GB2255095A

GB2255095A - Spring strip for furniture

Info

Publication number: GB2255095A
Application number: GB9208618A
Authority: GB
Inventors: Thomas Kunnemeyer; Fritz Kunnemeyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-04-17
Filing date: 1992-04-21
Publication date: 1992-10-28
Anticipated expiration: 2012-04-21
Also published as: FR2675361A1; FR2675361B1; GB9208618D0; AT401861B; DE9116304U1; ATA68292A; GB2255095B; DE4112554C1

Description

2 2,53 5 SPRING STRIP FOR FURNITURE ETC.

This invention relates to a spring strip for sprung frames which are used in couches, beds, upholstered furniture and the like. They are constructed as straight strips or have a slight convex curvature, upwards for example. In practice, these sprung frames are also described as slatted bases. Such spring strips and sprung frames usually consist of wood, and in use have to take up not insignificant loadings with considerable deformations, often over a long period of time with a large number of changes of load. This requires a high fatigue strength.

The spring strips known in practice from which the invention stems are worked from solid wood. Solid strips of beech wood are mainly used. Their manufacture is costly. The fact that the known spring strips become "worn out" cannot be ruled out. In this respect, the lifetime of the known spring strips in the sense of their long-term fatigue strength is in need of improvement.

A basic object of the present invention is to provide a spring strip for the purpose explained, which is inexpensive to manufacture and is characterised by a long life.

According to a first aspect of the invention there is provided a spring strip of high fatigue strength for use in a sprung frame for couches, beds, upholstered furniture and the like, wherein the strip is cutout from a single- or multilayer particle board, the chips of which are formed into a particle board with urea- and/or phenol-formaldehyde resins as the binder with the application of pressure and heat, with at least the chips in the region of tensile loading being mainly oriented in the longitudinal direction of the strip.

Other aspects of the invention are a sprung frame for furniture incorporating at least one spring strip as defined above, and an item of furniture, such as a couch, bed, or other upholstered item, incorporating at least one such sprung frame.

The chips in the region of tensile loading are preferably formed as narrow chips which are several centimetres long.

Particle boards which also have oriented chips are widely known. The invention is based on the recognition that particle boards can be used as a preliminary product for the manufacture of spring strips if they are formed with particles which extend longitudinally and which are oriented in the manner stated. Particle boards have hitherto not been used as spring elements for longterm loading with a large number of load changes, neither in the form of sprung bases nor in the form of spring strips. Particle boards are known in which the chips are formed as narrow chips several centimetres long, which are oriented in a particular way, and which are bonded with urea- andlor phenol- formaldehyde resins. In particular, such particle boards are known as OSB boards (OSB = oriented strand boards). However, only their bending strength and transverse tensile strength, i.e. their static behaviour, has hitherto been utilised (see Kieser, fermann "Dispersion station for oriented, dispersed particle boards with 3 - is possibilities of application", reprinted from HolzZentralblatt [Wood - Central Information Sheet], 1979, Nos. 95 and 97). In contrast to this, the invention is based upon the recognition that spring strips manufactured from such chips and binders, where the chips have the stated shape and orientation, have a surprisingly high fatigue strength and long- term fatigue strength, which leads to lifetimes of ten years and considerably longer for the spring strips in sprung frames, couches, beds, upholstered furniture and the like. In this respect, the invention utilises qualities of the particle board or of the spring strips manufactured from it which have hitherto not been taken into consideration in relation to dynamic loading with a large number of load changes and often large amplitudes, even if the frequencies are low. It is understood that the geometric dimensioning of the spring strips is otherwise effected according to the rules of statics, as for "a beam on two supports" or as "a loaded beam" as it were, according to the loads to be taken up.

For the characteristic of the invention that at least the chips in the regional of tensile loading of the spring strip are formed as narrow chips several centimetres long and are oriented as stated, it must first be stated that the spring strip can be constructed as a multi-layer strip, e.g with the narrow chips in an upper and/or lower layer, whilst the central layer can consist of short chips with arbitrary orientation. Narrow chips can also be used in this respect. In general, at least 50 weight % of the chips in the spring strip should be formed as narrow chips in the manner stated and 4 - should be oriented as stated. The spring strip preferably has exclusively the narrow chips in the stated orientation. Within the scope of the invention, the "region of tensile loading" characteristic means the region of the spring strip which is subjected to the loading of a person lying on the sprung frame, for example, or which is under a tensile stress due to prestressing. Bending theory according to classical engineering mechanics, or tests, permit this region to be determined without further considerations.

In particular, several possibilities exist within the scope of the invention for further forming and fashioning. Thus the invention recommends that the chips have a length in the region of 3 to 10 cm, preferably about 4 to 8 cm. The width of the chips should lie in the range 0.3 to 2.5 cm. According to a preferred form of the invention, the chips have a thickness of less than 0.7 mm, preferably about 0.5 mm. In practice it has been shown that, for a predetermined percentage of narrow chips of the stated length and orientation in the spring strip, the fatigue strength is higher the thinner the chips are. Moreover, in relation to the orientation, a preferred form of the invention is characterised in that an angular deviation of the chips from the orientation in the longitudinal direction of the spring strip occurs with a frequency of about 15 % for an angular deviation of up to 10%, and with a frequency of about 20% for an angular deviation of up to 20%. The numerical values given are particularly important for the form of construction which originates from the OSB boards defined above.

As for the known strips, the spring strips have an overall thickness of 6 to 15 mm, for example, preferably about 8 mm to 12 mm. The spring strip is advisedly curved towards the load-bearing side. This can be achieved by means of a special chip structure in the dispersed mats which are to be pressed to form the particle board, e.g. by means of a twolayer structure with different chips in the layers. The moulded spring strip blanks which are subsequently cut out of a particle board are preferably given a convex curvature by the application of heat and pressure, possibly by the application of moist heat. In particular it falls within the scope of the invention that the spring strip is mounted prestressed in the sprung frame and by this means is given a convex curvature or an additional convex curvature towards the load-bearing side. However, the spring strip can also be given a concave curvature towards the load- bearing side.

As already indicated within the context of these technological explanations, the spring strip can form the core of a multi-layer strip, and for this can have an outer layer on at least one surface. This can be designed as a type of reinforcing layer which increases the strength and the fatigue strength. In this connection a preferred form of the invention is characterised in that the outer layer is disposed on the surface of the spring strip which is subjected to a tensile stress in the loaded andlor prestressed state, and is also designed as a tension boom. The outer layer is preferably formed as a layer of wood veneer. However, the outer layer can also be a coating layer based on a synthetic resin. The outer - 6 layer is subsequently applied to the spring strip formed as a cutout from a particle board, or is even applied to the particle board as an outer layer and cut out from the particle board with the spring strip.

The invention will be explained in more detail below by means of the drawings, which merely illustrate examples; the drawings are schematic representations, where:

Figure 1 is a longitudinal section through a spring strip constructed according to the teaching of the invention; Figure 2 is another form of construction of Figure 1; Figure 3 is a third form of construction of Figure 1 and Figure 4 shows a sprung frame with spring strips corresponding to Figure 2.

The spring strips 1 shown in Figures 1 to 3 were formed by the use of a strip-shaped cutout from a single- or multi-layer particle board, the chips of which were formed into a particle board with urea and/or phenolformaldehyde resins with the application of pressure and heat. It is indicated in Figures 1 to 3 that at least the chips 3 used in the region of tensile loading of the spring strip 1 are formed as narrow chips several centimetres long, and are mainly oriented in the longitudinal direction of the spring strip. The chips 3 have a length, width and thickness as given in

Claims

Claims 1 to 4; these dimensions cannot be illustrated in the drawing for

reasons of scale. This also applies to the angular deviation of the chips 3 from the orientation in the longitudinal direction of the spring strips and to the

7 - thickness of the spring strips, for which reference is made to Claims 5 and 6.

Figure 2 clearly shows that the spring strip 1 has a convex curvature towards the load-bearing side; this can be produced by the application of heat and pressure. Figure 4 shows that the spring strips 1 according to the invention are mounted prestressed in the sprung frame 2; by this means they can be given a convex or an additional convex curvature towards the loadbearing side. However, they can also be constructed as straight strips. Figure 3 shows that the spring strip 1 forms the core of a multilayer strip 1, 4, and that an outer layer 4 in the form of a wood veneer is disposed on the upper side.

is CLA TMS:

A.

A spring strip of high fatigue strength for use in a sprung frame for couches, beds, upholstered furniture and the like, wherein the strip is cutout from a single- or multilayer particle board, the chips of which are formed into a particle board with urea- andlor phenol-formaldehyde resins as the binder with the application of pressure and heat, with at least the chips in the region of tensile loading being mainly oriented in the longitudinal direction of the strip.
2. A spring strip according to Claim 1, wherein the chips in the region of tensile loading are formed as narrow chips several centimetres long.
3. A spring strip according to either one of Claims 1 or 2, wherein the chips have a length in the range 3 to 10 cm, preferably 4 to 8 cm.
4. A spring strip according to any one of Claims 1 to 3, wherein the chips have a width of 0.3 to 2.5 cm.
5. A spring strip according to any one of Claims 1 to 4, wherein the chips have a thickness of less than 0.7 mm, preferably about 0.5 mm.
6. A spring strip according to any one of Claims 1 to 5, wherein the angular deviation of the chips from the orientation in the longitudinal direction of the strip amounts to a frequency of about 15% for an angular deviation of 10%, and amounts to a frequency of about 20% for an angular deviation of up to 20%.
7. A spring strip according to any one of Claims 1 to 6, with the stipulation that the spring strip is given a 9 - convex curvature towards the load-bearing side by the application of pressure and heat, possibly moist heat.
8. A spring strip according to any one of Claims 1 to 7, with the stipulation that the spring strip is mounted prestressed in the spring frame and by this means is given a convex or additional convex curvature towards the load-bearing side.
9. A spring strip according to any one of Claims 1 to 7, with the stipulation that the spring strip is given a concave curvature towards the load-bearing side.
10. A spring strip according to any one of Claims 1 to 9, with the stipulation that the spring strip forms the core of a multi-layer strip and has an outer layer on at least one surface.
11. A spring strip according to any one of Claims 1 to 10, with the stipulation that the outer layer is disposed on the surface which is subjected to a tensile stress in the loaded and/or prestressed state, and is designed as a tensile boom, considered statically.
12. A spring strip according to any one of Claims 1 to 11, with the stipulation that the outer layer is formed as a layer of wood veneer.
13. A spring strip according to any one of Claims 1 to 12, with the stipulation that the outer layer is a coating layer based on synthetic resin.
14. A spring strip according to any one of Claims 1 to 13, with the stipulation that the outer layer is subsequently applied to the spring strip which is formed as a - cutout from a particle board.
15. A spring strip according to any one of Claims 1 to 13, with the stipulation that the outer layer is applied to the particle board and is cut out with the spring strip.
16. A spring strip substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.
17. A sprung frame for furniture incorporating at least one spring strip as defined in any one of Claims 1 to 16.
18. A sprung frame substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.
19. An item of furniture, such as a couch, bed, or other upholstered item, incorporating at least one sprung frame as defined in Claim 17.