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Hi! I'm Dan Rustin, alias, Dr. Dan. I've created this section to try to answer commonly asked questions in easy laypeople's language. In addition to providing education on specific topics, I hope I also manage to entertain you a little. I promise to do my best to avoid technobabble, which may make you sleepy.
Because this is brand new, I've put together a couple of the frequently ask questions about some of the products we manufacture, and some we distribute to get things rolling. You can select any of the questions you would like to have answered by clicking on the "Dan's Wisdom" button. And for some of my more long winded responses, you'll probably want to print it out and read it in your favorite stall instead of last weeks newspaper that no one remembered to throw away.
Ask Dr. Dan a plastic fabrication question or a question about Acrilex by filling out the short form below:
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Can you vacuum form Acriglas®?
What are the differences between "Extruded", "Continuous Cast", and "Cell Cast" acrylic sheets?
Why do I have problems gluing Acriglas® to my stock acrylic sheet?
Why does acrylic mirror often have a bow to it?
Why does cast acrylic cost more than extruded?
Can you vacuum form PETG with the film masking on?
How do you make Acriglas®?
Why can't you glue acrylic sheets of Quarite® or Lucite XL® with solvent?
Can you glue PETG?
Why does cell cast acrylic vary so much more in its thickness than other acrylic?
Can you vacuum form Acriglas®?
Yes I can! But if you want to know if you can, then I'll tell you about some of its limitations.
First of all, the minimum thickness we can cast Acriglas® is 1/8". This in itself will limit the depth of draw and the sharpness of corners and finer details that are possible. Acriglas® may not be able to achieve the desired effect for very complex vacuum form applications. Match mold forming, pressure forming with plug assist, and techniques other than just simple vacuum forming can help to overcome some of these limitations, but not all.
Additionally, if we know in advance that you wish to form the Acriglas®, we can make adjustments to its chemistry that may help. For example, adding plasticizers to the sheet will help allow the material form at slightly lower temperatures. It will also make it more pliable, more impact resistant, and less apt to tear in the forming process. And other adjustments can be made as well. The more we know about what you are doing with Acriglas®, the better we can help you work with it. Because everything is custom cast, modifications to composition are really no problem.
Standard thermoforming is no problem at all, and sheets do not require annealing or pre-drying before forming. So knock yourselves out! Be creative and get the look you want in Acriglas®.
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What are the differences between "Extruded", "Continuous Cast", and "Cell Cast" acrylic sheets?
That's a big question and the answer can get very technical. But to avoid putting everyone to sleep answering it, I'll stick to the primary differences. The obvious difference is that each is manufactured according to a different process.
Extruded Acrylic is manufactured on automated machinery which combines "pellets" of resin with acrylic monomer and catalyst, dispenses the mixture through a "die-block", runs it in semi-molten form through rollers which produce the final thickness, and finish or texture, and cuts and trims the sheets to their final size. Because the machinery is very expensive and requires a fair degree of effort to change rollers and set the die blocks, it is ideally suited for producing large volumes of commodity materials. A typical extrusion company may run as much as 40,000 lbs. of material in one color and thickness before they will begin manufacturing another product. At that volume, it is becomes the most economical way to produce a plastic sheet. At least in the United States.
Continuous Cast materials are also mass-produced, but don't utilize die-blocks or rollers. Essentially, big vats of Acrylic Monomer and catalyst are batch mixed and then poured onto highly polished stainless steel belts about 10'ft wide and 300'long and separated on the top and bottom by a space equal to the thickness of the material desired. These belts continuously convey material through a series of cooling and heating units to regulate the curing of the acrylic and saws at the end of the line cut the material "on the Fly" to it's final size. Because of the high cost of polishing these belts and the capital investment to build a continuous cast sheet line, the cost of materials is typically higher than extruded, but because it is again totally automated, still cheaper in general, than cell-cast acrylic.
Finally, "Cell cast" sheets are produced by assembling a mold for each individual sheet, and then pouring the acrylic materials into the mold with a funnel or other device. These molds, typically made of two large glass plates separated by a gasket the thickness of the desired material, are then placed into curing tanks, followed by being placed in a post-curing oven. The molds are then cooled, disassembled, and the sheets removed and inspected prior to masking. It is by far the most labor-intensive method for producing acrylic sheets, and although the capital investment in equipment is lower than the previous two technologies, the investment in American laborers is much greater.
So, what does it all mean? Well, the different processes produce materials with different properties, which may effect the end use.
Cell Cast acrylic is generally considered to have the best optical clarity of all the materials. It also has greater surface hardness and machines more cleanly than continuous Cast or Extruded. It comes in many more colors and thickness' and is easier to get custom colors and special effects, which is why we've chosen it as our method of manufacturing Acriglas®. However, it also has the down side of having more thickness variation than the other methods, which may present difficulties in applications where thickness tolerance is very important i.e.: fitting into extrusions, thermoforming applications where walls must maintain uniform thickness, and assembly of complex structures.
Continuous Cast is the next best thing for clarity, and it has the benefit of maintaining uniform thickness as sheets and in thermoformed parts. It is the material of choice for most Skylight manufacturers. Also during thermoforming, it does not exhibit the differences in the amount of shrinkage that extruded materials exhibit. It has the down side of not being as hard as Cell Cast materials which means that it may show scratches more readily and does not machine as cleanly as Cell cast without adjustments to feed rates, bit or blade geometry's, and technique. Additionally, it is also not offered in very many colors or thickness', making it somewhat limiting in design options when compared to cell cast.
But the industry workhorse would still be extruded sheet. It comes in a fair selection of colors and sizes, and advancements in extruder technology have allowed the entry of materials of up to one inch in thickness, without noticeable die lines in the sheet which in the past have been a barrier for these material. Extruded sheets are the most uniform in their thickness and because of the automation are also the most economical. They satisfy the needs of most acrylic applications because of the combination of cost and quality. The down side is that they are also the softest in the acrylic family. Fabricators complain of "gumming" during fabrication and more awareness is required to eliminate this as a problem. They also absorb fast drying solvents faster than cell cast and extruded, so complaints of joint failures or incomplete glue joints are not uncommon. While this is easily remedied by working wiser and changes to slightly slower drying solvents, many fabricators still expect this material to glue like cast sheets. Finally, this material exhibits the property of shrinking along the extruded direction and expanding across the extruded direction which may present difficulties during thermoforming if the former does not anticipate this in advance.
The bottom line is, understand what your application requires before you select a product to use. Not all clear acrylic is created equal for all applications, and the price should be the last consideration when planning your project, not the first. Most problems occur when purchasing people buy a "deal" on clear acrylic without fully understanding its intended end use. This unfortunately is not the fault of the Acrylic chosen, just the person choosing it unwisely.
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Why do I have problems gluing Acriglas® to my stock acrylic sheet?
The problem, if you want to call it that, may lie in the fact that you are using a fast solvent with dissimilar materials, which absorb the solvent at different rates. If you are using something like a stock clear material like Acrylite® FF, which is extruded, it will absorb methylene chloride solvent faster than the Acriglas®, which is cast acrylic. The softer extruded material will starve the glue joint because it has soaked up the bulk of the solvent before the harder cast material has had a sufficient time to soften and fuse together with the extruded.
The solution is simple. You can either make sure you use a sufficient amount of solvent to ensure a good bond, or slow down the rate of absorption by cutting the solvent with 10% Glacial Acetic acid, or buying a slower absorbing solvent to begin with. This will also give the two dissimilar materials enough time to fuse together. Between an adjustment to your gluing technique and a different solvent, you should no longer experience any difficulties.
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Why does acrylic mirror often have a bow to it?
That is a very common question. The material is not defective, as many fabricators have claimed. That is the nature of the material. Acrylic is a hydroscopic material, that is to say, it has an affinity for water and it will absorb moisture into the microscopic pores in its surface. Normally, in the cast of clear acrylic without the mirror backing, it absorbs moisture evenly on the face side and the backside and releases it evenly depending on the relative humidity.
The bowing in the material occurs when you seal the backside with a non-porous coating, which prevents the normal absorption or release of moisture on the coated side. This produces an imbalance within the sheet, which may be exacerbated by conditions of high humidity during the summer months, or near coastal areas where humidity is highest.
For most applications, this characteristic of acrylic mirror is not a problem, but should be considered if flatness is of critical importance in your application. Glass mirror, for all its obvious limitations is still a better choice for flatness. Just don't drop it!
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Why does cast acrylic cost more than extruded?
That is a loaded question. Cast doesn't always cost more than extruded. If the acrylic is imported from overseas, it may in fact cost less than extruded acrylic. The answer has to do with the cost of American labor vs. foreign labor, and the comparison of that to automation.
Extruded Acrylic is run on automated machinery with a minimum of human contact, and very little manual labor or handling of individual sheets. Cell casting involves assembling and disassembling individual molds for each sheet of acrylic to be made. Time is consumed in curing tanks and ovens, which does not allow for additional material to be made while the current batch is curing. Therefore the quantity of materials which are capable of being made in a 24-hour period are vastly different when comparing the two processes.
Additionally, American laborers are paid more per hour, receive benefits, and employers pay for things like workmen's compensation, social security, unemployment insurance, liability insurance, proper waste disposal, etc., which in foreign countries are not all factors to be considered. So while cast sheets from domestic sources always costs more than domestic extruded, cast sheets from foreign sources are competitive with and sometimes less than domestic extruded sheets.
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Can you vacuum form PETG with the film masking on?
In general the answer to this question is no. There are risks involved and is not usually recommended by any of the extruders of PETG to make a practice of vacuum forming with the film masking on.
However, PETG can be purchased with a vacuum formable film masking if specified. It is not the same masking that is normally used for general purpose applications, so those companies wishing to perform this kind of work, need to pay special attention to what they order. There may also be adjustments required on heating and cycle times to consider, so some experimentation should be done prior to production to ensure the best results.
To date, only one supplier that we have worked with provides this type of film masking, though we are told by some of our other suppliers that they have similar products in development.
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How do you make Acriglas®?
Well I could tell you, but then I'd have to kill you!
Seriously though, we make Acriglas through a process called Cell casting. The technology is almost a century old, and nothing revolutionary has come along to change it much, but what we do to achieve some of our special effects is proprietary.
No other manufacturer of cast acrylic has figured out how to cast a "brushed metallic" acrylic sheet, but Acrilex. And as for Acrifluor, we again are the only manufacturers of a translucent fluorescent product in acrylic, which has the properties of light diffusion that it exhibits.
And while other manufacturers overseas can produce pearlescent, marble, granite and metallic colors, none can offer the degree of customization offered by Acrilex, especially in short run quantities, with the consistent quality of Acriglas. And none can turn around and order in less than two weeks. Our magic is very special. We are very proud of what we can do, and love the challenges our customers send our way.
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Why can't you glue acrylic sheets of Quarite® or Lucite XL® with solvent?
Both materials are not in the same category as regular acrylic sheets. These brands of material fall into a category called "cross-linked" acrylic.
What this essentially means, is that an additional chemical has been added to give these materials greater resistance to harsh chemicals and staining agents. As a result, they resist the solvents that would normally dissolve and fuse regular acrylic sheets. To properly bond these types of materials, you will need to use adhesives, rather than solvents. These take longer than solvents to cure, so many fabricators rule them out right away because of the effect that curing times have on large volume production.
Although, I have observed that "cross-linked" acrylic can be solvent bonded with regular acrylic, though the strength of the bond may not be as strong. Consider the end use of the product before performing this type of bonding.
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Can you glue PETG?
Some fabricators say no, others say yes. The one's who say yes have learned that you can't just take what you know about gluing acrylic and apply it to PETG and expect it to work. It's not just the solvent you're using but your technique at applying the solvent that matters most. Weldon 4, Schwartz Chemical's SC-94, and Rez-N-Bond will all work acceptably as long as you make sure to use a generous amount of it, have clean, machined, smooth edges, and clamp your parts with light but firm pressure for a sufficient amount of time before moving on to additional steps.
Also, other adhesives may be used but will have longer curing times. Most people accustomed to acrylic fabrication will reject adhesives outright because of the length of time for curing, so for PETG they will not make any new exceptions. For those people interested in learning more about gluing PETG, I recommend cruising Sheffield's web site on Vivak, http://www.sheffieldplasticsinc.com/sheffield/techtips/vivakfab/vbond.htm
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Why does cell cast acrylic vary so much more in its thickness than other acrylic?
Because of the processes involved in manufacturing them. There are many reasons why cell cast acrylic is often the material of choice on many projects, but close tolerances on thickness is not one of them.
The molds used for cell cast acrylic, typically glass, are subject to their own thickness variations, which may effect the thickness of the acrylic. And of course, each sheet comes out of a different mold, which may compound the difference from sheet to sheet. But even more difficult to control than the flatness of the molds, is the balance of pressure inside vs. outside of the mold. The latter is the primary reason for greater variations in thickness. This is why on sheets larger than 2' x 3', it is virtually impossible to guarantee tolerances much better than ± 10% of the overall sheet thickness.
Extruded and Continuous Cast acrylics are both produced on automated equipment which force material between either rollers or belts that are separated by fixed distances. Because they are produced continuously, not separately, there is greater uniformity of thickness. At least more so than cell cast sheets.
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