Busted Poly Top

[Chaos2358]

Greetings all, I'm sending you this out of curiosity and as a warning as well. A friend of mine recently had the poly top of his Maze3 block crack rather badly. After looking it over it seems that one of the bolts that held the top to the copper block had been screwed down to tight and the pressure eventually split the whole top. Has anyone else ever had this happen? It would be good to know how often this sort of thing happens.

[JFettig]

oh man, btw its not poly, its lucite, not nearly as strong as poly, and iv been seeing a lot of these lately! its scaring me! email dden asap!

[Ct. Strangelove]

dude what sucks it that thier site is down. I have a DD maze 3, N. bridge and GPU cooler. I am very tentitive to put pressure on the barbs. It should no be that way. O, well.

[Iron Hawk]

Well, i when i put my plastic top on my maze 3 i tightend it as tight as i could, no signs of crackage yet.

[[EG]~NaTz~]

yah masked lucite should be stronger yet more brittle than poly. so stronger may not be the word u are looking for. and i trust it just as much as i trrust tehe weak art of soldering.

[Frodo Baggins]

man, all I've hear in the past months are stuff about the plastic tops cracking...sheesh

[safemode]

tis part of the reason why i got the copper top(tm) and the other reason why is lucite is a wussy name for a plastic that is going on your cpu to water cool it. Cant we get some transparent aluminum (aluminium) in there or at least a plastic with 5 syllables ?

[DodgeViper]

If you over tighen the machine screws you will risk taking a chance of cracking the top. Lexan is brittle and will fracture very easy.

[Starfoxer]

i sure am glad i got an aluminum top dtek spiral :D

[gone_fishin]

Originally posted by [EG]~NaTz~
yah masked lucite should be stronger yet more brittle than poly. so stronger may not be the word u are looking for. and i trust it just as much as i trrust tehe weak art of soldering.

More misinformation, lucite is not stronger than poly.

[gone_fishin]

Originally posted by DodgeViper
If you over tighen the machine screws you will risk taking a chance of cracking the top. Lexan is brittle and will fracture very easy.

Lexan (or the generic name polycarbonate) will not fracture easily unless scored, it is a "notch sensitive" material . It is also 400 times stronger than acrylic (also known as lucite or plexi).

[DodgeViper]

Really, well I have a few broken lexan tops. When you place a NPT thread into Lexan, Plexi, Lucite, and you begin to tighten the barb you are displacing the material in a direction that will cause stress. Once stress is applied the cracking of the material will begin.

[gone_fishin]

Originally posted by DodgeViper
Really, well I have a few broken lexan tops.

That is because they were not made properly and came pre-notched for your enjoyment:D

[DodgeViper]

From gone_fishin, Lexan (or the generic name polycarbonate) will not fracture easily unless scored, it is a "notch sensitive" material . It is also 400 times stronger than acrylic (also known as lucite or plexi).


From G E,

LEXAN, which is a polycarbonate has an extremely high impact resistance and is transparent. Polycarbonates have 250 times the impact strength of glass and 30 times the impact of acrylic. Maintenance such as cleaning and scratch removal is lower also. LEXAN is manufactured by the General Electric Company. GE also holds the patent to LEXAN. It is designed to be the most UV / abrasion-resistant polycarbonate on the market: The sheet is virtually unbreakable.

Depending upon your aviary design, acrylic is the most widely used plastic because of cost and flexability. If your designing an aviary for commercial use, LEXAN may be the answer.

[JFettig]

lexian is poly, poly is lexian, its all the same stuff

[gone_fishin]

PMMA Polymethylmethacrylate (Acrylic)

LEGEND
A = amorphous - Cr = crystalline - C = clear - E = excellent - G = good - P = poor - O = opaque - T = translucent- R = Rockwell - S = Shore


STRUCTURE: A

SPECIFIC DENSITY: 1.16

WATER ABSORBTION RATE (%): 0.3

ELONGATION (%): 48

TENSILE STRENGTH (psi): 7000

COMPRESSION STRENGTH (psi): 11500

FLEXURAL STRENGTH (psi): 10500

FLEXURAL MODULUS (psi): 310000

IMPACT (IZOD ft. lbs/in): 1.1

HARDNESS: R120

FABRICATION
- BONDING: E
- ULTRASONIC WELDING: E
- MACHINING: E

DEFLECTION TEMPERATURE (deg. F)
- @ 66 psi: 187
- @ 264 psi: 170

UTILZATION TEMPERATURE (deg. F)
- min: -94
- max: 176

MELTING POINT (deg. F): 212

COEFFICIENT OF EXPANSION: 0.000055

ARC RESISTANCE: 80

DIELECTRIC STRENGTH (kV/mm): 17

TRANSPARENCY: C

UV RESISTANCE: G

CHEMICAL RESISTANCE
- ACIDS: G
- ALKALIS: E
- SOLVENTS: P



PC - Polycarbonate

LEGEND
A = amorphous - Cr = crystalline - C = clear - E = excellent - G = good - P = poor - O = opaque - T = translucent- R = Rockwell - S = Shore


STRUCTURE: Cr

SPECIFIC DENSITY: 1.2

WATER ABSORBTION RATE (%): 0.16

ELONGATION (%): 100

TENSILE STRENGTH (psi): 10000

COMPRESSION STRENGTH (psi): 12000

FLEXURAL STRENGTH (psi): 14000

FLEXURAL MODULUS (psi): 330000

IMPACT (IZOD ft. lbs/in): 2.4

HARDNESS: R75

FABRICATION
- BONDING: G
- ULTRASONIC WELDING: E
- MACHINING: E

DEFLECTION TEMPERATURE (deg. F)
- @ 66 psi: 287
- @ 264 psi: 270

UTILZATION TEMPERATURE (deg. F)
- min: -145
- max: 275

MELTING POINT (deg. F): 300

COEFFICIENT OF EXPANSION: 0.000039

ARC RESISTANCE: 11

DIELECTRIC STRENGTH (kV/mm): 15

TRANSPARENCY: C

UV RESISTANCE: G

CHEMICAL RESISTANCE
- ACIDS: G
- ALKALIS: P
- SOLVENTS: P






Polycarbonate/ABS Alloy

--------------------------------------------------------------------------------


Specific Gravity 1.14
Shrinkage,in/in,1/8 in. thick 0.0060
Shrinkage,in/in,1/4 in.thick 0.0070
Water Absorption,% 24hrs 0.150
MECHANICAL
Impact,Izod,Notched (Ft-Lb/In) 8.00
Impact,Izod,Unnotched(Ft-Lb/In) NO BREAK


You are correct in them figures but,
it depends on which numbers are compared, unnotched it is considered unbreakable whereas glass and acrylic is not.

[safemode]

actually no. any other polycarbonate would not have the same exact properties as lexan since GE owns the patent. Any such plastic would be infringing on the patent and be illegal unless it happened to have a different molecular makeup and same properties. Thus those that are trying to be comparable to lexan most likely are inferior in one or more ways from lexan. A polycarbonate is a very wide scoping group of molecules. There are a wide variety of characteristics within it. All a polycarbonate has to be to be a polycarbonate is be a molecule in which carbon atoms make the link between them. Big deal there. That could describe a huge range.

That's like saying glass is bullet proof glass, bullet proof glass is glass. It's all the same stuff. That's completely false. You ignore the fact that bullet proof glass has minerals like quartz and such to increase it's strength.

The problem with lucite tops with screws is if you drill the whole a bit too small, your screw scores the plastic horizontally something like lexan would probably not really be bothered by this. but brittle plastics will not stretch and instead crack. Overtightening screws on such a plastic would require massive force. I rather think the problem with the lucite top that cracked was due to the threads in the screw cutting into the plastic instead of riding on threads that were made for it.

[DodgeViper]

LEXAN, like other plastics, is subject to dimensional change due to thermal expansion and contraction.

When working with LEXAN, allow a minimum edge engagement of 1/2" plus an additional 1/8" for expansion allowance for a total rabbet depth of 5/8”.

Through bolting or use of other inflexible fastenings must provide for expansion and contraction allowances of 1/16" per linear foot. Holes drilled in the LEXAN must be oversize accordingly and at least 2 times fastener diameter from the edge of the sheet. Silicone may be applied in each drill hole for extra protection.

Do not over tighten bolts or screws. To do so will prevent thermal movement.

Countersinking screws and the use of a taper or NPT thread should be avoided. I know of one block builder that is taking steps to use a straight-sided barb with an o-ring to solve this problem. Instead of countersinking the machine screws, the use of a button top machine screw is a better choice. This type of screw places even pressure on the Lexan surface and does not displace or expand the Lexan to the sides.

Personally I like the clear top, but I do believe in time it’s going to disappear. Those that are building water blocks to sale are going to be flooded with complaints that their tops have broken, when in fact the user who has no knowledge of using such material over tightens and break the top.

[gone_fishin]

With the use of a good gasket material, and a washer, assuming an un notched hole, a mounting screw may be tightened down till the copper threads strip out and it will not crack. The hole should be oversized also so that the screw threads do not create a score. The use of a washer under the head eliminates the possibility of the turned head from scoring the material. The full supporting gasket allows for expansion. Finally when the hole is drilled it must be done with a proper bit and rotation and feed speeds so as not to stress the material and cause microcracking which will eventually spread.
If the material is machined and applied properly there will be a higher confidence in the clear tops.

[gone_fishin]

The material is too thin, I don't see any gasket, them are a classic spread of cracks that were already present, microcracks. Are you even sure that it is polycarbonate?

Here is a shot of a grouping of holes I did that are extremely close to one another and to the edges of the material. This is in 1/2" polycarbonate. I will tell you from experience that this would be impossible to do in any sort of acrylic material.


http://www.nscooling.com/oc2/bulletproof_top1.jpg

[DodgeViper]

I can't answer for Peter, but I do recall speaking to him by phone and I asked if he was using poly. His answer was yes. Now here is an updated photo of his blocks. If you notice he nolonger is countersinking the machine screws, but is using a button top screw. Danger Den has gone to this same method. Why? It has been talked about already.

Gone_Fishin, I think we both are on or near the same page with using polycarbonates. It's the best choice for a clear top, given the fact it's machine correctly. Your using a much thicker top than what the current block makers are using and your holes are not as close to the edge as what I have pictured. You may even be correct that some of these so called polycarbonate tops are not poly at all. If they (water block builders) are using Plexiglas then this is a major problem. But even with polycarbonate I would not countersink screws into the top.

[Nico3k]

hmm i think what many people fail to realize is that your supposed to have the waterblock on it so it touches and doesnt move.... not until u cant tighten it anymore

[DodgeViper]

hmm i think what many people fail to realize is that your supposed to have the waterblock on it so it touches and doesnt move.... not until u cant tighten it anymore

What are you trying to put across to us? Were talking about the clear top attaching to the copper bottom.

[Tecumseh]

Someone should actually make tops out of tempered glass.
If there were a WC standard for tops like screw placement than
one tempered glass design could be used on ANY design WB,
commercial or personal, that met the standard.

This IS possible, but who could organize the whole thing? :)