In the manufacture of dosage forms of the powder, in addition to mixing and pressing, the operations of grinding, granulation and tableting are carried out.
The grinding of the drug is used to achieve homogeneity of mixing, elimination of large constituents in clumps and glued materials, improving technological and biological effects.
Grinding of powders contributes to a certain increase in strength and the number of contacts between particles and, as a result, to the formation of strong conglomerations. The coal industry uses the method of running durable granules of the powder.
Fine grinding of medicinal powders, despite the possible advantages of bioavailability, has not found application, with the exception of certain cases. It is widespread use in the technology of solid dosage forms’ manufacturing. It happens due to the fact that the crystal is a rigidly formed structure with minimal free and high internal energy.
Therefore, for its destruction, a significant external effort is required. At the same time, in the system of crystals simultaneously with grinding, friction increases, which reduces the applied external load to values that can only cause elastic or slight plastic deformation. Therefore, the grinding effectiveness decreases rapidly especially in crystalline substances with a high melting point.
A certain amount of the liquid phase is injected into the milled powder to increase plastic deformation.
An increase in the free energy of crystals during grinding can serve as a cause of the mechanochemical destruction of preparations and a decrease in their stability during storage.
Grinding of highly plastic materials with low melting points, such as lubricating substances, can lead to a significant increase in their effectiveness in the tablets’ manufacturing.
Some soft conglomerations of powders can be eliminated by filtration or wiping them through perforated plates or filtrates with a certain size of holes. In other cases, filtration is an integral part of grinding to obtain a mixture with a specific particle size distribution.
Grinding is also used for processing substandard granules and tablets.
A number of devices with various working bodies are used to implement the cut of powders and granules. Often grinding units are included in the complex of equipment for processing the initial substances and final products – granules (granulators, mixers, granulators, classifiers, etc.).
The choice of the optimal technological scheme for the production of tablets depends on the physicochemical and technological properties of medicinal substances, their amount in the composition of the tablet, resistance to environmental factors, etc.