The present invention relates to a device for quickly mounting a back rest on a mechanism for office chairs.

Office ch a i rs are known gen eral ly cons isti ng of a su pport base provided with wheels or with a rotatable column of variable height, the upper end of which is inserted into a box support, the interior of which houses the adjustment mechanisms for the seating portion and back rest. The seating portion and back rest are generally securely coupled to their supports by suitable screws.

Sol utions are currently sought for simpl ifying and accelerating the assembly of these components to enable self-assembly of the structure by the final user, by enabl ing the components (back rest, seating portion, support boxes , col u m n a nd spokes) to be sent sepa rately to ach ieve low-cost packaging and transport. Consequently the ability to reduce the size and weight of these components is of fu ndamental importance in ach ieving competitive products of quality.

In swivel chairs the back rest is hinged to a support box and supported in the movements wh ich the user imposes on it by by an elastic support element able to withstand the user's weight.

The object of the invention is to provide a device wh ich enables the back rest to be easily and quickly mounted on the support box, wh ile at the same time enabling the back rest to be rotated rearwards.

Th is object is attained accord ing to the invention by a device for quickly mounting a back rest on a mechanism for office chairs as described in claim 1 . The present invention is further clarified hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a chair provided with the device according to the invention,

Figure 2 is an exploded perspective view showing the support box with the hinge mechanism,

Figures 3, 4 and 5 show longitudinal sections through the support box with the hinge mechanism,

Figure 6 is a perspective view of the back rest,

Figure 7 shows the back rest during its application to the box with the mounting mechanism,

Figures 8, 9, 1 0, 1 1 and 1 2 show schematically the steps in assembling the back rest to the box structure,

Figure 13 shows schematically the stage of rearward rotation of the back rest.

As can be seen from the figures, the device according to the invention is appl ied to a mechanism for office chairs, it consisting of a swivel support com prising a fixed box structure 2 provided lowerly with a frusto-conical socket 3 for the insertion of the upper end of a column 4 of a traditional gas pump, the purpose of which is to support the swivel support on a support base 6.

A connecting piece 10 is pivoted on a pin 8 to the fixed box structure 2 and is also pivoted on a pin 1 2 to the plate 1 4 wh ich supports the chair seating portion 16. The plate 14 is also hinged to the fixed box structure 2 by two pins 1 8, 20 inserted in two slotted holes 22 and 24 provided in the lateral wall of the plate 14.

The pin 20 is rigid with the fixed box structure 2.

A spring support 26 housed within the fixed box 2 is mounted on the pin 18, and on it there acts a coil spring 28 acting against a transverse baffle 30 provided in the plate 14.

The pin 1 8 is also inserted into the fixed box structure 2, passing through a pai r of L-shaped slots 32 formed in a lateral wall thereof and forming a longitudinal first branch 34 and a vertical second branch 36 presenting two striker surfaces 38 and 40 at its upper and lower ends.

By the effect of the slot 22 and the elastic counteraction of the spring 28, the pin 1 8 l ies in the intermed iate position within the slot 32 when the chair is unassembled and unstressed.

The invention also comprises a back rest 42 provided with a bracket 44 provided at its end with a fork 46, the prongs 48 of which are provided with a front longitudinal cavity 50 having a housing seat 54 and with a substantially inverted L-shaped rear cavity 52 provided with a housing seat 56.

To fit the back rest to the support box, the procedure is as follows: the prongs 48 are positioned to the sides of the structure 2 and above the pin 20, such that the ends of the pin 18 engage in the housing seats 54 of the cavities 50, so that the pin 20 is also able to engage the surface 60 of the cavities 52 (see Figures 8-10). On applying a downward rotation to the back rest, the prongs 48 are compelled to undergo a longitudinal movement, with the pin 1 8 consequently sliding along the horizontal branch 34 of the slot 32.

As a resu lt of th is sl id ing , the pin 1 8 temporarily compresses the spring 28 until the pin 20, by overcoming the tooth 58 of the cavity 52, jumps into the housing seat 56, to securely lock the back rest 42 relative to the box 2 (see Figures 1 1 and 12).

A rearward thrust by the user causes the back rest 42 to rotate about the fixed pin 20, with the movable pin 18, guided by the housing seat 54 of the back rest 42 compressing the spring 28, and rising along the vertical branch 36 of the slot 32 of the fixed box structure 2, to halt its movement against the striker surface 38.

All th is ensures that du ring normal use the back rest is u nable to disengage from the support (see Figure 1 3). When the back rest needs to be released, it is urged from the rear, but being unable to rotate, it causes the pin 1 8 to slide along the horizontal branch 34 of the slot 32, so compressing the spring 28 and releasing the pin 20 from the housing seat 56. As soon as the pin 20 overcomes the tooth 58 with an upward rotation, it disengages from the cavity 52 to enable the back rest 42 to be released.

From the aforegoing it is apparent that the device according to the invention presents numerous advantages, and in particular:

- it enabl es weig hts and d imensions to be l im ited , hence econom izing storage and transport in that the chairs can be trasported disassembled and be assembled and disassembled quickly and easily, it enables the number of components to be l imited in that the spring and pins utilized by the linkage mechanism are used to enable the back rest to be easily connected to the chair structure.