WO1996014928A1

WO1996014928A1 - Method and apparatus for producing and drying spherical particles

Info

Publication number: WO1996014928A1
Application number: PCT/IT1995/000177
Authority: WO
Inventors: Lorenzo Rodriguez; Maurizio Cini
Original assignee: G.S. S.R.L. Coating System
Priority date: 1994-11-09
Filing date: 1995-11-06
Publication date: 1996-05-23
Also published as: IT1274101B; ITBO940491A1; ITBO940491A0

Abstract

The method for sphering particles (2) includes transporting them, suspended in a fluid carrier means constituted by an air flow that gradually dries the particles. An apparatus that carries out this method includes a pan (1) aimed at receiving a mass of particles (2) to be sphered, a recirculation conduit (5) that extends axially from the pan (1) and that leads to the opposite side thereof, a pipe (6), aimed at introducing an air flow forming the fluid carrier means for conveying the particles (2) along the conduit (5), that is situated inside the pan (1), in coaxial relation therewith, and leads to a conical section (4) thereof.

Description

METHOD AND APPARATUS FOR PRODUCING AND DRYING SPHERICAL PARTICLES

TECHNICAL FIELD

The present invention relates to sphering corpuscular articles.

BACKGROUND ART

It is known that it is often necessary to sphere various corpuscular articles.

These particles are supplied in a plastic state, with a high humidity degree, due to the presence of e.g. solvents, aqueous or not, and therefore they must be dried after the sphering has been completed.

DISCLOSURE OF THE INVENTION

The object of the present invention is to propose a method that permits to sphere and dry, in an innovative way, various, even very small parti¬ cles, in a rapid working cycle, without producing powder.

Another object of the present invention is to propose a simple and versatile apparatus, carrying out the above mentioned method.

The above mentioned objects are obtained by means of a method for sphering and drying particles, that includes provoking a recirculation of particles to be sphered, conveyed suspended in a carrier fluid formed by an air flow aimed also at gradually drying the particles . The above mentioned method is carried out by means of an apparatus for sphering and drying parti¬ cles, that includes a pan, designed to receive the mass of particles to be coated, a recirculation conduit extending axially from the pan and leading to the opposite side thereof, and a pipe aimed at introducing an air flow forming the fluid carrier for conveying the particles along the conduit, and situated inside the pan, in coaxial relation there- with, and opening in a conical narrow section there¬ of.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristic features of the present invention are pointed out in the following descrip¬ tion with reference to the enclosed drawings, in which: - figure 1 shows a schematic longitudinal section view of the apparatus for sphering and drying parti¬ cles,-

- figure 2 shows a correspondent partial plan view of this apparatus.

BEST MODE OF CARRYING OUT THE INVENTION

With reference to the above described fig- ures, the particles 2 to be sphered and dried, are introduced into the pan 1 of the apparatus .

In its lower part, the pan 1 features a narrow portion 3, suitably connected with the wider central band of the pan. A narrow portion 3 of the pan is connected, by a conical section 4, with a recirculation conduit 5; this recirculation conduit 5 is linked with the pan l at its other end.

More precisely, a section 5a of the recircu¬ lation conduit 5, tangential with respect to the pan 1, leads to the upper part of the central band of the same pan.

A pipe 6, aimed at introducing an air flow, is inserted within the pan 1, in coaxial relation therewith, and opens in a narrow part of the conical section 4 of the same pan 1.

At its free end, the pipe 6 features a ta-

■ pered section 7. The tapering angle of the section 7 is smaller than the tapering angle of the conical section 4 of the pan, so that the free section between the two of them decreases in direction of the tapered section free end.

The air flow creates a kind of fluid bed conveying the particles 2 along the recirculation conduit 5. In its upper part, the pan 1 features also a plurality of outlets 8, through which the recircula¬ tion air goes out.

Therefore, the particles 2, introduced into the pan 1, undergoes the action of the air flow introduced through the pipe 6.

The air flow that enters the recirculation conduit 5 sucks the particles 2, due to Venturi effect produced, at the outlet of the pipe 6, by the narrowing of the conical section 4 of the pan. In this way, along the recirculation conduit 5, a fluid carrier is formed, constituted by an air flow fed by the pipe 6 ,- particles 2 are conveyed suspended in this carrier for being sphered, while simultaneously, the air flow dries them. The fluid carrier returns to the pan 1, where the air goes out through the upper outlets 8, while the particles 2 fall down in the lower part of the pan 1, so as to continue the processing cycle.

Consequently, the process of sphering the particles 2 is further advanced with each passage through the recirculation conduit 5.

The number of passages for the particles can be reckoned on a statistical principle, so, in a sufficiently long period of time, all the particles

2 are supposed to have performed the same number of sphering cycles.

Obviously, the processing time depends on the ■ characteristics of the products to be obtained, i.e. in particular on the type of processed particles.

It is to be noted that, in case the particles 2 are dry, they will rub against each other and against the wall of the recirculation conduit 5. In this way, the angles of the particles will be po¬ lished and, gradually will become round.

Powder produced by this process will deposit on the particles during the passages.

In case the particles are plastic (e.g. because of their humidity) , they will be sphered mainly due to their rolling.

It is to be noted that the air flow, flowing in the recirculation conduit 5, is reintroduced into the pan 1 according to a tangential direction: as a consequence, the particles 2, dragged by the said flow, during their descendent movement, are set in vortical movement, like a whirlwind, while the bigger part of the air reintroduced to the pan, goes out through the outlets 8.

This allows to mix the particles 2 in a better way, optimising the downward movement and separation of discharge air, and consequently, obtaining a final product of better quality.

In order to improve the mixing efficiency, it is possible to create a relative movement of the pan 1 with respect to the pipe 6, be e.g. making the pan 1 rotate axially.

Obviously, this operation would need suitable connections of the mutually rotating parts.

It is also possible to pre-heat the air introduced in the pan 1, so as to improve drying efficiency. It is also possible to suck the air inside the pan, instead of delivering it under pressure.

This modification would require a suitable depression inside the pan 1, improving the drying of the particles.

The disclosed method and apparatus allow to sphere various particles in an innovative way. In particular, it is possible to process all kinds of particles, even very small.

It is to be pointed out that the quantity of powders and the like is drastically reduced during the sphering process,- in addition, the powders formed during the coating stages, set down on the particles as a kind of coating, in particular when humid particles are sphered; in such situation it is possible to introduce suitable kind of powder into the pan 1.

It is understood that what above has been described as a mere, not limitative example, there¬ fore all possible constructive variants are protec¬ ted by the present technical solution, as described above and claimed in the following.

Claims

1. Method for sphering and drying particles, charac¬ terised in that it includes provoking a recircula- tion of particles to be sphered, conveyed suspended in a carrier fluid formed by an air flow aimed also at gradually drying the particles.

2. Apparatus for sphering and drying particles, characterised in that it includes: a pan (1) designed to receive the mass of particles (2) to be coated; a recirculation conduit (5) extending axially from the pan (1) and leading to the opposite side there- of ; a pipe (6) , aimed at introducing an air flow forming the fluid carrier for conveying the particles (2) along the conduit (5) , and situated inside the pan (1) , in coaxial relation therewith, and opening in a narrow section (3) thereof.

3. Apparatus, according to claim 2, characterised in that a section (5a ) of the recirculation conduit (5) , tangential with respect to the pan (1) , enters an upper, wider part of the central band of the same pan, so as to set the particles, dragged by the said air flow, at the outlet of the recirculation conduit (5) , in vortical movement.

4. Apparatus, according to claim 2, characterised in that a conical section (4) , linking the said pan (1) with the said recirculation conduit (5) , in cooperation with a tapered part (7) , made at the free end of said pipe (6) , produce a Venturi effect, due to which the air flow that enters the recirculation conduit (5) sucks the particles (2) .

5. Apparatus, according to claim 2, characterised in that in its upper part, the pan (1) has a plurality of outlets (8) , for allowing discharge of the air getting out from the recirculation conduit (5) .

6. Apparatus, according to claim 2, characterised in that the said pan (1) is rotated with respect to the said pipe (6) introducing air.