There are two experimental stations in which one may study polymer processing with its attendant problems an phenomena. The devices available in the laboratory are an extruder and an injection molding machine. The devices and typical experiments are described below. These stations are:
Purpose
The extruder is one of the most common machines used in polymer processing. It admits its use for experiments on melting of polymers, drag flow, pressure flow, mixing, flow through a die, and viscous heating.
The parameters which may be varied are:
The following effects can be studied:
- residence time distribution,
- mixing
- pressure, temperature, flow rate, and the interrelations, and
- comparison to a model for flow in an extruder.
- die swell
Experimental Set-up
The hardware consists of a Killion 1 inch single screw extruder with a die mounted at the end, each having a separate heater and temperature controller. There are several dies and a supply of a number of different resins, some of which are colored. For concentration measurements in the study of the residence time distribution, a UV-Visible spectrophotometer is available. For die characteristics, a pressure transducer and pressure tap has been installed.
Operational Notes
Start Up
The extruder and the die must be heated to the operating temperature before any polymer is introduced, their temperatures set uniformly at approximately 60°K above the 'melting point' of the polymer. Near the hopper the barrel is cooled with water. When the desired temperature is reached, the motor is turned on and the one or two cups of polymer are added into the hopper.
Experimental Options
Transport behavior is observed by slowly feeding new polymer onto the visible screw. By adding some colored polymer as a tracer, the residence time distribution in the extruder could be measured. Keeping the die resistance low in the initial phases of experimentation, the flow rate may be measured as a function of the speed of rotation and of the die pressure.
Purpose
Polymer articles are often made by injection of a molten polymer into a mold. One ubiquitous piece of equipment found in the polymer industry is the Injection Molding Machine. The device consists an extruder, a ram, and a mold. As in an extruder, the injection is thermally controlled and the mold is cooled.
The parameters that can be varied are:
- injection pressures and temperatures,
- mold gating
- cycle times
The following effects can be studied directly:
- part strength
- its temperature dependence,
- effect of cycle times
- weld line integrity in multiply gated parts
Experimental Setup
A Boy 15-ton Injection Molding machine is fitted with a tensile bar mold which is designed to be used as single- or double-gated. The machine has a self-contained control unit allowing heating and cooling of the extruder and the mold.
Typical Experimental Program
Produce single and double-gated tensile bars for which the polymer has been introduced to the molds at a series of temperatures. Evaluate the effect the weld line on the strength of the part.
Operational Notes
An instruction manual for the Injection molding machine is available from the Chemical Engineering Shop.