HK1030190B - Large surface high tensile geo-grid and its use as draining and reinforcing mesh grid as well as fence - Google Patents

Description

The present invention relates to large-area high-tension geogrid grids, their manufacturing process and device and their use as drainage and reinforcement grids.

Such geogrides are used, for example, to secure road and railway structures, to secure the ground, to stabilize embankments and to secure landfill sealing systems.

Since the late 1970s, the Tensar® geogrid grids of Netlon have been used worldwide in a wide variety of applications.

The manufacture of such geogrides involves perforating extruded polyethylene or polypropylene tracks at regular intervals. The tracks are heated and stretched either longitudinally (inaxially) according to UK patent 2 073 090 or longitudinally and transversely (bi-axially) according to UK patent 2 035 191. The stretching process moves the polymer molecules from an arbitrarily arranged position in an orderly and aligned position in the direction of stretching. This process increases the tensile strength and rigidity of the geogrides.

In order to improve the strength to weight ratio per square metre, DE-PS 41 37 310 (Akzo) describes a process for the manufacture of geogrids in which strips are first made of two layers of polymers with different melting points and then stretched (molecular bicomponent strips). The strips are then placed in rows so that the side of the strips with the lower melting point is crossed. The joint thus formed is then subjected to a temperature that exceeds the melting point of the polymer with the lower melting point but is below the melting point of the polymer with the higher melting point. This makes the adjacent cross-streets interconnected with the lower melting point.

A similar process is envisaged in the United Kingdom patent application 2 314 802 (Mercer), where the state of the art description states that the company Synode produces geogrids from molecularly oriented polyester straps coated on one side with a low melting plastic (bicomponent straps) which are then cross-layered so that the low melting sides are on top of each other in the cross-sections and then the cross-sections are softened.

The disadvantage of these geogrids has been that the bond strength at the cross sections, which is dictated by the lower melting polymer components, is not satisfactory.

To overcome this disadvantage, a process was developed in accordance with the above-mentioned British patent application 2 314 802 (notified on 2 July 1996 and published on 14 January 1998), which also uses molecular bicomponent strips, but with the change that one sub-bicomponent strip and one upper bicomponent strip are run in the direction of the machine per lattice truss, so that the two strips with their lower melting sides are superimposed on each other after the introduction of the transverse strips.

Although this method increases the strength of the bonding at the cross section, the disadvantage from the material side is that two different polymers are required to produce the bicomponent strips and two bicomponent strips are required for each of the respective gate components.

The present invention is therefore intended to provide a large area high tensile strength geogrid made of single-layer homogeneous molecularly oriented high tensile bars, which do not have any additional coatings, by welding in such a way that, on the one hand, a satisfactory bonding strength is achieved in the welded intersections of the plastic bars without significantly affecting the molecular orientation, i.e. the tensile strength of the plastic bars in the intersections, and, on the other hand, an economic speed of production is ensured.

This is achieved by using single-layer homogeneous molecular-oriented high-strength plastic rods and by applying the vibration welding technique, whereby a large number of intersecting sections of intersecting single-layer homogeneous molecular-oriented high-strength plastic rods are connected simultaneously under the same conditions by clock-wise pressure.

Vibration welding is a process whereby the intersecting areas of the plastic rods are not plasticized by heat from outside but by direct conversion of friction energy into heat. To this end, the plastic rods are vibrated at such frequencies and amplitudes in their intersection areas that the surfaces soften and thus weld under high pressure. The main characteristic of vibration welding is therefore the surface and back movement to produce friction, so that the surface heat is only lost on the surface surfaces and the molar heat is only lost on the total surface area of the plastic band. This process is effective because the production bands can be heated and produced in a short time, at a distance of at least 2.5 m.

This was not originally thought possible, since it was assumed that, with an expected surface compression of about 1.5 N/mm2 and a width of the plastic rods of, say, 12 mm for a 3 cm grid and about 5000 intersection areas to be welded, forces of about 1,000,000 N would be generated which would not allow controllable welding in any way.

Surprisingly, however, it was found that with the appropriate heavy-duty design of the welding tables, these forces can be intercepted and it is possible to weld, for example, 500 to 8000 intersections at once.

The essential element in this was the development of a new vibration welding device according to the invention, equipped with a large-area oscillating plate and corresponding substrates and corresponding control and pressure systems and rod-fitting devices.

Since a single vibration welding device according to the invention can weld 100 to 500 intersection areas depending on the spacing of the intersection areas and the width of the bars, which was previously unthinkable, it has become possible according to the present invention to produce large-area geogrid grids of any width, preferably in widths from 3 to 6 m, by placing an appropriate number of vibration welding units according to the invention next to each other.

The lengthwise rods, hereinafter referred to as longitudinal rods, are preferably fed in parallel at equal distances from each other. The lengthwise rods, hereinafter referred to as transverse rods, are placed at right angles to the longitudinal direction by laying them on the longitudinal rods, the longitudinal and transverse rods preferably forming square or less or highly elongated rectangular grid spaces.

The spacing between the longitudinal bars on the one hand and the transverse bars on the other hand may be chosen at will, preferably in the range of 10 mm to 100 mm, and in particular in the range of 20 mm to 80 mm, measured from the edge of the bars to the edge of the bars.

In the case of the large-area geogrid according to the present invention, the arrangement of so many plastic rods in the machine direction and of a corresponding number of plastic rods in the transverse direction is such as to obtain a total width of the geogrid of 3 m to 6 m, preferably 5 m, and a total length of 25 m to 500 m, preferably 50 m to 100 m.

The plastic rods used in accordance with the invention shall have either a square cross-section, preferably with side lengths of 2,0 mm to 6,0 mm, in particular, 2,5 mm to 4,5 mm, or a rectangular cross-section, preferably with a width of 5 mm to 40 mm, in particular, 10 mm, 12 mm or 16 mm, and a thickness of preferably 0,4 mm to 2,5 mm, in particular, 1,0 mm to 1,5 mm.

A special design uses plastic rods that are wider and/or thicker than the transverse rods as longitudinal rods.

The preferred thermoplastic plastics used include polyester (PES), e.g. polyethylene terephthalate (PET), polyolefins, e.g. high density polyethylene (PEHD) or polypropylene (PP), polyamides (PA), e.g. PA 6 and PA 66, aramide and polyvinyl alcohols (PVA).

In particular, polyethylene terephthalate (PET) or polypropylene (PP) are used as thermoplastic plastics. To ensure the highest tensile strength, the PP should have a maximum tensile strength ratio of 1:15 and preferably 1:9 to 1:13.

The strength of plastic rods is preferably between 300 N/mm2 and 800 N/mm2 and they can be flexible or rigid.

As the interaction between the reinforcement grating and the ground is based on the activation of frictional forces between the ground and the grating, the grating rods may preferably have a profile/impingement on their top and/or bottom to increase friction/contact with the ground.

For example, the printing depth should be between 0.5% and 30% of the thickness of the plastic rods, for example, the printing depth should be 0.15 mm per side for a plastic rod of 1.5 mm thickness.

Other possible imprints are: Long-sleeved curls curls web structures red structures with spikes, knobs, spikes, etc. or combinations of the engravings mentioned above.

The invention is further explained by the following illustrative statements, but not limited to them.

The high tensile strength plastic rods are extruded by means of a horizontal extruder with an automatic melt filter.

The plastic rods are stretched upwards through several racks, hot air channels and spray channels with rod-guided routes, and molecular orientation takes place.

The extruded and stretched plastic rods are rolled up on coils, e.g. up to a length of 15,000 lfm, by means of a winding machine.

For the further processing of high tensile strength plastic rods into large geogrides with widths preferably from 3.0 m to 6.0 m, in particular from 5.0 m, the coils produced are presented on coil grilles. The individual coil recordings preferably include a brake device to ensure controlled coiling of the coils. With a working width of 5.0 m and an assumed distance of 30 mm between the plastic rods and the plastic rods at a width of 10 mm, 167 recordings should be available.

As mentioned above, other spacings in the range of 10 mm to 100 mm can be chosen, since, for example, drainage mats, the spacings are preferably reduced to about 10 mm or less to ensure pressure-stable drainage flow rates.

All plastic rods to be laid longitudinally are preferably parallel to each other, as also mentioned above.

The longitudinal plastic rods (long rods) are pulled through a pull-off group. The pull-off group contains a cross-sectional system for separating the rods during rolling and a connecting device for automatically connecting the new rods to the rest of the old rods.

The pneumatically operated brakes ensure a controlled retraction of the individual length bars into the drawbar assembly.

The plastic rods (crossbars) running transversely to the longitudinal bars are laid over a load head, which preferably allows the simultaneous laying of up to 50 crossbars.

Individual brakes ensure a constant voltage in the individual crossbars during the application.

The crossbars are supplied via a crawler slide or a pull-off from the actual welding unit for the lattice cross sections. The crawler slide consists of one downward fixed duplex chain and two horizontally drivable duplex chains. To ensure sufficient compressive force between the two duplex chains to stretch the crossbars, a pressure hose is located under the lower chain guide that presses the lower crawler chain against the upper crawler chain.

The cutting equipment is used to cut the displaced, tensioned crossbars just before transport to the welding plant.

The vibration welding device, for example, consists of 10 vibrating oscillators arranged side by side, each with a large oscillating plate with an integrated oscillating frame, drive generators, amplitude control panel and oscillating device. The dimensions of the individual vibration oscillators are, for example, 475 mm x 720 mm, so that all 10 vibrating oscillators together allow welding of, for example, about 4000 to about 8000 individual welds in one operation.

The 10 vibration swingers each have a complete machine frame. The 10 corresponding sub-tools are located on 10 welding tables, each lifted by 4 hydraulic cylinders for welding.

After welding, the finished large-area geogrid can be fed through a main extraction unit of a casing station, for example for nonwovens, fabrics, textiles or films, to produce composite products, e.g. of grids and nonwovens, for use as a plastic drainage element or as a separating and reinforcing element in a process directly following the production of geogrid.

The geogrid grids covered with film according to the invention are excellent for covering plans for freight and lorries, as well as for spare roofs.

The geogrides of the invention themselves may be used, in addition to their main applications mentioned at the outset, for the construction of fences, for example, as wildlife protection fences, or for the construction of fences in livestock farming or for the construction of fences for construction site security, avalanche protection or rock impact protection.

Claims (20)

1. Method for the continuous production of geogrids which have a large surface area and comprise thermoplastic bars which cross one another and are joined together by welding at the areas where they cross one another, characterized in that single-layer, homogeneous, molecular-oriented plastic bars with a high tensile strength are used and a multiplicity of crossing areas arranged next to and behind one another are intermittently welded simultaneously using the vibration-welding technique.
2. Method according to Claim 1, characterized in that from 500 to 8000 crossing areas are welded simultaneously.
3. Method according to Claim 1 or 2, characterized in that a plurality of vibration-welding devices are made to vibrate simultaneously at equal pressures and amplitudes and frequencies, the amplitudes lying in the range from 0.5 mm to 2.5 mm, preferably from 1 mm to 2 mm, and the frequencies lying in the range from 60 to 300 Hz, preferably from 150 to 180 Hz.
4. Method according to one or more of the preceding Claims 1 to 3, characterized in that the plastic bars which cross one another are positioned in such a way that the plastic bars which run transversely to the direction of the machine (transverse bars) cross the plastic bars which run parallel to one another in the direction of the machine (longitudinal bars) at an angle of from 45° to 90°.
5. Method according to one or more of Claims 1 to 4, characterized in that the plastic bars are arranged in such a way that they are at a distance of from 10 to 100 mm, preferably from 20 mm to 80 mm, from one another, i.e. from side edge to side edge.
6. Method according to one or more of the preceding Claims 1 to 5, characterized in that the number of plastic bars in the direction of the machine and the corresponding number of plastic bars in the direction transverse thereto are such that the overall width of the geogrid is from 3 m to 6 m, preferably is 5 m, and its overall length is from 25 m to 500 m, preferably from 50 m to 100 m.
7. Method according to one or more of the preceding Claims 1 to 6, characterized in that the plastic bars used have a tensile strength of from 300 to 800 N/mm².
8. Method according to one or more of the preceding Claims 1 to 7, characterized in that plastic bars which are square in cross section, preferably with a side length of from 2 mm to 6 mm, in particular from 2.5 mm to 4.5 mm, or which are rectangular in cross section are used, preferably having a width of from 5 mm to 40 mm, in particular of 10 mm, 12 mm or 16 mm, and a thickness of preferably from 0.4 mm to 2.5 mm, in particular from 1.0 mm to 1.5 mm.
9. Method according to one or more of the preceding Claims 1 to 8, characterized in that the plastic bars used have been stamped on their top and/or bottom sides.
10. Method according to Claim 9, characterized in that the plastic bars used have a stamped depth on their top and/or bottom sides of from 0.5 to 30%, based on the thickness of the plastic bars, the stamping preferably forming a diamond-shaped structure.
11. Method according to one or more of the preceding Claims 1 to 10, characterized in that the longitudinal bars used are plastic bars which are wider and/or thicker than the plastic bars used in the transverse direction (transverse bars).
12. Method according to one or more of the preceding Claims 1 to 11, characterized in that the plastic bars used consist of polyethylene terephthalate (PET) or polypropylene (PP).
13. Method according to one or more of the preceding Claims 1 to 12, characterized in that nonwoven, woven or knitted fabrics or sheets are additionally laminated onto one or both sides of the finished large surface area geogrid by means of a heated tool, hot air or adhesive.
14. Large surface area geogrids which have a high tensile strength and comprise thermoplastic, single-layer, homogeneous, molecular-oriented bars which cross one another, have a high tensile strength and are welded at the points where they cross one another by means of the vibration-welding technique.
15. Large surface area geogrids which have a high tensile strength according to Claim 14, characterized in that they have been produced as described in one or more of the preceding Claims 1 to 13.
16. Vibration-welding apparatus for producing large surface area geogrids which have a high tensile strength and comprise plastic bars which cross one another and have a high tensile strength, characterized in that the apparatus has at least one vibration device which can be used to weld at least 100 crossing areas, preferably up to 500 crossing areas, simultaneously.
17. Vibration-welding apparatus for producing large surface area geogrids which have a high tensile strength and comprise plastic bars which cross one another and have a high tensile strength, characterized in that 10 vibration devices are arranged next to one another and are made to vibrate simultaneously at equal amplitudes and frequencies under pressure, by means of suitable control units, in order for up to 8000 crossing areas to be welded simultaneously under pressure.
18. Use of large surface area geogrids with a high tensile strength as described in one or more of the preceding claims as drain or reinforcement grids for constructing earthworks.
19. Use of large surface area geogrids as described in one or more of the preceding claims as fencing elements.
20. Use of large surface area geogrids which are laminated to sheets on one or both sides as tarpaulins.