Measuring and testing – Vibration – By mechanical waves
Patent
1995-05-25
1997-07-15
Oda, Christine K.
Measuring and testing
Vibration
By mechanical waves
73801, G01H 1100
Patent
active
056486103
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for characterizing the compaction of powder materials acoustic emission occurring during compaction of said materials, and a device for examining the compressibility of powder materials and monitoring the compaction process.
BACKGROUND OF THE INVENTION
Compaction means compressing powdery materials to greater density and smaller volume. Compaction is a common material-technological procedure in many fields of technology, particularly in metallurgy and ceramics. Compaction usually precedes a further phase, such as sintering.
In the pharmaceutical industry, compaction is used especially in making granules, particularly in dry granulation, when granules are made from moisture-sensitive materials. The pieces made during compaction are broken down into granules of desired shapes and sizes. Granulation, on the other hand, is one of the most important part processes of tabletting in pharmaceutical technology. Roughly speaking, granulation methods can be divided into wet and dry methods, depending on whether liquid is added to the powder mass or not. The purpose of granulation is to produce, from the powder, granules of appropriate size and strength in the shape of grains or balls. More broadly speaking, granulation means enlarging the size of powder particles. In granulating powders or powder compounds the aim is, for example, to improve the flow and distribution accuracy of the mass, reduce dusting, improve binding when compressing tablets, reduce separation of components, and accomplish a certain microstructure for the compacted powder.
Compaction is usually carried out as a batch process, but can also be performed as a continuous process, for example, by means of a roller compactor. Compaction can be carried out at room temperature or at an elevated temperature. The pressures used normally vary within the range of 70-700 MPa.
The properties most closely related to the behavior of the powder being compacted are the compressibility and green strength of the piece. Compressibility is an indicator of the change in density obtainable through compaction. Green strength is an indicator of the cohesion of the compacted piece.
A common problem of compaction processes is that the powder to be compacted does not become compressed in the expected manner. Especially where the compacted product is to be further worked into granules, it is a considerable disadvantage if loose powder has remained inside the compacted product, because this produces reject in the granulation process. If, on the other hand, the product to be compacted should remain in one piece as it is, for example, for the purpose of sintering or some other work phase, it is extremely disadvantageous if the compacted product splits during the compaction process.
One reason for the compaction problems is that the wrong compressing pressure has been selected with respect to those properties of the powder to be compacted that have an effect on compressibility. The most important properties affecting the compressibility of an organic powder are the capability of the powder to form van der Waals' bonds, particle size and shape, and particle size distribution. The appropriate compression pressure is dependent mainly on these properties. Different powder types are examined on laboratory and pilot scale, in an attempt to find the suitable compression pressure for each powder and powder compound type, with a view to the production process. In practice it has, however, been found that selecting the compression pressure merely on the basis of these parameters will not give a satisfactory compaction result. Thus, in practice, extensive series of test compressions have to be made with the powder or powder compound to be compacted in order to find the suitable compression pressure for the production process. Preparing such test batches is obviously laborious and very slow.
The aim of the present invention is to eliminate the above problems and to present a new method and device for monitoring the compressibility o
REFERENCES:
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Derwent's Abstract No. 89-213103/29, Week 8929, SU, A2, 1453314 Jan. 23, 1989.
International Journal of Pharmaceutics, pp. 29-36, vol. 36, 1987, M.J. Waring et al., "Acoustic Emission of Pharmaceutical Materials During Compression". (No month).
Hakanen Arvi
Jalonen Harry
Jokinen Juha
Laine Ensio
Linsaari Kari
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