On page 9 and page 10, we looked at the first four stages in the manufacturing process for tablets. On this page we will see how the tablet is pressed from the granulated and dried ingredients.
picture 5.5 Inspecting the tablet press.
5. Pressing.
The tablet press is a high-speed mechanical device. It 'squeezes' the ingredients into the required tablet shape with extreme precision. It can make the tablet in many shapes, although they are usually round or oval. Also, it can press the name of the manufacturer or the product into the top of the tablet.
Each tablet is made by pressing the granules inside a die made of hardened steel. The die is a disc shape with a hole cut through its centre. The powder is compressed in the centre of the die by two hardened steel punches that fit into the top and bottom of the die.
The punches and dies are fixed to a turret that spins round. As it spins, the punches are driven together by two fixed cams - an upper cam and lower cam. The top of the upper punch (the punch head) sits on the upper cam edgeThe bottom of the lower punch sits on the lower cam edge.
The shapes of the two cams determine the sequence of movements of the two punches. This sequence is repeated over and over because the turret is spinning round.
The force exerted on the ingredients in the dies is very carefully controlled. This ensures that each tablet is perfectly formed. The turret holds up to 75 dies and pairs of punches. It spins extremely fast and can produce up to 600, 000 tablets per hour. Because of the high speeds, they need very sophisticated lubrication systems. The lubricating oil is recycled and filtered to ensure a continuous supply.
Picture 5.7 the die and punches. Roll your cursor over the stages to see how they make a tablet.
Sequence of punch movements - roll your cursor over the stages
Top punch is driven into the die by the upper cam
Bottom punch is raised by the lower cam
Both punch heads pass between heavy rollers to compress the powder
Having been pressed, the tablets pass through a de-duster. As its name suggests, this ensures that the tablets are dust-free before they go on to the next stage.
CONTROL POINT
Samples of tablets from the press are checked regularly, whilst the machine is running to ensure that:
they are within the specified weight limits
their strength in compression is within specified limits
their thickness is within specified limits
there are no metal particles accidentally trapped within the tablet
they disintegrate in a liquid at 37.7° C (body temperature)
