Lexan (Electric Meter Covers) Pressure Vessel Limit

Found this, but it seems to be pretty common knowledge, and not spot-on focus to polycarbonate only.

http://www.nationalboard.org/index.aspx?pageID=164&ID=246

This may get interesting before anything takes place such as an actual test. I really do not want this bursting in my little home shop, or near it.

This is the resulting two halves joined after pouring the silicone gasket over the weekend.

Obviously, this is not a pressure cooker. I like the idea of using the ring structure between the two halves, then I can still "see" what takes place inside the reactor later. For example, if I used a metal reactor, it would have to be insulated from the electrolysis bath somehow (epoxy paint?? might not hold up?) and block prevent viewing anything interesting taking place inside the reactor such as bursts of light being emitted by interesting effects taking place in the electrolysis.

If a ring is used, then a number of problems can be addressed simultaneously, and be done without introducing undue stresses on the plastic? Ring diameter is obvious, ring height does not need to be more than about an inch I suppose.

Oh, it's clear.

Look at it with polarized glasses and you'll see the stress lines.

Now that I've seen your picture, I see no problems at all.

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If you align the axis of symmetry horizontally then your ring could be shaped to also form the gas divider plate, the gas ports angled in the ring to come out on the respective side of the divider..

This is a great project.

Shouldn't be a problem. If something were to happen more than likely the silicone will be what blows out before the Lxan breaks up anywhere.

Yes, I was hoping for more of a poof than pop! The only reason for pressure at all is the need to enclose the experiment, meter the gases produced (maybe even keep the oxygen, hydrogen separated or effect separation using an ultra-filtration membrane set-up.), then months down the road provide for a means to burn the hydrogen or use it on a fuel cell, then condense the water and send it back for another go around.

There only need be enough pressure to keep the gases moving. Obviously, mixtures of hydrogen and oxygen (there will be a divider plate in the upper half, but that will effectively do nothing to separate the gases completely), are very dangerous toward explosion ignition. Flame velocities almost too fast to measure, etc.

It seems that Wright-Patterson researchers did some work in premixed hydrogen-oxygen burns up to about 10 atmospheres pressure, but had hell with unstable ignition blowing up the burner feed tubing. Not something I want happening in my neighborhood. It attracts too much attention!

Maybe I would be better off playing with baking soda and vinegar?

Ithe shouldn't take very much pressure at all to bubble the evolved gas through water a couple times as flash-back traps

I doubt you will even need 2 psi unless you are cranking out some serious volume through thin tubing and multiple deep bubblers.

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Stay away from any edges when drilling holes. Back the but out frequently to clear the hole....but more importantly to make sure things stay pretty cool. If your insert is metal or something else hard drill the hole a little oversized then seal with something like silicone...have to allow for differences in thermal expansion.

PC has a glass transition that is pretty high and is rigid enough to be handled at around 120 C....so 90 C shouldn't be a problem.

If you don't have enough surface area to keep the joints together, consider some wide straps.

Thanks for the information. I agree edges are not the place to drill. There will be a divider plate installed somewhere near the middle line of the upper cylinder, supposedly to reduce gas mixing. I plan to to place the hydrogen take off near this, and the oxygen vent line on the opposite side of the divider. Water addition port will be on the side of the upper cylinder. I will post a photograph here in a bit.

You could build a sample, attach a plastic tube extending 11.55 feet upward, and fill this whole assembly with water. That amount of vertical head equates to 5 psi, giving you a cheap, easy, and safe hydro test.

Also investigate the type of anti-flashback check valves as used in oxyacetylene systems; those might be useful in two or three locations.

I can envision that easily enough, with the tube extending downward into the bottom cylinder below a water line, then to read head, one simply breaks out the tape measure, got it.

I will definitely contact my local welding suppliers about flashback arrest valves.

(1) The total bonded area is the key here. Will the surfaces to be joined be flat or have a radius? Some minimum area will give you an idea of the force being exerted on the bond line.

(2) If the part is round, my guess is that it may have had a center gate. That would be evident as a round flat (probably machined) circle in the center of the cover.

The stress will be evenly distributed along the top of the lid and I would suggest not drilling in the center of the cover, but that depends on how good the molding parameters were controlled by the molder.

Use ONLY lubricants specified for PC use and drill slowly to keep the heat to a minimum. Tap using a sharp tap and tap slowly, reversing the tap every 1/8-1/4 turn to break the chips.

I'm with tcmtech, I think this is totally doable and the bond will fail before the PC.

If you have some to play with dip one in MEK and stress it. That will show you where the stresses are.

So drill not at the edge, but definitely away from the center line. Got it. It seems the upper part of the top cylinder (meter cover) is basically flat, with one raised triangular portion on it. I should stay away from that area when drilling, right? Pictures to follow later.

I would machine a ring to go between the two halves and insert all of the ports into the ring so you have no stress points introduced. If the ring was thick enough to add a groove so the each side could sit on an O ring even better. I would then take two thicker pieces of lexan/perspex/glass and clamp the whole assembly between these with long tension studs so that the flat ends of the meter covers are reinforced and will not bow out into a convex shape. Lexan can only successfully be bent when heated. The side wall should not be a problem. If the flat end is allowed to bow the lexan will crack at the corners. The sharper the edge on the circumference of the face the more likely it will fail then the face bows.

Actually I like your idea very much, and I owe you (and everyone else) many thanks.

Obviously better not to drill the Lexan at all, if one does not have to. The metal ring really does not have to be a ring at all, but could be the upper half of the vessel. If using a metal ring, as long as it does not stay immersed in the electrolysis bath liquids, corrosion should not be huge issue, but it would still have to be coated to avoid shorting to the electrodes of the bath. This would also make the ring a convenient place to introduce all feed through connections for wiring the electrodes (4 total, 2 main, 2 aux waveform), all gas and liquid ports, etc.

If the upper part did not have to Lexan (and it really doesn't as I just thought it would be cool to use Lexan), then fabrication become a lot easier. I have a cowboy welder friend or two out there that can take care of it for me, or I could probably go buy a cheap machine for the cost of having the job done. The pressure I plan on is not really a boiler, so I could be possibly excused for not being boiler certified.

Certifiable, yes, certified no.

One remaining safety item, is a reactor dump for if and when pressure/temperature surges. That requires a fairly large drill hole, or I could forego this, and just encase the Lexan in a blow out sleeve? This would be only in a dire emergency that such an event would occur.

I have tried to break 1/4 inch 12"x 12" piece of lexan by dropping a 7+ pound piece of lead from 12 feet. The lexan was on 4 inch corner supports to get of the floor. After about 10 drops there was no cracks or flaws in the material. I have also tried to break a 1" thick lexan rod with out success. The stuff is amazingly resiliant. After all it is used for bulletproof windows

My learning taught me that silicon adhesive/sealant cannot be used on PC/Lexan. I used to install Lexan sheeting and the product sheet said that no silicon product is to be used. The glazing used a gasket to seal.

As for drilling PC and acrylic i "sharpened" a drill ( bit ) by ensuring there was NO clearance angle. The cutting angle is prescribed by the twist in the drill but the clearance angle is ground by the user. It can be large for wood etc. and small for stainless steel where a high load has to be put on the cutting edge. You can put the drill in a lathe and spin at speed then bring an angle grinder to the drill and grind the point that way. This ensures a 0 deg clearance angle. It won't cut metal but will cut plastic without shatter on break out and with almost no stress raisers. Having said that it won't cut metal;- I have used this to drill thin sheetmetal. It does so without grabbing at breakout. I could hold the sheetmetal down with one finger and drill the hole. Sweating all the while, as if it did grab, my finger would be left sitting on the floor.

Jim

There are two different curing mechanisms for single part silicone adhesives.

One evolves acetic acid when it cures. Bad for PC. The other does not. OK for PC. I think James is aware of this. Primers, otoh, may be an issue if they are used.

Special drills for plastic are available.

The red silicone I used was from Smooth-On, cures by 10:1 mixture, the lower fraction being an alkaline liquid (blue) that is to be thoroughly mixed before pouring. This silicone is typically used for making molds for low melt temperature castings, such as pot metal or pewter, but not aluminum. It does not adhere much to anything but itself, and apparently has no corrosive effect on PC (Lexan), based on first pour results.

A side remark: I have used "window caulk silicone" on a Lexan pane over one of my phonon batteries in the past, and it even did not apparently harm the Lexan.

I am not entirely satisfied with my gasket pour on this project, as I ran out of Smooth-On 60M, thus I only finished the pour on the lower half, but had the lip raised about 1/4", about 1/16" short from sealing both halves .

I still like the added metal band (ring) idea to help with sealing, and allow pass through without even having to drill the Lexan. JimRat's idea of grinding down a drill bit is absolutely brilliant, though, so I may have a go that way. I have plenty of meter covers to experiment with, so no problem.

One last remark: Will probably use plywood as first pass for the ring, and also the top and bottom clamp halves. All thread will be used to tension the clamp halves down on the Lexan vessel parts. My issue is that my lathe is too small to fabricate the metal ring regardless of the metal used (mini-lathe). Do have access to a full 10" throw South Bend out on the farm my buddy has. We will be doing the long-term electrolysis experiment at his place anyway. I can't wait until vacation arrives.

You are certain that this is PC, and not acrylic, right?

I am of the opinion that it wouldn't matter if it was acrylic. 5 PSI isn't much.

Acrylic tolerates solvents/chemicals well enough.

I agree the pressure is unlikely to be a concern. Not sure about the resistance to specific additives for electrolysis.

The thing I was thinking about was glass transition temperature. Acrylic typically has a lower glass transition temp than PC. Acrylic glass transition temps vary significantly with additIves; some down to 90C.

They are thermoplastics.

At 5 PSI Tg hardly matters.

Then I got to mulling around on the web at a plastics supplier and found these:

http://www.usplastic.com/catalog/item.aspx?sku=85273

and these:

http://www.usplastic.com/catalog/item.aspx?sku=85286

it might be easier to fit electrodes to the rectangular shaped containers, but sure about any pressure ability at all on these. Might be worth popping one to find out (just with hot water and air)....from a safe distance at mini-myth buster ranch.

Of course glass transition temp matters. Above that it takes little force to change shape.

I am sure I have PC, and the bath will be kept no higher than 80 C by design.

I have other plans for an outer bath as thermal inertia, with its own cooling coil. Not saying right now what will be flowing through this coil.

Little is a relative term. You'd need to look at the stress-strain curve of this material to determine if 5 PSI will have any effect on this particular material.

Maybe you are right, but I'll stand by my assertion.

Duly noted.

From US Plastics website:

How can I tell Polycarbonate from Acrylic?

How to tell Polycarbonate from Acrylic

In the formulation of Polycarbonate, a bluing agent is used. While Acrylic and Polycarbonate both appear clear on the surface, you will notice the edge of the Polycarbonate looks blue, while the Acrylic is clear.

Note: View in natural light for best effect.

The electric meter covers are definitively bluish hue in natural light, but in Coors, they appear a bit blurrish. After further review, the play on the field is upheld.

My belief is they are PC. I have not totally confirmed that, so I should check into this a bit more. I suppose I should test some and compare. In fact, it might be acrylic, PC, or CA (plexiglass). I really should do more of my homework, huh?

Having a better idea of what the material is would give you better insight into compatability of fluids and adhesives, as well as suggesting a maximum working temperature.

....but as Lyn notes, at these low pressures you aren't creating something very dangerous, so even if you get it wrong, bad results are unlikely to cause bodily harm (assuming normal reasonable precautions apply).

I was researching something, I forget what, and I ran across CR-39 optical plastic that is used for a etch track detector material for alpha particles, neutrons, etc. Also learned about another one that has been used in Radon badge detectors for a long time: Kodalpha film (made by Kodak).

I found the article related to etching, basically 6M NaOH solution 70 °C for 7 hours. I microscope is required for studying the etch marks/tracks.

The solution I will be using will be very slightly alkaline in the beginning and turn alkaline (high pH) over time, but not enough to destroy or really corrode the PC to any appreciable extent. Other gents in my group have used this PC material with good success.

A redeployed domestic pressure cooker vessel would be a better starting point, for its design can already withstand the temperatures and pressures indicated. The source of supply is practically unlimited and no compromising materials need be introduced into the design.

Do note that size, pressure difference and wall thickness of any pressure-containing structure are inter-related, and respond easily to mechanical design calculations once the tensile strength of the wetted materials are known.

That is true, and was considered, although most pressure cookers are Aluminum, and this metal is inconsistent with use as an electrolysis bath container.

Thus if Aluminum vessel is to be used, it would need to be coated carefully with something very resistant to an alkaline bath, and this material cannot be electrically conductive, as the voltages and currents applied can short out, or present a serious shock hazard to personnel. On the other hand, much easier to drill for ports, pass through for electrical, etc.

I am not aware of epoxy vessel lining temperature limits, but I am sure this would be a good starting point.

The only other issue: What if some dummy such as myself wants to visually inspect what is taking place inside the vessel? OK, I get it, cut another port and install the Lexan window there.

The real fun part is when I start attempting to prevent blowing the entire apparatus by attempting H2/O2 separation off the vessel, then igniting it in a diffusion type burner. Have thought to try a premixed burner design, but in these the velocity of flow vs. flame front velocity has to be (1) balanced, and (2) flame velocity cannot exceed flow velocity at any single point in time. It is more than a bit touchy.

Objective: make a closed system to extract the energy of the off-gases, and account for all the heat flows in and out by effectively turning the entire apparatus into a flow calorimeter, to the extent possible. If excess heat is produced it will be measured, camera hopefully will also be installed to monitor any unusual events in the bath. Our group has witnessed large scoops of the bath being thrown out on the concrete nearby in the past, along with some radiation that quickly dissipates with the heat. This is not your father's HHO machine. By the way, all baths up to this point were done as an completely open system, totally not conducive to caloric measurement.

Some of the variables we will input to our controller: about ten different temperatures, all of the voltage and current to all electrodes, pressure gauges, flow sensors of some type or another (have not come up with as yet, but they will not be thermal based sensors for obvious reasons.) Water input will also be made continuous for the first time, or nearly so by an inverted sipping tube arrangement.

At first, all of the heat content of electrolysis gases will be measured most likely by heating a volume of water adiabatically. Later on this will be put to use in a heat engine of one class or another, perhaps several for tests. Eventual objective is to close the power/material loop on this system make it as nearly self-sustaining as possible. If thermal gain has been found, and consistently produced, then attempts will be made to exploit it - far beyond a mere cup of hot tea.

Sorry I didn't get back with you before now. What would recommend coating the pressure cooker with to avoid the problem of aluminum corrosion in high alkaline pH? It needs to be this way since sodium bicarbonate is the typical water additive in these set ups.