GB2433712A

GB2433712A - A hand held grinding machine with braking mechanism

Info

Publication number: GB2433712A
Application number: GB0625556A
Authority: GB
Inventors: Steffen Tiede; Joao Jorge Bergner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-12-27
Filing date: 2006-12-21
Publication date: 2007-07-04
Anticipated expiration: 2026-12-21
Also published as: DE102005062459A1; GB0625556D0; DE102005062459B4; GB2433712B; CN1990180A

Abstract

A hand-held grinding machine, in particular an eccentric grinder, has a machine housing 10 with a rotating grinding tray 11 disposed in a manner spaced apart from the underside 101 of said machine housing. The grinding tray may have a supporting bearer (31, fig 7). A braking device 20 operates between the machine housing and the grinding tray to slow down the rotation of said grinding tray. The braking device consists of a braking member 21 constructed on the grinding tray and a running face constructed on the underside of the housing. The braking member is pressed onto the running surface in a springy manner. The braking member preferably consists of a large number of hook-shaped braking elements 17 which are disposed on a base circle which is concentric with the axis of the grinding tray and are attached to the tray body 12 of the grinding tray in one piece. Alternatively the braking member is constructed as a rubber ring (24, fig 3) attached to the tray body.

Description

Application No. GB0625556.6 RTM Dale.27 April 2007 The following terms

arc registered trademarks and should be read as such wherever they occur in this document: Velcro.

22. 12. 2005 ROBERT BOSCH GMBH, 70442 Stuttgart Hand-held grinding machine

Prior art

The starting point of the invention is a hand-held grinding machine, in particular an eccentric grinder, according to the pre-characterising clause of claim 1.

A known eccentric grinder (DE 101 48 339 Al) has a machine housing in which an electric motor with a downwardly extending motor shaft is accommodated. Said motor shaft carries an eccentric at its free end. Disposed in a manner spaced apart from the underside of the machine housing is a grinding tray which is screwed axially to the eccentric in a rotationally entraining manner via a threaded bolt.

Seated in a central bore in the grinding tray is a rolling bearing which encompasses the eccentric with its inner race. The rotational entrainment of the grinding tray by the eccentric takes place, in dependence upon the bearing friction, via the rolling bearing. On its underside, the grinding tray possesses a face for receiving an abrasive disc, on which face an abrasive disc is held by means of a velcro-type fastener.

In a known grinding tray for a hand-held grinding machine (EP 0 557 773 B1), said grinding tray has a supporting plate made of hard plastic and a grinding pad, which is foamed onto said supporting plate, as a bearer for a grinding means. The underside of the grinding pad forms a flat bearing face for an abrasive disc and is covered with a velcro-type fabric to which the velour back of the abrasive disc adheres.

Another known grinding tray for a hand-held grinding machine (DE 103 57 144 Al) has a tray body with a supporting structure and a flat bearing plate on which a bearing face for an abrasive disc is constructed. Said bearing face is provided for the purpose of connecting the abrasive disc to the grinding tray and is provided with velcro-type hooks. The tray body with the supporting structure and bearing plate is designed in one piece in conjunction with the velcro-type hooks, and is produced from just one plastic component in a single-component injection-moulding process. As the material, use is made of plastic with a high heat resistance, such as polyamide for example. Alternatively, the tray body may be injection-moulded from two plastic components of differing hardness in a two-component process. In this case, the bearing plate, with velcro-type hooks moulded onto it in one piece, is manufactured from a softer plastic, and the supporting structure which carries the bearing plate is manufactured from a plastic which is harder than the aforesaid plastic.

In order to prevent the grinding tray, which is rotating without being driven after the motor has been switched off, from severely damaging the surface of the workpiece when the eccentric grinder is placed on said surface again, in some eccentric grinders the rotational speed of the grinding tray, which is idling without being driven, is reduced by means of a braking ring, or else the idling grinding tray is brought to a complete standstill. The braking ring is clamped in between the grinding tray and the housing and is held on the latter in a torsion-proof manner.

Advantages of the invention The hand-held grinding machine according to the invention having the features in claim 1 has the advantage that a separate mounting part, such as the braking ring in known eccentric grinders, is dispensed with by realising the braking device with a braking member which is linked to the grinding tray. The braking member is a fixed constituent part of said grinding tray, and is manufactured with the latter in the same working operation when said grinding tray is produced. When the grinding tray is attached to the machine housing and fastened on the eccentric, the braking device is produced with it at the same time, without any separate mounting action being required. As a result of the elimination of a separate mounting part and of simplified assembly, manufacturing costs and assembly time are reduced. The construction of the running face on the underside of the machine housing for the braking member to bear on in a force-locking manner requires no additional manufacturing step, since said running face on the underside of the machine housing is also brought into being automatically when said housing is injection-rnoulded from plastic.

Advantageous further developments of, and improvements to, the hand-held grinding machine indicated in claim 1 are possible as a result of the measures set out in the other claims.

According to one preferred form of embodiment of the invention, the grinding tray has a supporting bearer and a grinding pad which is linked to said supporting bearer and is made of a flexible material with a bearing face for an abrasive disc. The braking member is constructed as a braking ring which rests, at the end face, on the running face on the housing, is moulded onto the grinding pad in one piece, and consists of the same plastic material as said grinding pad.

According to one advantageous form of embodiment of the invention, the grinding tray has a tray body made of plastic with a bearing face for an abrasive disc. The braking member consists of a large number of hook-shaped braking elements which are disposed on a base circle concentric with the axis of the tray body and are attached to the latter in one piece. The tray body and braking elements are rnoulded from the same plastic material in the same working operation.

Drawings The invention is described in greater detail below with the aid of exemplified embodiments which are represented in the drawings, in which: fig. 1 shows a side view of a grinding tray in association with the machine housing of a hand-held grinding machine, part of which housing is represented in longitudinal section; fig. 2 shows a plan view of the grinding tray in fig. 1; fig. 3 a representation which is the same as that in fig. 1, but with a second exemplified embodiment of the grinding tray; fig. 4 shows a plan view of the grinding tray in fig. 3; fig. 5 shows a section along the line V-V in fig. 4, in conjunction with the machine housing, part of which is represented in longitudinal section; fig. 6 shows a plan view of a grinding tray according to a third exemplified embodiment; fig. 7 shows a section along the line Vu-Vu in association with the machine housing, part of which is represented in longitudinal section; fig. 8 shows a plan view of a grinding tray according to a fourth exemplified embodiment; fig. 9 shows a section along the line IX-IX in association with the machine housing, part of which is represented in longitudinal section; fig. 10 shows a plan view of a grinding tray according to a fifth exemplified embodiment; and fig. 11 shows a section along the line XI-XI in association with the machine housing, part of which is represented in longitudinal section.

Description of the exemplified embodiments

The grinding tray 11, which can be seen in side view in fig. 1 and in plan view in fig. 2, for an eccentric grinder as an exemplified embodiment of a hand-held grinding machine, of which grinder the lower end of the machine housing 10 can be seen, merely in part, in longitudinal section in fig. 1, is disposed, after being mounted on said eccentric grinder, on the underside of the machine housing at the distance of a gap from said underside 101 of said machine housing 10. A complete representation of the eccentric grinder with an electric motor, an eccentric driven by the latter, and a grinding tray 11 fastened to said eccentric, can be found in DE 101 48 339 Al, so that the reader is referred to the latter in that respect.

In the exemplified embodiment according to figs. 1 and 2, the grinding tray 11 has a tray body 12 with a supporting structure 13 formed from ribs, and a flat plate 14 which is moulded onto the underside of said structure. The underside of the plate 14, which underside faces away from the supporting structure 13, is constructed as a flat bearing face 15 for an abrasive disc 16. Said bearing face for the abrasive disc is provided with velcro-type hooks 17 or other means of adhesion which secure the abrasive disc 16 in position on the grinding tray 11. The tray body 12 with the supporting structure 13, plate 14 and velcro-type hooks 17 is of one-piece design and is produced from just one plastic component in a single-component injection-moulding process. A plastic which has a high heat resistance, for example polyamide, serves as the material.

Alternatively, the tray body 12 is injection-moulded from two plastic components of differing hardness in a two-component injection-moulding process. In this case, the plate 14, with velcro-type hooks 17 moulded onto it in one piece, is manufactured from a soft plastic, and the supporting structure 13 which carries the plate 14 is manufactured from a plastic which is harder than the aforesaid plastic.

In order to reduce the rotational speed of the idling grinding tray 11 after the eccentric drive has been switched off, or to bring said idling grinding tray 11 to a complete standstill, a braking device 20 is provided, which operates between the grinding tray 11 and the machine housing 10. Said braking device 20 possesses a braking member 21 which is constructed on the grinding tray 11, and a running face 22 which is present on the underside 101 of the machine housing 10 and onto which the braking member 21 is pressed axially. In the exemplified embodiment in figs. 1 and 2, the braking member 21 consists of a large number of hook-shaped braking elements 23 which are disposed on a base circle which is concentric with the axis of the tray body 12. The braking elements 23 consist of the same plastic material as the tray body 12 and are moulded onto the latter in one piece. When the grinding tray 11 is attached to the eccentric drive in the machine housing 10, the hook-shaped braking elements 23 are brought to a certain initial tension, so that they give rise to a braking effect on the running face 22.

The grinding tray 11 according to the exemplified embodiment represented in figs. 3 to 5 differs from the grinding tray 11 previously described exclusively through a different kind of construction of the braking member 21 on the grinding tray, so that those components of the grinding tray 11 in figs. 3 to 5 which correspond to the components in figs. 1 and 2 are provided with the same reference numerals. In this case, the braking member 21 is constructed as a braking ring 24 which surrounds the axis of the tray body 12 concentrically and is attached to said body. Said braking ring 24 consists of a soft plastic which forms a chemical compound with the plastic of the tray body 12. alternatively, the braking ring 24 may consist of rubber and be rnoulded onto the tray body 12 with said body when it is produced. When the grinding tray 11 is attached to the eccentric drive in the machine housing 10, the braking ring 24 is pressed axially against the running face 22.

The grinding tray 30 according to the exemplified embodiment represented in figs. 6 and 7 has a supporting bearer 31 made of a hard plastic, and a grinding pad 32 which is linked to said supporting bearer 31 and is made of a flexible material, for example polyurethane foam. On its underside that faces away from the supporting bearer 31, the grinding pad 32 carries a bearing face 33 for the abrasive disc, which bearing face is covered with a layer of adhesive 34, for example a velcro-type fabric, for the adhesion of said abrasive disc to the grinding tray 3D.

The braking member 21 of the braking device 20 which operates between the machine housing 10 and the grinding tray 30 is constructed as a braking ring 24 which is rnoulded onto the grinding pad 32 in one piece.

The grinding tray 30 according to the exemplified embodiment represented in figs. 8 and 9 differs from the grinding tray 30 according to figs. 6 and 7 merely through a modification of the braking device 20, so that structural elements which correspond to the structural elements referred to in figs. 6 and 7 bear the same reference numerals. The braking member 21 of the braking device 20 is likewise designed as a braking ring 24 which surrounds the axis of the grinding tray 30 concentrically. In contrast to the exemplified embodiment according to figs. 6 and 7, the braking ring 24 is now attached to the supporting bearer 31 consisting of a hard plastic. The braking ring 24 consists of a soft plastic which combines chemically with the hard plastic in the manufacturing process.

The grinding tray 30 according to the exemplified embodiment represented in figs. 10 and 11 again differs from the grinding tray 30 described in connection with figs. 8 and 9 merely in a modification to the braking device 20, so that components which are identical are provided with the same reference numerals. The braking member 21 of the braking device 20 consists of a large number of hook-shaped braking elements 23, such as have already been described previously in the exemplified embodiment in figs. 1 and 2. The hook-shaped braking elements 23 are disposed on a base circle which is concentric with the axis of the grinding tray 30 and are injection-rnoulded onto the supporting bearer 31. Said hook-shaped braking elements 23 consist of an elastic plastic and rest, with pretensioning, against that running face 22 of the braking device 20 which is constructed on the underside 101 of the machine housing 10.

Claims

22. 12. 2005 ROBERT BOSCH GMBH, 70442 Stuttgart Claims 1. Hand-held

grinding machine, in particular an eccentric grinder, having a machine housing (10), a rotating grinding tray (11; 30) disposed in a manner spaced apart from the underside (101) of said machine housing (10), and a braking device (20), which operates between the machine housing (10) and the grinding tray (11; 30), for slowing down the rotation of said grinding tray, characterised in that the braking device (20) has a braking member (21) constructed on the grinding tray (11; 30) and a running face (22) which is constructed on the underside (101) of the housing and onto which said braking member (21) is pressed axially in a springy manner.

2. Hand-held grinding machine according to claim 1, characterised in that the grinding tray (11) has a tray body (12) made of plastic with a bearing face (15) for an abrasive disc, and that the braking member (21) consists of a large number of hook-shaped braking elements (23) which are disposed on a base circle which is concentric with the axis of the grinding tray (11) and are attached to the tray body (12) in one piece.

3. Hand-held grinding machine according to claim 2, characterised in that the tray body (12) and braking elements (23) are moulded from the same plastic material in a single working operation.

4. Hand-held grinding machine according to claim 1, characterised in that the grinding tray (11) has a tray body (12) made of plastic with a bearing face (15) for an abrasive disc, and that the braking member (21) is constructed as a braking ring (24) which is disposed concentrically with the axis of the grinding tray (11) and is attached to the tray body (12) 5. Hand-held grinding machine according to claim 4, characterised in that the braking ring (24) consists of rubber and is moulded or injection-moulded onto the tray body (12) 6. Hand-held grinding machine according to claim 4, characterised in that the braking ring (24) consists of a soft plastic which forms a chemical compound with the plastic of the tray body (12).

7. Hand-held grinding machine according to claim 1, characterised in that the grinding tray (30) has a supporting bearer (31) and a grinding pad (32) which is linked to said supporting bearer (31) and is made of a flexible material with a bearing face (33) for an abrasive disc, and that the braking member (21) is constructed as a braking ring (24) which is disposed concentrically with the axis of the grinding tray (30) and is attached to the grinding pad (32) in one piece.

8. Hand-held grinding machine according to claim 7, characterised in that the grinding pad (32) and braking ring (24) are moulded from the same plastic material in a single manufacturing step.

9. Hand-held grinding machine according to claim 1, characterised in that the grinding tray (30) has a supporting bearer (31) and a grinding pad (32) which is linked to said supporting bearer (31) and is made of a flexible material with a bearing face (33) for an abrasive disc, and that the braking member (21) is constructed as a braking ring (24) which is disposed concentrically with the axis of the grinding tray (30) and is attached to the supporting bearer (31) 10. Hand-held grinding machine according to claim 9, characterised in that the supporting bearer (31) consists of a hard plastic and the braking ring (24) consists of a soft plastic which combines chemically with the hard plastic.

11. Hand-held grinding machine according to claim 1, characterised in that the grinding tray (30) has a supporting bearer (31) and a grinding pad (32) which is linked to said supporting bearer (31) and is made of flexible material with a bearing face (33) for an abrasive disc, and that the braking member (21) consists of a large number of hook-shaped braking elements (23) which are disposed on a base circle which is concentric with the axis of the grinding tray (30) and are injection-moulded onto the supporting bearer (31).

12. Hand-held grinding machine according to claim 11, characterised in that the hook-shaped braking elements (23) consist of elastic plastic.

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