WO1997043469A1

WO1997043469A1 - Process and device for producing a mowing fibre

Info

Publication number: WO1997043469A1
Application number: PCT/EP1997/002247
Authority: WO
Inventors: Klaus Bloch; Barbara Bloch; Andrej Jodl
Original assignee: Klaus Bloch; Barbara Bloch; Andrej Jodl
Priority date: 1996-05-10
Filing date: 1997-05-02
Publication date: 1997-11-20
Also published as: EP0912779A1

Abstract

The invention relates to a process for producing a mower monofilament which is extruded and drawn from a plastic, whereafter its cross-section is altered, reduced and shaped by the removal of plastic material by laser beams or mechanical cutting blades. During this process, in addition to its straight longitudinal movement, it is rotated or oscillated about its longitudinal axis or the laser beams or blades perform a rotary or oscillating movement about the longitudinal axis of the monofilament.

Description

description

Method and device for producing a mowing line

The invention relates to a method for producing a monofilament mowing thread made of a thermoplastic, extrudable and stretchable plastic, the cross section of which in the longitudinal extension of the mowing thread is changed in some areas, a monofilament being extruded from the plastic and subsequently at a temperature below the melting temperature of the plastic by two is stretched up to ten times and then cooled to room temperature, whereby a stretched monofilament of high strength is obtained, and an apparatus for carrying out the method according to the invention.

Mowing threads made of plastic for brush cutters with a drive motor have been known for a long time. The

Cutting thread clamped at one end and set into very fast rotational movement by the drive motor at up to 15,000 revolutions / minute, the cutting thread following the prevailing centrifugal force extending in a straight line rotating about the axis of rotation and plant stalks or the like. cut with the same cutting edge. As a result of these high speeds, the known plastic mowing threads are subjected to high loads during operation, and the requirements with regard to wear resistance and thus the service life - service life - are set accordingly high. In order to increase the wear resistance and the mechanical resilience of a mowing thread, the mowing threads extruded from a suitable, in particular plastic plastic as monofilament are used in a 1 stretched below the melt temperature and then cooled to room temperature to stabilize the stretching, which increases the strength accordingly.

Suitable extrudable and stretchable thermoplastic materials which are suitable for the production of such cutting threads include, for example, suitable high-strength plastics, such as polyamides, nylon, polyurethanes, modifications of these plastics and

Mixtures of thermoplastics including processing aids, stabilizers, colorants or the like are understood.

Due to the high number of revolutions in the

In addition, the cutting thread of the mower thread that is clamped in place causes considerable noise disturbance due to eddy separation of the mowing thread rotating at high speed. It has therefore already been proposed on various occasions to reduce this high level of noise pollution by the fact that the straight tear-off edge of the air masses flowing around the cutting line forming during the rotation of the cutting line along the rectilinear surface line of the cutting line is responsible for the eddy separation in connection with the increased noise level is to interrupt in certain areas and thus counteract the generation of noise.

It is known from DE 94 12 925 Ul to design a mowing thread made of a monofilament with a polygonal cross-section such that the position of its cross-section, based on its longitudinal axis, changes continuously by a constant angular amount per unit length of the longitudinal axis. As a result of this continuous change in cross section, the side edges of the monofilament having a polygonal cross section run helically around its longitudinal axis. This continuously changing position of the cross-section of the monofilament is achieved in the known mowing thread in that the monofilament is produced along its length Longitudinal axis is twisted and thus the helical course of the side edges is established. In order to fix this twisting of the monofilament, the monofilament is subsequently heated up to its plastic state area and in this way the structure inside the monofilament is changed and the monofilament is fixed in its twisted position. However, this heating has the result that any stretching of the monofil with the desired increase in strength is lost again during the heating of the monofil and the monofil obtained in this way has only the low strength of an undrawn monofil and an inadequate service life.

From DE 40 05 879 Cl a mowing thread for brush cutters is known which has at least one helically extending groove and / or elevation on the outer surface of its base body which forms almost the entire cross section of the mowing thread. According to DE 40 05 879 Cl, such a cutting thread is extruded or injected as an integral part. Such after the

DE 40 05 879 Cl integrally produced cutting thread by extrusion or spraying can no longer be subjected to consolidation by stretching, since subsequent integral stretching of the monofilament would remove the integral desired cross-sectional shape of the cutting thread previously produced by extrusion or spraying. The mowing thread according to DE 40 05 879 Cl thus has the same disadvantages of low strength, low wear resistance and short service life as the mowing thread according to DE 94 12 925 Ul.

The invention is based on the object of proposing a method and a device for producing a mowing thread which has both high strength and wear resistance of a stretched monofilament and also enables a substantial reduction in the noise level during operation. This object is achieved in a generic method for producing a monofilament mowing thread in that the monofilament obtained after the extrusion and stretching in the direction of the longitudinal axis of the monofilament continuously or intermittently by means of laser beams or mechanically for the area-by-part removal of plastic while changing and reducing the cross-section of the monofilament is processed and the monofilament in addition to its transport movement in the direction of the longitudinal axis of the monofilament during mechanical processing or processing by means of the laser beams about its longitudinal axis, performs a rotary movement in only one direction of rotation or an oscillating rotary movement or during the transport movement of the monofilament in the direction of its longitudinal axis mechanical processing or processing by means of the laser beams rotating or oscillating about the longitudinal axis of the monofilament.

According to the invention, a stretched, that is to say high-strength, monofilament is subsequently machined, the use of rotating or oscillating rotating cutting knives according to the features of claim 2 being provided for mechanical machining, the monofilament continuously in the direction of its longitudinal axis on at least one around the longitudinal axis of the monofilament rotating or oscillatingly rotating cutting knife is passed and the plastic cutting knife is used to peel off areas in part, changing and reducing the cross-section of the monofilament, and cutting surfaces on the monofilament with cutting edges running on the circumference of the monofilament are formed by the action of the cutting knives which correspond to the rotational or oscillating movement of the cutting blades in the longitudinal extension of the monofilament and the obtained monofilament which is profiled in the longitudinal and transverse directions and forms the mowing thread Maintains strength obtained by stretching.

The method according to the invention is therefore based on a conventional, straight and stretched and due to this stretching good strength

Monofils. Such a rectilinear monofilament, however, has unfavorable noise emissions, since in operation at the high rotational speeds along the surface lines of such a rectilinear monofilament, a continuous tear-off edge is formed for the air masses flowing around the cutting thread, which is responsible for the noise development. According to the invention, therefore, the monofil obtained after extrusion and stretching is processed by means of the cutting knives rotating or oscillating about the longitudinal axis of the monofilament such that cut surfaces with cut edges corresponding to the circumference of the monofilament are formed by peeling off cross-sectional areas. Since the cutting knives rotate in the longitudinal direction around the longitudinal axis during the simultaneous movement of the monofilament, the cut surfaces and the associated cut edges are applied helically around the longitudinal axis of the monofilament. In this way, the forming along the surface line and cutting edges of the cutting line thus prepared separation edges in rotation in a brushcutter through the helical arrangement of the cutting edges are interrupted at periodic intervals, ^'what is already known to premature or late outline of the flow and thus the significant reduction in

Noise development of such a mowing line contributes. This design of the cut edges in a helical arrangement does not require any fixation, for example by supplying heat, since the structure located inside the monofilament is not changed by the design of the cut edges, but remains constant in the same orientation that it is during the extrusion and the subsequent one Stretching has received. Using the cutting knives, only a desired surface profile of the monofilament with the helically surrounding cutting edges is introduced.

As a result, in the mowing thread produced according to the invention, a fixation necessary after stretching, for example by means of heating, is not necessary and the advantageous ones Strength properties of the mowing line are retained while at the same time causing considerable noise reduction.

Instead of mechanical processing, the monofilament according to the invention can also be reduced in cross-section by means of the action of laser beams and the geometry of the cross-section can be changed, and on the monofilament by the action of the laser beams and evaporation of plastic in the longitudinal direction of the same, intermittent areas or continuous cut surfaces with am The circumference of the monofilament cut edges are formed, which are coiled according to the rotational or oscillatory movement of the monofilament. According to the invention, the cut edges can be continuously coiled or can also be intermittent, such as sections or areas limited.

With the method according to the invention it is not only possible to produce a mowing thread as a monofilament made of plastic in extruded and stretched and thus high-strength form, but at the same time to give it a form which counteracts a noise formation of the mowing thread during operation. Usually, at the high speed of rotation of a brush cutter with mowing line, the eddies are periodically detached at the free end of the mowing line. However, the cutting edges on the mowing thread that form cutting edges that are formed by means of laser beam processing enable early eddy separation at always different locations, which enables a considerable reduction in the noise level.

With the method according to the invention, it becomes possible for the first time to produce a mowing line with a relatively high wear resistance and service life, and a lower noise level with brush cutters equipped with such mowing line at 10,000 to 15,000 revolutions per minute. Advantageous embodiments of the method according to the invention can be gathered from the characterizing features of the subclaims.

The mowing thread according to the invention made of a stretchable and extrudable plastic which is extruded and stretched two to ten times is characterized in that it has at least three helical tear-off edges running in the longitudinal direction on the outermost circumference of the monofilament, either only in one spiral direction or an alternating spiral direction corresponding to an oscillating movement is present. According to the invention, the mowing thread has edges, i.e. sharp edges, in contrast to the rounding of the outer circumference in beads according to US Pat. No. 4,186,239. Also when the cutting thread is extruded

DE 4005879 C1 no sharp edges of grooves are reached, but slightly rounded transitions are usually produced.

It is known in both material processing

Welding of plastics and metals as well as laser for cutting and drilling. The energy can be metered exactly and the laser beam can be focused and localized very precisely, so that it is possible to carry out the processing according to the invention, i.e. Cutting or trimming monofilaments for the production of mowing thread with a cross section varied in the longitudinal extent of the mowing thread with cutting edges as tear-off edges with high precision. When processing plastic by laser for the purpose of cutting or removing material

Changing the cross-sections removes the plastic in the areas that come into contact with the laser beam by evaporation. A certain amount of material removal is also associated with the cutting. This creates precise, relatively sharp edges on the circumference of the monofilament machined in this way, both with continuous cut surfaces and with area-by-zone removals, for example the formation of notches. Θ

According to the invention, the helical course of the cut edges is achieved in that the cut surfaces, which are produced on the monofilament by means of a laser beam or mechanically by means of a cutting knife, are turned by a corresponding rotary movement of the monofilament and thus the cut edges, in which the cut surfaces end on the circumference of the monofilament. It is of course also possible to pull the monofilament straight through during processing by means of the laser beam or the cutting knives and to let the laser beams or cutting knives carry out a corresponding rotary movement around the monofilament, for example continuously rotating or oscillating, as a result of which analog cut surfaces and cutting edges are produced on the monofilament . Correspondingly, this method can also be carried out in accordance with the characterizing features of subclaims 3 to 11 if, instead of the monofilament, the laser beams or cutting knives carry out the rotary movement.

In the event that the monofilament is rotated in order to obtain the correspondingly coiled cutting edges and cutting surfaces, it may be expedient, in order not to rotate the entire monofilament over the entire guide path including the supply roll, to have the monofilament only perform an oscillating movement via a corresponding one Angles, for example preferably only up to 180 °, in particular only up to 90 °, back and forth. Accordingly, even with straight guidance, only the laser apparatus for the laser beams or cutting knives can be moved back and forth or rotating about the longitudinal axis of the monofilament.

In order to ensure a uniform and constant action of the cutting knives on the monofilament passed by the cutting knives, the invention proposes that the monofilament can be arranged downstream of the cutting knives in the direction of transport of the monofilament in the form of a perforated disc, the through hole of which is one of the Outer contour of the cross-section corresponding to the cross-section of the monofilament, which has not yet been changed by means of the cutting knife, is guided.

The remain during the entire processing of the monofilament

Cutting knife with respect to the longitudinal axis of the monofilament preferably rotates stationary when rotating about the longitudinal axis of the monofilament.

The method according to the invention can be applied to various cross-sectional shapes.

According to a further development of the method according to the invention, a monofilament with a relatively large circular cross-section is extruded and then stretched, preferably four to eight times and then the monofilament is severed by means of two mutually perpendicular laser beams, the theoretical crossing point of the laser beams preferably being on the Longitudinal axis of the monofilament is located, so that four individual cutting threads, each with a cross-section corresponding to a quarter circle with three longitudinally extending cutting edges in one direction or alternating spiral directions, are produced as tear-off edges from the extruded and stretched monofilament in accordance with the spiraling cutting surfaces, which by means of the Laser beams are generated. The quarter-circular cross-sections of the monofilaments, which are almost triangular, have relatively sharp tear-off edges, namely three, due to the process technology according to the invention, whereby due to their compact cross-sectional shape and the stretching they have high strength and thus wear resistance and, due to the coiled tear-off edges due to early multiple Vortex shedding during operation produces less noise compared to uncoiled mowing thread. This procedure according to the invention has the further advantage that, for example, four cutting threads can be produced from a monofilament, which also means by means of Laser beam processing a relatively high productivity can be achieved.

According to a preferred embodiment, an extruded and stretched monofilament with a preferably circular cross section is used as the monofilament, with two diametrically opposed rotating or oscillatingly rotating cutting knives or two mutually parallel laser beams running parallel to one another acting in such a way that two are opposed to one another Sides of the monofilament preferably sections of equal size are continuously separated from the cross section of the monofilament in the longitudinal extension or removed by evaporation of the material and a mowing thread with four helical cutting edges running in the longitudinal extension is produced. Two circular sections are advantageously separated from the cross section of the monofilament. Such a mowing thread made from a monofilament with a circular cross-section looks like a twisted mowing thread after its completion, however, its internal structure is not subject to any change in position, but the helical arrangement of the cut edges is achieved solely by peeling off areas of the cross-section of the monofilament the longitudinal axis of oscillating cutting knives causes surface profiling. The mowing thread produced by the method according to the invention thus experiences only a surface profiling which is advantageous for the development of noise due to the processing by means of laser beams or the cutting knife, while at the same time its increase in strength caused by the stretching is retained.

The sections of equal size, which are processed on opposite sides of the monofilament by means of laser energy, can either be straight sections, i.e. there is a flattening or flattening of the

Cross-section of the monofilament or also in the form of concave to groove-shaped courses. w

In a further embodiment of the invention it is proposed that an extruded and stretched monofilament with a circular cross-section is used as the monofilament and a cutting knife acts on the monofilament in such a way that a circular section is peeled off from the cross-section of the monofilament and preferably a monofilament with a crescent-shaped cross-section is obtained, wherein the cutting edge resulting from the cutting off of the circular section on the monofilament is coiled in the longitudinal direction of the monofilament.

Furthermore, it is possible that an extruded and stretched monofilament with a star-shaped cross-section with protruding star points is used as the monofilament and at least one rotating cutting knife acts on the monofilament in such a way that sections of the protruding star points are continuously cut out in the longitudinal direction and a mowing thread is used Monofilament with helical cut lengths and corresponding cut edges is obtained in the longitudinal extension over the star points. The sections continuously cut out from the star teeth along the cut edges in turn cause an interruption of the tear-off edge which forms in a straight line along the generatrix of the mowing line, which causes the advantageously low noise level of the mowing line produced by the method according to the invention.

Of course, other cross-sectional shapes of monofilaments can also be used within the scope of the invention. It is also possible to produce desired straight and / or curved cut surfaces or cut surfaces with incorporated recesses and notches or the like by appropriate grinding of the cutting knives.

A monofilament with a diameter of 5 to 10 mm is advantageously extruded and subsequently stretched four to eight times and then by cutting or removing cross-sectional areas from the circumference of the monofilament by means of the rotating or oscillating cutting knives or \ l Laser beams processed into a profiled mowing thread with an average diameter of approx. 1.5 to 4 mm and helical cutting edges.

In order to achieve a favorable vortex detachment when operating the mowing line at high rotational speeds, which result in a correspondingly lower noise level, it is proposed to choose the helical slope of the tearing edges of the mowing line so that the length of the mowing line is 1 to 2.5 cm a demolition takes place, ie the distance between two intersecting cutting lines of the cutting thread successively crossing cutting edges is 1 to 2.5 cm. The active part of a mowing thread in the brush cutter, which rotates at high speed, is usually between 15 and 20 cm in the known devices. In this way, according to the method of the invention, the mowing thread can be designed so that six to ten tears, i.e. Vertebral detachments on a mowing line can take place during operation.

The mowing thread is preferably machined in a mirror-symmetrical manner and has a correspondingly mirror-symmetrical cross section.

According to the invention, it is also possible to tear edges on the

To produce the surface of the monofilament that is only present in some areas, for example by forming notches through the over-exposure of laser beams to the surface of the monofilament and evaporation, i.e. Removal of plastic in the desired areas according to the characterizing features of claim 10. The notches can have the same size and shape and uniform arrangement on the monofilament, but irregular, possibly repetitive repetitive arrangements and / or configurations of the notches are possible in order to quality

To loosen the angle of the mowing line and achieve a correspondingly high level of noise reduction. To increase the economic viability of the method according to the invention, it is proposed that the plastic peeled and cut off from the monofilament by means of the cutting knives be collected and fed again into the extrusion process for producing monofilaments for mowing threads.

A device according to the invention for carrying out the mechanically working method has a cutting device which is rotatably arranged around the monofilament by means of a drive and has at least one cutting knife, past which the monofilament is guided and thereby peeling off the cross-sectional areas of the monofilament. Immediately downstream of the cutting device in the transport direction of the monofilament is a guide device which is formed from a perforated disc, the through hole of which is formed with a cross section corresponding to the outer contour of the cross section of the monofilament which has not yet been changed by means of the cutting knives. One is for guiding the monofilament past the cutting knives and pulling the monofilament through the guide device

Deduction device provided for the monofilament. It is possible within the scope of the invention to directly, i.e. downstream of the extrusion system with stretching device for the production of the stretched monofilament or the monofilament is first wound up on a supply roll after its extrusion and stretching and guided from this supply roll by means of the take-off device through the cutting device and the guide device and then wound up again as a finished mowing thread.

The cutting knives are advantageously held in a holding device which has a toothed ring on the outside and can be driven by a drive device, such as an electric motor, by means of a chain or belt drive, so that the cutting knives inside the holding device rotate around the monofilament guided by the cutting device or can rotate in an oscillating manner, depending on the type of drive used.

The cutting knives held in the holding device are advantageously held in the holding device in a radially adjustable manner with respect to the monofilament, so that an adaptation to different monofilament diameters and desired cutting depths of the cutting knives as well as the state of wear of the cutting knives is possible.

Mowing threads can be produced particularly economically if two or more monofilaments are processed simultaneously. In this case, two or more

Holding devices with at least one knife each and associated guide devices for each monofilament driven by a common drive, which enables a particularly inexpensive device to be produced.

In such a case, when several monofilaments are processed into mowing threads at the same time, can also advantageously be used as

Guide element can be provided a single perforated disc with through holes formed according to the number of monofilaments.

Embodiments of the inventive method for

Generation of cutting thread and cutting thread according to the invention are explained in more detail below with reference to the drawing. Show it

Fig. La scheme of the extrusion system with stretching to produce a monofilament

Fig. Lb scheme of the production of four mowing thread with coiled tear-off edges from a monofilament

2a, b, c the different cross sections for producing the

Mowing thread made of a monofilament according to Fig. Lb Fig. 3 enlarged view of the cross section of a single cutter thread according to Fig. 2c

4 is a perspective view of a mowing thread according to FIG. 2c and FIG. 3

Fig. 5 shows a schematic representation of the manufacture of the

Mowing thread according to FIGS. 2c, 3 and 4 by means of

Laser beams

Fig. 6a, b cross section through a monofilament and processing the same using a laser to produce a

Cutting thread

Fig. 6c perspective view of the cutting thread according to

Fig. 6b

7a, b a further variant of the cross sections of the

Monofilament and a cutting thread made from it by laser processing

Fig. 8 perspective detail of a cutting thread with notches

Fig. 9 in a schematic representation of a medium

Cutting knife device for producing a cutting thread from a stretched monofilament made of thermoplastic material

10 shows a schematic view of a part of the device according to FIG. 9 in the transport direction of the monofilament

11a is a view of an embodiment of an extruded and stretched monofilament for

Production of a cutting thread 11b shows the monofilament according to FIG. 11a after the action of the cutting knife

11c is a perspective view of a cutting thread according to FIG. 11b

12a shows the view of a further embodiment of an extruded and stretched monofilament for producing a cutting thread

Fig. 12b in a perspective view from the

Monofilament produced according to FIG. 12a.

Fig. La shows schematically an extruder E with a nozzle tool W with a circular cross section for extruding the

Monofilament la made of a high-strength thermoplastic, such as polyamide homo- and copolymers or thermoplastic polyurethanes or polyurethane elastomers (TPU) or blends of polyamides with flexibilizing additives. Of the homopolymeric polyamide molding compositions, for example PA6 or PA66 or PA11, optionally in a flexibilized form, are used. The extruded monofilaments 1 are subsequently drawn at a temperature below their melt temperature, see the indicated stretching device S, whereby they are usually stretched two to ten times, preferably four to eight times, and a correspondingly solidified monofilament is formed, which subsequently follows the roll R is wound up.

The extruded and drawn monofil 1 thus produced is subsequently, as shown in FIG. 1b, processed into the desired mowing thread of a specific configuration. The stretched and solidified monofilament 1 is unwound from the supply roll R according to FIG. 1b and fed to a processing station equipped with lasers LI and LII. Laser beams LSI, LS2 are generated by means of the lasers LI and LII, with the aid of which the monofilament 1 with respect to its cross section is changed. One possibility is that the laser beams LSI and LS2 generated by the lasers I and II act on the monofilament 1 in mutually perpendicular planes, as can be seen in FIG. 5, the theoretical crossing point of the two laser beams LSI and LS2 on the longitudinal axis X of the monofilament. By means of the laser beams LSI and LS2 arranged in this way, the monofilament 1, as can be seen in FIG. 5, is severed vertically and transversely in the center, so that four smaller monofilaments 11, 12, 13, 14 of changed geometry are obtained from the monofilament 1, which the desired Form cutting thread. These four mowing threads 11, 12, 13, 14 are, as can be seen in FIG. 1b, individually wound on supply rolls Rl, R2, R3, R4 and can then be supplied for consumption.

During the action of the laser beams LSI, LS2 on the

Monofil 1 there is at the same time a relative movement of the monofilament and the laser beams with respect to one another, in such a way that either monofilament 1 performs a rotational movement D1 or D2 in one direction or the other about its longitudinal axis, or an oscillating, i.e. back and forth movement Dl, D2, or the laser beams LSI, LS2 are guided so that they rotate around the monofilament, either continuously in the direction of Dl or D2 or oscillating back and forth Dl, D2. The devices for generating a rotational movement of either the monofilament 1 or the

Laser beams LSI, LS2 and / or lasers I, II while the monofilament 1 is being pulled through in the direction of arrow T through the path impinged on with the laser beams are not shown in detail. Due to the longitudinal movement of the monofilament 1 in the direction of arrow T with simultaneous rotary movement of either the laser beams or the monofilament, cuts S1, S2 are produced by means of the laser beams LSI or LΞ2, which form helical cutting surfaces and thus correspondingly helically shaped cutting threads 11, 12, 13, Cut out 14 from the original monofilament 1 with a circular cross-section. The monofilament 1, see FIG. 5, is guided in guides H1, H2. In addition, a cooling device, for example in FIG Shape of blowing air, and in the area of the laser station, a suction station for the evaporated plastic material can be arranged in the area of the cut surfaces generated.

2a-2c is the schematic again

Shape change process for producing cutting thread from the extruded and drawn monofilament 1 with a circular cross section shown in FIG. 2a. In the area of the laser station, the monofilament 1 in the hatched cut areas S1, S2, see FIG. 2b, is cut by means of the laser beams LSI, LS2 and, at the same time, the material is removed by evaporation in the area of the cut areas with a gap thickness d. In this way, processing by means of the laser beams LSI, LS2 produces four parts 11, 12, 13, 14 from a monofilament 1, as can be seen in FIG. 2c. 3 and 4, a single cutting thread 11 thus produced is shown enlarged in detail. The cutting thread 11 cut out of the monofilament 1 by means of laser beams has a quarter-circular cross-section 110, the cutting surfaces 115, 116 together with the outer surface 114 forming a compact cutting thread 11 with three tear-off edges 113, 112, 111.

As can be seen from FIG. 4, the cut surfaces 115, 116 and thus also the lateral surface 114 run helically, since the monofilament 1 has been subjected to a rotational movement D1 about its longitudinal axis X along its axis X in addition to its longitudinal movement T. In Fig. 4 it can be seen that the mowing thread 11 coiled by 90 ° over the first path a between A and B and on the following path a between B and C extends by a further 90 ° in the same direction. The configuration, that is to say the helical course of the cutting thread 11, is not carried out by deforming the same during the extrusion or subsequently in a corresponding shaping or drawing tool, but exclusively by the corresponding guidance of cuts produced by means of laser beams through the extruded stretched monofilament. The helical mowing thread 11 shown in FIG. 4 has thus the high strength of an extruded and stretched product, which at the same time has the desired helical or helical contour of at least three sharp cutting edges as tear-off edges 111, 112, 113. When using the mowing thread in a brush cutter, where it rotates freely hanging on one side at a working length of 15 to 20 cm at up to 15000 revolutions per minute, these tear-off edges 111, 112, 113 do not allow the swirl to be detached only at the end of the thread, i.e. once , but at any point where a tear-off edge, viewed in the longitudinal extent of the mowing thread, crosses another tear-off edge along a surface line, ie in the embodiment according to FIG. 4 after each distance a. The vertebral detachment laid in this way significantly reduces noise.

In the mowing thread 11 shown in FIG. 4, the direction of rotation D1 could also be reversed after a first distance a in region B, so that the cut surfaces 115, 116 and thus also the outer surface 114 run in the opposite direction and at point c take the position again as shown at A. This would correspond to an oscillation at an angle of 90 °, while the representation according to FIG. 4, if the direction of rotation Dl is not changed, corresponds to the first half-wave of a helical design of the mowing thread 11 and if after the section C the direction of rotation Dl is reversed , this would correspond to an oscillation with a rotation angle of 180 °.

For example, it is possible to extrude a polyamide 6 monofilament with a diameter of 8 mm and subsequently to stretch it six times to a monofilament with a diameter of 3.27 mm. From this monofilament, four cutting threads 11, 12, 13, 14 can be produced by cutting with laser beams LSI, LS2, as shown in FIGS. 5 and 2, which still have an average diameter after melt loss of approximately 1.5 mm . lo

6a shows a further possibility of processing a monofilament 1, viewed schematically in cross section, by means of laser beams LSI, LS2. In this case, the laser beams LSI, LS2 are aligned parallel to one another in such a way that they cut off and evaporate circular sections S1, S2 on two opposite sides of the extruded and stretched monofilament. At the same time as the transport movement in the longitudinal extension of the monofilament, see FIG. 5, the monofilament 1 or the laser beams are subjected to a rotary movement, so that the cut surfaces run correspondingly helically on the monofilament. The core remaining after cutting off the circular sections S1, S2 then forms the mowing thread 10, see FIG. 6b, with the cut surfaces 101, 102, the remaining lateral surfaces 103, 104 and the cut edges as tear-off edges 10a, 10b, 10c, 10d. As can be seen in the perspective schematic illustration according to FIG. 6c, the cut surfaces 101, 102 and thus also the remaining jacket surfaces 103, 104 run helically around the longitudinal axis X of the former monofilament and form the desired twisted mowing thread 10

Tear-off edges. The rotary movement of the monofilament 1 during processing by means of the laser beams LSI, LS2 can, as already explained in FIG. 4, take place, namely either oscillation by 90 ° or oscillation by 180 °, as shown in FIG. 6c, or rotary movement continuously in one Direction. In addition, it is also possible, with a continuous transport movement in the direction T, to carry out the rotary movement or oscillating movement intermittently for producing helical cut surfaces and thus helically shaped cutting thread from a monofilament, so that coiled sections with non-coiled sections, but cut sections, so that in each If continuous tear-off edges are formed, they are formed alternately. 6c shows only an example of how, after rotation of the monofilament or laser during cutting on path 2a by 180 ° and subsequent turning back on path b between C and F by 180 °, an oscillating movement can be carried out on the monofilament . λl

The distance 2a is equal to the distance 2b between A and

C or C and F according to FIG. 6c and corresponds in each case between A and C or C and F to a half-wave of the spiral.

7a shows a further possibility of changing the cross section of the extruded and stretched monofilament 1 for producing a cutting thread. According to the variant according to Fig. 7a, two laser beams LSI, LS2 act on one axis in the opposite direction, i.e. on two opposite sides of the monofilament and work out a dent or concave indentation or groove 101, 102 by evaporation of the plastic in the area S1 and S2, see FIG. 7b. Also in this mode of operation by means of laser beams LSI, LS2, the monofilament 1 or the laser beams is rotated in one direction or oscillating about the longitudinal axis X of the monofilament 1, so that the indentations run as helical or helical grooves on the circumference of the mowing thread 10 made from the monofilament 10 and at the same time form four tear-off edges 10a, 10b, 10c, 10d, see FIG. 7b.

It is of course also possible not to carry out the action of the laser beams LSI, LS2 according to FIGS. 7a, 7b continuously, but rather intermittently. Then, at appropriate intervals, by evaporation of the plastic in the area of processing by means of the laser beams, notches or groove areas are obtained, which are also arranged, depending on the rotation of the monofilament 1, during transport along the axis X in a corresponding slope on the circumference of the monofilament. The depth and width of the notches worked into the surface can be varied and the diameter of the monofilament 1 can also be adapted.

8 schematically shows the example of the formation of tear lines by means of notches 105 on a monofilament 1. The monofilament 1 is extruded from a suitable high-strength thermoplastic and drawn so that it already receives the final drawn diameter dm intended for the cutting thread. In order to make this monofilament 1 noise-reducing in addition to the high-strength equipment, notches 105 are worked into the circumference of the monofilament in a regular or even irregular, possibly repetitive, arrangement using one or more laser beams. Due to the action of the laser beams selectively on areas of the surface of the monofilament, the notches are formed in the desired depth and size by evaporating plastic. The monofilament 1 is guided in the transport direction T parallel to its longitudinal axis X at the point of action of the laser beams LS, with a rotational movement about the longitudinal axis X, for example in the direction D1 shown, taking place at the same time. Depending on the speed of the transport movement T and the rotary movement D1, the arrangement and gradient of the notches 105 on the circumference of the monofilament 1 and the size of the notches take place, this also depends on the duration of action of the intermittent, ie intermittent, intermittent interruptions on the surface of the monofilament Laser beam LS. The monofilament thus provided with notches 105 then forms the mowing thread, the marginal edges of the notches forming the so-called tear-off edges for the mowing thread.

As can be seen from FIG. 9, a stretched monofilament 1, see FIG. 1 a, is moved in the transport direction T through a device 5 equipped with cutting knives and subsequently pulled through a guide device in the form of a perforated disc 6 which has a through opening 60 to produce the mowing thread has a cross-section corresponding to the outer contour of the monofilament unwound from the roll 4. In this way, a play-free guidance of the monofilament 1 in the perforated disc 6 is effected.

The cutting device 5, which has an annular holding device 50, is arranged directly in front of the perforated disk 6, 2.3 wherein the monofilament 1 through the ring opening 52

Cutting device 5 is passed and the holding device carries two cutting knives 53, which are arranged diametrically opposite one another in the holding device 50 with respect to the monofil 1 and which come into engagement with the monofil 1, see also FIG. 10. Along the outer circumference of the cutting device 5 a toothing 51 is applied so that the cutting device 5 together with the holding device 50 and the cutting knives 53 attached to it can rotate about the longitudinal axis of the monofilament 1. A chain or belt drive 9 is placed over the toothing 51, which causes the rotary movement P2 of the cutting device 5 by continuous or oscillating movement of a drive in the direction of arrow M.

As a result of this rotation of the cutting knives 53 in the direction of arrow P2 about the longitudinal axis of the monofilament 1 guided past the cutting knives 53 in the direction T, cross-sectional areas of the monofilament 1 are peeled off and helical cutting edges 101, 102 are produced. The profiled monofilament 10 is subsequently fed as a mowing thread from a take-off device 7 to a winding station 8.

The plastic masses S that occur when the cross-sectional areas of the monofilament 1 are peeled off, for example chips of the

Monofilament or the like , Can be collected from the cutting device 5 and fed back to the extrusion process for producing the monofilament, thereby ensuring a particularly economical production of the mowing thread.

As can be seen from FIGS. 9 and 10, the immediately successive arrangement of cutting device 5 and perforated disk 6 ensures precise guiding of monofilament 1 during processing by means of cutting knives 53, so that constant profiling of monofilament 1 is possible. The cutting knives 53 held in the holding device 50 are arranged in a manner not shown in relation to the monofil 1 which is being guided past, so that the cutting knives 53 simply have different monofilament diameters and different desired ones

Depths of cut and their state of wear can be adjusted.

In this way it is possible, for example, to process a monofilament 1 with a circular cross-section shown in FIG. 11a such that sections S1, S2 of the same size are preferably removed from this cross-section of the monofilament 1 along the longitudinal axis X and a monofilament with a cross-section as shown in Fig. 11b is obtained.

The profiled monofilament 10 obtained after the peeling of plastic in the areas S1, S2 to form a mowing thread has two opposite sides 103, 104 left in the form of a circular path corresponding to the original cross-section, which over two of the

Cutting knives 53 produced straight cutting edges 101, 102 are connected to one another via corners 10a, 10b, 10c, 10d.

The representations of the monofilament according to FIGS. 11a and 11b are to be regarded as purely schematic, since, due to the rotation of the cutting knives 53 just described, the cutting edges 101, 102 are arranged in the longitudinal direction of the monofilament following this rotation.

As a result of the rotation of the cutting knives 53 in the direction of arrow P2 caused by the drive by means of the chain or belt drive 9, see FIG. 10, the cutting edges 101, 102 caused by the cutting knives 53 run helically in the longitudinal extent X of the monofilament, which is shown in FIG. 11c is. The four cut edges 10a, 10b, 10c, 10d also run helically in the longitudinal extent X of the monofilament 10 according to the cut surfaces 101, 102 and cause the imaginary surface line of the monofilament 10 along the path AF in the example shown in FIG. 11c to total four times its straight, straight course is slightly drawn inwards, which is indicated schematically by arrows P in FIG. 11c. When such a monofilament 10 is used as a cutting thread in a corresponding free-cutting device, these cutting lines, as the surface line of the rotating cutting thread and stretched due to the centrifugal force, form the tear-off edge for the air masses flowing around the rotating cutting thread. As a result of the indentations P of the surface line caused by the helical arrangement of the cutting edges 10a, 10b, 10c, 10d, this tear-off edge is viewed several times in the longitudinal direction, which leads to premature or delayed flow stops along the longitudinal extension X of the mowing line, which is only advantageous low noise is caused.

The monofilament produced by the method according to the invention not only has a particularly smooth running in one of the known brush cutters, but also a particularly long service life due to its good strength caused by the stretching, since the stretched structure of the customer material is due to the mechanical processing for profiling the mowing thread and thus the monofilament is preserved.

For inexpensive, temporally offset eddy detachments at the tear-off edge during operation of the mowing line in one

To achieve brush cutter at high speeds, which result in the correspondingly low noise, it is proposed to choose the helical slope of the cutting edges 101, 102 of the mowing thread so that the length a of 1.0 to 2.5 cm of the mowing thread a

The tear-off edge is interrupted, ie the distance a between two successive indents P of the imaginary surface line of the mowing thread is 1.0 to 2.5 cm. The active one currently

Part of a mowing thread in a brush cutter, which rotates at high speed, is usually between about 7 to 20 cm in the known devices. In this way, according to the monofilament 10. Fig. Llc manufactured mowing thread are formed so that six to ten

There are interruptions in the tear-off edge with corresponding temporally offset eddy detachments during operation. By a suitable combination of monofilament feed speed in the direction of arrow P3 according to Fig. 9 and rotational speed of the cutting knife 53 in the direction of arrow P2 acc. 10 such desired gradients of the cut edges 101, 102 are freely selectable.

In addition to the cutting thread shown in FIGS. 11a to 11c, which was obtained from a monofilament 1 with a round cross-section, it is also possible within the scope of the invention to use other advantageous cross-sectional shapes for the production of the cutting thread, which is shown in FIGS. 12b is shown using the example of a monofilament 30 with a star-shaped cross section.

The monofilament 30 with a star-shaped cross section has protruding star points 30a, b, c, d, e and f which run continuously along the longitudinal axis X of the monofilament 30. Analogous to the monofilament shown in FIGS. 11a to 11c, this monofilament shown in FIG. 12a is also machined by a cutting knife 53 that can be set in the direction of arrow P1, the cutting knife 53 about the longitudinal axis X of the monofilament 30 in the direction of arrow P2 by, for example, in FIG Fig. 10 drive rotates. The processing by the cutting knife 53 causes the profiling of the monofilament 30 shown in FIG. 12b.

As shown in this FIG. 12b, sections S3 are continuously cut out of the star-shaped monofilament 30 in the longitudinal extension X of the monofilament 30 from the protruding star points 30a, 30b, 30c, 30d, 30e, 30f, these sections being along the successive star points arranged in a helical pattern one behind the other. The cut surfaces created in the star serrations are designated 301, 302, the cut edges along the circumference of the monofilament 31a, 31b. The groove-shaped egg cuts obtained by the cut-out sections S3 in turn cause interruptions in the tear-off edges of a mowing line formed from the monofilament 30 formed on the outer surface lines of the star points during its use in a brush cutter. In this exemplary embodiment shown with a star-shaped monofilament 30, a mowing thread is thus obtained which exhibits particularly low noise development during operation, but at the same time its high strength values, which were achieved by stretching the extruded monofilament, by the subsequent formation of the interrupted tear-off edges by means of the Cutting knife 53 is not affected.

Even with such a mowing thread made of a monofilament 30 with a star-shaped cross-section, a particularly high noise reduction during operation is achieved if the slope of the cut edges 31a, 31b along the cut surfaces 301, 302 of the sections S3 is selected such that on each star point 30a, 30b, 30c, 30d, 30e, 30f an interruption of the tear-off edge is effected every 1.0 to 2.5 cm by a cut-off section S3. Monofilaments with 3, 4, 5 or 6 star points can be provided.

In addition to the use of monofilaments with a round or star-shaped cross section, triangular, quadrangular or pentagonal cross-sectional shapes of monofilaments are also used in the context of the invention.

Claims

Patent claims

1. A method for producing a monofilament mowing thread from a thermoplastic extrudable and stretchable plastic, the cross section of which in the longitudinal extension

Mowing thread is changed in some areas, whereby a monofilament is extruded from the plastic and subsequently stretched at a temperature below the melt temperature of the plastic by two to ten times and then cooled to room temperature, whereby a stretched monofilament of high strength is obtained, characterized in that the After extrusion and stretching, the monofilament (1) obtained in the direction of the longitudinal axis (X) of the monofilament (1) is processed continuously or intermittently by means of laser beams or mechanically to remove plastic in certain areas while changing and reducing the cross section of the monofilament and the monofilament in addition to it Transport movement in the direction of the longitudinal axis (X) of the monofilament (1) during mechanical processing or processing by means of the laser beams about its longitudinal axis (X) performs a rotary movement in only one direction of rotation or an oscillating rotary movement or during the transpo movement of the monofilament (1) in the direction of its longitudinal axis (X), the mechanical processing or processing by means of the laser beams is carried out rotating or oscillating about the longitudinal axis (X) of the monofilament.

2. The method according to claim 1, characterized in that the monofilament (1) is continuously guided past at least one cutting knife (53) rotating or oscillatingly rotating about the longitudinal axis (X) of the monofilament (1) and by means of the Cutting knife (53) plastic is peeled off in some areas while changing and reducing the cross-section of the monofilament (1) and cut surfaces (101, 102; 301, 302) with cut edges (10a, 10b,) running on the circumference of the monofilament (1) on the monofilament (1). 10c, 10d; 31a, 31b) are formed by the action of the cutting knives (53), which, according to the rotational or oscillating movement of the cutting knives (53), run in the longitudinal direction (X) of the monofilament and the resultant, in the longitudinal and transverse directions profiled monofilament forming the cutting thread essentially maintains the strength obtained by stretching.

3. The method according to claim 1, characterized in that with continuous processing of the monofilament by means of laser beams on the monofilament (1) in the longitudinal extent of the same cut surfaces (115, 116; 101, 102) with correspondingly extending cut edges (111, 112, 113) on the circumference of the monofilament ; 10a, 10b, 10c, lOd) are formed by the action of the laser beams which are coiled in accordance with the rotary or oscillatory movement of the monofilament.

4. The method according to any one of claims 1 to 3, characterized in that two parallel laser beams or two diametrically opposite cutting blades (53) act on the monofilament (1) such that preferably on two opposite sides of the monofilament the same Large sections (S1, S2) of the cross section of the monofilament (1) in the longitudinal extension (X) are removed or continuously separated by evaporation of the plastic and a mowing thread (10) with four helical cutting edges (10a, 10b, 10c, lOd.) running in the longitudinal extension ), possibly changing spiral direction, is generated.

5. The method according to claim 4, characterized in that two circular sections are separated from the cross section of the monofilament (1).

6. The method according to claim 4, characterized in that two grooves are generated on the cross section of the monofilament.

7. The method according to any one of claims 1 to 6, characterized in that a monofilament with a

Extruded diameter of 5 to 10 mm and subsequently stretched four to eight times and from this by processing by means of laser beams or by peeling or cutting off cross-sectional areas of the circumference of the monofilament by means of rotating or oscillating

Cutting knife a cutting thread with an average diameter of the cross section of about 1.5 to 4 mm and helical cutting edges is obtained.

8. The method according to claim 1, characterized in that the monofilament performs an oscillating movement by an angle of rotation α of 180 °, preferably 90 °.

9. The method according to any one of claims 1 to 8, characterized in that the helical slope of the tear-off edges is selected so that on a length (a) of 1 to 2.5 cm of the cutting thread there is a tear, the length being a distance ( a) viewed between two 'longitudinal extension of the cutting thread, corresponds to an imaginary surface line intersecting cut edges.

10. The method according to any one of claims 1 to 9, characterized in that the processing of the cross section of the monofilament by means of laser beams or mechanically in the longitudinal extension of the monofilament is carried out intermittently and that in the case of intermittent processing of the surface of the monofilament notches the same l \ or different dimensions m uniform or irregular arrangement along, transversely or obliquely to the longitudinal axis of the monofilament in the surface of the monofilament by removing plastic, whereby cut edges are formed on the notch edges for the noise reduction of the mowing line.

11. The method according to claim 1 or 3, characterized in that act on the monofilament two mutually perpendicular laser beams whose theoretical crossing point is preferably on the longitudinal axis (X) of the monofilament (1) and cut the monofilament in two mutually perpendicular cutting planes and in this case four individual cutting threads (11, 12, 13, 14) each having a cross section corresponding to a quarter circle with three longitudinally extending cutting edges (111, 112, 113) extending in the longitudinal direction, possibly changing spiral direction, are produced from the monofilament (1).

12. The method according to any one of claims 1 to 3, characterized in that the cutting knife (53) or laser beams during their rotation about the longitudinal axis (X) of the monofilament (1) m with respect to the longitudinal axis (X) of the monofilament (1) remain stationary.

13. The method according to any one of claims 1 to 2, characterized in that an extruded and stretched monofilament (1) with a circular cross section is used as the monofilament, and on the monofilament (1) acts a rotating or oscillating cutting knife (53), such that at least one circular section is peeled off from the cross section of the monofilament (1) and preferably a monofilament with a crescent-shaped cross section is obtained, the cut edges resulting from the cutting off of the circular section on the monofilament run helically in the longitudinal extent (X) of the monofilament (1).

14. The method according to any one of claims 1 to 2, characterized in that an extruded and stretched monofilament (3) with a star-shaped cross section with protruding star teeth (30a, 30b, 30c, 30d, 30e, 30f) is used as the monofilament and on the monofilament (3) at least one rotating cutting knife (53) acts in such a way that in the longitudinal extension (X) of the monofilament (3) sections (S3) are continuously cut out from the protruding star points (30a, b, c, d, e, f) and a mowing thread (30) is obtained with a monofilament with cutting edges (31a, 31b) running in the longitudinal direction over the star points.

15. A device for producing a profiled mowing thread made of a monofilament extruded and drawn from a thermoplastic material according to claim 2, characterized in that a cutting device (5) having at least one cutting knife (53) and rotatably arranged around the monofilament by means of a drive is provided and A guide device in the form of a perforated disc (6), the through hole (60) of which is designed with a cross section of the cross section of the monofilament that has not yet been changed by means of the cutting knives (53), is provided directly downstream of the cutting device in the transport direction of the cutting device, and a trigger device for guiding the monofilament past the cutting knives (53) and pulling the monofilament through the guide device in the transport direction (P3).

16. The apparatus according to claim 15, characterized in that the cutting knives (53) are held in a holding device (50) which has a toothed ring (51) on the outside and can be driven by means of a chain or belt drive (9) and the cutting knives (53) are held in the holding device (50) in a radially adjustable manner with respect to the monofilament.

17. The device according to one of claims 15 to 16, characterized in that for the simultaneous

Processing two or more monofilaments two or more holding devices (50) with at least one cutting knife (53) and each associated guide device for each monofilament can be driven by a common drive and as

Guiding element with a perforated disc according to ^'the number to be processed monofilament through holes formed is provided.