GB2357054A

GB2357054A - Hand-held grinder

Info

Publication number: GB2357054A
Application number: GB0022873A
Authority: GB
Inventors: Klaus Wurst; Sieghard Amann; Albrecht Siedler; Steffen Wuensch; Uwe Krieg
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-09-20
Filing date: 2000-09-18
Publication date: 2001-06-13
Anticipated expiration: 2020-09-18
Also published as: GB0022873D0; FR2798610A1; DE19945060A1; SE0003338L; GB2357054B; SE519330C2; DE19945060B4; SE0003338D0; FR2798610B1

Abstract

A hand-held grinder, e.g. an eccentric or an oscillating grinder, comprises a grinding platen (20, fig. 1) for receiving a grinding disc (40, figs. 1 and 10). The platen (20, fig. 1) has slot-shaped axial through-holes 28 for dust extraction passing right through it, the through-holes being at least twice as long as they are wide The through-holes 28 extend radially outwards from the centre of the platen (20, fig. 1) and lie perpendicularly to the platen's sole (25, fig 1). The longitudinal sides of each of the through-holes 28 may be surrounded by ribs (38 and 39, figs. 4-6). Through-holes 28 may be crossed by arcuate grooves 29 formed in the platen's sole (25, fig. 1), the grooves 29 being curved to form a spiral with the concave side of each lying in the direction of rotation of the platen (20, fig. 1). The grooves 29 each end at a blind hole 27 for dust extraction.

Description

2357054 Han 1-held grinding machine tool

Prior art

The starting point of the invention is a hand-held grinding machine tool in accordance with the pre-characterising clause of claim 1.

Hand-held grinding machine tools having a grinding tray are known, which can be fitted with a grinding disc, the said grinding discs and grinding trays being provided with through-bores for dust, through which dust and shavings occurring in the course of grinding can be extracted from the machining face. In this connection, use is made, for extraction purposes, either of integrated dust-extraction by means of a fan or else of an external dust-exhauster which can be connected to the hand-held machine tool via a hose-type connection.

is In most known hand-held grinding machine tools, the grinding trays carry circular through-apertures which communicate, via bent or oblique ducts, with the sole of the grinding tray, from which they are in operative connection with an extraction device, for example by means of a bell-like cover. Under these circumstances, there can be placed on the underside of the grinding tray a grinding disc which is provided with circular through-holes for dust which are disposed congruently with those in the grinding tray. Precise disposition of the grinding disc on the grinding tray in such a way that the through-holes for dust are centred in relation to one another, is relatively difficult. Therefore, the complete diameter of the through-hole for dust in the grinding tray is mostly not clear for dust-extraction purposes because of incorrect disposition of the grinding discs, and the dust-extraction capacity remains below the possible optimum in most cases. In addition, the oblique or bent ducts tend to become clogged or blocked with grinding dust, so that the extraction capacity is further reduced.

2 At the same time, the previous dust-transporting apertures, which are circular, at least on the upper side of the grinding tray, are disposed over only a single partial circle.

This is standardised and the grinding discs are also provided with extraction holes which comply with this standard. In some grinding trays, the dust- transporting apertures are offset on the upper side, compared with the underside, and are connected to one another by obliquely extending ducts. This makes manufacture more expensive. In addition, the air sucked in is deflected a number of times as a result, and is thereby obstructed.

Advantages of the invention The hand-held grinding machine tool according to claim 1 has the advantage that optimum dust-extraction is ensured with any kind of perforated grinding discs.

is Through the fact that the through-holes for dust are configured as slots which pass through the grinding tray in an axially straight manner and whose longitudinal ends intersect, in each case, two standard hole circles in ordinary grinding discs, the dust is able to pass through at least two circular holes in ordinary grinding discs with the aid of the one through-hole for dust in the grinding tray. The flow- resistance of the air which is sucked through the slot in the grinding tray and which transports the dust, is low and the efficiency of the dust-extraction is particularly high.

Particularly efficient dust-extraction over the entire face of the grinding tray, or rather of the grinding disc, is possible through the fact that the grinding tray cames six slot- like extraction holes which pass right through and which are disposed at a uniform distance from one another and at the same distance from the middle of the grinding tray.

3 Through the fact that reinforcing ribs are disposed on the upper side of the grinding tray, parallel to the longitudinal edges of the slot-like through-holes for dust, the grinding tray is, inherently, particularly stiff and the oscillating behaviour neutral, so that the development of noise is minimal.

The stiffness of the grinding tray is further improved through the fact that the ribs continue axially downwards towards the underside of the grinding tray.

The dust-extraction is further improved through the fact that two of the slots, in each case, are in communicating connection by way of an arcuate groove which is machined into the sole of the grinding tray and runs radially outwards in a sickle shaped manner.

The dust-extraction is still more efficient because of the fact that end of the arcuate is groove which lies furthest out radially forms an additional, circular through-hole for dust.. According to this, it is crucial that the arcuate groove is curved in the direction of rotation in such a way that one flank of the said groove is curved, in a scoop-like manner, towards the direction of rotation, and a scooping effect is thereby able to evolve and conveys dust residues inwards in the form of a helix in the direction of the two slots at which the extraction is most effective.

The fact that grinding discs associated with the grinding tray are provided with through-holes for dust which are disposed on a number of hole circles and which overlap with the through-holes for dust in the grinding tray, is of particular advantage.

It is of particular advantage if use is made of grinding discs which have a structure which is open or porous in a net-like manner, and form a multitude of small through apertures for dust which can be operated by the slot-like through-holes for dust in the grinding tray which pass right through.

4 It is also of advantage if the grinding discs used have a velour layer of particularly coarse structure which can be brought into operative connection with the burr-type system on the grinding tray and through which the sucked-in grinding dust can conveniently pass to the through-holes for dust in the said grinding tray.

It is also of advantage to use gas-tight grinding-disc material which carries a multitude of matrix-like holes, about two to three millimetres in size, which are distributed over the entire face, particularly in rows. A grinding disc of this kind merely has to be disposed so as to be centred in relation to the periphery of the grinding tray, efficient dust-extraction through the many small holes in the grinding discs being ensured as a result of the large, slot-like through-holes for dust in the gnnding tray.

The slot-like extraction apertures which pass through the grinding tray in an axially straight manner allow the extraction air through without any change in direction, so that the flow-resistance is distinctly reduced and the extraction effect improved.

The enlargement, as a result of the slot shape, of the apertures for transporting away the dust distinctly enlarges the active extraction face on the sole of the grinding tray, so that even grinding discs with a hole pattern which is distributed densely over the entire face in a matrix-like manner, and grid-like abrasive-carriers can be employed in a particularly effective manner, because the grinding dust is picked up on the whole of the underside of the grinding tray and cannot clog the grinding faces.

Drawings The present invention is explained in greater detail below with the aid of an exemplified embodiment with appertaining drawings, in which:

figure 1 shows a hand-held grinding machine tool in longitudinal section, figure 2 shows an enlarged detail of the grinding tray region illustrated in figure figure 3 shows a bottom view of a grinding tray according to the invention, figure 4 shows a side view of the grinding tray illustrated in figure 3, figure 5 shows a top view of the grinding tray illustrated in figure 3, figure 6 shows a bottom view towards the supporting plate of the grinding tray, figure 7 shows a top view of the supporting plate illustrated in figure 6, figure 8 shows an axial section through the grinding tray illustrated in figure 3, figure 9 shows a bottom view of another exemplified embodiment of a grinding tray, figure 10 shows a top view of a grinding disc associated with the grinding tray illustrated in figure 9, figure 11 shows a bottom view of a grinding tray as illustrated in figure 9, but with a reverse direction of rotation compared with the one according to figure 9, figure 12 shows an axial section through the grinding tray illustrated in figure 11, and figure 13 shows a top view of the grinding tray illustrated in figure 11.

Exemplified embodiment The hand-held grinding machine tool 10 shown in longitudinal section in figure 1 is an eccentric grinder, whose housing 12 has a handle 14, from the rear of which there emerges an electric cable 15 for supplying current to a motor 17 which serves to drive a grinding tray 20. The said motor can be switched on and off via the switching button 16 of a switch, of which no further details are portrayed, which switching button is disposed in the handle 14.

6 The motor 17 transmits its rotary motion to an eccentric shaft 18 to which a fan 19 and the grinding tray 20 are connected in a torsion-proof manner. When the motor 17 rotates, an exclusively rotating motion is imparted to the fan 19, and a turning and circling motion to the grinding tray 20. Via the grinding tray 20, the fan 19 gives rise to a negative pressure at the workpiece to be machined and thereby extracts grinding dust located between the underside of the grinding disc 40 and a workpiece, from the upper side 21 of the grinding tray through slot-like through-holes 28 for dust in the said grinding tray 20 and through circular through-holes 44 for dust in the said grinding disc 40. In the process, the extraction air is guided, together with the grinding dust, towards the outside through an extraction connecting piece 31 and into a dust receptacle, which is not represented.

The upper side 21 of the grinding tray 20 is, at the same time, the outer side of a supporting plate 22 which carries, on its underside, an elastic cushion 24 whose underside forms a sole 25 on the grinding tray 20. The sole 25 carries a burr-type fastener 26 in the form of small hooks, for engagernent in the velour- type back 42 of a grinding disc 40.

The grinding tray 20 carries six through-holes 28 for dust of slot-like configuration, which are uniformly spaced apart from one another and lie opposite one another in pairs, symmetrically to the middle of the said grinding tray 20.

The grinding tray 20 has a central through-aperture 30, passing through which is a screw 32 which passes into a threaded bore 34 in an eccentric shaft 18 and secures the grinding tray 20 axially on the said shaft. The eccentric shaft 18 is eccentrically mounted in a rotatable manner in a bearing bore in the fan 19.

On its upper side, the grinding tray 20, or rather the supporting plate 22 carries, eccentrically in relation to its middle, a centering ring 36 for the form- locking 7 engagement of an entrainment means on the eccentric shaft 18, of which entrainment means no further description is given but via which the grinding tray 20 is fixed in a torsion-proof manner, together with a grinding disc 40.

On its upper and lower sides, the supporting plate 22 has upper and lower ribs 3 8, 3 9 which stiffen the grinding tray 20 as a whole and ensure that its inherent frequency is high and it does not resonate at the usual rotational speeds when the eccentric grinder is in oscillatory states.

Figure 2 shows an enlarged detail of the hand-held grinding machine tool 10 illustrated in figure 1, wherein it is possible to make out the housing 10, the fan 19, and the grinding tray 20 with the supporting plate 22, the cushion 24, the burr-type fastener 26 and the through-holes 28. In addition, it is possible to make out particularly clearly the sole 25, the central through-hole 30, the eccentric shaft 18 and the centering ring 36.

Figure 3 shows the bottom view of the grinding tray 20, wherein it is possible to clearly make out the slot-like through-holes 28 for dust which pass straight through, and the central through-aperture 30. It also becomes clear that the ends of the radially oriented through-holes 28 for dust, which lie opposite one another in pairs, intersect two hole circles 46a and 46b in each case.

Figure 4 shows the side view of the grinding tray 20, wherein it is possible to clearly make out the location of the upper ribs 39 on the upper side 21 of the said tray, and the location of the sole 25, or rather of the burr-type layer 26.

Figure 5 shows the top view of the upper side 21 of the grinding tray 20, wherein it is possible to make out particularly easily the disposition of the slot- like dust- 8 extraction holes 28 between two of the upper ribs 39 in each case. Here, it becomes clear that the dust-extraction holes extend in an axially straight manner.

Figure 6 shows the supporting plate 22 of the grinding tray 20 as an individual item in a bottom view, wherein it is possible to make out the upper ribs 39 which pass through in the downward direction and form the lower ribs 38 underneath and which enframe the slot-like through-holes 28 for dust, which are disposed opposite one another in pairs.

Figure 7 shows a top view of the upper side of a supporting plate 22 without upper ribs 39. Here, it is possible to easily make out the slot-like through- holes 28 for dust, which are disposed opposite one another in pairs, the central through- hole 30 and the centering ring 36.

Figure 8 shows an axial section through the grinding tray illustrated in figure 3, wherein it is possible to clearly make out the supporting plate 22 with the upper and lower ribs 38, 39, the centering ring 36, the central through-aperture 30, the through- holes 28 for dust and the burr-type fastener 26.

Figure 9 shows another exemplified embodiment of a grinding tray 200 with the aid of the top view of its sole 25. The said sole carries the same slot-like through-holes 28 for dust as illustrated in the previous exemplified embodiments. However, these through-holes additionally have an arcuate groove 29 passing through them, which is curved in a sickle-shaped manner. The end of the arcuate groove 29, or rather of its concave side, points in the direction of rotation of the grinding tray 200 so that, in the course of grinding, the arcuate groove 29 picks up dust like a sickle in a cutting operation - and guides it, in a scoop-shaped manner, radially from the outside inwards to the dust-extraction holes 28, where it is transported away essentially 9 perpendicularly to the surface of the workpiece and can no longer impair the grinding operation.

The tip of the arcuate groove 29 is formed by a circular blind hole 27 which serves as an aperture for sucking-in dust and guides the dust sucked in to the dust-extraction holes 28 via the arcuate groove 29. As a result of the three-fold disposition of arcuate grooves 29 extending to the centre in the fonn of a spiral, grinding dust is picked up over a very wide radial region of the grinding tray 20 and conveyed to the centre thereof in the form of a spiral - as by air-conducting scoops. This results in improved efficiency, particularly in the central region of the grinding tray 20 where the peripheral speed of the said grinding tray 20 is lowest.

This counteracts the disadvantage, which occurs particularly when grinding paints and lacquers, that the grinding disc 40 becomes clogged in the middle or that its surface is becomes fouled at that point. The other disadvantage associated therewith, that the grinding action declines and the machined surface suffers, is likewise eliminated thereby.

In previously known round grinding discs or ones with corners, the extraction holes are located on only a single hole-circle diameter.

Figure 10 shows the top view of a grinding disc 40 with three different hole circles 46a, b, c, on which a circular through-hole 44 is disposed so as to be offset by 120' in each case. Under these circumstances, the hole circles 46 coincide with those of the grinding tray 200 illustrated in figure 9.

The dust-extraction holes 44 on the second hole-circle diameter 46b are offset by 60' compared with the extraction holes 44 on the hole circle 46a, so that they are located precisely on gaps in relation to these extraction holes. The extraction holes 44 on the outermost hole circle 44c lie, in each case, on a common radius with the extraction holes 44 on the inner hole circle 46a.

When mounting the grinding disc 40 on the grinding tray 200, all that is necessary is to bring the three extraction holes on the outermost hole circle 46c into congruence, compared with the extraction holes 27 in the grinding tray 200, for the remaining extraction holes in the grinding disc to be also correctly aligned, compared with the dust-extraction holes 28 or the arcuate groove 29.

Figure 11 shows a top view of the sole 25 of a grinding tray 220, which can be rotated in the reverse direction compared with the grinding tray in figure 9 and the arcuate grooves 291 in which are curved or orientated in the reverse direction to those illustrated in figure 9, so that the scooping effect in the transporting- away of dust can become operative in accordance with the direction of rotation. The linking of the arcuate grooves 291 to the dust-extraction holes 28, 27 acts in the same way, from the outside radially inwards, as in figure 9, so that the grinding discs 40 illustrated in figure 10 also fit the grinding tray 220 in the optimum manner.

Figure 12 shows an axial section through the grinding tray 220, in which the slot-like configuration of the dust-extraction holes 28 becomes clear.

Figure 13 shows a top view of the grinding tray 220. In principle, this is identical to the grinding tray 20 illustrated in figure 5, except that no upper ribs are present, but use is made of a supporting plate 22a, as illustrated in figure 7, which is smooth on top.

Because of the sickle-shaped or spiral-shaped disposition of the arcuate grooves 29, 291, the dust-extraction effect resulting from the air flow is supplemented by a 11 mechanical one resulting from the flanks of the arcuated grooves 29, which act like impellers.

The disposition of slot-like dust-extraction holes or of arcuate grooves is not restricted only to round, rotating grinding trays, but is also of advantage in the case of grinding trays with comers, for example in oscillating grinders without a rotating movement of the grinding tray.

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Claims

1. Hand-held grinding machine ( 10), in particular an eccentric grinder, with a grinding tray (20) for receiving a grinding disc (40) with axial through-holes (27, 28, 44) for dust, characterised in that the through-holes (28) for dust in the grinding tray (20) are configured as a slot, in particular a smooth slot, which passes right through and which is at least twice as long as its smaller diameter.

2. Hand-held grinding machine according to claim 1, characterised in that each of the through-holes (28) for dust extends radially outwards longitudinally on a line from the middle of the grinding tray (20).

3. Hand-held grinding machine according to claim 1 or 2, characterised in that six through-holes (28) for dust are disposed on a common partial circle, uniformly spaced apart from one another.

4. Hand-held grinding machine according to claim 1, characterised in that the through-holes (28) for dust are so dimensioned that they are disposed with their radially internal region on a first partial circle (46a) which is standardised for grinding discs (40), and with their radially external region on a second partial circle (46 b) which is likewise standardised.

5. Hand-held grinding machine according to claim 4, characterised in that the through-holes (28) for dust pass through the grinding tray (20) parallel to its central axis or normally to its sole (25).

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6. Hand-held grinding machine according to claim 5, characterised in that the slot-like through-holes (28) for dust are enframed by ribs (38, 39) on their longitudinal sides.

7. Hand-held grinding machine according to claim 6, characterised in that the through-holes (28) for dust are crossed by an arcuate groove (29) which is curved in the form of a spiral and extends in the sole (25) of the grinding tray (20).

8. Hand-held grinding machine according to claim 7, characterised in that two through-holes (28) for dust, which are adjacent on the partial circles (46 a, b), are crossed in each case by the arcuate groove (29), which ends at a third partial circle (46 c).

9. Hand-held grinding machine according to claim 8, characterised in that the arcuate groove (29) ends in another through-hole (27) for dust, and that a grinding disc (40) is with holes (44) which are congruent with the through-holes (27, 28) for dust, is associated with the grinding tray (20, 200, 220).

10. Hand-held grinding machine according to claims 7 to 9, characterised in that the arcuate groove (29) points, with its concave side or with its radially outer end, in the direction of rotation of the grinding tray (20, 200, 220).

11. A hand-held grinding machine substantially as herein described with reference to the accompanying drawings.