Punches And Dies Basics and product quality

Dear Friends,.

Last article we saw the principle of working of  a tabletting machine and how some  defects that arise during compression be eliminated or minimised by altering the machine setting
Today we shall see what is a Tablet Tooling and some important terminologies that as a shop floor chemist we should know about and teach others also we see

 how defects in the tooling would give raise to tablet quality issues.

1.Type of Toolings and it's specifications

2. Tooling an it's pressure ton settings

3.Compression force.

4.Tooling deficiencies and its related product quality issues.

 Tooling varities

For this purpose different types of punches are used:

Flat- faced bevel- edged.

Shallow concave (Round/ Capsule shaped)

Standard concave (Round/ Capsule shaped)

Deep concave (Round/ Capsule shaped)

Extra deep.

Modified ball
The basic mechanical unit in all tablet-compression equipment includes a lower punch which fits into a die from the bottom and an upper punch, having a head of the same shape and dimensions, which enters the die cavity from the top after tablet material fills the die cavity.

MOC to be used
(HCHC/OHNS)

HCHC: High Carbon High Chromium

OHNS: Oil Hardened non shrinking Steel

     Special requirements like: Concavity, embossing, chrome plating etc.

Tablet Tooling

There are following types of Tooling available: 

TYPES OF TOOLING

‘B’   -Tooling
‘D’   - Tooling
‘BB’ -Tooling 
'DB’ - Tooling

Tablet Tooling Parts
Following definitions for direct terminology for tooling (Punches and dies).

1. Head: The end of the punch that guides it through the cam track of tablet machine during rotation.

2. Head flat (Dwell Flat): The flat area of the head that receives the compression force from rollers (in upper punches) and determines the weight and ejection height (in lower punches).

3. Outside head Angle: The area gets in touch with the roller prior to head flat, while compression.

4. Inside Head Angle:This is the area, which pulls down the lower punches after ejection and lifts the upper punches after compression.

5. Neck: The relived area between the head and barrel, which provides clearance for the cams.

6. Barrel: This area guides the punch (while going up and down) with reference to turret guides.

7. Stem: The area of the punch opposite the head, beginning at the tip and extending to the point where the full diameter of the barrel begins. If the chamfer is present the barrel usually reaches its full diameter just above the chamfer.

8. Tip: This determines size, shape & profile of the tablet.

9. Tip face: This area of punch is where the tablet is formed. Good surface finish is required here to bet quality tablets.

Working length: This distance between bottom of the cup and the head flat is called as working length which determines weight and thickness of the tablet.

10. Overall length: Distance between top of the cup and the head flat.

11. Key Angle: The relationship of the punch key to the tablet shape. The keys position is influenced by the tablet shape, take-off angle, and turret rotation.

12. Domed Heads: Increases the dwell time and hence help to achieve the better tablet hardness.

13. Dwell time: The time punches spends below the pressure roller while rotating in the machine.

Tooling and it's pressure Ton setting:

Quiet often we neglect pressure ton settings provided in the tabletting machine in as much as of insufficient knowledge about it's benefits.

Adjusting pressure ton in accordance to the tool size is most crucial to avoid breakage of punch tip and wearing of punches and die

Bad workmen quarrel with tools

Operating at high pressure ton could even result in excessive compaction force affecting dissolution of the tablets 

Yes clear knowledge about tonnage setting is very essential to produce good quality product and also to avoid breakges of punches during compression.  For readers reference a general guideline is given hereunder and however it is subject to vary depending on various other parameters of formulation too.

Compression Force

It is important to first understand that there are a few factors that relate to maximum compression force to take into consideration. The point maybe made easiest when talking about older tablet presses because newer presses can have interchangeable turrets which requires that the tablet press be capable of the higher compression force rated turret. Traditional “B” & “BB” type  tablet presses have a maximum rating of 4.5 tons (45kn), while a “D” type press Unitshave maximum rating of 7-10 tons (70-100kn).

How much compression force do you need?
This depends more on the tool tip size than it does on the maximum force rating of the tablet press. As an example I could use a 10 ton press to make a ¼” or 6mm round diameter tablet. One would simply need to reduce the overload compression force setting to make certain that the press will release to whatever load rating I require. In the case of a ¼”/6mm diameter tablet the maximum load a tool can take before bending or breaking would be in the range of 1.0-2.5 tons (10-25kn), so having a press that can exert 10 tons of pressure does little good, unless of course I also need to produce a big ¾” or caplet.

If the formulation is not prepared properly (which happens on a very regular basis) it may take more tonnage to make the tablet than should be safely applied to the tooling (also a very common issue). This is where proper press setup comes into play.

We should always set the overload pressure release set point (compression force) to the maximum limit of the tooling tip size configuration.
Most tablet press manuals contain a chart with the maximum load rating based on tip size. This same information is available in the TSM (Tablet Specification Manual) which is published by the APHA. However, I would suggest that when ordering the tooling from your vendor that you specify that they provide the maximum compression force rating with the tooling order.

If you cannot make a satisfactory tablet within the tooling compression force rating then you must not blame the tooling or the press…you must formulate or process the powders to work within that acceptable force range, period! Many of us make the mistake of going beyond the maximum load rating and damaging the tooling and the press (when a punch breaks nothing good happens).

Tablets tooling defects related product deficiencies:

As bad workmen quarrel with tools 🔨like wise bad tools quarrel with the products and the machine. 

Quality implication of the product due to deficient tools shall be seen  in the part iii....

Till then,

Cheers

Srikanth Santhanaraman.