Mixing equipment are used in pharmaceutical industries for the purpose of blending and kneading stages of the tablets, capsules & dry powder suspension manufacturing. These mixing equipment may include double cone blender, bin blender, rapid mixing granulator,ribbon mixer or any other high shear or low shear mixers.
Did you ever think about what is the exact and recommended practice for mentioning the capacity of these mixers?
It is commonly observed that about 90% professionals use the word kilogram to mention the capacity of these mixing equipment but the fact is that the capacity of these mixing equipment in kilograms is not the right practice. The correct practice is to mention the capacity of mixing equipment in litres.
Now the question is why the capacity of mixing or blending equipment is taken in liters not in kilograms? If you know the answer, do mention it in the comment box before reading this article and if you are not aware of the fact then this article will help you to understand the logical reasoning.
The simple phenomena is that these blending or mixing equipment are used to add or mix some solid materials like powders or granules and we are familiar that the bulk density of all the powders and granulated product is not same.It vary from excipient to excipient and active pharmaceutical ingredients to active pharmaceutical ingredients.
So due to the difference in the bulk density we cannot add the same quantity of two different materials of different bulk densities in the same blender.
Suppose we have a blender and we mentioned it has a capacity of 300 kilograms, when we use the word kilogram basically we are limiting the blender capacity only for the 300 kilograms,it means this equipment can hold 300 kilograms of any material. But in reality it is not possible & what is the reason we will discuss it with the example.
Example
Suppose we have a blender having the capacity of 300 kilograms and we want to add two different products into it up to 300 kilograms.
We have two products e.g one is product A calcium carbonate and the other is product B aerosil. We are familiar that calcium carbonate is a heavy material and we can easily add maybe above 200 kilograms of calcium carbonate in our double cone blender but when we take aerosil due to its very lightweight or having very low bulk density we will not be able to add 300 kilograms of the aerosil in the same blender & it will be filled with only 30 to 40 kilograms of the aerosil.
Due to this limitation the capacity of blenders or mixing equipment is always mentioned in liters and we take the bulk density of that specific material which we want to add in a blender or mixer and from that we can easily estimate how much quantity of any material can be mixed in any blender.
For example if we claim that our blender has the capacity of 300 liters then we can easily calculate the capacity of this blender for the product A calcium carbonate and product for B aerosil by taking their bulk densities.
Suppose the bulk density of calcium carbonate is 0.9 g/ml and the density of aerosil is 0.1 g/ml, now we can calculate the capacity of our blender for these materials by following formula
Capacity in liters × bulk density
So for calcium carbonate
300×0.9 = 270 kilograms
For Aerosil
300×0.1 = 30 kilograms
270 kg & 30 Kilograms is the brimful capacity for calcium carbonate and aerosil respectively & working capacity is taken as 70 to 80% of brimful capacity.
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