Did you ever think about how we can measure the exhaust efficiency of a tablet coating machine?Before going into details first we will check what the exhaust system in a tablet coating machine is and how it works?
The exhaust system in a tablet coater is the outlet duct of the machine from where air is removed out of the pan.
The hot air in a tablet coating pan is introduced through an inlet air duct and is removed through a return duct.When the air is removed out of the coating pan the fine particles of the coating materials are also removed out of the pan which are suspended after evaporation of solvent.
The opening and closing of the return duct or exhaust duct is controlled by a butterfly valve.How much coating material is lost along with return air at a specific level of exhaust opening is a serious concern because if exhaust loss is high it will result in less weight gain and high wastage of coating materials.
In this article we will calculate the percentage weight loss of coating materials after completing the coating process.
Practical Example
We will calculate the loss of coating materials from a practical example, suppose we have a batch having 200,000 tablets and average tablet weight is 200 mg.The total batch weight is 40 kilograms and we have 3% coating material for this product which is 1.2 kg.
First of all we will calculate the theoretical weight gain of the tablets after coating from the provided coating material which is 1.2 kg.For this we will convert the value 1.2 kilograms in milligrams and will divide it by the total number of tablets which in our case are 200,000.
1.2×1000×1000
200,000
= 6mg
So total theoretical tablet weight after coating should be 200mg+6mg = 206 mg.
Now let’s check and calculate how much actual weight gain was achieved after the completion of the tablet coating process.
The actual average tablet coating weight was 204 mg means 4 mg weight gain was achieved during tablet coating and 2 mg per was lost along with the exhaust air.
%age Weight Loss
Now we will calculate the percentage weight loss of the coating materials through the exhaust.We know that the theoretical weight gain was 6 milligrams but actually it was 4 mg after coating so will use following formula,
Theoretical weight gain – Practical weight gain / Theoretical weight gain × 100
Put values in above formula
6 – 4/6 × 100 = 33.33%
33.33% coating material was lost during the coating process and we can reduce it by reducing the exhaust opening or through any other proactive measures.
We can also calculate the weight loss in terms of kilograms,the initial weight of coating materials was 1.2 kilograms and we have 4 mg per tablet after tablet coating so 4×200000/1000×1000 = 0.8 kilograms coating material was deposited on the tablets and materials loss in kilograms will be
1.2 – 0.800 = 0.4 kg.
400 grams or 0.4 kg coating material was lost during our tablets coating process.
Also Read