Sieving is the most important process which is performed during the manufacturing of different pharmaceutical products specially for tablets and capsules.
The passing of powders or granules through a series of uniform sized holes is known as sieving or screening.
When We Perform Sieving
In pharmaceutical industries the sieving is performed where the usage of powder or granular materials is involved.
No doubt the sieving step is also performed for the raw materials used for liquid, semisolid and other dosage forms but its implementation is very important for tablet and capsules manufacturing.
Purpose Of Sieving
Main purposes of the sieving process are given below
- To Break Down Large Lumps
- To Get Uniform Sized Materials for mixing
- To Remove Foreign Contaminants.
- To get uniform size granules for compression
To Break Down Large Lumps
Sieving is performed to break down the large lumps of the excipients or active pharmaceutical ingredients.Many raw materials used for manufacturing of various products are received in form of large lumps so it is important to break down the large lumps before further processing.
Example
Metformin or sitagliptin phosphate has many hard lumps which must be broken down by using an oscillating granulator or any other cutting mill to get the uniform sized product.
To Get Uniform Sized Materials for mixing
Sometimes we need a very fine particle size of all material to ensure uniform mixing and for this purpose we use fine mesh to sieve all the materials having different sizes.
After passing through the same sized mesh we get uniform sized particles which prevents chances of segregation and ensures uniform mixing.
To Remove Foreign Contaminants
The basic purpose of the sieving process is to remove any foreign contaminants present in the raw materials.
Example
Some materials may contain broken components of rubber band,tie clip,gloves etc so the process of sieving is done to ensure that our raw materials have no foreign materials.
To get uniform size granules for compression
When we are manufacturing the tablets by wet or dry granulation process then the use of sieve for sieving dry granules or slugged material play an important role.
The size selection at this point have great impact on following
- Flow Properties
- Die Filling
- Tablet Disintegration
- Tablet Dissolution
If sieve selection is wrong and very fine mesh is selected then more fine will be produced that will result in poor flow of product from the hopper of the compression machine.
Sieve selection also has an impact on the die filling during the tablet compression process.
If tablet weight is less and mesh hole is wider then large granules will be produced.Large granules will disrupt the die filling and weight variation may be observed.
The size of granules also has impact on the critical tablet properties like disintegration time and dissolution time.
Large size granules may result in prolonged disintegration time resulting in poor dissolution profile.
Equipment Used For Sieving
Following are most commonly used equipment for sieving in pharmaceutical industries.
- Russell Sifter
- Oscillating Granulator
- Fitz Mill With Mesh
- Co Mill
- Manual Sieves
Russell Sifter
Russell sifter is used for safety screening and to get uniform size products.
Russell sifter is not able to break down the large lumps.
Oscillating Granulator
Oscillating granulator is used for sieving of both hard lumps as well for getting the uniform sized particles.
Fitz Mill
Fitz mill is also used to break down and sieve the hard lumps.Fitz mill is not able to sieve the fine grade powders.
Co Mill
Co Mill is not able to sieve the very hard granules.It is used to sieve the granules after drying to get uniform sized particles for compression.
Manual Sieves
It is the most conventional method of safety sieving to remove any foreign materials from the product.
Manual Sieves are also used to get the uniform sized particles and can sieve the granules after drying which are not very hard.
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