Ok so Melev is adamant about using cell cast acrylic instead of extruded for sump building. Can someone please explain the difference between the two in detail and in relation to performance and visual qualities? The reason i ask is because cell cast acrylic is roughly 2-3 times the cost of regular extruded acrylic from what i've been able to gather from several local glass shops. What would happen if i built a standard 55g tank out of extruded instead of cell cast? If the difference is purely visual, why not just use extruded for the sump?
Cell Cast Acrylic vs. Extruded Acrylic
- Thread starter cpeisher
- Start date
From what I've read, cast is stronger and more clearer then extruded acrylic. From what I've seen, most do suggest cast for sump and/or tank build. Extruded becomes brittle faster over time and is prone to cracking and breaking. For baffels and such, I'd say use extruded, but for piece of mind I'd pay the extra $$$ for cast strength.
hyperfocal
New member
Cell-cast is *much* easier to work with. Extruded chips and cracks easily when machined (cut or drilled). I used to think that extruded was 'good enough' and cell-cast wasn't worth the extra money... until I actually used some cell-cast. Now I'm a convert.
I still use some extruded but only for bits and pieces, anything major I go cell-cast all the way. It's worth every penny and more. I couldn't imagine building a tank out of extruded; I can't see building a sump out of either when there are so many other cheap alternatives (Rubbermaid containers, glass aquariums, buckets, etc) that are easier to work with, clean and replace when necessary.
I still use some extruded but only for bits and pieces, anything major I go cell-cast all the way. It's worth every penny and more. I couldn't imagine building a tank out of extruded; I can't see building a sump out of either when there are so many other cheap alternatives (Rubbermaid containers, glass aquariums, buckets, etc) that are easier to work with, clean and replace when necessary.
Horace
New member
I will first just say that if your even asking this question, you probably shouldnt even attempt to build your own sump out of acrylic. You would probably be better off and more safe to just get a standard glass tank and put baffles in it, or get a tub of some sort. Im pretty handy myself, and ive worked with acrylic, and I dont know if I would trust myself to build a tank that holds a ton of water which could end up on my floor. For the cost savings, im just not sure its worth the money or the risk unless you really know what your doing.
BeanAnimal
Premium Member
Cpeisher, the data is available from any of the major manufacturers websites.
There is a member here named James (Acrylics) that can rattle off the information quicker than you can look it up.
What the others have stated is pretty much all you need to know. Cell Cast should be used for tanks. One thing not mentioned is that (as I remember) cell cast also absorbs slightly less water than the extruded material.
There is a member here named James (Acrylics) that can rattle off the information quicker than you can look it up.
What the others have stated is pretty much all you need to know. Cell Cast should be used for tanks. One thing not mentioned is that (as I remember) cell cast also absorbs slightly less water than the extruded material.
hyperfocal
New member
I looked into the water absorption thing way back when, and from all the info I could gather from the acrylic manufacturers' web sites both cast and cell-cast had identical absorption numbers. I thought I had stashed away the links, but I can't find them now 
BeanAnimal
Premium Member
Hrmm... that actually may have been what I SHOULD have remembered from the the conversation. It now occurs to me that I may have been involved in that (or a similar) thread.
It may have been polycarbonate that absorbs more water than both cast or extruded acrylic.
I am sure James will drop in and set me straight before I can waste the time looking it up
It may have been polycarbonate that absorbs more water than both cast or extruded acrylic.
I am sure James will drop in and set me straight before I can waste the time looking it up
Major difference between the two is the amount of stress they can handle.
In virtually all physical properties, they are both either equal or close enough to equal to not make a difference. The major difference is in molecular chain lengths which (for acrylic) determines the amount of stress they can handle. No other physical quality, optical quality, or any other quality matters for our purposes. The two are nearly identical in all qualities other than the previously mentioned chain lengths. Due to these high molecular chain lengths (aka molecular weight,) cell cast simply can handle stresses that extruded can't handle. Since aquaria are pressure vessels, it is advised to use a high quality cell cast acrylic for aquaria.
HTH,
James
(hope you didn't look it up Bean)
In virtually all physical properties, they are both either equal or close enough to equal to not make a difference. The major difference is in molecular chain lengths which (for acrylic) determines the amount of stress they can handle. No other physical quality, optical quality, or any other quality matters for our purposes. The two are nearly identical in all qualities other than the previously mentioned chain lengths. Due to these high molecular chain lengths (aka molecular weight,) cell cast simply can handle stresses that extruded can't handle. Since aquaria are pressure vessels, it is advised to use a high quality cell cast acrylic for aquaria.
HTH,
James
(hope you didn't look it up Bean)
hyperfocal
New member
You were, Spazz too -- both of you being why I was double-extra-careful when researching that detail
Just thought i'd post this article...
MORE ON THE MANUFACTURING OF ACRYLIC SHEET
Editor's Note
In our January/February 2000 issue, "The Basics" column discussed the differences between "Extruded", "Continuous Cast", and "Cell Cast" acrylic sheet. The article was written to briefly illustrate the different production methods used to manufacture these three types of sheet with particular reference to how it impacts their cost and fabrication. As a follow-up to that article, the following column provides a more detailed look at the manufacturing process and includes a recap of the key differences in the finished products. For reference, the original article can be found in the "Articles" section of our website at www.plasticsmag.com.
Acrylic sheet is commonly manufactured by one of three techniques. All offer unique benefits from cost and physical properties to variety of color and finish. Depending on the fabricators needs, one type may be more appropriate than another. This article is meant to provide a layman's explanation of the manufacturing methods and reiterate the differences between the end products. Volumes have been written on these processes and our intention is only to help differentiate them for you.
Extruded Acrylic Sheet
Extrusion is a continuous production method of manufacturing acrylic sheet. In the process, pellets of resins are fed into an extruder which heats them until they are a molten mass. This mass is then forced through a die as a molten sheet. The molten sheet is fed to calender rolls, the spacing of which determine the thickness of the sheet and in some cases the surface finish. The continuous band of sheet may then be cut or trimmed into its final size.
In the manufacture of acrylic resin there is not a 100% conversion of monomer to polymer. The monomer is the unpolymerized form of a compound, in this case methyl methacrylate, which is the major component of the polymer. The polymer is a chemical molecule formed by the successive addition/joining of monomer units to form a molecule of high molecular weight. In the case of acrylics this polymer molecule is a chain of perhaps 100-1000 units (monomer) in length. A few percent of monomer may remain in the resin if the manufacturer has not removed the major amount of it in the pellet formation. Further, resin absorbs water if it is exposed to humid air. However, the feed stock, or pellets going to the extruder, will usually contain a small amount of water, if it has not been dried thoroughly before being processed. In an effort to obtain high quality sheet with a high yield, some production lines extract, in early stages of the melting process, the monomer and water from the feed stock. This may give some observers the false impression that monomer is being added to the pellets rather than being removed.
As an aside, monomer which is left in the molten resin can cause bubbles or streaks in the extrudate. Monomer left in sheet can reduce the hardness, promote crazing when the sheet is fabricated, and in extreme cases lower physical properties such as tensile strength and modulus of elasticity (rigidity or stiffness). The severity of these phenomena will depend on the level of residual monomer.
The final product of extrusion exhibits much closer thickness tolerances than cast sheet. Because of the volume at which extruded sheet is produced, it is the most economical form you can buy. It is available in a fair selection of colors, finishes and sizes. Extruded acrylic sheet is prone to shrinking along the extruded line and expansion across it. This is of particular note if you plan to use it for thermoforming. Extruded material also has a tendency to gum during fabrication when the cutting is too fast (linear feed rate) because it has a lower molecular weight. It also may absorb fast drying solvent cements faster than cast or continuous cast material. This can result in joint failures and incomplete gluing. To remedy this, use slower drying cements and tooling designed for cutting extruded acrylic.
Continuous Cast Acrylic Sheet
Continuous Casting is also a mass production form for manufacturing acrylic sheet. The process involves the pouring of partially polymerized acrylic (somewhat less viscous than "Karo" syrup) between two highly polished stainless steel belts. The belts are separated by a space equal to the thickness of the sheet and the "syrup is retained by gaskets at the edge of the belts. The belts move through a series of cooling and heating units to regulate the curing and are cut "on the fly" to size at the end of the production line.
One further advantage is achieved by the partial polymerization of the material prior to casting. Some of the heat of polymerization, heat which is evolved as the liquid monomer is converted to a solid resin, is removed before the "syrup" is fed to the belt system. This contributes to the control of the continuous process.
The final discussion of the cost of the continuous cast sheet process merits a comment. The material cost for continuous cast vs. extruded sheet favors continuous casting. The cost of monomer is much less than that of polymer pellets. Further, the production cost per unit of product, lbs./hr./$ capital investment, will be less for extrusion. A statement as to which process is more economical will depend on the capacity and utility of the facilities being compared as well as the cost of materials and equipment.
In terms of competitive pricing between continuus cast and extruded acrylic, there are a dozen extruders of acrylic sheet and only two continuous cast manufacturers in the U.S. This will have obvious effects on competitive pricing.
Cell Cast Acrylic Sheet
Cell Casting historically has been carried out using any of three processes. The first is the water bath technique. Acrylic syrup is poured into a mold typically constructed from two tempered glass sheets separated to produce the desired thickness of the sheet and sealed with a gasket at the edge. The mold is submerged in a bath which maintains/controls a curing temperature and efficiently removes heat generated in the process when the monomer is converted to polymer. Note - Monomer is not used in cell casting. The viscosity of acrylic monomer must be raised somewhat to avoid leakage of the molds or cells.
The two other casting techniques currently used include the original process which involved placing the "molds" containing a "syrup" in a circulating air oven in which air at a controlled temperature passes at a moderately high velocity over the surface of the mold.
The third method is an advancement over the water bath process, was developed by the Polycast Company. It involves the use of a piece of equipment similar to a plate and frame filter press. Sections which serve as the mold for the sheet are alternately configured with sections through which water at a regulated temperature is circulated to promote the polymerization and cure of the sheet.
Cell Cast products should be subjected to a "post-cure" or "annealing" process. The sheet, as taken from the oven, bath or casting machine, will usually have a "high" residual monomer content. The polymerization process is not complete. Post-curing reduces the residual monomer content and serves to insure that no bubbling of the sheet occurs if the sheet is heated for thermoforming.
In casting sheet from syrup a change in density (specific gravity) of the ingredients occurs. A shrinkage of about 20% is experienced. In the cell casting process most shrinkage occurs in the thickness direction. The surface of the mold (tempered glass sheet) restrains the plastic sheet from shrinkage in the length-width direction. Hence, the annealing, in which the sheet is heated to its softening point, allows it to relax or shrink removing residual stress.
Which sheet is right for your fabrication job? Cell Cast products provide optical clarity, greater surface hardness and machine cleanly. They are offered in many colors, finishes, and thicknesses They do, however, have greater thickness variation making them less desirable for fitting into extrusions or thermoforming where uniform wall thickness must be maintained.
Continuous Cast acrylic offers good optical clarity, more uniform thickness and limited shrinkage during thermoforming. However, it is not as hard as Cell Cast material which means it is prone to show scratches and does not machine as cleanly without adjustments to feed rates and tool geometry. Being mass produced, it also does not offer as many color and thickness options.
Extruded sheet is by far the most uniform and usually the most economical. It is offered in a growing number of colors, finishes and thicknesses which should satisfying most acrylic applications.
Written by George Graf, Graf Enterprises, Inc. Mr. Graf has over 50 years working in the acrylic resin manufacturing and processing industry. His background includes 39 years with Du Pont and 15 years as a consultant to the industry. Recognized as an authority in the economics of plastic processing and converting; he holds patents for fabric reinforced resin constructions and acrylic polymer manufacture. Mr. Graf is now retired. If you wish to contact him you may do so care of this magazine.
MORE ON THE MANUFACTURING OF ACRYLIC SHEET
Editor's Note
In our January/February 2000 issue, "The Basics" column discussed the differences between "Extruded", "Continuous Cast", and "Cell Cast" acrylic sheet. The article was written to briefly illustrate the different production methods used to manufacture these three types of sheet with particular reference to how it impacts their cost and fabrication. As a follow-up to that article, the following column provides a more detailed look at the manufacturing process and includes a recap of the key differences in the finished products. For reference, the original article can be found in the "Articles" section of our website at www.plasticsmag.com.
Acrylic sheet is commonly manufactured by one of three techniques. All offer unique benefits from cost and physical properties to variety of color and finish. Depending on the fabricators needs, one type may be more appropriate than another. This article is meant to provide a layman's explanation of the manufacturing methods and reiterate the differences between the end products. Volumes have been written on these processes and our intention is only to help differentiate them for you.
Extruded Acrylic Sheet
Extrusion is a continuous production method of manufacturing acrylic sheet. In the process, pellets of resins are fed into an extruder which heats them until they are a molten mass. This mass is then forced through a die as a molten sheet. The molten sheet is fed to calender rolls, the spacing of which determine the thickness of the sheet and in some cases the surface finish. The continuous band of sheet may then be cut or trimmed into its final size.
In the manufacture of acrylic resin there is not a 100% conversion of monomer to polymer. The monomer is the unpolymerized form of a compound, in this case methyl methacrylate, which is the major component of the polymer. The polymer is a chemical molecule formed by the successive addition/joining of monomer units to form a molecule of high molecular weight. In the case of acrylics this polymer molecule is a chain of perhaps 100-1000 units (monomer) in length. A few percent of monomer may remain in the resin if the manufacturer has not removed the major amount of it in the pellet formation. Further, resin absorbs water if it is exposed to humid air. However, the feed stock, or pellets going to the extruder, will usually contain a small amount of water, if it has not been dried thoroughly before being processed. In an effort to obtain high quality sheet with a high yield, some production lines extract, in early stages of the melting process, the monomer and water from the feed stock. This may give some observers the false impression that monomer is being added to the pellets rather than being removed.
As an aside, monomer which is left in the molten resin can cause bubbles or streaks in the extrudate. Monomer left in sheet can reduce the hardness, promote crazing when the sheet is fabricated, and in extreme cases lower physical properties such as tensile strength and modulus of elasticity (rigidity or stiffness). The severity of these phenomena will depend on the level of residual monomer.
The final product of extrusion exhibits much closer thickness tolerances than cast sheet. Because of the volume at which extruded sheet is produced, it is the most economical form you can buy. It is available in a fair selection of colors, finishes and sizes. Extruded acrylic sheet is prone to shrinking along the extruded line and expansion across it. This is of particular note if you plan to use it for thermoforming. Extruded material also has a tendency to gum during fabrication when the cutting is too fast (linear feed rate) because it has a lower molecular weight. It also may absorb fast drying solvent cements faster than cast or continuous cast material. This can result in joint failures and incomplete gluing. To remedy this, use slower drying cements and tooling designed for cutting extruded acrylic.
Continuous Cast Acrylic Sheet
Continuous Casting is also a mass production form for manufacturing acrylic sheet. The process involves the pouring of partially polymerized acrylic (somewhat less viscous than "Karo" syrup) between two highly polished stainless steel belts. The belts are separated by a space equal to the thickness of the sheet and the "syrup is retained by gaskets at the edge of the belts. The belts move through a series of cooling and heating units to regulate the curing and are cut "on the fly" to size at the end of the production line.
One further advantage is achieved by the partial polymerization of the material prior to casting. Some of the heat of polymerization, heat which is evolved as the liquid monomer is converted to a solid resin, is removed before the "syrup" is fed to the belt system. This contributes to the control of the continuous process.
The final discussion of the cost of the continuous cast sheet process merits a comment. The material cost for continuous cast vs. extruded sheet favors continuous casting. The cost of monomer is much less than that of polymer pellets. Further, the production cost per unit of product, lbs./hr./$ capital investment, will be less for extrusion. A statement as to which process is more economical will depend on the capacity and utility of the facilities being compared as well as the cost of materials and equipment.
In terms of competitive pricing between continuus cast and extruded acrylic, there are a dozen extruders of acrylic sheet and only two continuous cast manufacturers in the U.S. This will have obvious effects on competitive pricing.
Cell Cast Acrylic Sheet
Cell Casting historically has been carried out using any of three processes. The first is the water bath technique. Acrylic syrup is poured into a mold typically constructed from two tempered glass sheets separated to produce the desired thickness of the sheet and sealed with a gasket at the edge. The mold is submerged in a bath which maintains/controls a curing temperature and efficiently removes heat generated in the process when the monomer is converted to polymer. Note - Monomer is not used in cell casting. The viscosity of acrylic monomer must be raised somewhat to avoid leakage of the molds or cells.
The two other casting techniques currently used include the original process which involved placing the "molds" containing a "syrup" in a circulating air oven in which air at a controlled temperature passes at a moderately high velocity over the surface of the mold.
The third method is an advancement over the water bath process, was developed by the Polycast Company. It involves the use of a piece of equipment similar to a plate and frame filter press. Sections which serve as the mold for the sheet are alternately configured with sections through which water at a regulated temperature is circulated to promote the polymerization and cure of the sheet.
Cell Cast products should be subjected to a "post-cure" or "annealing" process. The sheet, as taken from the oven, bath or casting machine, will usually have a "high" residual monomer content. The polymerization process is not complete. Post-curing reduces the residual monomer content and serves to insure that no bubbling of the sheet occurs if the sheet is heated for thermoforming.
In casting sheet from syrup a change in density (specific gravity) of the ingredients occurs. A shrinkage of about 20% is experienced. In the cell casting process most shrinkage occurs in the thickness direction. The surface of the mold (tempered glass sheet) restrains the plastic sheet from shrinkage in the length-width direction. Hence, the annealing, in which the sheet is heated to its softening point, allows it to relax or shrink removing residual stress.
Which sheet is right for your fabrication job? Cell Cast products provide optical clarity, greater surface hardness and machine cleanly. They are offered in many colors, finishes, and thicknesses They do, however, have greater thickness variation making them less desirable for fitting into extrusions or thermoforming where uniform wall thickness must be maintained.
Continuous Cast acrylic offers good optical clarity, more uniform thickness and limited shrinkage during thermoforming. However, it is not as hard as Cell Cast material which means it is prone to show scratches and does not machine as cleanly without adjustments to feed rates and tool geometry. Being mass produced, it also does not offer as many color and thickness options.
Extruded sheet is by far the most uniform and usually the most economical. It is offered in a growing number of colors, finishes and thicknesses which should satisfying most acrylic applications.
Written by George Graf, Graf Enterprises, Inc. Mr. Graf has over 50 years working in the acrylic resin manufacturing and processing industry. His background includes 39 years with Du Pont and 15 years as a consultant to the industry. Recognized as an authority in the economics of plastic processing and converting; he holds patents for fabric reinforced resin constructions and acrylic polymer manufacture. Mr. Graf is now retired. If you wish to contact him you may do so care of this magazine.
Sigh...no, it isn't. Name any physical property which reflects any significant difference in terms of strength.
as a blanket statement..not true.
No, it isn't. It bows far more, isn't as clear, scratches easier, (generally) doesn't glue as well, and costs more.. How is this a good option? 25x stronger than acrylic? in what way? perhaps impact resistance? in what way is this critical to aquaria?
James
jimmyj7090
aka John K
James, could / would you mind clarifying definitions for us?
"Stress handling" vs "strength"?
I'm guessing the polycarb built tank would be more bullet resistant than a normal acrylic tank
"Stress handling" vs "strength"?
I'm guessing the polycarb built tank would be more bullet resistant than a normal acrylic tank
Sure, but explaining is easier by example. Stressors come in many varieties, from load to chemical to thermal and so on. Let's say you have two standard and properly built 125 (48 x 24 x 24") tanks, built exactly the same way; one built from 1/2" cell cast and one from 1/2" extruded. Both flame polished edges which is standard in the industry. With me so far? The tanks will bow the same amount, so the load makes no difference. The cutting, routing, gluing, and polishing all induce a certain amount of stress on the materials; these are constants, and both materials can handle everything very well to this point.
Now, let's say you accidentally clean both tanks with Windex or similar cleaning solvent. The cast tank might craze a little, but the extruded tank can become overstressed by the simple addition of the solvent and craze to the point that the material fails on a molecular level.
In the above example, the chemical stressor, ammonia/citric acid/alcohol/whatever is what turned the material past it's threshold for handling stress. The materials are no different in terms of physical strength; moduli of elasticity and all other physical properties are similar, it's simply the addition of the solvent as a chemical stressor that breaks apart the molecular chains causing the material to fail.
And the same thing can happen whether the tank is filled or not, so "strength" or any definition of similar is absolutely irrelevant. It comes down to the length of molecular chains that determines the material's stability.
For culture, try it at home. Get two pieces of tube; one cast and one extruded, flame polish the edges (using butane torch or similar) and spray alcohol on them. The extruded will craze to failure, the cast will not. Neither is under any load, so "strength" is a non-issue. It is simply the combination of stressors; rapid heating/cooling and then alcohol which broke apart the chains. Which would you rather use to build your new reactor?
While not a textbook definition, hope this demonstrates how stress resistance is different than any standard physical property that can be generally defined as "strength." This is the primary reason cell cast is used rather than extruded in aquaria. There are other reasons to be sure, extruded can't be made thicker than 1" as an example.
Depends, given similar thicknesses - yes, but I've built quite a few tanks that were made with bullet resistant acrylic as wellI'm guessing the polycarb built tank would be more bullet resistant than a normal acrylic tank
I could go on with this stuff forever, love bullet testing materials 
James
jimmyj7090
aka John K
Thks
Divorce attorneys in their office entryway..go figure ;-)
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