CUTTING FILAMENT

Abstract: The present invention relates to a cutting filament intended for trimming and cutting vegetation, such a cutting filament being used on rotary-head motorized cultivators such as brush cutters and edge trimmers. During use such cutting filaments generate a substantial and unpleasant amount of high-frequent noise which is added to the noise of the motor for driving the rotary head. These noises lead to outdoor noise pollution. Legislatory requirements aiming to limit the noise to a level deemed to be acceptable are being drawn up and could shortly come into force. The cutting filament according to the present invention is characterized in that the cutting filament (1; 10') has undulations (2; 6; 12') that recur in the longitudinal direction of the cutting filament (1; 10').

Description: Cutting filament The present invention relates to a cutting filament intended for trimming and cutting vegetation, such a cutting filament being used on rotary-head motorized cultivators commonly called brush cutters and edge trimmers. These implements are generally equipped with an electric motor or an engine, which drives in high-speed rotation, a revolving head supporting one or more cutting filaments. As the head rotates, and under the effect of centrifugal force, the cutting filament or filaments run out radially and thus cover a certain circular region, in which they slice through the vegetation they meet. In a known fashion, the cutting filaments may be plant-based, synthetic, metal, or metallo-plastic filaments of the mono-filament or multi-filament type, and these filaments may have either a round section or a polygonal section, for example square or in the shape of a star. During uεe, such cutting filaments generate a substantial and unpleasant amount of high-frequent noise which is added to the noise of the motor for driving the rotary head. These noises lead to noise pollution which is all the more annoying since their very nature means that brush cutters and edge trimmers are being used out of doors. In addition legislatory requirements aiming to limit the noise of these implements to a level deemed to be acceptable are being drawn up and could shortly come into force. In order to attempt to reduce the noise generated by cutting filaments during use, various solutions have already been put forward. From US-A-5, 220, 774 known cutting filaments having straight or helical longitudinal grooves of rounded or angular section, in varying numbers (one or more longitudinal grooves) ,- the drawback of theses grooves is that they adversely alter the surface quality of the filament, which is an important factor in the quality of its cutting. Another known solution, applicable especially to a cutting filament of square section, consists in twisting the filament. This solution iε relatively effective, but the reduction in noise is still a function of the number of twists in cutting filament per unit length of said filament. What is more, the torsion in the filament adversely alters its surface quality; it also makes this filament more complicated and more expensive to manufacture . Cutting filaments with a special profile in the shape of a teardrop or aerofoil have also been proposed, these profiles being supposed to improve penetration through the air. This solution allows only a quite small reduction in noise, and is therefore not particularly efficent. Finally, mention may be made of attempts to produce cutting filaments which have small dimples at their surface, like a golf ball. Aside from the manufacturing difficulties, this last solution leads to an adverse alteration to the surface quality of the filament. The present invention aims to avoid these drawbacks by providing an improved cutting filament which affords a substantial reduction in operating noise without adversely altering the essential properties of the filament, even improving its cutting ability which iε asεociated with its surface quality, as well as its resistance to breaking at the eyelet, and to achieve all thiε with the filament εtill being simple and economical to produce. To this end, the subject of the invention is a cutting filament for brush cutters and edge trimmer, characterized essentially in that it haε undulationε which recur in the longitudinal direction of thiε cutting filament and run in at least one radial direction relative to the longitudinal axis of the said cutting filament . Thus, the solution put forward by the present invention consists, in general, in giving the cutting filament an undulated appearance. The undulations very significantly improve the coefficent of penetration of the cutting filament through the air. It is this improvement in the coefficient or penetration through air, and therefore the reduction in the impact that the filament has on the air, which generates the drop in noise, said drop may be in the order of 10 to 12 decibels. By way of general explanation of the improvement provided by the εolution put forward, it may be pointed out that the undulationε create numerouε regions allowing the air encountered by the filament as it rotates to be discharged outwardε. The εolution put forward by the preεent invention affords numerous and appreciable advantageε. The improvement in the penetration of the cutting filament through the air allowε, aside from the εubεtantial reduction in noise, a reduction in the motive power required to drive this filament, and hence, less strain on the electric motor or engine or the implement in queεtion, which results in less energy expenditure (for a given rotational speed) . Another result of thiε is that, for a given motive power, the rotational speed of the cutting filament can be increased by approximately 10 to 15%, which increases the inertia of the filament and improves the cut made by this filament. What is more, the principle of undulating the cutting filament can be applied, with no particular difficulty, to filament of any section: round, oval, triangular, square, hexagonal, star-εhaped, etc., and of any diameter or any thickness . Finally, this undulated appearance of the cutting filament conεiderably improves itε cutting ability and also its resistance to breakage at the eyelet where the filament emerges from the rotating head of the brush cutter or of the edge trimmer, as a result of the "work hardening" effect achieved by passing this filament between pinions or rollers (see later) designated to undulate it. The result of thiε iε, aε a whole, and in all reεpects, a very marked improvement in the behaviour of the cutting filament in use. Moreover, from the point of view of the manufacture of this cutting filament, the undulations may be obtained simply and economically, for example by passing the filament between two toothed wheels, pinions or rollers rotating in opposite directions, and this can be done either at the end of the filamen -manuf cturing line or subεequently (undulations produced as a separate operation) . In particular, these may be simple undulations, keeping the initial section of the cutting filament along its entire length, or undulations which are accompanied locally by a marking or the cutting filament, by crushing. The undulations themselves may be more or lesε rounded or angular and more or less pronounced with regular or irregular shapes. Angular undulations, creating more or less pointed teeth or ridges, actually improve the cutting ability of the filement. According to a simple embodiment of the invention, the undulationε of the cutting filament run in a single radial direction relative to the longitudinal axis of the εaid cutting filament. In other wordε, the undulated filament developε in a εingle plane and, for example, has the appearance of a εinusoid. According to a further improved embodiment, the undulationε of the cutting filament run in multiple radial directionε relative to the longitudinal axis of the said cutting filament. In particular, these undulations may run in two radial directions forming an angle of 90° to one another. In this way, the undulations develop in two perpendicular planes. As will readily be understood, the presence of such undulations makes it possible to obtain the sought-after effect of reducing the operating noise, irrespective of the instantaneous orientation in space of the cutting filament. The mid-planes of the undulations may be perpendicular to the longitudinal axis of the cutting filament, or oblique to this longitudinal axis, with unrestricted angle of inclination. Undulations thus inclined may be obtained, in a simple way, by making the filament pass between two helical pinions, rollers or die . In particular, if they are inclined outwards (with respect of the position of the cutting filament and to its direction of rotation during operation) , these undulations actually favour the expulsion of air and thus contribute, as a result of their orientation, to noise reduction. In any case, the invention will be better understood with the aid of the description which follows, with reference to the attached diagrammatic drawing which represents, by way of examples, a few embodiments of this cutting filament for brush cutters and edge trimmers. Fig. 1 is a side, slightly perspective, view of a length of cutting filament in accordance with the present invention, of round section, undulated in a plane (X,Y) ; Figs. 2-6 show alternative forms of the cutting filament of Fig. 1, all of initial round section; Fig. 7 represents another embodiment of the cutting filament according to the invention, of variable section; Figε . 8 and 9 show a cutting filament according to the invention, of which the undulations run in two perpendicular radial directions; Figs. 10 and 11 show undulated cutting filaments in accordance with the present invention, of square or rectangular section; Figs. 12 to 30 show other sections of cutting filaments which may have undulations according to the invention; Fig. 31 very diagrammatically represents a device making it possible to obtain an undulated cutting filament in accordance with the invention. Fig. 32 showε a side view of a further embodiment of a cutting filament according to the present invention; Fig. 33 shows a perspective view of a slightly modified embodiment of the cutting filament according to Fig. 32; and Fig. 34 shows schematically a device for manufacturing the cutting filament according to Figs. 32 and 33. Fig. 1 showε a length of cutting filament 1 of round section for brush cutters or edge trimmers. The cutting filament 1 has undulations 2 which recur ad infinitum in the longitudinal direction of this cutting filament l, indicated by its mean longitudinal axis X. Here the undulationε 2 are εimple and not very accentuated; they are the result of alternately "ascending" and "descending" portionε connected by bends . These undulationε 2 run in a single radial direction Y perpendicular to the longitudinal axiε X of the cutting filament 1. Thuε, in the firεt example considered here, the undulations 2 run in a single plane and form a sort of broken or sawtooth filament. The noise generated by the cutting filament 1 during use is subεtantially reduced as a reεult of εuch undulationε. Fig. 2 shows a cutting filament 1 similar to the previous one, but having more pronounced undulations 2. Fig. 3 shows another cutting filament 1 of round section, of which the undulations 2 are alεo very pronounced but more rounded than the previous ones, which gives the cutting filament 1 a sinusoidal appearance. Fig. 4 shows a cutting filament 1 similar to the previous one, but having less accentuated sinusoidal undulations 2. In Fig. 4 the filament diameter is designated D, the wave height is designated Δ h and the wave length is designated L. The following relation should be present between the diameter D and the wave length L: 3D ≤ L ≤ 10D. Between the diameter D and the wave height Δ h the following relation should be valid: 0.5D ≤ Δ h ≤ 2D. Fig. 5 εhowε a cutting filament 1 which has undulationε 2 of a round overall shape. However, marks 3 are produced here, these forming flats in the troughs of the undulations 2. Fig. 6 showε another cutting filament 1, in which the undulations 2 have more angular shapes. In all the foregoing examples, the cutting filament 1 has a round and constant initial section, and its undulations 2 run in a single axial direction Y, the filament 1 thus developing in a single plane X, Y. Fig. 7 showε a cutting filament 1 of round, but non- constant section, the filament 1 having substantially spherical large-diameter portions 4 which alternate with narrower portions 5. The cutting filament 1 thus has an undulated longitudinal profile 6 in every radial direction. Figs. 8 and 9 show a cutting filament 1 of initially round section which has undulationε in a firεt radial direction Y and also in a second radial direction Z perpendicular to the previous direction. Fig. 10 shows a cutting filament 1 of square or rectangular section which haε undulations 2 lying in a single plane, and having the same appearance as the oneε described with reference to the first figures. Fig. 11 showε another cutting filament 1 of square εection, the undulated longitudinal profile of which results from twisted regions 7 alternating with straight lengthε 8. For the clarity of the drawing, the foregoing examples deal with undulated cutting filamentε 1 of εimple, that iε to say round, square or rectangular, εection. The εame principle of undulationε can nevertheless be applied to cutting filaments of various sections, possibly more complicated ones, with a polygonal and/or curved contour; Figs. 12 to 30 illustrate various examples of sections of cutting filaments which may be undulated and, as appropriate, marked. The undulationε 2 of the cutting filament 1 can be obtained by meanε of a device like the one represented in Fig. 31: the initially εtraight filament, advancing in the direction of an arrow 9, passes between two oppposed pionionε 10 and 11 which are mounted so that they can rotate about respective axes 12 and 13. By passing between the respective toothing 14 and 15 of the two pinions 10 and 11 which rotate in opposite directions as indicated by the arrows 16 and 17, the filament 1 adopts an undulated configuration, and its undulations 2 are conserved insofar as the deformation is of the plastic (rather than elastic) type. A tubular guide 18 through which the still straight portion of the filament 1 passes, directs this filament between the two pinions 10 and 11. Thiε device may be placed at the end of the manufacturing line for the filament 1. The εurface of the pinionε 10 and 11 that contactε the cutting filament 1 is preferably adapted to the shape of the cutting filament 1. If e.g. the cutting filament 1 has a circular cross-section, said surface of the pinions 10 and 11 should be concave in axial direction of the pinions 10 and 11. By making the filament 1 pass between two helical pinions 10 and 11, undulations 2 are obtained in which the mid- planes have an oblique orientation relative to the longitudinal axiε X of the filament 1. As will be εhown later, such undulations make it possible to obtain an even further improved result, as far as the reduction in operating noise is concerned. The undulated cutting filament 1 can be made of a synthetic substance, especially polyamide, of a plantbased substance εuch as hemp, of metal, or of metalloplastic complex. Thiε may be a filament of the mono-filament or multi-filament type. In any case, the cutting filament 1 has an undulated appearance, that is to say a longitudinal profile with an alternation of more or leεε pronounced creεts and troughs εituated in a εingle plane or orientated in different planes and able to give thiε cutting filament 1 the appearance of a simple undulation, of a small chain, of a braid, etc. capable of reducing the noise generated by the cutting filament during use. Trials undertaken have made it possible to confirm the substantial reduction in noise level which is obtained by virtue of the undulations of the cutting filement, as previouεly described. These trials were undertaken at a location where the background noise level was 50.5 decibels, uεing laboratory equipment comprising a rotating head (capable of taking various filaments) , driven in rotation by an electric motor at a nominal speed of 5000 revolutions/minute. The noise level measured with the motor rotating at this speed under no load, that is to say the head not carrying any filament, waε 79.1 decibels . A first series of trials consisted in rotating the head carrying a conventional cutting filament of round section with a diameter equal to 2.4 mm, without undulations. The mean of the noise intensitieε measured (uεed aε a reference for the εubsequent trials) was 101.47 decibels. A second series of trials was undertaken with a filament of the same round section, having undulations of which the mid- plane was perpendicular to the longitudunal axiε of the filament. As the plane of the trajectory of the filemant is horizontal, the undulations of the filament were arranged lying flat and standing vertically, in turn. With the undulations lying flat, the mean of the noise intensities measured rose to 89.48 decibels, namely a reduction of 11.99 decibels. With the undulations standing vertically, the mean of the noise intensities measured rose to 92.79 decibels, namely a reduction of 8.68 decibels. Since the orientation in space of the filament is in actual fact random, the mean of the previous two values, namely a mean redcution of 10.33 decibels, may be taken to be meaningful. A third series of trials was undertaken with a filament of the same round section having undulations of which the mid- plane was inclined to the longitudinal axis of the filament, the inclination being outwards. As before, the undulations of the filament were arranged lying flat and standing vertically, in turn. With the undulationε lying flat, the mean of the noise intensities measured rose to 88.58 decibelε, namely a reduction of 12.89 decibels. With the undulations standing vertically, the mean of the noise intensities measured rose to 93.24 decibelε, namely a reduction of 8.23 decibelε. The mean reduction (mean of the previous two values) therefore went up to 10.56 decibels. By way of comparison, a final series of trials waε carried out with a filament of the same round section, still having undulations of which the mid-plane was inclined to the longitudinal axiε of the filament, but of which the in¬ clinations pointed inwards, in contrast to the previouε series . With the undulations lying flat, the mean of the noise intensities measured roεe to 91.64 decibels, namely a reduction of 9.83 decibels. With the undulations standing vertically, the mean of the noise intensitieε roεe to 99.31 decibelε, namely a reduction of 8.16 decibels. The mean reduction (mean of the previouε two valueε) therefore went up to 9.00 decibelε. Theεe trialε confirm the appreciable reduction in noise level obtained by the undulations in the filament, and the even greater reduction obtained in the case of oblique undulations, provided that these undulations point outwards. The cutting filament 10' disclosed in Fig. 32 has also undulated contours 12' in the plane of the paper. The undulated contours 12' have been achieved by a pair of diametrically applied firεt indentationε 26' in the cutting filament 10', one of said first indentations being hidden since it is located at the rear side of the cutting filament 10' in Fig. 32. Said pair of first indentations 26' are thuε located in a plane perpendicular to the paper in Fig. 32 and they are arranged at a certain center to center distance L' that correspondε to the wave length of the embodiment according to Fig. 32. As indicated by dotted lines in Fig. 32 a pair of second indentations 28' are applied in the plane of the paper in Fig. 32, said second indentations 28' being located between the first indentations 26', i.e. the indentationε 26' and 28' are applied in two planes perpendicular to each other. Also the indentations 28' are arranged at a center to center distance from each other that is the same as the center to center distance between the indentations 26' . Said pairs of firεt and εecond indentationε 26' and 28' respectively overlap each other in the longitudinal direction of the cutting filament 10' . Thereby it iε guaranteed that along itε entire length the cross-section of the cutting filament is changed from the original, i.e. the crosε-εection before the indentations are applied. The change of the cross-εection from the original iε favourable for decreasing the noiεe generation as the cutting filament 10' rotates. In the embodiment according to Fig. 32 the indentations 26', 28' are prismatic. Within the scope of the invention other types of indentations are posεible, e.g. conical or hemi- εpherical . In the embodiment according to Fig. 32 indentations 26', 28' are applied in two planes perpendicular to each other. Such a design is most suitable for certain cross-sections, e.g. circular, square or rectangular. Within the εcope of the invention it is also posεible that pairε of indentations are applied only in one plane. Such an embodiment seems to be most εuitable for a drip shaped cross-section. Thuε, the crosε- sectional shape of a cutting filament that is provided with pairs of diametrical indentations may vary in several ways. The perspective view disclosed in Fig. 33 of a slightly modified embodiment of the cutting filament 10' illustrates in a more obvious way the appearance that is given to the cutting filament 10' by the indentations 26' and 28' applied in two planes perpendicular to each other. The modification is that the overlap between the indentations 26' and 28', in the longitudinal direction of the cutting filament 10' , iε larger in Fig. 32 than in Fig. 33. The device εhown in Fig. 34 includeε four emboεεing wheels 14' , 16' and 15' , 17' respectively. The wheels 14' and 16' cooperate and the wheels 15' and 17' cooperate. The embossing wheels 14-17' are mounted on adherent shafts 18' , 19' , 20' and 21' . At the periphery of the embossing wheels 14' -17' embossing projections 23' are provided. The oppoεite, cooperating embossing wheels 14' , 16' and 15' , 17' respectively are synchronized in such a way that when rotating the embossing projections 23' are located directly opposite to each other in the area where the indentations 26' and 28' of the cutting filament 10' takes place, i.e. the area where the cooperating embossing projections 23' are closest to each other. Further the pairs of embossing wheels 14', 16' and 15' , 17' are so synchronized that they alternately effect pairs of indentations in the cutting filament 10' . One pair of embossing wheels 15' and 17' in Fig. 34 is located in front of the other pair of embossing wheels 14' and 16' in Figure 34, seen in the feeding direction of the cutting filament 10' , εaid direction being indicated by the arrow 25' in Fig. 34. By such an arrangement the cutting filament 10' is allowed to expand freely in a direction perpendicular to the direction of indentation when a pair of the embossing wheels 14', 16' or 15', 17' work the cutting filament 10', i.e. when the indentations 26' are made in the cutting filament it is allowed to epxand to create an undulation in a plane perpendicular to the direction of indentation. Although not shown in the schematic Fig. 34, the embossing wheels 14' -17' are provided with concave portionε in the circumferential direction, εaid concave portionε being located between the emboεsing projections 23' . Thereby it is guaranteed that the undulation created by the indentations 26', 28' is not reduced by the portions between the embossing projections 23' of the embossing wheels 14' -17' when the cutting filament 10' pasεeε between said embossing wheels 14' -17'. In the embodiments shown in Figs. 32 and 33 the embossing projections 23' are so closely arranged on every embossing wheel 14' -17' that the indentations 26' and 28', located in the planes perpendicular to each other, overlap each other, said overlap being larger in Figure 32 than in Fig. 33. From studying the indentations 28' in Fig. 32 it can be learnt that said indentations do not meet each other but an esεentially non-affected material portion 29' remains between the opposite indentationε 28'. The croεε dimenεion T' , in the plane of the paper in Fig. 32, of εaid material portion 29' may of course vary. It is realised that when the cross dimenεion T' decreaεes the undulation increases in a plane perpendicular to the paper in Fig. 32 and when the cross dimension T' increases the undulation decreases in said plane. When manufacturing a cutting filament 10' according to Figs. 32 and 33 a heated filament blank is fed between the cooperating embossing wheels 14', 16' and 15', 17' respectively and indentationε 26' and 28' are created in the cutting filament 10' . Aε pointed out above in connection with Figures 32-34 it iε favourable if the croεs-section of the cutting filament is changed from the original along itε entire length. When the indentations 26' , 28' are applied preferably no material should be displaced in the longitudinal direction of the cutting filament, i.e. the displacement of material should take place by expansion transverse to the longitudinal direction of the cutting filament. If no displacement of material in the longitudinal direction of the cutting filament takes place then the crosε-εectional area of the cutting filament will remain εubstantially constant. By using a prismatic projection 23' the expansion trans- verse to the longitudinal direction of the cutting filament is emphasized. As an alternative to the manufacturing process described above and shown in Fig. 34 the cutting filament according to the present invention may be manufactured by injection moulding. In such a case cutting filaments of a certain length are manufactured, the length being preferably 30-40 cm. Such cutting filaments are especially suitable for rotary-head motorized cultivators that are for hire. As goes without saying, the invention is not limited merely to the embodiments of the cutting filament for brush cutters and edge trimmers which have been described hereinabove by way of examples; on the contrary, it encompasses all alternative forms of embodiment and of application thereof which use the same principle. In particular, it would not be departing from the scope of the invention if the detail of the shapes of the undulations in the filament were modified, or if other methods were used to obtain these undulationε, or alternatively if such an undulated cutting filament or similar cutting tool were specified for any other suitable motorized cultivator.

Claims: C L A I S 1. Cutting filament intended to trimming and cutting vegetation , which can be uεed on rotary-head motorized cultivatorε such as brush cutters and edge trimmers, characterized in that in order to reduce the operating noise, the cutting filament (1;10') has undulations (2,-6; 12') which recur in the longitudinal direction of this cutting filament (1;10') and run in at least one radial direction (Y,Z) relative to the longitudinal axis (X) of the said cutting filament (2) . 2. Cutting filament according to Claim 1, characterized in that the undulations (2) run in a single radial direction (Y) relative to the longitudinal axis (X) of the εaid cutting filament (1), which thuε developε in a single plane (X,Y) . 3. Cutting filament according to Claim 1, characterized in that the undulations (2, 6;12') run in multiple radial directions (Y,Z) relative to the longitudinal axis (X) of the said cutting filament (1) . 4. Cutting filament according to Claim 3, characterized in that the undulations (2;12') run in two radial directions (Y,Z) forming an angle of 90° to one another. 5. Cutting filament according to any one of Claims 1 to 4, characterized in that the undulations (2) are accompanied locally (at 3) by a marking of the cutting filament (1), by crushing. 6. Cutting filament according to any one of Claimε 1 to 6, characterized in that the undulationε (2,-12') are rounded. 7. Cutting filament according to any one of Claims 1 to 5, characterized in that the undulationε (2) are angular. 8. Cutting filament according to any one of Claimε 1 to 7, characterized in that the mid-planeε of the undulations (2) are perpendicular to the longitudinal axis (X) of the cutting filament. 9. Cutting filament according to any one of Claims 1 to 8, characterized in that the mid-planes of the undulations (2) are oblique to the longitudinal axis (X) of the cutting filament. 10. Cutting filament according to Claim 9, characterized in that the undulations (2) are inclined outwards with respect to the position of the cutting filament (1) and to its direction of rotation during use. 11. Cutting filament according to any one of Claims 1 to 10, characterized in that the undulations (2,-12') are obtained by passing the filament (1;10') between at least two toothed wheels, pinions or rollers (10, 11,-14, 16' : 15',17') rotating in oppoεite directionε (arrows 16,17) . 12. Cutting filament according to Claims 9 and 11 taken together, characterized in that the oblique undulations are obtained by pasεing the filament (1) between two helical pinions or rollers (10,11) . 13. Cutting filament according to any of Claims 1 to 12, characterized in that the undulations (12') are obtained by providing indentations (26', 28') in the cutting filament (10') 14. Cutting filament according to Claim 13, characterized in that the indentationε (26', 28') are arranged in pairε, the indentationε (26', 28') of one pair being opposite to each other. 15. Cutting filament according to any one of Claims 1 to 4, characterized in that although the shape of the crosε-εection iε changed when manufacturing the cutting filament (10') the area of the croεε-section is maintained substantially constant. 16. Cutting filament according to any one of Claimε 1 to 10, characterized in that cutting filament iε manufactured by injection moulding. 17. Cutting filement according to any one of Claimε 1 to 12, characterized in that the undulationε (2) keep the initial εection of the cutting filament (1) along itε entire length.

Inventors: LANDEN GOERAN, LEGRAND EMMANUEL, LANDEN, GOERAN, LEGRAND, EMMANUEL
Applicants: HUSQVARNA AB, LANDEN GOERAN, LEGRAND EMMANUEL, HUSQVARNA AKTIEBOLAG, LANDEN, GOERAN, LEGRAND, EMMANUEL
Application year: 1996
Main classification: A01D34
IPC codes: A01D34