Heterogeneous material mixes no longer a problem

Powerful cutting mill

The SM 300 cutting mill excels especially in tough jobs where other cutting mills fail. It has a freely selectable speed range from 700 to 3000 min-1 with high torque. The mill is convenient to operate and easy to clean. Reliable and extremely efficient sample preparation in the laboratory is now guaranteed with the SM 300.

Dr. Andreas Theisen

Cutting mills are used in many different areas of sample preparation for subsequent analyses. Typical applications include size reduction of secondary fuels, processing of biomass for renewable energy research, control of products in the context of RoHS and WEEE regulations or the recovery of precious metals – the variety of sample materials is huge. To meet all the requirements of such varied applications, the mill needs to be flexible and powerful. Even though the existing cutting mills developed by Retsch already offer a high level of performance and operating convenience, the company’s recently launched SM 300 cutt-ing mill demonstrates that it is still possible to set a new standard when it comes to preparing samples of medium-hard, tough-elastic and fibrous materials.
Easy adaptation to complex milling tasks
The SM 300 has a freely selectable speed range from 700 to 3000 rpm for optimal adaptation to the sample properties, for example breaking behaviour and temperature sensitivity. It is thus possible to grind a great variety of products with one mill.
When processing circuit boards, a low speed of 700 min-1 should be selected to prevent the sample from becoming too hot. The energy required for grinding such hard metals is obtained from the high torque of 20 Nm. In addition, the low speed helps to reduce wear on the grinding tools.
A speed of 1500 min-1 unites the maximum power of 3 kW with the maximum torque of 20 Nm. This speed is ideal for all materials that are neither particularly heat-sensitive nor too tough. The maximum speed of 3000 min-1 is suitable for materials which would otherwise not be discharged from the grinding chamber or which, due to their elasticity, could cause the rotor to slow down or stall completely. Due to the additional flywheel mass, the SM 300 ensures successful grinding without rotor blockage, even when high throughput is required. A high torque alone would be insufficient here, but the rotational energy stored in the flywheel mass in combination with the maximum power of 3 kW guarantees excellent grinding results.
Thanks to the fold-back housing, the grinding chamber is fully accessible which – in combination with the smooth surfaces – greatly facilitates cleaning the mill after grinding. The push-fit rotor can be removed quickly and safely from the open chamber. The SM 300 can be optionally equipped with a cyclone-suction combination. In addition to a cooling effect, this also improves the discharge of material from the grinding chamber and is therefore recommended for grinding small volumes or low-density materials. The improved product flow, which was achieved by an asymmetrically arranged sample feed, and the double-acting cutting bars in the grinding chamber significantly enhance the performance of the new cutting mill.
The diagram below shows the torque (green) and the power (blue) of the drive as well as the temporarily achievable peak power (red) against the speed. The peak power increases over the entire speed range. In other words, the higher the speed, the more power is temporarily available for cutting events. In the speed range up to 1500 min-1, the power results from the product of torque and speed (power = torque x speed). It ascends linearly until reaching the nominal power. This means that if the speed is doubled from 750 to 1500 min-1, the power is also doubled from 1.5 to 3 kW (maximum drive performance).
At speeds >1500 min-1, the power remains constant (maximum drive performance). The available torque decreases because of the aforementioned proportionality. In this speed range, the available peak power is produced by the enormous flywheel mass. The power here corresponds to the rotational energy stored in the flywheel mass, which increases quadratically with the speed. If the speed is doubled from 1500 to 3000 min, the temporarily available peak power is quadrupled from 5 to 20 kW.

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