GB2407053A

GB2407053A - Plate insert for a grinding plate of a hand-held grinding tool

Info

Publication number: GB2407053A
Application number: GB0422744A
Authority: GB
Inventors: Joerg Dehde
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-10-18
Filing date: 2004-10-13
Publication date: 2005-04-20
Anticipated expiration: 2024-10-13
Also published as: DE10348930A1; CN1608805A; CN100509295C; GB2407053B; GB0422744D0

Abstract

A plate insert 1 for a grinding plate 2 of a hand-held grinding tool comprises a receiving region 3 with means for connection to a drive and an edge region 5 connected thereto by means of spokes 40 with empty space 41 therebetween, thereby reducing the mass of the plate insert 1. At least one substantially annular rib 42 runs between suction holes 45 in the plate insert 1 and interconnects spokes 40. The mass of the plate insert 1 is further reduced by making it from a plastics material, decreasing spoke wall thickness 43 and/or spoke height (44, Fig. 2) towards the edge region 5 and decreasing spoke height (44, Fig. 2) towards the receiving region 3. The plate insert 1 is covered with foam 20 to form the grinding plate 2.

Description

ROBERT BOSCH GmbH, 70442 Stuttgart Plate insert for a grinding plate of a

hand-operated electric grinding tool

Prior Art

The invention takes as its starting point a plate insert for a grinding plate of a hand-operated electric grinding tool having the generic features of Claim 1.

Plate inserts are known which have a solidly constructed, continuous thin base plate on which a ribbed structure is constructed for stabilising purposes. This base plate extends from a receiving region in the centre of the plate insert to an edge region. In plate inserts for eccentric grinders, this edge region is of a circular construction.

Here, the plate edge is adapted for a foam covering. The foam covering is applied to the underside around the edge of the edge region and extends along the upper side to the receiving region. In a bonded grinding plate, the bonding agent is usually only applied partially to the ribbed structure or flat along the base. The known grinding plates have a high total mass made up of the plate inserts and the foam applied around them. Although a grinding plate of this type has good rigidity it has to be balanced by an even greater mass.

Advantages of the invention In contrast, an inventive plate insert having the features of Claim 1 is advantageous in that the significantly smaller mass in the connecting region results in a lower heating-induced load on the bearing and a considerable reduction in the vibration of the electric grinding tool.

The said advantages are achieved in spite of the fact that the deformability remains the same - or is even improved - and the strain is distributed more evenly over the plate insert. Moreover, a plate insert according to the invention has good rigidity.

As a result of the fact that the plate insert is made from a plastics material, the mass is further reduced and the above-mentioned advantages are further reinforced. With an individual choice of the plastics material used, it is moreover possible to match the plate insert precisely to the specific application.

As a result of the fact that the spokes proceed in a radial direction from the receiving region, excellent stability is achieved in the radial direction with the lowest possible mass.

As a result of the wall thickness of the spokes, and/or the height of the spokes, decreasing towards the edge region and/or the height of the spokes decreasing towards the receiving region, the mass is further reduced with adequate rigidity of the plate insert, again reinforcing the abovementioned advantages.

As a result of the annular rib being constructed in a circle shape, the spokes are best supported in an azimuthal direction, resulting in excellent rigidity in this direction. In this case, the annular rib is preferably arranged concentrically around the receiving region.

As a result of the annular rib connecting suction holes to one another, the weakness caused by the suction holes in the structure is again compensated and the structure is even further strengthened. It is thus possible to achieve the known advantages of suction holes in electric grinding tools whilst at the same time achieving the enormous reduction in the mass of the plate insert.

As a result of the wall thickness of the receiving region being reduced, and radially extending ribs being constructed therein, the necessary rigidity combined with a simultaneous reduction in weight is achieved in the region in which the plate insert is connected to the hand tool. A washer can moreover be extensively supported by the ribbed structure.

As a result of the wall of the edge region being arranged at a setting angle to the base surface of the plate insert which corresponds to the assumed working angle, a force is introduced directly into the end face of the edge region.

The absorbed force is then introduced extensively into the spoke structure.

As a result of the wall being constructed in a circle shape and being arranged concentrically around the receiving region, it is particularly easily possible to construct a plate insert for an eccentric grinder which realises all the advantages of the invention.

As a result of the structure of the spokes being honeycomb shaped, the rigidity values achieved are the same as for a radial arrangement of the spokes and a circular construction of the annular rib in the manner of a spider's web.

Further advantageous constructions of the invention are the subjectmatter of the subalaims.

Drawings An exemplary embodiment of the invention is explained in more detail in the description below, with reference to the associated drawing.

The Figures show: Figure 1 a schematic illustration of a first exemplary embodiment of a plate insert according to the invention, from above; Figure 2 a section through the plate insert of Figure 1, along the line AA; Figure 3 a schematic illustration of the plate insert from Figures 1 and 2, from below; Figure 4 a schematic illustration of the plate insert from Figures 1 to 3, which is embedded in a foam covering; and Figure 5 a schematic illustration of a second exemplary embodiment of a plate insert according to the invention, from above.

A first exemplary embodiment of a plate insert 1 according to the invention is illustrated in Figures 1 to 4.

This plate insert 1 belongs to a grinding plate 2 (see Figure 4) for an eccentric grinder.

The plate insert 1 is made from a plastics material and is therefore very light. It has substantially three regions.

Located in its centre, there is a receiving region 3 which is connected to an edge region 5 by way of a connecting region 4.

The receiving region 3 primarily serves to connect the plate insert 1 to the drive means of an electric grinding tool (not illustrated) so that it can be driven by the electric grinding tool. For this, it has a base plate 33 which is provided with a number of holes 32. The material thickness of the base plate 33 is reduced. On the upper side (illustrated in Figure 1), the radial coupling of the driver in the wall thickness is reduced. This is compensated on the underside of the base plate 33 by ribs 31 (see Figure 3) so that the receiving region 3 has good rigidity. As a result of these ribs 31, a washer (not illustrated) is moreover extensively supported.

The connecting region 4 constitutes the actual core piece of the invention. It has a plurality of radially extending spokes 40. These spokes 40 extend in a star shape from the receiving region 3 to the edge region 5. The wall thickness 43 decreases towards the edge region 5 (see also Figure 3).

The radially extending spokes 40 are connected to one another by way of a circular annular rib 42. This ensures excellent rigidity in the direction of the circular line, i.e. upon rotation of the plate insert 1 in the azimuthal direction. Some of the spokes 40 are interrupted by suction holes 45. These suction holes 45 are each delimited by a suction ring 46. The annular rib 42 is arranged at the height of the suction holes 45. Its imaginary continuation passes through the central point of the suction holes 45.

Thus, the weakness of the structure of the radially extending spokes 40 is not only compensated, but even further strengthened.

Apart from the radially extending spokes 40, the suction rings 46 and the annular rib 42, the connecting region 4 has no further masses. Empty spaces 41 are respectively formed between the three elements mentioned above. This results in an extremely light plate insert 1 since the greatest area is "filled" by empty spaces 41. At the same time, the abovementioned structure, which has the form of a spider's web, results in excellent rigidity with simultaneous deformability.

The mass of the plate insert 1 is even further reduced in that the height 44 of the spokes 40 decreases towards both the receiving region 3 and the edge region 5 (see Figure 2). This is possible since the loads on the spokes 40 are lower towards both the centre, i.e. towards the receiving region 3, and the outside, i. e. towards the edge region 5.

The edge region 5 is substantially constructed as a thin wall 50 into which the spokes 40 proceed. The wall 50 is constructed at a setting angle to the base surface 10 (see Figure 2) which corresponds to the assumed working angle, i.e. to the direction of the main load. As a result, when working with the plate insert 1, the force is introduced directly into the end face of the wall 50. This results in an edge region 5 with very good rigidity, through which the force is introduced extensively into the spokes 40 of the connecting part 4. This applies substantially to the inner region 51 of the wall.

The outer region 52 of the wall 5 serves substantially for the foam-induced stability - mainly in no-load operation - of a grinding plate 2 illustrated in Figure 4. For this, foam holes 53 are incorporated in the outer region 52, through which improved through- foaming is achieved. In addition to the plate insert 1, this grinding plate 2 has a foam covering 20. The foam covering 20 can, amongst other things, be foamed around the plate insert 1 as PUR foam. It is moreover possible for the foam covering 20 to consist of cellular rubber or known similar materials and to be bonded to the plate insert 1. It is furthermore also possible to use a two-component injection-moulded body as the foam covering 20, in which the second component is an elastomer.

Here, the relatively large mass is generally compensated by a smaller bushing in the plate insert 1. The above- mentioned embodiments of the foam covering 20 are however in no way conclusive. Instead, all known foam coverings 20 can also be used for the plate insert 1 according to the invention.

In summary, it can be emphasized with regard to the first exemplary embodiment of an inventive plate insert 1 illustrated in Figures 1 to 4 that it attains enormous rigidity and stability as a result of its connecting region 4 being constructed in the manner of a spider's web.

This follows the principle that an accumulation of material is required at points at which high loads occur and there can be a reduction in material at points with a smaller load. As a result of the illustrated optimization of the structure, it is possible to achieve a reduction in weight of 15- and more with a foam-covered grinding plate 2 for an eccentric grinder in which the deformation values are the same as those for the prior art. In the present case, a reduction in weight of more than 30% has even been achieved through adaptation to the actual requirements. This results in a corresponding reduction in the Loads, bearing temperatures and vibrations caused by unbalanced masses.

The principle shown can be applied to all hand-operated electricallydriven grinding tools having an eccentric or rotary drive. In addition to the above-described example of a plate insert 1 for an eccentric grinder, this can be applied equally to plate inserts 1 for delta grinders and oscillating grinders.

It goes without saying that the illustrated number of 24 spokes 40 is only exemplary. It is likewise possible to use a smaller or higher number of spokes 40 which then have a correspondingly greater or smaller wall thickness 43. It is equally possible to provide a plurality of annular ribs 42 instead of only one annular rib 42.

Fig. 5 shows a second exemplary embodiment of a plate insert 1 according to the invention. This plate insert 1 is designed for an oscillating grinder plate. Contrary to the principle of a spider's web according to the first exemplary embodiment in Figures 1 to 4, a honeycomb structure of the spokes 40 is realised here. As known from nature, honeycomb structures - for example those of a beehive - also have good stability.

The structure shown has additional crossbars 47 in addition to radially arranged spokes 40 and annular ribs 42. These crossbars 47 are partly linearly constructed and also partly lie with a very large radius against a portion of an arc. In terms of rigidity and strength combined with a low mass and therefore low weight, the information provided above in relation to the first exemplary embodiment is equally valid. The advantages described above are therefore also produced for a structure according to the second exemplary embodiment illustrated in Figure 5. It goes without saying that, in addition to the concretely illustrated pattern of the honeycomb construction having the illustrated spokes 40, annular ribs 42 and crossbars 47, different structures of the above-mentioned elements also provide the same result. These are also covered by the invention.

Claims

Claims 1. A plate insert (1) for a grinding plate (2) of a hand-operated

electric grinding tool having a receiving region (3) and having an edge region (5) connected thereto by way of a connecting region (4), the edge region (5) having a circumferential wall (50) and the receiving region (3) having connecting means (3) to drive means of the electric tool, characterized in that the connecting region (4) has solid spokes (40) between which empty spaces (41) are formed and which extend from the receiving region (3) to the edge region (5), and has at least one annular rib (42) which is arranged at a spacing from the receiving region (3) and connects the spokes (40) to one another.
2. A plate insert (1) according to Claim 1, characterized in that it is made of a plastics material.
3. A plate insert (1) according to Claim 1 or 2, characterized in that the spokes ( 40) proceed in a radial direction from the receiving region (3).
4. A plate insert (1) according to one of the preceding claims, characterized in that the wall thickness (43) of the spokes (40) decreases towards the edge region (5).
5. A plate insert (1) according to one of the preceding claims, characterized in that the height (44) of the spokes (40) decreases towards the edge region (5) and/or towards the receiving region ( 3).
6. A plate insert (1) according to one of the preceding claims, characterised in that the annular rib (42) is constructed in a circle shape.
7. A plate insert (1) according to Claim 6, characterised in that the annular rib (42) is arranged concentrically around the receiving region (3).
8. A plate insert (1) according to one of the preceding claims, characterised in that the annular rib (42) connects suction holes (45) to one another.
9. A plate insert (1) according to one of the preceding claims, characterised in that the wall thickness (30) of the receiving region (3) is reduced and radially extending ribs (31) are constructed therein.
10. A plate insert (1) according to one of the preceding claims, characterised in that the wall (50) of the edge region (5) is arranged at a setting angle to the base surface (10) of the plate insert (1), which corresponds to the assumed working angle.
11. A plate insert (1) according to one of the preceding claims, characterised in that the wall (50) is constructed in a circle shape and is arranged concentrically around the receiving region (3).
12. A plate insert (1) according to one of the preceding claims, characterised in that the structure of the spokes (40) is honeycombshaped.
13. A plate insert for a grinding plate substantially as herein described with reference to the accompanying drawings.

13. A plate insert for a grinding plate substantially as herein described with reference to the accompanying drawings. - l]

List of reference numerals 1 Plate insert 2 Grinding plate 3 Receiving region 4 Connecting region Edge region Base surface Foam covering 30 Wall thickness 31 Rib 32 Hole 33 Base plate Spoke 41 Empty space 42 Annular rib 43 Wall thickness 44 Height Suction hole 46 Suction ring 47 Crossbar Wall Amendments to the claims have been filed as follows Claims 1. A plate insert for a grinding plate of a hand- operated electric grinding tool, comprising a receiving region having an edge region connected thereto by a connecting region, the edge region having a circumferential wall and the receiving region having connecting means for connection to drive means of the electric tool whereby the edge region is coupled to the drive means via the connecting region and the receiving region, wherein the connecting region has solid spokes between which empty spaces are formed and which extend from the receiving region to the edge region, and the connecting region has at least one rib extending around the receiving region at a spacing therefrom and interconnecting the spokes.

2. A plate insert according to Claim 1, wherein the plate insert is made of a plastics material.

3. A plate insert according to Claim 1 or 2, wherein the spokes extend radially from the receiving region.

4. A plate insert according to anyone of the preceding claims, wherein the wall thickness of the spokes decreases towards the edge region.

5. A plate insert according to anyone of the preceding claims, wherein the height of the spokes decreases towards the edge region and/or towards the receiving region.

6. A plate insert according to anyone of the preceding claims, wherein the rib follows a circular path.

7. A plate insert according to Claim 6, wherein the circular path is concentric with the receiving region.

8. A plate insert according to anyone of the preceding claims, whereinrib inter-connects suction holes.

9. A plate insert according to anyone of the preceding claims, wherein the the receiving region has a reduced wall thickness between radially extending ribs providing in the receiving region 10. A plate insert according to anyone of the preceding claims, wherein the wall of the edge region is arranged at a setting angle to the base surface of the plate insert which corresponds to the assumed working angle.

11. A plate insert according to anyone of the preceding claims, wherein the wall is and is concentric with the receiving region.

12. A plate insert according to one of the preceding claims, wherein several intersecting spokes are provided.