Sieving Equipment for Dry Bulk Powders
A comprehensive look at screeners and sifters for dry bulk powders
A vibro screen is a traditional part of processing dry bulk powders and is commonly known as a gyratory separator or vibrating screening machine. It separates material by using a combination of horizontal and vertical movements which cause particles to pass through a mesh screen. The mesh apertures are set to gain the required particle size. By controlling the flow patterns of the material over the mesh screen efficiency of the vibro screen has been improved. This has enabled the replacement of larger diameter machines for smaller models without performance being affected.
Functions and different types of vibro screens
1) Check/safety screening: used to ensure product quality by removing foreign contamination and oversized material.
2) Grading/sizing: used to grade and segregate material into different particle sizes.
3) Recovery screening: used to recover valuable materials in the waste stream for re-use.
The evolution of separation equipment
In the past vibro screens have been in a rectangular or square shape and use a simple reciprocating movement to segregate the powder.
During the early 1930’s small, circular, orbital movements or gyratory motion was introduced and these machines became known as gyro screens. Following on from this circular vibro screens were developed. These offered much more usage of screen area and increased the capacity per unit mesh area. Since then, the design and appearance of screening machines has somewhat evolved but in addition the component parts have also undergone major improvements as well as the development of machines for specific applications/industries.
Achieving faster speeds
Over the years the design of vibro screens used for grading materials has been developed. One design which is most commonly available because it is simple to manufacture is fitted with a vibrating motor mounted on a spring suspension.
A different method is to fit a standard, non-vibratory drive motor with a separate vibrator placed over the mount on a rubber suspension. Examples of such machinery are the Finex Ultima™, Finex Separator™ and Finex 22™ from Russell Finex (find more information here: sieving machine manufacturers for powders and liquids). Most machines vibrate at 1400 rpm, in this type of design where the mount is separated from the rubber suspension it is possible with high out-of-balance forces to increase the operating speed up to 2800 rpm. This development means efficiency of the screen is increased allowing the use of smaller diameter machines without adversely affecting the performance. For example a 22″ diameter machine operating at 2800 rpm can significantly defeat the performance of a 48″ diameter machine operating at 1400 rpm.
Seeking smaller footprints
In an effort to minimize space usage and to allow sieving machines to fit into process lines easily, one of the biggest technological developments has been to reduce the size of machines. Most companies have realised that sieving is an important step in their process but there is still concern about the amount of floor space required for this function. Therefore suppliers aim to produce smaller units whilst still being able to meet demanding throughput requirements. Russell Finex offers the Russell Compact Sieve®, which is a low level machine that removes the concern of taking up valuable floor space but still offers the same if not better performance as larger sized machines.
Most industries now widely use these smaller sized screens. In companies’ where space requirements are often a concern they appreciate having a unit with a small footprint which does not compromise in capacity level or become a bottleneck in the process which would compromise profitability.
Even though manufacturers have quickly adopted small separation equipment like the Russell Compact Sieve® many producers have started looking for more specialized sieving solutions which can be customized to fit their specific needs.
For example, many food manufacturers experience difficulty in the check screening of bagged ingredients. Operators have to put too much effort into lifting bagged ingredients to the vibro screen. Added to this many ingredients mostly flour based create a lot of dust during the screening process. This not only causes discomfort to the operators inhaling the dust but also brings a safety risk as charged flour particles are volatile by nature and can cause explosions if not safely handled.
High quality mesh – what to look for
Before purchasing mesh for vibrating screens, companies need to carefully examine the quality of mesh being used and need to look at the mesh screen material, mesh size and mesh tension. A poor quality mesh can easily break down causing unnecessary downtime, loss of money and poor product quality. The most common material used is woven stainless steel wire mesh and for more specific applications other metals such as bronze can be used. Stainless steel is suited to most applications because it is a reliable and durable material. Where chemical compatibility is a concern synthetic woven meshes are also available.
There are many different types of vibrating sifters and vibro separators available which can all be customized according to specific requirements. For companies who are looking for bespoke solutions they should consult a reputable vibro screen manufacturer in India who has the necessary experience to understand their application and recommend a solution.
Most suppliers use product testing and/ or past experience to decide the right machine for the application. Deciding on what machine to use is not done on any simple mathematical formula. There are many aspects which need to be considered including particle size, density, moisture content, and temperature and space available.
In conclusion, vibro screens and separators might appear to be simple pieces of machinery. However, they have undergone many years of development to ensure they meet the needs of dry bulk powder manufacturers. Any company looking to ensure the quality of their product should ensure they have a vibrating sifter or vibro separator placed within their manufacturing facility.
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