Purpose:

The extruder is one of the most common polymer processing machines. Experiments for examining polymer viscosity, drag flow, pressure flow, mixing, die swell, and viscous heating are performed.

The parameters that can be varied are:

• screw speed
   
• barrel temperature distribution
   
• screw geometry
   
• die resistance
   
• resin type

• residence time distribution
   
• mixing
   
• pressure, temperature, flow rate (and their interrelations)
   
• die swell
   
• comparison to flow model

The hardware consists of a Killion KL-125 single-screw extruder with interchangeable dies interfaced and controlled by a PC running LabVIEW software. Temperature is controlled in three zones along the barrel and independently at the die head. Pressure is measured at the die head. Transport behavior can be observed by slowing feeding new polymer onto the visible screw. For concentration measurements in the study of the residence time distribution, a UV-Vis spectrophotometer is available. 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 die pressure.

Commercial thermoplastic polymers including polycarbonate, polystyrenes, and acrylonitrile-butadiene-styrene terpolymer (for die swell studies) are available. The resins available for this year’s laboratory experiments (all obtained from GE Plastics) are Cycolac VW55 (180 F), Lexan 141 (200 F) and Lexan ML6339R (200 F).

• The extruder and die must be heated to the operating temperature before any polymer is introduced. When the desired temperature is reached, the motor is turned on and one or two cups of polymer are added to the hopper.
   
• Leave the laboratory staff a note indicating the desired temperature you want the extruder set at.
• Because the temperature takes a while to cool down, make sure that you start your experiments at lower temperatures and increase throughout the course of the afternoon. Very high temperatures will result in bed fluidization, and you will not achieve polymer extrusion.
   
• Keep an eye on the pressure transducer, which needs to be cleaned on a regular basis. If the pressure does not decrease alert the laboratory staff that the transducer may need to be cleaned.
   
• The end of the screw is visible (with a flashlight). The tachometer is broken, so the readings on the computer are meaningless. You must measure the speed by counting the number of screw rotations.
   
• The polymer should be dried prior to experimentation (2 – 4 hours). Alert the laboratory staff the day before and they will turn on the ovens for you. Put about ½” of polymer layer on each tray for drying.
   
• Do not run polymer through the extruder to cool the machine!
   

Purpose

The students will learn about one of the most common processes for shaping polymeric parts. Polymer particles are often made by injection of a molten polymer into a mold. The mold filling process will be demonstrated by making 'short shots' and by using pigment tracers. Then various processing conditions will be used to manufacture tensile bars of a commercial polymer (polystyrene), and the resulting mechanical properties will be measured. The complicated interaction of process parameters and polymer properties on mechanical behavior provide an ideal opportunity for the students to apply the concepts of experimental design.

The parameters that can be varied are:

• polymer temperature
   
• mold temperature
   
• injection speed
   
• pressure during cooling
   
• mold configuration

• flow patterns
   
• mechanical properties (tensile test)

Samples are prepared using a Boy 15-Ton injection molding machine. The device consists of an extruder, a ram and a mold. As with the extruder, the injection is thermally controlled and the mold is cooled. Various molds are available including single- and double-gated tensile bars and a spiral die. Mechanical properties of dogbones are determined using an Instron Tensile Test machine.

• Obtain all of the necessary data for one mold (die) at a time – it is not simple to change the dies.
   
• The polymer should be dried prior to experimentation (2 – 4 hours). Alert the laboratory staff the day before and they will turn on the ovens for you. Put about ½” of polymer layer on each tray for drying. This will minimize the formation of bubbles in your product.
   
• Only load the necessary amount of polymer into the “hopper” – about ½ way up the window. This will make it easier to change materials.
   
• Make sure to remove all pieces before beginning the next run.
   
• The temperature must be at least 20 – 30 C above the melting temperature.
   
• An instruction manual for the injection molding machine is available from the laboratory staff.
   

Additional Documentation:

Injection Molding Manual

Extrusion Manual

Extrusion Manual Update