Dwell Time in Tablet Compression: A Complete Guide

In the production of tablets, there are many variables that must be carefully controlled in order to achieve the desired characteristics of the tablets. One of the most important of these variables is dwell time, which plays a crucial role in the tablet manufacturing process. By understanding how dwell time can be manipulated, it is possible to produce specific types of tablets.

What is compression dwell time?

To know what is dwell time during compression, we need to know how the tablet compression machine works briefly.

Take a normal rotary  tablet press as an example, it has three steps in making tablets from the powder——filling, compression and ejection. The dwell time is during the compression process.

When the powder is compressed into tablets, it gets pre-compression to get rid of air, and the main compression compress the half-compressed mixture into tablets.

However, the upper punches and lower punches won’t leave each other immediately after the compression process is finished. The remaining time of punch sets after the main compression is done is called the dwell time.

Some people may start to count the dwell time when the compression first takes place. That would start from the first contact between rollers and punches. We don’t think it’s precise enough.

Punch head flat dimension divided by the turret tangential velocity would be a better way to add up the whole dwell time of tablet compression.

The importance of dwell time in tablet compression

The dwell time can be a decisive parameter during tablet production. Rigidity of tablet is mainly determined by hardness, tensile modulus, flexural strength, and flexural modulus.

It is one of the structural properties of tablets, referring to the ability to resist elastic and plastic deformation under stress. The most effective way to increase the rigidity of the tablet is to maintain an appropriate dwell time during the compression process.

The usage of tablets decides the length of the dwell time, not just the longer the better. Tablets are the most widely used dosage form of drugs in clinical application. Due to the complex composition and hard texture of tablets, they are difficult to control during the compression, molding, coating production and processing of drugs, drug transportation, storage, and the formation of tablets in the human body.

Disintegration, dissolution or release, in vivo efficacy, a series of processes are closely related to the microstructure and mechanical properties of the drug. The microstructure and mechanical properties of the drug can be comprehensively expressed as drug rigidity, and its data can be characterized by the texture characteristics of the drug. 

For example, a tablet released in the stomach is generally less rigid than a tablet absorbed in the intestinal tract. In order to resist the erosion and friction loss of gastric acid, the dwell time of the latter is generally longer than that of the former during the compressing process, and it will be covered with a film. 

Longer dwell time also helps to press more air out from the tablet. The less air remains in the pill, the less likely it would crack or act fragile. During packing and long terms of preserving, these tablets are welcomed by the consumers.

During mass production, the dwell time also helps to higher the utilization rate of each punch, making the machine more cost efficient.

Tooling and dwell time

The tools to adjust the dwell time are the punches. Their punch heads have different effects on dwelling time. The longer the punch heads are, the longer dwell time they remain during compression process.

Some might think it possible to lower the spinning speed of turrets during production. Since it also reduces the overall efficiency of the machine, most companies won’t choose this method.

There are four tooling types, B, D, BB and DB. Type B and D are often used in most cases. B tooling is quite small, so it leaves more space for die cavities. Thus, it is usually used in bulk production in pharmaceutical industry.

D tooling is larger judging to the tablet size it can provide. The tablet size is around one inch, since the D tooling has longer dies and bigger heads. These features of D tooling both enable the powder to have a quite long period of dwell time during compression.

B tooling, however, focuses more on the efficiency of tablet making. The tablet size it can make is quite small. Thus, the punch sets in the turret are also smaller. This means in every circulation of turret, more punch sets can work compared to D tooling.

The dwell time in B tooling is quite short, so we should really maintain the balance between the quality and the quantity of the tablets.

The tablet standards in different countries and regions are what we need to learn while choosing the right tooling as well. The Euro standard (EU) and the Tablet Specification Manual (TSM) are the only published tooling configurations for pharmaceutical industry.

The die cavity is straight in EU standard, while it has angles on the top in TSM. Taking “B” punches as an example, the inside head angle of “B” punch in EU is 7°larger than in TSM. The latter has an angle of 30°.

Despite the head thickness of the punches, the punch length in EU is 0.01 inch longer than in TSM. This also provides longer dwell time.

Get the tooling you need for tablet manufacturing at iPharMachine

The dwell time can help you to choose the desirable tablet press tooling you want. iPharMachine is a top-notch supplier of pharmaceutical equipment. As an expert in the pharmaceutical and pharmaceutical packaging industry, iPharMachine has provided solutions for hundreds of pharmaceutical and health product manufacturers for 17 years. 

We offer all kinds of rotary tablet presses as well as single punch ones. All the features are well prepared for you to check in order to purchase the right goods.