Purification of grinding water using a vacuum belt filter

The Franconian company Apollo-Optik GmbH& Co. KG in Schwabach, as a part of the Pearle group, has more than 700 branches in Germany. The company’s product range reaches from cutting-edge eyeglass frames and fashionable sunglasses to special glasses and high quality contact lenses.

One production step is the full and semi-automatic grinding of customer-specific spectacle lenses, which are sent, together with the frames, to the branches for the final assembly.

Preliminary remark

For the production of spectacle lenses, mineral materials (silicate glass) and synthetic glass is used, whereby especially polycarbonate becomes increasingly important. The lenses are made from a blank. A high proportion of the material is shaped by stock removal. To cool the lenses and to remove the chips, large amounts of grinding water is needed.


The water used for the lens processing has to be treated so that it can be recirculated. There are three common processing principles used to separate abrasive particles:

  • Sedimentation
  • Centrifugation
  • Filtration

A filtration process has been chosen, due to the small density difference between plastics material and water.


The effluent from the different processing stages is fed to a central grinding water tank. Coarse material as for example glass breakages is removed by a coarse filter-basket.

The water is fed to the vacuum belt filter using special effluent pumps. All filterable particles are separated and the purified water flows into a clean water tank. Water losses can be compensated by adding fresh water into the tank. The clean water is then fed back to the manufacturing machines.

Furthermore, controls a separate circuit the temperature in the clean water tank, ensuring a steady flow temperature, which is necessary to produce high quality lenses.

Filtration within smallest space:

The cleaning system could be realised within smallest space using the Leiblein vacuum belt filter. The external dimensions are only (l x w x h approx.) 2,6 x 2 x 2 m. A very dry abrasion is gained through the integrated vacuum unit.

Generous design

The plant was constructed for a throughput of approx. 15m³/h. The capacity of the effluent and clean water tank had been generously designed to compensate for fluctuations during production. Furthermore, high demands were placed on the operating reliability; therefore, several pumps were designed redundantly.

Future proof

The chosen concept allows to react efficiently to possible capacity enlargements. The system is modular expandable, which means that further filtration systems can easily be integrated parallel to double or rather multiply the throughput.

Satisfied customers

Due to the modular design and deliberated planning the whole system was installed within a few days. The plant with the required tanks and accessories were pre-assembled as far as possible and installed directly from the transport vehicle onto the prepared base. The integration into the existing system was straight-forward. Further adaption and change requests can be met spontaneously and without difficulty.

Grinding water treatment using a vacuum belt filter – an ideal solution!


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