The most effective method to increase spray rates for a tablet coatign process is to increase the number of spray guns within the coating pan. An increased spray zone is accomplished by lengthening the coating pan while maintaining the same diameter. The “stretched” design can incorporate as many as ten spray guns (each spray gun capable of 300 mL/min/gun).

Additionally, the “stretched” design creates shorter process times and minimizes tablet attrition by reducing the tablet bed depth when compared to similar batch sizes in larger diameter pans.

Using these spray gun to bed distance guidelines will minimize your coating defects.  The distance from the tablet surface to the gun placement, as outlined below, should be 20-25 cm for aqueous coatings and 15-20 cm for organic solvents.

The distance across the tablet surface and from top to bottom of the coating pan, as illustrated below, should be 1/3 to 1/2.  If the distance is less than 1/3, you may blow the coatings through the bed.  Additionally, you could spray dry vs coat your materials.   If the distance is greater than ½, you will encounter over-wetting, tackiness, clustering and transfer of coatings to pan.

Spray Guns

It is important to assess how uniform the spray zone is covered and how well the liquid is being atomized.  Freund-Vector’s uses AT spray guns system which allows for the width of the spray pattern to be modified independently of the atomization air pressure.  In the illustration below, it is showing the versatility of the AT pattern adjustment (the gun is traveling from left to right).

All tubes required to operate the spray guns are encased within the spray bar. A single gasket and clamp design allows for very quick change-over and cleaning. There are no flexible tubes or fittings inside the pan area. All connections are made at the end of the spray bar.

The VHC Fully Perforated HI-COATER^® has a fully welded pan cabinet, eliminating seals and gaskets that are impossible to clean. During the cleaning operation, the lower cabinet is filled with water, allowing the bottom of the coating pan to soak and rotate in cleaning solution.