Compression machines

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.

Refrigeration is needed for processes that require temperatures below those that can be economically obtained with cooling water. For temperatures down to around 10 0, chilled water can be used. For lower temperatures, down to -30°C, salt brines (NaCl and CaCF) are used to distribute the refrigeration" around the site from a central refrigeration unit. Vapor compression machines are normally used. 

There are many ways in which foams can be processed and used as slabs, blocks, boards, sheets, molded shapes, sprayed coatings, extruded profiles, foamed in place in existing cavities, in which the liquid material is poured and allowed to foam, and as structural foams (Chapter 6, STRUCTURAL FOAM). Conventional equipment such as extruders, injection, or compression machines is used. However specially designed machines are available to just produce foamed products. 

Tablets are made in rotary compression machines that convert powders and granules into uniform sizes. Usual maximum diameter is about 1.5 in., but special sizes up to 4 in. dia are possible. Machines operate at 100 rpm or so and make up to 10,000 tablets/min. 

Images of spray and combustion in the rapid compression machine obtained for conditions representative of typical HSCI-engine operation. The sequence of four images covers the period immediately after injection—far left, and until the full development of a reacting jet—far right. (From Lu, P.-H., Han, J.-S., Lai, M.-C., Henein, N., and Bryzik, W., Combustion Visualization of DI Diesel Spray Combustion inside a Small-Bore Cylinder under Different EGR and Swirl Ratios, SAE, 2001-01-2005, 2001. With permission.)... 

FEP, PEA conventional molten-state processing methods are usable, such as injection, extrusion, compression machining is also suitable. 

All the molten-state methods are usable but the main ones are extrusion, injection, compression, machining and welding. 

Commonly when a pharmaceutical industry purchases a new compression machine, a PQ is conducted. First, the company must select some of its well-known products and prepare them until the compression phase as usual. The product must be compressed by the new equipment using the same compression conditions, such as compression force and tablet output. The obtained tablets must meet all the specifications of that product. The parameters specified could be aspect, hardness, thickness, diameter, average mass and uniformity of mass, friability, and tablet output. If the tablets obtained comply with specifications, the compression machine is considered reliable to obtain a product with good quality and in a reproducible manner and the equipment is considered performance qualified. 

Fill-weight variation tends to be more prominent with high-speed compression machines. This phenomenon was studied with various machine speeds for SMCC and MCC, and the former showed lesser fill-weight variation than the latter (44). 

Compaction, also known as tableting, involves the compression of the blend into a unit dose. The mechanism for this type of processing has remained unchanged for quite some time. The main components of the compression cycle are pressure rolls, weight adjustment cam, ejection cam, and feed frame. The main considerations when scaling up is compression speed. Compression speed effects dwell time and feed rate. As you go from a small development compression machine to a high-speed production machine, the powder is processed much more rapidly. 

Rotary compression machines convert powders and granules into hard tablets of quite uniform weight, notably of pharmaceuticals, but also of some solid catalyst formulations. The process is illustrated in Figure 12.8(a). A powder is loaded into a die where it is retained by a lower punch then it is compressed with an upper punch, and the tablet is ejected by raising both punches. 

Ignition delays, investigated in adiabatic compression machines (89, 91, 92, 106, 182, 209, 212, 213), have been correlated with knock (90, 93-5, 111, 158, 160, 194, 203). Ignition occurs in two stages. Levedahl (106) examined the effects of temperature, density, and fuel type on the induction periods, ti and r2, corresponding to each ignition stage. A close correlation existed between total delay, r, and knock resistance. Sensitivity was explained in terms of the relative partial contributions of n and r2 to r. 

Bombs, tube apparatus, rapid compression machines, and engines have been used extensively in knock studies. In recent years refinement of the engine as a research instrument has made possible detailed and quantitative investigations of the knock... 

The compression machine is specified by reference to ISO 5893 grade 0.5 One suspects that this is an error as the 1% accuracy of grade 1 is more reasonable. The usual practice is to use a universal tensile machine in compression mode with autographic recording of force and deflection. If this is the case, care must be taken that the machine is sufficiently stiff such that the deflection reading is not significantly affected. The deflection measurement is to conform to class C of ISO 5893 which at 2% makes the force requirement overkill. 

A small rotary press is most likely used when the initial formulation and process is developed at small scale. However, a large rotary press, used in a production area, may have significant differences in the number of stations, dwell time, and compression speed compared with smaller compression machines. Thus, early formulation design should consider the performance requirements of commercial production. Compaction simulators provide a useful tool able to reproduce the punch speeds of production machines and require only small quantities of powder blends for testing.86 The simulators can play an important role in formulation and process development and can also facilitate the technical transfer from development to commercialization. 

The compression of a powder is a complex process that is usually affected by different kinds of problems. These problems have been widely investigated and mainly concern the volume reduction and the development of a strength between the particles of the powder sufficient to ensure tablet integrity [82], The application of ultrasonic energy shows a great ability to reduce and even avoid these problems [83], Ultrasound refers to mechanical waves with a frequency above 18 kHz (the approximate limit of the human ear). In an ultrasound compression machine, this vibration is obtained by means of a piezoelectric material (typically ceramics) that acts as a transducer of alternate electric energy of different frequencies in mechanical energy. An acoustic coupler, or booster, in contact with the transducer increases the amplitude of the vibration before it is transmitted (usually in combination with mechanical pressure) to the material to be compressed. 

Bogda, M. J. (2002), Tablet compression Machine theory, design, and process troubleshooting, in Swarbrick, J., and Boylan, J. C., Eds., Encyclopedia of Pharmaceutical Technology, Marcel Dekker, New York, pp. 2669-2688. 

Murtagh, R. (2002), Identifying Improvements to Current Industry Practice for the Validation of Automated Tablet Compression Machines, M.Sc. Dissertation, University of Manchester Institute of Science and Technology, Manchester, U.K. 

There is no direct experimental evidence for this complex decomposition and it may well occur by several steps [107]. However, substantial yields of unsaturated carbonyl compounds are formed particularly at high pressures [78] under initial reaction conditions where cool flames propagate. For example, the cool-flame oxidation of 2-methylpentane at 525 °C and 19.7 atm in a rapid compression machine [78] yields no less than 14 unsaturated carbonyl compounds viz acrolein, methacrolein, but-l-en-3-one, pent-2-enal, pent-l-en-3-one, pent-l-en-4-one, trans-pent-2-en-4r one, 2-methylbut-l-en-3-one, 2-methylpent-l-en-3-one, 4-methylpent-l-en-3-one, 2-methylpent-l-en-4-one, 2-methylpent-2-en-4-one, 2-methyl-pent-2-enal and 4-methylpent-2-enal. Spectroscopic studies of the preflame reactions [78] have shown that the unsaturated ketones account for ca. 90 % of the absorption which, occurs at 2600 A. At lower initial temperatures and pressures acrolein and crotonaldehyde are formed from n-pentane [69, 70] and n-heptane [82], and acrolein is also formed from isobutane [68]. 

CSTR = Continuously-stirred tank reactor, PER = Pressurized flow reactor, RCM = Rapid compression machine, JSR = Jet-stirred reactor, JSFR Jet-stirred flow reactor. 

Fig. 6,7. Pressure and light output records typical of those observed from the two-stage ignition of hydrocarbons. These results were obtained by the authors during the combustion of n-pentane in a rapid compression machine. The duration of the compression stroke was 22 ms, as shown in the lower pressure record. The first- and second-stage time intervals, measured from the end of compression, are marked as ti and T2 respectively. Compressed gas temperature derived from (6.16) was 740 K [49].

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