Petra-Wasserkocher Deckel (Kettle Lid)

prusaprinters

After many years of using my trusted PETRA waterkettle, its lid started to crumble. It It literally disintegrated in the hot 100°C steam and little plastic pieces got mixed into the water. The original lid was probably made out of ABS, which is not the most human body friendly material, so I decided to dispose of the lid. Well and does that mean I have to dispose of the entire waterkettle too? It still works fine. So I started to look for a replacement part. There aren't any commerically available. The vendor produces new designes every year and has no way to identify the historic part that I'd need. They - as expected - recommend to by a new model. How about 3D-printing one? We need material that can withstand 100°C for a short term without falling appart. PLA becomes soft around 60°C, PETG at ca 80°C. That does not work. So we need to print in ABS again? Well, no. Surprisingly no. E.g. https://extrudr.com have excellent datasheets with fine details about their "Durapro ABS" filament. They say it softens at 92°C, that is still too low. Filaments that can withstand more than 100°C are available, but quite expensive. To keep cost at a reasonable level, I decided to try an ASA sample from an unknown vendor, that I still had lying around. According to extrudr.com, ASA (their DuraPro ASA) withstands 96°C. Done. Tested, and even when boiling way too much steam from the kettle, the lid is perfectly stiff. This was in June 2021. A year later (as I am finally uploading to thingiverse) it is deformed. Cooking tea is a daily routine more than once per day. So how does the printed lid look like a year later? It's top is pretty much the same, except that the geometry is somewat distorted where horizontal parts meet vertical or angled parts. At some places cracks formed, at other places material bulged outwards. Odd forces must be working inside the material. The lower ring of the lid that fits into the kettle (and touches the metal) no longer is a nice ring. It bends inwards, as if the ring wanted to shrink. At least, ASA does not disintegrate at all. No particles can be scratched off. Update: two and a half years later. I am fed up with the now shabby looking design. Nobody will believe this was intentionally designed the way it looks now. The bottom ring is pulled inwards almost horizontally. The cracks on top are widening. The material does not become brittle or soft. Let's print a fresh one. I've now updated the freecad drawing, to add fillets and curved walls where cracks formed, so that there is material that can stretch better. Exported a new STL and also uploaded the 3mf file from prusaprinter with the settings I am now using with durapro ASA. The photos show a gray and a white lid. Gray is the old one after 2 1/2 yeas of daily use. The old STL file from June 2021 is still included for comparison. Category: Containers