HIGH ENERGY BALL MILL


FASTER – FINER – Emax Benchmark test: fi neness and grinding time


Grind sizes at the nanoscale can only be achieved by wet grinding (see article on colloidal grinding, page 12). For this method a large number of grinding balls with 0.1 mm to 3 mm Ø is used to create as much friction as possible. The resulting grinding energy is extended even fur- ther by the high speed of 2,000 min-1


in the Emax. The


high energy input is fully exploited as the unique liquid cooling system quickly discharges the frictional heat. With- out effective cooling both sample and mill would overheat. Depending on the sample characteristics and grinding mode, cooling breaks of approx. 60 % of the total grinding time are re commended for conventional planetary ball mills to


prevent overheating. The Emax, on the other hand, is suit- able for continuous grinding without breaks thanks to its effi cient liquid cooling system.


In a comparative trial, the pigment titanium dioxide was pulverized in the most powerful planetary ball mill and in


the Emax (50 ml grinding jar of zircomium oxide, 110 g matching grinding balls 0.1 mm Ø, 10 g sample, 15 ml 1 % sodium phosphate).


After 30 minutes the d90 value of the Emax sample


was 87 nm. The planetary ball mill achieved a grind size of only 476 nm after this time (excl. cooling breaks). Con-


sequently, the Emax provided a 5 times higher fi nal fi neness than the planetary ball mill (fi g. 4).


Benchmark test: grinding time


The superiority of the Emax is even more visible when look- ing at the grinding time. Figure 5 shows the results of grinding graphite in the Emax at 2,000 min-1


(50 ml grinding


jar of zirconium oxide, 110 g matching grinding balls 0.1 mm Ø, 5 g sample, 13 ml isopropanol) and in the most power- ful planetary ball mill. Graphite is a lubricant and therefore requires a particularly high energy input for size reduction.


After only 1 hour of grinding 90 % of the Emax sample possessed a fi neness of 13 microns. This grind size was achieved by the planetary ball mill only after 8 hours of grinding (excl. cooling breaks). Regarding


the fi nal fi neness achieved in the Emax after 8 hours of grinding, its superior performance again is quite apparent: With a d90


value of 1.7 μm the grind size is 7 times fi ner than the one achieved in the planetary ball mill (12.6 μm). 20


13 μm 10


0 0 1.0 2.0 3.0 4.0 5.0 grinding time 8 x faster


Abb 5: Pulverization of graphite. The water-cooled Emax is highly superior to the planetary ball mill without cooling system both in speed


and achieved fi nal fi neness. page 06 | the sample 39 | www.retsch.com 6.0 7.0


8.0 [h]


Comparison of grinding time and fineness in the Emax and in a planetary ball mill


all mill


Grinding time Emax


Final fi neness


Graphite: 8 x faster 7 x fi ner


1 h 2 h 4 h 13.0 μm 8.2 μm 5.5 μm


Planetary ball mill (excl. cooling breaks) 1 h 2 h 4 h


Final fi neness [μm] 50 40 30


Planetary ball mill (best result)


High energy ball mill Emax 2,000 min-1


25.0 μm 20.3 μm 16.2 μm


Grinding of titanium dioxide in the Emax and in a planetary ball mill


d10 Emax (after 30 min.)


Planetary ball mill (after 30 min. excl. cooling breaks)


Q3


100 90 80 70 60 50 40 30 20 10 0


10 [%] d90


Planetary ball mill (best result)


High energy ball mill Emax / 2,000 min-1


57 nm 66 nm d50


Titanium dioxide: 5 x fi ner


d90 69 nm 105 nm 87 nm 476 nm q3


3.0 2.5 2.0 1.5 1.0 0.5 0


100 87 nm 476 nm particle size x[nm]


Fig. 4: The Emax pulverizes the sample not only faster and to a fi ner size, it also produces a signifi cantly narrower particle size distribution.


1,000 10,000


Direct contact: 866-473-8724


particle size


percent by volume


relative frequency


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