Rotary press
A rotary press is a press that is primarily used to manufacture tablets on an industrial scale.
Basic structure and working method
The core element of the rotary press is a round plate (die table) , usually made of stainless steel , which contains concentric round recesses that contain the die (shaped piece) for the punch. The upper and lower punches are placed above and below the recesses and vary in number and shape depending on the model. The punches are moved towards each other by a heavy roller and at the same time the filling material is compressed into a tablet. The lower punch is movable compared to that of the eccentric press, so that the force that acts on the filling material through the punch during the pressing process is exerted evenly from the top and bottom of the die. In the case of rather small presses, the number of dies is 3 to 6, while large, industrial tablet presses can have more than 70 dies. In contrast to the eccentric press, the upper and lower punches are movable and perform horizontal movements in opposite directions. Another difference to the eccentric press is the filling of the dies through the filling shoe. This is fixed in the rotary press and is filled with the product through the permanent rotation of the die table. The product is compressed in a wave-like, horizontal movement and as many tablets as there are matrices are obtained per pass. Here, too, the rotary press differs in the way it works from the eccentric press, in which only one tablet can be pressed per operation. This also results in the superior performance of the rotary press, so that it is used almost exclusively as a tablet press in the pharmaceutical industry. By using pairs of punches, several filling and pressing stations within one work step, the work performance can be increased significantly. This means that up to 1,000,000 tablets can be produced per hour. The maximum achievable pressing pressure varies greatly depending on the machine and is generally between 500 and 1000 MPa. Pressure- sensitive components (e.g. piezo elements ) measure the pressure that is transferred from the stamps to the product and adjust it so that the tablet's breaking strength meets the desired requirements. However, the type and amount of the binding agent contained in the product also have an influence on the breaking strength of the tablet .
Due to the fixed filling shoe, the risk of the filling material segregating is lower than with the eccentric press, as the vibrations triggered by the movements, based on the so-called "Brazil nut effect", collect small particles on the bottom of the filling shoe, while coarser particles in the upper Layers of the filling material remain. This leads to compression of the product and subsequently to inaccurate dosing when filling the die. A fluctuation in the active ingredient content in the tablet is the consequence and must be minimized in any case.
disadvantage
The biggest disadvantage of a rotary press compared to the hand press or the eccentric press is its financing. In the pharmaceutical industry, they are large, finely tuned machines that are expensive to maintain and repair. Constant monitoring and control of the process parameters (e.g. stamp pressure, composition and fineness of the product, etc.) as well as the condition of the machine itself (e.g. signs of wear and tear on the stamps, lubrication of friction points) is therefore essential.
literature
- Alfred Fahr : Pharmaceutical Technology. 12th edition, ISBN 978-3769261943 .
