2.810 Manufacturing Processes and Systems (2006) Group F Environmental Analysis on Thermoforming Summary of Thermoforming Analysis The environmental analysis is made up two components 1) energy used to create the thermoformed shell, 2) emissions as a result of the process. The energy used to create n thermoformed shells can be found by the following equation: MJ 17.26)]*(n 1.007)*(n [3 Energy ++= (f1) The formula takes into account that approximately 1min 30 secs is used to fixture and defixture a part/shell. This formula should be used whenever a group is thermoforming a new batch of shells. The energy used while the machine is idling between cycles is determined by: MJ 0.18]*[n Energy Idle = (f2) This formula is to determine the energy used for any extra time on the thermoforming machine aside from that which is accounted by equation (f1). Emissions from the process are assumed to be CO2, SO2 and NOx CO2 emissions for n thermoformed shells: kg 0.186} * 17.26)]*(n 1.007)*(n [3 1.86*{n+++(f3) SO2 emissions for n thermoformed shells: kg }10*7.63 * 17.26)]*(n 1.007)*(n [3 {-4++ (f4) NOx emissions for n thermoformed shells: kg }10*3.75 * 17.26)]*(n 1.007)*(n [3 {-4++ (f5) Practical Procedure 1) Keep track of the number of thermoformed shells created 2) Keep track of the total time, and back calculate the idle time between cycles 3) Apply formulas(f1-f5) to calculate the environmental impact2.810 Manufacturing Processes and Systems (2006) Group F Environmental Analysis on Thermoforming Measurements Measured Power Properties Process Power Time Warm Up 10kW 4 min 43 sec ≈ 5 min Idle 3kW Operating (Heater) 3kW 3 min 30 sec Breakdown of Operating Time Heater: 2 min 20 sec Vacuum: 40 sec (assumption) Fan: 30 sec (assumption) Duty Cycle: sec 30min 3 : sec 30min 1 timeoperating : timeidle n)(assumptio gdefixturin :sec 45n)(assumptio fixturing : sec 45 Plastic Properties Type of thermoplastic: Acrylonitrile Butadiene Styrene (ABS) Density of thermoplastic: 1010 – 1210 kg/m3 Volume of thermoplastic: 23” x 18” x 0.0625” = 25.875 in3 = 0.424*10-3 m3 Weight of Plastic: 1210 * 0.424*10-3 = 0.513 kg Primary Energy required for thermoplastic manufacture: 91 – 102 MJ/kgiElectrical Grid energy used for single piece of plastic): 0.33 * 0.513 * 102 = 17.26 MJ CO2 emission from manufacture of thermoplastic: 3.27 – 3.62 kg/kg of thermoplastic CO2 emission from a single shell: 3.62 * 0.513 = 1.86kg Venturi Vacuum Pump and Air Compressor Properties Time to evacuate the mold = 2 secs (assumption) Volume of Mold: 18” x 14” x 8” = 2016 in3 = 1.1666 ft3 (overestimate) Flow rate of air out of the mold: cfm3560*21666.1= Pressure of the vacuum to hold the mold: 28.5” Hg = 13.9 psi (assumption)iiPressure difference between mold and surroundings: 14.7 – 13.9 = 0.8 psi Pressure drop at the point of evacuating the mold: 3 psi (observed/assumption) Key Assumptionsiii: 1) air compressors deliver 4-5 cfm per hp at 100 psi 2) every 2 psi of pressure increases of decreases the power draw of a compressor by 1 %. Assume air compressor UP6-20-135 ( 20hp, 83 cfm @ max psi, 125 max psi )iv Air compressor provides 4.15cfm per hp at 125 psi For 35 cfm, compressor utilizes 8.43 ≈ 8.5hp at 125 psi At 3 psi, 61% reduction in hp, energy used: 3.3hp (2.46kW) At 1 psi, 62% reduction in hp, energy used: 3.23hp (2.40kW)2.810 Manufacturing Processes and Systems (2006) Group F Environmental Analysis on Thermoforming The difference in power consumption is small, the higher power consumption will be used to calculate the energy consumption of the air compressor and venturi pump system. Fan Properties Power used by fan: 300W (assumption) Energy Model Calculations Process Energy (Single Cycle) Process Power Time Energy Warm Up 10kW 4 min 43 sec ≈ 5 min 3MJ Operating (Heater) 3kW 3 min 30 sec 0.63MJ Operating (Vacuum) 2.46kW 40 sec 0.098MJ Operating (Fan) 300W 30 sec 0.009MJ Idle 3kW 1 min 30 sec 0.27MJ Total 4.007MJ Material Energy used for 1 single thermoformed shell: 17.26MJ Total Electrical Grid Energy for 1 single thermoformed shell: 21.26MJ Energy Usage for n thermoformed shell: MJ 17.26)]*(n 1.007)*(n [3 ++ Energy Usage for n idle mins (idle time between 2parts): MJ 0.18]*[n Energy required to warm up the thermoforming machine should always be included into the environmental accounting even if the thermoforming equipment is switched on, and whenever there is a break in the thermoforming of batches of shells. Emissions CO2 emissions for n thermoformed shell: kg 0.186} * 17.26)]*(n 1.007)*(n [3 1.86*{n+++ SO2 emissions for n thermoformed shell: kg }10*7.63 * 17.26)]*(n 1.007)*(n [3 {-4++ NOx emissions for n thermoformed shell : kg }10*3.75 * 17.26)]*(n 1.007)*(n [3 {-4++2.810 Manufacturing Processes and Systems (2006) Group F Environmental Analysis on Thermoforming i http://www.grantadesign.com/solutions/education/ABS.htm ii http://plastics.turkavkaz.ru/processes/thermoforming/parametres.htm iii http://www.maintenanceresources.com/ReferenceLibrary/AirCompressors/kaeserpage8.htm iv
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