Abstract
As housing affordability decreases and the construction industry continues to contribute greatly to total greenhouse gas emissions, finding new ways to improve the affordability and sustainability of housing is critical. In the last ten years, 3D printing has made its way into the construction industry. This technology has some very promising benefits over traditional construction techniques and is becoming a viable option for residential home construction. The National Science Foundation is funding a project to develop a 100% biologically based composite material called PrinTimber using wood particles to construct sustainable and affordable housing using 3D printing technology. Previously, a single screw extruder has been used which requires batch mixing of the composite ingredients. This current project focuses on the design, manufacturing and testing of a counterrotating twin screw extruder drive and feed systems. This new design allows for continuous mixing which permits larger scale and higher efficiency prints. This advancement is made by developing a mechanical system that couples a 3 hp AC motor to the twin screw extruder and integrating wood and sodium silicate feeders while also testing performance and evaluating the extrudate. The use of the twin screw extruder successfully achieved continuous feeding and mixing. Feeder implementation, extrudate characterization, extrusion rates, and cooling systems effectiveness were all tested in this study. Additionally, micro-CT scans were used to compare the density of extrudate from a single screw extruder and a twin screw extruder. It was found that premixed extrudate from the single screw extruder produced more uniform density over the cross section compared to the extrudate from the twin screw. However, results from ball indentation hardness tests and compression tests show that the twin screw extruder produces extrudate that can support significantly higher loads than extrudate from the single screw extruder. Additional testing should be performed to better understand the mechanical properties of the extrudate.