CASTING PLASTIC PROCEDURES
As an introduction to liquid plastics and its many uses, we will start with
a simple application. We will fabricate a base for a printed circuit etching
tank. There are several reasons why liquid plastic is excellent for this project.
- is easy and quick to fabricate
-resistant to acid
-provides a perfect seal
-results in stable base.
- Teflon pan.
- plexiglass sheet and cutter from hardware store.
- instant glue ( Crazy Glue ).
- Smooth On # 326 liquid plastic.
- disposable mixing container.
- graduated container.
- adequate stirring stick.
- Smooth On liquid plastic dye (optional).
- vacuum chamber (optional).
a. Wipe the teflon pan clean.
b. Place the pan on a level surface.
c. Fill the pan with water up to the desired level.
d. Pour water into graduated container to determine how much liquid is required.
e. Dry the pan.
f. Cut the plexiglass, bend with heat gun, glue ends and let dry (glue vapours can discolour the plexi).
g. Suspend plexi at desired depth and position in the pan.
h. Pour into the mixing container 1/2 the required quantity using part B.
i. Add a small quantity of dye and stir thoroughly.
j. Mix in the other 1/2 of required liquid using part A and stir again, taking care to scrub the sides and bottom of the container.
k. Pour mix in the pan.
l. Let cure
m. Remove the plexi supports once liquid has hardened.
Always read the manufacturer's detailed instructions and notes before proceeding. There are important recommendations that must be followed such as adequate ventilation, eye protection and other safety issues. If there is a contradiction between this text and the manufacturer's instructions, the manufacturer's instructions prevail.
Some of the concerns using this particular model of plastic include:
- shrinkage must be taken into consideration when designing large pieces.
- more liquid in a given area will generate more heat from the chemical reaction. A thin slab will take longer to cure than a thick one.
- disturbing the liquid once it is poured will result in discolourations , let gravity do its thing.
- air bubbles can be removed using one of two techniques:
1) placing the mix in a vacuum chamber for 3 minutes prior to pouring. Care must be taken to chose a container large enough to handle the expansion of the liquid during the process.
2) placing the mold and poured plastic into a high pressure chamber. This is cumbersome and requires a chamber large enough to support the mold. A weakness in the chamber can be catastrophic, while a low pressure chamber has less risk (but still a risk nonetheless).
The air was not removed in this pour since it was of little concern, neither was the discolouration from using a stick to burst most of the surface air bubbles. The finished product is not for sale and will be used in the workplace. This particular plastic, # 326 , is a good all-around plastic. It is strong and lightweight, it can be coloured, painted, machined, drilled and tapped. There are also special powders available that can simulate aluminium, gold and bronze finishes.
Other lessons will deal with fabricating a vacuum chamber and using silicone molds. There are other brands of liquid plastic available, Smooth On was chosen because it offers a wide variety of silicone, rubber, plastic and many other art suppliers. Detailed information is available at http://www.smooth-on.com/