On the previous page, we looked at the first two stages of making tablets where the raw materials are received and checked.
3. Mixing and Granulation.
The powdered ingredients are then placed inside a mixer like a large food mixer. They are mixed to ensure that the active elements are combined uniformly with the excipients. Unless this process happens thoroughly, one tablet may have too much activity and another none at all. Water is then added to granulate the mixture. The water binds the powders together to form granules (like instant coffee). This stops the powders from separating (or demixing) whenever the mixture is moved.
Picture 5.3 Graph of current against time for the granulator motor.
CONTROL POINT
The progress of this process is monitored by checking on the current drawn by the motor that powers the mixing blade, or impeller. This gives a measure of the amount of turning force (torque) it is using to mix and granulate the ingredients. When the process is nearing its end, the ingredients are uniformly mixed and have formed into granules. The torque required to turn the granules is greater, and the motor draws a bigger current. An average time for this part of the process is 10 minutes.
4. Drying.
Picture 5.4 The outside of a fluid bed dryer.
The granules are dried in a fluid bed drier. This has a large fan facing upwards. It creates giant currents of heated air. The air picks up the granules and carries them up in a warm flow. The granules fall down and are picked up by more hot air.
The granules pass from the fluid bed drier through a sieve. This breaks up the oversized granules and ensures the size is uniform. The powder of fine granules is then ready to be pressed into tablets.
