Why the Stem of the Lower Punch is Longer Than the Upper Punch

In this article, you are going to learn the key differences between an upper and lower punch in a tablet compression machine. The functionalities assigned to each punch of a tablet press are also discussed. 

If you think about how the tablet gets ejected from the die onto the turret surface after compression you can easily understand the concept.

In tablet compression machines the shaping and forming of tablets is attributed to the upper and lower punches. So we can understand that punches are very important for tablet compression. The punches are designed according to the tablet size and shape, based on the tablet dimensions punches are designed and installed to the compression machine. These punches can be changed based on the product. Pharmaceutical companies maintain spare punches also if any punch faces get damaged so that they can be easily replaced.

The next question is why the lower punch stem is longer than the upper punch that we are going to discuss further in this article

Generally, upper punches are placed in the upper punch holders above the turntable whereas the lower punches are positioned below the die table 

UPPER PUNCH VS LOWER PUNCH 

The difference in the size of the stem between upper and lower punches serves significant functionality, now let us see the upper punch functionality

From the hopper the powder fills into the die cavity, and then the upper punch enters the die bore to compress the powder into a tablet.

The role of the upper punch lies in applying the downward pressure on the powder in the die cavity to form tablets and after compression the upper punch lifts back with the help of the lifting cam, leaving the formed tablet inside the die cavity.

But the lower punch unlike the upper punch remains in the die cavity throughout the compression process. The lower punch helps in lifting the formed tablet i.e. it pushes the tablet out of the die cavity as the head of the lower punch moves over the ejection cam.

The long stem of the lower punch is essential in lifting the tablet or ejecting it.

So, for the happening of tablet ejection, the lower punch stem is designed to be longer than the upper punch, where the upper punch role ends after it applies the pressure.