Geotechnical net of large surface area and high tensile strength, method of and apparatus for manufacturing same as well as application thereof in drainage, concrete reinforcing and fencing as well

Description of the invention

The subject of the invention is a geogrid with a large area and high tensile strength, a method and device for the production of a geogrid, and the use of a geogrid.

These types of geogrids are used, for example, for fixing road and track structures, fixing soil, stabilizing slopes and securing landfill sealing systems.

Since the late 1970s, Netlon's so-called Tensar® geogrids have been used in a wide variety of fields around the world.

In the production of this type of geogrid, extruded polyethylene or polypropylene webs are perforated at regular intervals. The webs are then heated and simultaneously stretched, either according to British Patent No. 2,073,090 in the longitudinal direction (uniaxially) or according to British Patent No. 2,035,191 in the longitudinal and transverse (biaxial) directions. Stretching shifts the polymer molecules from a disordered system to an ordered system in the direction of stretching. This method increases the tensile strength and stiffness of the geogrid. Another construction of this geogrid is disclosed in US-PS 4,618,385 (Mercer). A problem with these geogrids is that the nodes of the mesh cannot be stretched in the same way as the ribs therebetween, so the strength of such geogrids in terms of a square meter weight is not fully satisfactory.

In order to improve the strength-to-weight ratio of one square meter, DE-PS 41 37 310 (Akzo) proposes a method for producing geogrids in which strips are first produced with two layers of polymers with different melting points and then stretched. , resulting in particle oriented bicomponent belts). The strips are then placed crosswise in rows so that the sides of the strips with the lower melting point are in contact with each other. The directional mat thus formed is then subjected to a temperature which is above the melting point of the lower melting point polymer and at the same time which is below the melting point of the higher melting point polymer. As a result, the crossing points of the adjacent rows are joined together by a polymer with a low melting point.

A similar process is the starting point for British Patent Application No. 2,314,802 (Mercer). In the prior art introduction to the description, it is stated herein that Signode produces geogrids from particle-oriented polymer tapes coated on one side with a low-melting plastic (two-component tapes). These two-component polymer tapes are then cross-layered so that the low-melting surfaces are in contact with each other at the crossing areas of the tapes. The areas where the strips cross are then welded.

The disadvantage of these geogrids is the fact that the bond strength in the area of ​​the crossing of the strips, determined by the lower melting polymer components, is not satisfactory.

To overcome this inconvenience, the above-mentioned British Patent Application No. 2,314,802 (filed July 2, 1996 and published January 14, 1998) developed a method which, although also used particle-oriented two-component belts, with the difference that in in the direction of machine operation, one two-component trouser belt and one two-component outer belt are led onto one mesh rib in this way, that after the introduction of the transverse strip, the two belts adjoin each other with their lower fusible sides over the entire surface. The two-component trouser belt and the two-component overlay belt are then joined together over the entire surface, with a cross belt inserted between them, by hot gas welding or hot air welding.

Although this method makes it possible to increase the strength of the connection in the area of ​​the crossing of the belts, the disadvantage is that, from the material aspect, two different polymers are needed for the production of the two-component belt, and two two-component belts are needed to make the rib.

The object of the invention is to provide a high-area, high-tensile geogrid, manufactured from monolayer homogeneous rods with oriented particles and high tensile strength, which rods do not have any additional coatings, by welding in such a way that on the one hand it achieves satisfactory connection strength in the welded crossing areas of plastic rods, without significant damage

Particle orientation, that is to say, the tensile strength of the plastic bars in their crossing areas is compromised, and on the other hand, a cost-effective production speed is ensured.

The method of continuous production of large-area geogrids from crossing thermoplastic plastic rods, which are joined together in the crossing areas by welding, according to the invention, is characterized in that single-layer homogeneous plastic rods with oriented particles and high strength are used. tensile, and a large number of them placed one after the other and one next to each other, the cross-over areas of the bars are welded using the stream welding method with the simultaneous use of the vibration welding technique.

Preferably, 500 to 8,000 rod crossing areas are welded simultaneously.

Preferably, several vibration welding units are used simultaneously, vibrating with the same pressure and with the same amplitude and with the same frequency, the amplitudes being in the range from 0.5 to 2.5 mm, preferably from 1 to 2 mm, and the frequencies are in the range of 60 to 300 Hz, preferably from 150 to 180 Hz.

Preferably, the crossing plastic bars are guided such that the plastic bars running transversely to the machine running direction, called transverse bars, intersect with plastic bars running parallel to each other in the machine running direction, called longitudinal bars, underneath the machine. an angle from 45 to 90 °.

Preferably, the plastic rods are arranged such that their mutual spacing, measured from the side edge * to the side edge, is from 10 to 100 mm, preferably from 20 to 80 mm.

Preferably, so many plastic rods are placed in the machine running direction and a corresponding number of plastic rods transverse to it that a geogrid with a total width of 3 to 6 m, preferably equal to 5 mm, and a total length are obtained. from 25 to 500 m, preferably from 50 to 100 m.

Preference is given to using plastic rods with a tensile strength of 300 to 800 n / mm².

Preferably, plastic rods are used with a square cross-section, preferably with a side length of 2 to 6 mm, in particular 2.5 to 4.5 mm, or rods with a rectangular cross-section, the width of which is preferably from 2 to 6 mm. 5 to 40 mm, especially 10, 12 or 16 mm, and the thickness is preferably 0.4 to 2.5 mm, especially 1.0 to 1.5 mm.

Preference is given to using plastic rods whose upper and / or lower surface is embossed.

Preference is given to using plastic bars, the embossing of which on the upper and / or lower surface has a depth of 0.5 to 30% with respect to the thickness of the plastic bars, the embossing of which preferably has a rhombic structure.

Preferably, the longitudinal bars are plastic bars which are wider and / or thicker than bars oriented in the transverse direction, known as transverse ones.

Preference is given to using plastic rods in the form of polyethylene (PE) or polypropylene (PP).

Preferably, the finished, large-area, plastic rod geogrid is additionally laminated on one or both sides, using a hot wedge or hot air, with nonwovens, woven fabrics, knitted fabrics or films.

The high-area, high-strength geogrid of crossing thermoplastic plastic rods according to the invention is characterized in that the thermoplastic plastic rods are monolayer homogeneous rods with particle oriented and high tensile strength welded together in areas crossing using the vibration welding technique.

A vibration welding device for producing large-area, high-tensile geogrids from crossing plastic rods with high tensile strength, according to the invention, is characterized in that it comprises at least one vibrating unit by means of which at least 100 are simultaneously welded. crossing areas, preferably up to 500 crossing areas.

Advantageously, the device comprises ten adjacent vibrating welding units which, by means of suitable control devices, are simultaneously vibrated with the same amplitude and frequency, with simultaneous pressure, simultaneously welding up to 8,000 cross-bar areas.

PL 193 239 B1

A geogrid with a large surface area and high tensile strength, according to the invention, is used as a drainage or reinforcement mesh in the production of earthworks, as elements of a fence or, in a variant laminated on one or both sides with films, as tarpaulins.

The vibration welding technique includes a friction welding method in which the crossing areas of the plastic rods resting thereon are plasticized not by applying heat from the outside, but by directly converting the frictional energy into heat.

To this end, the plastic rods are vibrated at such frequencies and amplitudes in the areas where they cross with each other that the surfaces are softened and thus welded together under high pressure. The essential feature of vibration welding is therefore movement back and forth to create friction whereby the heat of fusion only acts on the surfaces of the bars and the orientation of the particles is lost only on the surface of the plastic bars.

In addition, this method has the advantage of short heating and cooling times, since heating only takes place on the surfaces of the bars, which makes it possible to shorten the cycle times, ensuring the desired cost-effective production speed, which means that the geogrids of the invention having a large surface area with a total width of e.g. m and a distance of the plastic strips from the center of the strip to the center of the strip of about 3 cm can be produced at a speed of at least 2.5 meters per minute.

This was originally considered impossible as it was assumed that with an expected surface pressure of about 1.5 N / mm², a width of plastic rods of, for example, 12 mm, a mesh pitch of 3 cm and about 5,000 welded crossing areas, forces of about 1,000,000 N would arise, which would make it completely impossible to control the welding process. Moreover, it was assumed that in the case of vibrations with a frequency of 60 to 300 Hz and a large number of simultaneously welded areas of rod crossing, the destruction of the machine parts would take place.

It has surprisingly been found, however, that with a suitably bulky design of the welding tables it is possible to absorb these forces, which in turn allows for the simultaneous welding of, for example, 500 to 8000 crossover areas.

It was important here to provide, according to the invention, a new vibrating welding unit, equipped with a large-area shock plate and suitable supports and suitable control and pressure systems, as well as bar feed systems. Several of these new vibration welding units are placed side by side and made to vibrate simultaneously with the same clamping parameters and the same amplitude and frequency. The amplitudes and frequencies are thereby controlled such that the amplitudes are in the range from 0.5 to 2.5 mm, preferably from 1 to 2 mm, and the frequencies are in the range from 60 to 300 Hz, preferably from 150 to 180 Hz.

Since, depending on the spacing between the crossing areas and the width of the bars, 100 to 500 crossing areas can be welded using the vibration welding unit according to the invention, which has not been possible hitherto, the present invention allows the production of geogrids with a large surface area and any width, preferably with a width of 3 to 6 m, placing a suitable number of vibration sealing units according to the invention side by side.

The feeding of the bars arranged along the machine, hereinafter called longitudinal bars, preferably takes place parallel and equidistant from each other. The laying of bars arranged transversely to the longitudinal direction, hereinafter referred to as transverse bars, preferably takes place at right angles to the longitudinal direction, by laying on the longitudinal bars, with the longitudinal and transverse bars forming in the mesh preferably square or more or less elongated rectangular spaces indirect. Of course, the transverse bars, as well as the parallel longitudinal bars, may cross at an angle of 45 to 90 °.

The distances between the longitudinal bars on the one hand and the transverse bars on the other hand may be arbitrary, but preferably in the range from 10 to 100 mm, preferably from 20 to 80 mm, the distance being measured from the side edge to the side edge of the bars. In the production of the geogrids having a large area according to the invention, so many plastic rods are placed in the machine direction and a corresponding number of plastic rods in the transverse direction that a geogrid with a total width of 3 to 6 m is obtained, preferably equal to 5 mm, and an overall length from 25 to 500 m, preferably from 50 to 100 m.

PL 193 239 B1

The plastic rods used according to the invention have either a square cross-section, preferably with a side length of 2 to 6 mm, in particular 2.5 to 4.5 mm, or a rectangular cross-section, preferably of a width of 5 to 40 mm, especially 10, 12 mm. or 16 mm, and a thickness of preferably 0.4 to 2.5 mm, especially 1.0 to 1.5 mm.

In a particular embodiment, the longitudinal bars used are plastic bars that are wider and / or thicker than the transverse bars.

Preferred thermoplastics are polyester (PS), e.g. polyethylene terephthalate (PET), polyolefins, e.g. low pressure polyethylene (HDPE) or polypropylene (PP), polyamides (PA) e.g. PA6 and PA66, aramid and polyvinyl alcohols ( PVA).

The thermoplastics used are, in particular, polyethylene terephthalate (PET) or polypropylene (PP). In order to obtain the highest possible tensile strength, the strain ratio for PP should be at most 1:15, preferably 1: 9 to 1:13. In the case of PET, a maximum strain ratio of 1:10, preferably 1: 6 to 1: 8 is recommended, which allows the elongation to be achieved with the highest tensile force of 5 to 20%.

The strength of the plastic rods is preferably from 300 to 800 n / mm²they may be flexible or rigid.

As the interaction between the reinforcement mesh and the ground consists in activating the frictional forces between the ground and the mesh, the mesh bars should be profiled / embossed on their upper and / or lower surfaces to increase friction / contact with the ground.

Possible embossing are, for example, diamond-shaped structures with an embossing depth of 0.05 to 0.5 mm. The embossing depth should, however, be between 0.5 and 30% of the thickness of the plastic rods.

For example, for a 1.5 mm thick plastic rod, the embossing depth is 0.15 mm on each side.

Other possible embossments can be, for example:

- longitudinal grooves,

- transverse grooves,

- honeycomb structures,

- diamond-shaped structures with spikes,

- protrusions, spikes and the like,

- or combinations of the above-mentioned ribs.

The subject matter of the invention is described below on the basis of exemplary data, without being limited thereto.

Plastic rods with high tensile strength are extruded using a horizontal extruder with an automatic filter of the molten plastic.

The plastic rods are stretched to give them a high tensile strength by means of several tensile elements, hot air channels and spray channels with rod-bending elements, the orientation of the particles taking place.

The extruded and stretched plastic rods are wound onto spools, for example, to a length of 15,000 running meters.

For the further processing of the high-tensile plastic rods into geogrids with large surfaces and widths, preferably 3.0 to 6.0 m, in particular 5.0 m, the finished spools are placed on the frames. The holders for the individual spools preferably include a brake device ensuring controlled unwinding of the spools. With a working width of 5.0 m, an assumed distance between the centers of the plastic bars of 30 mm and a width of the plastic bars of 10 mm, 167 holders should be used.

As already mentioned, other distances in the range of 10 to 100 mm can also be chosen, since, for example, for drainage mats, the spacing is preferably up to about 10 mm or even less, in order to obtain a drainage structure with pressure-resistant parameters.

All the plastic rods that are laid in the longitudinal direction are preferably guided, as already mentioned, parallel to one another.

PL 193 239 B1

The plastic bars laid in the longitudinal direction (machine direction) (longitudinal bars) are unwound by means of the tensioning unit. The tensioning unit has a cross cut system to separate the longitudinal bars when changing the spool and a coupling device to automatically connect the new longitudinal bars to the rest of the old longitudinal bars. Preferably, ultrasonic or vibration welding units are used for the joining.

The pneumatically actuated brakes ensure a controlled drawing of the individual longitudinal bars into the tensioning unit. The tensioning unit is designed in such a way that a constant tension of the individual longitudinal bars is ensured during the subsequent welding process.

Plastic bars that run transversely to the longitudinal bars, called transverse bars, are laid with the laying head. Advantageously, up to 50 crossbars can be stacked simultaneously. The laying head is designed such that it is possible to stack up to 50 transverse bars, preferably in both directions when driving over the longitudinal bars.

The individual brakes ensure a constant tension in the individual crossbars during paving.

The arranged transverse bars are fed with the help of a caterpillar hoist to the proper welding unit for the crossing areas of the mesh bars. The track hoist consists of a lower fixed double chain and two horizontal movable double chains respectively. In order to ensure sufficient pressure between the two double chains to tighten the cross bars, there is a pneumatic sleeve under the lower chain guide that presses the lower track chain against the upper track chain.

Following cutting devices cut the stacked taut cross bars just prior to their transport to the welding device.

The vibration welding device comprises, for example, 10 juxtaposed vibrating units each comprising a large shock plate with an integrated shock frame, drive generators, an amplitude adjustment plate and a vibration limiter. The dimensions of the individual vibrating units are, for example, 475 x 720 mm, so that all ten vibrating units allow a total of, for example, about 4,000 to about 8,000 individual welds in one working operation. The welding process preferably takes place in the range from 60 to 300 Hz, in particular in the range from 150 to 180 Hz, with amplitudes up to 2 mm.

Each of the ten vibrating units has a complete frame. Ten suitable lower tools are provided on ten welding tables, each of which is raised for welding by 4 hydraulic cylinders. Separating combs located in the area of ​​the welding tools are used to guide the plastic rods.

After the welding process, the finished large-area geogrid is fed through the main tensioning unit to a laminating station, e.g. as a drainage element made of plastic or as a separating or reinforcing element. One- or two-sided lamination can be performed by hot wedge, hot air, glue and other means. After lamination, the composite products are directed to a cutting and winding unit.

The geogrids according to the invention, laminated with foils, are very suitable for tarpaulins for transported goods and trucks, and also as auxiliary roofing.

The geogrids according to the invention themselves can, apart from their main fields of application, also be used for the production of fences, for example for protection against wild animals, or for the production of fences used in animal husbandry, as building protection, avalanche protection or as protection against falling stones.