yet (maintaining constant pressure at varying temperatures and finding pressure controls that can handle 180-200C hot air is one of the next points on my list), but I found solutions to the other plumbing issues: I’m heating the pressure pot from the outside with flexible silicone heaters (from Watlow, 600w each for a total of 4.2kW). That eliminates extremely hot heating elements and the need for wiring into the pressure pot, saves space in the autoclave and provides better heat distribution. For the thermocouple (or RTD) I’ll go with a long, bendable, pressure tight screw-in probe in a threaded hole the center plug of the lid. Attached is a photo of that type of thermocouple. Omega and other manufacturers offer a wide variaty of thermocouples or RTD’s that can handle 5+ times the max 110 psi in the pressure pot.

Marcus

#3

I have thought of this before but heating up a 90PSI pressure pot with was not intended to do such task holds me off. Please keep us posted if you ever get this project done.

#4

Some pressure pots are designed to also be used with hot asphalt etc. Ours is new and ASME certified for 110psi at 200 degrees F. The minimum safety factor per standard is 3 (design margin). The tensile strength of the particular stainless steel that this one is made of decreases by 6% between 200F and 400F. So it should be able to withstand at least 310psi at 400F, but in burst tests it’s usually at least 2 times that number. We run it with two safety valves and a separate back pressure regulator, eight cut-out thermocouples (two internal and one at every heater) and in an insulating steel enclosure that has 4 times the volume of the pressure vessel and large over-pressure vents. The heaters self-destroy at about 600F, just in case. So I guess we should be ok… Yeah, it’s over-engineered. It has to be, because I’m a crazy perfectionist. And a safety engineer :wink:

If you think about building one, keep in mind that there are a couple of interesting challenges if you want to do it safe. Like keeping the pressure constant while the temperature changes. Our setup has 14 valves and 4 regulators in total (pressure + vacuum). All rated for at least 450F, which means industrial/instrument parts (and prices)…

#5

Hi Marcus,

I must first applogize for not responding back in December, for some reason i didnt see or get the notification and gave up checking after a few weeks, as i also managed to muddled out my pressure issue with the vaccuum.

At this stage still haven’t built the unit as my work situation changed andi had to re focus some of my attention but have been slowly gathering parts.

Could you upload or pm me some photos as would be keen to see your lid layout. Again sorry for not responding, as always really appreciate people taking the time to help out and generally always try to return the courtesy.

TINGC911 Sorry not much to go on yet as mentioned above have been side tracked with work and some personal commitments. Will certainly respond with my progress.

Cheers,
.adrian

#6

Hi Adrian,

Attached are some photos. Insulation is obviously missing at the moment, as are heating and cooling systems and the control panels (on the sides between the pillars; one side for pressure/vacuum, the other for heating/cooling).

Best,
Marcus

#7

Hi Adrian,

Below is a photo of the lid hinge. We’ve mounted the hinge to the reinforced side of the container that the pressure pot sits in. The weight of the lid rests on a stainless tee that goes into the 1/2" NPT thread (open whole on the picture). That fitting has an OD of 3/4" and could hold a few tons. The fit is intentionally slightly loose. The upper slot with the 3/8" fitting keeps the lid upright; it does not hold weight.

We plan on using an Omega CN8Pt process controller. We’ve got a couple of CNi3200’s with separate thermocouples that we’ll use as overtemp. cut-outs (connected in series between the CN8’s output and the main heater relay).

The autoclave is a project that I do with our kids (8 and 10). They’ve got some great ideas and are pretty good with Autodesk Inventor, Fusion 360 etc. We do the engineering together and they do the programming. Two years ago we got a 3D-printer, but those parts aren’t strong enough, so we got the Tormach. That was fine for some time, but we actually need light parts… Some of the first will probably be sandwich parts (honeycomb and free form balsa), fan blades for a wind tunnel and parts for MTB’s (we’re into downhill).

Cheers,
Marcus

#8

Thanks Marcus,

Like the idea of hanging it off the two front fittings.

Please keep us posted with your progress as keen to see how you get on. I am about to head away for 6 weeks. But the time will give me a chance to rethink my design. Will also checkout the omega process controllers.

Cheers,
.adrian

#9

Hi Adrian,

Hanging the lid off the fittings makes it easy to get the few degrees of freedom in all directions that you need when tightening the bolts.

The Omega Platinum Series controllers seem a perfect fit. They start at $205. Our configuration would be ~ $390.

Cheers,
Marcus

#10

We are manufacturer of Composite Autoclave
contact us for further discussion

Rakesh Verma (Overseas Manager)
rakesh@olymspan.com
+86-13861177443
www.compositeautoclave.wordpress.com

#11

Stop with the spam messages on old topics.

#12

Is there any update on this topic? I.e. Did you build the diy autoclave and if so, how well did it work out?

I think that the best option for a diy autoclave is an old steel or aluminum gas tank. They are designed to handle 4500 or 3000 psi. All you would have to do is cut a door and figure out how to seal and secure it. Vacuum and pressure lines can be easily fed in with drilled and tapped holes.

For an easy heat source, you can find oven heaters designed for use on large BBQs and smokers for very little money. They plug straight into the wall.