WO1995006402A1

WO1995006402A1 - Trimmer line

Info

Publication number: WO1995006402A1
Application number: PCT/AU1994/000499
Authority: WO
Inventors: Alan Wesley Talbot
Original assignee: Alan Wesley Talbot
Priority date: 1993-08-30
Filing date: 1994-08-26
Publication date: 1995-03-09

Abstract

A trimmer line for a powered line trimming apparatus comprises a pair of line elements (2) releasably secured together along parallel longitudinal axes by a frangible adhesive (3) which in use permits separation of the line elements (2) under the influence of centripetal force when trimmer line is released from a hub on which it is wound.

Description

TITLE TRIMMER LINE

FIELD OF INVENTION This invention relates to powered line trimmers for cutting grass, weeds, brush and light undergrowth and is particularly concerned with the consumable line utilised by such trimmers.

BACKGROUND ART Typically, a line trimmer comprises a portable machine for cutting or trimming vegetation such as grass and other plant material which is primarily of a non-woody nature. It comprises a long shaft having an electric or petrol drive motor at one end and a rotatable housing at the other.

The rotatable housing includes a single cord or line wound on a spool which feeds out through either one or two apertures in the housing and provides the cutting action as it rotates. This line is typically manufactured from an extruded plastics material such as nylon and is consumed during use. Further line must therefore be periodically extended from the housing during use. This can be done manually by stopping the machine, releasing the spool in its housing, turning the spool by hand to unwind more line, pulling the required length of line through the apertures in the spool, retightening the spool retaining housing, and restarting the machine.

This is obviously a time-consuming and inefficient process and for this reason, automatic line feed housings have been developed. These comprise a modified rotatable housing which enables the line to feed out under the action of centripetal force when the spool is temporarily disengaged from the spinning housing by pushing a spring biased release button in the centre of the housing while it is spinning. In practice, this automatic feeding is done by "bumping" the release button against the ground when it is perceived that more cutting line is required.

There are a number of problems with such automatic feed systems. Depending upon the impact force of the "bump" and the duration thereof, more or less line is ejected under the effects of centripetal force. For this reason, a sharp blade is often provided at the perimeter of a safety guard to trim excess length of released line as too great a rotational diameter of the line can reduce the torque of the drive motor. Frequently, this leads to excessive consumption of trimmer line.

Moreover, it is found that the line(s) do not eject when required; the lines are difficult to wind onto the spool; and the housings wear out rapidly due to excessive bumping in an attempt to make the lines eject. In many instances, they cannot do so because they become tangled on the spool during rotation, or they have not been correctly wound onto the spool to begin with, or the spool has not been properly installed in the housing.

All of these problems can be traced back to the line itself rather than the design of the housing. Typically, line trimmers have two lines extending through mutually opposed apertures in a circumferential wall of the housing. The "two lines" are, in effect, the ends of a single line which has been folded in two and wound onto the reel. For this reason, all prior art line trimmers are limited to single or opposed twin line cutting heads.

The line is cut from a supply coil or purchased in the required length for the particular size of the housing, and has to be wound onto the spool by the user. However, since it is difficult to wind two lines onto the spool with great uniformity, a certain degree of overlapping and/or intertwining of the two lines occurs. Also, as soon as the winding tension is relieved such as when the line ends are to be individually threaded through the apertures in the housing, further intertwining of the lines occurs. Consequently, during rotation of the housing, the lines become tightly entangled. This results in the lines not ejecting as required, breaking off, or uneven wear occurring with resultant reduced cutting power. In both cases, the machine has to be turned off and the housing disassembled so that the spool of cutter line can be untangled.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a trimmer line which will obviate or at least minimise at least some of these disadvantages .

According to the one aspect of the present invention, there is provided a tangle resistant trimmer line for line trimming apparatus, said trimmer line comprising:- two or more trimmer line elements releasably secured together along substantially parallel longitudinal axes, said trimmer line elements being secured by a securing means, in use, frangible under operating conditions to cause separation of said two or more trimmer line elements under the influence of centripetal force when trimmer line is released from a hub on which it is wound.

The trimmer line may comprise from two to eight trimmer line elements.

Suitably the trimmer line comprises two trimmer line elements.

Preferably the trimmer line comprises two or more trimmer lines releasably secured along substantially parallel axes to form a member with one transverse dimension having a width at least twice that of a further transverse dimension orthogonal thereto. The trimmer line is suitable for use with the same housing which is used for conventional single stranded lines but has the advantage during loading that it does not need to be doubled over to enable winding onto it's spool. Obviously, however, if the trimmer line has more than two strands, the housing would need more than two openings through which the individual strands could be fed.

The capacity of the trimmer line to separate "in use" into its individual strands means that the strands separate from each other as they feed from the spool to the exterior of the housing under the action of centripetal force when the hub is temporarily disengaged to enable release of trimmer line. It will also be apparent to the skilled addressee that the strands may likewise be separated from each other manually as the centripetal force is likely to be less than that which can be exerted by two hands pulling individual strands in opposite directions. As mentioned, the trimmer line can have a multiplicity of strands. The actual number will be determined by the particular application and thus the cutting requirements of the line cutter. For most practical purposes the number of strands will not generally exceed six or eight and in the majority of instances there will only be two strands. Two strands are preferred since such trimmer lines can be used in conventional line cutter housings without the need to modify the housings in any way. Parallel stranded lines are also preferred from the point of view that they can be made with a substantially planar top and bottom surface region which facilitates winding onto the spool without tangling - an especially important consideration if winding is to be done by the end user - and maximum utilisation of the winding volume without leaving voids. Multiple stranded trimmer lines may be of prime consideration for commercial usage for higher powered motors, especially when dense and woody plant material is to be cut, or where very fine trimming is necessary.

The individual strands of the trimmer line may comprise a solid core of one or more materials, a layered structure of several materials, or a plurality of fibres of filaments of the same or different materials which may be twisted together. Suitable materials include plastics materials such as nylon, polyvinylchloride , HD polyethylene and/or polypropylene, and cross-linked methylmethacrylate copolymers and the like high strength copolymers; ceramic whiskers, carbon fibres or glass fibres in an appropriate binding medium; metallic filaments; and combinations of these materials with other materials from the recited group or with other known materials. The most preferred material is nylon as it is easy to manufacture, durable, can be readily formed into multiple strands, and is relatively inexpensive.

The cross-sectional dimensions of the trimmer line will be determined by the nature of the material from which it is fabricated, and the intended end use. In this context, it is to be borne in mind that the actual strands of the trimmer line will be substantially the same diameter as the diameter of conventional trimmer lines for a given trimmer motor power so that an equivalent cutting effect is produced, and there is therefore essentially no more material used.

For high strength trimmer lines composed of high tensile strength material, the individual strands will usually be commensurately small in diameter, in the order of 0.5 mm or less; whereas for low strength trimmer lines composed of low tensile strength materials, the individual strands will usually be several millimetres in diameter. However, it will be appreciated that applications of use may arise where these size preferments are reversed in each of these instances. Each strand of the trimmer line will preferably be of the same cross-sectional configuration and size as the other(s). The preferred shape of the strands is circular which, for a two stranded trimmer line will give an over-all figure-eight cross-section. Other particularly suitable shapes for the strands include square, rectangular and D-shaped.

The strands may be joined to each other by a wide range of techniques including fusion or friction welding, adhesion, and web formation. The joint may be continuous along the length of the trimmer line or may be discontinuous at regular or irregular intervals.

Fusion welding can be effected only on those materials which can be melted by specific radio frequencies and is thus confined to certain types of plastics materials. To achieve the fusion, the strands are brought together and held under an applied pressure while a controlled beam of electromagnetic radiation is directed through the strands at their point of contact. The radiation is applied for a sufficient time to enable the outer regions fo the strands to melt and coalesce together so that a frangible connection is produced. Preferably, such fusion welding is effected at regular intervals along the length of the trimmer line.

Friction welding, as the term implies comprises a generation of heat sufficient to partially fuse adjacent strands under the influence of mechanical friction therebetween. Adhesion is effected by the use of a suitable adhesive applied either continuously along the strands or, more preferably, at intermittent regular regions. The adhesive chosen will be such as to provide a sufficiently strong bond that the strands will not normally come apart until a force is exerted upon them by the centripetal force which is to be applied to the trimmer line during use.

The adhesive used will primarily depend upon the composition of the trimmer line strands and will generally be of a synthetic nature. Typical synthetic adhesives will be selected from elastomer-solvent cements^', polysulphide sealants, thermoplastic resins, thermosetting resins and silicone polymers and cements. The most preferred general purpose adhesive which is suitable for the majority of strand compositions, is a urethane-methacrylate cement sold under the trade name LOCTITE 180 (TM) .

The third most common form of joint referred to above, viz the web joint, essentially comprises a region of weakening produced between line elements along the length of the trimmer line which enables the strand components to be peeled away from each other. This web joint is generally formed integrally with the adjacent line elements. That is, instead of initially making separate strands which are subsequently joined together, a single trimmer line member is produced, usually by extrusion, which has a multi-core construction wherein the individual cores are held together by a thin web.

It is possible, however, to form a web joint subsequent to the manufacture of the strands. Thus, for instance, a web joint may be effected by coating the strands with a material which hardens to form an all-encompassing membrane. Such a material will preferably be chosen so as to not form a significant bond with the elements or, at most, only very weak bonds. The membrane coating can cover the entire trimmer line or only portions thereof. Generally, the membrane will be very thin, in the order of micrometers in thickness.

According to another aspect of the invention there is provided a method of manufacture for a trimmer line according to the invention, said method comprising the steps of:- releasably securing in a frangible manner, at least two trimmer line elements along substantially parallel longitudinal axes whereby in use, said trimmer line elements are separable under the influence of centripetal force when trimmer line is released from a hub of a line trimmer.

If required, said at least two trimmer line elements may be releasably secured by a fusion process. Suitably, said at least two trimmer line elements may be releasably secured by a frangible web extending between adjacent line elements.

Preferably said at least two trimmer line elements may be releasably secured by a frangible adhesive.

The frangible web may be formed integrally with said at least two or more line elements.

According to yet another aspect of the invention, there is provided an apparatus for the manufacture of trimmer line according to the invention, said apparatus comprising:- guide means for guiding two or more line elements into substantially parallel longitudinal axes; and, adhesive applicator means for forming a frangible joint between adjacent line elements.

The guide means may comprise an extrusion die having adjacent orifices for respective line elements.

Suitably the extrusion die includes slotted apertures extending between adjacent orifices to form a frangible web between adjacent said line elements.

Alternatively said guide means may comprise means to urge said one or more line elements into substantially parallel longitudinal axes.

The adhesion means suitably comprises an adhesive applicator adapted to apply adhesive continuously or discontinuously between adjacent line elements. BRIEF DESCRIPTION OF DRAWINGS

In order that the invention may be more fully understood and put into practical effect, preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which:-^'

Figure 1 is a perspective view of a trimmer line according to one aspect of the present invention;

Figure 2 is a perspective view of a trimmer line according to a second aspect of the present invention; Figure 3 is a perspective view of a trimmer line according to a third aspect of the present invention;

Figure 4 is a partial view of a rotatable line trimmer housing having a trimmer line according to the invention; Figure 5 is a cross sectional view through A-A in Figure 4;

Figure 6 is a schematic representation of an arrangement for manufacturing the trimmer line of Figure 1 ; Figures 7a-7f are views of various forms of double stranded trimmer line according to the present invention.

Figure 8 shows a form line trimmer head in accordance with a further aspect of the invention. DETAILED DESCRIPTION

In Figure 1 the trimmer line 1 comprises extruded monofilaments 2 of nylon which are secured together with substantially parallel longitudinal axes by a cyano-methacrylate adhesive 3 which may be solvent based or otherwise which may be cross-linkable under the influence of a catalyst such as UV radiation.

As shown, the adhesive 3 is applied in a discontinuous fashion at regularly spaced intervals.

Figure 2 shows a variation of the embodiment shown in Figure 1 wherein three nylon monofilaments 2 are joined at spaced intervals by adhesive 3. Figure 3 shows yet another variation of the embodiment of Figure 1 wherein a first pair of monofilaments 2 is secured by adhesive 3 to a second pair of monofilaments 2a, also secured together by adhesive 3. Both pairs 2 and 2a are secured together by mutual cohesion of adhesive 3.

Figure 4 shows an exposed view of a line trimmer head 4 comprising an inner hub 5, a drive shaft 6 and a housing 7 having opposed apertures 8 through which separated elements 9, 10 of a trimmer line of Figure 1 extend. The end cap incorporating a bump button is omitted for the sake of clarity.

Figure 5 is a cross sectional view through A-A in Figure 4. As can be seen in Figure 5, the paired trimmer line 11, because of its "tape-like" configuration, is able to be wound on hub 5 in a more orderly manner than otherwise would a single monofilament or pair of single unconnected filaments. In this manner, the tape like configuration of the paired trimmer line is not susceptible to tangling and jamming on hub 5 with variations in line tension as otherwise is the case with separate monofilaments of prior art trimmer hubs.

Referring to Figure 6, the schematic arrangement for manufacturing double stranded trimmer line having a nylon core comprises a feed support consisting of an axle 16 on which two drums 17, 18 of monofilament lines 19, 20 are rotatably supported. The drums include a clutch mechanism (not shown) so as to provide tension in the lines as they unwind from the drums. The monofilament lines are conventional nylon trimmer lines which typically vary in diameter between 0 . 5 and 3 . 0 mm .

The feed system comprises two drums 21 , 22 fixed to a rotatable shaft 20 and about which drums the trimmer lines are wrapped. A primary sprocket wheel 23 is journalled to the shaft 20 so as to drive a cam 26 by way of a secondary sprocket wheel 25 journalled to a secondary shaft 27 through the agency of drive chain 24. The cam 26 is coupled to an adhesive applicator 28. A ^' cross linkable liquid urethane-methacrylate resin is charged to a reservoir associated with applicator 28 and issues as droplets from the outlet at predetermined intervals. The rate of release is governed by the cam 26 which acts in concert with the operating mechanism.

In a modified form of the apparatus (not shown) the adhesive applicator comprises a variable frequency pulse generator which is coupled to a pneumatic valve, in turn coupled to a diaphragm valve powered by pneumatic pressure. The pulse generator is operable to control both the duration and frequency of the diaphragm valve applying adhesive to the adjacent line elements.

In this manner adhesive is released intermittently onto the junction of the two lines 19, 20 passing below.

After application of the adhesive following passage through guide rollers 40, the paired trimmer line 41 enters a curing chamber (not shown) in which the adhesive composition is exposed to ultra violet radiation. Within the curing chamber are compression rollers 42 which retain the line elements 19, 20 in juxtaposition while initial curing of the adhesive takes place. After initial curing, the paired line 41 travels through a festoon accumulator 43 while final curing occurs.

When curing is complete, the paired line 41 is wound on take up roller 43.

Figure 7 illustrates various forms of trimmer line according to the present invention.

In Figure 7a the trimmer line comprises monofilaments 45 joined and encapsulated by a membrane covering 46 which comprises an applied glue membrane or an extruded plastics membrane.

In Figure 7b the trimmer line comprises monofilaments 46 encased in a sheath 47 of low tensile strength adhesive or a coextruded plastics material.

Figures 7c and 7d show alternative forms of coextruded monofilament 48 with an integral web 49.

Figure 7e shows an alternative configuration of the trimmer line of Figures 7c and 7d wherein the monofilament elements 48 are of a D shaped cross section.

Figure 7f shows yet another embodiment wherein the trimmer line comprises four adjacent elements 50 secured at spaced intervals by an adhesive 51. Figure 8 shows a four line trimmer head in accordance with yet another aspect of the invention.

In Figure 8, the head 60 comprises a housing 61 having four apertures 61, 62, 63, 64 therein. Head 60 and line hub 65 are mounted on a drive shaft 66 for rotation.

Wound around hub 65 is a four element line 67 of the type generally shown in Figure 7f, the free ends 67a, 67b, 67c and 67d extending through respective apertures in housing 61. It will be clear to a skilled addressee that the present invention enables a self expelling line system for line trimmers having more than two cutting lines whereas prior art trimmers are inherently limited to one or two lines, both with inherent problems of tangling within the trimmer head.

Whilst the above has been given by way of illustrative example of the ^' invention, many modifications and variations may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention in its various aspects.

Claims

1. A tangle resistant trimmer line for line trimming apparatus, said trimmer line comprising:- two or more trimmer line elements releasably secured together along substantially parallel longitudinal axes, said trimmer line elements being secured by a securing means, in use, frangible under operating conditions to cause separation of said two or more trimmer line elements under the influence of centripetal force when trimmer line is released from a hub on which it is wound.

2. A trimmer line according to claim 1 wherein the securing means comprises an adhesive composition.

3. A trimmer line according to claim 2 wherein the adhesive composition is applied between adjacent trimmer line elements.

4. A trimmer line according to claim 2 wherein the adhesive composition extends about the peripheral surface of adjacent trimmer line elements.

5. A trimmer line according to any one of claims 2 to 4 wherein the adhesive composition is applied continuously along adjacent trimmer line elements.

6. A trimmer line according to any one of claims 2 to 4 wherein the adhesive composition is applied discontinuously along adjacent trimmer line elements.

7. A trimmer line according to claim 1 wherein the securing means comprises a continuous or discontinuous frangible web extending between adjacent trimmer line elements .

8. A trimmer line according to claim 7 wherein the frangible web is formed integrally with adjacent trimmer line elements.

9. A trimmer line according to claim 7 wherein the frangible web is formed of a material dissimilar to the line element material.

10. A trimmer line according to claim 1 wherein the securing means comprises continuous or discontinuous regions of fusion between adjacent line trimmer elements.

11. A method for the manufacture of a trimmer line according to claim 1 , said method comprising the steps of:- releasably securing, in a frangible manner, at least two trimmer line elements along substantially parallel longitudinal axes whereby in use, the trimmer line elements are separable under the influence of a centripetal force when trimmer line is released from the hub of a line trimmer apparatus.

12. A method as claimed in claim 11 wherein said line trimmer elements are frangibly secured by an adhesive composition.

13. A method as claimed in claim 11 wherein said trimmer line elements are frangibly secured by a fusion process .

14. A method as claimed in claim 11 wherein said trimmer line elements are frangibly secured by a frangible web extending between adjacent line elements.

15. An apparatus for the manufacture of trimmer line according to claim 1, said apparatus comprising:- guide means for guiding two or more line elements into adjacent substantially parallel longitudinal axes; adhesive applicator means for forming a frangible joint between adjacent line elements; and curing means for curing adhesive applied to adjacent line elements.

16. An apparatus as claimed in claim 15 wherein said curing means comprises a source of infra red radiation.

17. An apparatus as claimed in claim 15 wherein said curing means comprises a source of ultra violet radiation.

18. A line trimmer housing for a rotatable bump release line trimmer head, said housing comprising:- three or more substantially evenly spaced peripheral apertures to receivably locate separated trimmer line elements of a trimmer line according to claim 1.