Classifying – separating – and assorting solids – Sifting – Distributers or spreaders
Patent
1995-03-06
1997-08-05
Dayoan, D. Glenn
Classifying, separating, and assorting solids
Sifting
Distributers or spreaders
2093651, 310325, B07B 142
Patent
active
056533462
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns an apparatus and a method of sieving, grading, sifting, filtering or sorting dry solid substances or solid substances in liquids.
It is known that the oscillating movements generated by ultrasound, particularly in sifting and fine sieving operations, exert an advantageous influence on the sieve throughput and the material being sieved; the material being sieved is treated carefully by the transmitted oscillating movements, in the micron range, the agglomeration forces and surface tensions are considerably reduced and the general tendency to clogging of the sieving machines decreases or is entirely eliminated.
EP 0 369 572 A2 discloses a sieving apparatus with a sieving surface which is clamped in a frame, and a piezoelectric transducer which is coupled to that surface. The transducer is a multi-part component and is clamped between two bodies of different masses, of which the one which is nearer to the sieving surface comprises two parts; one part is glued to the sieve while the other is interchangeable. Also described is a regulating circuit which is intended to keep the sieve mesh under load in a resonance condition, that however is thought not to be possible from a technical point of view.
The ultrasonic transducer is referred to as a composite transducer in the book `Ultraschall` [Ultrasound] by Wilhelm Lehfeldt 1973, Vogel-Verlag, ISBN 3-8023-0060-2, page 40, and can be employed in all areas of active ultrasound uses such as for example ultrasound welding and ultrasound cleaning. Page 48 of that book mentions circuits with automatic frequency tracking or adaptation of the control circuit indicated in EP 0 369 572 A2.
All previously known methods suffer from the disadvantage that sound distribution over the entire active sieve mesh, which in most cases comprises a wire mesh, is very poor. The reason for that characteristic is that the sieve mesh, which is generally mounted tautly in a round or rectangular steel frame, cannot be excited in a resonance condition at the working frequency. The physical requirements for that purpose do not exist. The sieve mesh can serve only as a relatively poor ultrasound conductor. If in addition material to be sieved lies on the mesh, the resulting damping effect results in a further reduction in sound conductivity.
Those interrelations mean that after just a few centimeters in distance from the sound source, the level of intensity of the sound, and therewith also the conveyor effect, is greatly reduced.
In consideration of those factors the inventor set himself the aim of substantially eliminating those disadvantages by means of a suitable design configuration.
SUMMARY OF THE INVENTION
The invention seeks to provide that sieving and grading or screening operations as well as machines therefor are improved and sieving in the dry and wet areas by means of ultrasound are favored.
The invention further seeks to provide that resonators are so designed that the sieve is displaced with an undamped oscillating movement as far as possible over the entire surface area thereof.
That object is attained by the teachings of the present invention.
In accordance with the invention, associated with the ultrasound transducer is at least one resonator which bears against the sieve surface and which is tuned to the resonance of the ultrasound transducer and which can be caused thereby to oscillate, in particular with flexural oscillations.
In addition it has been found desirable for the resonator to be provided with resonance-transmitting elements which project finger-like from it on the sieve surface.
In other words the invention provides that no region on the active sieve surface is more than about 20 to 30 cm from the nearest ultrasound source. That is achieved with a system of resonator bars which operate in the flexural resonance mode and which are excited by a single ultrasound transducer. In relation to the round vibrating or shaking sieving machines which are frequently used, it is desirable for the ultrasound transducer to be
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Frei Karl
Solenthaler Jurgen
Dayoan D. Glenn
Telsonic AG
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