This page contains a Flash digital edition of a book.
temperatures (>2,192F or >1,200C). Tese ceramics act to preheat product material while that material is also under microwave energy exposure.


Once the material is exposed to microwave energy, it almost immediately begins to absorb the energy and dissipates that energy as heat, which aids in heating both the process area and product material, in this case waste sand. Te prototype process- ing unit has 10kW of output power, supplied by on-board mag- neton power sources. Te entire unit is about 12 ft. in length and 2 ft. (0.61m) in diameter and has a pro- cessing zone of 6 ft. (1.83m) in length and 6 in. (0.15m) in inner diameter. Te input section is a microwave-


system was setup to rotate at 0.75 rotations per minute (rpm), 1.5rpm and 2rpm. Waste sand, which


Fig. 3. This is a dual stage thermal and microwave rotary system.


consists of a two-part resin (phenolic urethane nobake), red iron oxide (Fe2O3, hematite, from additions), and black iron oxide (Fe3O4, magnetite, from additions), was placed in the sand stor- age bin above the microwave unit and fed to the input of unit through dual slide gates, used to control flow, located on the storage bin. Te temperature of the


a four-degree incline angle with the input end being raised to allow the flow of material from input to output as would be customary with most conventional rotary processing systems (Fig. 4). Above the microwave unit directly


safe feed tube that leads to the process- ing zone. Te input and output sections are designed specifically to contain microwave energy but allow materials to freely pass in and out of unit. Temperature is monitored by


type-K thermocouples attached to the surface of the rotating section and extending inside the kiln along the radius.


Experimenting Te microwave unit was set on


over the input section is a sand stor- age bin with a fed pipe leading to the input section. And beneath the output section a bin was placed for collection. Prior to processing waste sand,


the microwave unit is preheated to temperatures for each experiment. The set-point temperatures, which are input by the operator from the microwave control panel, examined in this initial development study were 977F (525C), 1,292F (700C) and 1,337F (725C). The rotary


Table 1. Heating of Resin-Coated Sand in Quartz Fiber Crucibles in a Batch Microwave System at 932F (500C) as a Function of Time


Bake Time Average Initial Weight (g) Average Weight Lost (g) Average % Lost 1 min. 2 min. 3 min. 4 min. 5 min. 6 min. 7 min. 8 min. 9 min.


10 min. 11 min. 12 min. 13 min. 14 min. 15 min. 20 min.


10.002 10.000 10.002 10.004 10.002 10.001 10.002 10.002 10.003 10.003 10.002 10.001 10.003 10.001 10.001 10.003


38 | MODERN CASTING April 2016


0.005 0.005 0.006 0.003 0.021 0.049 0.057 0.058 0.074 0.083 0.098 0.098 0.093 0.109 0.099 0.097


0.05% 0.05% 0.06% 0.03% 0.21% 0.49% 0.57% 0.58% 0.74% 0.83% 0.98% 0.98% 0.93%


0.109% 0.99% 0.97%


sand was measured as the sand exited the microwave unit to understand the effect of microwave on the sand heating. LOI was tracked for the various


sample conditions, and photographs cataloged the tested and processed samples. LOI measurements were performed by Carley Foundry, Blaine, Minnesota.


Discussing the Results


Several issues were encountered with the prototype in installation and initial test runs at MMP because this prototype was not originally devel- oped for use with metalcasting sand. However, the system was able to dem- onstrate the feasibility in removing resins from waste sands to give LOIs of less than 0.1. Tables obtained from work ongoing


at Grede-St. Cloud describe comple- mentary work comparing the weight loss and LOIs at 932F (500C), varying time at temperature. Table 1 shows the microwave processing of waste core sand in a crucible and Table 2 shows the results of using the concept of direct hybrid processing, using tech- niques analogous to processing within the microwave rotary system. A comparison of Tables 2 and


3 shows the difference in process- ing time when a crucible of sand is processed by microwave versus when the sand is allowed direct contact with microwave absorbing ceramics emitting thermal energy in combina- tion with microwave energy. Use of microwave and thermal techniques


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60