Thursday, May 21, 2009

Embedments in Plexiglass Acrylic

Embedments in Solid Plexiglas Acrylic

Lucite® is a high quality acrylic product. The versatility of Lucite® allows it to be custom designed into a variety of shapes and sizes, incorporating many different types of embedded elements. However, due to chemical reactions during the process, not everything can be embedded. Here's the top of a champagne bottle (removed with a sword) cast into Plexiglass by a factory.

The process starts with two basic ingredients, an acrylic resin powder and monomer, a crystal clear liquid. The powder and monomer are mixed together in specific proportions. The result is a thick, opaque liquid. The mixture is hand poured into molds and allowed to partially harden. Objects to be embedded are then hand placed into the Lucite® layer. Another layer is poured over the embedded object and the Lucite® is again allowed to harden. Heat and pressure are applied to the parts to remove any air bubbles and completely harden the part. Parts are then sanded to size then buffed by hand to a bright crystal-like finish.

Sounds simple? You need an AUTOCLAVE to actually cast the Lucite or Plexiglass materials. Unfortunately, these chemicals are not available in a DIY shop or to the general public. Then again, not many of us have autoclaves in the kitchen. No, a toaster oven duct-taped shut won't work.

So - a lot of us turn to polyester resins - clear casting resins that emulate this process of clear casting of plastics - and embedding in plastic.

I have successfully cast certain bugs that decided to enter my office or my garage - but I probably "cooked" even more by putting too much catalyst in the resin mix. The problem with casting "organic" items in resin is that they contain water and when they warm up as the plastic is turning to a solid - they expand.

Putting catalyst into polyester casting resin activates the molecules to form a solid. A pretty neat trick. But to do that, the temperature must be raised. Trust me, this can get out of control and you can start a fire with too much catalyst. But when you put something organic - like paper, flowers, crickets and the like, the water in them will go gaseous and muck up your casting.

Pennies, rings, teeth are more stable and you have more successes. The shapes you see in these pictures are cast ACRYLIC shapes that are standard - and that can be used for embedding items into by a factory - not DIY stuff (sorry).

Remember, always try this FIRST on something similar. Write down the ambient temperature, and the amounts of resin and catalysts. When casting in layers, let the layer beneath cool before adding another layer...until you are skilled and learn to adjust the catalyst downwards for the next layer.

Casting resins are not UV stable so make sure you don't put your cool new casting in the sunlight.

Wednesday, May 6, 2009

Calculate Aquarium Thickness - How THICK must the Plexiglas be?

To determine the proper thickness for an aquarium made of ACRYLITE® GP acrylic sheet...
OK - this is for all you Einsteins out there - even if it's high school physics and math... please don't ask me the calculate this.. :-) - check out the Cyro Tech-Knowlogy site for a spreadsheet to help. You have to login in - but it is a killer info site.
The aqaurium in the picture is 12ft long, 4ft high and about 3ft wide in the middle. It was constructed of 2" thick acrylic sheet, the outer walls were thermoformed into convex sheets, and please note the "top cap" made of 1" thick plexiglas sheet, then routed out for access holes. This top cap also creates a structural member that keeps the outer walls from bulging under pressure. This aquarium is now doing service in upstate Michigan.
CYRO recommends that all acrylic water vessels, including aquariums, should be constructed with cell cast ACRYLITE GP sheet. This requirement exists for two reasons:
  1. ACRYLITE GP sheet is more capable of withstanding continuous loads than continuously manufactured or extruded sheet.
  2. ACRYLITE GP sheet maintains a high level of mechanical strength after water absorption has reached equilibrium.
Cemented joints must withstand the effects of the continuous hydraulic pressure and the high level of water absorption for many years. Two-part polymerizable cements are recommended for this to meet this requirement. See Weld-On #40 information in the blog. Solvent cements are NOT recommended.
To determine what thickness acrylic sheet should be used, the calculation below can be used assuming the base is uniformly supported.

T - thickness of sheet
H - height of tank
L - length of tank
Required Thickness T (in)=           
q = maximum water pressure (lbs/in.2) = (0.0361 lbs water/in3)* H (inches)
H = aquarium height (inches)
α = maximum permissible stress for ACRYLITE GP in an aquarium (750 psi)
β = coefficient from L/H relationship as follows:
L/H 0.25 0.50 0.75 1.00 1.50 2.00 3.00 4.00
β 0.037 0.120 0.212 0.321 0.523 0.677 0.866 0.940
Note: For L/H ratios not shown, use the β value for the next higher ratio.
L = 36 in.
H = 15 in.
L/H = 2.4 therefore: b = 0.866 (taken from the chart for L/H = 3.0)
q = (0.0361 lbs/in3) x (15 in) = 0.542 lbs/in2

T (in) =

= 0.375 inches

If a top is cemented on (this would have 2 cutouts to prevent bowing), the recommended thickness in 0.375 inches. With an open top use a safety factor of 1.5, bringing the recommended thickness to 0.563 inches to be used in this size tank. Since a thickness of 0.563 is not made, simply increase this to 0.740" (3/4") which is stock.
OK - did I blow your mind? WWPGD? If you want to build an aquarium, and the edges are hidden by framework, or the mounting in a wall, etc. then use 1/2" CAST ACRYLIC SHEET for aquariums that are 15" high x 20" wide x 36" long. Make sure there is a top cap to keep sides from bulging. 24" x 24" x 48" - use 3/4" sheet and 30"x30"x48" use 1" sheet. Always use a top cap sheet to hold side together!
If you are not skilled with gluing Plexiglas, search out a local plexiglass fabricator in your area. Typically under the Yellow Page heading of Plastics - Fabricators. If the edges are showing, make sure the fabricator defines how bubble-free their bonds will be and the quality of the edge polishing. Expect to place a 50% deposit on the order and the balance when complete to your satisfaction. To save money, identify what edges do NOT need to be polished - that saves time and your money!

Thanks to

Download the XLS from Evonik - Calculate Aquarium Thickness  

Tuesday, May 5, 2009

Fiberglass FRP Pultrusion process and shapes

Fiberglass Reinforced Plastics (FRP) can be manufactured several ways. Let's explore the pultrusion process of making fiberglass sheet, shapes, and profiles. The pultrusion process allows production of continuous lengths of fiber-reinforced polymer profiled pultruded shapes, angles, rod, beams, and tubes.

Check out the picture above.

First, from the left, fiberglass in the form of continuous roving filaments, or fiber bundles, is drawn though the liquid resin, which saturates the glass reinforcement. Next, this combination of resin and glass is then pulled through a special die using a continuous pulling device (hence the name pultrusion for pulling through, rather than extrusion which is pushed through).

The die is made of metal, with a highly polished interior to allow the rather corrosive fiberglass and resin mixture to pass through easily. The mass of materials conforms to the shape of the die and is heat-set into a permanent, structurally reinforced shape. Fully cured when exiting the end of the heated metal die.

The resulting high-strength profile is cut to length -- ready for use when it leaves the pultrusion machine.

Pultruded products provide manufacturers and designers with the benefits of high strength-to-weight ratios, corrosion resistance, heat resistance, dielectric properties, dimensional stability and weatherability. In the end, pultruded products are a cost effective and versatile alternative to traditional materials.

Here is 48" wide sheet being pultruded...

The fiberglass material is typically produced in 3 grades:

1. Standard with isopthalic polyester resin and various layers of fiberglass roving and mat.
2. Fire Retardant and UV resistant chemicals added to the Standard Grade
3. Vinyl Ester Resin, FR and UV additives - for extreme chemical resistance.

Standard colors are Green, Gray, and Beige respectively. Any color can be run if the quantity is high enough.

A short list of pultruded products in the marketplace: Tool handles, ladder sides, skateboard decks, fiberglass stairs and platform systems, fiberglass grating, fiberglass decking, u-channel, I-Beams, structural profiles of all sorts. Photos: (courtesy of Liberty Pultrusions)

Saturday, May 2, 2009

SHOJI Chrysalis Resin Panel fabrication

Plastic Fabrication using Chrysalis HD resin panels is pretty cool. I can't do this with 3-Form or Lumicor panels. That is really SHOJI (shogi) paper inside the sheet. Duraglas, the maker of Chrysalis HD, uses a patented process to manufacture these panels. The base sheet is PETG (same stuff as soda bottles) and is thermoformable. The surface is unique in that it is "self healing" - small scratches (yes, scratches) can be removed with a small heat gun such as a cooking torch or industrial hot air gun. A few short passes will heal the surface.

Chrysalis and Ridout Plastics will be at the NEOCON show June 15-17, 2009 to show off all of the patterns available and some interesting fabrications at BOOTH 8-3130C. For you technical types, the material has a CLASS 1 FIRE RATING, is GREENGUARD & LEEDS COMPLIANT, is BACTERIOSTATIC and GRAFFITI RESISTANT. You can use as a DRY ERASE board OFF THE SHELF - no special coatings and Chrysalis HD resin panels are 40x MORE IMPACT RESISTANT THAN GLASS. That said, it is more expensive than Plexiglass or Lexan - but then again, there is nothing like it!

Friday, May 1, 2009

Glastron Boat Windshield Fabrication

Glastron boats, as well as many other OLDER outboard motor boats, have thermoformed plexiglass acrylic windshields. After a few years, usually 30-40 years, owners want to spiff up their motor craft and put a new windshield in. Problem is, Glastron doesn't make them anymore.

Here's Bryan with a recent windshield sent in to the shop for a replacement. We don't have a mold either, so I thought I would share a few pix from the process....

The boat windshield starts out as a FLAT sheet. A rectangle that fits the outline of the finished windshield if you could lay it out flat. Now, when the plexiglas is heated up to forming temperature, about 350F, the material will SHRINK about 2%. But according to the laws of expansion and contraction, the material will also EXPAND when heated. So a fabricator has to be a bit of an artist to attempt this particular job.

But wait - there is no mold. Or is there? Our man Bryan has decided to use the OLD windshield as a mold. It's not a perfect mold - if you lay the heated plexiglass OVER the old windshield, the new one will be slightly bigger. Using the inside as a mold will result in a windshield that is smaller. We decided to use the outside as a mold and then use a heat gun to wrap the sides after the windshield has cooled - a secondary operation.

The end result? A perfect match - new for old - and the new windshield is masked to protect it on its journey back to its owner.

SBA Family Business Award

This is something that everyone at Ridout Plastics ( is proud of. The United States Small Business Administration decided to create a special award for Family Owned businesses across the country in 1995. In each major metropolitan region, they hand selected a short list of contenders. You could not apply to be considered. You had to be nominated by a qualified local organization and these organizations could only nominate one company. The San Diego Chamber of Commerce chose Ridout Plastics as their nominee and we underwent a grueling series of tests and reference checks.

After about 6 months of interviews and checks, their were 5 contenders vying to be the first recipient of this prestigious award in San Diego. We won this based on our years of contributions to the local community, a successful transition from one generation to the next, and our excellence in customer service. Basically, for being good guys. There is an article in Entrepreneur Magazine from back then.

It might have been 14 years ago, but we remind ourselves every day why we earned this recognition and strive to exceed customer expectations each and every day.