As a core piece of equipment for mass production of tablets in the pharmaceutical, food, and chemical industries, the rotary tablet compressor operates on a principle revolving around four continuously circulating working zones. Each zone has a clearly defined function and is closely integrated, functioning like a miniature "tablet production line," completing the process from powder filling to finished product compression in one step. These four core working zones are the feeding zone, filling zone, pre-compression and main compression zone, and tablet ejection zone. Their specific functions and operational logic are as follows:
I. Feeding Zone: "Feeding Station"—Precisely Supplying Material to the Mold
The feeding zone is the "starting point" of tablet production. Its core task is to evenly and stably transport the powder to be compressed (such as pharmaceutical powder or food additive powder) into the "mold cavity" (i.e., the cavity of the middle mold) of the tablet compressor, laying the foundation for subsequent molding.
Core Components: Primarily composed of a feeding hopper and a feeder (commonly known as a "crescent-shaped feeder" or "star-shaped feeder"). The feeding hopper stores batches of powder. The feeder below, closely attached to the rotating turntable (the core rotating component of the tablet press, with dozens of intermediate dies evenly distributed on it), rotates slowly and synchronously with the turntable.
Working Logic: When the turntable moves the intermediate dies to the feeding area, the powder in the feeder continuously fills the cavity of the intermediate dies under the influence of gravity and the scraper. Simultaneously, the feeder uses a scraper to remove excess powder from the surface of the intermediate dies, ensuring an initial uniformity of powder filling in each die—this step directly affects the weight uniformity of the subsequent tablets. Uneven feeding can easily lead to excessive tablet weight variation.
Key Requirements: The powder must possess good "flowability" (to prevent clumping and clogging the feeder) and "filling properties" (to evenly fill the cavity of the intermediate dies). If the powder flowability is poor, a stirring or vibrating device is usually installed in the feeding hopper to assist the powder's descent.
II. Filling Area: "Measuring Cup Calibration Station"—Precise Control of Tablet Weight
The filling area, adjacent to the feeding area, is a crucial step in "weight setting." Although the feeding area has been initially filled with powder, variations in the machining precision of different dies and powder density can lead to slight differences in the amount of powder filled. The filling area's function is to "adjust the filling depth" to ensure that the powder weight within each die meets the set standard.
Core Components: Primarily composed of a lower punch (a cylindrical component that moves up and down beneath the die) and a filling cam (a track-type component that controls the lower punch's movement). Each die is equipped with a lower punch, and the lower ends of all lower punches are engaged on the track of the "filling cam." As the turntable rotates, the lower punch moves up and down along the cam track.
Working Logic: When the die carrying powder rotates to the filling area, the filling cam moves the lower punch downwards—the greater the downward distance of the lower punch, the larger the "effective volume" of the die cavity, and the more powder is filled; conversely, a smaller downward distance results in less powder being filled. By adjusting the track height of the filling cam, the downward movement of the lower punch can be precisely controlled, thereby calibrating the powder filling amount of each die to the set value (for example, if the weight of each tablet is set to 0.5g, the filling area will ensure that the powder weight of each die is exactly 0.5g).
Key Function: This step is crucial for ensuring that the "tablet weight variation" meets the standard. If the filling cam is not properly adjusted, some tablets will be heavier than others, failing to meet the quality standards for pharmaceuticals or food.
III. Pre-compression and Main Compression Area: "Compression and Forming Station"—Compressing Powder into Tablets
The pre-compression and main compression area is the "core working area" of the rotary tablet press and a key step in tablet forming. The powder is loose in the die and needs to be compacted into tablets with a certain hardness, thickness, and shape (such as round, oval, or irregular shapes) by the "compression force" of the upper and lower punches. This process is divided into two steps: "pre-compression" and "main compression," proceeding gradually to avoid powder splashing or tablet cracking.
Core components: Composed of an upper punch (a cylindrical component passing above the middle die), a lower punch, a pre-pressure cam, a main pressure cam, and a pressure sensor. The upper and lower punches are respectively mounted on the tracks of the pre-pressure cam and the main pressure cam. The main pressure cam has a much longer "pressure stroke" than the pre-pressure cam, providing a stronger extrusion force.
Working Logic:
- Pre-compression Stage: When the die carrying the powder moves to the pre-compression area, the pre-compression cam drives the upper punch downwards and the lower punch upwards, performing "preliminary compression" on the powder. This step removes air from the powder (preventing air expansion during main compression, which could cause the tablets to become loose or crack), and simultaneously compresses the loose powder into a "semi-formed blank," preparing it for subsequent main compression.
- Main Compression Stage: After pre-compression, the die continues to rotate to the main compression area. The main compression cam drives the upper and lower punches to compress the powder with greater force (the main pressure is typically 5-10 times the pre-compression pressure; for example, pre-compression 1-5kN, main pressure 5-50kN). This compacts the semi-formed blank into tablets with uniform density and suitable hardness. Simultaneously, a pressure sensor monitors the main pressure in real time. If the pressure is abnormal (too high or too low), the equipment will automatically alarm to prevent tablets that are "too soft and easily broken" or "too hard and difficult to disintegrate."
Key parameters: The magnitude of the main pressure and the parallelism of the upper and lower punches directly affect the tablet's hardness, thickness, and disintegration properties (for example, if the drug needs to disintegrate and be absorbed in the body, excessive hardness will lead to slow disintegration).
IV. Tablet Ejection Area: "Finished Product Conveying Station"—Delivering tablets out of the mold.
The tablet ejection area is the "end point" of tablet production. Its core task is to smoothly eject the compressed tablets from the "mold cavity" and transport them to subsequent collection or packaging stages, while simultaneously resetting the lower punch to prepare for the next feeding.
Core components: Mainly composed of the tablet ejection cam and the scraper (or tablet ejection track). The tablet ejection cam is similar to the filling cam, also a track component controlling the lifting and lowering of the lower punch, but its track direction is opposite to that of the filling cam.
Working Logic: When the tablet-pressing die rotates to the tablet ejection area, the ejection cam moves the lower punch upwards—the height of the lower punch's ascent is precisely enough to "push" the tablet out of the die surface. Subsequently, the tablets, rotating with the turntable, are scraped off the turntable surface by a fixed scraper and fall into the lower ejection channel or conveyor belt, being transported to the hopper or packaging machine. Simultaneously, guided by the ejection cam, the lower punch gradually resets to its initial position and continues rotating with the turntable, entering the next cycle of "feeding - filling - pre-compression - tablet ejection."
Key Requirements: The ejection cam's track must be smooth, and the lower punch's upward speed must be uniform to avoid tablet breakage due to excessive ejection force or tablet jamming within the die due to insufficient ejection (i.e., "punch jamming").
Summary:
The "Collaborative Operation Logic" of the Four Zones
The four working zones of a rotary tablet press form a closed loop around the continuous rotation of the turntable: with each rotation, the dozens of intermediate dies sequentially pass through the four zones of "feeding → filling → pre-compression → tablet ejection," completing one tablet production cycle. Continuous rotation of the turntable enables "continuous batch production" (for example, a medium-sized rotary tablet press can produce tens of thousands to hundreds of thousands of tablets per hour). The precision of the connection between these four zones and the parameter settings (such as feeding speed, filling depth, and main pressure) directly determine the weight variation, hardness, appearance, and production efficiency of the tablets. These are also the core concerns for daily operation and maintenance (e.g., regularly cleaning the feeder to avoid powder residue and calibrating the main pressure to ensure stable hardness).