The Different Types Of Tablet Press

A tablet press, also known as a tablet compressing machine or tableting machine, is used to compress pharmaceutical powder formulations into tablet form, creating tablets of uniform size, shape and weight. The tablet press may also be used for the manufacture of products in the form of tablets for other sectors such cosmetics, cleaning products and catalysts for the petrochemical industry.

Tablet making process
The tablet making process starts with the formulation of a powder. This is usually a mixture of several components. For pharmaceutical products, these include the active pharmaceutical ingredient (API) or drug, and various inactive but essential excipents, which include diluents, lubricants and binders. The powder may undergo a process of granulation to achieve the required particle size distribution before it is fed to a tablet press. The powder is fed into a hopper on the tablet press from where it is metered into a cavity formed by a die and two punches (an upper and lower punch). The dies and punches are what define the size and shape of the finished tablet and are usually known as the tablet tools. Force is applied to the punches which press on the powder to fuse together the materials and create the solid tablet form.

Basic Components of Tablet Press
Hopper – this holds the materials that are to be compressed
Die – this is the cavity that defines or moulds the size and shape of the powder
Punches – the punches compresses the materials within the die
Cam track – this helps or guides the movement of the punches
Feeding mechanism – it moves the materials from the hopper to the die

Types of Tablet Press

Single Station
Also known as a single punch or eccentric press. This is the simplest of all types of tablet making machine. It uses a single tooling station that has a die and a pair of upper and lower punches. It can be operated by hand or by an electric motor. The compression force is exerted by the upper punch only – during the compression step the lower punch is stationary.

Multiple Station
Multiple station tablet presses are also know as rotary tablet presses. The distinguishing features of the rotary press are the die table, the turrets that hold the punches, and the cams and cam tracks that control the punches and the tablet ejection process, In the rotary press many dies are located near the edge of the large circular die table that is able to rotate horizontally. The upper and lower punches that correspond to each of the dies are located on turrets above and below the die table. As the die table rotates, cams above the upper turret and below the lower turret cause the appropriate punches to move up or down in such a way that (a) the lower punch is stationary for the compressive step in which the upper punch forces down on the powder compressing it into a tablet, and (b) once the tablet is formed, the upper punch withdraws upwards, and at the same time the lower punch also rises so as to eject the newly formed tablet from the die. As the head of the machine rotates, the fixed cam tracks controls the filling, compression, and the ejection process.

Tableting Machine Tooling
The size, shape and the identification marks of the tablet are determined by the compression machine tooling, i.e., the punches and dies. The tooling must meet the specific requirements to satisfy the needs of dosage uniformity, production efficiency and aesthetic appearance. Internationally there are two recognized standards for tablet compression tooling: the TSM standard and the EU standard. TSM is acronym for the ‘Tablet Specification Manual’, widely recognized and exclusively used in the United States. The EU or ‘European Standard’ is probably more widely used than the TSM standard.

Based on the TSM and EU standards, tablet tooling is mainly classified as B tooling and D tooling. The B tooling punches and dies can be further classified as BB, and D tooling can also be used on B tooling machine that is call as DB. The dimensions of these standard tools are given in the table below.

How a tableting machine works

Single Station

Filling
The upper punch is withdrawn from the die by the upper cam, the bottom punch is then lowered and powder is allowed to fall from the hopper to fill the die. The bottom punch then move upwards to adjust the fill of the powder (and hence weight of the product) and excess powder is swept from the die table.

Compression
The upper punch is forced downwards into the die by the upper cam; the bottom punch may also be raised by the lower cam. Both punches are forced in between heavy rollers to compress the tablet.

Ejection
The upper punch is withdrawn by the upper cam while the lower punch is pushed upward to expel the tablet. The tablet is then removed from the die surface by the surface plate.

Multiple Station
The multiple station tablet press is an altogether more complex machine whose operation is difficult to describe in a few words. The process is essentially the same as the single press in that the tablets are produced by compression between upper and lower punches within a die. In a multiple station press there are many sets of tools (punches and dies) and these are accurately aligned in such a way that the whole head comprising die table and turrets uniformly rotate in the horizontal plane.

Filling
Material to be formed into tablets is placed/fed into the fixed hopper which then feeds a fixed frame that fills several dies simultaneously as the die table rotates.

Compression
Compression, as with the single station press, is performed by the punches which are controlled by cam tracks and rollers that guide the movement of the punches as the table rotates.

The compression sequence starts by the lower cam guide pulling a lower punch to the bottom of the dies. This action allows particular die to be overfilled with powder

The lower punch will then rise according to a weight control process at which point excess powder is removed by a swipe blade. The blade pushes material into the oncoming die.

The lower punch drops slightly allowing the upper punch to penetrate into the die and contact the upper surface of the powder. This is the point at which compression begins.

In modern presses, there is a pre-compression step in which both punches are forced by pre-compression rollers to squeeze the powder to form a tablet within the die. As the table rotates, so the punches are engaged by the main compression rollers which are substantial rolls, exerting a massive force on the powder. Both punches have forces applied and both move to compress the tablet (unlike the single table press in which only the upper punch moves during the compression step).

Ejection
After the full compressive force has been applied, the upper punch is withdrawn by the upper raising cam, and the lower punch also rises to bring the tablet above the surface of the die (and die table).

At this point the tablet is fully formed and is swept off the die table from the feed frame towards a chute and container located beneath the die table to catch the tablets.

The lower punch will then be engaged by the pull-down cam to be withdrawn to the bottom of the die, and the whole process starts again.

Advantages of Tablet Machines

Single Station
These machines are used to press a variety of drugs, that may or may not contain excipients, into round tablets. They can be used for batch production or laboratory production runs, and can be manually operated to allow precise setting of fill, tablet size, and compressive force. In addition a single station tablet press –

* is relatively compact
* is easy to operate and has high utilization ratio
* uses high pressure to reduce weight difference between tablets while maintaining a low noise level
* provides continuous control over raw material loading as well as tablet’s thickness.

A single station tablet press can be used for making:
* Chewable tablets – containing e.g., mannitol, lubricants and other binders and ingredients.
* Effervescent tablets – containing e.g., tartaric acid or citric acid with sodium bicarbonate.
* Other compressed tablets – containing a variety of ingredients e.g., disintegrants, lubricants, active drug, and diluents.

Multiple Station Tablet Press
This machine is widely used throughout the industrial, medical and pharmaceutical sectors. It is more cost efficient than a single station press and can work continuously without any significant increase in maintenance expenses compared with a single station.

It is the best machine to use to manufacture tablets in high volume due to its efficiency and accuracy in producing uniform shapes and sizes of tablets. It is therefore preferred by many in the industry due to its high output.

The machine can be used for all types of active ingredients producing. In addition –

* It provides independent control of hardness and weight
* Setting up is much more streamlined and efficient than the trial and error approach often encountered in setting up a single station press.
* It can be fine tuned to meet all product specifications
* Markedly reduces waste of the formulation.
* Pressure at the compression step is controlled by adjusting the weight control lever
* Automatic and consistent powder fill is achieved with all dies.
* Supplied without punches or dies – allowing producers to specify their own design of tools.
* Much higher production rate than a single station press. Typical output: 9000 - 12000 tablets/hr.

Essential requirements
Tablet presses are essential equipment for the pharmaceutical industry. A modern tablet press must allow the operator to adjust the lower and upper punches to control accurately the tablets weight, density and thickness. This is achieved by using rollers, cams and other trackers. Mechanical systems are also incorporated for ejecting, filling and removal of the tablet after compression. Pharmaceutical tablet presses are required to be cleaned and configured quickly so that they can be used for manufacturing a variety of products.