Team Vision for System-Level Design Phase
The goal of the team during this phase was to decide on the overall design for the plastic melter. To do this, the current machine design was broken down into sub-functions and design components. This was accomplished in the Functional Decomposition and Concept Selection sections. Then possible solutions for components and sub-systems were brainstormed in the Benchmarking Table and Morphological Table. These tables were then used to brainstorm possible system concepts and compared in the Pugh Chart. While going through the concept selection process the team found that the heating, melting and compression aspects of the system needed the most design work and research. During this phase testing was done on the previous team's device and on the best way to melt plastic. Eventually the team came to a conclusion on a preliminary design.
A working copy of the Functional Tree can be found here .
A working copy of the Transformation Diagram can be found here.
BenchmarkingThe purpose of benchmarking was to research current designs and products to gain a better understanding of what is currently available on the market. The results from the benchmarking allowed the team to make logical decisions when selecting the final concept design.
Working copy can be found here.
Morphological ChartThe morphological chart is a summary of expected functions of the melter with a variety of solutions of how the function will be performed.
Working copy can be found here.
Concept DevelopmentThe following table is a summary of the six proposed concepts for the design of the melter created with solutions from the Morphological Chart.
Working copy can be found here.
- Heats Up Quickly
- Minimal Safety Risks
- Low Cycle Time
- Easy to Use
- Completely Melt Plastic
- Quality of Melted Plastic
- Low Cost
- Low Usage of Power
- Easy to Transport
- Cools Quickly
The concepts were narrowed down to three main concepts: The practical design which is similar to the current system, an injection molding design, and a surface heating design which is an insulated version of the current system. After comparing these three concepts more closely, it was found that the injection molding design would cost too much, and that with the current inability to melt the plastic insulation is needed.
Working copy can be found here.
Feasibility: Prototyping, Analysis, Simulation
P18433 Melter TestingThe melter constructed by MSD team P18433 was retrieved to perform testing and analyze the system. The handoff notes and PRP discussed many issues with the system such as a dangerous compression system, uneven melting of the PET chips, lack of cooling system, and problems with controlling the temperature. The team performed two tests running the melter for 45 minutes and 90 minutes and measured the temperature of the heating plates and various locations of the mold with an IR temperature gun in 15 minute increments. The PID was not functioning throughout the testing process.
The first test consisted of placing a thin layer of PET chips in two corners of the mold and was occasionally compressed during the test. After the 45 minutes had elapsed, the system was turned off and the jack was uncompressed. The final inside temperature of the plate when opened was 220°F and the plastic temperature was 225°F. The plastic was very brittle and turned white but was not fully melted together. The main outcomes from this test were to investigate the electrical availability in El Sauce and to design removable sheets to put chips on and then remove once heated to allow another sheet to be inserted for melting.
The second test used the same set up as the previous test. The system was on for 90 minutes and reached a final inside temperature of 360°F in the back and 280°F in the front and the plastic temperature was 370°F. The observations from the test were that heaters were unevenly distributing heat on the plates because of the placement of the heaters.
Overall, this testing allowed the team to operate P18433's melter and understand components of the system that were unsuccessful and brainstorm alternative designs and continue research for the final concept.
Feasibility TestingFeasibility testing was performed using a variety of heating sources including a panini press, an electric wall oven, and a stove top. The purpose of this testing was to observe the melting characteristics of the PET chips and to compare the standard melting and glass transition temperatures to the actual melting temperatures.
The team used a Hamilton Beach panini press to investigate the possibility of designing a melter similar to the model. The press had one set temperature (exact temperature was not found in user's manual or online) and a timer that turned the system on and off. Parchment paper was placed inside the press and a thick layer (~1/2") of PET chips was placed in between the parchment paper and plates. The press was checked in 5 minute increments for a total of 30 minutes. The PET chips changed from clear to white with some areas appearing glossy, but were still freely moved after an hour in the press. The team concluded that press's limited temperature was not close to the PET melting temperature.
Test 2:The oven was pre-heated to 425°F and a thin (~1/8") of PET chips was spread evenly between two baking sheets with a layer of parchment paper on either side of the plastic. Four dinner plates and two baking dishes were placed on top of the baking sheets to provide compression during the melting process. The chips were checked in 10 minutes increments for 50 minutes. At 30 minutes, the bottom layer chips were melted together and could be moved as one sheet with the top layer still unmelted. After checking the chips at 50 minutes, the entire sheet of chips was flipped onto the opposite tray to begin melting the top half (now bottom half). The temperature was increased to 450°F at 60 minutes, the "plate" of chips broke into a few larger plates from the previous flipping. The temperature was increased again to 505°F at 70 minutes until testing was completed at 90 minutes. Small sections of the chips melted on the corners, changing back to a clear state. Overall, this testing resulted in slightly better results than the P18433 melter testing. The sections that experienced full melting cooled very quickly when exposed to ambient air. Further testing in the oven should include a higher initial temperature and even compression on the entire baking sheet.
Test 3:The first test on the stove top oven used a Cuisinart skillet with a non-stick interior, aluminum core, and a metallic protective finish to heat the PET chips. During the first test, the stove was preheated on temperature 6 (simmer, 1,2,3,4,5, 6, high) for 3 minutes. A thin layer of plastic chips were placed on the skillet and instantly changed colored/melted/curled. The plastic was not thick and sticky and was difficult to stir. The skillet was placed under cold water and cooled in less than 30 seconds. The plastic was thin and easily removed from the skillet.
During the second test on the stove top, the skillet was preheated at temperature 3 for two minutes. A thicker layer of PET chips was placed on the skillet and a lid was used to enclose the heat. Visual changes of curling occurred at 2 minutes and the heat was increased to temperature 4. At 7 minutes, the chips were pushed to one side of the pan and recovered with the lid and reducing the heat to temperature 3 at 8 minutes. The bottom was clear and fully melted and the heat was decreased to temperature 2. After 10 ½ minutes, the skillet was removed from the heat and placed under cold water and then removed. The plastic was very smooth, the bottom was clear and the top was not fully melted and still had visible chips in the melted sheet. The plastic was flipped so the uneven side was in contact with the skillet and melted for five minutes at temperature 4. Throughout the melting, the plastic was compressed against the skillet with a spatula and removed at 9 minutes. The final sheet was almost completely clear, some areas remained white after the second time exposed to heat.
|A thin layer of plastic chips were placed on parchment paper and then on a cookie sheet with no compression, the oven was set to 505°F. The plastic melted in 10 minutes, warped upon cooling with no compression.|
|Thicker layer of plastic placed on parchment paper in a smaller square pan with no compression, the oven was set to 505°F, did not melt in 10 minutes.|
|The same pan was used again with a thinner layer of plastic chips on parchment paper at 505°F. It was in the oven for 10 minutes and melted thoroughly.|
|The pan with the unmelted chips was later placed back into the oven for 30 additional minutes at 505°F without compression, it then melted with an uneven surface.|
Economical Feasibility AnalysisThe chart below outlines a economic analysis with varying amounts of workers, work hours, and product prices. Further research is needed to determine cost of plastic chips, this will be added into the cost of operation so the final numbers are subject to change. Estimated Profit is per day.
A working copy can be found here.
Heat Transfer Feasibility AnalysisAn analysis of the heat transfer within the mold will enable us to select adequate insulation to assure we lose as little heat as possible to the surroundings. This will be researched and completed more in the future.
Systems Architecture and Design
The Plastic Bottle Chip Melter is comprised of five main subsystems/components:
- The Support Structure
- This is the overall structure that supports the mold and heating/compression components that is stable and durable.
- The Compression Component
- This will most likely be a car jack like the current design. This allows the heated plastic to be compressed into the mold.
- The Controller
- This is what will be keeping track of the temperature of the system and supplying the power to the heaters.
- The Mold
- The mold is where the plastic chips will be placed and compressed, as well as removed from when they are done cooling. It needs to be of higher quality for the end product as well as durable.
- The Heating Components
- This is the part that will be melting the plastic chips to transform them into an end product (currently a flat 12'x12' sheet). There have been issues in the past projects of not being able to melt the plastic completely, so the heating subsystem will be a main focus for the team.
Failure ModesSome potential failures modes of this system could include:
- Not melting the plastic fast enough
- The system not reaching the plastic melting temperature
- Not being able to control the temperature
- Compression being insufficient
- The end product being damaged or deformed during compression or extraction
- Injury to operaters
- The equipment not being durable enough, or parts getting lost
Detailed Design of MoldTaking a closer look at the design selected, both the top and the bottom of the mold will have slots cut out for the heating strips and insulation around the heaters and the mold. The bottom of the mold will be attached to the car jack and have a removable tray that will act as the main mold for the plastic chips so it can be removed and cooled while another tray and plastic chips are heated and compressed.
The initial risks were re-assessed and modified to fit the final design concept of the melter. These risks will be continuously evaluated throughout the remainder of the project and mitigation plans will be created for the top risks.
The working Risk Assessment document can be found here
StandardsThe following standards may relate to our project and will be further investigated. Standards in Nicaragua will also be researched to ensure the melter will meet all federal standards and regulations.
- ASHRAE Standard 62.1 2013, Ventilation for Acceptable
Indoor Air Quality
- Intended to minimize adverse health effects
- PET technically doesn't need ventilation (Harbec interview P18433), but it's not a bad idea
- Will the melter be able to operate in El Sauce inside without ventilation?
- ASHRAE Standard 62.1 2013
- IEEE C2-2017, National Electrical Safety Code (R) ,
- Safeguarding persons from hazards from installation and operation of electrical supplies
- Melting system will have electrical/safety concerns
- IEEE C2-2017
- UL 499, Standard for electric heating appliances
- Standard for electric heating rated at 600V or less
- Melter is a heating system, need to be aware of standards in US and Nicaragua
- UL 499
- NAICS code 326199, Standard for All Other Plastics Product Manufacturing
Design Review Materials
- Presentation and/or handouts
- Notes from review:
- Notes will be added after review
- Action Items
Plans for next phaseIn the upcoming weeks the team would like to have completed further research, continue testing and prototyping as needed, and finalize the design of our device to start working on pricing parts and modeling sub-systems.
Team Project Plan for Phase 3
- More feasibility testing and research
- Determine volume in mold
- Determine quantity of chips needed to fill mold
- 3D models of components and assembly
- 2D Drawings of components and assembly
- More detailed heating system design
- Bill of Materials
Questions for Next Phase:
Three week plans for team members at the end of Phase 2: