|flat flakes (up to 300µm)|
|Typically, ductile metal samples will become flat out during grinding in a planetary ball mill (like the used Planetary Mill PULVERISETTE 5 classic line).|
main disk speed: 360 rpm
250 ml grinding bowl made of stainless steel
+ 15x 20 mm ø stainless steel grinding balls
||+distilled water 100ml|
||30 min / 120 min / 240 min|
||ca. 100µm / ca. 300µm / 150µm (flakes)|
500 g of ~ 70 µm metal sample pieces (determined by optical microscopy) have been used for this test.
We added ~ 100 ml of distilled water to avoid a sticking of sample to bowl and balls. To avoid overpressure, we ground the sample in steps of 2 minutes, followed by a programmed pausing time of 10 minutes. After several cycles, the outside temperature of the bowl should be checked (remain below 80°C); grinding time or programmed pausing time might be readjusted afterwards. We recommend not using water for a grinding of steel as desired. Abrasion can form gas pressure which lead to a leakage of the bowl. By using e.g. benzine, grinding times of ~ 5 minutes can be set (with the higher boiling point of benzine, also higher temperatures of the used bowl can be tolerated too).
Fineness has been checked after 30’; 120’ and after 240 minutes by optical microscopy. It has shown, that sample became pressed to flat flakes quickly. Fe found particles with up to 100 µm after 30 minutes, up to 300 µm after 2 hours of grinding time. After 4 hours of grinding, size has been reduced to 150 µm again. Always, the height of the found particles has been much smaller; sample just became pressed to flat flakes.
This is a typical result for most of metal samples. The softer and more ductile the sample use to be, the faster flat flakes will be displayed during grinding.
Faster results will be achieved, when hardmetal tungsten carbide with its higher density will be used instead of steel (hardmetal tungsten carbide: 14,9 g/ml; tempered steel: 7,9 g/ml).