DE20309876U1 - Powered hand-held hedge trimmer has serrated edge cutting blades working in opposition to trap blades - Google Patents

Abstract

A powered hedge trimmer has a first set of cutting blades (2) and a second set of trap-blades working in opposition. The cutting blades esp. have serrated (6) edges (4). The blade angle is pref. 45[deg].

Description

The present invention relates to a hedge trimmer, in particular for cutting a garden hedge according to the preamble of claim 1.

The utility properties of hedge trimmers are determined by the target group and the area of application of the device and are designed accordingly. Firstly, the quality of a hedge trimmer is determined by its drive power and its cutting properties. Important features are safety, reliability, operation, vibration of the blade, weight of the tool and the service life of the cutting mechanism.

The cutting mechanism of a hedge trimmer is often formed by a cutting blade and a catch blade, which are usually driven by a motor in opposite directions. Cutting and catch blades are formed by blade strips, each of which has V-shaped and laterally protruding blade blades on both sides, each with two V-shaped cutting edges that converge and are determined by slanted cutting surfaces. The arrangement can be symmetrical, asymmetrical or anti-symmetrical. There are also hedge trimmers with asymmetrical blades, where both blade strips have catch teeth on one side and cutting teeth on the other. Both blade strips are then mounted one on top of the other so that there is a row of catch and

Forstenrieder Allee 59 D-81476 Munich Tel. +49(0)89-745541-0 Fax +49 (0)89 - 7593869

FrShJingstr.43A ·* · · *· ö-*4äV3c.Essen!.· *··* *··* Tel. +49 (0)201 - 84230-0 Fax +49 (0)201 - 84230-20

L>e410»«Leipzi§·

Phone, +49(0)341 - 1495860

Fax +49(0)341 - 1495868

Pc$ecJtxpCDe Espana No.l,4-Izda

ES-CJ3002 ATicante

Phone +49(0)89-745541-0

Fax +49 (0)89 - 7593869

&psgr; ·

Cutting teeth are arranged. The catching blades are blunt and the fangs usually protrude at least 8 mm over the cutting teeth. The blunt protrusions of the fangs can be rounded, teardrop-shaped, mushroom-shaped or even cone-shaped.

The cutting blades, which slide against each other during cutting, grasp the material to be cut between the blades, which is then separated by the cutting edges. The different number of blades and their spacing, as well as the length of the blade strips, determine the possible use and requirements for a hedge trimmer, depending on the drive. The properties of the cutting mechanism, its material and its coating also have a corresponding effect on the cutting performance and the service life of the cutting edges.

In conventional hedge trimmers, the cutting edges are mostly ground in a wedge shape and gradually lose their sharpness during use. Another problem is that the cutting teeth are conical, so that part of the material being cut can be pushed to the side during operation before it can be caught and cut by the blade. The result is poorly cut hedges, which requires additional work through laborious and time-consuming post-processing. Devices are known in which the geometry of the lower blade is designed to be drop-shaped at the end or an asymmetrical cutting mechanism is used to avoid these problems, but this entails manufacturing effort without improving the cutting properties. In addition, the manufacture of the upper blades, in particular the grinding of the cutting geometry, is technically relatively complex. Therefore, blunt cutting blades cannot be reground to a good quality without specific technical equipment. This reduces the cutting performance of the device due to the blunting of the cutting edges.

The aim of the invention is to improve the cutting results by using a cutting geometry with a higher degree of efficiency and thus to extend the service life of the knives. Another aspect is that any regrinding of the cutting edges should be eliminated.

·· »♦♦ ·

This object is achieved according to the invention in a hedge trimmer, in particular a motor-operated hedge trimmer with at least two counter-rotating blade strips, each of which has a number of spaced-apart blade blades with cutting edges delimited by cutting surfaces, in that at least some, but preferably all, of the cutting edges have a toothing. This can be provided on or at the cutting edge in some areas, but is preferably formed essentially along the entire cutting edge.

Preferably, the hedge trimmer according to the invention has a cutting angle on the cutting edge of the cutting surface, which is bevelled in a wedge shape running outwards from the surface of the blade bar, wherein the cutting angle is in the range of 30 to 50°, preferably 45°.

As a rule, the serration of the profile of the cutting edge has at least a first flank angle, wherein the flank angle is in the range of 90 to 120°.

Furthermore, the knife blades of the knife strip can be arranged in a symmetrical, asymmetrical or anti-symmetrical arrangement. The design of the cutting edges with serrations is only possible on one knife strip, in particular on the upper blade, but it is advisable for all knife strips to be serrated on their cutting edges or to be provided with corresponding serrations.

Preferably, the angle of inclination of the cutting surfaces to the perpendicular to the center of the knife strip is 22 to 26°.

A preferred embodiment of the invention is described below with reference to the drawing, which shows purely schematically

Figure 1: a top view of a hedge trimmer blade bar,

Figure 2: a detailed view of a cutting edge toothing,

Figure 3: a side view of the cutting edge serration of Figure 1.

Motor-driven hedge trimmers usually have two blade strips arranged one above the other, which have V-shaped tooth-like blades on both sides. These blade strips are driven or moved relative to each other by a motor in order to cut the material being cut, i.e. branches, hedges, etc. A distinction is usually made between asymmetrical and symmetrical arrangements of the blade strips. In the asymmetrical arrangement, one blade strip has blunt fangs on one side and cutting teeth on the other that are shorter than the fangs. The second blade strip also has the fangs on one side and the cutting teeth on the other. The two blade strips are then arranged in the hedge trimmer in such a way that the fangs on one side of one blade strip correspond with the cutting teeth on the other blade strip, i.e. work together. There are also symmetrical hedge trimmers, where one blade strip has the cutting teeth on both sides and the other blade strip has the fangs on both sides. All of these blade strips can be designed according to the invention, whereby the design according to the invention can be applied to both the fangs and the cutting teeth. It can also be applied to only some of the teeth, as will be explained below.

The blade strip 1 used in the hedge trimmer according to the invention as shown in Figure 1 has preferably V-shaped tooth-like blades 2 to the left and right of the center of the blade strip. The blades 2 are arranged equidistantly and are designed to be mirror-symmetrical on both sides and to protrude outwards, but this is only an example and not mandatory. Depending on the cutting speed and the material to be cut, a certain spacing of successive blades 2 is provided in a suitable manner. The size of the blades 2 can be determined by the outwardly protruding length of the cutting edges 3 of the blades arranged on both sides and the angle of inclination α from the perpendicular L to the center M of the blade strip, for example, but can also be varied. A cutting edge 3 could also be polygonal if necessary. In

»&psgr;

·

In the present example, the two cutting surfaces 4 arranged around the perpendicular L to the center line M of the knife strip 1 are symmetrical. It goes without saying that in addition to the trapezoidal profile of the knife blades 2 sketched here as an example, other profile shapes are also possible, for example with radii, sinusoidal shapes, but also other wave shapes. This also applies to the profile of the cutting edges. The cutting surface 4 of a knife blade 2 has a bevel that runs diagonally from the surface of the knife strip towards the underside of the knife strip 1 and encloses the angle β there (see schematically in Figure 3). A toothing 6 is embossed on this cutting surface 4, which runs diagonally to the underside of the knife strip 1, and is shown enlarged in Figure 2. This can be done by rolling or grinding, if necessary also by a milling process or cutting and embossing process, whereby tooth-like grooves are introduced, which form this toothing on the cutting edges.

According to Figure 2, which shows a single cutting tooth or knife blade 2, this is a type of helical gearing. For the top side of the knife strip 1, a first flank angle 9 is defined between two flanks 7, 8, which can deviate from a second flank angle 10 defined for the bottom side of the knife strip 1.

Figure 3 shows a side view of the knife strip 1 in the direction of the cutting tooth 2, whereby it was assumed, for example, that the thickness of the knife strip 1, i.e. the cutting surface running over the cutting surfaces 4 of the cutting tooth 2, is kept constant. It is understood, however, that the thickness of the knife strip 1 can also vary over the cutting surface 4 or can be beveled on one side, two sides or in a wave shape towards the outside. The cutting edge 3 can also be designed accordingly. Since the cutting edges 3 of the knife strip 1 have now been changed in such a way that the cutting edge 3 is no longer ground smooth as a single knife blade, the basic shape of the cutting edge 3 is now formed in a number of pointed teeth 7, 8, which form the toothing 6. The inclination β of the cutting surface 4 according to the invention advantageously results in a wedge effect, which is very favorable for the cutting effect. Due to the inventive design of the cutting surface as a profiled toothing 7, 8 with V-shaped teeth that taper to a point at the top, the surface gain increases the actually available cutting surface 4 with the same external dimensions, for example to

Double the cutting teeth 2, which also maximizes the cutting performance. In the embodiment shown, the toothing is provided from the tip essentially over the entire cutting edge, although a partial formation of the toothing, for example in the area of the tip or in the middle edge area, is also suitable.

Depending on the material to be cut, in particular the type of wood, but also the application, for example whether thinner or thicker branches are to be cut, the toothing 6 can be adjusted accordingly. This is done in particular by varying the number of sharp teeth 7, 8 for each cutting edge. The thinner the material to be cut, the more suitable a knife with a finer toothing is, in which more grooves are incorporated per cutting edge or cutting surface and thus more teeth 7, 8 are formed. For this reason, the knife strips are manufactured in practice with different coarse or fine toothing structures, which remains reserved for the respective application.

During cutting, the tips 11 of the teeth 2, i.e. the tips of the cutting edges jagged by the toothing, first penetrate into the material to be cut, which has the advantage that the material to be cut is no longer pushed away due to the number of tooth tips 11. The cut then takes place over the tooth flanks 7, 8 of the individual teeth 2. The cutting geometry thus interrupted according to the invention and the sharp edges of the toothing 7, 8 increase the efficiency of the penetration and cutting and correspond to a constantly new tearing and cutting when separating the material to be cut.

Surprisingly, it was discovered that the service life of the knife is also improved by the inventive toothing of the cutting edge 3. This means that the inevitable blunting, as is the case with ground cutting edges, can no longer occur with the geometry according to the invention. Even if the material from which the knife strip is made according to known methods is reduced in size due to material removal and wear, the sharpness of the cutting edges is guaranteed to remain constant. In particular, the toothing according to the invention remains intact even when it is worn, so that the knife thus resharpens itself, so to speak. This increases

The service life and also the utility value of a hedge trimmer itself are considerably increased by the inventive toothing of the cutting surfaces.

Claims (8)

1. Hedge trimmer, in particular motor-operated hedge trimmer, with a cutting blade and a catch blade, which can be driven in opposite directions to each other and are each provided with a number of knife blades ( 2 ), characterized in that at least some of the cutting edges ( 4 ) of the knife blades ( 2 ) of the cutting blade have a toothing ( 6 ). 2. Hedge trimmer according to claim 1, characterized in that the cutting edge ( 4 ) of the cutting surface ( 5 ) has a cutting angle (β) which is bevelled in a wedge shape running outwards from the surface of the blade bar, wherein the cutting angle is in particular in the range of 30-50°, preferably 45°. 3. Hedge trimmer according to claim 1 or 2, characterized in that the serration of the profile of the cutting edge ( 4 ) has at least one flank angle (χ) which is in the range of 90-140°, in particular 90-120°. 4. Hedge trimmer according to one of claims 1 to 3, characterized in that opposing cutting teeth ( 2 ) of the blade bar ( 1 ) pointing outwards from the center are designed in a symmetrical, asymmetrical or anti-symmetrical arrangement. 5. Hedge trimmer according to claim 4, characterized in that the angle of inclination (α) of the cutting surfaces ( 4 ) to the perpendicular (L) to the center ( 11 ) of the blade bar ( 1 ) is 20-30°, preferably 22-26°. 6. Hedge trimmer according to one of the preceding claims, characterized in that the knife blades protrude laterally outwards and have two cutting edges running at an angle to one another, on or at which the toothing is provided. 7. Hedge trimmer according to one of the preceding claims, characterized in that the toothing ( 6 ) is provided in regions or over the entire length of the cutting edge ( 4 ). 8. Hedge trimmer according to one of the preceding claims, characterized in that the number of teeth of the toothing ( 6 ) on a cutting edge is selected depending on the material to be cut, wherein cutting edges with a larger number of teeth ( 7 , 8 ) of the toothing ( 6 ) are preferably used for thinner material to be cut.