Polycarbonate Tops... a scientiffic analysis! - Page 3

Cova · 03-14-2003, 12:49 PM

After reading that link bb2k posted very early in this thread about the polycarbonate windows for cars, I'm under the belief that simply drilling a hole in it will cause microcracks to form. Threading the hole after that will likely make it worse. WinFlex - take that piece of Lexan that got the crap beat out of it, drill a little hole in it somewhere, and then hit it a few more times.

Skulemate · 03-14-2003, 01:38 PM

But before you do, prop one end up on a piece of scrap metal... then see how many blows it'll take.

WinFlex · 03-14-2003, 02:56 PM

we just used the old shitty manual mill to see how much shear it can take, just pushed the collet up against the lexan while it was being held in the vice. I was unable to break it that way, which is pretty amazing. Again, this has really nothing to do with microcracks tho

MadDogMe · 03-14-2003, 03:14 PM

Quote:

But before you do, prop one end up on a piece of scrap metal... then see how many blows it'll take.

I think the idea was to get it to haze/crack, not snap

, how well do you think Cu or ALu would stand up to this scientific test

...

**************************************

Quote:

I'm under the belief that simply drilling a hole in it will cause microcracks to form. Threading the hole after that will likely make it worse.

That's what I thought, but I can't see it mattering under normal usage (ie, Gorrila and 24inch pipe wrench[not]), but then again I think these failures would happen anyway without the microfissures being the starting point the way some people ham fist Lexan tops :shrug: , using allen bolts without washers, torquing up NPT barbs till they're tight as a mouses ear. I hav'nt heard of a failure yet that was a result of 'factory fitting'...

I'm interested in seeing how it stands up with two or three holes drilled into it as well, a normal water jacket scenario, not that ballpane hammers come into a normal water jacket scenario... often

...

theetruscan · 03-14-2003, 03:44 PM

Yeah, lexan's really not that tough. It took less than 1 full clip from an AR-15 rifle at 30 yards to completely destroy a 3/4" piece. That's all I can really contribute. Been reading up on the microfissures, and I'm almost 1/10 of the way to caught up on this issue.

bigben2k · 03-14-2003, 04:10 PM

Quote:

Originally posted by MadDogMe
I think the idea was to get it to haze/crack, not snap , how well do you think Cu or ALu would stand up to this scientific test ...

They'll bend

Skulemate · 03-14-2003, 04:39 PM

WinFlex, I am sure that you understand that compression, shear and tension are quite different things altogether. Ben's precisely correct, if you do this to any material it will bend, and this will cause the lower face of it to go into tension. Since it's a tension field around these barbs that's causing these micro fractures to propogate I thought it might be helpful to turn up the tensile stresses within the polycarbonate so to speak. I would bet that after this "scientific" test you'd see some serious cracking present near any drilled holes, etc. Shearing the block and pounding on it to introduce compression have nothing to do with micro cracks forming (as Bill has already pointed out).

bigben2k · 03-14-2003, 04:51 PM

Right on Skulemate, as usual!

It's interesting to look at glass' properties, wether it's tension, shear or compression: glass can make for an excellent structural piece, in compression, but very poor in tension. Also, the microfractures in glass can be quite spectacular, when looked at with the right scope (safety glass is different).

Skulemate · 03-14-2003, 05:01 PM

[off topic]

I'm taking a studio course right now as a fourth year elective. It's a collaborative design class that's mixed engineers and architecture students. Anyhew, this course has offered a series of weekly lectures, and among them was a lecture by Jonathan Sakila, who works in structural glass. It was an amazing presentation... I would never have guessed that glass could be used in such a wide variety of structural roles... beams, columns, walls, entire staircases... really quite awesome stuff.

[/off topic]

Anyhew, back on topic... I was looking at some material properties of polycarbonate, and noticed that it's tensile capacity is quite high (9000psi / 62.1 MPa) compared to its compressive strength (12000psi / 82.7MPa), and that it's flexural capacity is quite high as well. Still, quite aparent that it will fail in tension, as Bill has said.

By the way, I got those numbers here.

redleader · 03-14-2003, 05:13 PM

I onced taped a 2inch diameter clear PVC pipe w/ 3/8NPT threads. because of the curvature the threading was extremely thin. Only two or three complete threads.

What worked really well was some adhesive (I used Marine Goop as several people recommended it for bonding to plastics). I was quite rough with the job, bus simply slimeing up the threads with it and gently turning the barbs in a few turns (not enough to make a tight seal without adhesive) resulted an in extremely tight seal. Its been 8 months now without so much as a drop has leaked, dispite heavy abuse due to my clumsiness. Considering my experience, I'd say adhesive or chemical bonding is absolutely the way to go.

Blackeagle · 03-14-2003, 05:39 PM

Where I work there are some control panels covers made of 1/2" Lexan. These have been cut to make a center lockable access door that is also made of lexan. This door is mounted with a piano hinge and the opening is rimmed in alum. frame work. The lexan has been drilled in numberous places as well along the outer edge for mounting purposes. Bolts pass through these holes and into the main fram of the control panel. These covers were put in place back in late summer of "95" and have been openned and shut countless times, sometimes slammed shut. I've seen people sit on them ect. And in a few cases they have been struck some heavy blows.

They are scratched in numerous places.

There are alos small cracks next to some of those drilled holes. The cracks are small not extending more than 1/2" from the hole they have started from.

I work in a prison as a corrections officer. Not one of these panels has ever failed us. That is the best recommendation I can give.

Yes they have a few very small cracks starting around some of the drilled holes, but not many. And this is after 8 years of hard use and abuse.

LEXAN IS TOUGH STUFF!!!!!!!!!!!!!

MadDogMe · 03-15-2003, 04:27 AM

Quote:

WinFlex, I am sure that you understand that compression, shear and tension are quite different things altogether.

Twas me not Winflex!, and I was joculating

...

*******************************************

theetruscian!, I would'nt use anything that took less than two clips from a AR~15, you've completly changed my 'take' on lexan!

...

UnloadeD · 03-15-2003, 06:59 AM

Just a few thoughts I'd like to add.

1) There were quite a few cases of failures with "factory fittings". One example would be the gemini blocks. It seems the failure weren't caused by the thread/barb area though. There were two revisions. Here's what they say about the revision:

"Revision 2 Changes vs Original Block
> Wider Channels provide less flow restriction and allow an overall higher flowrate
> Machined out center inlet provides less backpressure, which enables the pump to push out the same flow while doing less work. The less work the pump does, the less watts are absorbed by the water.
> New measures to prevent Polycarbonate cracking."
Here are pics of both Rev1 and Rev2. The only change (regarding top) I can see is that the bolt holes are no longer countersunk. I suspect the countersinking along with the thin top caused the problems for them. The other poly topped blocks that I've seen people report troubles with (DD, TC-4 & Spir@l) all had brass or chrome barbs, so I'm not sure where their troubles came from.

2) Re: Methylene Chloride treatment of threads. I've used this stuff making quite a few pieces for my system and the capillary action is pretty impressive. I'm not sure how this would work, but might be worth a try. Rather than treating the threads before installing the barb, and possibly deforming the threads. It might be better to put the barb in and then apply it. I'm sure the capillary action would draw it from one end ofthe threads to the other. It would only act on the polycarb threads and do nothing to the brass or polyprop ones. This should seal any micro fissures and also form the polycarb to the inserted threads, making a psuedo molded thread. There's quite a bit of speculation here on my part, but I think it would be worth looking into.

3) Seems most are leaning towards thicker tops and putting more thought into machining them. One thing I haven't seen mentioned is the actually quality of the material as in cell cast vs. extruded. The cast stuff has much better qualities for our use and should be noted.

Thats my $.03

peace.
unloaded

bigben2k · 03-15-2003, 10:42 AM

Quote:

Originally posted by UnloadeD
2) Re: Methylene Chloride treatment of threads. I've used this stuff making quite a few pieces for my system and the capillary action is pretty impressive. I'm not sure how this would work, but might be worth a try. Rather than treating the threads before installing the barb, and possibly deforming the threads. It might be better to put the barb in and then apply it. I'm sure the capillary action would draw it from one end ofthe threads to the other. It would only act on the polycarb threads and do nothing to the brass or polyprop ones. This should seal any micro fissures and also form the polycarb to the inserted threads, making a psuedo molded thread. There's quite a bit of speculation here on my part, but I think it would be worth looking into.

Thank you for that! (including speculation!)

Did you have any difficulty in obtaining the Methylene Chloride?

UnloadeD · 03-15-2003, 10:52 AM

No trouble at all $3.75 for 4oz bottle:
http://www.tapplastics.com/plastics/...rylcement.html
You'll also want one of these, I use the squeeze type:
http://www.tapplastics.com/plastics/...pplicator.html

4oz of the stuff doesn't seem like much, but it goes a loooong way, 1 drop (maybe 2) per joint. It's a pretty mean solvent, so be sure to use care with it.

peace.
unloaded

WinFlex · 03-15-2003, 05:33 PM

yeah, only tools countersink lexan. counterbores are allright tho, because then there is only compressional forces, not radial expansive ones

MadDogMe · 03-18-2003, 04:37 AM

Counter bores are |_| shaped as oppossed to counter sinks \ / shape right?. the ' Vee' shape is acting as a wedge causing the failure is'nt it?...

I'd say it's best to use a normal allen bolt and forget about 'sinking' it at all. You can get 'smooth topped' allen bolts that have a rounded off top that's nicely low profile (Maze 3 second revision(?) use them). I believe they had problems sinking the bolts as well (which rev2 countered)...

03-14-2003, 01:38 PM	#52
Skulemate Cooling Savant Join Date: Jul 2002 Location: Toronto, Canada Posts: 381	But before you do, prop one end up on a piece of scrap metal... then see how many blows it'll take. __________________ Michael E. Robbins M.A.Sc. Candidate, University of Toronto 12.1 GHz of AMD's finest (17.7 GHz total) crunching proudly for the AMDMB.com Killer Frogs SETI BOINC: Dual Opteron 246s (Iwill DK8N) \| XP2800+ (Shuttle SN41G2) \| 3x XP2400+ (ASUS A7N266-vm) SETI BOINC: 2x P4 2.8E (ASUS P4R800-vm) \| Crunching 24/7

03-14-2003, 04:39 PM	#57
Skulemate Cooling Savant Join Date: Jul 2002 Location: Toronto, Canada Posts: 381	WinFlex, I am sure that you understand that compression, shear and tension are quite different things altogether. Ben's precisely correct, if you do this to any material it will bend, and this will cause the lower face of it to go into tension. Since it's a tension field around these barbs that's causing these micro fractures to propogate I thought it might be helpful to turn up the tensile stresses within the polycarbonate so to speak. I would bet that after this "scientific" test you'd see some serious cracking present near any drilled holes, etc. Shearing the block and pounding on it to introduce compression have nothing to do with micro cracks forming (as Bill has already pointed out). __________________ Michael E. Robbins M.A.Sc. Candidate, University of Toronto 12.1 GHz of AMD's finest (17.7 GHz total) crunching proudly for the AMDMB.com Killer Frogs SETI BOINC: Dual Opteron 246s (Iwill DK8N) \| XP2800+ (Shuttle SN41G2) \| 3x XP2400+ (ASUS A7N266-vm) SETI BOINC: 2x P4 2.8E (ASUS P4R800-vm) \| Crunching 24/7 Last edited by Skulemate; 03-14-2003 at 05:11 PM.

03-14-2003, 04:51 PM	#58
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Right on Skulemate, as usual! It's interesting to look at glass' properties, wether it's tension, shear or compression: glass can make for an excellent structural piece, in compression, but very poor in tension. Also, the microfractures in glass can be quite spectacular, when looked at with the right scope (safety glass is different). __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

03-14-2003, 05:01 PM	#59
Skulemate Cooling Savant Join Date: Jul 2002 Location: Toronto, Canada Posts: 381	[off topic] I'm taking a studio course right now as a fourth year elective. It's a collaborative design class that's mixed engineers and architecture students. Anyhew, this course has offered a series of weekly lectures, and among them was a lecture by Jonathan Sakila, who works in structural glass. It was an amazing presentation... I would never have guessed that glass could be used in such a wide variety of structural roles... beams, columns, walls, entire staircases... really quite awesome stuff. [/off topic] Anyhew, back on topic... I was looking at some material properties of polycarbonate, and noticed that it's tensile capacity is quite high (9000psi / 62.1 MPa) compared to its compressive strength (12000psi / 82.7MPa), and that it's flexural capacity is quite high as well. Still, quite aparent that it will fail in tension, as Bill has said. By the way, I got those numbers here. __________________ Michael E. Robbins M.A.Sc. Candidate, University of Toronto 12.1 GHz of AMD's finest (17.7 GHz total) crunching proudly for the AMDMB.com Killer Frogs SETI BOINC: Dual Opteron 246s (Iwill DK8N) \| XP2800+ (Shuttle SN41G2) \| 3x XP2400+ (ASUS A7N266-vm) SETI BOINC: 2x P4 2.8E (ASUS P4R800-vm) \| Crunching 24/7 Last edited by Skulemate; 03-14-2003 at 05:20 PM.

03-14-2003, 12:49 PM	#51
Cova Cooling Savant Join Date: May 2002 Location: Canada Posts: 247	After reading that link bb2k posted very early in this thread about the polycarbonate windows for cars, I'm under the belief that simply drilling a hole in it will cause microcracks to form. Threading the hole after that will likely make it worse. WinFlex - take that piece of Lexan that got the crap beat out of it, drill a little hole in it somewhere, and then hit it a few more times.

03-14-2003, 02:56 PM	#53
WinFlex Cooling Neophyte Join Date: Feb 2003 Location: Boston, MA, USA Posts: 51	we just used the old shitty manual mill to see how much shear it can take, just pushed the collet up against the lexan while it was being held in the vice. I was unable to break it that way, which is pretty amazing. Again, this has really nothing to do with microcracks tho

03-14-2003, 03:44 PM	#55
theetruscan Cooling Neophyte Join Date: Jan 2003 Location: OR/CA/NY Posts: 81	Yeah, lexan's really not that tough. It took less than 1 full clip from an AR-15 rifle at 30 yards to completely destroy a 3/4" piece. That's all I can really contribute. Been reading up on the microfissures, and I'm almost 1/10 of the way to caught up on this issue.

03-14-2003, 05:13 PM	#60
redleader Thermophile Join Date: Jun 2001 Location: The deserts of Tucson, Az Posts: 1,264	I onced taped a 2inch diameter clear PVC pipe w/ 3/8NPT threads. because of the curvature the threading was extremely thin. Only two or three complete threads. What worked really well was some adhesive (I used Marine Goop as several people recommended it for bonding to plastics). I was quite rough with the job, bus simply slimeing up the threads with it and gently turning the barbs in a few turns (not enough to make a tight seal without adhesive) resulted an in extremely tight seal. Its been 8 months now without so much as a drop has leaked, dispite heavy abuse due to my clumsiness. Considering my experience, I'd say adhesive or chemical bonding is absolutely the way to go.

03-14-2003, 05:39 PM	#61
Blackeagle Thermophile Join Date: Oct 2002 Location: U.S.A = Michigan Posts: 1,243	Where I work there are some control panels covers made of 1/2" Lexan. These have been cut to make a center lockable access door that is also made of lexan. This door is mounted with a piano hinge and the opening is rimmed in alum. frame work. The lexan has been drilled in numberous places as well along the outer edge for mounting purposes. Bolts pass through these holes and into the main fram of the control panel. These covers were put in place back in late summer of "95" and have been openned and shut countless times, sometimes slammed shut. I've seen people sit on them ect. And in a few cases they have been struck some heavy blows. They are scratched in numerous places. There are alos small cracks next to some of those drilled holes. The cracks are small not extending more than 1/2" from the hole they have started from. I work in a prison as a corrections officer. Not one of these panels has ever failed us. That is the best recommendation I can give. Yes they have a few very small cracks starting around some of the drilled holes, but not many. And this is after 8 years of hard use and abuse. LEXAN IS TOUGH STUFF!!!!!!!!!!!!!

03-15-2003, 06:59 AM	#63
UnloadeD Cooling Savant Join Date: Oct 2002 Location: MidWest USA Posts: 176	Just a few thoughts I'd like to add. 1) There were quite a few cases of failures with "factory fittings". One example would be the gemini blocks. It seems the failure weren't caused by the thread/barb area though. There were two revisions. Here's what they say about the revision: "Revision 2 Changes vs Original Block > Wider Channels provide less flow restriction and allow an overall higher flowrate > Machined out center inlet provides less backpressure, which enables the pump to push out the same flow while doing less work. The less work the pump does, the less watts are absorbed by the water. > New measures to prevent Polycarbonate cracking." Here are pics of both Rev1 and Rev2. The only change (regarding top) I can see is that the bolt holes are no longer countersunk. I suspect the countersinking along with the thin top caused the problems for them. The other poly topped blocks that I've seen people report troubles with (DD, TC-4 & Spir@l) all had brass or chrome barbs, so I'm not sure where their troubles came from. 2) Re: Methylene Chloride treatment of threads. I've used this stuff making quite a few pieces for my system and the capillary action is pretty impressive. I'm not sure how this would work, but might be worth a try. Rather than treating the threads before installing the barb, and possibly deforming the threads. It might be better to put the barb in and then apply it. I'm sure the capillary action would draw it from one end ofthe threads to the other. It would only act on the polycarb threads and do nothing to the brass or polyprop ones. This should seal any micro fissures and also form the polycarb to the inserted threads, making a psuedo molded thread. There's quite a bit of speculation here on my part, but I think it would be worth looking into. 3) Seems most are leaning towards thicker tops and putting more thought into machining them. One thing I haven't seen mentioned is the actually quality of the material as in cell cast vs. extruded. The cast stuff has much better qualities for our use and should be noted. Thats my $.03 peace. unloaded

03-15-2003, 10:52 AM	#65
UnloadeD Cooling Savant Join Date: Oct 2002 Location: MidWest USA Posts: 176	No trouble at all $3.75 for 4oz bottle: http://www.tapplastics.com/plastics/...rylcement.html You'll also want one of these, I use the squeeze type: http://www.tapplastics.com/plastics/...pplicator.html 4oz of the stuff doesn't seem like much, but it goes a loooong way, 1 drop (maybe 2) per joint. It's a pretty mean solvent, so be sure to use care with it. peace. unloaded

03-15-2003, 05:33 PM	#66
WinFlex Cooling Neophyte Join Date: Feb 2003 Location: Boston, MA, USA Posts: 51	yeah, only tools countersink lexan. counterbores are allright tho, because then there is only compressional forces, not radial expansive ones

03-18-2003, 04:37 AM	#67
MadDogMe Thermophile Join Date: Aug 2002 Location: Just shut up ;) ... Posts: 1,068	Counter bores are \|_\| shaped as oppossed to counter sinks \ / shape right?. the ' Vee' shape is acting as a wedge causing the failure is'nt it?... I'd say it's best to use a normal allen bolt and forget about 'sinking' it at all. You can get 'smooth topped' allen bolts that have a rounded off top that's nicely low profile (Maze 3 second revision(?) use them). I believe they had problems sinking the bolts as well (which rev2 countered)...

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