Forming Cast & Extruded Acrylic Sheet

Acrylic sheet becomes soft and pliable when heated-behaving almost like a sheet of flexible rubber. It may then be formed into almost any shape. As the sheet cools, it hardens and retains the formed shape, provided it has been held in place during the cooling process.

The only functional difference between Cast and the Extruded acrylic sheet is the temperature ranges in which they are pliable. DO not exceed them. Excessively high temperatures may cause the sheets to blister and burn. Extruded acrylic sheet will give better definition in tight radii or deep draws.

Cast acrylic sheet should be heated to between 340° and 380°F (171° and 193°C).

Extruded sheet should be heated to between 290° and 320°F (145° and 160°C).

Line bending or thermoforming Abrasion Resistant acrylic sheet is not recommended. Cold forming is possible. To calculate the minimum bend radius of curvature, multiply the thickness of the sheet to be used by 330. Tighter radii may result in crazing or cracking of the coating.

 

Never heat acrylic sheet in a kitchen oven. Acrylic sheets give off highly flammable fumes when decomposed overheating. These gases are potentially explosive if allowed to collect in an unventilated area.

Most kitchen ovens do not have accurate temperature control. Temperatures can be off as much as 75°F (42°C), possibly allowing the acrylic to overheat.

And because air is not forcibly circulated in a standard kitchen oven, the fumes will accumulate. When they come into contact with the heat source, there is likely to be an explosion. Repeat: DO NOT heat acrylic in a kitchen oven.

 

Forming with a strip heater

A strip heater is without doubt the most useful acrylic-forming device in the home craftsman’s arsenal. Used properly, it is perfectly safe. A correctly assembled strip heater will not exceed safe heat.
Unfortunately, a strip heater can only be used to form straight-line bends; but that is usually all that’s necessary for most home projects. It will allow you to make those bends with a minimum of trouble-and a minimum of electricity.

A strip heater heats only the area to be formed-there’s no need to heat the entire sheet if you only intend to make a straight-line bend. It heat quickly. And with little care you’ll get excellent results, because the rest of the piece stays cool.

Heating and forming acrylic sheet with a strip heater is not difficult. When properly heated, the acrylic may be easily bent into smooth, clean corners. With patience and a little practice you should soon be able to achieve excellent results.

First, remove the masking paper from the line of the bend. The rest of the masking paper should be left in place to protect the unheated area. Then lay the sheet on the heater with the bend line directly above the exposed heating element so hat the bend will be made away from the heated side. The length of heating time will vary according to the thickness of the sheet. Acrylic sheet thicker than 3/16” (4.5 mm) should be heated on both sides for a proper bend. Heat the sheet until it begins to sag at the bend line. Don’t try to bend the sheet before it is fully heated, or after it has partially cooled. This will result in irregular and creased corners and high internal stress.

Forming jigs and clamps should be used for best results. They can be made of wood and used over and over. Make preformed jigs for certain angles, or even special shapes for individual projects. Variable angle jigs can be made with two pieces of wood hinged together and help at the desired angle with a variable brace, as shown. Felt, flannel, or flocked rubber should be used to line any surface that may come into contact with the heated acrylic. Wear heavy cotton gloves when handling heated acrylic sheet. They’ll protect your hands as well as the sheet.

 

Note: Acrylic sheet may be formed into almost any shape. However, specialized heating and forming equipment is usually required for all but the simplest projects

Article Title:
Forming Cast & Extruded Acrylic Sheet
Article Summary:
Instructions on heat forming acrylic sheet
Article Date:
4/9/2009
Article ID:
583
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