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1/2" polycarbonate (makrolon) cracking
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mtnhillsman Offline
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Post: #1
1/2" polycarbonate (makrolon) cracking
OK, this is redicuils...

My first cell, shame on me, overtightened the inlet/outlet fittings, probably overtightened the perimeter bolts, after OVER A WEEK of running my poly cracked. Didnt go too crazy, used a 1/4 inch drive in a 4 inch ratchet and tightened everything finger tight, but wasant being too critical since it is 1/2 inch material, probably overestimated its strength. Started from the corner bolts and worked my way in. My nylon fittings i did overtighten, probably 2 turns past finger tight but it didnt feel like it was anything too crazy. This cell ran fine for over a week, one side cracked when i adjusted my barb fittings to point up instead of down.

Had 2 more pieces of polycarbonate ready to repair it, so I drilled, threaded and assembled. This time tightening the perimeter bolts JUST enough to mostly compress the lock washers, again using a 1/4" 4" handle ratchet, this time only tightening them with the pressure of 2 fingers. The nylon fittings, screwed them in hand tight and 3/4-1 turn to get them pointing in the direction i wanted them. Ran the cell overnight lastnight, the pictures are of the rebuilt cell, this time cracks after only one night of running, all around the nylon fittings.

Heat was never an issue in either cell, the first one never went above 150 degrees F. The new cell rebuild it ran at 10 amps overnight and remained around 90 *F.

So thats $100 in polycarbonate down the drain, its times like this that make me wish i never got into HHO.

http://www.onlinemetals.com/merchant.cfm...op_cat=181

This is where i got it, im sure its error on my part but this is good material right??


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(This post was last modified: 03-12-2009 09:45 AM by mtnhillsman.)
03-12-2009 09:15 AM
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benny Offline
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Post: #2
RE: 1/2" polycarbonate (makrolon) cracking
(03-12-2009 09:15 AM)mtnhillsman Wrote:  OK, this is redicuils...

My first cell, shame on me, overtightened the inlet/outlet fittings, probably overtightened the perimeter bolts, after OVER A WEEK of running my poly cracked. Didnt go too crazy, used a 1/4 inch drive in a 4 inch ratchet and tightened everything finger tight, but wasant being too critical since it is 1/2 inch material, probably overestimated its strength. Started from the corner bolts and worked my way in. My nylon fittings i did overtighten, probably 2 turns past finger tight but it didnt feel like it was anything too crazy. This cell ran fine for over a week, one side cracked when i adjusted my barb fittings to point up instead of down.

Had 2 more pieces of polycarbonate ready to repair it, so I drilled, threaded and assembled. This time tightening the perimeter bolts JUST enough to mostly compress the lock washers, again using a 1/4" 4" handle ratchet, this time only tightening them with the pressure of 2 fingers. The nylon fittings, screwed them in hand tight and 3/4-1 turn to get them pointing in the direction i wanted them. Ran the cell overnight lastnight, the pictures are of the rebuilt cell, this time cracks after only one night of running, all around the nylon fittings.

Heat was never an issue in either cell, the first one never went above 150 degrees F. The new cell rebuild it ran at 10 amps overnight and remained around 90 *F.

So thats $100 in polycarbonate down the drain, its times like this that make me wish i never got into HHO.

http://www.onlinemetals.com/merchant.cfm...op_cat=181

This is where i got it, im sure its error on my part but this is good material right??

Design I am not to keen on WRT the plate and gasket edges being well inside the bolts. This setup will put a fair bit of leverage on your plates. Doesn't take a lot of overtightening to do damage.
I much prefer to bring both plate and gasket edges to at the very least just outside, but preferably more, the centre line of the bolts. That way you get fairly even loading without stressing the end covers.
Stress is what is causing your fracturing.

Don't know that brand name of plastic, but make sure it is polycarbonate, and not acrylic. Acrylic tends to be brittle in nature, fracturing easily under stress. Polycarbonate is a lot more robust.

You could use spacers/standoffs (bits of metal tubing) on your bolts to limit compression. These would need to be cut the same length, and you would need to allow for compression of your gaskets when measuring same..
03-12-2009 11:33 AM
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mtnhillsman Offline
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Post: #3
RE: 1/2" polycarbonate (makrolon) cracking
(03-12-2009 11:33 AM)benny Wrote:  Design I am not to keen on WRT the plate and gasket edges being well inside the bolts. This setup will put a fair bit of leverage on your plates. Doesn't take a lot of overtightening to do damage.
I much prefer to bring both plate and gasket edges to at the very least just outside, but preferably more, the centre line of the bolts. That way you get fairly even loading without stressing the end covers.
Stress is what is causing your fracturing.

Don't know that brand name of plastic, but make sure it is polycarbonate, and not acrylic. Acrylic tends to be brittle in nature, fracturing easily under stress. Polycarbonate is a lot more robust.

You could use spacers/standoffs (bits of metal tubing) on your bolts to limit compression. These would need to be cut the same length, and you would need to allow for compression of your gaskets when measuring same..

It is polycarbonate definitely, makrolon is just a brand i guess. The bolts actually touch the gasket material for ease of assembely so there's no gap there, the bolts are as close as they can be. Also for strength the polycarbonate comes out a full inch from the edge of the gasket. I could go larger if necessary.

I suppose i could run the bolts through the plates and gaskets and insulate them, however take a close look at where the cracking was. The cracking was not around the bolts at all, all cracks began around the nylon fittings. Each crack progressed outward an inch or so, in the worse case all the way to the edge. Note that the crack did not go TO any of hte bolt holes, it seems to me if there was alot of pressure at one or all of the bolts the crack would spider out from the fitting and go to a bolt (or start at a bolt), even for the reason of bolt hole being a weakpoint even if there was no stress from the bolt.

I'm thinking that its cracking from the fittings or my threading, how far do you normally thread a NPT tap into the material, Its half inch and i've been threading it deep enough so the end of the tap comes about 1/8" through the other side of the polycarbonate. thats about the point where its taking quite a bit of pressure to turn, about all i can do with a 4" 1/4" drive ratchet, so i then back it out. I also lubricate with soap.

Do you think it could be caused by me forcing the tap too far into the hole, causing microfractures to form, then when the cell heats/cools these fractures spread?? I ran the first cell for several days with no issues, then, adjusted the fittings to point up instead of down, so, one side i had to tighten 1/2 turn, the other side i had to loosen 1/2 turn. BOTH sides fractured around the fittings within 4 hours of use. Again, only around the fittings and in that case the outer bolts were untouched.
(This post was last modified: 03-12-2009 12:02 PM by mtnhillsman.)
03-12-2009 12:00 PM
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benny Offline
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Post: #4
RE: 1/2" polycarbonate (makrolon) cracking
Quote:

I suppose i could run the bolts through the plates and gaskets and insulate them, however take a close look at where the cracking was. The cracking was not around the bolts at all, all cracks began around the nylon fittings. Each crack progressed outward an inch or so, in the worse case all the way to the edge. Note that the crack did not go TO any of hte bolt holes, it seems to me if there was alot of pressure at one or all of the bolts the crack would spider out from the fitting and go to a bolt (or start at a bolt), even for the reason of bolt hole being a weakpoint even if there was no stress from the bolt.

I'm thinking that its cracking from the fittings or my threading, how far do you normally thread a NPT tap into the material, Its half inch and i've been threading it deep enough so the end of the tap comes about 1/8" through the other side of the polycarbonate. thats about the point where its taking quite a bit of pressure to turn, about all i can do with a 4" 1/4" drive ratchet, so i then back it out. I also lubricate with soap.

Do you think it could be caused by me forcing the tap too far into the hole, causing microfractures to form, then when the cell heats/cools these fractures spread?? I ran the first cell for several days with no issues, then, adjusted the fittings to point up instead of down, so, one side i had to tighten 1/2 turn, the other side i had to loosen 1/2 turn. BOTH sides fractured around the fittings within 4 hours of use. Again, only around the fittings and in that case the outer bolts were untouched.

Sorry if this is teaching granny to suck eggs, but . . .

I assume you are using a tapered tap to tap out the hole. Any time I have tapped polycarbonate (Quite a few at my last place of work) I have taken the tap all the way through, giving me a parallel thread through the polycarb, Are your fittings of the tapered thread type, or are they flanged?
If flanged you may need a sealing washer, if tapered, then the taper barb will find its own depth in the hole. In either case I would also use PTFE thread tape (Plumbers thread tape) to ensure a good seal.

What I do is use the same method as for tapping steel. Make sure your tap is sharp (new condition). Work the tap backward and forward, gradually increasing the depth until the tap is fully through the polycarb. Seems to avoid any problems that way. You should not need to use much force to tap Polycarb. Most difficult part is getting a start in the thread.

I find that, if you rush this, the polycarb tends to heat when tapping, and you end up with a ragged thread, and quite possibly small cracks. Especially if using a blunt tap.

One more thing. A tip to help prevent breaking at the inlet/outlet holes.

Cut washers from a cut off of polycarb, making the hole big enough to allow your barb thread to fit through into the thread on your unit, and glue this using an appropriate glue, to the outside of your plates. Helps stop any cracks from forming, or spreading.
You can, if so desired, glue a piece of poly, doesn't need to be washer shaped, to your end plate before boring and tapping.
Much stronger area for drilling and tapping. Less chance of fractures. Just ensure if you use this method, that you completely seal between the end plate and the extra piece of poly, with the glue. No air bubbles between them

As to your polycarb not fracturing to/from the bolt holes, try bending a thin piece of same. It will usually fracture along a line where there is greatest stress, or where there is a weakness in the material. This is not necessarily where your bolt holes are, but badly tapped threads could be a starting point for cracking. Acts similar to glass, with crack expanding over time.
(This post was last modified: 03-12-2009 01:31 PM by benny.)
03-12-2009 01:18 PM
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mtnhillsman Offline
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Post: #5
RE: 1/2" polycarbonate (makrolon) cracking
It is a tapered tap. Turning the tap all the way through the material would be out of the question unless I was using a breaker bar.... Now maybe that was because I was threading rather quickly, and it was getting pretty hot. I'll test driving it all the way through a piece of my scrap slowly not allowing it to heat and see what happens. The tap is brand new btw.

Good ideas about making it a bit stronger. Ill have to go that route...reluctantly, kind of ugly to have these big blocks of poly glued on the cell but necessary, if its cracking in a mild environment on the bench i can only say it must be built to higher standards to endure a wide temp range and any shock in the vehicle. Im also going to go with larger washers, nylon lock nuts instead of lock washers, and buy a torque wrench.
03-12-2009 06:20 PM
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benny Offline
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Post: #6
RE: 1/2" polycarbonate (makrolon) cracking
(03-12-2009 06:20 PM)mtnhillsman Wrote:  It is a tapered tap. Turning the tap all the way through the material would be out of the question unless I was using a breaker bar.... Now maybe that was because I was threading rather quickly, and it was getting pretty hot. I'll test driving it all the way through a piece of my scrap slowly not allowing it to heat and see what happens. The tap is brand new btw.

Good ideas about making it a bit stronger. Ill have to go that route...reluctantly, kind of ugly to have these big blocks of poly glued on the cell but necessary, if its cracking in a mild environment on the bench i can only say it must be built to higher standards to endure a wide temp range and any shock in the vehicle. Im also going to go with larger washers, nylon lock nuts instead of lock washers, and buy a torque wrench.

The only other thing I can add is to make sure you have the correct size of drill for the tap you are using, and take care when drilling. Polycarb has a bad habit of 'snatching' when drilling.
Try using a smaller diameter drill to make a pilot hole for your tapping size drill.

Also any add on piece of plate is only as ugly as you make it. Crazy
Think sheet steel with welded nuts.Cool

One last thought. It is also possible to make up add on plates, pre-tapped, and glue these over a drilled untapped hole with just enough clearance to allow any protruding barb thread to pass through. Also handy for repairing any tapped holes where some slight cracking has already occurred. Just be sure to use the correct glue for the material, and allow enough curing time for the glue to set properly before putting into production
(This post was last modified: 03-13-2009 01:08 AM by benny.)
03-13-2009 12:50 AM
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saltmine Offline
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Post: #7
RE: 1/2" polycarbonate (makrolon) cracking
I encountered the same problem threading fittings into end plates, too. It didn't matter what they were made of, they all seemed to crack after a time. Then, I started tapping the threads deeper, and using teflon tape (about 3-4 wraps) on the fittings, and not tightening them so tight. The teflon did the trick. no more leaks....or cracking.

Like Benny says, placing the bolts outside the gaskets does create quite a "lever arm" to distort and fracture the material. Which is probably why the Sid Cell is so popular with it's bolts going through the gaskets instead of outside of them.
(This post was last modified: 03-13-2009 04:02 PM by saltmine.)
03-13-2009 03:58 PM
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Cudaman Offline
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Post: #8
RE: 1/2" polycarbonate (makrolon) cracking
Just my 2 cents but I would forget the Poly crap. I think the electrolyte reacts to the material and makes it crack. I have built 5 units out of it and the last out of the same material as you 1/2" and after around 3 days it started to crack just like the others.
I'm looking at PVC type material now. Won't be able to see into it but with the tests I have done it looks like it will not react like the Poly.
Safety windows in our machining centers at work do the same thing due to the coolant reaction.
03-14-2009 10:51 AM
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freddyhho Offline
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Post: #9
RE: 1/2" polycarbonate (makrolon) cracking
Yep, I'm to suffer the same problem, build 5 times the same dry cell because the polycarbonate crack from the inlet and outlet threaded holes, no matter what size. The problem goes when I change to Nylamide or PVC material. You can see this:
http://www.fuel-saver.org/showthread.php?tid=2734
You can see some photos in there.

1995 Dodge Ram 2500
V8 5.9L 360
Tero Dry Cell 19 plates (3 cells 5 neutrals)
MAP and EFIE Enhancers
Water Vaporizer
Gasoline Vaporizer
03-17-2009 10:10 PM
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Hawkman Offline
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Post: #10
RE: 1/2" polycarbonate (makrolon) cracking
I found this chart. Just confirms our experiences.
http://www.millerplastics.net/chemical_r...chart.html[/url]
03-18-2009 12:09 AM
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