The University Of Wisconsin-Madison
In the laboratories of the Polymer Engineering Center at the University of Wisconsin-Madison we have a wide range of polymer-processing machines, including a lab-scale 8-ton injection molding machine, an instrumented single- screw extruder with sensors and a multi-function co-injection molding machine for both research and education. Since those machines are used for research purposes, we run a series of polymers at different processing conditions.
One of the machines that need to be purged frequently is the extruder. We use different techniques depending on the previous and following material to be processed, with some materials being difficult to purge.
HDPE, LDPE, POM, PS, PEEK, PLA, PM MA, PP.
Problem to be solved:
When switching from a low temperature profile to a high temperature profile material and vice versa, the extruder has to be taken apart at times to be cleaned. For that reason, a transition/cleaning material is required. In addition, the processing of high performance thermoplastics such as PEEK can only be accomplished by using transition material. Without a transition material with high cleaning effect, the switch from low temperature materials such as HDPE and even POM to higher temperatures up to 400 °C, would result in the degradation of that material and black specks in the following material. After the production with PEEK, it would be impossible to clean the screw without a high temperature purging material.
Purging material characteristics:
Transition materials from ASACLEAN were tested when changing from PEEK (processing temperature 360-380 0C) to POM (processing temperature 200-2100C) and vice versa
Three grades of ASACLEAN purging compound were used. ASACLEAN U grade is commonly used in the 176.6°C to 360°C range and the SX grade in the 298.8°C to 390.5°C range. In addition, PX grade could be used instead of the SX grade. The PX grade has better cleaning properties due to the presence of fibers. These purging compounds were utilized to transition up or down in temperature. The U grade was used to purge at the low end of the PEEK temperature range because it was found to have really low viscosity at the high end of the range to purge out the PEEK well.
After working with PEEK, ASACLEAN purging compounds were used to clean the machine with overall good results. In the first trial we used 5 pounds of SX Grade and finished the cleaning process with 0.5 pounds of PX Grade material which was enough to complete the cleaning of the PEEK. Optimization of the cleaning process led to a reduction of the purging material and cleaning time. We found that cleaning results with the PX grade were more efficient for our purpose. Below are pictures of the cleaning steps.
|Start (Cleaning PEEK-Black Color)||SX Grade||PX Grade||End (No PEEK-Extruder Cleaned)|
|Start (Cleaning PEEK-Black Color)||PX Grade||PX Grade||End (No PEEK-Extruder Cleaned)|
With the ASACLEAN purging compounds the overall process of cleaning out the extruder became much faster, and overall much simpler. In the past, the extruder had to be taken apart at times to be cleaned in the oven because of the excess material that was not fully cleaned. This took a lot of manpower and wasted a lot of time. ASACLEAN made it possible for our team to clean the extruder without having to take it apart which minimized the cleaning time from a business day down to one hour. This process involves heating the extruder up, running it, cleaning it, and making sure all old material is extruded out of the machine.
In addition processing of different materials with wide range temperature profiles is only possible by using transition materials such as ASACLEAN, which even make the process fast and simple.