GB2349352A

GB2349352A - Grinding tool with dust protection cover

Info

Publication number: GB2349352A
Application number: GB0000348A
Authority: GB
Inventors: Albert Kleider
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-01-13
Filing date: 2000-01-07
Publication date: 2000-11-01
Anticipated expiration: 2020-01-07
Also published as: DE19900928C2; GB0000348D0; GB2349352B; DE19900928A1; JP2000202773A

Abstract

A dust protection cover for a grinding tool comprises a shell 5 and an attached metal element such as a spring 11 or a metal grid in which there are air passages. The metal element and the tool's grinding body (4, fig. 1) project from an open face of the shell 5, the metal element being elastically compressible in a direction perpendicular to this face, thereby allowing the grinding body (4, fig. 1) to come into contact with a work surface. The interior of the shell 5 may comprise flexible hooks 10 for attachment of the metal element. When the metal element is a spring 11, the first winding (12, fig. 3) which forms the end for attachment to the shell 5 has a smaller diameter than the other windings, while the opposite end is closed and has a ground end winding (13, fig. 3). The air passages are formed by spaces 14 between the windings of the spring 11.

Description

2349352 Grinding Tool and Dust Protection Cover thereof The invention

concerns a grinding tool and a dust protection cover for a grinding tool. Such dust protection covers are used, for example, on motonised grinding tools such as concrete grinders, where they surround a usually rotating driven grinding body of the grinding tool in order, on use of the grinding machine, to prevent any dust created being distributed into the environment, which is undesirable not only with regard to dirt but can also constitute a risk to health if certain types of grinding dust are inhaled by people.

DE 43 22 284 Al describes a hand-guided grinding tool which has a dust protection cover with a shell of rubber-like flexible material. The shell is formed such that when the grinding body of the tool touches a surface to be machined, the edge of the shell also lies against this surface. Air is extracted from the inside of the shell during operation of the tool in order to collect the dust created. As a result of the reduced pressure thus created, the edge of the shell is pressed against the surface to be ground. If the grinding tool is then moved to and fro on the surface to be ground, the edge of the shell rubs on the surface, which makes the movement of the tool difficult and leads to wear on the edge due to friction, so the shell requires frequent replacement.

DE 195 03 201 describes a dust protection cover according to the preamble of claim I and a grinding tool fitted with such a cover. This known cover is formed so that the enclosed grinding body of the grinding tool projects over the edge of the shell so that on use of the grinding tool the shell need not come into direct contact with the surface to be ground. On the edge of the shell is provided a holder for a ring which extends along the periphery of the shell and carries brushes which seal the gap remaining 2 between the edge of the shell and the surface to be ground. The grinding device avoids direct friction wear on the dust protection cover. The brushes however wear and must be changed regularly. When the operator reverses the direction of movement of the grinding tool, the brushes execute a folding movement. If the tool is handled carelessly, this can lead to the grinding body tippm'g slightly against the surface to be ground, which can lead to undesirable marks on the surface. Also the extraction effect is not optimum because the brushes, 'in particular when soiled after longer periods of use, may not allow sufficient air-flow through. This can firstly lead to an unsatisfactory dust extraction effect and secondly it can lead to the dust protection cover being sucked firmly onto the surface, which again means more force is necessary to handle the tool and increases the wear on the brushes.

Advantages of the Invention According to the invention, on the edge of the shell is arranged a metal element which projects over this edge and has air passage openings. N"en the grinding tool is used, this element maintains a gap between the edge of the shell and the surface to be ground. This element is scarcely affected by friction wear and therefore has the same life expectancy as the shell. Therefore it can be produced together with the shell or on production of the shell be firmly or even inseparably connected with it, which simplifies production and saves costs. The metal element could for example be a grid and, in a particularly preferred form, a coil spring where with the latter the spaces between the individual wMidings form the air passage openings. These air passage openings are sufficiently large that - in contrast to the brush crown - they cannot be blocked by dust deposits, which allows an essentially constant effective dust 3 extraction even beyond the life of the dust protection cover.

To guarantee even sliding to and fro of the coil spring used as a metal element on the surface to be ground, preferably an end widing of the coil spring is closed and ground.

To fix the metal element to the spring, preferably a multiplicity of flexible hooks are provided on the inside of the shell.

Also preferably the metal element is elastically compressible in the direction perpendicular to the edge of the shell so that when the grinding tool is placed on a surface to be ground, the grinding body by compression of the metal element can come into contact with the surface. The shell itself under these circumstances can be made rigid or at least more rigid than the metal element.

Further features and advantages of the 'invention anse from the following description of a design example in relation to the figures.

Figures Here: Figure 1 shows a grinding tool according to the invention in cross section; Figure 2 shows an enlarged section through the dust protection cover of the tool in figure 1; and 4 Figure 3 shows the coil spring of the dust protection cover in figure 2.

Description of the design example

Figure I shows in cross section a grinding tool according to the invention. This comprises in a housing I an electric motor 2 which via a bevel gear 3 drives a disclike grinding body 4. A dust protection cover has a shell 5 of essentially trwcated cone form which is mounted on a base 6 on housing I and surrounds the grinding body 4. The grinding body 4 essentially covers the entire opening 7 of the shell 5 up to an edge area. The shell 5 consists of a material of adequate rigidity to ensure that the grinding body 4 under normal conditions of use cannot come into contact with shell 5, for example made of metal or rigid plastic.

An extraction connection not shown 'in the figure to extract dustcontaining air from the dust protection cover is provided directly on shell 5 or on housing I in connection with the inside of the shell, As can be seen more clearly in fig 2, the grinding body 4 lies partly outside, that is in the orientation of figure 2, below the edge 9 of shell 5.

On its inside, the shell 5 carries at even angular intervals a multiplicity of flexible hooks 10, for example three or four, holding a metal element 11 which extends essentially cylindrically about the outer periphery of the grinding body 4 and in the example shown here is formed by a coil spring. This metal element I I is shown isolated in figure 3. It is a coil spring with a small number of windings, for example three to four, where the top windmig 12 in which hooks 10 engage has a smaller diameter than the others. The reduced diameter excludes the possibility that on use of the grinding tool, the distal ends of hooks 10 will become trapped between successive windings and thus disrupting the spring compression. The lowest winding is closed and ground at its end as is seen in particular at 13 in order to guarantee that the spring lies evenly on a surface to be machined around its entire periphery.

Spaces 14 between the various windigs form openings through which air is drawn into the inside of shell 5, as shown by arrows 15 'in figure 2. These spaces 14 lie in an area of the coil spring at the top in relation to the figure; in their lower area the individual windings touch each other and form a closed barrier.

In operation of the grinding tool, this is placed with the grinding body 4 on a surface to be machined where the coil spring is compressed slightly in the direction of the axis of rotation of the grinding body such that the underside of grinding body 4 and the lowermost winding of the coil spring 11 rest together on the surface to be machined. Dust extracted by the grinding body and flung axially outwards during grinding of the stuface is deposited either on the adjacent windings of the coil spring I I or, due to the air extraction, is caught in the backdraught in the air passage openings 14 whereby it remains inside the dust protection cover and is extracted. The large cross-section area of the air passage openings 14 guarantees a low flow resistance of the air extraction and thus a high volume throughput at low power.

6

Claims

1. Dust protection cover for a grinding tool with a shell (5) formed to hold a grinding body (4) projecting over an edge (9) of the shell, characterised in that on the edge of the shell (5) and projecting over the edge of the shell is arranged a metal element (11) with air passage openings (14).

2. Dust protection cover according to claim 1, characterised in that the metal element is a grid.

3. Dust protection element according to claim 1, characterised in that the metal element (11) is a coil spring.

4. Dust protection cover according to claim 3, characterised in that the coil spring has a closed and ground end winding (13).

5. Dust protection cover according to any of -the previous claims, characterised in that the shell (5) has on its inside a multiplicity of flexible hooks (10) to engage in the metal element (11).

6. Dust protection cover according to any of the previous claims, characterised in that the metal element (11) is elastically compressible in the direction perpendicular to the edge (9) of the shell (5).

7 7. Grinding tool with a dust protection cover according to any of the previous claims.

8. Grinding tool according to claim 7 with an extraction connection to extract air from the shell (5).

9. A dust protection cover for a grinding tool substantially as herein described with reference to the accompanying drawings.

10. A grinding tool with a dust protection cover substantially as herein described with reference to the accompanying drawings.