Technical Know-How

Selection of grinding media

The best size of grinding media depends on the particle size of the milling product at the BEGINING of the milling process and the desired particle size at the END of the milling process. Thus, good pre-milling and de-agglomeration for primary reduction of particle size are of utmost importance for an efficient use of properly selected grinding media.

Wet milling is a process which takes place by impact, attrition and shear forces developed within the grinding chamber. Grinding efficiency is achieved through the following principles:

  • The smaller the grinding media the greater the number of beads in the grinding chamber and hence greater the grinding efficiency

  • The number of beads is proportional to the bead size which, in turn is proportional to the bead diameter. Since the relationship of the bead volume to its diameter is a cubic one, a reduction of the bead size by half will increase the number of beads 8 times

  • The grinding media should be 2 – 3 times bigger than the separator or filter of the mill (slotted pipe or gap, screen cartridge)

  • The grinding media should also be at least 5 times smaller than the distance between the stirrer disc and the wall of the mill chamber

  • The grinding media should be about 20 to 30 times bigger than the particle size of the milling product at the beginning of the milling process. The feasible average particle size of the milling product is about 1/1000 x of the grinding media. (Example bead size 2 mm /1000 = 0,002 mm = 2 µm)

  • The specific weight and density of the bead also plays an important role as this determines the kinetic energy with which the bead accelerates through the product slurry, hence playing its part in grinding efficiency.

CHARACTERISTICS

A 150 years old Company with each production batch undergoing strict Product Quality checks (diameter, sphericity, corrosion behaviour, internal structure and specific weight).

SiLi also deal intensely with wet grinding technology, being constantly in contact with all the world’s leading mill manufacturers. The wear and tear rate of our micro-bead grinding media is among the best in the industry.

PRODUCT CERTIFICATIONS

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ISO 9001:2008 Certification

Protocols conforms with DIN ISO 15378 for pharmaceuticals Glass beads are conform to EC regulation 1935/2004/EC