Process Development

Upon returning to Cambridge, the team were motivated to improve the machine designs given their insight into the community and environment of Takaungu. The first two months after our return was largely a documentation and reflection process, to draw a line under the trip and think about how to move forward. Two main areas for improvement were identified in this time: the low rate of manufacture of the kiln and the non-renewable power source used to melt the plastic bottles. The team split accordingly into ‘process’ and ‘power’ sub-teams to tackle these issues.

The focus of the process team’s work was to improve the manufacture, efficiency and safety of the kiln. This required detachment from the current solution to a fresh set of ideas. This began in December 2019, with an extensive period of ideation and concept generation. To avoid idea fixation, a common pitfall for designers in the initial stages, the whole team of six each conceived multiple designs to tackle the aforementioned issues, before the process team assessed their advantages, disadvantages and feasibility. The designs with the most potential were shortlisted for further discussion and this continued until only two designs remained to be analysed by prototyping.

Both designs optimised the liquid behaviour of molten plastic, by including moving parts and ramps to decrease manual handling time during the extraction of the mixture into moulds. Basic tests were carried out to establish the approximate size of the new design features. Flour and water were mixed to a similar viscosity of the molten plastic and sand mixture. The mixture was tested on ramps at increasing angles and the mass of mixture transferred was recorded. Using this, the process team was able to quantify what the optimum ramp height was given the dimensional constraints on the kiln and guided decisions for which design to take forward.

Two kiln designs were taken forward for detailed design. One utilised a novel horizontal mixing mechanism with a trapdoor on the base of the kiln’s melting chamber to direct the mixture into a removable moulding tray. The second design comprised a hinged surface on which the plastic would melt with the surface in a horizontal position. The surface could be tilted to an angled position, which would allow the mixture to flow down into moulds.

Both designs had merits and drawbacks and the process team decided to prototype and model them on CAD (computer aided design) and later run thermo-fluid analyses on both of them to investigate the flow of smoke and heat transfer.

In 2019, before the current team implemented the technology in Takaungu, the kiln design team made many assumptions throughout the design process. However, now the team was able to leverage their experiences in the field and re-design with the knowledge of the community in Kenya which was invaluable when assessing the two designs. For example, the capabilities of the welders was now known as well as the availability of certain materials, which has a great influence on how the machines are designed and built.

The first three months of 2020 were spent developing and iterating the two main design ideas from ideas into scale cardboard prototypes. This was an extensive process consisting of daily design meetings, testing and analysis of components for optimum efficiency. Before the COVID pandemic hit the UK in March, the process team had begun to manufacture parts of their design in metal to better understand the mechanisms.