GB2114923A

GB2114923A - Abrasive marking device

Info

Publication number: GB2114923A
Application number: GB08204371A
Authority: GB
Inventors: Philip Arthur Aston
Original assignee: STOP THIEF Ltd
Current assignee: STOP THIEF Ltd
Priority date: 1982-02-15
Filing date: 1982-02-15
Publication date: 1983-09-01
Also published as: GB2114923B

Abstract

A device for marking a surface by the blasting of abrasive particles has a stencil holder in the form of a container (1) with an open end which is applied to the surface to be marked. A plastics stencil (3) is held in position by a spring clip (5) which grips a folded portion (4) of the stencil against the bottom wall of the container, with the edges of the stencil (3) overlapping forwardly directed bearing surfaces on the container. To prevent the escape of abrasive particles from the front and rear faces of the stencil, a flexible foam rubber or foam plastics sealing ring (10) encircles the stencil so as to bear against the surface to be marked around the perimeter of the marking area. <IMAGE>

Description

SPECIFICATION Abrasive marking device This invention relates to an abrasive marking device, intended primarily for marking a pattern on a glass surface by projecting abrasive particles at a stencil adjacent the surface.

Such devices are known in particular for marking vehicle registration numbers or other means of identification on vehicle windows to discourage vehicle thieves intending to sell stolen vehicles with changed registration plates. In such devices a stencil holder in the form of an open ended box is fitted with the required stencil covering the open end, and the box is held against the vehicle window whilst the abrasive particles are blasted by a compressed air source from the other end of the box. A difficulty of many of these devices is that the high velocity of the abrasive particles leads to the escape of particles, for example around the edges of the stencil, leading to inadvertant marking of nearby parts of the glass surface or vehicle bodywork.Escaping abrasive may also cause discomfort for the operator who may need a mask to prevent inhalation of particles and dust, and a visor for eye protection.

It is an object of this invention to provide a device which largely prevents unwanted escape of abrasive particles.

According to one aspect of this invention, there is provided a device for marking a pattern on a surface by abrasive blasting, wherein the device comprises a stencil container having an opening at one end surrounded by a sealing member, means connected to the container for directing abrasive particles towards the open end, and a stencil removably mounted in the container at the open end within the sealing member. The stencil does not interfere with the sealing of the open end.

According to another aspect of the invention the stencil container has means for releasably gripping a folded portion of a stencil, which portion extends inwardly away from the open end of the container. The stencil preferably comprises a folded sheet of abrasive resistant plastics material, the main, perforated portion of which lays against the surface to be marked surrounded by the sealing member. The folded portion extends approximately perpendicularly away from the said surface and is held by gripping means in the form of a spring metal clip arranged to pinch the folded portion between the clip and a planar interior wall of the box.When the abrasive particles are directed at the stencil, flexibility of the stencil material at the fold allows the main portion to take up a position in which it lies flat against the surface to be marked so as to produce a clear, neat engraving of the required pattern on the surface. The clip serves merely to locate the stencil in the open end of the container and to prevent it dropping from the container when it is removed from the marked surface.

In the preferred embodiment of the invention the container opening is rectangular, with the clip extending along the bottom edge of the opening, and with outwardly facing surfaces on the other three sides for abutting the inner face of the stencil. The stencil thus covers the whole opening, abrasive striking the surface to be marked only through the perforations in the stencil. The sealing member is preferably a relatively soft flexible material, such as foam rubber, and is in the form of a ring encircling the opening outside the stencil and the bearing surfaces. The seal material is advantageously slip resistant to reduce the possibility of moving the stencil container on the marking surface during use.

The invention is illustrated by way of example in the drawings, in which: Fig. 1 is a sectioned side view of the preferred embodiment of the invention; Fig. 2 is a front end view of the apparatus of Fig. 1; and Fig. 3 is a perspective view of a stencil.

Referring to the drawings, a preferred marking device in accordance with the invention comprises a stencil holder 1 having an interior space 2 open at its front end, which is to the left as seen in Fig. 1. In use of the device, the front end opening is covered by the main, perforated portion of a stencil 3 (see Fig. 3), the folded portion 4 of the stencil being gripped by an inclined spring metal clip 5 attached to a raised block 6 on the bottom wall of the holder 1. To allow the stencil 3 to overlap the forward facing surfaces of the holder 1, a slot 7 is cut into the base of each side wall to receive the side edges of the folded portion 4. The stencil 3 is preferably made from a flexible p.v.c.

sheet material, for example "Mylar" (RTM), and is less than 0.5 mm in thickness.

The rear end of the device is provided with a circular or oval aperture 8 for the nozzle 9 of an abrasive gun. In operation of the device, the front end of the stencil holder 1 is brought into contact with t:ie surface to be marked (not shown), and airborne abrasive particles, e.g. silica or aluminium oxide, are directed at high velocity towards the front end of the holder. The front end opening is surrounded by soft foam rubber or plastics sealing ring 10 bonded to rebated forward facing perimeter surfaces of the holder 1 so as to surround the stencil and prevent escape of abrasive from the marking area. In Fig. 1, the sealing ring 10 is shown uncompressed.Before the front end of the holder 1 is brought into contact with the surface to be marked, the stencil 3 may be spaced slightly from the bearing surfaces of the holder 1 as shown by the dotted lines, but as the holder is pressed against the surface to be marked, the sealing ring 10 is compressed into the rebate and the stencil 3 is pushed upright to lay flat against the marking surface. The folded portion 4 may also be pushed further under the clip 5.

Once the sealing ring 10 is in its compressed sta e, , blasting of the surface to be marked can be carried out, the nozzle 9 being moved from side to side in the aperture 8 for uniform coverage of the stencil. Spent abrasive collects in the bottom of the holder 1 and is conducted away by a pipe connected to an outlet 11, either to be deposited away from the vicinity of the holder 1 or to be collected for recirculation.

The interior surfaces of the holder 1 are lined with an abrasion resistant sheet material 12, such as Perspex (RTM) or polyvinylchloride (p.v.c.). This material is also used to form a screen 1 3 for the clip 5 and block 6.

The device enables clear engravings to be made on flat or slightly curved smooth surfaces such as vehicle windows with minimum unwanted escape of abrasive material and dust.

Claims

1. A device for use in marking a surface by abrasive blasting, which device has a blasting chamber with a front blast opening masked by a stencil and is arranged for location against the surface so that abrasive particles supplied to the chamber from propelling means are projected at the surface through the stencil, wherein the device includes external sealing means extending around the stencil for engaging the surface around the perimeter of an area to be marked.

2. A device according to claim 1, wherein the stencil comprises a sheet of flexible plastics material having a perforated portion covering the blast opening and a mounting tongue extending rearwardly from an edge of the perforated portion.

3. A device according to claim 1, wherein the chamber is defined by a container with a front wall portion surrounding the opening and having a forwardly directed surface extending around the opening, and wherein the sealing member comprises a flexible gasket located in registry with the forwardly directed surface.

4. A device according to claim 3 wherein the gasket is a loop of foam material.

5. A device according to claim 3 or claim 4, wherein the stencil comprises a ;heel of flexible plastics material extending across the blast opening and having edge portions which overlap a bearing surface within an area surrounded by the gasket, the bearing surface forming a part of the forwardly directed surface.

6. A device according to claim 5 wherein the gasket is located on a rebated part of the forwardly directed surface.

7. A device according to claim 5 or claim 6, wherein the blast opening is rectangular.

8. A device according to claim 7, wherein the stencil has a perforated portion extending across the blast opening and overlapping the bearing surface on three sides of the opening, and a rearwardly folded mounting portion which lies on an inner surface of the said front wall portion along the fourth edge of the opening.

9. A device according to claim 8 including a spring clip for holding the mounting portion in position on the inner surface.

10. A device according to claim 8 or claim 9, wherein the front wall portion has internal grooves at opposite ends of the fourth edge of the opening for housing side edges of the folded portion of the stencil.

11. A device according to any of claims 3 to 11, wherein the container has a rear wall with an aperture for receiving the nozzle of means for propelling the abrasive material.

12. A device according to any of claims 3 to 11, wherein the container has an outlet for the disposal of spent abrasive particles.

13. A device for use in marking a surface by abrasive blasting, which device has a blasting container with a front blast opening masked by a removable stencil and is arranged for location against the surface so that abrasive particles supplied to the container from propelling means are projected at the surface through the stencil, wherein the stencil comprises a perforated sheet of flexible material masking the blast opening and a mounting portion extending rearwardly from the perforated sheet to mounting means associated with a wall of the container.

14. An abrasive marking device constructed and arranged substantially as herein described and shown in the drawing.