GB2202382A

GB2202382A - Hand-held machine tools

Info

Publication number: GB2202382A
Application number: GB08806240A
Authority: GB
Inventors: Gunther Berger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1987-03-16
Filing date: 1988-03-16
Publication date: 1988-09-21
Anticipated expiration: 2008-03-16
Also published as: FR2612679A1; DE3708436C2; GB2202382B; DE3708436A1; FR2612679B1; GB8806240D0; HU203898B

Abstract

A hand-held machine tool having an electric resistor, consisting of two anodized aluminium plates (8, 9) and an interposed meander-shaped resistance wire track (1). The oxide layers (10, 11) insulate electrically but are good thermal conductors. The resistor can be advantageously used as starting resistor, for example in the case of electric tools. Its production is particularly simple and inexpensive. <IMAGE>

Description

Hand-held machine tool State of the art This invention relates to hand-held machine tools.

Electric power tools having starting resistors comprising a ceramic basic element having a coil of resistance wire inserted are already known. These resistors have the disadvantage that because of their poor heat dissipation and the cramped conditions in hand-held electric power tools they become. very hot, making necessary a high outlay for cooling and for ensuring that the resistor is heat resistant. This makes the already expensive construction of a resistor of this kind more expensive still. Moreover, the space requirement is relatively high because of the inflexible shape of the resistor.

Advantage of the invention In contrast, the hand-held machine tool according to the invention and having the characterizing features of claim 1 has the advantage that the starting resistor is more efficiently cooled and is constructionally smaller. The triple function of the aluminium plates as resistor housing, insulating layer and as cooling elements and the inserted adhesive layer lead to considerable cost advantages and a great simplification in production. At the same time, the conducting off of the heat produced in the resistance wire by the only very thin anodized oxide layer, which is moreover itself a good heat conductor, is substantially improved. The size of the aluminium plates can be matched to the particular power loss of the machine.

Advantageous developments and improvements of the hand-held machine tool specified in the main claim are possible by the measures indicated in the subclaims. The application of grooves and strips engaging these grooves at the edges of the aluminium plates, which prevent the penetration of dust, is particularly advantageous. To increase the cooling capacity of the aluminium plates, cooling ribs can also be provided.

Drawing An illustrative embodiment of the resistor of a hand-held machine tool is shown in the drawing and explained in greater detail in the following description. Figure 1 shows a top view of a dismantled resistor, Figure 2 shows the completely mounted resistor according to a section following the line II-II in Figure 1. Figure 3 shows a section according to line III-III of Figure 2.

Description of the illustrative embodiment The meander-shaped resistance track 1 exhibits at its ends enlargements 2, 3 and, if necessary, thinner extensions 4, 5 to which temperature-resistant connecting lines 6, 7 are applied, for example by crimping. The resistance track 1, which can also exhibit another space-saving shape, is preferably produced by stamping. The resistance track 1 is surrounded by two anodized aluminium plates 8, 9 (see also Figure 2) which, if necessary, exhibit cooling ribs 25. The oxide layers 10, 11 on the sides facing the resistance wire track 1 have a thickness of 10 to 60 p. 40 p will be sufficient for reliably preventing a short circuit for most cases of application. If necessary, however, layers with a thickness of more than 60 p can also be anodized on.

To accommodate the connecting lines 6, 7, troughs 12, 13, 14, 15, which are enlarged in the area of the connecting points, are arranged in the plates 8,9. The aluminium plates 8, 9 are elongated on one side opposite the resistance wire track 1 and exhibit holes 16, 17, 18, 19 which, on the one hand, are used as auxiliary holes during anodizing and, on the other hand, can be used for attaching the resistor in a housing or similar. It is advantageous if the aluminium plates 8, 9 are adapted in a space-saving manner to the housing shape of the electric device, that is to say, for example, are not rectangular, and if the resistor is arranged in the cooling air stream of the electric device into which it is inserted.

Around the resistance track 1, one 8 of the aluminium plates carries a peripheral groove 20 and the other one 9 carries a peripheral strip 21 which engages the groove 20 in a positive-locking manner. For better sealing, a sealant, for example a layer of fusible adhesive, can be applied to the strip 21. Instead of a strip, the second aluminium plate can also exhibit a groove into which, for example, an O-ring is inserted.

Similarly, one or several foils, not shown, which melt under the influence of heat and seal the resistor, can be inserted between the plates 8,9.

The two aluminium plates 8, 9 are held together by means of a simple holding clamp 22 which - but not necessarily - engages in recesses 23, 24 on the outsides of the plates 8, 9 (Figure 3). The holding clamp 22 can be used at the same time for attachment in or to a housing. The shape of the holding clamp 22 is not restricted to the illustrative embodiment. Other simple bending parts such as paper clips or clamping pins also fulfil the purpose. If an adhesive (sealing) agent is used, holding clamps can also be completely dispensed with.

The described resistor is particularly suitable as a starting resistor for high power electric motors for hand-held machine tools, for example a right angle grinder.

Claims

CLAIMS:

1. A hand-held machine tool having an electric motor, for example an angle grinder, which has an electrical resistor to limit the starting current having a resistance track supported by a carrier, characterized in that the resistance track is inserted with the arrangement of insulating layers between two metal plates, in that the metal plates are aluminium plates and in that the insulating layers are formed by oxide layers on the aluminium plates.

2. A hand-held machine tool according to claim 1, wherein the oxide layers have a thickness of 10 to 60 p.

3. A hand-held machine tool according to claim 1 or claim 2, wherein the resistance track is enlarged at its ends and connecting lines are attached thereto.

4. A hand-held machine tool according to any of the preceding claims, wherein the aluminium plates have grooves and strips engaging the grooves at the edges for sealing the internal space.

5. A hand-held machine tool according to any of the preceding claims, wherein the aluminium plates are held together by one or several holding clamps which, at the same time, can be used as attachment device in the housing.

6. A hand-held machine tool according to any of the preceding claims, wherein a fusible or adhesive layer, which seals and/or bonds the resistor under the influence of heat, is applied to the plates.

7. A hand-held machine tool according to any of the preceding claims, wherein a foil, which melts and seals under the influence of heat, is inserted between the plates.

8. A hand-held machine tool according to any of the preceding claims, wherein the aluminium plates have cooling ribs.

9. A hand-held machine tool according to any of the preceding claims, wherein the shape of the aluminium plates is adapted to the housing shape of the electric device into which the resistor is inserted.

10. A hand-held machine tool according to any of the preceding claims, wherein the resistor is arranged in the cooling air stream of the electric device into which it is inserted.

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