Introduction
The pharmaceutical tablet press machine is mainly used for tablet processing in the pharmaceutical industry. It is an automatic continuous production equipment that presses particulate matters into round, special-shaped tablets carrying characters, symbols and graphs, with a diameter of no more than 13mm. Some pharmaceutical tablet machines, if burrs and dust are generated during tablet pressing, should be equipped with a tablet de-duster to remove dust (more than two times) at the same time, and must meet GMP specifications.
The pharmaceutical tablet press machine can be divided into six types: single-punch tablet machine, flower basket tablet press machine, rotary tablet press machine, sub-high speed rotary tablet machine, automatic high-speed tablet machine and rotary core-spun tablet press machine.
Principle
(1) Punch and die: punch and die are basic components of the tablet machine. Each set of punch and die is made up of upper punch, middle die and lower punch with the same structure for upper and lower punches and the same diameter. The lower and upper punches are matched with the holes on medium die, allowing free movement of punches in the hole without gap that may lead to leakage of powders. The processing dimensions of punches and dies are standard to ensure interchangeability. The 14 specifications of punches and dies are decided by punch diameter or hole diameter of medium die with range of 5.5-12mm generally, between which the difference is 0.5mm.
The punches has various types and its shapes depend on the shape required for pills, which can be divided into seven types according to punch die structure and shapes or punch section shapes, i.e. round shape, special shape (including polygon and curve), flat, shape with bevel edge, shallow concave, deep concave and comprehensive shape. The punches of flat or bevel edge could be used for making flat cylinder pills, shallow concave for biconvex pills, deep concave for core of coated tablets and comprehensive shape for special shape pills. To identify and facilitate taking drugs, drug name, dose and marks such as horizontal & vertical lines can be engraved on end face of punch die. Proper punch die shall be selected for pressing tablets of different dose.
(2) The operating process of the pharmaceutical tablet press machine can be divided into the following steps:
1. The head of lower punch stretches into the holes of middle die from the bottom (with working position upward) to seal hole bottom of middle die;
2. Feeder is used to charge drugs into holes of middle die;
3. The head of upper punch falls into the holes of middle die from the top (with working position downward) for a certain stoke to press drug powder into pill;
4. Lifting of upper punch out from holes. Pills are pushed out from hole of middle die during lifting of lower punch to finish one cycle of tablet pressing.
5. The lower punch is lowered to original position to prepare for next filling.
(3) Principle of pharmaceutical tablet press machine
① Control of dose. Different doses are required for different pills and large dose adjustment is realized by selecting punch die with different punch diameter, such as 6mm, 8mm, 11.5mm and 12mm. after punch die size is selected, small dose adjustment is realized by changing the actual length of holes of middle die after backing to adjust filling volume of drugs in die hole through adjustment to stretching depth of lower punch in hole of middle die. Therefore, a mechanism to adjust the original position of lower punch in die hole shall be provided on the tablet press machine to meet dose adjustment requirement. Due to difference in specific volume of powder preparation for different batches, this kind of adjustment function is necessary.
In dose control, operating principle of feeder may exert a great influence. For example, when drug particles roll into holes of middle die under the action of their gravity, their filling may be loosen; if several times of forced filling are adopted, more drugs will be filled into die pore and the filling will be relatively compact.
② Control of tablet thickness and compression degree. Dose of medicine is determined according to prescription and pharmacopeia and change at will is prohibited. To meet storage, transportation and disintegration time limit requirements, requirements on pressure for certain dose during tablet pressing will affect actual thickness and appearance of pills, thus it is necessary to adjust pressure during tablet pressing, which is done by adjusting down travel of upper punch in die hole. Some tablet press machines not only involve downward action of upper punch during tablet pressing, but also upward action of lower punch to complete tablet pressing process together by lower and upper punches. However, pressure adjustment and control are generally realized by the mechanism adjusting downward of upper punch.
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