The invention relates to the technical field concerning the production of spring mattresses obtained from the plurality of spring tubes.

According to a widely used constructive technology, the springs use to manufacture spring mattresses are enclosed in a plastic tube, which keep them firmly side by side at a prefixed reciprocal distance. This is obtained by welding the facing parts of the tube walls comprised between adjacent springs to each other, for example by ultrasonic welding, so that each spring is contained in a portion of tube, closed and separated from the adjacent portions.

Afterwards, the tube with the springs is cut into pieces to form spring packs having a selected length, and the spring packs are joined, side by side, so as to obtain an assembly formed by longitudinal and transversal rows of springs.

The joint between one spring pack and another is obtained, e.g. by a plurality of glue-spots, applied centered with respect to the spring height, in the touching areas between one spring pack and another.

The assembly of spring packs has length and width corresponding to the dimensions of the mattress to be manufactured.

Then, the assembly of spring packs is wrapped into the usual coverings, which form the mattress facings and sides.

The disadvantage of the mattress obtained according to the above mentioned constructive technique derives from the fact that the assembly of springs does not resist elastically in homogeneous way, because the elastic reaction depends on whether the weight is applied prevailingly extending longitudinally or transversally:

• In particular, it is observed that the spring deformation diminishes when the weight is loaded more on the rows of springs arranged along the spring packs extension rather than on transverse rows formed by springs of different adjacent spring packs.

The reason lies in the different load conditions which the springs of the rows along the spring pack extension, for example the ones disposed longitudinal along the mattress, must bear with respect to the springs of rows perpendicular to the mattress.

It appears that, for example, if a single spring is compressed, the adjacent springs belonging to the same spring pack will be also partially compressed by the tube.

Due to the compression of the first spring, the tube distributes part of the load to the adjacent springs, while no load is transferred to the springs adjacent in transversal direction, since they belong to different spring packs, joined to each other, as already said, only in the central area,

Because of these differences of the load distribution, a different softness of the mattress results with the same load, depending on whether the load Is distributed in a longitudinal or transversal way. In practice, considering that a mattress is aimed at receiving a human body, the above mentioned softness asymmetry depends on the way in which the body lies on the mattress, thus affecting the comfort condition.

Document WO 2005/102115, which comprises the features of the preamble of claim 1, discloses a spring mattress comprising a plurality of strings interconnected side by side, each string comprising a plurality of continuous casings and, enclosed therein, coil springs. Moreover, between at least some of the springs in at least one of the strings a slot is arranged which opens towards the upper or lower side of the mattress. According to an embodiment, the springs between which the slot is arranged are separated with an intermediate separation distance, which separation distance exceeds about 10% of the diameter of the largest turn of the adjoining springs.

The object of the present invention is to propose a spring mattress shaped in such a way, as to avoid the above mentioned disadvantage, thus obtaining a homogeneous reaction of the springs independently from the load orientation and distribution.

It is therefore specific object of the invention a spring mattress, including a plurality of spring tubes joined side by side, each spring tube comprising a continuous tube and a plurality of springs, enclosed into the tube and arranged side by side, at a selected distance, with facing parts of the tube walls between one spring and a subsequent one, joined by welding lines made parallel to the axes of the springs, so that each spring is contained in a respective portion of said tube, closed and separated from the adjacent portions, wherein longitudinal cuts are made starting from at least one side of the spring tube and extending inwards along and into said welding lines, to form at least one tubular segment for each portion of said portions, said welding lines having a predetermined minimum width, sufficient to keep the relevant portions sealed after the cuts are made, said spring mattress being characterized in that said spring tubes are joined by a plurality of substantially vertically aligned glue spots, applied to each portion.

Always according to the invention, each cut of said cuts could be made in a central part of the relevant welding line.

Still according to the invention, said opposite cuts could extend inwards for a predetermined depths.

Furthermore according to the invention, two opposite cuts could be made for each welding line starting from opposite sides of the spring tube and extending inwards.

Advantageously according to the invention, said opposite cuts could have equal length.

Always according to the invention, said springs have different elastic behavior, so as to define differentiated softness areas.

The characteristic features of the invention will be pointed out in the following description of a preferred embodiment of the proposed spring mattress, according to what is proposed by the claims and with the help of the enclosed drawings, in which:

• Figures 1a and 1b show partial, lateral views of the proposed spring tube in a first and a second embodiments respectively;
• Figure 2 is a partial, top view of a spring assembly obtained by a plurality of spring tubes of Figure 1;
• Figures 3a (according to the present invention) and 3b (not part of the present invention) show section views taken along the section lines III-III of Figure 2, with an exemplification stress acting on a single spring of the first and second embodiments respectively;
• Figure 4 (not part of the present invention) is a section view taken along the section line IV-IV of Figure 2, with the stress of a single spring being pointed out.

Referring to the above mentioned Figures, reference numeral 1 indicates the spring tube from which the spring mattresses proposed by the invention is obtained.

The spring tube 1, like the known ones, includes a tube 10 of floppy plastic material, within which the springs 2 are enclosed and kept arranged side by side, at a selected distance.

The parts of the tube wall between one spring 2 and the subsequent one, are joined by welding lines 12, crossing the whole tube side to side, obtained e.g. by ultrasound welding. The welding lines are parallel to the axes A of the springs 2, so that each spring is contained within a closed portion 13 of the tube 10, separated from adjacent portions 13 (Figure 1 a and 1b).

According to the invention, the welding lines 12 have a width L sufficient to assure the sealing of the portions 13 even after having done longitudinal cuts 120 along a center line of each portion 13.

According to a first preferred embodiment of the invention, better shown in figure 1a, the cuts 120 are made starting from one side only of the tube and extend inwards.

The continuity of the tube 10, between one portion 13 and another, is maintained by the central part 12A of the welding line 12, and the remainder of the welding line, extending from the central part up to the side of the tube opposite to the one having the cut.

The cuts 120 define in each portion 13 a tubular segment 130 which is separated from the tubular segment 130 of the adjacent portions 13. Each tubular separated segment 130 permits independent axial compression of the relevant spring 2, which do not interfere with the axial extension of the adjacent springs of the same spring tube 1.

According to a second preferred embodiment, the cuts 120 start from both the sides of the tube 10 and extend inwards along the welded portions 13 for a predetermined depth H (see Figure 1b).

The continuity of the tube 10, between one portion 13 and another, is maintained in this case only by the central part 12A of the welding line 12, which is not reached by the cuts 120; according to the shown non-limiting example, the extension of the central part 12A is about one third of the total.

In this case, the cuts 120 define at both sides of the tube, in each portion 13, two tubular, opposite segments 130, each of which has axial extension as the cuts 120.

The tubular segments 130 of each portion 13 are separated from the adjacent ones and permit independent axial compression of the spring 2, which do not interfere with the axial extension of the adjacent springs.

For both the embodiments, this feature is maintained unchanged also after the preparation of an assembly P (partially seen in Figure 2), formed by prefixed lengths of the spring tube 1, joined side by side to one another, until the length and width dimensions of the mattress to be produced are obtained.

Joining one spring tube 1 to another is obtained, e.g. by glue-spots C, applied from centered positions, with respect to the spring 2 height, up to the side of the tube without the cuts, for the first embodiment, as can be seen in figure 3a, and only in centered positions with respect to the spring 2 height for the second embodiment, as it can be seen in figure 3b. In both cases, the glue spots C are applied along the touching areas between one spring tube 1 and another.

According to the invention, the one with the cuts 120 along only one side of the tube 1, permits application of more glue spots C for each portion 13, for example there are three glue spots C visible in figure 3a, thus keeping the assembly joined with more strength.

The assembly P comprises longitudinal rows FL and transversal rows FT formed by the springs 2; according to the shown example, the spring tubes 1 are arranged to form the longitudinal rows FL, however the resulting softness is exactly the same both in the longitudinal extension and in the transversal extension.

As it is clearly seen in Figures 3a, 3b and 4, a single spring 2 of each longitudinal row FL, or of transversal row FT, can be compressed independently without transferring parts of the load to the adjacent springs, unlike the spring packs of the prior art, mentioned in the introductory note.

Subsequently, according to the known technique, the assembly P of spring tubes 1 containing the springs 2, is covered with usual coverings (not shown), which form the mattress facings and sides. The advantageous functional aspect of the so obtained mattress lies in the fact that it offers a homogeneous softness, and consequently improved comfort, independently from orientation of the body lying thereon.

Obviously, the proposed spring tube 1 allows, if desired, to use springs 2 of different elastic reaction to obtain orthopedic mattresses with differentiated softness areas with different softness degrees, as there are no effects due to the spring interconnections caused by the tube 10, which are present instead in the spring packs of known type.

The proposed spring tube can be produced with the same technologies and apparatuses already used for known spring tubes, with obvious advantages. The cuts along the welded strips can be easily made in the same welding station or in a subsequent one.

Consequently, the proposed spring tube offer important functional advantages, which improve the mattresses characteristics, with practically no cost increase.

However, it is understood that what above has a value of a not limiting example, therefore possible detail changes remain in the same protective scope defined by the claims below.