1. Punch and die: Punch and die are the basic parts of tablet press, each pair of punching die consists of 3 parts: upper punch, middle die and lower punch. The upper and lower punches are similar in structure and their punches are equal in diameter. The punches of the upper and lower punches are compatible with the die hole of the middle die, so they can slide up and down freely in the hole of the middle die, but there is no gap that can leak the powder. The die size is standardized and interchangeable. The size of the die is expressed in terms of the diameter of the punch or the hole of the die, generally 5.5-12 mm, with each 0.5 mm being a specification, and there are 14 specifications.
The punch and die are subjected to great pressure during the pressing process and are often 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 is determined by the desired shape of the tablet. According to the shape of the die structure, they can be classified as round, shaped (including polygonal and curved); the shape of the punch section is flat, beveled, shallow concave, deep concave and integrated. Planar and beveled punch are used to press flat cylindrical tablets, shallow concave is used to press biconvex tablets, deep concave is mainly used to press coated tablets of chips, and comprehensive is mainly used to press shaped tablets. In order to facilitate the identification and taking of drugs. On the end face of the die, drug name, dosage and vertical and horizontal lines can also be engraved. For pressing different doses of tablets, a suitable size of die should be selected.
2. The 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 (whose working position is facing upward) is extended into the middle die hole by the lower end of the middle die hole and seals the bottom of the middle die hole.
(ii) Filling the middle die hole with drug by using a gaco.
③The punch part of the upper punch (whose working position is facing down) drops into the middle die hole from the upper end of the middle die hole and travels down for a certain stroke to press the drug powder into tablets.
④The 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 is lowered to the original position to prepare for the next filling.
3. Tablet press production principle
①Dose control. Various tablets have different dose requirements, and the large dose adjustment is achieved by selecting different punch diameters, such as 6mm, 8mm, 11.5mm, 12mm and other punches. After selecting the die size, the minor dose adjustment is done by adjusting the depth of the lower punch into the middle die hole, thus changing the actual length of the middle die hole after sealing and adjusting the filling volume of the drug in the die hole. Therefore, a mechanism for adjusting the original position of the lower punch in the die hole should be available on the tablet press to meet the dose adjustment requirements. This adjustment function is necessary because there is always a difference in the specific volume of the drug powder formulated for different batches.
In the dose control, the action principle of the doser also has considerable influence, for example, the granular drug is by its own weight, when it rolls freely into the middle die hole, its loading situation is looser. If forced into the situation for many times, more drugs will be filled in the hole, and the filling situation will be denser.
②The thickness of the tablets and the degree of compaction control. The dosage of the drug is determined according to the prescription and pharmacopoeia and cannot be changed. For storage and transportation, preservation and disintegration time requirements, the pressure of a certain dose is also required during tablet compression, which will also affect the actual thickness and appearance of the tablets. Pressure regulation during tablet pressing is essential. This is achieved by adjusting the amount of downward movement of the upper punch in the die hole. Some tablet presses have not only the downward movement of the upper punch, but also the upward movement of the lower punch, so that the relative movements of the upper and lower punches together complete the tablet pressing process. However, the pressure adjustment is mostly done by the mechanism of adjusting the amount of downward movement of the upper punch to achieve pressure adjustment and control.