GB2124944A - Abrading device - Google Patents

Abstract

An abrading device for marking surfaces, e.g. for marking car windows with the registration number of the car, includes a gun (1) connectible to a source of compressed air via coupling (9), the gun having a barrel (2) and a nozzle (2a) at the end of the barrel. The barrel (2) is connected to a reservoir (6) of an abrasive material by a dip-pipe (7) so that the reduced pressure caused by the flow of air through the barrel (2) causes abrasive material to be drawn into the barrel where it is entrained in the airflow and so propelled onto the surface to be marked (22), optionally through a stencil (21). Spent material is removed under vacuum through coupling (5). The barrel (2) is located in a housing (3) and is surrounded by a perforated shield (11) which prevents the suction applied through coupling (5) from deflecting the material as it leaves the nozzle (2a). <IMAGE>

Description

SPECIFICATION Abrading device The present invention relates to abrading devices and particularly to devices for marking the registration number of a motor vehicle on its windows.

The marking of car windows with the car registration number is a well-known deterrent to thieves. In order to mark a car window, a stencil bearing the number is placed against the window and a jet of gas with abrasive entrained in it is directed through the stencil mask at the window.

One device for marking car windows, which is described in British Published Application No.

2,021,450 A, has a gun for directing abrasive material onto the surface to be marked and a protective housing into which the nozzle of the gun is inserted.

At the end of the housing opposite the gun nozzle, there is an opening, the rim of which is pressed against the surface to be marked, thereby forming a seal, and the abrasive material is then propelled towards the surface by a stream of pressurised gas.

The spent abrasive material, i.e. the material after it has hit the surface, falls back into the housing and is removed therefrom under suction through an exit port.

One disadvantage of the device described above is that the flow of gas within the housing caused by the vacuum removal of spent abrasive material diverts the passage of fresh material from the gun to the surface to be marked. This results in a reduced marking efficiency. On the other hand, if vacuum removal of spent abrasive material is dispensed with, the spent material can become clogged in the housing. A further problem that sometimes occurs in abrading devices, particularly those without vacuum removal of spent material, is that the seal between the housing and the surface to be marked is poor at least partly because the propellant gas causes a higher than atmospheric pressure within the housing. This poor seal can allow abrasive material to escape with consequent safety hazards, and problems with cleanliness.

According to the present invention there is provided an abrading device for marking surfaces which device comprises a gun having a nozzle for propelling abrasive material against a surface to be marked, a protective housing into which the gun nozzle is inserted, the housing having an opening in a position opposite the gun nozzle and also having an axit port for removing spent abrasive material under suction, and a shield located within the housing and extending forwardly of the gun nozzle towards the opening in the housing, the shield having an aperture to allow abrasive material to pass from the gun nozzle to the opening in the housing and being perforated along at least part of its length.

We have found that the use of the shield in an abrading device improves its performance. The optimum effect has been observed when the gun has a barrel, part of which is located within the housing and the only perforations in the shield are in that part of its length behind the gun nozzle. On the other hand, we have also found that the shield is still advantageous when it contains perforations located forwardly of the nozzle.

In a preferred embodiment, the aperture in the shield lies in the opening of the housing. With this arrangement, a compliant sealing bead can be placed around the rim of the shield aperture and also around the housing opening thereby providing a double seal that is effective in preventing the escape to atmosphere of used abrasive material. It will be appreciated that, in this arrangement, the design of the perforations in the shield should be such that they allow spent abrasive material to pass easily out from the inside of the shield under the influence of suction applied to the exit port so as to prevent a build-up of spent material inside the shield.

A device in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawing which shows a schematic cross-sectional elevation of the device.

The device consists of a gun 1 having a barrei 2, and a housing 3 in which most of the gun barrel is located. At the end of the barrel 2, there is a nozzle 2a. Below the housing there is an extension 4 ending in a hose-coupling 5 to which a vacuum line (not shown) is, in operation, attached. Within the extension 4, there is located a hopper 6 containing fine-grained abrasive material, e.g. sand or grit. The inside of the hopper is in communication with the inside of the gun barrel 2 by way of a dip feed-pipe 7 that extends from the barrel 2 into the hopper 6, the hopper being sealed around the pipe by a grommet 8.

The gun 1 has a hose coupling 9 to which, in operation, one end of a pressure hose (not shown) is afixed. The other end of the pressure hose is connected to a source of compressed gas, e.g. a compressor or a gas cylinder. A trigger 10 is provided to permit or prevent compressed gas from passing into the barrel 2.

Inside the housing 3 and extending from one end to the other thereof is a shield 11 which surrounds the gun barrel. The space between the gun barrel 2 and the shield 11 is closed off by means of brush seals 12, while the space between the shield and the housing is sealed by a solid wall 13.

Along the length of the shield 11, but behind the nozzle 2a of the gun, are several perforations 14. The front end of the shield is open and defines an aperture 15.

Sealing beads 16 and 17 are provided around the rim of the housing 3 and the shield 11 respectively.

With the arrangement illustrated, a stencil 21 bearing the mark to be made is applied to the surface 22 to be marked, e.g. by adhesive tape. Alternatively, instead of beads 16 or 17 there may be provided a stencil carrier which holds the stencil against the aperture 15 in a position opposite the nozzle 2a of the gun 1. This latter arrangement is not illustrated.

The device also includes a hand guard 18.

As will be seen from the drawing, the annular space 19 between the shield 11 and the housing 3 is in direct communication with the vacuum coupling 5. The interior 20 of the shield is, in operation, connectible with the source of compressed gas via the coupling 9 and the gun 1 when the trigger is activated.

Before the device is used, the vacuum line and the compressed gas line must be secured to the couplings 5 and 9 (respectively) and the hopper 6 must be filled with abrasive material, e.g. sand. In order to apply a mask to the surface 22, e.g. a vehicle window, a stencil 21 bearing the desired mask is secured to the surface, and the device is pressed against the surface with the mask on the stencil being completely covered by the aperture 15 of the shield 11. The beads 16 and 17 should be pressed firmly against the surface to provide a good seal.

Then the trigger 10 is squeezed allowing the compressed gas to pass through the barrel 2. The passage of gas through the barrel generates a reduced pressure at the top of tube 7 causing the abrasive material to be sucked up the tube 7 into the gas flow in the barrel 2. The material is thus entrained in the gas flow and is propelled along the barrel 2 and against the stencil. Some of the material will pass through the holes in the stencil and impinge on the surface, thereby marking it. Thus the mask is applied to the surface. Spent material rebounds off the surface 22 and the stencil 21 and falls in the interior space 20 within the shield 11.

Due to the supply of compressed gas to the interior space 20 within the shield 11 and by virtue of the connection between the annular space 19 and the vacuum coupling 5, a higher pressure is maintained in the interior space 20 than in the annular space 19. This pressure difference causes gas to flow from the interior shield space 20, through the perforations 15, into annular space 19 and from there into the extension 4, leaving the device through the vacuum coupling 5. Spent abrasive material does not collect in the interior shield space 19, but is carried out of the device into the vacuum line by the gas flow. The spent abrasive material can either be discarded or recycled for further use.

In order that the whole of the stencil 21 is uniformly bombarded with abrasive material, it may be necessary to move the gun 1 within the housing 3 so as to direct the material onto different parts of the stencil.

Claims (5)

1. An abrasive device for marking surfaces, which device comprises a gun having a nozzle for propelling abrasive material against a surface to be marked, a protective housing in which the gun nozzle is located, the housing having an opening in a position opposite the gun nozzle and also an exit port for removing spent abrasive material under suction, the device also including a shield located within the housing and extending forwardly of the gun nozzle towards the opening in the housing, the shield having an aperture to allow abrasive material to pass from the gun nozzle to the opening in the housing and being perforated along at least part of its length.

2. A device as claimed in claim 1, wherein the gun includes a barrel, at least part of which is located in the housing and at least part of which is surrounded by the shield, wherein the shield is perforated only in that part of its length behind the gun nozzle.

3. A device as claimed in claim 1 or claim 2, wherein the aperture in the shield lies in the opening in the housing.

4. A device as claimed in claim 3, wherein a compliant sealing bead is placed around the edge of the shield aperture and around the edge of the housing opening.

5. A device substantially as hereinbefore described in connection with and as illustrated in the accompanying drawing.