GB2408710A

GB2408710A - Attaching an abrasive sheet to a backing plate using suction

Info

Publication number: GB2408710A
Application number: GB0426603A
Authority: GB
Inventors: Steffen Wuensch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-12-06
Filing date: 2004-12-03
Publication date: 2005-06-08
Anticipated expiration: 2024-12-03
Also published as: GB2408710B; DE10357143A1; GB0426603D0; CN1623732A

Abstract

A hand-held electric grinding tool comprises a rigid base plate 11 on one face of which is fastened a backing plate 12 against which a sheet of abrasive 13 may be held. The backing plate 12 has through-holes 17 along which suction air can flow. The abrasive sheet 13 also has through-holes 19 which are approximately congruent with through-holes 17 in the backing plate 12, although they are fewer in number. Thus some of the through holes 17 in the backing plate 12 are used to extract dust and others are used to hold the abrasive sheet 13 against the backing plate 12. The mutually facing surfaces of the backing plate 12 and abrasive sheet 13 are provided with films for enhancing their mutual adhesion.

Description

Grinding assembly for an electric hand-held machine tool

Prior art

The invention takes as its starting point a grinding assembly for an electric hand-held machine tool with dust extraction by means of suction air, particularly for a hand-held grinding machine, e.g. vibrating grinder, delta grinder or eccentric grinder, according to the precharacterising clause of Claim 1.

In a known grinding assembly of this type (DE 198 00 025 Al), known therein as a grinding plate, the abrasive-medium bearing plate has a touch-and-close fastening track on its underside - the side remote from the base plate - which serves for the detachable attachment of the abrasive sheet.

In an alternative construction, the touch-and-close fastening track is omitted and the underside of the bearing plate is covered by an abrasive sheet which is placed over it and is clamped at its end on a machine-side vibrating plate by means of a holding device.

The base plate is detachably fastened to the vibrating plate by means of screws, said vibrating plate being displaceable in an oscillating movement by means of an eccentric drive. The vibrating plate is fixed such that it is resiliently movable with respect to the machine housing.

Constructed on the housing, there is an outlet fitting through which air charged with grinding dust is drawn off, said air being sucked into a flow chamber through holes in the vibrating plate and in the base plate and bearing plate by means of a driven fan impeller arranged in the housing.

The bearing plate, which is made of a soft material, is provided on its underside with semi-circular openings at the edge and with through-holes passing through the bearing plate, which are connected to the edge openings by way of deepened channels which are open towards the underside of the bearing plate, so that the dust extraction is effected through the through-holes and air and dust are sucked in from the outside by way of the openings and channels. The bearing plate furthermore contains holes through which the fastening screws reach for fastening the base plate to the vibrating plate of the machine.

In a known vibrating grinder having a delta-shaped grinding plate for receiving a delta-shaped abrasive sheet (DE 298 11 654 U1), the abrasive sheet is placed on the grinding plate by means of an adhesive coating. The grinding plate is fastened to a vibrating plate which is suspended on the machine housing by means of resilient vibrating elements and is displaced in a circular and orbital vibrating movement by way of a cam driven by a driven shaft. A fan impeller of a suction fan is fastened on the free end of the working shaft for the purpose of extracting grinding dust. A connecting fitting for a dust- collection bag, which forms the pressure outlet of the suction fan, is constructed in the vicinity of the fan impeller on the housing.

Advantages of the invention The grinding assembly according to the invention, which has the features of Claim 1, is advantageous in that the fastening systems for fixing the replaceable abrasive sheet on the bearing plate, such as an adhesive film, a touch-and close fastening track on the bearing plate and velour on the rear side of the abrasive sheets or mechanical clamping devices, are not required since the abrasive sheet is fixed on the bearing plate exclusively by the suction force of the dust extraction means of the machine or a separate dust extraction device. The omission of the fastening system greatly reduces costs since, for example, it dispenses with the velour covering of the abrasive sheets which is required for fastening purposes. For the operator, the replacement of the abrasive sheet is very comfortable and simple and can be carried out very quickly. Unlike with adhesive coverings and mechanical clamping systems, the shift of the abrasive sheet in relation to the bearing plate is very small, resulting in good abrasion. A gradual deterioration in the adhesion between the abrasive sheet and the bearing plate, and with this a significant increase in the relative shift between the abrasive sheet and the bearing plate such as occurs as a result of dust and chips dirtying the touch-and-close covering, is prevented.

Advantageous further developments and improvements in the grinding assembly indicated in Claim 1 are possible as a result of the measures described in the further claims.

According to an advantageous embodiment of the invention, the abrasive sheet is fixed in position by the suction air, in that the abrasive sheet has through-holes through which the suction air can flow and which are arranged such that they are approximately congruent with the throughholes in the bearing plate. The number of through-holes in the abrasive sheet is smaller than the number of through-holes in the bearing plate so that, in terms of their function, the through-holes in the bearing plate are divided into suction holes for fixing the abrasive sheet and extraction holes for the grinding dust.

The number of through-holes in the bearing plate is determined by the surface area of the bearing plate.

According to an advantageous embodiment of the invention, the maximum possible value of the total proportion of through-holes with respect to the total area of the cover plate is specified at cat 20. In order to ensure that the abrasive sheet is held securely during the grinding operation, according to an advantageous embodiment of the invention the function-based division of the through-holes in the bearing plate into suction holes and dust extraction holes is determined such that the total area of the suction holes is cat 50 - 70% of the total area of all through holes in the bearing plate.

Drawing The invention is described in more detail below, with reference to an exemplary embodiment illustrated in the drawing, which shows: Fig. 1 an exploded illustration of a grinding assembly for a vibrating grinder; Fig. 2 a plan view of a base plate of the grinding assembly; Fig. 3 a section along the line III - III in Fig. 2.

Description of the exemplary embodiment

As an exemplary embodiment for an electric hand-held grinding machine with dust extraction, the grinding assembly (illustrated in Fig. 1) for a vibrating grinder is composed of a rigid base plate 11, a bearing plate 12 of foam rubber and a replaceable abrasive sheet 13 which contains an abrasive medium. The base plate 11, bearing plate 12 and abrasive sheet 13 have the same contour and the same surface area and are constructed in a triangular or delta shape in the exemplary embodiment. However, depending on the application, they can also be rectangular or circular. The bearing plate 12 is fastened to the underside of the base plate 11, for example by adhesion.

The base plate 11 is fastened to a vibrating plate of the hand-held grinding machine, and to this end, has a total of four fastening holes 14 for guiding through fastening screws which are screwed into the vibrating plate. DE 197 08 068 Al and DE 298 11 654 Ul illustrate examples of an electric hand- held grinding machine having a vibrating plate.

The base plate 11 has a plurality of air-conducting channels 15 which are open towards the bearing plate 12 and lead into an annular channel 16 (Figs. 2 and 3). When the base plate 11 is placed on the vibrating plate, the annular channel 16, which is open towards the vibrating plate of the hand-held grinding machine, is connected to the dust extraction fan of the hand-held grinding machine, as described in the two publications mentioned. The bearing plate 12 lying against the underside of the base plate 11 covers the air-conducting channels 15 and has a plurality of through-holes 17 which are preferably distributed evenly over the plate surface. When the suction fan is switched on, air is sucked in through the through-holes 17 by way of the air-conducting channels 15 and the annular channel. The total proportion of through holes 17 with respect to the area of the bearing plate 12 is, at most, 20%. On average, the through holes 17 are constructed with a hole diameter of around 4 mm. Moreover, the bearing plate 12 has four holes 18 through which the fastening screws for the base plate 11 reach, said holes being arranged congruently with the fastening holes 14 in the base plate 11.

The abrasive sheet 13 likewise has a plurality of through holes 19 whereof the number is much smaller than the number of through-holes 17 in the bearing plate 12. The through- holes 19 are arranged such that, when the abrasive sheet 13 lies with a matching contour on the bearing plate 12, they are congruent with through- holes 17 in the bearing plate 12. The number of through-holes 19 in the abrasive sheet 13 is selected such that the abrasive sheet 13 covers cat 50 - 70% of the total area of all through-holes 17 in the bearing plate 12, and therefore 30 - 50% of the total area of all through-holes 17 in the bearing plate 12 are congruent with the through-holes 19 in the abrasive sheet 13. Thus, in terms of their function, the through-holes 17 in the bearing plate 12 are divided into suction holes for the abrasive sheet 13 and extraction holes for the grinding dust, which are flush with the through holes 19 in the abrasive sheet 13. The hole diameter of the through-holes 19 in the abrasive sheet 13 is determined in the same way as the hole diameter of the through-holes 17 in the bearing plate 12.

To promote the adhesion between the abrasive sheet 13 and the bearing plate 12, the mutually facing surfaces of the bearing plate 12 and abrasive sheet 13 can each be provided with a thin film. The films of course have the same hole pattern as the associated cover plate 12 and the associated abrasive sheet 13.

During operation of the hand-held grinding machine, the abrasive sheet 13 is fixed on the bearing plate 12 by the suction force of the suction air, the suction force and the suction power of the hand-held grinding machine being determined by the number of through holes 17 in the bearing plate 12 which are covered by the abrasive sheet 13.

The invention is not restricted to the exemplary embodiment described. Thus, the suction power can also be generated by a separate dust extraction device instead of the suction fan integrated in the hand-held grinding machine, said dust extraction device being connected to an extraction fitting which is constructed on the housing of the hand-held grinding machine and is in communication with the annular channel.

Claims

Claims 1. A grinding assembly for an electric hand-held grinding machine

with dust extraction by means of suction air, particularly for a hand-held grinding machine, having a rigid base plate (11) which can be placed on the machine and connected to its dust extraction means, having an abrasive-medium bearing plate (12) which is fastened to the underside of the base plate (11) - the side remote from the machine - and has throughholes (17) through which the suction air can flow, and having a replaceable abrasive sheet (13) which lies on the bearing plate (12) and contains an abrasive medium, characterized in that the abrasive sheet (13) is fixed on the bearing plate (12) by the suction air.
2. A grinding assembly according to Claim 1, characterized in that the abrasive sheet (13) has through- holes (19) through which the suction air can flow and which are arranged such that they are approximately congruent with through-holes (17) in the bearing plate (12), and in that the number of through-holes (19) in the abrasive sheet (13) is smaller than the number of through-holes (17) in the bearing plate (12).
3. A grinding assembly according to Claim 2, characterized in that the total proportion of through-holes
4. A grinding assembly according to Claim 2 or 3, characterized in that the total proportion of all throughholes (19) in the abrasive sheet (13) with respect to the total area of all through-holes (17) in the bearing plate (12) is cat 30 - 50.
5. A grinding assembly according to one of Claims 2 - 4, characterized in that the hole diameter of the through holes (17, 19) in the bearing plate (12) and abrasive sheet (13) is around 4 mm.
A grinding assembly according to one of Claims 1 - 5, characterized in that the abrasive sheet (13) and the bearing plate (12) are each provided on their mutually facing surfaces with a film promoting the adhesion between them.
7. A grinding assembly according to one of Claims 1 - 6, characterized in that the base plate (11) has a plurality of air-conducting channels (15) which are open towards the bearing plate (12) and lead into an annular channel (16) which is constructed for connection to the machine-side dust extraction means.
8. A grinding assembly according to one of Claims 1 - 7, characterized in that the bearing plate (12) is made of foam rubber.
9. A grinding assembly for an electric hand-held grinding machine, substantially as herein described with reference to the accompanying drawings.