Difference Between Upper & Lower Punches

Compression Machine punches

Compression Machine tooling is used to compress powder or granules into tablets & it consists of upper punch, lower punch & dies. This set of punches & dies which is known as compression machine tooling plays an important role in determining the shape & dimensions of the tablets. The powder or granules are filled in the die and compressed with the help of the upper punch & lower punch.

What Is The Difference Between Compression Punches

We will discuss the difference between upper and lower punch based on physical appearance as well as its role during the compression cycle.

Before going into detailed differences, first have a look over a brief overview of how the tablet is compressed & ejected with the help of upper & lower punches.

As the name indicates lower punch is on the lower side of the die & upper punch is on the upper side of the die, after the powder fills in the die the the upper punch comes down & lower punch moves up to apply pressure over the powder or granules to compress a tablet.

When the tablet is compressed the upper punch is pulled back & the lower punch is pushed up to remove the compressed tablet from the die.

Now Let’s try to understand the difference between upper and lower punches. 

A punch usually consists of the following main parts.

  • Punch Head
  • Barrel
  • Punch Stem
  • Punch Tip
 
upper and lower punches
 

Image Credit

Image Source – Google | Image By – I HOLLAND

Most people are not able to differentiate between upper and lower punch on physical examination because both have the same length & shape but there is a difference which is given below based on physical appearance & role.

Punch Stem

The neck or stem of the upper punch is short & the stem of the lower punch is long.

Why?

The punch tip length or stem of the lower punch is long because the lower punch has to move up in the die to remove the tablet after compression.

The purpose of the long stem of the lower punch is mainly to aid in the ejection process because the short neck will not be able to remove the tablet from the die.

Tip Stay Time In Die

The upper punch tip comes out of the die before filling & after compression but the lower punch tip always remains inside the die.

Why?

The upper punch tip must remain out of the die before filling to allow the entry of powder or granules into the die.

The upper punch must come out of the die after the compression phase to ensure the ejection of the tablet. 

The lower punch tip must always remain inside the die to retain powder or granules in the die.

If the lower punch tip does not remain inside the die the powder or granules spillage will occur.

Punch Movement

Upper punch has two types of movement & lower punch has only one.

How?

The upper punch can move up & down in the die when it comes under the roller & second is the free movement of the upper punch along the turret when it comes out of the die.

Lower punch can only move up & down in the die & has no free movement as it does not come out of the die.

Punch Penetration

Upper punch penetration is used to control the tablet capping & lower punch to control tablet ejection.  

How?

Punch penetration is an important phenomenon which plays an important role in controlling tablet capping, for this upper punch penetration plays its role. The penetration of the upper punch in the die can be increased or decreased depending on requirements.

Lower punch penetration in the die is used to control the tablet ejection.

Share To Others