Working principle of tablet press

1. Basic components of tablet press

Punch and die: Punch and die are the basic components of tablet press. Each pair of punches consists of three parts: upper punch, middle die and lower punch. The structures of upper and lower punches are similar, and their punch diameters are also equal. The punches of upper and lower punches match the die holes of the middle die, and can slide freely up and down in the middle die holes, but there will be no gaps that can leak drug powder. The processing size of the punch die is a unified standard size and is interchangeable. The specifications of the punch die are expressed by the punch diameter or the middle die hole diameter, which is generally 5.5-12mm, with each 0.5mm as one specification, and there are 14 specifications in total.

The punch and die are subjected to great pressure during the tableting process. They are usually made of bearing steel (such as crl5, etc.) and heat treated to increase their hardness.

There are many types of punches, and the shape of the punch depends on the shape required for the tablet. According to the die structure shape, it can be divided into round and special shapes (including polygonal and curved shapes); the cross-section of the punch has flat, beveled, shallow concave, deep concave and comprehensive shapes. Flat and beveled punches are used to press flat cylindrical tablets, shallow concave is used to press biconvex tablets, deep concave is mainly used to press the core of coated tablets, and comprehensive is mainly used to press special-shaped tablets. In order to facilitate the identification and taking of drugs, the drug name, dosage and vertical and horizontal lines can also be engraved on the end face of the die. To press tablets of different dosages, a die of appropriate size should be selected.

2. Working process of tablet press

The working process of tablet press can be divided into the following steps:

① The punch part of the lower punch (its working position faces upward) extends from the lower end of the middle die hole into the middle die hole to seal the bottom of the middle die hole;

② Use the feeder to fill the drug into the middle die hole;

③ The punch part of the upper punch (its working position faces downward) falls from the upper end of the middle die hole into the middle die hole, and moves downward for a certain distance to press the powder into tablets;

④ The upper punch lifts out of the hole, and the lower punch rises to push the tablet out of the middle die hole, completing a tablet pressing process;

⑤ The lower punch drops to its original position to prepare for the next filling.

3. Tablet pressing mechanism tableting principle

① Control of dosage. Various tablets have different dosage requirements. The large dosage adjustment is achieved by selecting dies with different punch diameters, such as punches with diameters of 6mm, 8mm, 11.5mm, 12mm, etc. After the die size is selected, the tiny dosage adjustment is to adjust the depth of the lower punch into the middle die hole, thereby changing the actual length of the middle die hole after the bottom is sealed and adjusting the filling volume of the drug in the die hole. Therefore, the tablet press should have a mechanism to adjust the original position of the lower punch in the die hole to meet the dosage adjustment requirements. Since the preparation of different batches of drug powder always has differences in specific volume, this adjustment function is very necessary.

In dosage control, the action principle of the feeder also has a considerable influence. For example, when the granular drug falls into the middle die hole by its own weight and rolls freely, its filling situation is relatively loose. If multiple forced entry methods are used, more drugs will be filled in the die hole, and the filling situation will be denser.

② Tablet thickness and compaction control. The dosage of the drug is determined according to the prescription and pharmacopoeia and cannot be changed. In order to meet the requirements of storage, transportation, preservation and disintegration time limit, there are also requirements for a certain dose of pressure during tableting, which will also affect the actual thickness and appearance of the tablet. Pressure adjustment during tableting is essential. This is achieved by adjusting the downward movement of the upper punch in the die hole. Some tablet presses not only have the downward movement of the upper punch, but also the upward movement of the lower punch during the tableting process, and the tableting process is completed by the relative movement of the upper and lower punches. However, pressure regulation is mostly achieved by adjusting the downward movement of the upper punch to achieve pressure regulation and control.