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Official Standards of Powders, Sieves and Size Separation

Pharmaceutical powders are governed by the Indian Pharmacopoeia. According to the I.P., powders can be categorized into five types.

Official Standards of Powders

Pharmaceutical powders are governed by the Indian Pharmacopoeia. According to the I.P., powders can be categorized into five types:

Coarse powder - An all-purpose powder! Fine powders are defined as material that passes a sieve with an aperture of 1.7 millimeters (No. 10, No. 44 sieve), but at most 40% passes a sieve with an aperture of 355 millimeters (No. 10 sieve).

Moderately coarse powder - Powder with a nominal mesh aperture of 710 m or more passes through a sieve having a diameter of 250 m or less (No. 60 sieve) is considered moderately coarse.

Moderately fine powder - Powders in this category pass through sieves with an aperture of 355 microns (No. 44 sieve) and 180 microns (No. 85 sieve), respectively.

Fine powder - Fine powder is considered to be one that passes through a 180 m thick mesh sieve (No. 85 sieve).

Very fine powder - The powder is considered very fine when it passes through a sieve with an aperture of 125 m (No. 120 sieve).

Official Standards of Sieves

Using meshes of brass, bronze, stainless steel, or other materials, wire cloth is formed into sieves. There should be no coatings or plating on these wires and they should have a uniform circular cross-section. If you are sifting something from a sieve, it should not react with the substance being sifted from it. The following specifications must be met by sieves used in tests:

Number of sieve - The mesh number indicates how many meshes there are per wire in each direction within a measured length of 2.54 cm.

Nominal size of aperture - The nominal aperture size determines the wire spacing. There is a nominal aperture size on each side of the rectangle. According to the I.P., mesh apertures are measured in mm or in cm for a majority of sieves.

Nominal diameter of wire - Mesh sieves are made from wires with a certain diameter, allowing an aperture size to be customized and a mesh that is sufficiently strong to prevent distortion.

Approximate percentage of sieving area - Measuring the mesh area as a percentage of the full sieve's area, this standard specifies the mesh area. A sieve number is determined by the size of the wire used. The sieve's strength should be at least 35 to 40%, and generally between 35 and 40%.

Tolerance average aperture size - When expressed as a percentage, aperture tolerance averages are known as differences in aperture size.

Size Separation

It is useful to separate particles by size since particles can be sorted solely based on their size, regardless of density, surface, etc. It is possible to create narrow fractions from a dry or wet powder using this method. The equipment used to do this works by using agitation, brushing, and centrifugal forces.

Agitation method

Different ways can be used to agitate a sieve or sieve in a set.

Oscillation

An inclined frame or rack mounts the sieve in this way allowing it to oscillate. Rolling material onto the sieve surface creates a ball at times, which is the most simple and common mechanism. The shaft of the rotating motor is used to produce this movement.

Vibration

It is possible to pass powder through vibrating sieves that operate mechanically or electrically. Vibrations can be sinusoidal or gyratory. Vibrations associated with sinusoidal motion occur in a plane tilted towards the vertical. A wave pattern's vibration is determined by its frequency and amplitude. The sieve may move up and down or left and right.

Gyration

Rubber attachments attached to a rotating eccentric flywheel hold the sieves in place. The material will move when the amplitude and intensity of the movement are determined. The rotation of particles allows them to spin around meshes and pass through them. An oscillatory motion occurs when a reciprocating motion side-to-side occurs at a low angle near the level plane.

Brushing method

Brushes are used to feed different directions of material through sieves in order to separate it by size. While the brush rotates around the axis of circular sieves, it rotates across the axis of horizontal cylindrical sieves. The meshes can be kept clean with brushes. Sticky, greasy, or damp materials can be removed using this method.

Centrifugal method

Vertical cylindrical mechanical sieves are used in this method. It uses centrifugal force to force particles onto a sieve using a rotor inside the cylinder. An air stream created by the rotation of the rotor separates the particles. Within the cylinder, there can be installed an air jet for even greater particle separation. A particle separation process can also rely on gravity, density, or electrostatic force. Gravity causes the material discharged from the sieve to fall to a lower level when it is released. Gravity also causes the particles to pass through the sieve media. Density determines the stratification of materials. Material weight is used to classify this material. Electrostatic force can be used to help sift particles that are overly wet or dry.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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