IL114963A - Abrasive blasting head - Google Patents

Description

man ΙΑΙΚΊ ABRASIVE BLASTING HEAD Elblast Ltd 31-7-95 specsOOl/95013-IL.DOC FIELD OF THE INVENTION The present invention relates generally to abrasive blasting of surfaces, and in particular to devices for generating and accelerating a stream of liquid-abrasive mixture use of compressed air.

BACKGROUND OF THE INVENTION Numerous devices are known for abrasive blasting of surfaces, for the purpose of removing therefrom paint, rust or other substances.

An indication of the sate of the art is provided by US Patents Nos. 4,633,623; 4,771,580; 4,922,664; 4,995,202; 5,054,249; and 4,965,968, as well as by USSR Patent No. 1,227,440 to Eizner, one of the present inventors.

US Patent No. 5,054,249 to Rankin discloses a method and apparatus for liquid-abrasive cleaning, wherein abrasive particles are accelerated in a high pressure stream and transmitted by a liquid onto a surface to be cleaned. There is further provided a flow regulator for regulating the flow rate of the abrasive particles as they are drawn into the nozzle by the high pressure liquid stream.

US Patent No. 4,922,664 to Spinks et al relates to a liquid sand blast nozzle and to a method of use thereof. In this publication there is described delivery of air and an abrasive mixture to a propulsion chamber, whereat it mixes with water supplied at high pressure, thereby to cause acceleration of the abrasive mixture.

US Patent No. 4,633,623 to Spitz is directed to a sand blasting nozzle, particularly for the decontamination of radioactive surfaces. This nozzle comprises an intake device able to produce a flat water jet passing through a vacuum chamber into which a mixture of gas and abrasive particles is delivered.

Disclosed in US Patent No. 4,771,580 to Male is a device for spraying particulate material, wherein a stream of dry sand is delivered to a nozzle unit which is disposed in a nozzle housing so as to form an annular passage between the nozzle unit and the housing. Water under pressure is delivered to this passage so as to form an annular water stream at the nozzle outlet. The annular water stream surrounds a stream of dry sand provided via the nozzle outlet, thereby to accelerate the sand stream, while at the same time reducing the dispersion of dust into the atmosphere.

US Patent No. 4,965,968 to Kelsey describes a blast cleaning device employing as an abrasive particles of ice or other frozen liquids.

Many of the above-described devices are characterized by an insufficient flow rate of abrasive material.

US Patent No. 4,995,202 to Gardener et al describes a nozzle unit and method for using wet abrasives to clean hard surfaces, wherein an increased flow rate is achieved as compared with that achieved in prior devices. There is provided a nozzle unit formed from two members joined together and having a bore shaped as a venturi nozzle. Inside the nozzle is an annular cavity connected into a source of water. There is also provided a mixing chamber connected by air passages with air surrounding the nozzle unit. In this chamber an abrasive material, such as sand, mixes with water and air to form a wet abrasive stream.

While, as stated, the above device enables an increased volumetric flow rate, a disadvantage of this apparatus is the intensive wear of the nozzle outlet edge due to the action of the abrasive material.

An attempt to overcome this problem is found in USSR Patent No. 1,227,440 to Eizner, one of the present inventors. This patent discloses a nozzle in which an air-abrasive stream is generated and accelerated by provision of an annular air stream at the nozzle outlet. The air stream is provided by supply of pressurized air via longitudinal passages formed in the nozzle side surface, thereby to surround the abrasive stream at the nozzle outlet edge, thus also providing some protection to the nozzle outlet edge from abrasion by the abrasive stream.

In this nozzle, the air energy is not fully exploited for acceleration of the abrasive, thereby resulting in a relatively slow flow rate. Furthermore, while some protection of the nozzle edge from wear is provided, it has been found that at the nozzle outlet edge, there is irregular peripheral distribution of the abrasive, thereby providing a corresponding irregular wear of the outlet edge.

SUMMARY OF THE INVENTION The present invention seeks to provide an improved abrasive blasting head which overcomes disadvantages of known art.

In particular, it is sought to provide an abrasive blasting head which employs a source of pressurized air to substantially reduce abrasive wear on the blasting head, and which, further, is constructed so as to exploit the energy of the air source so as to provide a high flow rate of the resultant abrasive stream.

There is thus provided, in accordance with a preferred embodiment of the invention, an improved abrasive blasting head which includes a housing, having one or more pressurized gas inlets for permitting entry of a pressurized gas into the interior of the housing, the housing further having an outlet; and nozzle apparatus arranged in the housing, wherein the nozzle apparatus includes an inlet for a liquid-abrasive suspension, a central passage for permitting throughflow of a stream of liquid-abrasive suspension, the central passage extending between the inlet and an outlet arranged in coaxial registration with the housing outlet, apparatus for permitting entry of the pressurized gas from the interior of the housing into the central passage of the nozzle apparatus at high velocity, thereby to draw the liquid-abrasive suspension therethrough in the form of a stream, including apparatus for providing an annular gas cushion between the stream and the nozzle apparatus, thereby to prevent substantial abrasive wear of the nozzle apparatus by the liquid-abrasive stream.

Additionally in accordance with a preferred embodiment of the invention, the central passage extends along a longitudinal axis, and the apparatus for permitting entry includes at least one annular intake passage extending along the axis, for directing an annular stream of gas from the interior of the housing into the passage so as to flow along the central passage, coaxially with and surrounding the liquid-abrasive stream, and including apparatus for adjusting the cross-sectional area of the annular passage, thereby also to adjust the velocity of the annular gas stream and thus also the pressure thereof.

Further in accordance with a preferred embodiment of the invention, the nozzle apparatus includes a rear nozzle member including the liquid-abrasive inlet, an outlet, and a passage extending between the inlet and the outlet, and further defining an outlet end having a generally conical external configuration and extending along the longitudinal axis; and one or more additional nozzle members arranged along the longitudinal axis and including an inlet, an outlet, a passage extending between the inlet and the outlet, and openings formed about the periphery thereof so as to permit flow of pressurized gas into the passage from the housing, and wherein the inlet of the additional nozzle member has a generally conical internal configuration, and wherein the conical inlet end of the additional nozzle member partially surrounds the conical outlet end of the rear nozzle member, thereby to define an at least partially annular, conical passage therebetween, thus constituting the at least one annular intake passage.

Additionally in accordance with a preferred embodiment of the invention, wherein the apparatus for adjusting the cross-sectional area of the annular passage includes apparatus for connecting to the rear nozzle member the at least one additional nozzle member adjacent thereto, including apparatus for permitting selectable linear translation of the adjacent nozzle member along the axis, relative to the rear nozzle member, and apparatus for selectably locking the adjacent nozzle member.

Further in accordance with a preferred embodiment of the invention, wherein the at least one additional nozzle member includes at least an intermediate nozzle member adjacent to the rear nozzle member, and a front nozzle member adjacent to the intermediate nozzle member wherein the conical inlet end of the intermediate nozzle member partially surrounds the conical outlet end of the rear nozzle member, thereby to define an at least partially annular, conical passage therebetween, thus constituting an annular gas intake passage, and wherein the conical inlet end of front nozzle member partially surrounds the conical outlet end of the intermediate nozzle member, thereby to define an at least partially annular, conical passage therebetween, thus constituting a further annular gas intake passage.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood and appreciated form the following detailed description, taken in conjunction with the drawings, in which: Fig. 1 is a side-sectional illustration of an abrasive blasting head constructed in accordance with a preferred embodiment of the invention; Fig. 2 is a side-sectional illustration of the nozzle unit of the blasting head of Fig. 1; Figs. 3A-3D are side elevations of the housing, rear nozzle member, intermediate nozzle member, and front nozzle member, respectively, of the present invention; and Figs. 4A, 4B and 4C are cross-sectional views of the blasting head of the present invention in use, as seen in Fig. 1, and taken along respective cut lines 4A-4A, 4B-4B and 4C-4C therein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to Fig. 1, there is provided an abrasive blasting head, indicated generally by reference numeral 10, constructed in accordance with a preferred embodiment of the present invention. The blasting head 10 has a housing 12, seen also in Fig. 3 A, configured as a truncated cylinder, and having a longitudinal axis 11. Housing 12 has a rear end opening 14 (Fig. 3 A) which is closed and hermetically sealed by a cover member 16 (seen also in Fig. 3B), as by a screw fastening. Accordingly, there are seen an internal screw thread, referenced 17, formed in opening 14, and a complimentary external screw thread, referenced 17', formed on cover 16, seen in Fig. 3B. Housing 12 further has a front end portion 18 which has a conical convergence 20, terminating in a cylindrical portion 22 defining an outlet 24 through which a liquid-abrasive stream is discharged.

The housing 12 has at least one gas inlet conduit, referenced 26, via which a gas is provided from a pressurized gas source 27. Typically, the gas employed is air.

Referring now also to Fig. 2, blasting head 10 also includes a nozzle unit, referenced generally 28, disposed longitudinally inside housing 12 so as to form an annular chamber, referenced 29 (Figs. 1, 4A, 4B and 4C) between the exterior of nozzle unit 28 and the interior surface 30 of housing 12.

It is seen that nozzle unit 28 includes a rear nozzle member 32 (shown also in Fig. 3B), at least one intermediate nozzle member 34 (shown also in Fig. 3C), and a front nozzle member 36 (shown also in Fig. 3D).

Referring now to Figs. 1, 2 and 3B, rear nozzle member 32 has a generally cylindrical shape and is formed internally so as to define a longitudinal passage 38, extending between an inlet 40 and an outlet 42. Externally, nozzle member 32 has a tapered configuration at its outlet end 33, thereby to deflect an incoming radial gas stream in a generally axial direction, as seen in Fig. 1. Nozzle member 32 further has a pair of rear and forward exterior screw threads formed thereon, respectively referenced 44 and 46. Rear screw thread 44 is provided for screwing engagement with a corresponding, interior screw thread 44' provided in an opening 48 formed in cover member 16, and through which rear nozzle member 32 extends such that inlet 40 thereof projects externally of housing 12. Screw threads 44 and 44' are provided so as * to facilitate selectable translation of rear nozzle member 32 along axis 11, relative to housing 12. A lock nut, referenced 50, is provided for screwing association with rear exterior screw thread 44 thereby to lock rear nozzle member 32 in a selected position.

Referring now to Figs. 1, 2 and 3C, intermediate nozzle member 34 has a generally elongate, conical shape, tapering towards a front end 52 thereof, and is formed internally so as to define a longitudinal passage 54, extending between a rear end 56 and an outlet 58, formed at front end 52. Rear end 56 is formed of a rear wall 60, having an opening 62 through which the outlet 42 of rear nozzle member 32 extends, and an intermediate air intake chamber, referenced generally 64. Air intake chamber 64 is essentially a hollow space defined by rear wall 60 and a plurality of openings 66 formed between axial ribs 67 (Fig. 3C), and through which air is supplied to the air intake chamber 64 and passage 54 of nozzle member 34. A rearwardly extending portion 68 (Fig. 2) of passage 54 has a conical configuration and accommodates the outlet end of rear nozzle member 32. The remainder of passage 54 is substantially cylindrical.

As described, the tapered outlet end 33 of rear nozzle member 32 extends through an opening 62 formed in rear wall 60 of intermediate nozzle member 34. As seen, opening 62 is provided with an internal screw thread 70, which is configured for screwing association with forward exterior screw thread 46 (Fig. 3B) of rear nozzle member 32, thereby enabling linear translation of intermediate member 34 along axis 11, as desired. A lock nut 72 (Figs. 1 and 2) is also provided for selectable locking of intermediate nozzle member 34 with rear nozzle member 32.

Referring now to Figs., 1, 2 and 3D, front nozzle member 36 has a truncated, conical shape, tapering towards a front end 74 thereof, and is formed internally so as to define a longitudinal passage 76, extending between a rear end 78 and a front end outlet 80. Rear end 78 is formed of a rear wall 82, having an opening 84 through which the front end 52 of intermediate nozzle member 34 extends, and an air intake chamber, referenced generally 86. Air intake chamber 86 is essentially a hollow space defined by rear wall 82 and a plurality of openings 88 formed between a plurality of axial ribs 89, and through which air is supplied to the passage 76 of nozzle member 36. A rear portion 90 of passage 76 has a conical configuration and accommodates the front end 52 of intermediate nozzle member 34. The remainder of passage 76 is substantially cylindrical.

As described, the tapered front end 52 of intermediate nozzle member 34 extends through an opening 84 formed in rear wall 82 of front nozzle member 36. As seen, opening 84 is provided with an internal screw thread 92, which is configured for screwing association with an exterior screw thread 94 (Fig. 3C) formed on intermediate nozzle member 34, thereby enabling linear translation of front nozzle member 36 along axis 11 (Fig. 3 A), as desired. A lock nut 96 is also provided for selectable locking of front nozzle member 36 with intermediate nozzle member 34.

It will thus be appreciated that the three nozzle members 32, 34 and 36 are disposed in series along and coaxially with longitudinal axis 11, and define a longitudinal passage through which a fluid-abrasive stream can be dispensed. The fluid-abrasive stream consists of two phases, namely, a liquid abrasive phase, which, as indicated in Fig. 1, is provided from a suitable a pressurized liquid-abrasive source to inlet 40 of rear nozzle member; and a gaseous phase, which, as described, is supplied, via inlet conduit 26, to the interior of housing 12.

Referring now also to Figs. 4A-4B, it is seen that, in fact, the pressurized gas is supplied to the gas intake chambers 64 and 86 of the respective intermediate and front nozzle members, and is thereafter deflected in a generally axial direction, towards outlet 24. This gives rise to formation of a high pressure annular gaseous protective "skirt", referenced 98, about the liquid-abrasive stream, referenced 100, thereby to protect the interior faces of the intermediate and front nozzle members, 34 and 36, from contact, and thus abrasion, by exposure to the liquid-abrasive stream.

In more detail, the blasting head 10 of the present invention operates as follows.

A pressurized gas, preferably compressed air, from a pneumatic circuit or compressor 27 (Fig. 1), is delivered via inlet conduit 26 to annular chamber 29 (Figs. 1 and 4A-4C). The gas exits blasting head 10 via outlet 24. From the annular chamber 29 the compressed gas passes through radial openings 66 and 89 of intermediate and front nozzle members 34 and 36, and into the passages thereof, 54 and 76, where it is accelerated and, as mentioned, exhausted to atmosphere via outlet 24.

The described flow of gas causes a reduction in pressure near the outlet 42 of the rear nozzle member 32, resulting in an inflow of liquid-abrasive mixture from a liquid-abrasive source 31, via inlet 40 and passage 38 of the rear nozzle member 32. The described inflow of this mixture is caused by the difference between the external atmospheric pressure and the reduced pressure near the outlet 42 of the rear nozzle member 32. As the liquid-abrasive mixture passes from passage 38 of rear nozzle member 32 into passage 54 of intermediate nozzle member 34, it is accelerated due to the drop in pressure therein, and it is further accelerated, by a similar drop in pressure, induced by the inflow of pressurized gas, as it passes through passage 76 of front nozzle member 36 and out through the outlet 80 thereof in the form of a concentrated stream.

The maximum velocity of the liquid-abrasive stream 100 is reached at the outlet 24 from the blasting head 10. This is due to the further acceleration caused by a portion of the pressurized gas flowing directly from annular chamber 29 to outlet 24.

It will further be appreciated, as described above briefly in conjunction with Figs. 4A, 4B and 4C, that entry of the pressurized gas into passages 54 and 76 of nozzle members 34 and 36, via openings 66 and 88, constitutes annular skirt or cushion, which prevents contact of the liquid-abrasive phase from coming into contact with the interior passage surfaces. This prevents abrasive wear of these surfaces, thereby greatly extending the useful life thereof.

As described, the three nozzle members are mutually adjustable along axis 11. Axial adjustment of one nozzle member relative to an adjoining nozzle member causes a corresponding change in the distance between the tapered surface of the outlet portion of the rearmost of two adjoining nozzle members and the conical surface of the interior of the more forward of the two nozzle members. It will be appreciated that this also causes a change in the cross-sectional area through which the pressurized gas enters the passage of the more forward of the two nozzle members, and thus, for a constant volumetric gas flow, causes an adjustment in the velocity of the gas stream therethrough, and a corresponding change in the gas pressure. As will be appreciated by persons skilled in the art, and as described above, the ability to control the pressure of the gas flow through the nozzle members of the blasting head of the invention, inherently provides the ability to control or adjust the rate of volumetric flow of the liquid-abrasive stream through blasting head 10, in accordance with different types of abrasive media, gas pressure, blasting surface conditions, and other on-site considerations.

Among different types of abrasive media that may be used, are materials such as aluminum oxide powder, glass and polymer balls, and ice particles.

In summary, use of the present invention permits an increase of the abrasive stream energy by increasing the speed of the liquid-abrasive flow at the nozzle outlet, thereby also inherently maximizing its efficiency, as well as a substantial reduction of abrasive wear of the nozzle elements due to the formation of the described annular gas cushion surrounding the liquid-abrasive stream.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been shown and described hereinabove, merely by way of illustrative example. Rather, the scope of the present invention is limited solely by the claims, which follow:

Claims (8)

1. An improved abrasive blasting head comprising: a housing, having at least one pressurized gas inlet for permitting entry of a pressurized gas into the interior of said housing, said housing further having an outlet; and nozzle means arranged in said housing, wherein said nozzle means comprises: an inlet for a liquid-abrasive suspension, a central passage for permitting throughflow of a stream of liquid-abrasive suspension, said central passage extending between said inlet and an outlet arranged in coaxial registration with said housing outlet, means for permitting entry of the pressurized gas from said interior of said housing into said central passage of said nozzle means at high velocity, thereby to draw the liquid-abrasive suspension therethrough in the form of a stream, including means for providing an annular gas cushion between the stream and the nozzle means, thereby to prevent substantial abrasive wear of said nozzle means by the liquid-abrasive stream.

2. An improved abrasive blasting head according to claim 1, wherein said central passage extends along a longitudinal axis, and said means for permitting entry comprises at least one annular intake passage extending along said axis, for directing an annular stream of gas from said interior of said housing into said passage so as to flow along said central passage, coaxially with and surrounding the liquid-abrasive stream, and including means for adjusting the cross-sectional area of said annular passage, thereby also to adjust the velocity of the annular gas stream and thus also the pressure thereof.

3. An improved abrasive blasting head according to claim 2, wherein said nozzle means comprises: a rear nozzle member comprising said liquid-abrasive inlet, an outlet, and a passage extending between said inlet and said outlet, and further defining an outlet end having a generally conical external configuration and extending along said longitudinal axis; and at least one additional nozzle member arranged along said longitudinal axis and comprising an inlet, an outlet, a passage extending between said inlet and said outlet, and openings formed about the periphery thereof so as to permit flow of pressurized gas into said passage from said housing, and wherein said inlet of said additional nozzle member has a generally conical internal configuration, and wherein said conical inlet end of said additional nozzle member partially surrounds said conical outlet end of said rear nozzle member, thereby to define an at least partially annular, conical passage therebetween, thus constituting said at least one annular intake passage.

4. An improved abrasive blasting head according to claim 3, wherein said means for adjusting the cross-sectional area of said annular passage comprises means for connecting to said rear nozzle member said at least one additional nozzle member adjacent thereto, including means for permitting selectable linear translation of said adjacent nozzle member along said axis, relative to said rear nozzle member, and means for selectably locking said adjacent nozzle member.

5. An improved abrasive blasting head according to either of claims 3 or 4, wherein said at least one additional nozzle member comprises at least an intermediate nozzle member adjacent to said rear nozzle member, and a front nozzle member adjacent to said intermediate nozzle member wherein said conical inlet end of said intermediate nozzle member partially surrounds said conical outlet end of said rear nozzle member, thereby to define an at least partially annular, conical passage therebetween, thus constituting an annular gas intake passage, and wherein said conical inlet end of front nozzle member partially surrounds said conical outlet end of said intermediate nozzle member, thereby to define an at least partially annular, conical passage therebetween, thus constituting a further annular gas intake passage.

6. An improved abrasive blasting head according to claim 5, wherein said means for adjusting the cross-sectional area of said annular passage comprises: first means for connecting said intermediate nozzle member to said rear nozzle member, including means for permitting selectable linear translation of said intermediate nozzle member along said axis, relative to said rear nozzle member, and means for selectably locking said intermediate nozzle member relative to said rear nozzle member, and second means for connecting said front nozzle member to said intermediate nozzle member, including 114963/2 means for permitting selectable linear translation of said front nozzle member along said axis, relative to said intermediate nozzle member, and means for selectably locking said front nozzle member relative to said intermediate nozzle member.

7. An improved abrasive blasting head according to any of claims 1-6, and substantially as shown and described in conjunction with any of Figs. 1-4C.

8. An improved abrasive blasting head according to any of claims 1-6, and substantially as shown in any of Figs. 1-4C. For the Applicant, Yirm ya u . Ben-David Patent Attorney office\specsOO l\95013-iJ.doc