Tablet ejection stages

The specific material properties of most import to the compaction operation are elastic deformation behavior, plastic deformation behavior, and viscoelastic properties. These are also referred to as mechanisms of deformation. As mentioned earlier, they are equally important during compression and decompression i.e., the application of the compressional load to form the tablet, and the removal of the compressional load to allow tablet ejection. Elastic recovery during this decompression stage can result in tablet capping and lamination. 

After decompression, the tablet remains in the die until it is ejected. During this time, a residual die wall force is exerted by the tablet on the die wall. Tablet ejection is defined by three stages ... 

FIGURE 4 Stages of tableting process (a) filling (b) compression (c) ejection. 

The manufacturing process of tablets principally consists of three stages filling the die with the powder, compressing the powder, and ejecting the tablet from the die. 

The process of tablet compression is divided into three stages filling, compression, and ejection of the tablet (see Figure 1). 

After formation of the tablet by application of a compression force follows the decompression stage, where the compression force is removed and the upper punch leaves the die. Then, the formed tablet undergoes a sudden elastic expansion followed by a viscoelastic recovery during ejection when the lower punch moves upward. 

The upper punch is withdrawn from the die, and so the force being applied to the tablet is removed. The effect of this might be to cause the deformed particles to return to their former shape, which would result in a decrease in interparticulate contact and hence tablet strength. It is essential that this does not occur. As the upper punch leaves the die, the lower punch moves upwards, pushing the tablet before it. During the compression stage, the particles are forced into intimate contact with the interior die wall. It follows that attempts to remove the tablet will be opposed by frictional forces and so successful ejection demands lack of adhesion between the tablet and the diewall. 

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