Tablet tooling punch

Extrinsic lubrication is provided via mechanisms that apply a lubricating substance, normally paraffin oil, to the tableting tool surface during processing. One method makes use of an oiled felt washer attached to the lower punch below the tip. This washer wipes the die cavity with each tablet ejection. To avoid having tablets stick to the punch faces, materials such as poly-tetrafiuorethylene or polyurethane have been applied to the faces. Another lubrication method sprays a thin layer of lubricant (either liquid or solid lubricant) onto the tool surfaces after one tablet is ejected and before the granulate of the next tablet enters the die cavity. 

All tableting presses employ the same basic principle—they compress the granular or powdered mixture of ingredients in a die between two punches with the die and its associated punches being called a station of tooling. Tablet machines can be divided into two distinct categories ... 

Figures 15 and 16 provide a summary of the compression cycles for rotary and single-punch tablet presses. The formation of the tablet compact in these two types of presses mainly differs in the compaction mechanism itself, as well as the much greater speeds achieved with rotary type presses. The single punch basically uses a hammering type of motion (i.e., the upper punch moves down while the lower punch remains stationary), while rotary presses make use of an accordion-type compression (i.e., both punches move toward each other). The former find their primary use as an R D tool, whereas the latter, having higher outputs, are used in most production operations.

All operations take place simultaneously in different stations. Sixteen stations were commonly used in earlier machines with outputs between 500 and 1000 TPM and tablet diameters up to 15 mm. Presses with outputs orders of magnitude greater than the above are now widely available. The dies are filled as they pass beneath a stationary feed frame, which may be fitted with paddles to aid material transfer. The die cavities are completely filled and excess ejected prior to compression. Compression involves the movement of both punches between compression rolls, in contrast to single station operations where only the upper punch effects compression. Ejection occurs as both punches are moved away from the die on cam tracks until the tablet is completely clear of the die, at which point it hits the edge of the feed frame and is knocked off the press. Tooling pressure may be exerted hydraulically, rather than through the use of mechanical camming actions, as is the case with machines produced by Courtoy. 

A second flow measurement to be considered during scale-up is the ability of the granulate/powder to fill the dies. This can most efficiently be monitored by punch force variability and individual core weight measurements. Acceptable weight control (<3% RSD) and force (<5% RSD) may be masked at slower compression speeds typically used for development or when a tablet press is not fully tooled. Production operations will tend to run at the high end of any validated range, so flow must be consistent from batch to batch. 

A standard IPT Type B tooling was used with a f " round flat tool tip. Tablets were made one at a time, and the compression force as well as the upper punch displacement and lower punch displacement were recorded. Tablet weight, thickness, and breaking hardness were measured for each tablet. 

The basic unit of any tablet press is tooling consisting of two punches and a die, called a station. The upper and lower punches come together in the die that contains the tablet formulation. Principally, two different types of machines are used, the eccentric and the rotary press. The eccentric press produces about 50-130 tablets per minute. The rotary press has a multiplicity of stations arranged on a rotating table with the dies. A few or many thousands of tablets can be produced per minute. There are numerous models of presses, manufactured by a number of companies, ranging in size, speed, and capacity. 

Core benefits include the avoidance of tablet manufacturing problems such as punch tip breakage from the outset. Immediate and accurate punch tip load calculations and 3D dynamic rotation of punch tip stress allow for instant decision making on design issues. iTAB is also unique in that it incorporates tooling and tablet... 

High-Speed Rotary Tableting Machines High-speed rotary machines work with the same principles as all other rotary machines. They possess a huge number of punch and die sets and often two filling stations. Another possibility is to use punch and die sets which are able to produce several tablets simultaneously. Special tooling can be used for this purpose however this is not the subject of this chapter. As... 

Punches and dies are essential tools in the tableting process and therefore are critical to the quality of the tablets produced. Both tools are designed for long life under normal conditions of working, but, in spite of this, they are not proof against careless handing. 

It is important for those working with a tablet press to be familiar with the terminology used in the industry concerning the punches and dies. Table 1 describes the commonly used terms related to press tooling. Some of the press tooling parts can be identified in Figure 5. 

Regarding the importance of compression tooling to the performance of the tablet press and the quality of the tablets, it is of paramount importance that punches and dies are handled with care. The first criterion is the identification of the tooling that is, punches and dies should be identified according to the standard and be designated by upper punch without key, upper punch with key, lower punch with key, lower punch without key, or die, the reference of the standard (e.g., TSM, EU, JN, ISO), and the punch or die diameter. Punches and dies should also have a marking that includes at least the manufacturer s identification, the number of the punch in the series, and/or the identification number. Upon... 

Damage to the punches and dies should be avoided. Therefore, they should not be transported from place to place without protective package. During transportation, installation, and removal of tooling from the tablet press, cleaning, inspection, and storage, care must be taken to avoid hitting the tips of the punches. 

Press-coated tablets were produced on modified rotary tablet machines using special tools with hollow punches, where first an inner tablet was formed and then the outer shell was compressed in the same die ( tablet-within-a-tablet ). ... 

Precompression and Main Compression Rollers. After die fill and scrape-off, the punches rotate to the precompression station where an initial force is applied to the compact. The tablet is frequently partially formed during the precompression stage. Subsequently, the upper and lower punches move together under the main compression rollers where the final tablet is formed. The main compression roller is usually larger than the precompression roller. However, latest advances suggest that similar sizes for precompression and main compression rollers with the ability to apply similar loads may result in optimal tablet formation. The compression rollers are made of premium tool steels and are surface hardened. 

During tablet compression, the distance between the rollers remains constant unless a machine adjustment is made to change tablet hardness or thickness. Additionally, all tooling dimensions (tooling length and die cavity size) are constant within established standards. Under these conditions, for a specific material of uniform density, if the same volume of material is delivered to each die, the maximum measured compression force for each punch station is the same. If, on the other hand, different volumes of material are delivered to each die, the maximum measured compression force for each punch station is different. On this basis, adjustment of fill depth (fill volume) to maintain a constant compression force should result in a constant tablet weight. This concept is the general basis of all rotary tablet press force control systems. 

Curled/damaged punches promote tablet capping. Under these conditions the tools should be reworked or replaced. 

Take-off force is monitored by mounting a strain gage to a cantilever beam on a press feed frame (in front of the take-off blade, Fig. 6). It is done to measure adhesion of tablets to lower punch face. Such adhesion is indicative of underlubricated granulation, poor tooling face design, die-wall binding, and tablet capping. ... 

In single-punch tablet presses (reciprocating tablet presses), the punches are fixed to the punch holders which travel up and down, and in many cases fixation screws are used. Each make has its own holder design for punches and dies, and consequently for the tooling sets as well. Therefore little can be said in general terms, but it would appear that on the whole the remarks on the rotary press tooling apply correspondingly. 

The amount of clearance (space) between interacting parts like punch/die and barrel/turret guide, depends on the tolerance range (deviation from theoretical dimensions due to practical manufacturing reasons) of tooling dimensions. The clearance between the die wall and the punch tip affects the tableting process as well as the mechanical properties of the finished product while the powder is compressed, air needs to be released, and when the compressed tablet is moved upwards within the die bore, friction on the die walls is affected by the clearance. 

Fig. 1 General terminology of tooling (sets of upper and lower punches and dies) for rotary tablet presses.

Nickel-chromium-boron alloying coat applied on both punches and dies has been described and compared to untreated tools. Surprisingly, depending on the material under compression, the coating had the expected effect, or there was a total lack of effect, or they even increased ejection forces. The authors concluded that anyway, the tablets were superior in appearance. 

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