How to calculate Dwell time at compression machine and what’s the benefits of Dwell time.
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Dwell time in compression is the amount of time it takes for the punches to stop moving vertically and to achieve maximum penetration in the die under the primary compression rollers. Dwell time takes place when the compression rollers make contact with the punch head flat.
In tableting, dwell time is measured in milliseconds and it’s counted as the time the surface of the head flat is in contact with the main compression rollers. You may consider increasing dwell time if you have a difficult product to press or if you have issues like capping and lamination. Dwell time directly contributes to a tablet’s strength.
Dwell time is directly affected by these factors:
The size of your head flat, as the compression roller comes into direct contact with your head flat, the size of it is important. Changing from a B to a D-type tooling will extend your head flat and increase your dwell time but can be costly and require modification to your tablet press.
The shape of your tooling, sometimes using shaped tooling requires more compression and higher dwell time.
Speed, the speed of your tablet press will affect how fast your punches will pass through the compression rollers. One of the most popular ways to create extra dwell time is to slow down your press, ensuring your punches are being compressed at their peak value for longer. A major downside to this is the cost of slower output.
However, it’s important to note that if you have an air entrapment issue such as capping or lamination, tapered dies, and pre-compression are also great options to reduce those issues.
Often overlooked, Dwell time will directly affect the quality of your tablet. Hence, it’s important to take into account that all granules have different properties and some granules will require a longer dwell time to create a stronger bond within them.
Whilst in some formulations, dwell time doesn’t need to be considered and is not dwell sensitive. Every formulation will be and will act differently under compression forces as they contain elastic properties so may require a longer dwell time to force the particles to bond.
Whatever method you choose, it’s always important to research your formulation, tablet press, and tooling before making your decision.
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