Different Kinds of Nozzles Used in Tablet Coating

At one time or another, all of us have had to take medicine, often in the form of a tablet. You have probably noticed that some of the pills you take for headaches and other minor pains are coated. These coatings are almost always applied as liquid sprays, using any of a few different kinds of spray nozzles to get the thin, even coating needed for the tablet.

Twin-Fluid Spray Nozzles

• Twin-fluid spray nozzles provide a finely atomized spray that results in the even coating crucial to tablet coating. These nozzles need frequent cleaning because they can be prone to bearding---a phenomenon that occurs when deposits build up around the opening of the nozzle as the liquid droplets are being sprayed. Bearding can distort the formation of the droplets and lead to uneven coverage.

Hydraulic Spray Nozzles

• Like twin-fluid nozzles, hydraulic nozzles use atomized surfaces to spray droplets of coating over tablets. But while twin-fluid nozzles are air-atomized, hydraulic nozzles use the pressure energy of the liquid itself. Hydraulic nozzles usually produce higher velocity sprays and they come in different spray patterns: flat fan, hollow cone and full cone.

Ultrasonic Nozzles

• Ultrasonic nozzles work on a specific frequency, usually determined in large part by the length of the nozzle. The liquid is sprayed out at a low velocity, which results in the necessary thin coating and very little overspray. The atomizing surface of the nozzle may be either flat or cone shaped, depending on how large the coverage area is. A cone-shaped surface spreads the liquid out in a wide pattern, which is typically needed in tablet coating. Flat surfaces are used for spraying narrow areas.