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If, for example, tablets are pushed out with a damaged or uneven surface, this indicates that the mass adheres strongly or lacks glidants, or the pressing surfaces are not smooth enough. If the tablet has edges, then the diameter of the punches used is small. If the surface of the tablet is knocked down, then the lower punch does not rise high enough and its position must be adjusted.
If the tablets disintegrate during ejection, increase the compaction pressure or add more binders. Peeling of the tablets indicates that the pressure is too high or that the granulate is too dry. In the process of tabletting, tablets can be obtained with the following defects, such as: Insufficient mechanical strength - observed with a slight pressure of the press, insufficient concentration of a binder, adhesive and lubricant, as well as low plasticity of the substances. Poor coating of tablets. It can be avoided by adding microcrystalline cellulose to the coating, which improves the ductility of the coating. Gluing. With a higher adhesion of the particles of the tablet mass to the punch than between each other, particles adhere to the tool. Adhesion at high humidity of the mass to the upper punch can lead to failure of the device. High humidity of the mass, insufficient amount of disintegrants also lead to bonding. Excessive rubbing. Strong rubbing of the mass can lead to bonding of the matrix parts. There is a decrease in the weight of the tablet, the formation of a non-gloss surface. Reduced shelf life - may occur as a result of the use of an inaccurate amount of loosening, binders, moisturizing auxiliary substances, insufficient pressure, which ultimately leads to an incomplete action of the active substance. Inaccurate dosage. With insufficient fluidity of the tablet mass, the matrix is filled unevenly. This can be avoided by optimizing particle size or by adding an auxiliary substance such as aerosil. Therefore, in order to avoid defects during the tabletting process, in each case, the optimal parameters should be chosen.
During the loading operation, the roller of the upper slider with the punch is at the highest point of the upper capir (stage I). He then glides down the inclined capir. The punch touches the matrix hole, immerses in it and squeezes the material. The pressure rises and reaches a maximum at the moment when the roller of the slider is under the pressure of the roller (pressing operation - stage II). After that, the roller with the punch begins to rise up the capir and reaches a maximum. The lower slider makes the following movements: at the loading stage, its roller is supported by a roller regulating the volume of the matrix hole. The lower slider moves in a straight capir. During the pressing operation, its roller is lifted by a pressure roller, due to which the lower punch in turn exerts pressure on the tablet material. Next, the capir goes a little up, as a result of which the lower punch pushes the tablet out (the ejection operation is stage III).
After this, due to the lowering of the capir, the lower punch also drops down and everything is repeated again. The following is a description of the features of domestic rotary tablet machines. In general, RTMs can have from 12 to 55 matrices (positions) in the rotor. In addition, they can be single-threaded (with one loading funnel) and two-threaded (with two loading funnels). In the latter case, the entire production process ends in a half-turn of the rotor and, as a result, the performance of the RTM sharply increases. Such a high-performance machine is, in particular, the RTM-41, which is a two-line and has 41 pairs of press tools. This machine allows the production of tablets with a diameter of 5-15 mm and 20 mm. The RTM-300M machine is used for the production of cylindrical tablets of small diameters with flat and spherical ends. Since the pressure in the RTM is bilateral and increases (is removed) gradually, the tablets are of high quality. These machines work evenly, do not dust. A stirrer can be installed in the feed hopper. The rotating rotor allows the installation of devices for dusting the matrix holes before loading, as well as after it (for dusting the surface of the filled matrix). Some designs include brush wipers or cleaning tools to ensure the punches are clean. Rotary presses are manufactured, equipped with a vibrating feeder, which can, by adjusting the amplitude and frequency of vibrations of the vibrating filling part of the feeder, break the adhesion forces between the powder particles, thereby significantly increasing its mobility and compensating for the lack of flowability.
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The performance of machines equipped with a vibrating feeder is increasing. In this case, granulation is also necessary, but with a slight reduction in the requirements for uniformity of the granulate. In domestic tablet presses, the tablet mass and possible mechanical inclusions are controlled during the tabletting process. To control the mass, there are automatic devices - in case of deviation of the mass of tablets from the preset, the signal lamp turns on. Automatic control of metal inclusions is performed using a device that detects and extracts tablets with metal inclusions from the stream. Dust collectors are used to remove dust particles from the surface of tablets leaving the press. The tablets pass through a rotating perforated drum and are cleaned of dust, which is sucked out of the dust collector by special devices. Tabletting of drugs usually occurs at pressures of 25-250 MPa; higher pressure is used extremely rarely. In the table. 4.8 gives an example of the main technical indicators of rotary tablet machines. Although RTMs are technically far superior to eccentric ones, they have some disadvantages, namely: complex design; require more spare punches and dies. The quality of the tablets is influenced by the magnitude of the pressure, the speed of pressing, the condition and wear resistance of the press tool, which is subject to fairly strong wear, as it experiences heavy loads. The resistance of the matrices is 2-3 times lower than that of the punches, which is explained by the chemical interaction of the matrix material with the tableted mass, the rigid loading of the matrix, the friction of the particles of the pressed material and the tablet on the matrix walls;
more difficult preparation for pressing; more time-consuming cleaning; a large variation in the deviation of the mass from the face value due to the use of dozens of sets of press tools. Eccentric machines use only one set of press tools and therefore the fluctuations in the mass of individual tablets are less than when pressing on RTM. Based on the above disadvantages, we can conclude that rotary tablet machines are only cost-effective in mass production. Before pressing, any tablet machine must be tuned, calibrated and adjusted optimally. Before starting the process, they carry out trial tabletting, starting the machine manually, as a result of which they achieve the necessary tablet mass, proper strength and disintegration, as well as eliminate external flaws.