SPECIFICATIONChair backrestThe invention relates to a backrest for chairs.
In a previously disclosed embodiment of a chair backrest, the bearing blocks and the sheet-metal plate, together with their means of attachment, e.g. a screw-fastening, are covered by a corresponding moulding of the rear shell. For the manufacture of the rear shell, this arrangement requires, on the one hand, a comparatively complicated and hence expensive die for producing this moulding. On the other hand, there is disadvantage that, following completion of the manufacture of the backrest, access to the devices which retain the supporting member is no longer possible without destroying the connection between the front and rear shells.
Any repairs or refitting work which may be necessary, e.g. the subsequent tightening of screws fastening the sheet-metal plate which have not been screwed in tight enough, are consequently no longer possible.
The object of this invention is, as applied to a chair backrest of the kind referred to, to reduce the diecosts for manufacturing the rear shell, whilst at the same time rendering the attachment point of the supporting member accessible.
Accordingly, the present invention provides a backrest for chairs, in particular office swivel chairs, comprising two shells, made of plastic, the front shell being provided with bearing blocks which project into the interior of the backrest and possess openings for introducing a supporting memberforthe backrest, the outer surface of the bearing blocks and the openings being masked by a sheet-metal plate which is fastened to the bearing blocks, characterised in that the rear shell possesses a cut-out, whose outline is substantially identical to the outline of the bearing blocks and surrounds the latter, and in that the bearing blocks and the sheet-metal plate are masked by a trough-shaped fairing made of plastic.
The production of the cut-out in the rear shell involves significantly lower costs than the formation of the previously disclosed moulding. The troughshaped fairing is a comparatively small plastic component, which can be manufactured without difficulty. The assembly costs for attaching the fairing are virtually negligible, since a- simple pushing-on operation is sufficient for this purpose. After pulling off the fairing, which is equally easy, free access is obtained to the attachment and bearing-point of the supporting member on the rear shell, and/or to its bearing blocks.
Further advantages and features of the invention can be inferred from the additional sub-claims, and from the description of an illustrative embodiment, according to the invention, given in the text which follows. In the drawing:Figure 1 shows a backrest, designed in accordance with the invention in longitudinal section;Figure 2 shows a projection onto Figure 1, corresponding to the arrow A, the rear shell being omitted;Figure 3 shows a section conforming to the line Ill-Ill in Figure 2; andFigure 4shows the fairing, on its own, viewed in a projection corresponding to arrow B in Figure 2.
The backrest comprises a front shell 1, an upholstered part (not illustrated in detail), a rear shell 2, a supporting member 3 and a trough-shaped fairing 4.
The two shells 1,2 are connected to one another in a manner which is not explained in further detail, because it is known. Both the shells, and the fairing 4, are made of plastic.
Bearing blocks 6 are located on the front shell, these blocks projecting into the interior 5 of the backrest and preferably being manufactured integrally with the material of the front shell, that is to say together with the latter. Openings 7 are provided in the bearing blocks 6, for the insertion of cylindrical projections 8 of the supporting member 3, the cross-section of these openings being approximately semi-circular. Constrictions 9, formed in the plastic at the outer ends of the openings 7, serve to centre the projections, and hence the supporting member, with respect to the openings 7 and the bearing blocks 6.
The rear shell 2 possesses a cut-out 2', which is matched, at least in outline, to the outline of the bearing blocks 6, and which surrounds the bearing blocks. In the preferred embodiment of the invention, illustrated here, the trough-shaped fairing 4 is pushed into the gap which is situated between the bearing blocks and the inner edge of the cut-out 2'.
This means that the inner contour of the cut-out 2' must correspond to the outer contours ofthe fairing 4, represented in Figure 2 by means of dash/dotted lines. The fairing masks not onlythe bearing blocks 6, but also a sheet-metal plate, which is securely held against the bearing blocks by means of screws (not illustrated) which can be screwed into the threaded holes 11 in the bearing blocks 6, and thereby ensures that the projections 8 of the supporting member 3 are securely retained in the bearing blocks 6. For the sake of greater clarity, the sheet-metal plate 10 is represented in Figure 2 by means of a dash / dot - dot I dash line.It can be seen that the sheet-metal plate 10 possesses a valley 10' in the pivoting zone of the supporting member 3, this valley enabling the shells 1, 2 to pivot with respect to the supporting member 3, within a certain angular range. It is additionally possible for that portion of the sheet-metal plate which is situated above this valley to possess a domed-out region, not shown in the drawing, towards the rear shell.
The trough-shaped fairing can have sufficient intrinsic resilience to enable it to grip the bearing blocks 6 by clamping. Instead of this, it would also be possible to provide a latching feature between the fairing and the bearing blocks. These latching features could be located on the bearing blocks themselves, but this would lead to correspondingly increased costs in the manufacture of the moulds (dies) for casting or injection-moulding the blocks.
In a particular embodiment of the invention, illustrated in Figure 3, wedge-shaped projections 12, located on the inside of the fairing 4, engage below the sheet-metal plate 10 which is mounted on the blocks 6 by means of screws. In this design, the inclined surface 13 of the wedge-shaped projection 12 is shaped in such a way that it facilitates theaction of snapping in behind as the fairing 4 ispushed on.
Figure 4 shows the narrow longitudinal side of the fairing, in which the recess 15 serves for theleading-through of the supporting member 3. Theprojections 12 can be located on this side, on tongues 14. This arrangement ensures a greater degree of elasticity when the supporting member is inclined in relation to the shells 1,2, and prevents the narrow side of the fairing, shown in Figure4, from being damaged. Furthermore, removal of the fairing 4 from the blocks 6 and the sheet-metal plate 10 can be assisted by bending the tongues 14 outwards.