by Steve Lee
Some of the most troublesome filled-capsule defects occur in the capsule closing process, and are termed splits, telescoped capsules, folds and cap tucks. These defects occur during capsule closing, as the edges of the cap and body collide, in many cases causing product leakage. These defects may therefore be critical in acceptable quality level (AQL) criteria and will lead to additional processing.
Many factors may contribute to closed-capsule defects, including challenging formulations, worn tooling, improper machine set-up and poor capsule quality. Factors involving the equipment are often the cause; getting those factors in order can help even when running challenging formulations. There are several factors to ensuring optimal machine conditions for closing capsules successfully.
Proper Closing Station Set Up
In the process of closing capsules on filling equipment, pressure is applied to the dome of the body of the capsule, causing the cut edge of the body to move out of the lower tooling toward the cut edge of the cap. As the body of the capsule enters the cap, there should be minimal movement of the cap allowed within the machine tooling. This movement is controlled by the counter pressure applied by the filling equipment on the dome of the cap. If the gap between the counter-closing function and the cap dome is too high, the cap will be pushed upward, losing the tight stabilizing effect of the tooling walls, available only at the base of the bore. For this reason, many equipment suppliers offer size-specific format rings for the counter-closing function of the filler. When changing capsule sizes, use the appropriate modifiers to ensure closed-capsule quality.
Many people fail to consider the impact of the empty capsule cap length in closing station set-up. The cap length specifications differ between capsule vendors, and may require slight set-up adjustments to account for these differences. For machines with non-stationary counter-closing (i.e. counter-bearing, upper-closing pin), it is a simple machine adjustment wherein the upper-closing is set at 0.003 to 0.005 inches above the dome of the cap when the upper closing is at its lowest position. For machines with non-stationary closing, shimming of the closing station may be required to establish that gap. Once the proper gap is applied, use the upward movement of lower-closing pins to achieve the proper closed length. The minor time investment to fine tune the counter closing can save valuable time and materials caused by inspection and re-work.