Super sieve from Guttridge

With traditional vibratory screening techniques particles on the surface of the mesh are all under the influence of a single external frequency with each particle responding to its own optimum frequency. Each particle, therefore, ‘waits’ to fall through the separating mesh aided by gravity; this can lead to screen blinding and efficiency and quality problems.

As an alternative to these traditional methods, scientists working at Kroosh Technologies have developed a multi-frequency vibratory screening system. Sold under the Virolat name, the system is uncomplicated and uses tried and tested mechanical components.

The sieve system comprises a special adapter fitted beneath the mesh of a conventional vibratory sieve screen (circular or rectangular). The adapter absorbs energy from the standard vibration motors and re-applies it to the screen as a multi-frequency vibration. No additional or external power is required.

Due to the strong non-linear nature of the vibration that is applied, the distribution of frequencies on the surface of the mesh is chaotic and changes 25 times per second. This allows every particle of the product to instantly find its resonant frequency, ensuring that all layers of the material on the mesh surface are worked over and effectively screened. The forces imposed on the sieve-support structure are smaller than with most conventional sieves, allowing more of the energy to reach the mesh where it is needed.

The Virolat system is said to offer a number of benefits over conventional screening technology including:

• an increase in feed capacity
• processing of sticky and irregular-shaped particles, as well as conventional dry products and slurries
• screening material down to 20µm
• improved efficiency (quality) of separation
• mesh apertures remain clear and lumps of agglomerated product easily break up instead of being rejected as oversize material.

The system is virtually maintenance free, with low power consumption and low-cost mesh replacement. It can also be used as an alternative to non-vibratory machines such as centrifuges, cyclones and classifiers.

A Virolat screen has been installed at Shafir Quarries near Jerusalem where they found that a single conventional multi-deck screen could not produce the 30 tonnes/h of fines they needed. The screening process was inefficient with poor separation and additional screens would have been required to allow as much as 130 tonnes/h of material to be processed in order to produce the fines required. After installing a single-deck Virolat unit the quarry is able to produce up to 25 tonnes/h of fines from just 35 tonnes/h of feed material.

As with all relatively new technologies, Guttridge say that client confidence is best gained through client-specific testing. They have, therefore, established a dedicated test facility at their Lincolnshire factory and invite potential customers to arrange testing to accurately assess the performance of their materials.