More specifically, this invention relates to a dust filtering and collecting device whose structure is such that it can be used, for example, in industrial environments where process waste in the form of fine particles is produced, or even in locations connected to the food industry where products in the form of fine particles, such as for example, flour, meal or the like, are present.

BACKGROUND ART -At present, the collection of dust and machining waste is normally carried out using one of two systems, the first comprising a machine sub-assembly, a conveyor and a container, and the second comprising a distributor installation and silos.

In the first system, the machine sub-assembly is a special container placed under the machine tool, in direct contact with the machining area. With the aid of a lubricant/coolant liquid, the machining waste is first collected in this container and then expelled from the

machine through a system of conveyors connected to the container. The sub-assembly includes a screen designed to separate the lubricant/coolant liquid from the solid waste.

The conveyors are self-contained mechanical devices comprising any suitable device designed to carry the waste material from the machine sub-assembly or from a tank to external containers where the waste material is collected. There are several different types of conveyors: screw conveyors, belt conveyors, drag conveyors or magnetic conveyors. Through these conveyor systems, the waste material is carried out of the machine tool to the collection areas.

The containers may be directly in contact with the machine or they may at the end of the conveyor, where, through a system of conduits, the waste material is accumulated before being extracted for recycling.

Distributor installations constitute the second means of carrying the waste material to the collection areas. These installations extract the waste material from the machine working areas and through a system of pipes-constituting a pneumatic system, carry the waste to special silos where it is prepared to recycling.

The silos represent the final destination of the waste material when it is removed from the machine through a distributor installation. They are located outside the production facility and receive all the waste from the machine, including the lubricant/coolant liquid, which is then separated into solid and liquid using suitable filters. In the silos, the solid waste is

accumulated in special chambers and-from there discharged through tubes onto waiting vehicles outside the silos which take it away for disposal.

This procedure makes the distributor installation very safe since, in addition to hot waste from the processing areas, the tubes also have passing through them certain gases produced during the process cycle and which might spark off highly dangerous explosions.

In the case of process waste constituted by dust suspended in the air, the only way of dealing with the waste, at present, is to install extraction systems consisting of fans and to provide workers with face masks.

One drawback is the fact that the air is not sufficiently treated and still contains microparticles produced by machining processes and-which present a danger to workers since they are the main cause of diseases such as silicosis.

Another drawback is the fact that process waste of this type is not collected and recycled but only extracted, as far as possible, from the working environment.

Yet another drawback is inflexibility, due to the fact that dust extraction equipment is purpose designed and constructed for a particular machine tool arrangement in the working area and therefore cannot usually be adapted to suit other arrangements.

DESCRIPTION OF THE INVENTION The aim of this invention is to provide a device for

filtering and collecting microparticles which is capable of. eliminating or significantly reducing the above mentioned drawbacks.

A further aim of the invention is to provide a device for filtering and collecting microparticles which is highly flexible, adaptable to any type of working environment, and able. to be transported and used at any place where dust and process waste needs to be collected.

Yet another aim of the invention is to provide a device for filtering and collecting. microparticles which is reliable, safe-and requires very little maintenance.

This is achieved by a device for filtering and collecting microparticles having the features described in the main claim.

The dependent claims describe advantageous embodiments of the invention.

The device for filtering and collecting microparticles according to the invention comprises a casing for housing a central chamber that communicates with a hopper below and with a hood above, operating machines designed to suck in dusty air from the atmosphere and to deliver treated air, the central chamber being equipped with self cleaning filters for retaining fine-grain particles, and the hopper housing a station for filtering medium-grain microparticles.

According to the invention, the central chamber is divided into a large, first half-chamber that communicates with the hopper and a smaller, second half- chamber adjacent to the hood. The large, first half- chamber has an aperture to allow in the dusty air and

houses most of the self-cleaning filters, which may consist of upright tubular cartridges made of paper or fabric folded into a segmented configuration.

Advantageously, the top end of each cartridge is housed in the smaller, second half-chamber in contact with a nozzle which cyclically blows compressed air into the cartridge in order to shake dust off it, thus reducing maintenance to a minimum.

The station for filtering medium-grain microparticles is housed in the hopper below and consists of a porous diaphragm against which compressed air is directed in order to blow the medium-grain dust. This blowing action creates a"fluid bed"and makes it possible, using a suitable suction unit, to extract the heavy microparticles from the hopper so that they can be collected in a container and, where possible, recycled as a raw material for making other products.

The casing that houses the device is wheel mounted so that it can be moved to any point where dust must be extracted near the machine tool being used at any given time.

The device is also equipped with standard electrical connectors and compressed air fittings.

The particles extracted are further treated by a transfer and microfiltering station to obtain extremely clean air, free of practically all dust particles.

Since some types of dust particles tend to become electrostatically charged and thus to adhere to the inside walls of the device, the transfer station, in one advantageous embodiment of the invention, is provided

with vibrating means for detaching dust from the walls of the device.

Advantageously, the device for filtering and collecting dust particles can be used on particles having a medium grain size ranging from about 1 u to about 3 mm.

DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will become evident on reading the following description of one form of embodiment of the invention, given as a non- restricting example, with the help of the accompanying drawings,. in which: - Figure 1 is a front elevation section view of the device according to the invention, with some parts illustrated schematically.

- Figure 2 is a scaled-up front elevation view of a two-stage microfiltering station ; - Figure 3 is a plan view of Figure 2 ; - Figure 4 is a scaled-up front elevation view of a three-stage microfiltering station; and - Figure 5 is a section and plan view of a three-stage microfiltering station.

DESCRIPTION OF A FORM OF EMBODIMENT In the accompanying drawings, the numeral 10 denotes in its entirety a device for filtering and collecting microparticles, in this particular case, a device 10 for transferring the dust produced in an industrial environment during surface finishing of stone material.

The device 10 comprises a casing (not illustrated in

the drawings), possibly wheel-mounted, designed to house a central chamber 11 that communicates with a hopper 12 below and with a hood 13 above.

Near the hood 13, the chamber 11 has a wall 14 that divides it into a large half-chamber 15, which communicates with the hopper 12, and a smaller half- chamber 16 adjacent to the hood 13.

The large half-chamber 15 has an inlet aperture 17 designed to allow in the mixture of dust and air sucked in from the outside of the device by an operating machine (not illustrated in the drawings).

The aperture 17 may be fitted with a section of pipe 18 curved downwardly towards the bottom 19 of the central chamber 11. The bottom 19 may be screened so as to allow the heavier, medium-grain microparticles to fall into the hopper 12.

The hopper 12 comprises a funnel 20 that communicates with a collection box 21 below it. The box 21 is divided by a porous diaphragm 22 into an upper portion 23 and a lower portion 24.

The lower portion 24 has a compressed air inlet fitting 25, while the upper portion 23 has an outlet fitting 26 for the medium-grain dust particles extracted from the surrounding air.

The central chamber 11 is designed to house self- cleaning filters which may consist of upright tubular cartridges 27 whose top ends 28 are housed in the smaller, second half-chamber 16. The latter also houses a conduit 29 equipped with nozzles 29a positioned at the top ends 28 of the cartridges 27.

The hood 13, communicating with the smaller half- chamber 16, comprises a power-driven suction'unit 30 designed to extract the treated air from the chamber 11 and to channel it, through a conduit 31, towards an outlet 32 which may be connected to a stack (not illustrated) surmounting the device 10.

The device 10 for. filtering and collecting microparticles also comprises: - an electrical panel 33 ; - a pneumatic sequencer 34; - a compressed air tank 35; - a station 36 for regulating the pressure of the compressed air; - a unit 37 for transferring the microparticles extracted from the dusty air.

The electrical panel 33 is connected to the mains power supply and has a cable 38 providing electricity for the power unit 30 and another cable 39 to supply the pneumatic sequencer 34. The latter is connected to the tank 35 by means of air valves 40.

The pressure regulating station 3, 6 receives compressed air from the main supply and has a pipe 41 connecting it to the tank 35, a. pipe 42 connecting it to the fitting 25 of the lower portion 24 of the box 21 and another pipe communicating with the transfer unit 37.

The microparticle transfer unit 37 has a pipe 37a connecting it to the fitting 26 of the upper portion 23 of the box 21.

The electrical panel 33, the sequencer 34 and the pressure regulating station 36 can be electrically

connected to an electronic unit (not illustrated in the drawings) designed to control the device 10.

The device 10 for filtering and collecting microparticles works as described below.

The dusty air is sucked in from the surrounding atmosphere to be cleaned and enters the chamber 11 through the aperture 17 in the direction indicated by the arrow labelled"A".

The air is channelled by the curved pipe section 18 , and flows into the upper part of the chamber 11 (in the direction indicated by the arrows labelled"B") and towards the hopper 12 (in the direction of the arrows labelled"C"). At this point, the heavier medium-grain microparticles tend to fall by gravity into the box 21, whilst the swirling movements created inside the funnel 20 cause the lighter microparticles to rise (arrows"D") towards the large upper half-chamber 15.

Thanks to the compressed air supplied by the pressure regulating station 36 through the pipe 42, the heavy dust particles are-subjected to a vortical force (arrows"E") which creates a"fluid bed"that keeps them suspended in the air above the porous diaphragm 22. Thus, the heavy dust particles can be easily extracted from the upper portion 23 of the box 21 using a suitable suction unit to suck them out through the pipe 37a.

From the transfer unit 37, the heavy microparticles can be easily extracted (arrow"F") and stored in any suitable container until needed for recycling.

The fine-grain, lightweight dust particles in the large half-chamber 15 settle on the cartridge filters 27

whose top ends 28 receive a pulsed supply of compressed air from the nozzles 29a. The regular bursts of compressed air applied to the cartridges 27 shake the dust particles off the cartridges 27, thus keeping the filters clean. The dust particles shaken off the filters tend to fall towards the hopper 12 from where they can be collected in the transfer unit 37.

The power unit 30 sucks the clean air out of the device 10 through the outlet 32 (arrow"G").

Figures 2 and 3 illustrate, a transfer and microfiltering station 44 designed to further treat the dust particles from the transfer unit 37.

This form of embodiment is especially suitable for a device 10 operating in a screen-printing shop where the presence of toner dust makes it more difficult to clean the air.

The transfer and microfiltering station 44 comprises: a first inlet stage 45 for the pre-treated air arriving from the transfer unit 37 through the conduit 46; a second extraction stage 47, communicating with the first stage 45 and equipped with an opening 48 for discharging the extracted dust particles and with a fitting 49 connected to a pipe 50 through which the treated air flows out ; an operating machine, for example a vacuum pump 51, presenting the suction pipe 50 and a second pipe 52 for delivering the treated air to a conduit 53.

The conduit 53 may be connected to the aperture 17

so as to run the air through another filtering cycle.

The vacuum pump 51 may be connected to a regulator 54 to keep the vacuum at a desired level.

Each stage 45, 47 consists of a truncated cone shaped chamber tapering in the direction of air flow.

This shape imparts vortical motion to the air in such a way that the dust particles tend to settle on the walls of the stages 45,47 themselves from where they then fall by gravity towards the outlet opening 48.

The second stage 47 may be equipped with vibration means 55, operating on compressed air ; for example, and designed to cyclically agitate the transfer station44 so that any dust particles still adhering to the truncated cone shaped inside walls are shaken off and made to fall.

As shown in Figures 4 and 5, the transfer station 44 may have an intermediate stage 56 in order to improve dust extraction performance, especially for devices 10 used to treat massive air flows.

The transfer and microfiltering station 44 can be housed in a respective casing 57 fitted with damping means consisting, for example, of linear passive actuators 58.

The invention is described above with reference to some preferred forms of embodiment of it. However, it will be understood that the invention may be modified and adapted in several ways without departing from the scope of the inventive concept. For example, in other forms of embodiment, the invention might be specifically adapted to extract dust particles of a different nature, such as those resulting from the production or processing of flour or meal in the food industry.