Pressure rollers in tablet compression machine
In modern Double rotary tablet press mainly 8 pressure rollers are present 4 at precompression and 4 at main compression Thickness of tablet could be controlled using pressure rollers by altering the position of rollers up and down.
Modern tablet compression machines provide us the feature of precompression which is beneficial to control capping which is the most common defect of tablet press precompression rollers are used to tamp the blend to remove the trapped air from the blend and thus finally preventing capping.
Uniformity of pressure rollers is must to make uniform tablets variation in uniformity of pressure rollers will lead to tablet defects.
Precompression checks of rollers in tablet press
Dial gauge can be used to check the concentricity of rollers uniformity of .003 mm is best for pressure rollers.
Pressure roller should rotate freely.
Overload assembly or hydraulic assembly acts as a cushion to pressure rollers.
Sometimes, Upper punch penetration is also used to control capping as we know if compression is occurring too deep in die it will lead to capping due to inability of air to escape from die in that case upper punch penetration can be changed by altering the position of upper-pressure roller slightly upward 1.5 to 3.0 mm of punch penetration is best for pharmaceutical products. However to control the capping problem due to compression occurring too deep in die nowadays tapered dies are used.
Some fines are exposed to the air if vacuum pickup is not working properly and fines get deposited on pressure rollers adhering to lubrication on rollers causing deterioration of rollers.
So, deterioration of pressure roller occurs from 3 sources
- Passage of blend from lower seal.
- Passage of blend from upper seal.
- Damage due to fines or nature of the drug.
Pressure roller degrades with time and needs replacement be sure to replace them or it can lead to quality issues in tablet formed.