CARBON FIBER RECYCLER: OVEN HEATING SYSTEM
TESTING
In order to properly evaluate the success of the Oven Heating System, a variety of tests must be conducted to ensure all design requirements in section 1D have been met. These primary tests intend to measure both the speed and accuracy of the oven to reach pyrolysis temperatures and perform correctly. Prior to testing the success of pyrolysis that achieves recyclable carbon fiber, the capabilities of the oven to perform to standards had to be verified first.
One issue during testing was the oven smoking and heat leaking from the cracks at the top of the oven. This was combatted by adding more insulation to those leakage points which resulted in no smoke being released from the oven by the third trial.
Test 1: Preheat Test
The first test on the JCATI Oven Heating System was the Preheat Test. This test aimed to meet design requirements 3 in section 1D; The oven must reach target temperature within 15 minutes. The target temperature is 500°C. Using a stopwatch, hand-held K-type thermocouple, and temperature controller, the oven temperature was measured and two points to test if it met the necessary criteria within the desired time constraints. As displayed in figures 2 and 3, the oven took a minimum of 24-27 minutes to reach target temperature.
One thing that was modified during the first test was the total time it took to measure temperatures. Initially, each trial was only set up to measure the temperature of the oven for the first 15 minutes. Since the oven did not reach pyrolysis temperatures by then, the trial times were extended to continue measuring values until target values were reached. This was necessary to know how long preheating actually took versus how hot it got in 15 minutes since reaching target temperatures were more important than the time limit.
Figure 1: Preheat Test Setup
Figure 2: Time vs Thermocouple Temperature Graph
Figure 3: Time vs Temperature Controller Graph
Preheat Test Videos
Test 1
The videos is Test 1 show the process of measuring and recording the oven temperature using two instruments. In addition, the proper shut down and cool down process for the Preheat Test are demonstrated.
Test 2: Temperature Test
The second test was the Temperature Test. This test intended on confirming design requirements 2 and 5; The oven temperature must maintain 500°C ± 5 °C during the 30-minute pyrolysis process and the oven’s outer surface must not exceed 45°C. In addition, the argon gas was setup to fill the oven and displace all oxygen to simulate a full pyrolysis environment. The flow meter on the argon gas tank was used to control and measure the gas release rate. Since the temperature controller comes with a K-type thermocouple, it was able to measure the inner oven temperature while the Oven Heating System was on, and a hand-held thermocouple was used to record the outside surface temperature as well. The graph in Figure 7 show that during the majority of the 30-minute time interval, the temperature controller was able to keep the temperature within required range apart from 2 data points in trials 1 and 2. However, with the auto-tuning function on, the third trial was successful in keeping the temperature at a 10 degree range during the necessary time. Unfortunately, the maximum surface temperature measured went as high as 57°C, as shown in Table 1, which surpassed the temperature requirement of 45°C.
For the second test, an update made to the procedure was the locations that the surface temperatures were measured. The first two trials measured the left, right, and top surfaces of the oven. However, the third trial measured all five walls of the outer oven. This change was necessary in analyzing the results and understanding why some points in the oven may be hotter than others.
Figure 4: Temperature Test Setup
Figure 5: Purge Gas Flow Meter
Figure 6: Target Temperature
Figure 7: Time vs Temperature Graph
Table 1: Surface Temperature
Test 3: Resin Removal Test
The last test was the Resin Removal Test. This test was designed to measure requirement 7 - the pyrolysis process must remove 90% of resin from the composite material. One batch of the shredded carbon fiber composite that came through on the conveyor was weighed prior to entering the oven, which was already filled with argon gas, and then underwent pyrolysis. The composite material was then weighed at several time intervals during its pyrolyzing process. The general ratio of carbon fiber to epoxy resin aided in both the prediction and final calculation to confirm if the required amount of resin was removed from the composite. While design requirement 7 entailed a 90% resin removal rate, the graph in Figure 11 shows that it only produced a 77% removal rate. The graph also shows that the majority of the resin removal occurred in the first 10 minutes of pyrolysis and began to flatline after 20 minutes. Although the last test failed to meet criteria, there were still usable observations and data gathered from this test which will help in the future.
One modification to the procedure was to weigh material mass at several time stamps during the same pyrolysis process as opposed to just before heating and after 30 minutes. This was done to produce a visual graph display of the trend in resin removal over the course of one heating cycle. In addition, due to lack of composite material available, which was less than one wing trimmings worth, this final test was limited to only one trial being conducted.
Figure 8: Resin Removal Test Setup
Figure 9: Shredded Composite Material
Figure 10: Material in the Oven Heating System
Figure 11: Resin Removal Rate