Mail your plastic questions to: ADOffice@Acrylic-Designs.com
| What are the differences between Acrylic, Plexiglas and Lexan? |
| Forming Plastic - the basics |
| How do I remove scratches from Lexan or Acrylic? |
| Technical information about GE LEXAN |
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| What are the differences between Acrylic, Plexiglas and Lexan? |
| Answer: Most people have no idea how many types of plastic there are. Literally thousands. The two we are interested in here are acrylic and polycarbonate. Acrylic is the generic term used to describe the clear hard material we all know as Plexiglas or Lucite. The chemical term is polymethylmetacrylate or PMMA for short. It was first introduced to the United States in 1930. Plexiglas is the brand name originally used by Rohm & Hauss, the early developers of this plastic type. Lucite is the brand name of DuPont's acrylic material. It's like Kleenex has become a term we use for tissue. I hear that in South America, Gillette is used for razor. Acrylic is the clearest of plastics, about 8 times clearer than glass. It has good strength but is breakable. Acrylic is fairly rigid, as plastics go but will flex much more than glass. Polycarbonate is even more flexible. Acrylic is a thermoplastic, meaning that it can be heated to a rubbery state and formed in various ways. It is the material of choice for museum cases and displays because of its clarity and workability. We can make glued seams that nearly disappear. We use acrylic almost exclusively for our products because of its workability and high quality. The exposed edges of acrylic may be polished to a clear finish. It can be bent like a sheet of paper by heating a line. Acrylic, as most plastics, will scratch if not cared for properly. That is probably its worst downfall. Lexan is another type of plastic. The generic term is polycarbonate. Polycarb for short. It's main differences to acrylic are that it is nearly unbreakable, bulletproof when thick. It's main drawback is, it scratches more easily than acrylic. The properties that makes it unbreakable, namely its elasticity and flexibility, give it a softer surface. Lexan is the trademark for GE's polycarb product. Polycarb is less clear than acrylic but clearer than glass. Also a thermoplastic, polycarbonate may be formed in various ways, similar to acrylic. One property of polycarb that causes problems when heating and gluing is that it is more porous than acrylic and tends to absorb moisture from the air. The moisture will boil when heated causing the sheet to turn white or bubble as the vapors expand, destroying the material. In gluing, the chemical that bonds will react with the moisture and may cause the seams to turn white in places. Very ugly. The only way around it is to dry the material in an oven before heating or gluing. This can obviously be a problem if you don't have a large oven handy. We really dislike fabricating polycarb. Usually it is limited to uses where looks are secondary to strength such as machine guards. |
| Forming Plastic - the basics |
| Andrea writes, Hi I'm trying to bend a thin sheet of acrylic into a wavy shape at home any suggestions on how to do this? |
|
First of all let me give you little background on forming plastics in
general. As acrylic plastic heats, it shrinks. approximately 1/4 of an inch per foot in
cast acrylic. Extruded acrylic shrinks one way and can expand the other. You should test a
piece if length is critical or be prepared trim the length after forming. Acrylic plastic becomes flexible at around 280 degrees. You should set your oven at 350 to 400 degrees. It will take 2 to 8 minutes to heat depending on actual temperature, thickness of material and what you place the plastic on to heat. If you need to have an exact shape for the part you want you will need to create a form or mold. This can be any smooth surface. I have used glasses, bowls, cups, aluminum cans, about anything I have laying around that can be close to the shape I want. We use Formica pieces, cardboard tubes or any firm flexible surface to make larger curved parts. Sometimes, with small pieces, you can just use gloves to hold it. Another important thing to remember is that when the sheet is flexible, it will get "mark off" from any surface it comes into contact with. We use cotton flannel to cover the surface of our form. Glass is often smooth enough by itself. Dust particles will leave imprints. The plastic should be put into the oven on a piece of smooth hardboard, Formica, or cardboard. Corrugated cardboard will not burn at these temperatures in 15 minutes. Keep it away from elements or flame and don't put it in until the oven is hot. Use reasonable caution. I have used aluminum foil in a pinch but it tends to stick. You can take the plastic out of the oven on the board, or carefully cradle it out with gloves. It will be hot so gloves need to be worn. You can get a cheep $3.00 to $5.00 pair of leather gloves at a hardware store. Try not to grab it with your fingers as you will leave imprints. |
| Nathan asks, Hello, I'm interested in trying to construct an aquarium out of acrylic. I'm considering what the best way to glue the pieces together with is. I've heard that some chemicals actually form a weld between the pieces. Thank you, Nathan |
| Answer: Gluing
Acrylic and Polycarb There are several types of glue used with acrylic. The main type and most common are solvent adhesive. They are available thickened and water thin. The water thin is used in common fabrication. It uses capillary action to flow between the pieces of acrylic. The chemical is actually a solvent and breaks down the plastic surface, allowing the pieces to flow together. The solvent evaporates and you have a beautiful seam. We use methylene chloride, (MDC), as our solvent adhesive. We mix it with a small amount of another chemical that allows us to adjust for temperature. It is applied using an applicator bottle that has a needle tip. Edge preparation prior to glue application is of utmost importance. Your final seam will never be better than your beginning edge. We use a joiner to prep the edge for general assembly but a hand scraped finish used on our art quality work yields the best results. The other glue is 2 part. Basically,
2 part uses a thick liquid material that is part acrylic and a catalyst
to make the reaction that hardens it. It is much harder to use, messier and in my opinion
does not give as long a lasting or strong seam on average. It is
used most often in furniture manufacturing where seams are made using very
thick material. Solvent adhesives are harder to use on thick
acrylic. Acrylic often forms some gas as the solvent reacts.
Usually it can escape to the side of the seam but at 3/4 to 1"
and above, small bubbles may form. For solvent adhesives, I recommend Craftics Inc. They can ship them. We do not have a haz mat license. For polycarb you want to us weld-on #4. For acrylic, you can use weld-on #4 or #5 You will also need an applicator, smallest needle diameter, 16 gage or the water thin solvents. We think the 2 oz bottle is easiest to handle. Craftics web site is http://www.craftics.com For other fabrication information, try http://www.Cyro.com |
| Removing Scratches: Dave wrote, I need to remove a fairly deep scratch in a lexan motorcycle windshield. What should I use and what precautions are necessary. I have heard about Novus scratch removal products, is that appropriate? Dave |
|
Novus is a good scratch remover. 210 plus is another. Novus is available
at some auto parts stores. Use a soft cotton cloth, like kids pajama
flannel. We use a dust cloth called "One Wipe" from Guardsman.
Available here at Ace hardware stores. Cut into small pieces, the waxy
coating that makes dust stick to them seems to help prevent scratching if
you allow the towel to get to dry while polishing. Unfortunately, you will never get a deep scratch completely out. The best you can hope to achieve is to polish the bottom of the scratch and make it less visible. There will be a dimple line in place of the scratch. Work in an oval motion along the scratch line. You may have to work directly in line with the scratch at first to get to the bottom. Then work in a circular - oval direction. Don't let the compound dry on you while polishing, it will scratch. Keep adding small amounts of the polish to your towel. If elbow grease doesn't do it, it is possible to use mechanical buffing wheels but extreme care must be exercised to not burn the material. You can quickly make things worse. A small Dremal buffing wheel at a slow to medium speed is fairly easy to use and safer. Do not let the polish dry out. If the scratch is really bad, you may have to do some sanding first. But that's a whole other story and lots of time involved. |
| Additional technical
information about GE Lexan can be found at : http://geplastics.emarkethost.net/mk/get/EBULII6?_ED=lBiUhq9rUjU0WQZP6bONZu |