Textiles: knitting – Fabrics or articles – Warp
Reexamination Certificate
2000-01-28
2001-06-26
Worrell, Danny (Department: 3741)
Textiles: knitting
Fabrics or articles
Warp
C442S312000
Reexamination Certificate
active
06250117
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to a warp knitted fabric having large grid openings, especially a Geo-grid, and a method for the production of such a warp knitted fabric which exhibits a biaxial, specifically a textile structure, having stay- and weft threads being arranged in groups in a crossing array.
Such knitted structures having large grid-like openings are applicable, especially as Geo-grid fabrics, in different regional as well as civil areas. For example, in the highway construction as a reinforcement for asphalt, as a reinforcement in the banks of canals or as a reinforcement for an embankment in man-made slopes.
Warp knitted fabrics with large grid openings, simply called Geo-grid fabrics hereafter, are also used as an intermediate product in the production of, for example, reinforced planar foiles, in plaster and cement reinforcements or as a carrier in layered products, all because of its specific characteristics that is, low weight, low cost and good permeability.
Heretofore Geo-grids, produced under currently known methods, consist of stay- and weft threads being combined crosswise in groups relative to each other which are firmly connected to or knitted with each other by so-called warp threads which form stitches. The continuously formed stitches around the stay threads serve as an additional stabilizing factor at the crossing points of the stay- and the weft threads as well as in the spacing between the crossing points of the Geo-grid material. However it has been shown, as a disadvantage. that the speed of the production of such a Geo-grid fabric cannot be raised, during a short term duration of the RPM of the machine and the concomitant high frequency of stitch forming because it is technically not feasible .
DE 198 16 440 C1 describes a method for the production of a warp knitted fabric in which arbitrary pattern variations with differing pattern repeats can be produced by lateral conveyors which vary in their speeds. In this arrangement, the lateral conveyor is driven independently from the drive of the knitting machine. This method is unsuitable in the efficient production of a Geo-grid fabric having an unchanged grid pattern because the production speed finally cannot be increased. One can merely obtain variable grid spacings by way of the differing speeds of the lateral conveyors but not, however, by variable pull-off speeds of the knitted fabric.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an increase in the production of a knitted fabric having large grid openings therein, and yet exhibiting a high grade quality, and a method that provides an effective and simple way of producing such a knitted fabric.
This object is achieved by way of the warp knitted fabric having the characteristics of claim
1
as well as a method for the production of such a knitted fabric including the steps as recited in claim
6
.
Appropriate further developments and embodiments have been recited in respective dependent claims.
The warp knitted fabric according to claim
1
consists of biaxially arranged stayand weft threads having large spacings and further consists of warp threads forming stitches which bind the stay threads therein. In the crossing areas of the stay and the weft threads, the weft threads and the stay threads are knitted together by the warp threads, whereby the number of the stitches per unit length (stitch density) within a repeat and in the section of the crossing areas of the stay and the weft threads is at least partially smaller than the crossing areas per se.
Thereby on one hand, the necessary supply of warp threads in the knitted fabric is less according to the invention when compared to the state of the art. The stay- and weft threads, at their crossing points where a firm connection is mandated, are merely knitted together by the warp threads including a high number of stitches. In the spacing between the crossing areas, however, where properly no connections need to be made, the knitted fabric has a low stitch density and thereby a lower number of stitches. That means that within a repeat, the knitted fabric exhibits differing stitch densities. That is, in those sections where a connecting function of the stitches is important, there is the presence of a high stitch density and in those sections where the stitches merely serve as a reinforcement, that is, a sideways connection with the stay threads, the fabric exhibits a lower stitch density.
On the other hand, the total number of stitches in the knitted fabric, according to the invention is less than in heretofore known knitted fabrics. Therefore, the knitted fabric can be produced at a higher speed than until now, because the time consuming stitch formation has been reduced. In this manner, a high quality Geo-grid fabric can be produced which has a high tensile strength, a firm cohesion of the stay- and the weft threads in their crossing areas, and has a high slide resistance and a possible low elongation and furthermore can be produced in a cost effective manner and a high productivity.
In an advantageous embodiment of the invention, each of the stay threads is bound in individually, that is, stay threads that are adjacent to each other are bound in individually. This has the advantage that the stay- and the weft threads that are arranged biaxially, respectively, are knitted separately by way of stitches. This is especially advantageous when the Geo-grid is to be used as a composite material or as a carrier in layering. An example is in the casting of the knitted fabric in an epoxy resin.
In a further advantageous embodiment of the invention, there are at least two adjacently lying stay threads connected to each other. In this manner, the knitted material, that is, the Geo-grid is especially useful in a further development because the biaxially crosswise structure has form stability and is formed evenly over the whole structure of the Geo-grid, that is, it is formed as an even and unitary knitted unit.
According to a further advantageous embodiment of the invention, a special fleece is provided below the weft threads and/or between the weft- and the stay threads. Thereby, the knitted material is especially suitable as a planar compound material in areas where a partial permeability or an impermeability is mandated. For example, this could be the case in bank emplacements or in the construction of street beds. The cover layer, that is, the fleece preferably consists of a coarse material having good adhesion characteristics.
According to the inventive method for the production of a biaxial structure of a warp knitted fabric having large openings. stay- and weft threads are arranged crosswise and in groups and are thereafter knitted together by way of warp threads forming stitches. Thereby, the number of stitches within a repeat of the structure is reduced in the spacing between the crossing areas of the stay- and weft threads when compared to the number of stitches within the crossing areas. The structure is pulled off, according to the repeat, at a slower rate in the crossing areas than between adjacent crossing areas. Because of the differing pull-off speeds of the knitted fabric, the stitch density can be varied in a simple manner without a change in the RPM of the machine, meaning the actual speed of knitting. The speed of the pull-off can be varied within small intervals, that is, several times within a repeat of the pattern. The decrease in the stitch density results in that altogether less stitches have to be formed in the production of the knitted fabric whereby the productivity of the inventive method is considerably increased. Furthermore, the needed amount of the warp thread supply is less when compared to the state of the art of the technology using unchanged stitch densities. This also is results in savings in cost and thereby to an increase in the productivity.
According to a further development of the inventive method, a special fleece runs in below the weft threads having a speed which is essentially the same as the stay thread
Banner & Witcoff , Ltd.
Liba Maschinenfabrik GmbH
Worrell Danny
LandOfFree
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