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#26
04/09/2007, 01:20 AM
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and i quote "ACRYLITE FF sheet also absorbs water when exposed to high relative humidities, resulting in expansion of the sheet. At relative humidities of 100%, 80%, and 60%, the dimensional changes are 0.6%, 0.3% and 0.2%, respectively." if your skimmer gained 6% in all directions it wouldnt be bad. but if it gained 6% in one direction on the main tube and 6% in the other direction of the base plate then you would be looking at one big mess on the floor. hannimister is correct when he states extruded expands alot. although i think it around 40% by weight not 60%. either way its alot of expantion. here is where i copied this information from. please note that not all acrylic sheets will have the same expansion rates or absorb the same amounts of water. this is just a quick search and only represents 1 brand of acrylic. http://www.cyro.com/Internet/SiteCon...df?OpenElement
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a wise man once told me.... " there is no right way to build a reef tank but there is alot of wrong ways to build a reef tank". |
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#27
04/09/2007, 01:45 AM
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I think acrylicman was the one who said it absorbs up to 60% by weight... not just pulling random numbers. 40%, 60%, whatever... its enough. Its not all that much when you think about it either... water is what, 8x heavier than acrylic or something like that (that was a number out of thin air)... so its really only something like 5% by volume or so.
Bottom line... Extruded fails unless you use some fancy flexible bonding stuff with ABS or something like Deltec does.
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"If at first, the idea is not absurd, then there is no hope for it" -Al Einstein |
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#28
04/09/2007, 01:59 AM
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There's more expansion due to absorption than I expected; .6% is one-tenth of an inch over an 18" run. Certainly nowhere near 40-60% by weight (the linked document says .2% weight over 24 hours) however check out page 16 of http://www.spartech.com/plastics/Pro...mmary_2003.pdf and you'll see that cell-cast acrylic (at least from this vendor, who mentions aquarium use specifically) has a similar overnight absorption (.2%) and actually absorbs from 1.6% to 2.6% (over a 26 day immersion) -- 8 to 20 times as much as the overnight absorption.
It looks like cell-cast suffers at least as much as extruded, if not more... it's late and I'm too tired to look for a second document on cell-cast. Based on this though I'll save money and stick with extruded for equipment and keep the cell-cast for aquarium building. |
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#29
04/09/2007, 02:13 AM
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the dimensional changes are 0.6%, 0.3% and 0.2%, respectively
That is much less than 1%. I would not worry at all, I have built many, none had any problem. Some brand name sumps/fuges/wd filters are extruded, some of ER skimmers are extruded, Aqua C, DAS skimmers are extruded. |
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#32
04/09/2007, 10:49 AM
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there is no reason to be sarcastic. more than one person has been thrown off r/c for there attitude problems. hanimister and i are just giving information. what have you provided to this thread other than sarcasm?
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a wise man once told me.... " there is no right way to build a reef tank but there is alot of wrong ways to build a reef tank". |
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#33
04/09/2007, 10:57 AM
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I paid extra for the cast for piece of mind. Kids, pets, and visitors all put my external recirc. skimmer at risk everytime.
A quality built skimmer can take a kick or drop onto hard surface, especially with the use of uniseals instead of glued plumbing. I have broken a skimmer before from lifting it out of my sump and it slipping and falling only ~ 12 inches and all water those 12". I can promise you that would not happen with my thick cast skimmer now.
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Smug Egotistical Contemptuous It's difficult to get a man to understand something that his salary requires him not to. |
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#34
04/09/2007, 12:02 PM
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bg |
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#35
04/09/2007, 12:07 PM
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It only takes one to ruin everything.
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Smug Egotistical Contemptuous It's difficult to get a man to understand something that his salary requires him not to. |
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#36
04/09/2007, 12:12 PM
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bg |
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#38
04/09/2007, 04:42 PM
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Keep poking the Bear with the stick... lol.
Something to keep in mind with those dimensional changes is how extruded will expand in comparison to cast. Cast, as its name suggests, has even interstitial properties throughout. When it expands, it expands in all directions evenly... so you can make 90degree joints and everything in the z-direction of one piece will mesh up with everything in the y-direction of another as it expands. Extruded doesnt expand evenly in all directions. It will expand more in its direction of extrusion... so if you bond an extruded piece to another at an angle, one piece will expand across the joint, and the other will not. I have seen extruded fail, and would not consider it unless on something with less than 12" of water height, and with an extra bead of Weld-On #16 in the corner. You may heckle, and claim that there are skimmer mfg's out there that use extruded... sure... there are 2 I can think of. I mentioned them before. Euroreef has on their RS series, and Deltecs. But like I said before, Deltecs also use a special cement to bond their acrylic to ABS, not other acrylic. In the case of the Euroreef, they will only use Extruded on the RS line, and with special bonding cements once again which allow for expansion. The RS line is an in-sump only skimmer, so the dangers of that leaking are none. There are also machining considerations. Extruded often cracks while drilling, isnt as strong as cast, etc. You can easily knock it and give it a crack much easier than Cast. FWIW, if you want to find an alternative to Cast, my suggestion would be to use Clear PVC instead. Then you can just use PVC cement and bond regular PVC fittings on for a skimmer. Its super-easy to machine with wood-bits, and its much more durable. Thats why ASM, Korallin, and others use it.
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"If at first, the idea is not absurd, then there is no hope for it" -Al Einstein |
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#39
04/09/2007, 06:38 PM
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I saw claims about certain failures due to extruded acrylics 40-60% absorption of water -- claims that, it turns out, aren't true at all. This is not to say there aren't advantages to using cell-cast acrylic. It is certainly easier to work with and is more forgiving of rough treatment during the build process and during use. Personally, in my opinion, your mileage may vary, etc. the additional cost of cell-cast acrylic does not make up for the benefits on smaller projects. Others obviously disagree. I just want the correct information to be presented so people can make their own informed decisions about what material to use. If I had to build my projects out of cell-cast, I'd be doing a lot less DIY... and I think it'd be a shame if other folks missed out on the fun of building their own skimmer/whatever because they're afraid of buggering up a $100 chunk of acrylic. That being said, if I *could* afford to use cell-cast acrylic I absolutely would 
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#40
04/09/2007, 11:01 PM
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Reactors too. Not one problem with joints. If you use the correct bonding agent, the two pieces meld to become one. So if the junction of the connecting pieces is now structurally part of the connecting pieces, why wouldn't it expand as well? Answer: it does! Guy |
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#41
04/09/2007, 11:56 PM
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So... if I weld a piece of aluminum to a piece of steel, then they both have the same structure? Wow... Then the Airforce should weld little pieces of steel to every piece of alumimum on a Jet and they would all be as strong as steel!
I think you get the point. Bonding one piece to another, through a chemical weld, or glue, does not extend the chemical properties of one material to another.
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"If at first, the idea is not absurd, then there is no hope for it" -Al Einstein |
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#42
04/10/2007, 12:33 AM
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#1) Dissimilar materials is also an issue. An extruded tube glued
to a cast base-plate, for example, would exacerbate the stress. Similar materials of similar thickness expand the same, minimizing stress at the glue joint. #2) I don't think extruded tube is available over 8-inches. Relatively small 6 to 8-inch tube expands less in absolute distance than a 12 to 15 inch tube. Still, 0.6% of 12-inches is less than one-tenth of an inch. A cast base-plate will also expand outward in all directions the same amount, so the glue joint has no additional stress from water absorption. #3) Any expansion is a one-time deal for skimmers, reactors, etc. It's not like wood expanding and contracting as the relative humidity varies. It's built, it's filled with water and expands, and that's it. |
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#43
04/10/2007, 01:02 AM
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As for bonding dissimilar acrylics, the expansion rates would likely be different. But whether or not the rates are severe enough to cause a joint failure, I don't know for sure. All I can vouch for is pieces I've built that have had zero problems with joint failure. Guy |
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#44
04/10/2007, 10:15 AM
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GuySmile,
thanks for the link to the tubing.....I to have built skimmers and reactors out of extruded tubing without any problems as well as many other's on RC.......using the right glue is the key!!! bg |
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#45
04/10/2007, 10:29 AM
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bg |
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#46
05/15/2007, 11:48 AM
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Eating Crow
I started building a new square-bodied skimmer this weekend. As part of the process, I pulled out my current DIY skimmer (6" dia extruded tube) to check a few measurements and noticed that some pretty serious cracks had started forming from a couple of the holes I had drilled for the uni-seals
 The cracks were a lot more serious than just crazing, they were fully through. A little tug on the recirc plumbing, and the uni-seal popped out with a ~3" square piece of acrylic still attached. One full side of the cylinder had completely lost it's integrity. It wouldn't have been long before the side burst out. Time for me to eat crow. Hahn, Spazz -- you guys were right about the fragility and long-term unreliability of extruded acrylic. I'll be spending the extra money for cell-cast, particularly for tubes... floods cost a lot more than the price difference between cell and extruded acrylic. Let the "Told ya so-ing" begin
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#48
05/15/2007, 01:12 PM
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Yeah, no 'I told you so's here... rather I agree with fuzzyt: thanks for being honest.
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"If at first, the idea is not absurd, then there is no hope for it" -Al Einstein |
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#49
05/15/2007, 01:29 PM
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i don't use extruded anymore myself (mostly because it cracks so easy while cutting/drilling), but things i've made years ago are still doing fine. both extruded tube glued to cast bases/tops and square tubes/bottoms made from extruded sheet. all glued with #4. if it really was that big an issue, problems would be *much* more prevalent and common knowledge. *lots* of people make stuff from extruded all the time. |
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#50
05/15/2007, 02:27 PM
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Linear Mode
