Factors Affecting Tablet Weight, Thickness, and Hardness in Tablet Press Operation

To obtain the desired results in tablet compression, one cannot simply run the tablet press and expect to get good tablets. A successful compression process begins with proper preparation and setup of the tablet press, especially when aiming to produce tablets that meet the specification for weight, thickness, and hardness. Here are some key factors that influence these tablet specifications.

Fill cam

Using the proper fill cam is important for achieving the desired tablet weight. The tablet press operates on the overfill principle. That means the die cavity is initially overfilled. The excess powder is the to be pushed upward and scraped off the die when it reaches the weight adjustment cam, which sets the desired fill depth.

Granule scraper

The granule scraper plays a crucial role in tablet compression process. Proper setup must be done to ensure that the scraper blade can remove excess powder from the die effectively without damaging the die table. This can be done by adjusting the tension mechanism of the scraper arm. The condition of the scraper blade also must be checked during the setup. The scraper blade must be replaced regularly, especially if significant signs of wear are present.

Punch working length

Punches are manufactured with high precision and minimal tolerances between each other. A newly manufactured set of punches has working length variation of only ± 0.025 mm. Usually, the tooling manufacturer provides an inspection report that shows the working length of each punch. It is very important to ensure that installed in the tablet press meet the ± 0.025 mm tolerance. Regular inspection of punch working length is essential. Failing to meet the tolerance will significantly affect the tablet weight, thickness and hardness – causing them to vary greatly and often the desired tablet specifications cannot be met.

Punch head condition

The condition of the punch head can affect the tablet hardness. This is because that is the part that comes into contact with the pressure roll and transfer the pressure to the punch tip. Variations in punch head condition between punches will result on different dwell time, which in turn affect the tablet hardness. It is important to check the punch head condition before installing them in the tablet press. Punches with significantly worn or uneven punch heads compared to the rest of the set should be sorted out and excluded from being installed in the tablet press.

Achieving consistent and desired tablet that meet specifications requires more than just running a tablet press. It demands attention to preparation and setup of the tablet press. Factors such as proper fill cam selection, granule scraper condition, punch working length, and punch head condition will contribute in our effort to produce tablets that meet the specifications for weight, thickness, and hardness. By carefully monitoring these factors, we can significantly reduce variability and improve the overall consistency of the compression process.

References:

• Rowley, F. (2018). Solid Dosage Training: Basic Tablet Press Operation [Presentation]
• American Pharmacists Association. (2006). Tableting Specification Manual (7th ed.).
• Tousey, M. (n.d.) Preventing and Fixing Weight and Hardness Defects: Strategies for Production Personnel. Retrieved from https://medium.com/@soliddosetraining/tablet-press-operation-df077b9a8f2a