US 3562825 A
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Description (OCR text may contain errors)
Feb. 16, 197i I R L. LARsEN 3,562,825
MATTRESS CONSTRUOTION AND PLASTIC NET SPRING BRIDGING ELEMENT FOR USE THEREIN Filed March 18, 1969 HIS ATTORNEY United States Patent Oflice 3,562,825 Patented Feb. 16, 1971 MATTRESS CONSTRUCTION AND PLASTIC NET SPRING BRIDGING ELEMENT FOR USE THEREIN Ronald L. Larsen, Minneapolis, Minn., assignor to Conwed Corporation, St. Paul, Minn., a corporation of Delaware Filed Mar. 18, 1969, Ser. No. 808,231 Int. Cl. A47c 23/30 US. Cl. -354 4 Claims ABSTRACT OF THE DISCLOSURE An extruded plastic net, having heavy strands in one direction and lighter strands in the other direction, is used to replace two previous elements i.e. (1) a wire-rope spring bridging unit, and (2) a cotton scrim in a mattress construction thus permitting sewing of the spring bridging unit to the cushioning material.
In present industrial practice it is common to provide a mattress with a spring foundation in which the springs are considerably spaced from each other and then to provide a cushioning material thereover. In order to adequately support the cushioning material and to distributethe weight of the sleeping occupant over the springs it is also common to use a spring bridging unit comprising a wire and rope unit between the spring foundation and the cushioning material.
In such constructions it is common to provide the cushioning material (commonly a cotton batt) with a cotton scrim sewed to each face thereof to permit handling during manufacture and for other purposes.
It is not possible to stitch the wire and rope spring bridging element to the cotton batt since the wire breaks the needles used in stitching. Accordingly, it i necessary to apply the wire and rope spring bridging element separately to the spring foundation.
One object of the invention is to reduce the number of parts in a mattress construction by utilizing a single plastic net spring bridging element stitched to the cotton batt thus eliminating one of the two cotton scrims and the former wire and rope spring bridging element.
Another object of this invention is to simplify mattress construction by utilizing fewer materials.
Another object of this invention is to simplify the method of manufacturing mattresses by eliminating one of the steps required in manufacture.
These and other objects of the invention will be apparent to those skilled in the art from the following specification and drawings in which:
FIG. 1 is a schematic showing of the assembly of a pad for mattresses,
FIG. 2 shows the plastic net spring bridging element of this invention,
FIG. 3 is a perspective view of the plastic net of FIG. 2, and
FIG. 4 is a cross section of a portion of a mattress construction utilizing the spring bridging element of FIG. 2.
In the mattress construction industry one of the more common means of constructing a mattress is to first build a spring foundation of coil springs tied together by wire ties of various kinds including, particularly, long coil springs wound across the outer coils of the main springs and attached at their ends to the wire border of the mattress. A wire and rope spring bridging element is then laid over the spring foundation. This wire and rope spring bridging element may be of the open or of the woven variety. In the so-called open variety a plurality of strands of twisted paper rope or other like cord are arranged parallel on various spacings varying, for example, from 1 inch to 5 inches or more on center. A plurality of Wire strands are arranged in the opposite direction and passing through the twisted paper rope which wire strands may vary similarly from 1 inch to 5 inches or more on center. In the woven variety of wire and rope spring bridging element the wire is shot through a layer of burlap. In either of these varieties the wire element or strands are typically a 19 gauge tempered steel wire.
Many manufacturers of such mattresses have their own equipment for constructing cotton batts such as a carding machine, one variety of which is referred to as a garnett machine. Such machines comb the cotton fibers into a loose batt which is then further provided with a cotton scrim on each side by sewing the scrim to the batt thus providing a more handleable batt. In some manufacturing operations a topper comprising a cushioning material to provide feel, such as a polyurethane foam, and the outer ticking are also applied to one surface of the cotton batt over the cotton scrim and sewed to the cotton batt as a unit at the same time the two cotton scrims are provided. This latter method is commonly done when a scroll pattern is desired on a deep quilted mattress. When the upper layer of cushioning material and the ticking (frequently called the topper) is not sewn as a unit to the cotton batt the same will be separately sewed and applied.
The cotton batt, sewn together as above described, is then applied over the wire and rope spring bridging unit and the topper (if not incorporated in the pad) is then applied and the mattress finished at the borders.
The wire and rope spring bridging element is provided to distribute the weight of sleeping occupants and bridge the spaces Within and between springs and to provide a stiffness to the mattress. In some instances this wire and rope spring bridging element is used only at the center of the mattress due to its cost; however, it frequently covers the entire mattress, particularly in the better quality of mattress. In any event, it is necessary to cut the wire and rope spring bridging element from a roll to the appropriate size and to apply the same to the spring foundation and secure the same thereto as by hog rings or other known mechanisms.
This invention is directed to a specific plastic net spring bridging element which not only replaces the wire and rope bridging element but also replaces the sewable cotton scrim on one side of the cotton batt when the mattress pad is formed. Thus one element of the previous construction is eliminated together with one of the steps of manufacture.
As shown in FIG. 1 the cotton batt portion 10 of the mattress pad is first formed in any suitable conventional forming means such as a garnett, indicated at 12. The cotton batt 10 is then conveyed to a suitable conventional stitching machine 14 which stitches through the batt 10 by means of a gang of needles generally indicated at 16.
Also fed to the stitching machine 14 is a light cotton scrim 18 on the top surface of the batt 10 and the sheet of plastic net 20. The cotton scrim 18 and the plastic net 20 may be fed from suitable rolls such as indicated at 22 and 24 respectively. The stitching machine 14 will then stitch the cotton scrim 18 and the plastic net 20 to opposite faces of the cotton batt thus forming the mattress pad 26 which is rolled onto a mandrel 28. If it is desired to combine the mattress pad 26 with the topper in one operation suitable materials such as sheet polyurethane foam may be fed from another roll 30 and the ticking or other covering may be fed from still an additional roll 32. Under such an arrangement the topper materials including the ticking would be stitched to the mattress pad in a single operaion.
The mattress pad 26 is then taken from the roll, cut to appropriate size, and applied to the spring base. If the mattress pad 26 includes the topper the entire construction is applied to the spring base or foundation in one step whereas otherwise the topper must be separately applied.
The plastic net of this invention is preferably an extruded plastic net having two sets of parallel strands with the strands of one set crossing the strands of the other set at substantially a right angle. Such a net may be readily extruded by use of the method and apparatus disclosed in United States Pat. No. 3,252,181. By use of the method and apparatus of said patent considerable variation in the strand count, diameter of strands, and the like may be achieved. The particular construction of the net 20 of this invention, as shown in FIGS. 2 and 3, comprises a plurality of parallel strands 34 forming one set of strands and a plurality of strands 36 forming a second set of strands. The strands 36 cross the strands 34 at substantially right angles thereto and integral joints 38 are formed at the intersection of the strands 36 and 34 during manufacture. Preferably, the plastic net is oriented after extrusion by heating the same and stretching the same along the strands in one direction while heated and then heating the same and stretching the other strands in their longitudinal direction and then cooling the net while so stretched. This tends to orient the molecular structure of the net and provide a stronger net per unit of weight. In the specific net 20 as shown in FIGS. 2 and 3, which is preferred, one set of strands 34 are either not oriented or only oriented slightly while the strand 36 are more highly oriented. With a proper combination of extrusion and orientation the strands 34 are provided having a considerably larger size in cross section than the strands 36. As seen in FIG. 3 strands 34 are considerably larger than the strands 36. In one preferred embodiment the heavy strands 34 have a diameter of 0.066" while the lighter strands 36 have a diameter of 0.016". It must be understood, however, that considerable variation in strand size may be tolerated by the construction and process of this invention and, additionally, the strands do not necessarily have a circular cross section but may be somewhat elongated in cross section as shown for the strands 34 in FIG. 3. The strands of greater orientation will tend to be more nearly circular in cross section. In the preferred embodiment of the net 20 and after orienting the extruded net the larger strands 34 are on 1 /2 centers and the smaller strands 36 are on A centers. Such a construction is excellent for use as a spring bridging element to firm the mattress and to bridge the space within and between coils in a construction such as that shown in FIG. 4.
As shown in FIG. 4 the spring foundation 40 is made up from a plurality of coil springs 42 tied together by long small coil springs 44 in known manner. The coil springs 44 are then fixed at their ends to the mattress border 46, also in known manner. Over the spring foundation 40 the mattress pad 26 is placed. As indicated above, the mattress pad 26 comprises the central cotton batt 10, the scrim 18 and the net 20. The three elements (the cotton batt 10, the scrim 18 and the plastic net 20) are stitched together by stitches 48. Any topper (not shown) 4 not incorporated therewith during the stitching operation at the stitching machine 14. The mattress pad 26 is then fastened to the spring foundation 40 in any conventional manner.
A spring bridging element such as the previously used wire and rope must be capable of distributing the weight forces over the various springs across the distances a between springs and across the spaces b within the top circular coil 43 of the coil springs 42. Previously, only the Wire and rope bridging element adequately bridged between the springs and gave the adequate firmness to the mattress. Stiffness is required to adequately bridge the spaces a, b. Accordingly, the stiffer strands 34 are arranged usually in the longer direction of the mattress to provide bridging over more springs. It has been found, surprisingly, that the plastic net of the invention may be utilized in place of the extremely strong wire and rope bridging element previously used, even though the plastic net of the invention is considerably less stiff and has considerably less tensile strength as indicated by tests referred to below.
A sample of wire and rope having wires 0.95" on center and made up from wires of 19 gauge tempered steel wire was tested for tensile strength both along the wire strand direction and transverse thereto. A plastic net sample of this invention having a heavy strand 0.066" in diameter and a light strand 0.016" in diameter with the heavy strands on 1 /2" centers and the smaller strands on A" centers was also tested for tensile strength in each direction with the following results:
TABLE I (Tensile strength) Sample: Pounds per inch width Wire and rope (along length of wire strand) 280.0 Plastic net (along length of heavy strand) 16.0 Wire and rope (transverse to length of wire strand) 20.0 Plastic net (along length of light strand) 21.5
Samples of the same two materials were then assembled over a spring foundation and use tested by a bouncing weight with the cycles of bounce reported for each sample tested. The two constructions gave the following results:
TABLE II (Use test) Sample: Cycles Wire and rope assembly 1,800 cycles (wire broke).
Plastic net assembly 20,000 cycles (test stopped at 20,000 cycles-no visible deterioration).
It will be seen from the above table that the wire and rope and the plastic net have approximately the same tensile strength transverse to the heavy strand (the wire strand of the wire and rope), and the wire and rope has a tensile strength 17 /2 times as great as the plastic net along the bridging strands (the wire of the wire and rope and the heavy strand 34 of the plastic net). However, surprisingly, in actual use the plastic net gave 11 times the use.
Since stiffness is an important criterion in a spring bridging element since it relates to the ability to distribute the load and to the firmness of the ultimate mattress, two samples like those used in Tables I and II were tested by a deflection test to determine the flexibility along the length of the bridging strand and transverse thereto. The test involved placing a 12" by 12" sample flat on a table with 6" overhanging the edge of the table. The distance from the outer edge of the material to the floor was then measured. Weights were added to the samples to achieve is then applied over the mattress pad 26 if the same is a deflection downwardly of at least 1". The distance from (Stiffness) Deflection 0.469 lbs/in.
Wire and rope (wire direction) Plastic net (heavy strand direction) 0.082 lbs/in. Wire and rope (transverse to wire direction) Deflected under its own weight. Plastic net (light strand direction) Deflected under its own weight.
Two samples of the same wire and rope and plastic net were constructed into mattresses and found to have substantially equivalent firmness even though the wire and rope was from to 6 times as stiff as the plastic net as shown in Table III.
The preferred polymeric material for the plastic is a polypropylene although other extrudable plastic materials may be used.
It is not known exactly why the plastic net, which has considerably less tensile strength and less stiffness should perform superior to the wire and rope when actually put together in the final construction as evidenced by the test results of Table II. Similarly, it is not known exactly why the mattress should be equally as firm with either the wire and rope or with the plastic net even though the plastic net is much less stifl than the wire and rope as indicated in Table III. While the reasons for these results are not known it is theorized that it is in part due to the nature of the polymeric plastic of the net i.e. polypropylene which has a tendency to increase in strength when flexed. Also, the plastic net 20 as shown in FIG. 3 has the upper surfaces 35 of the strands 34 substantially flat and substantially co-planar with the upper substantially flat surfaces 37 of the strands 36. When the plastic net 20 is stitched to the cotton batt 10 the net 20 is arranged with the relatively fiat co-planar surfaces 35, 37 of the strands 34, 36 respectively adjacent to the cotton batt 10; it is believed, but not known, that the substantially flat and substantially co-planar surfaces 35, 37 provide a smoother and flatter support for the cotton batt 10 than was previously the case with the wire and rope construction in which the wire and rope were of different diameters and in which the wire passed through the rope substantially centrally thereof. With the wire and rope the upper surfaces of the wire and the rope were at different levels and as such tended to abrade the adjacent surface of the cotton batt 10.
In prior art constructions it was common to provide an insulator material between the spring foundation and the wire and rope construction in order to insulate against the clicking noise that occurred when the wire of the wire and rope bridging element clicked against the wires of the springs. Such insulating elements comprised thin cotton batts or burlap or the like interposed between the wire and rope spring bridging element and the spring foundation. It has been found with the construction of this invention that not only does the plastic net eliminate the wire and rope spring bridging element and the cotton scrim previously sewed to the cotton batt, but also, the noise insulating element may be eliminated.
1. A spring cushion structure comprising a resilient metal wire spring foundation presenting a face with open spaces between a plurality of small wires in said face, said open spaces being large relative to said wires, cushioning material supported by said face, an open mesh net interposed between said face and said cushioning material, said net having a plurality of sets of polymeric plastic strands, strands of one of said sets crossing strands of another set at an angle, the strands of said one set being larger in cross section and stilfer than the strands of the crossing set, strands of said one set bridging said open spaces between said small wires, the upper surfaces of strands of said one set being substantially co-planar with the upper surfaces of strands of said crossing set.
2. The spring cushion construction of claim 1 in which the crossing of strands of said one set with strands of the crossing set are joints integral with the strands forming the joints and in which the upper surfaces of said integral joints are substantially co-planar with the upper surfaces of strands of said one set and with the upper surfaces of strands of said crossing set.
3. A spring bridging unit for bridging the spaces within and between the spring wires at the face of a spring foundation comprising an open mesh net material, said net having a plurality of sets of polymeric plastic strands, strands of one of said sets crossing strands of another set at an angle, the strands of said one set being larger in cross section and stiffer than the strands of the crossing set, the crossings of strands of said one set with strands of the crossing set being joints, said joints being integral with the strands forming said joints, and the upper surfaces of strands of said one set being substantially coplanar with the upper surfaces of strands of said crossing set.
4. The spring bridging unit of claim 3 in which the upper surfaces of said joints are substantially co-planar with the upper surfaces of strands of said one set and also with the upper surfaces of strands of said crossing set.
References Cited UNITED STATES PATENTS 2,556,590 6/1951 Long 24960X 2,649,899 8/ 1953 Williams 5354 3,087,171 4/1963 Hoagland 5--354 3,315,283 4/1967 Larsen 5354 BOBBY R. GAY, Primary Examiner A. M. CALVERT, Assistant Examiner US. Cl. X.R. 5-351; 297-452