[CASTING]
Once the molds are ready, it’s time to do the casting. The logic is that with flexible mold, you want to cast a hard material into it and vice versa, i.e. (hard) foam positive – (flexible) rubber negative – (hard) plastic cast or (hard) wax negative – (flexible) rubber cast.
Ventilation and pouring holes were added manually at this stage.
The molds were clamped with just enough force to keep them together whilst maintaining the shape of the doorknob.
Smooth Cast 300 Liquid Plastic (Polyurethane Elastomer) consists of two parts (A & B) which when mixed up together (1:1 ration) became reactive. It has a pot time of 3 minutes and 10 minutes cure time. Really useful for casting multiple times quickly.
HMIS (Hazardous Material Identification System):
Health = 2 (harmful by inhalation, irritation on skin)
Fire = 1
Reactivity = 1
Gloves and safety glasses must be worn when working with this material in a ventilated area.
The poured Smooth-Cast started to dry up after 3 minutes.
Each knob was cast using 5 oz of the liquid plastic. It was enough to allow the substance flowing out and around the edge of the rubber molds.
[COLOURING]
We experimented with the primary colours including the red pictured below. It’s found that 10 drops into the Part B this would give vivid colour to the cast. 2-5 drops were not sufficient and left the objects pale-coloured.
White Knob (no colouring).
Cheese Yellow Knob (2 drops of red and yellow).
Blue Knob (5 drops).
Red Knob (10 drops).
The American Knobs.
COMPLETE FABRICATION 