Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Plural – intermittent pressure applying
Patent
1996-04-23
1999-07-27
Theisen, Mary Lynn F.
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Plural, intermittent pressure applying
264123, 425345, 425353, B30B 1102
Patent
active
059285907
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the technical field concerning the production of aggregates by compressing powder or granular material.
In particular, the invention refers to a new operative method that defines the sequence of the steps of a compression cycle, usually performed by a rotary tabletting machine that includes opposed pair of punches.
BACKGROUND ART
In the prior art there are known various rotary tabletting machines, designed to produce the tablets from powder material, these machine comprising one turret driven to rotate around its axis.
Generally, the turret has means joined thereto for positioning and batching the material to be compressed, for compressing the powdered material and for ejecting the tablets; see e.g. U.S. Pat. Nos. 2,989,781-A1, 3,677,673-A1, 3,999,922-A1, 4,108,338-A1, 4,943,227-A1.
It is also known that the production of one tablet by a tabletting machine comprises a sequence of steps, that is, a filling step in which a suitable opening is filled with an appropriate quantity of material to be compressed, a volumetric batching of the material in the said opening, optionally a precompression step, and then the subsequent compression of the material, with consequent formation of a tablet having determined thickness. Finally, a step occurs in which the tablet is ejected from the opening.
All the above mentioned steps take place during respective angular sections of a rotation of the turret, and each working cycle can be carried out in a complete round or in a less extended arc.
The pre-compression step has the purpose of reducing the problems resulting from the fact that the tablet, in its interior, keeps embedded small quantities of air that can provoke microfractures, flackings or even explosion of the same tablet during ejection.
A tabletting machine that performs the pre-compression step is known from the European Patent 0204266-B1.
In another method, that has been proposed in a more recent time, a precompression load is kept constant for predetermined time, much longer than the usual precompression and compression times.
A tabletting machine performing a sequence which includes main and auxiliary compression steps is also known from DE 2.029.094. The said compression sequence comprises one or more main compression steps of around 2000 Kg, each of whose can be followed by an auxiliary compression step, provided by guide rails, of 300 to 1200 Kg.
Tablets obtained by applying these auxiliary compression steps are harder, and appear to have a smaller elastic return after compression.
Alternative or complementary methods, like the one that provides addition of binding materials, have been applied in order to reduce the above mentioned problems, but they have not resolved them definitely.
DISCLOSURE OF THE INVENTION
The object of the present invention is to propose a new operative method for compression of powders that permits to reduce, without affecting the throughput performance, the embedment of air inside the material during compression, and therefore, to obtain the tablets with the required hardness and compactness and without defects.
Consequently, the machines that carry out this method may advantageously apply lower compression loads with respect to tabletting machine that carry out other known methods.
The aforementioned object is obtained by means of a method for compression of powder or granular material by a rotary tabletting machine for the production of tablets inside openings, by compression means.
The subject method includes, for each tablet production cycle, the subsequent operative steps in the following order: compressed; increasing load is applied to the material, until said load reaches a first pre-established value; is substantially decreased or removed; precompression load of a second pre-established value is applied to the material; previous step is kept constant at the second value reached in this step; substantially decreased or removed; to be compressed, until a third value, identical or different from the precedent first and s
REFERENCES:
patent: 1803801 (1931-05-01), Spengler et al.
patent: 2989781 (1961-06-01), Frank
patent: 3677673 (1972-07-01), Shapiro
patent: 3999922 (1976-12-01), Shimada
patent: 4108338 (1978-08-01), Howland et al.
patent: 4943227 (1990-07-01), Facchini
patent: 5462427 (1995-10-01), Kramer
I.M.A. - Industria Macchine Automatiche - S.p.A.
Theisen Mary Lynn F.
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