Dust extraction system

Abstract

A dust extraction system comprises: an extractor unit having an inlet, a primary filter, and a fan for drawing air from the inlet through the filter; and a secondary filter unit (1) comprising a hollow body having: an inlet (7) connectable to a source of dust; an inlet flow passage with the body extending downwardly from the inlet into proximity with a dust tray (5) in the lower part of the body; an outlet (10) connected to the extractor unit; an outlet flow passage within the body extending upwardly from the dust tray to the outlet (10), whereby the air flow in the body reverses direction when passing from the inlet flow passage to the outlet flow passage above the dust tray (5); a removable filter (12) located within the outlet flow passage; and at least one baffle (16) located within the inlet flow passage and configured to introduce turbulence and to slow the air flow thereby allowing agglomeration of dust particles, the agglomerated particles being retained in the dust tray.

Description

DUST EXTRACTION SYSTEMField of the Invention

[0001] This invention relates to a dust extraction system for use with apparatus generating fine particles.Background to the Invention

[0002] Laser engraving of aluminium cans, for example for providing identifying markings or use-by dates, or for decoration, gives rise to dust (very fine and sub-micron airborne aluminium oxide particles). It is therefore necessary to provide dust extraction apparatus to draw the dust-laden air through a filter which catches the dust. Typically, the filter takes the form of replaceable cartridges, and it has been found that these need to be replaced frequently, becoming choked with dust after only 2 weeks. The cost of replacing the cartridges adds significantly to the cost of operation of the laser engraving unit.Summary of the Invention

[0003] The present invention provides a dust extraction system comprising: an extractor unit having an inlet, a primary filter, and a fan for drawing air from the inlet through the filter; and a secondary filter unit comprising a hollow body having: an inlet connectable to a source of dust; an inlet flow passage with the body extending downwardly from the inlet into proximity with a dust tray in the lower part of the body; an outlet connected to the extractor unit; an outlet flow passage within the body extending upwardly from the dust tray to the outlet, whereby the air flow in the body reverses direction when passing from the inlet flow passage to the outlet flow passage above the dust tray; a removable filter located within the outlet flow passage; and a baffle located within the inlet flow passage and configured to introduce turbulence and to slow the air flow thereby allowing agglomeration of dust particles, the agglomerated particles being retained in the dust tray.P2665GB

[0004] Further features of the invention are set out in the claims.

[0005] The dust extraction system of the invention enables the interval between replacement of filter cartridges in the main extractor unit to be significantly extended, reducing costs.

[0006] It will be appreciated that the dust extraction system of the invention can be used with any apparatus generating fine / sub-micron particles and is not limited to aluminium particles.Brief Description of the Drawings

[0007] In the drawings, which illustrate an exemplary embodiment of secondary filter unit of the invention:

[0008] Figure 1 is an isometric view from the front, above and to one side, showing the front access door open;

[0009] Figure 2 is a front elevation;

[0010] Figure 3 is an isometric side view from above and to the rear; and Figure 4 is a view corresponding to that of Figure 1 , but with the filter cartridges removed.Detailed Description of the Illustrated Embodiment

[0011] Referring first to Figures 1 and 2, the secondary filter unit comprises a sheet metal cabinet 1 , mounted on casters 2, and having a hinged access door 3 forming one side of the cabinet. The interior of the cabinet is divided into three zones by means of a vertical dividing wall 4 which extends from the top to a position just above a dust tray 5 which extends across the bottom of the cabinet and is configured to be capable of being slid out of the cabinet when the access door 3 is open. A first zone 6 occupies a minor part of the width of the interior of the cabinet and communicates with an inlet 7 for connection of a flexible conduit (not shown) which is in turn connected to the source of the dust (for example the cabinet in which the laser engraving is carried out). The second zone 8 is in the lowermost part of the interior of the cabinet and is occupied, in use, by the tray 5. Air flowing downwardly through the first zone 6 from the inlet 7 therefore undergoes an abrupt reversal of direction in the second zone 8 above the tray 5 to flowP2665GBinto the third zone 9, which occupies the greater part of the interior of the cabinet, and which has an outlet 10 therefrom in the upper part of the zone 9 for connection of a flexible conduit (not shown) which is in turn connected to a conventional fume extraction unit. An angled flange 1 1 extends horizontally around the interior of the cabinet just above the tray 5 to direct the airflow and any dust away from the interior walls of the cabinet and into the tray 5.

[0012] The third zone 9 contains a pair of filter cartridges 12, arranged side by side, each cartridge 12 being in the form of a cylinder of a porous filter medium mounted on a shelf 13 above the tray 5 so that the cylinder is closed at its lowermost end. The uppermost end of each cylinder is in contact with a closure plate 14 having holes 15 therethrough corresponding to the interior opening of the cylinder, so that air is drawn through the cartridges 12 from the outside, where the dust is retained by the filter medium, to the inside of the cylinders and upwards through the holes 15 towards the outlet 10.

[0013] Baffle plates 16 are mounted in the first zone 6, one on a wall of the cabinet and two on the dividing wall 4. Each baffle plate 16 is angled obliquely downward from the respective wall, and extends over approximately half the horizontal width of the zone 6. The baffle plates 16 are provided with an array of holes 17 therethrough, and serve to introduce turbulence and reduce the flow velocity, the holes 17 assisting this process while allowing dust particles to pass through without settling on the baffle plates. The steep angle of the plates 16 further assists in ensuring that dust does not accumulate on the plates. The purpose of the turbulence and reduction in velocity is to cause the particles to agglomerate and to drop into the dust tray 5, so that the dust load on the filter cartridges is reduced, extending their operational life.

[0014] Referring now to Figure 3, a pressurised air tank 20 is mounted on the rear of the cabinet 1 and delivers compressed air to a control unit 21 mounted in he upper part of the third zone 9 within the cabinet. The tank can be supplied from an air compressor or from a factory compressed air supply, for example. The control unit 21 contains solenoid valves and an electronic controller programmed to deliver air to a pair of nozzles 22 (Figure 2) positioned above aP2665GBrespective one of the two filter cartridges 12. The nozzles 22 are configured to deliver to the interior of the respective cartridges a flow of air which floods the internal surfaces of the cartridge and forces dust particles adhering to the external surfaces off the filter to drop into the dust tray 5 below. The operation of the solenoid valves under the control of the controller is such as to release a rush of pressurised air for a predetermined period of time. The valves are operated such that one filter is blown by the compressed air while the other continues to operate so that the extraction continues without the need to shut the system down. The other filter can then be blow by compressed air while the first filter resumes its filtering operation. The blowing of the filters is carried out at predetermined intervals to ensure that the filters do not become prematurely clogged. The tank 20 is configured such that the volume of air delivered is just sufficient to fill the respective filter cartridge and displace the particles from the external surface thereof, but without having an adverse effect on the filtering flow through the other filter, while at the same time allowing the displaced particles to settle into the tray 7.

[0015] The secondary filter unit is provided with pressure sensors to measure the differential pressure across the filters. When this exceeds a predetermined value, a warning may be given to the operator by illuminating a red light in the beacon 23 mounted on the top of the cabinet, so that the operator knows that it is time to change the cartridges 12 for new ones. The beacon 23 is configured to show, alternatively to the warning red light, a green light indicating that operation is within normal parameters, and an orange light when the filter blowing operation is being carried out.

[0016] Figure 4 illustrates the cabinet with the filter cartridges removed, showing the shelf 13 on which the cartridges 12 are mounted in use. The shelf 13 is provided with openings 24 therethrough, to each side of the pair of filter cartridges, each provided with an angled flange 25 to direct dust particles down into the tray 5 and to reduce blowback of the particles when the blowing of the filters is carried out. A handle 26 on the front of the shelf 13 can be rotated to lower the shelf to permit removal of the cartridges and to raise the shelf to lock the cartridges in place. In Figure 4, the shelf is shown pivoted to its lowered position. AP2665GBbracket 27 on the inside of the door 3 is configured to stop the door being closed if the handle 26 has not been fully turned to lock the cartridges in place.

[0017] A safety switch 28 is provided on the front of the control unit 21 to engage a stop member 29 attached to the inside of the door 3, when in the closed position. If the door 3 is opened while the blowing operation is being carried out, the release of the switch stops the operation.P2665GB

Claims

CLAIMS1 . A dust extraction system comprising: an extractor unit having an inlet, a primary filter, and a fan for drawing air from the inlet through the filter; and a secondary filter unit comprising a hollow body having: an inlet connectable to a source of dust; an inlet flow passage with the body extending downwardly from the inlet into proximity with a dust tray in the lower part of the body; an outlet connected to the extractor unit; an outlet flow passage within the body extending upwardly from the dust tray to the outlet, whereby the air flow in the body reverses direction when passing from the inlet flow passage to the outlet flow passage above the dust tray; a removable filter located within the outlet flow passage; and at least one baffle located within the inlet flow passage and configured to introduce turbulence and to slow the air flow thereby allowing agglomeration of dust particles, the agglomerated particles being retained in the dust tray.

2. A dust extraction system according to Claim 1 , wherein the baffle comprises a plate set at an oblique angle to the direction of flow in the inlet flow passage, the plate having a plurality of apertures therethrough.

3. A dust extraction system according to Claim 2, wherein the baffle extends over only a portion of the width of the inlet flow passage.

4. A dust extraction system according to Claim 1 , 2 or 3, wherein the dust tray is removably mounted within the body.

5. A dust extraction system according to any preceding claim, further comprising a compressed air source for periodically providing a reverse air flow through the filter to dislodge dust particles therefrom on to the dust tray.

6. A dust extraction system according to any preceding claim, wherein the filter comprises a parallel pair of filter cartridges, each cartridge having a tubular filter medium, the interior of each cartridge communicating with the outlet and the exterior of each filter cartridge communicating with the space above the tray.P2665GB7. A dust extraction system according to Claim 6, when dependent on Claim 5, wherein the compressed air source is configured to supply a reverse flow alternately to the filter cartridges, whereby one can remain in use while the other is supplied with the reverse air flow to dislodge dust particles therefrom.

8. A dust extraction system according to Claim 7, comprising a controller configured to operate the compressed air source according to a pre-programmed schedule.

9. A dust extraction system according to any of Claims 5 to 8, comprising a nozzle positioned above the filter and connected to the compressed air source.

10. A dust extraction system according to any of Claims 5 to 9, wherein the compressed air source includes a pressurised tank.P2665GB

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