PDA

View Full Version : Acrylic tank strength?


pmrossetti
05/19/2011, 04:30 AM
If acrylic tank seams are chemically bonded and so strong, how on earth do they seperate?

And why do they need such huge bracing on top?

peppie
05/19/2011, 04:51 AM
I am sure there are many variables that would cause a seam to split. In my case I belive I used the wrong type cell cast acrylic.
I thought I had done good research. Shame on me.
IMO if done right and with the proper material it is very strong and very reliable.
Before I build another I will be sure to ask James what type to use.

pmrossetti
05/19/2011, 05:54 AM
why such elaborate bracing if seams are so strong?

Acrylics
05/19/2011, 08:56 AM
why such elaborate bracing if seams are so strong?
Because acrylic is soft and flexible as compared to glass. The bracing is to keep deflection (bowing) down to a minimum. Big glass tanks need crossbracing as well, but because acrylic is softer and more flexible - needs more bracing.

The only reason lotsa bracing is needed is if you went too thin on the material used in the vertical panels. If you use thick enough material on those, the need for bracing on top is reduced.

They separate for 3 reasons and 3 reasons alone.
1) bad material being used to start with, use good quality material
2) bad technique in gluing it up, prepare your edges and material properly
3) degradation over time. This happens even on the best tanks in the world; over time the joints degrade..though this takes many many years

James

pmrossetti
05/19/2011, 09:26 AM
Because acrylic is soft and flexible as compared to glass. The bracing is to keep deflection (bowing) down to a minimum. Big glass tanks need crossbracing as well, but because acrylic is softer and more flexible - needs more bracing.

The only reason lotsa bracing is needed is if you went too thin on the material used in the vertical panels. If you use thick enough material on those, the need for bracing on top is reduced.

They separate for 3 reasons and 3 reasons alone.
1) bad material being used to start with, use good quality material
2) bad technique in gluing it up, prepare your edges and material properly
3) degradation over time. This happens even on the best tanks in the world; over time the joints degrade..though this takes many many years

James

thank you James,

trying to understand 3, if it's bonded how can it degrade over time? isn't it "melted into one unit? many, many years means 5, 10,15?

also,i've seen it mentioned that acrylic can yellow over time.true or myth?

thanks again

Acrylics
05/19/2011, 10:09 AM
thank you James,

trying to understand 3, if it's bonded how can it degrade over time? isn't it "melted into one unit? many, many years means 5, 10,15?

also,i've seen it mentioned that acrylic can yellow over time.true or myth?
For *most* practical purposes, it is chemically bonded to "one piece" but the bonding process does stress the surrounding material to a certain extent. Due to this, joints do degrade over time. As for time frames, depends on how the joints were done but I have tanks in public aquariums that are well over 20 years old and still in operation with no issues whatsoever. So using that as a scale; 10-15 years would be a good starting point. Of course it also depends on how "overbuilt" the tank is. The more overbuilt it is, the less further stress induced, therefore the longer it will last.

As for yellowing; no longer the case. Years ago cadmium was used as a molecular binder in the material and that would react with UV and begin to yellow. About 15-20 years ago, cadmium was removed from the formula and now it's simply no longer the case. So as a direct answer; it *was* true, but with today's material, not true. Make sense? :)

James

pmrossetti
05/19/2011, 10:23 AM
For *most* practical purposes, it is chemically bonded to "one piece" but the bonding process does stress the surrounding material to a certain extent. Due to this, joints do degrade over time. As for time frames, depends on how the joints were done but I have tanks in public aquariums that are well over 20 years old and still in operation with no issues whatsoever. So using that as a scale; 10-15 years would be a good starting point. Of course it also depends on how "overbuilt" the tank is. The more overbuilt it is, the less further stress induced, therefore the longer it will last.

As for yellowing; no longer the case. Years ago cadmium was used as a molecular binder in the material and that would react with UV and begin to yellow. About 15-20 years ago, cadmium was removed from the formula and now it's simply no longer the case. So as a direct answer; it *was* true, but with today's material, not true. Make sense? :)

James

definitely makes sense. I've had 2 acrylic tanks so far and really liked them, but they both had small bubbles and white areas on some of the front side seams. They were 125g and 135g, 125=72x18x20, 135=72x18x24. both less than 1/2" acrylic by a well known mfr. c----------e. was that poor craftsmanship?
I didn't know any better. Should I not accept that on a tank now?

your opinion, please. if given a glass and acrylic tank, say 84x30x30, both well constructed, which is safer from leaks, cracks. and which will last longer?

thank you again

Acrylics
05/19/2011, 11:09 AM
definitely makes sense. I've had 2 acrylic tanks so far and really liked them, but they both had small bubbles and white areas on some of the front side seams. They were 125g and 135g, 125=72x18x20, 135=72x18x24. both less than 1/2" acrylic by a well known mfr. c----------e. was that poor craftsmanship?
I didn't know any better. Should I not accept that on a tank now?

why do they give a "lifetime" guarantee?
A coupla small bubble (~<1, maybe 2mm) are no big deal but voids and larger bubbles should be avoided.

Lifetime guarantees are not really lifetime guarantees, unless it says "lifetime replacement" which is rare. Most of these guarantees are pro-rated at 10% per anum. Meaning if it breaks the first year - we replace it. 2nd year; you pay 10% of replacement and mfr pays 90%. 3rd year; you pay 20% of replacement, mfr pays 80%. And so on. So at 10 years to perpetuity, you still have a lifetime guarantee, but it's only good for 10% of the replacement cost. To lose 10% of the cost but get a repeat customer - not a bad gig for the mfr.

Most consumer tanks will not fail quickly unless there is some degree of alteration or mis-use by the end user, whcih will void your warranty. If you clean with Windex or other solvent and get some crazing - you're out of luck. You drill a hole or otherwise modify the tank - you're out of luck. Use MH bulbs over the material and the bracing fails - you're out of luck. And yes, a skilled eye can easily see all of this. I've seen warranties that only include 2 fillings.. :/

As for your tanks, IMO the material was too thin for the application, both should have been 1/2" minimum IMO. So a poor material choice IMO but not necessarily poor craftsmanship. I'd have to see the tank to even think on those terms. It is my personal opinion that many of these consumer tanks are engineered to last about 2 years. Long enough that odds are you'll "trade it in" on a bigger tank, modify it, lose interest in the hobby, or lose the warranty, if you registered it to begin with. So yes, the warranty was offered, but it's up to you to abide by it, which in this hobby - doesn't happen often to be honest.

I don't know who your mfr is/was as it was "***" out but please don't tell me. If I know, I have to keep my trap shut ;)

James

N+D frags
05/19/2011, 04:02 PM
if done right the first time it should never come apart

Acrylics
05/19/2011, 04:29 PM
if done right the first time it should never come apartNever? as in never ever? millions of years from now?
Care to elaborate on that? exactly how is it "done right"??
I'm always eager to learn, so if you've got something to share - I'm all ears.

I'm not arguing with ya, but a blanket statement like that with nothing else leaves one wondering...

Don_v
05/19/2011, 04:52 PM
I've had acrylic tanks separate at the seam.

Tank was made by a company that only makes acrylic tanks.

It would be interesting to see an acrylic seam "properly" sealed and then flexed and see where it breaks..



Sent from my iPhone using Tapatalk

Acrylics
05/19/2011, 05:10 PM
I've had acrylic tanks separate at the seam.

Tank was made by a company that only makes acrylic tanks.

As far as the "chemical weld" that is supposed to occur, I'm questioning how true that is..

It would be interesting to see an acrylic seam "properly" sealed and then flexed and see where it breaks..



Sent from my iPhone using Tapatalk
It shouldn't break the joint. It *should* crack the acrylic and that crack should run perpendicular to load centers. Physics rules in these cases if the joint is done well. This problem occurs more frequently in rimless tanks than in tanks with top bracing.

I've run that test literally hundreds of times in testing, joints themselves should not break if fairly new (<10-15 years)

James