Press punching

The rate of consolidation in an excentric press is governed by the speed at which the upper punch moves into the die. This in turn is governed by the lengths of the excentric arms of the press and its speed of operation. In a rotary press, punch speed is governed by the diameter of the die table, the diameter of the pressure roll, the geometry of the punch head, and the speed of operation. Formulae for the calculation of punch speeds at any point of the compression cycle for both types of press have been derived. ... 

FIGURE 2 Rotary tablet press punch and die terminology. Source Adapted from Ref. 6. 

Clarified lime juice, made by mixing juice with filter aid prior to passing through a filter press, is the one clarified citms juice that is a significant article of commerce. The pasteurized bottled juice is popular for drink mixes, punch bases, and fountain drinks (13). 

After pressure appHcation, the top punch is removed and the compact is ejected from the cavity by the bottom punch. The cavity is then refilled and is ready for another charge. This cycle is repeated automatically at a rate that varies with the part and size and the complexity and dowabiUty of the powder. Pressing equipment producing relatively small, simple parts can operate at up to 200 parts/min. Rotary presses with multiple die sets are even faster. Table 5 gives the ranges of pressures used for various materials during die compaction. 

Tablet Press. The main components of a tablet compression machine (press) are the dies, which hold a measured volume of material to be compressed (granulation), the upper punches which exert pressure on the down stroke, and the lower punches which move upward after compaction to eject the tablets from the dies. Mechanical components deflver the necessary pressure. The granulation is fed from a hopper with a feed-frame on rotary-type presses and a feeding shoe on single-punch presses. A smooth and even flow ensures good weight and compression uniformity. Using the proper formulation, demixing in the hopper is minimized.

The actual compression process is a cycle of die fill, compaction by intervention of the upper punch using great pressure on the granulation material in the die, and upward movement of both punches to achieve ejection of the tablet from the die. Singe-punch presses have only one die-and-punch arrangement and the compression is quick, with Httle dwell time of the top punch in die. 

Single-punch machines produce approximately 100—150 tablets per minute. Depending on numbers of die per punch units, standard rotary presses can produce 5000 tablets/min, and even more with a double-sided rotary press. The newest high speed presses can achieve 12,000 tablets/min. 

Some presses are equipped with strain gauges at key points in the overall feed—compress—eject cycle. Thus, these measure compression and ejection forces. Tight specifications for punch lengths and weU-designed and prepared granulations have led to better control of variations in tablet weight. In fiiUy automated presses, weight variations are adjusted by computer. 

Applications Pumps Compressors Fans Machine tools General use Electrical stairways Pulverizers Conveyors Punch presses Crushers Pumps Compressors Fans Machine tools General use... 

Punches, presses, shears Quarry plant Rubber machinery Screens (vibrating)... 

Stanz-porzellan, n. porcelain for punching, -presse, /. stamping press. 

Some ductile plastics, such as PC and ABS, can be fabricated like metals with punching and cold-forming techniques. These processing techniques are analogous to the hardness tests in that a rigid indentor is pressed into a sheet of a less-rigid plastic. 

Pressing is carried out within a cemented carbide die between two steel or cemented carbide punches. In order to impart enough mechanical strength to the blank to permit further manipulation without risk, removable organic binders (camphor, natural or synthetic waxes, latex or synthetic rubber, methyl polymethacrylate, polyvinyl alcohol, carboxymethylcellulose, ammonium alginate) are mixed into the powder, dissolved in a convenient volatile solvent. Some of these also act as lubricants thus minimizing the wear on the die. 

The compressibility of group-IVA and -VIA transition-metal boride powders is measured by the dimensions and weights of the blanks, by measuring the stroke of the punches with a cathetometer, or alternatively by electrical conductivity (based upon the metallic conductivity of most borides). The process of densiheation by pressing is defined by ... 

Pharmaceutical compressed tablets are prepared by placing an appropriate powder mix, or granulation, in a metal die on a tablet press. At the base of the die is a lower punch, and above the die is an upper punch. When the upper punch is forced down on the powder mix (single station press) or when the upper and lower... 

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 ... 

Those with a single set of tooling— single station (or single-punch ) or eccentric presses... 

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 commercial types of single station presses have essentially the same basic operating cycle (see Fig. 16), where filling, compression, and ejection of tablets from the die is accomplished by punch movement utilizing cam actions. Material is fed to the die from the hopper... 

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