Many people associate the material graphite with the common pencil. However, manufacturers in many different industries associate graphite with many more uses.
In technology industries, the conductive properties of graphite are commonly used in batteries. Medical industries also use graphite in a variety of forms. The issue is that processing graphite can be tricky, as the material facilitates oxidation, particularly at higher temperatures.
Prolonged exposure to graphite can contribute to corrosion of different metals—including stainless steel and aluminum. Studies featured in the International Journal of Electrochemical Science state that “CPP measurements showed that the presence of Gr [Graphite] and the increase of its content with Al [Aluminum] increased the corrosion current, corrosion rate and decreased the polarization resistance.”
So, when a client in the medical industry requested a custom stainless steel basket to hold small sheets of graphite through a basic sanitation process, Marlin’s engineers knew they had their work cut out for them.
For this cleaning process, there would be between 65-125 small graphite substrate sheets attached to a narrow wood block. Three such wood blocks would hold graphite sheets through the wash process, but it was very easy for the sheets to fall out during the process.
The wash process itself was relatively gentle, using plain tap water heated to a mild 175 degrees Fahrenheit. This combination of relatively low temperatures and plain tap water would make the wash process itself have very low impact on stainless steel.
In this process, the graphite sheets themselves posed the greatest risk of corrosion to the metal of the basket. However, as noted in old studies by the Oak Ridge National Laboratory dating back to the 1960s, “the lower temperature limit for significant diffusion between graphite and stainless steel [is] approximately 600°C.” Since the wash process was far below this temperature threshold, the contamination risk was somewhat reduced.
So, the basket had to have very small open space and be able to take repeated, prolonged exposure to graphite without corroding.
Engineering the Graphite Sheet Washing Basket
To best protect the graphite sheets, it was decided that an enclosed basket design was best—one chamber for each wood block holding the graphite sheets. These cylinders would then be loaded in a larger tray. This would help keep too many graphite sheets from intermingling at the bottom of the basket all at once.
Since the main mode of moving the basket from one place to the next would be by hand, a set of handles were added to the frame of the tray that the individual cylinders would be carried in.
Additionally, because the graphite sheets could easily fall out of the wooden block holding them or shatter into small pieces, the wire mesh of the basket had to have the smallest possible open space between wires without affecting the flow of water into or out of the basket.
By limiting open space, graphite fragments could be kept in the basket and not wind up floating in the washing machine used to clean them.
Once the design was completed, it was tested against the client’s washing process using advanced physics simulation software. The design was refined until it could pass the virtual test, and only then was it put into production.
By studying the process and the materials involved, Marlin’s team was able to make a custom parts washing basket that could not only meet, but exceed the client’s performance demands.