We explain what sieving is in the separation of mixtures, what types of sieves exist, their characteristics and some examples.

Even today flour is sifted to separate it from lumps produced by moisture.

What is sieving?

Sieving (or screening) is a method simple that allows to separate particles of different sizes by passing them through a sieve (a wire mesh filter) or fine strainer. During this process, small particles pass through the holes in the strainer and larger ones are retained.

The same element can be sifted solid, solids combined with each other or solids combined with a liquid, but it is not possible to use a sieve to separate different substances liquid.

Sifting was practiced in ancient times, for example, to separate the flour from the remains of straw, insects, corn husks or seeds. Currently commercial flour is refined, so it is not necessary to separate it from impurities or unwanted substances. However, it is sifted to remove lumps or masses produced by the humidity of environment.

Types of sieves

Household sieves also separate solids from liquids.

The main types of sieves can be:

  • For home use. Its main use is to sift flour and starch to achieve masses of a smoother, airy and homogeneous consistency, without lumps.
  • For industrial use.It can be a granulometer (for grains), stationary grill (to handle coarse solids) or rotating sieve (continuously separates solids that are in suspension in a liquid).

Sieves characteristics

The mesh of the sieve retains certain particles and the lumen of the mesh lets through others.

The sieves can be of different shapes and can be made of a wide variety of materials. For example, they can be cylinders of metal with a woven wire at its base, round and wooden with a weave of rods or fabric at its bottom, wooden in the form of a frame with a mesh fabric, in the shape of a bowl made of plastic or silicone, among others.

The interlacing of the mesh or wire mesh consists of a weft (set of crossed and interlaced threads) and the light of the mesh (the useful opening through which the particles smaller than the substance to be sieved).

In the professional field, such as laboratories or chemical industry, the sieving process is very important to define the quality of the final products. In the construction sector, the sieving process is also carried out to separate the sand from larger particles (such as stones), especially to prepare the mixture of the plaster of the walls.

Sieving Examples

The grains are separated from impurities through a sieve.

Some examples of sieving are:

  • The sifted flour is much lighter and allows it to be better mixed with other ingredients (avoiding the formation of lumps or masses).
  • Flour sifted with other dry ingredients, like cocoa powder, helps to combine them with the rest of the ingredients more evenly.
  • Sifted grains, such as rice or quinoa, can be separated from stones, impurities, or broken grains.
  • Precious metals (such as sifted gold nuggets) can be separated from the sand and dirt with which they are always mixed.
  • The coffee beans are sifted to separate them from toothpicks and leaves.
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