GB2207625A

GB2207625A - Engraving by blasting with erosine material

Info

Publication number: GB2207625A
Application number: GB08717138A
Authority: GB
Inventors: Michael John Ryan; Alfred Michael Wright
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-07-20
Filing date: 1987-07-20
Publication date: 1989-02-08
Also published as: GB8717138D0

Abstract

For engraving a glass plate 4, a mask is applied to it and a cowl having a vacuum connection 2 is applied to the glass at the mask. A gun 5 extends into the cowl which has a window for directing erosive material from the gun at glass areas exposed through the mask. Air is withdrawn from the cowl 1 through the vacuum connection to maintain a partial vacuum in it, to remove erosive material and keep the cowl in position. The erosive material is preferably supplied from a vessel which is pressurised by an air compressor 10, and an industrial vacuum cleaner 3 is connected to the vacuum connection 2. <IMAGE>

Description

Engraving Method and Apparatus The present invention relates to a method and apparatus for engraving in particular though not exclusively, vitreous material.

In a known method of engraving plate glass for a shop front for instance, the glass plate is positioned in a vacuum chamber and a mask is placed on the plate leaving exposed those parts of the glass which are to be engraved.

The actual removal of glass is performed by directing a stream of erosive medium such as aluminium oxide powder at the glass. The erosive medium is drawn via a venturi into.a pressure air stream from a holding vessel held at ambient pressure. In order to avoid build up of pressure in the vacuum chamber, the pressure air, introduced into the chamber via a gun used for directing the medium carried by the air, is withdrawn by a vacuum pump. Whilst this known method provides satisfactory engraving, it is expensive due to the necessity of working on the plate glass prior to incorporation of it into a building or even more disadvantageously, when the glass has been temporarily removed from the building.

The object of the present invention is to provide a method of and apparatus for in situ engraving of glass and indeed other materials.

In accordance with a first aspect of the invention a method of engraving consisting the steps of: (i) applying a mask to material to be engraved, the mask leaving exposed area(s) of the material to be eroded, (ii) applying a cowl to a locality of the material including the exposed area(s), (iii) withdrawing gas from within the cowl to create a partial vacuum therein, iv) passing a stream of compressed gas and erosive medium into the cowl from outside it, and (v) directing the said stream at the material to be eroded, thereby engraving the material.

When a sufficient depth of erosion has been achieved, the erosive stream is stopped; and the cowl and the mask are removed. Since the entire piece of material to be engraved is not enclosed in a vacuum chamber, the engraving can be performed in situ-without requirement for the piece of material to be dismantled if it is installed.

The mask, or an extension thereof, is preferably applied to an area having an extent beyond the cowl, whereby accidental misdirection of the erosive stream does not cause unwanted erosion.

The partial vacuum within the cowl is preferably such as to secure the cowl in position on the material to be engraved, at least when an erosive stream direction gun passes through an aperture for it in the cowl.

The erosive stream may be created conventionally by passing a compressed gas, preferably air, through a venturi to draw the erosive material into it. However, in the preferred embodiment, the erosive material is itself pressurized for production of the erosive stream from erosive material removed from the holding vessel by injection of pressure air to the vessel. Preferably further pressure air is mixed with the removed erosive medium. Conveniently the mixing occurs at a venturi. Pressurization of the medium in the vessel has the advantage of lowering the overall pressure of the erosive stream since less pressure air is required to move the erosive medium. The result is that less air requires to be evacuated from the cowl.

In the preferred embodiment, injection of pressure to the holding vessel and dumping of pressure therein is effected on switching ON and OFF respectively of the erosive stream.

The engraving may be carried out in more than one stage. At each stage following the first, the cowl is removed and one or more piece(s) of the mask are removed allowing deeper subsequent erosion of areas previously exposed than areas now freshly exposed.

According to a second aspect of the invention, there is provided apparatus for engraving with an erosive stream area(s) exposed through a mask of a material to be engraved, the apparatus including a cowl for delimiting locally to the exposed areas a partial vacuum, the cowl having a front perimeter for abutment against the mask and/or extension(s) thereof and/or the material to be engraved, walls extending rearwards from the front perimeter to substantially enclose with the material to be engraved - a volume in which the partial vacuum is established when the cowl is in use, an outlet for partially withdrawing therethrough the internal atmosphere of the cowl, and an aperture through which the erosive stream can be passed into the cowl.

Preferably the front perimeter of the cowl is provided with a seal for co-operating with the mask/extension/material.

Conveniently the seal is of a material providing frictional interaction with the mask/extension/material whereby the cowl is held in position by establishment of the partial vacuum therein. In the preferred embodiment the seal is of soft foam silicone elastomeric material to accommodate contours in the material to be engraved.

The cowl preferably has a transparent window for viewing the direction of the erosive stream towards the area(s) to be eroded. The window is conveniently of glass and may be covered interanlly by a protective layer of replaceable plastics material.

Whilst the erosive medium withdrawal outlet may be an open aperture, it is preferably a duct opening inside the cowl at a slot along a bottom extent of the front perimeter.

An outer end of the outlet is preferably provided with a vacuum pipe connection fitting.

The aperture for the erosive stream, which will normally pass into the cowl via a lance or gun, is preferably fitted with a resilient flap or flaps which deflect away from the lance or gun to permit air flow into the cowl at the aperture. A greater mass flow of air is withdrawn in use from the outlet than enters the cowl with the erosive stream and the balance passes in at the aperture, across which is present a pressure differential maintaining the partial vacuum.

The apparatus of the invention includes in the preferred embodiment a pressure vessel for the erosive medium, the vessel having a connector for supplying pressurized gas into it, an outlet for erosive medium therefrom and a mixer, preferably a venturi, for mixing further pressurized gas with erosive medium leaving the vessel under the influence of the pressurized gas therein.

Preferably the vessel has an ON/OFF valve for controlling supply of pressurized gas both into the vessel and to the mixer. The valve preferably dumps to ambient any pressure in the vessel when in its OFF position. The valve is conveniently foot operated.

To help understanding of the invention, a specific embodiment thereof will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of engraving apparatus of the invention; Figure 2 is cross-sectional side view of a cowl in accordance with the invention and shown in Figure 1; and, Figure 3 is a rear view of the cowl of Figure 2.

Referring first to Figure 1, there is shown an engraving apparatus including a cowl 1 having a connection 2 via which it is connected to a conventional industrial vacuum cleaner 3, capable of maintaining a partial vacuum of the order of 150mm of mercury with a-substantial- throughflow.

The cowl 1 is described in more detail below. Erosive medium for engraving a glass plate 4 is supplied into the cowl 1 via a lance 5 from a pressure vessel 6. The vessel 6 has a concave top 7 with a central aperture (not shown) normally sealed by an internal sealing disc 8. The disc can be displaced against the force of a spring 9 away from the aperture for filling of the pressure vessel with erosive medium typically fine grade alumina. A conventional air compressor 10 supplies compressed air through line 11 to the pressure vessel via a pedal operated ON/OFF valve 12, a regulator 13 and a Tee union 14. On the downstream side of the union 14 a flow regulating valve 15 leads pressure air to a venturi 16 at the bottom outlet 17 for alumina from the vessel 6.At the venturi 16 alumina blown from the vessel by pressure in it is mixed with air from the valve 15 and passed through line 18 to the lance 5. When the valve 12 is OFF, not only is supply of pressure air into the vessel 6 and to the venturi 16 switched OFF, but also pressure in the vessel is dumped via a non-shown line to the valve 12 and to atmosphere.

Turning now to Figures 2 and 3, the cowl 1 can be seen to be of truncated, rectangular-pyramid shape. It is conveniently of glass reinforced plastics material. A front perimeter 19 carries a soft foam silicone rubber seal 20. A top face of the cowl is apertured and closed by a glass window 21 bonded thereto on the inside of the cowl 1. The glass window is covered on its inside face by a transparent, replaceable plastics material layer 22, which protects the glass from being scratched by stray alumina. The bottom face 23 of the cowl has an inside wall 24 defining with the face 23 a duct 25 leading to the vacuum connection 2. The duct 25 opens inside the cowl at an elongate slot 26, extending along a lower, straight portion 27 of the front perimeter 19.At the truncated rear of the cowl, an aperture 28 is provided with a rubber fitting 29 having four flaps 30, each extending radially inwards and partially across the aperture 28.

In use, a mask 31 - typically of photo-resist material is applied to the glass plate 4. The area surrounding the mask 31 is masked with self-adhesive tape 32 to cover an area at least as great as the extent of the front of the cowl. The vacuum cleaner 3 is switched on to establish a partial vacuum in the cowl. Preferably this is sufficient to hold the cowl in place prior to insertion of the lance 5 through the flapped aperture 28. Once the lance is inserted, the pressure within the cowl is lowered, at least prior to operation of the foot valve 12, due to restriction of the aperture. However, even should the flaps contact the lance at rest, they deflect therefrom when the partial vacuum is established and thereby allow air flow into the cowl and control the partial vacuum, such that a continuous partial vacuum air flow through the cowl is maintained.On operation of the foot valve 12, an erosive stream of alumina and fluidizing air passes through the nozzle emerging at its nozzle 33. The stream is directed at exposed areas 34 of the glass plate 4 by manipulating the lance with its handle 35. Waste alumina is withdrawn at the slot 26 into the vacuum cleaner 3.

After engraving the erosive stream is stopped, allowing alumina propulsive pressure in the vessel 6 to be dumped and the cowl 1 is removed. At this stage, the mask 31 may be modified for instance by removing part of it to expose more glass. Then the engraving may be recommenced on re-establishment of the erosive stream. It may be convenient during such a stage of mask modification to open a bleed 36 in the vacuum line 37 to facilitate removal of the cowl from the plate 4.

The invention is not intended to be restricted to the details of the above described embodiment. In particular, materials other than glass can be engraved.

Claims

1. A method of engraving consisting in the steps of: (i) applying a mask to material to be engraved, the mask leaving exposed area(s) of the material to be eroded, (ii) applying a cowl to a iocality of the material including the exposed area(s), (iii) withdrawing gas from within the cowl to create a partial vacuum therein, (iv) passing a stream of compressed gas and erosive medium into the cowl from outside it, and (v) directing the said stream at the material to be eroded, thereby engraving the material.

2. A method of engraving as claimed in claim 1, including the further steps of removing the cowl, modifying the mask to expose further area(s) to be eroded, and repeating steps (ii) to (v).

3. A method of engraving as claimed in claim 1 or claim 2, including the steps in generation of the said erosive of passing pressure gas to a vessel containing erosive medium and withdrawing pressurized erosive medium from the vessel.

4. A method of engraving as claimed in claim 3, including the further step of mixing, preferably in a venturi, further pressure gas with the pressurized erosive medium withdrawn from the vessel.

5. A method of engraving as claimed in claim 3 or claim 4, including the further steps of interrupting the erosive flow after erosion, and of simultaneously dumping pressure from the vessel to ambient.

6. A method of engraving as claimed in any preceding claim, wherein the mask extends, or is extended by ancilliary material, to an extent beyond the extent of a front periphery of the cowl in contact with the mask and/or the extension thereof.

7. A method of engraving substantially as hereinbefore described with reference to the accompanying drawings.

8. Apparatus for engraving with an erosive stream area(s) exposed through a mask of a material to be engraved, the apparatus including a cowl for delimiting locally to the exposed areas a partial vacuum, the cowl having a front perimeter for abutment against the mask and/or extension(s) thereof and/or the material to be engraved, walls extending rearwards from the front perimeter to substantially enclose with the material to be engraved - a volume in which the partial vacuum is established when the cowl is in use, an outlet for partially withdrawing therethrough the internal atmosphere of the cowl, and an aperture through which the erosive stream can be passed into the cowl.

9. Apparatus as claimed in claim 8, wherein the front perimeter of the cowl is provided with a seal.

10. Apparatus as claimed in claim 9, wherein the seal is of frictional material.

11. Apparatus as claimed in claim 10, wherein the seal is of foam, silicone, elastomeric material.

12. Apparatus as claimed in any -one of claims 8 to 11, wherein the cowl has a transparent window, preferably of glass, for viewing the direction of the erosive stream towards the area(s) to be eroded.

13. Apparatus as claimed in claim 12, wherein the window is covered internally by a replaceable layer of protective plastics material

14. Apparatus as claimed in any one of claims 8 to 13, wherein the erosive medium withdrawal outlet is a duct opening inside the cowl at a slot along a bottom extent of the front perimeter.

15. Apparatus as claimed in any one of claims 8 to 14, wherein an outer end of the outlet is provided with a vacuum pipe connection fitting.

16. Apparatus as claimed in any one of claims 8 to 15, wherein the said aperture is provided with a resilient flap or flaps.

17. Apparatus as claimed in any one of claims 8 to 16, including a pressure vessel for the erosive medium, the vessel having a connector for supplying pressurized gas into it, an outlet for erosive medium therefrom and a mixer, preferably a venturi, for mixing further pressurized gas with erosive medium leaving the vessel under the influence of the pressurized gas therein.

18. Apparatus as claimed in claim 17, wherein the vessel has an ON/OFF valve for controlling supply of pressurized gas both into the vessel and to the mixer.

19. Apparatus as claimed in claim 18, wherein the valve is adapted to dump to ambient any pressure in the vessel when in its OFF position.

20. Apparatus for engraving with.an erosive stream area(s) exposed through a mask of a material to be engraved substantially as hereinbefore described with reference to the accompanying drawings.