Acrylic cylinder cracked

[Cresta]

I build a 24" tall DIY kalk reactor several weeks ago with 4" extruded acrylic tube. Reactor was fed by peristaltic pump and mixing done by a magnetic stirrer. After using it for about 3 weeks, the tube wall cracked. The tube was cut clean and glued with Weld-On #3 without any visible problem initially. Not until after several weeks did the tube started to crack starting at the bottom.

I then remove the entire setup and drained the reactor to prepare for more Weld-On to seal the crack. However, after two days, I found the crack to extend even further up the tube. This is with no liquid in the tube. It was just sitting there.

If the initial crack was caused by vibration or pressure build up in the reactor, I assume taking it apart will have already stopped it from cracking further. What is cause the tube to crack more?

I want to know so I can prevent it from happening again in the next reactor. I know cast acrylic is supposed to be stronger. But I assume it would only matter in the initial cutting (ie. less likely to chip in cutting).

 

[Anonymous]

Hi Ermin. Since it's the Easter holiday, you may have to wait a day or two for your answer, but do a search, as some others have begun addressing some acrylic repair issues. Also, we have amongst us an acrylic guru, known 'round these here parts as fergy. He's one of the MACO instructors as well. He grins a lot.

 

[fergy]

Okay, first off, never use extruded for these projects. Extruded has about 1/10 the molecular weight of cast. Both of these materials will absorb about 2% of their volume in water. So, when the extruded has absorbed that amount, it is much weaker than the cast.

Also, I'd make sure to use 1/4" wall, just for grins. I'm doubting you did that, since 1/4" extruded is pretty hard to find.

Cast is much stronger all around, not just when you're cutting it, but in everyday life. It's also utilizes purer acrylic monomers in general. Extruded tends to have fillers in it, like styrene, which is what gives off that sweet smell when you cut it.

It sounds like you stressed the plastic when cutting or drillling it, and the stress decided to release along the split you saw. Did you drill holes in the side of the tube? I'm betting...

BRIAN
_________________
Honda NT650

 

[Acrylics]

The reason in cracked more is because you added more solvent (the Weld-on), the condition is called crazing - which are stress fractures. Yet another reason to use cast acrylic for aquarium projects.
Extruded acrylic is stressed when made (essentually being squeezed out of a vat under pressure), then cut (friction=heat), then solvent applied. Crazing is "it's way" of relieving this stress. It's the same reason we don't use Windex or the like to clean acrylic tanks.
Cell cast is much more relaxed and stable due to a variety of reasons (Fergy pointed out quite a few) and is the preferred material for such projects.
For experimentation in this, try cutting a piece of extruded tube then heating it up slightly (any torch or lighter will do fine) then putting alcohol, ammonia, Weld-on, or any other solvent on it. You will see similar crazing as you saw in your reactor.

James[/quote]

 

[fergy]

Ah, James, I assumed his crack went all the way through, as a single split, not as crazing...good for pointing that out, if it was the case.

And now I will defer more to your expertise, since really you are still the master, and I merely the apprentice ;-)

BRIAN
_________________
deep chunk strawberry cough

 

[Cresta]

Here's a picture of the cracked tube. When I first noticed it...the crack line was about 1" tall from the bottom. After several days of it sitting there under zero load from pressure or water, the crack grew longer to form the "three-way split". Now it crack line has stopped to continue. The cracked "triangular portion" is intact still...the crack lines just went around to form the illusion of an opening.

Toward the top of the picture you'll see I drilled and tapped an airline barb to the tube. I was done before I glued the whole thing together.

Is there anyway I can save this project with the amount of cracks? Some people had told me to drill small holes at the end of the crack lines to prevent further cracking. However, even with a 1/8" hole, what can I use to fill it with? Its cylinderical, so I can't really glue a flat piece to patch the hole.

And yes, the cracks went all the way through.

Thanks for all your help!

 

[Acrylics]

Crazing in extruded tube will go all the way through. The crack *starts* as crazing then crawls up the tube as a full crack. It will get to a point such that you can literally pull pieces off with your bare hands.

James

 

[fergy]

Ah, and drilling and tapping the side of the tube didn't help either. I'll bet it heated a bunch during that process, plus the compression from the threaded fitting, and the notch-sensitivity of the tapped threads themselves.

I've actually not dealt with extruded tube enough to see how bad it can craze. Sounds like pretty extreme...

BRIAN
_________________
Acura MDX

 

[Cresta]

I glued the cracks and tested for cracks......so far it seemed ok. I sure hope I don't have to rebuild it....... casted is so expensive in comparison.

If it is so easy for extruded to crack like this....what are they commonly used for? I'm sure it will be glued in projects regardless. If it always cracks like this....even though approx $5 a foot....after cracking several, it adds up to the cost of a casted.

 

[ReefVan]

Wow, pretty bad news for the extruded acrylic tube...

I bought some 6" x 1/4" wall, cellcast acrylic tube that my supplier had left over as cut-offs. (cheaper) :wink: I'll be using that to build an DIY AquaC clone as seen on RC DIY.

For the skimmer foam riser tube I bought some 3" x 1/8" wall, extruded acrylic tube since no cheap cut-offs were available. Now you guys have me worried that maybe I should get some 3" x 1/4" wall, cellcast acrylic tube instead. $$$$ :?

This is the first time I hear of this situation, some of the DIY skimmer designs out there use 1/8" wall extruded, does that means after 6 mo -1 year they could start falling apart? 8O

I was wondering why manufacturer's were using 1/4" wall cellcast all the time to build their skimmers, yet it's so damned expensive! $$$$ :x

Too bad clear pvc isn't as optically clear as cellcast acrylic, i've built my Ca Reactors and KW Reactors with it. Does a beautiful job, looks great. Only drawback is that it's hard to see through, so for a skimmer you'd have a hard time judging bubble size in the skimmer column.

Van 8)

 

[fergy]

Simply put, extruded is crap, manufacturers who use extruded are making cheap crap, and you really want nothing to do with it.

It might last for your project, it might not. You never know. If you're really careful with it, maybe it will last. But, as James was saying, it crazes so easily that it's just not worth it. It has so much internal stress from the beginning, and as soon as you stress it further, be it with heat, solvent, etc, it's gone.

In general, suck it up, and pay for the cast.

BRIAN
_________________
Mercedes Benz MB100

 

[brokekyle]

here's the deal... extruded tube is fine for almost every application in the hobby.. (except for aquariums)
However!!!
Butt joints are never acceptable when working with round to flat stock.. Stress fractures will accur along the butt joint from the weight of the media and water in a Ca or KW reactor..
if you look how mine are built. http://home.pacbell.net/kylesr/mycalreactor3.jpg you'll see that I insert the cylinders through the flat stock for maxiimum support then butt joint the ends only to make it water tight.. However the end butt joints do not support any sheer weight of the assymbly.. Get it?

 

[fergy]

here's the deal... extruded tube is fine for almost every application in the hobby.. (except for aquariums)
However!!!
Butt joints are never acceptable when working with round to flat stock.. Stress fractures will accur along the butt joint from the weight of the media and water in a Ca or KW reactor..
if you look how mine are built. http://home.pacbell.net/kylesr/mycalreactor3.jpg you'll see that I insert the cylinders through the flat stock for maxiimum support then butt joint the ends only to make it water tight.. However the end butt joints do not support any sheer weight of the assymbly.. Get it?

Not if you use properly-sized and type of material in the first place. These problems only occur when you cheap out and use substandard material, such as narrow-wall extruded tube.

BRIAN
_________________
Greg Hastings Tournament Paintball

 

[Robin Goodfellow]

hi.
Welcome to RDO, James! I am sure many of us will benefit from your experiences on acrylic and related materials. Please check back often, in addition to just RAMR.

 

[brokekyle]

Not if you use properly-sized and type of material in the first place. These problems only occur when you cheap out and use substandard material, such as narrow-wall extruded tube.

OK..for example. Guess that New Nike ti. driver will allow me to hit a golf ball as long and as straight as Tiger Woods??.. I don't think so.. My only point is.. it's not only the material.. it's the USER(builder). build it right and it'll work and it won't crack or leak.
Regardless of the materials used, butt joints for reactors are poor quality workmanship. They are FAR FAR more likely to crack than inserted joints.
As my name implies I'm pretty frugal.. I don't spend money where it's not needed.. "Cell Cast" is way OVERKILL for this hobby and it only benifits the mass producer where it's cost can be tranfered to their customers.. For almost any DIY project in this hobby 1/4" extruded is fine(somtimes I use 3/8 for flanges)... If you wanna use cast ok.. it's better ,but for this hobby it's not needed..

 

[Anonymous]

Brokekyle,

What are your credentials in working with acrylic? From the statements you have made, I believe you are self-taught.

Even the slightest research into what type of acrylic for aquarium applications reveals that cast is the proper material.

Fergy is a fabricator and not a manufacturer. He has no reason whatsoever to lead you (or anyone) to spend any more money than is really necessary.

Louey

 

[brokekyle]

wow... it seems that you're attempting to attack my credentials rather than my methods or procedures.
If not would it be better if you direct any and all statements directly at my explanation for the cracking?
If you cannot reply to my "butt weld" statement I suggest you read and listen to what I have to say.
I'm open to all statements on the superiority of insert welds.
TYVM

 

[Robin Goodfellow]

hi.
I am not as strong a supporter of casted acrylic as the others when it come to calcium reactor, where a small volume is stored under relatively low pressure (<10psi).

However, I want to point out that some woodworking joinery technique are not directly translated into acylic work. This is acrylic lacks the orientiation of fibers and lamination in natural wood product, and it is a lot more homogenious than wood.

 

[Anonymous]

Kyle,

From your description and picture, I do not have a clear understanding of your insert seam. So I just went ahead and bashed you material selection instead.

Louey

 

[brokekyle]

Kyle,

From your description and picture, I do not have a clear understanding of your insert seam. So I just went ahead and bashed you material selection instead.

Louey

It's OK.. I knew you didn't understand. I actually figured by now you would've lowered youself to name calling.. 8) 8)