EP2866545A1

EP2866545A1 - Cutting head for a rotary-type mower, cutting element adapted to be fitted to such a cutting head and a rotary-type mower comprising such a cutting head

Info

Publication number: EP2866545A1
Application number: EP12880625.4A
Authority: EP
Inventors: Lothar Mitzlaff; Siegfried Kopp; Pär CHRISTENSSON; Niels CLASSENS; Johan Hallendorff; Matias Nybacka
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 2012-07-02
Filing date: 2012-07-02
Publication date: 2015-05-06
Also published as: CN104661512A; EP2866545A4; WO2014007688A1

Abstract

The invention in particular is directed to a cutting head (1 ) for a rotary -type mower, the cutting head (1 ) comprising a rotatable mounting base (2) and at least one removable cutting element (8), wherein the at least one cutting element (8) is mounted rotatably and with a predefined radial clearance (C) to the mounting base (2). The application also concerns a rotary-type mower comprising such a cutting head.

Description

CUTTING HEAD FOR A ROTARY-TYPE MOWER, CUTTING ELEMENT ADAPTED TO BE FITTED TO SUCH A CUTTING HEAD AND A ROTARY-TYPE MOWER COMPRISING SUCH A CUTTING HEAD

The present invention in particular is related to a cutting head for a rotary-type mower and a cutting element adapted to be fitted to a cutting head of a rotary-type mower. Conventional rotary-type mowers such as brush cutters or trimmers or lawn mowers may either be equipped with a rotating type cutting blade or a trimmer cord based cutting head. One disadvantage of cutting blades is that foreign objects, such as stones, metal objects, roots, brickwork and the like, in any case other than brush, grass or lawn to be cut, generally cause increased wear at respective cutting edges. The use of trimmer cords to some extent avoids these problems in that the cord easily can, by bending deformation, evade hard objects. Nevertheless, trimmer cords have a comparatively low durability as compared to cutting blades. A further disadvantage of trimmer cords is that fitting a new trimmer cord to the cord-type trimmer head is comparatively complicated. Therefore, it is an object of the invention to overcome the problems associated with prior art rotary-type mowers and cutting elements mentioned beforehand. In particular a cutting head for a rotary-type mower and a cutting element shall be provided, where the cutting element has improved durability and can easily be replaced.

This and further objects are solved by claims 1 and 15. Embodiments of the invention result from claims 2 to 14. According to claim 1 a cutting head for rotary-type mower is provided. The term rotary-type mower shall comprise any type of lawn mower, rotary scythe-type mower, trimmer, brush cutter, and the like. In particular, a rotary-type mower shall refer to trimmers and brush cutters.

The rotary-type mower comprises at least one cutting head, wherein the cutting head comprises a rotatable mounting base. The mounting base can be of circular, oval or polygonal, in particular rectangular or square, overall shape. Further, the mounting base comprises at least one removable cutting element. The at least one cutting element is mounted rotatably, i.e. pivotably, and with a predefined radial clearance to the mounting base. Therefore the cutting element rotates with the mounting base as a result of rotational movement of the mounting base and is pressed outwards as a result of the centrifugal force. The cutting element may be fixedly coupled to a respective pivot pin or bolt. It is also possible, and preferred that the cutting element is loosely coupled to a pin or bolt. The term "loosely coupled to" shall in particular mean that the cutting element may rotate around the pin during rota- tion of the mounting base. This may for example be the case if an inner face of a center bore provided in the cutting element rolls on an outer circumference of a respective pin passing through the bore. The term predefined radial clearance shall mean that, with respect to a rotational axis of the mounting base, the cutting element can be moved in radial direction by a predefined amount. Movement in radial direction in particular shall be independent from rotational movement of the cutting element around the pin, without excluding simultaneous rotation and radial movements, however. Radial clearance allows the cutting element to avoid or evade hard objects, such as stones, brickwork, rootage and the like, in that upon touching or getting in contact with a respective object, the cutting element can move radially inwards and thus avoid hard contact with the object. There- fore, at least hard collisions of the cutting element with objects can be prevented leading to reduced wear of respective cutting sides of the cutting element.

However, any contact of the cutting element, in particular cutting side of the cutting element with a hard object will cause some kind of wear. Thus, wear as such can not completely be avoided. If, however, the cutting element or the cutting side thereof is locally worn out, in particular chamfered, the worn out side of the cutting element will, at least in a non-load operation, move radially inwards due to centrifugal forces acting on the cutting element. As a consequence, a segment of the cutting element having less wear will be positioned at the outermost position and be available for cutting action.

In particular, the combination of rotatable cutting element with radial clearance has the advantage that reduced and approximately equal wear can be obtained over the cutting edge, in particular over the cutting element. This leads to prolonged service life of the cutting elements.

According to an embodiment, the radial clearance is dimensioned such that the at least one cutting element is al- lowed to substantially fully retract inside of an outer circumference of the mounting base. This shall mean that in case that the cutting element hits a hard object, the cutting element can essentially fully, preferably fully, re- tract into the mounting base, in particular into a pocket provided therein. In this configuration, the cutting element and respective cutting edges of the cutting element are largely shielded from getting into hard contact with respective hard objects. The retracted position can and generally will be obtained or occupied by rotational and/or radial movements of the cutting element. The mounting base can comprise a pocket or the like opening at an outer circumference of the mounting base and adapted and positioned such that it can accommodate the cutting element.

In one preferred variant, the radial clearance is obtained in that the cutting element comprises an inner bore, in particular a comparatively large inner bore, such that the cutting element is of or has a circular ring shape. The di- ameter of the bore may be and preferably is several times the diameter of the pin passing through the bore in the assembled state. In order to allow the cutting element to fully retract to the mounting base, a distance between an outer edge of the mounting base and the pin essentially corresponds to the maximal thickness of the circular ring of the cutting element. In this configuration, it is provided that the cutting element projects far enough from the outer edge of the mounting base so that good cutting results can be obtained.

In a different variant, radial clearance is obtained in that the cutting element is mounted rotatably to a pin or bolt which is moveable in a radial direction of the mount- ing base. Movement in radial direction preferably is obtained in that the pin or bolt is guided in a slotted link running in radial and/or curved radial direction with respect to the rotational axis of the mounting base. This variant also is effective in avoiding hard contacts of the cutting element with foreign objects, such as stones and the like, and in enhanced service life of the cutting element . In a yet further variant, radial clearance is obtained in that the cutting element is fixed via a flexible element, in particular a cord and/or wire to the mounting base. If the cutting element in this configuration hits a hard object, it can move radially inwards to thereby avoid hard contacts with the object. This variant also may be effective in improving service life of the cutting element.

In a further embodiment of the cutting head, the cutting element is a circular type cutting blade, preferably hav- ing, in circumferential direction, at least a section with a continuous cutting edge and/or at least a section with a segmented or toothed cutting edge. The cutting element in this embodiment may have a circular ring shape. It is possible, that the cutting element has at its outer circumfer- ence a single, circumferential cutting edge. The cutting edge may be a continuous, i.e. smooth, in particular non- toothed, cutting edge. The cutting edge may also be a toothed cutting edge. Different types of cutting type edges may be provided at the circumferential cutting edge. This may lead to a wider spectrum of application.

In the segmented variant, the cutting element may comprise several cutting segments, of concave or other shape, for example. Such cutting segments, in particular concave cutting segments, may be advantageous as the cutting angle in this case varies over the cutting edge. This may lead to enhanced cutting efficiency.

It shall be noted that also other types and shapes of cutting elements and cutting edges may be used. In particular, star-shaped cutting elements with radial extending cutting edges or blades may be used.

According to a further embodiment, the mounting base comprises a self-locking mechanism adapted to engage the cutting element in a self locking manner. A self locking mechanism may be advantageous for removing, in particular ex- changing, the cutting element in case that it is worn out. By providing self locking mechanisms, complex fastening mechanisms and related complex replacement actions can be avo ided . In one preferred embodiment, the self locking mechanism comprises at an outer circumference of the mounting base a pin or bolt. The pin may be attached fixedly to the mounting base. However, it is also possible that the pin or bolt is mounted moveable to the mounting base and is urged and/or can be fixed in a locked position. A further possibility is to provide a pin or bolt that is or may be loosely attached to the mounting base, in particular in respective holes of the mounting base. In any case, the pin is adapted to engage, in particular reach through or protrude through, a center bore of the cutting element. As already mentioned further above, a difference in diameter between center bore and pin results in radial clearance. It is of advantage, if the self locking mechanism is implemented as a quick-exchange mechanism allowing easy and fast exchange of cutting elements. Some self locking and quick- exchange mechanisms will be described in more detail fur- ther below .

In one configuration of the self locking mechanism, the pin at its loose end comprises a locking plate. The locking plate may be of oval, round and rounded rectangle shape, for example. The locking plate is adapted and attached to the pin to restrict movement of the cutting element in axial direction of the pin. Such a locking plate is favorable for implementing a quick-exchange mechanism. The dimensions of the locking plate may be selected such that it is possible to tightly thread or push the cutting element over the locking plate. In this case, escape of the cutting element from the pin can be largely avoided for most operational conditions of the cutting head. In a further embodiment, the mounting base comprises a pocket located radially inwards in relation to the pin, opening in radial outward direction and being adapted to accommodate at least a section of the cutting element. Such a pocket may prevent cut material to be tangled at the mounting base. Further, the pocket may contribute to enhanced mechanical strength of the mounting base and/or holding or locking mechanism of the cutting element. In addition, the pocket, in particular wall sections thereof may be used for implementing a self locking, quick-exchange mechanism.

In one embodiment, in which the pocket at least partially contributes to the self locking mechanism, it is provided that an outer edge of an upper wall section of the pocket is located somewhat higher than the upper surface of the locking plate and a gap of predefined width and shape is established between the outer edge and the locking plate such that the cutting element can be threaded through the gap onto the pin. In designing the outer edge of the pocket such that a gap as set out before is obtained makes it more difficult for the cutting element to escape or slip off from the pin, in particular from the space behind the lock- ing plate. Gaps in combination with locking plates as set out beforehand are effective in locking the cutting element to the pin, but also allow quick exchange of the cutting element . Note that the locking mechanism having a respective gap works best in connection with flexible or adequately benda- ble cutting elements. Respective cutting elements may be made from a plastic material, for example. With regard to suitable materials for the cutting element it shall be men- tioned that, in general, any types of materials may be used, in particular metals, plastics and similar. Plastic cutting elements may be preferred if damages to rootage, tree bark, but also to brickwork and plastered surfaces shall be avoided. Plastic cutting elements, in particular of circular and/or circular ring type design, may be manufactured by injection molding, in particular two -component injection molding. The cutting element may comprise materials of different degree of hardness. For example, an outer section of the cutting element, in particular comprising the cutting edge, may be a material of comparatively low or moderate hardness, whereas the material used in the center region or further inwards may have a higher degree of hardness. The cutting element in addition may be made from ma- terials of different colors. Here, an outer section may have a different color than an inner section of the cutting element. The outer color may be used as a wear indicator and the boundary between the different colors may indicate a wear limit. In case that predefined sections of the cutting element reach the wear limit, which can be easily recognized due to lacking material in outer color, exchange of the cutting element may be required.

In another embodiment, the self locking mechanism comprises a spring tongue acting at or on the pin for safely retaining the cutting element on the pin. The spring tongue and pin may be implemented as a one-piece part attached to the mounting base. In this case, a free end of the pin can be urged on or towards a wall or recess of the mounting base. It is also possible, that the tongue and pin are implemented as separate elements and that the tongue presses against a free end of the pin. A respective spring force in both cases is effective in securing the cutting element threaded or pitched to the pin.

In the embodiment comprising the spring tongue and pin, there also may be provided a pocket as described further above. In this case it is of particular advantage that, with respect to a rotational axis of the mounting base, the spring tongue extends radially outwards and is level with an upper wall of the pocket. In this case it is preferred that the pin is fixed to an outer edge of the spring tongue and is urged through the action of a spring force of the spring tongue towards a lower or bottom wall of the pocket.

Note that the pin may be urged onto the lower wall of the pocket or urged towards the lower wall to project into a recess at the lower wall. Providing the tongue at the upper wall of the pocket has the advantage that it is easily accessible to a user for exchanging the cutting element. For exchanging the cutting element, the tongue may be pulled upwards such that an adequate gap is formed between tongue and pin or between pin and lower wall. At this stage, a worn out cutting element may be removed and a new cutting element can be set in such that upon releasing the tongue, the pin passes through a center bore of the cutting element and the cutting element is secured to the pin by the action of the spring force. A grip or the like, adapted to ease lifting of the tongue may be provided at the upper side of the t ongue .

According to claim 13, a cutting element is provided. The cutting element comprises a cutting body with a bore, in particular with a center bore. The cutting element and bore are adapted to be fitted to a cutting head of a rotary-type mower according to at least one of claims 1 to 10. As to advantages and advantageous effects of the cutting element, reference is made to the description above. Further, it shall be mentioned that the cutting element as proposed beforehand can be designed and implemented in accordance with any cutting element described in connection with the proposed cutting head so far. In particular, the cutting ele- ment may be made from a plastic material and, in particular, manufactured by injection molding, in particular two component injection molding. The plastic materials can be selected as set out further above, in particular with respect to different colors.

In one embodiment of the cutting element, essentially corresponding to a cutting element described in connection with the cutting head further above, the cutting body is disc shaped, in particular annular shaped.

In a different embodiment, the cutting element comprises several outer cutting segments, in particular concave- shaped cutting segments. Such a design of cutting elements may be advantageous, as a cutting angle of the cutting element may vary during operation yielding efficient cutting results .

According to claim 15, a rotary-type mower is provided with a cutting head that is adapted to removably hold a cutting element as described in any embodiment and configuration further above .

Advantages and advantageous effects result from the description above and further above.

Selected embodiments of the invention will now be described in connection with the annexed figures, in which:

shows a cutting head of a first configuration; shows the cutting head of Fig. 1 attached to a tr immer ; shows a cr o s s - se ct i on of a cutting head according to a second configuration; shows a cr o s s - se ct i on of a cutting element of the second configuration; Fig . 5 shows a cr o s s - se ct i on of a further cutting element of the second configuration;

Fig . 6 shows a cutting head of a third configuration;

Fig . 7 shows a cr o s s - se ct i on along line VII-VII in Fig.

6;

Fig . 8 shows a cutting head of a forth configuration;

Fig . 9 shows a cross-section along line I X- I X in Fig. 9;

Fig. 10 shows a detail of Fig. 8; Fig. 11 shows a cutting head of a fifth configuration;

It shall be noted, that identical or similar, in particular functionally identical, elements or parts are and will be designated with identical, i.e. common, reference signs.

Fig. 1 shows a cutting head 1 of a first configuration. The cutting head 1 comprises a mounting base 2. The mounting base 2 has a central opening 3 with circumferentially ar- ranged screwholes 4, provided for attaching the cutting head 1 to a rotary-type mower. The rotary-type mower can be an electric mower as well as a petrol-driven mower.

Note that the cutting element 8 in the present case has a continuous circumferential cutting edge. However, any other type of cutting elements described below and further above may be used in connection with the cutting head of the first configuration. The mounting base 2 has an overall elliptic outer shape. At respective apex points of the elliptic mounting base 2 cutouts 6 are provided. In each cutout a pin 7 is attached to a lower bottom of the cutout 6. A circular ring type cutting element 8 with a comparatively large center bore 9 is threaded to the pin 7. The diameter of the center bore 9 is several times the diameter of the pin 7. The diameters of the center bore 9 and pin, the radial depth of the cutout and the distance of the pin 7 from the outer circumferential edge of the mounting base 2 are preferably selected such that the cutting element 8 can fully retract into the cutout 6. As can be seen from the left-hand cutout 6 in Fig. 1, the cutouts 6 during normal operation of the cutting head 1 are covered by adequate lids 10. The lids 10 are removably coupled to the mounting base 2, and in the mounted state define a pocket extending radially inwards from the pin 7 and opening radially outwards. As can be seen, the pockets are adapted to receive respective cutting elements 8. Pockets are advantageous as cut material can be prevented from catching up on the cutting head 1. In general, the term radially shall be understood in that the described component is oriented at least partially in a radial direction. However, the component described to be oriented radially can also be oriented in another direction, e.g. oriented partially radially and partially cir- cumferentially or partially in a direction towards the circumference of the mounting base (2) . From Fig. 1 it becomes obvious, that the cutting element 8 is mounted rotatably and with a predefined clearance C to the mounting base 1. More precisely, the clearance C is a free space, wherein radial movement of the cutting element 8 is allowed and wherein, due to the radial movement, the cutting element 8 can retract at least partially, preferably fully, to the inside of the outer circumference of the mounting base 2. Therefore, if the cutting element 8 hits a hard object, such as a stone and the like, the cutting element 8 will be urged in a rotational and/or radial movement into the pocked and thus be largely protected from further interactions with the object. As a consequence, wear of the cutting element 8 can be greatly reduced. Further, if the cutting element 8 at one location hits a hard object and is worn out, the worn out section will move radially inwards due to centrifugal forces acting in operation. At the same time, a section with less wear will be urged radially outwards. Hence, improved cutting results can be obtained. In all, uniform wear of the cutting element 8 along its entire circumferential cutting edge can be obtained, which greatly improves lifetime of the cutting element 8.

Fig 2 exemplarily shows a cutting head 1 of Fig. 1 which is attached to a motor shaft (not shown) of a trimmer. The cutting head 1 is mounted and positioned at a lower side of the motor and gear housing 5. The assembly shown in Fig. 2 may be mounted or coupled to a brush cutter or trimmer, for example. However, the proposed cutting head 1 and mounting base 2 are not restricted to brush cutters and trimmers, and may also be used with lawn mowers and the like.

Fig. 3 shows a cutting head 1 of a second configuration.

The cutting element 8 in the second configuration is cou- pled via two cords or wires 12 to a mounting base 2 rotata- bly mounted to the rotary-type mower. By mounting the cutting element 8 with respective cords 12, radial clearance C can be obtained. Hence the same advantages as described in connection with Fig. 1 and 2 can be obtained. Note that the cutting element 8 of Fig. 3, Fig. 4 or Fig. 5 may be designed and implemented similar to the cutting element 8 of Fig. 1 and 2. In particular, the cutting element 8 may be made from plastic material, in particular in form of a cir- cular plate or ring. Other materials than plastic are rubber materials and/or fiber composite materials, which can also be used for the cutting elements described further above and below. Fig. 4 shows a section of the cutting element 8 of the second configuration. The cutting element 8 in the present case comprises a central hole through which cord 12 is pitched and guided through. In the central hole there may be provided a wedge 23 fixing the cord 12 to the cutting element 8. The central hole, in particular the bending radius of respective edges, and the wedge 23 may be designed and shaped such that wear of the cord 12 at respective edges of the central hole are minimized. Instead of a wedge 23, the central bore may comprise a bushing through which the cord 12 is fitted. Upper and lower edges of the bushing may be designed such that wear of the cord 12 at respective edges is minimized. The bushing may be implemented as a type of inner bearing of the cut- ting element 8.

Fig. 5 shows a section of a further cutting element of the second configuration. Fig. 5 shows an alternative for at- taching the cord 12 to the cutting element 8. Each of the cords 12 in Fig. 5 comprises at its distal end a lug 14. The cutting element 8 in turn comprises two stub shafts 15 to which the lugs 14 can be connected to, for example in a click and snap connection. In this case wear of the cords 12 caused by rotation of the cutting element 8 can be prevented. Click and snap connections and the like between cutting element 8 and cord 12 constitute quick-exchange mechanisms favorable for time saving cutting element ex- change .

Fig. 6 shows a cutting head 1 of a third configuration. The mounting base 2 of the present configuration has a circular shape and comprises two diametrically opposed locations for respectively mounting a cutting element 8. Note that one or more locations may be provided. In case that only one cutting element 8 is provided a balancing weight is needed on the opposing side. For reasons of simplicity, only one cutting element 8 is shown in Fig. 6.

The cutting element 8 in the present case has a circular ring type shape, wherein sections or segments with concave cutting edges 16 are provided. The concave cutting edges 16 are equally distributed over the circumference of the cut- ting element 8. The concave cutting edges 16 provide advantages in cutting efficiency, as the angle of impact varies.

Each of the two diametrically opposed locations for respec- tively mounting a cutting element 8 comprises a pin 7. The pin 7, as can be seen from Fig. 7, extends upwards from a bottom wall of the mounting base 2. The pin 7 is adapted to engage the center bore 9 of the cutting element 8. Similar to the configuration shown in Fig. 1 and 2, the diameter of the center bore 9 in the third configuration is several times the diameter of the pin 7. Hence, radial clearance C of the cutting element 8 is provided. The diameters, dimen- sions of the cutting element 8 and distance of the pin 7 from the outer edge of the mounting base 2 may be selected such that the cutting element 8 can fully retract into the cutting head 1. In the region where retraction of the cutting element 8 is possible, a type of cover element 17 is provided defining a pocket 18 (see Fig. 7) towards the bottom wall of the mounting base 2. The pocket 18 is designed similar to that of Fig 1, in particular such that the cutting element 8 largely can enter into the pocket 18 in case that the cutting element 8 is caused or urged to move radially inwards, which may be caused by hard obstacles hit by the cutting element during operation. As to advantages and advantageous effects of providing a rotatable cutting element 8 with ra- dial clearance C, reference is made to the description above and further above.

Each of the pins 7 in the third configuration comprises at the respective loose end, the end facing away from the bot- torn wall of the mounting base 2, a locking plate 19. The locking plate 19 has an elongated slightly curved shape in accordance with a circumferential edge of the mounting base 2. The length of the locking plate 19 is preferably greater than the diameter of the center bore 9 of the cutting ele- ment 8. Therefore, the cutting element 8 can not easily pass over the locking plate 19. As can be seen, the locking plate 19 restricts movement of the cutting element 8 in axial direction of the pin 7. A further obstacle for the cutting element 8 to passing over the locking plate 19 and slipping from the pin 7 is provided by the cover element 17. In more detail and with particular reference to Fig. 7, an outer edge of cover element 17 is somewhat higher than an upper surface of the locking plate 19 and a gap 20 of predefined width and shape is established between the outer edge of the cover element 17 and locking plate 19.

The gap 20 is dimensioned such that the cutting element 8 can be threaded through the gap 20 and over the locking plate 19 onto the pin 7. In case that the cutting element 8 is made from a flexible material, the gap 20 may be dimen- sioned that threading the cutting element 8 onto the pin requires deformation of the cutting element 8. In this case the cutting element 8 can be securely held on the pin 7.

As can be seen from Fig. 6 and Fig. 7 and related descrip- tion, the pin 7, locking plate 19 and cover element 17 define or make up a self locking mechanism, adequate to securely retain the cutting element 8 on the mounting base 2 during ordinary operation. Note that the self locking mechanism in the present case also provides a quick-exchange mechanism.

As to further advantages and advantageous effects, reference is made to the description further above. Fig. 8 shows a cutting head 1 of a fourth configuration.

Here, only the major differences to the third configuration shall be described. One major difference to the third configuration shown and described in connection with Fig. 6 and 7 is the type of self locking mechanism. The fourth configuration uses an alternative self locking mechanism comprising a spring tongue 21 which is implemented as a one-piece part with the pin 7 (see Fig. 9) . The spring tongue 21 extends radially outwards and is level with the cover element 17 defining an upper wall of the mounting base 2.

Under the action of the spring force generated by the spring tongue 21, the pin is urged towards, preferably on, the bottom wall of the mounting base 2, in particular pocket 18. It is preferred, that the pin 7 can plunge into a depression formed at the bottom wall of the mounting base 2 or pocket 18. This may be advantageous as the pin 7 then can fully pass through the central bore 9 of the cutting element 8, and the cutting element 8 can be securely fixed by the pin 7.

In the present case, the pin 7 is implemented at a free end of the spring tongue 21. However, it is also possible that the pin is provided at any point between the fixed base and the free end of the spring tongue 21.

The spring tongue 21 in the present case comprises a pro- trusion 22 adapted to be pulled with a finger in order to raise the free end of the spring tongue 21 and provide free access to the pocket 18. This means that the cutting element 8 either can be removed from the cutting head 1 or that a cutting element 8 can be moved into the pocket 18 in such a way that the pin 7 in the end reaches through the central bore 9 of the cutting element 8. Fig . 10 shows a sketch in which a finger raises the spring tongue 21 for exchanging the cutting element 8 as described bef orehand . Fig. 11 shows a fifth configuration of a cutting head 1 having a mounting base 2. The mounting base 2 has a first portion 2a and a second portion 2b, wherein between the first portion 2a and the second portion 2b a pocket 18 is formed. First portion 2a and second portion 2b can be formed by separate disc-shaped elements which are connected to each other in their respective central sections. Alternatively the mounting base 2 can be formed integrally from one piece, e.g. from plastic material. The mounting base 2 has a plurality of recesses 24 which extend partially in a radial direction and partially in a circumferential direction.

Cutting elements 8 are mounted to recesses 24 by means of pins 25 which might be provided as nuts and screws. When attached to the respective cutting element 8, each pin 25 is freely movable along the extent of the recess 24 to which it is mounted to. The recesses 24 or slots are formed as a curve and run in a radial direction as well as in a circumferential direction. Thus, due to a rotational move- ment of the mounting base 2, the cutting element 8 is moved to and stopped at the radially outward end of the recess 24.

When hitting an object, the cutting element 8 will be urged along the extent of the recess 24 into the pocket 18 and thus is protected from further interactions with the object. In the shown figure, one cutting element 8 is in a cutting position, while an other cutting element 8 on the opposite side of the mounting base 8 is fully retracted into the pocket 18.

As can be seen from the above description, the cutting ele- ment as proposed herein has enhanced durability and can easily be replaced.

A specific advantage of all embodiments as shown in Fig . 6 to Fig. 11 is, that the energy consumption is lower com- pared to trimmers as known in the prior art.

List of reference numerals :

1 cutting head

2 mounting base

2a first portion

2b second portion

3 central opening

4 screwhole

5 gear and motor housing 6 cutout

7 pin

8 cutting element

9 central bore

10 lid

12 cord

14 lug

15 stub shaft

16 concave cutting edge

17 cover element

18 pocket

19 locking plate

20 gap

21 spring tongue

22 protrusion

23 wedge

24 recess

25 pin

C radial clearance

Claims

Cutting head (1) for a rotary -type mower, the cutting head (1) comprising a rotatable mounting base (2) and at least one removable cutting element (8) , wherein the at least one cutting element (8) is mounted rotat- ably and with a predefined radial clearance (C) to the mounting base (2) .

Cutting head (1) according to claim 1, wherein the radial clearance (C) is dimensioned such that the at least one cutting element (8) is allowed to substantially fully retract to the inside of an outer circumference of the mounting base (2) .

Cutting head (1) according to any of claims 1 and 2 , wherein the cutting element (8) is a circular type cutting element, preferably having, in circumferential direction, at least a section with a continuous cutting edge and/or at least a section with a segmented (16) or toothed cutting edge.

Cutting head (1) according to any of claims 1 to 3, wherein the mounting base (2) comprises a self-locking mechanism adapted to engage the cutting element (8) in a self locking manner.

Cutting head (1) according to claim 4 wherein the self locking mechanism comprises at an outer circumference of the mounting base (2) a pin (7, 25) adapted to engage a center bore (9) of the cutting element (8) . Cutting head (1) according to claim 5, wherein the mounting base (2) comprises a pocket (18) located at least partially radially inwards of the pin (7, 25) , opening in radial outward direction and being adapted to accommodate at least a section of the cutting element ( 8 ) .

Cutting head (1) according to claim 5 or 6, wherein the pin (7, 25) at its loose end comprises a locking plate (19) restricting movement of the cutting element (8) in axial direction of the pin (7) .

Cutting head (1) according to claim 7, wherein a gap

(20) of predefined width and shape is established between an outer edge of an upper wall section of the pocket (18) and locking plate (19) such that the cutting element (8) can be threaded through the gap (20) onto the pin (7, 25) .

Cutting head (1) according to claim 5 or 6, wherein the self locking mechanism comprises a spring tongue

(21) acting at or on the pin (7, 25) for safely retaining the cutting element (8) on the pin (7, 25) .

Cutting head (1) according to claim 9, wherein, with respect to a rotational axis of the mounting base (1) , the spring tongue (21) extends radially outwards and preferably is level with an upper wall of the pocket (18) , wherein the pin (7, 25) preferably is fixed to an outer edge of the spring tongue (21) and is urged through the action of a spring force of the spring tongue (21) towards a lower wall of the pocket (18) . Cutting head (1) according to any one of the preceding claims, wherein said mounting base (2) has at least one recess (24)and wherein said at least one cutting element (8) is movably mounted to said recess (24) and wherein said recess (24) allows said cutting element (8) to move at least in a radial direction.

Cutting head (1) according to claim 11, wherein sai recess (24) is formed as a curve and extends from a radially inner section of the mounting base (2) towards a radially outer section of the mounting base (2) .

13. Cutting element (8) comprising a cutting body with a bore, in particular with a center bore (9) , wherein the cutting element (8) and bore (9) are adapted to be fitted to a cutting head (1) according to at least one of claims 1 to 12. 14. Cutting element (8) according to claim 13, wherein the cutting body is disc shaped, in particular annular shaped and preferably comprises a continuous outer circumferential cutting edge or wherein the cutting element comprises several outer cutting segments, in particular concave-shaped and/or toothed cutting segment s .

Rotary-type mower comprising a cutting head (1) according to any of the claims 1 to 12, wherein the cutting head (1) is preferably adapted to removably hold a cutting element (8) according to at least one of the claims 12 to 13.