Patent Application
20180142432
Embodiments herein relate to a cutting tool.
When a surface layer of a paved area is exposed to different temperatures, ageing and vehicles driving over the surface, it may become worn and uneven. For example, heavy vehicles which starts and stops in front of a traffic light, causes the surface layer to shear relatively lower layers. The surface layer can be milled off, and a material of the surface layer may in some cases be recycled and used as aggregate when a new surface layer is paved to replace the old one.
The process of removing the surface layer can be referred to as asphalt milling, profiling, cold planning or pavement milling. During such a process a milling machine or cold planner provided with a large rotating drum equipped with cutting tools can be used. The drum, when rotating, grinds and removes the surface layer of e.g. a road or a parking lot. The cutting/milling is also commonly performed on various kinds of concrete surfaces, such as at bus stops, bridges and runways.
Such a drum can comprise a plurality of tool holders or attachment portions for cutting tools. An example of such a cutting tool is disclosed in US20140232172A1. In US20140232172A1, the cutting tool comprises a body, a shank which can be attached to a drum, and a cutting element.
Cutting tools are also used in several other applications, such as during coal mining or mechanical processing of rocks etc. Cutting tools may also be used during rotary drilling, such as described in WO2010099512A1. Cutting tools may also be referred to as milling tools or milling bits.
A body of the type disclosed in US20140232172A1 can be made of metal and the cutting element can be made of a hard material. When a drum with a number of cutting tools attached to a periphery of the drum is rotated on a paved surface each cutting element on each cutting tool shears away material and hereby the surface layer of the paved surface is removed.
The cutting tool disclosed in US20140232172A1 may be suitable in some applications but there remains a need for a cutting tool which can be used for a longer amount of time before it is worn out. There also remains a need for a cutting tool which decreases forces between a surface to be milled and a tool holder and also distributes the forces between the surface to be milled and the tool holder in an advantageous manner. Thus, a problem in this regard is that wear properties and required cutting forces of prior art cutting tools are not sufficiently good.
Embodiments herein aim to provide a cutting tool with better wear properties and lower required cutting forces than prior art cutting tools.
According to an embodiment, this is provided by a cutting tool comprising a tip, a body and a shank for attaching the cutting tool to a tool holder,
Since the body radius at half the depth of the recess is less than two times the tip radius the wall which forms the recess will be relatively thin or slender in comparison with the radius of the tip. This shape combined with a tip hardness of at least 1300 HV50 and a body hardness of at least 450 HV30 has surprisingly proven to work exceptionally well during milling operations. The tip hardness refers to the hardness of the hard metal alloy which forms the tip and the body hardness refers to the hardness of the steel alloy which forms the body. Test results are provided in the detailed description of this application. The combination of the above shape, tip hardness and the body hardness provides for an even wear on the body and the tip during milling. Due to the slender shape, the tip is subjected to relatively small bending forces relatively recess walls of the body during milling. Hereby it is possible to use a relatively hard and brittle material for the tip. This increases time of use before the cutting tool is considered to be worn out. Due to the slender shape also the total forces on the bit body are decreased. Hereby it is also possible to use a relatively hard, stiff and brittle steel material for the body. This also increases time of use before the cutting tool is considered to be worn out. The relatively stiff steel body improves the distribution of bending forces acting on the tip which decreases the risk for brittle failure of the tip.
The slender shape of the tip and the body will result in decreased cutting forces and thereby less vibration transferred to the tool holder to which the cutting tool is attached and accordingly also to a milling machine which comprises the tool holder and the cutting tool. As mentioned above, the tool holder may be arranged e.g. on/at a rotatable drum. Forces between the surface to be milled and the tool holder are hereby decreased. Hereby less power and energy are required from the milling machine and fuel consumption is decreased.
With the above design, tip hardness and body hardness, the resulting wear of the steel body is approximately the same as for the hard metal tip during milling. When the relatively thin and slender steel body is continuously worn during a milling operation the tip is continuously exposed. The cutting tool will therefore stay relatively sharp, i.e. it gets less blunt during cutting as compared to prior art tips. Forces will therefore be kept relatively low and constant. The steel wall of the body protects the tip for a relatively long time during milling. Hereby a relatively large portion, such as 50-90%, of a tip length can be worn down before the cutting tool has to be replaced. The tip length can hereby be optimized such that the tip extends into the body to a depth corresponding to a depth just before the wear reaches the tool holder or the drum during cutting/milling, This is advantageous since it is difficult and costly to replace the tool holder.
An operator of the cutting/milling machine will thus have a constant performance just until it is time to replace the cutting tools. He/she is made aware of the necessity of replacing the cutting tools as a forward movement of the cutting/milling machine will almost come to a stop before the wear reaches the tool holder or the drum. The appropriate time to exchange the cutting tools is thus easily recognized by the operator.
A cutting tool with the combination of the above-mentioned shape, tip hardness and body hardness has proven to have excellent wear properties both during milling of asphalt surfaces, concrete surfaces and other types of surfaces.
According to some embodiments the body radius along the depth of the recess is less than two times the tip radius. According to some embodiments the body radius along the depth of the recess is less than 1.5 times the tip radius. According to some embodiments the body radius at half the depth of the recess is less than 1.7 times the tip radius. The relatively thin, hard and stiff recess wall thus retains the tip safely and the contact surface between the tip and the body is relatively large. The relatively large contact surface also improves heat transfer from the tip to the body. The tip and the wall are evenly worn when the cutting tool is used and hereby even wear and low and even bending forces on the tip are achieved during the entire time of use before the cutting tool is considered to be worn out.
According to some embodiments, the tip is made of a hard metal alloy with a hardness of at least 1350 HV50 and the body is made of a steel alloy with a hardness of at least 465 HV30. Hereby a long time of use before the cutting tool is considered to be worn out is achieved.
According to some embodiments, the tip is made of a hard metal alloy with a hardness of at least 1400 HV50 and the body is made of a steel alloy with a hardness of at least 480 HV30. This provides for excellent wear properties and a long time of use before the cutting tool is considered worn out. According to some embodiments the tip is made of diamond composite with a hardness of at least 1400 HV30.
According to some embodiments the tip is made of a hard metal alloy with a hardness between 1400-1500 HV50 and the body is made of a steel alloy with a hardness between 480-550 HV30. This combination of the tip hardness and the body hardness has proven to work well in many applications such as e.g. during milling of asphalt and concrete.
According to some embodiments the body radius increases continuously from the recess portion to the shank. With a continuous increase of the body radius from a smaller radius at the recess portion towards a larger radius at the body portion facing the shank a initially small increase of forces between the cutting tool and the ground is achieved. An operator of the cutting/milling machine will thus have a constant performance. In some embodiments the shape of the body is concave along at least a part of its length. The increase of the body radius may be smaller near the recess portion and larger near the shank.
According to some embodiments the body radius increases continuously from the recess portion to the shank along a smooth curve. The smooth curve allows forces to increase in a foreseeable manner as the cutting tool becomes worn. It further increases the heat transfer from the tip. This will decrease the temperature of the tip and hereby thermal degradation is avoided or at least mitigated.
According to some embodiments a periphery of the body comprises longitudinal grooves. The longitudinal grooves increase the wear of steel alloy body in the longitudinal direction when the cutting tool is used, in particular near the shank. This may partially compensate a decreased wear due to the slightly increased body radius and hereby the wear over the body length will be more even. The longitudinal grooves also help the cutting tool to rotate when it hits the ground during a milling operation. Hereby the cutting tool will be evenly worn along the tip and its periphery. The grooves may also function as “chipbreakers”, i.e. they will improve breaking and removal of surface layer material.
According to some embodiments the recess comprises a wall portion and a bottom portion with a bottom-radius between the wall portion and the bottom portion. The bottom-radius between the wall portion and the bottom portion reduces the risk for cracks in the body near the bottom of the recess. According to some embodiments the bottom radius is at least 1 mm, preferably at least 1.5 mm. A bottom radius of at least 1 mm, preferably at least 1.5 mm may facilitate a corresponding large radius in the bottom of the tip which hereby also reduces the risk for cracks in the tip. It has been proved that these radii may be advantageous in applications where a wall thickness near the bottom of the recess is relatively small, as described in embodiments herein.
According to some embodiments the body comprises a ductile plate arranged in a bottom portion of the recess. A ductile plate arranged in a bottom portion of the recess transfer blows and forces between the tip and the body during milling operations. Hereby cracking of the tip is avoided. In addition, a ductile plate, made of e.g. cupper, improves thermal conduction from the tip to the body. Such a ductile plate can have a thickness of e.g. 0.5-1 mm.
According to some embodiments the tip is retained within the recess by shrink-fitting. According to some other embodiments the tip is retained within the recess by press-fitting. According to yet some other embodiments the tip is retained within the recess by a combination of shrink-fitting and press fitting. Shrink fitting and/or press fitting provides for a secure and cost efficient retaining of the tip within the recess, in particular when the wall which forms the recess is relatively thin.
According to some embodiments the first tip end is tapered with a first angle relatively the longitudinal axis of the tip, the second tip end is tapered with a second angle relatively the longitudinal axis of the tip and a cylindrical tip body extends between the first tip end and the second tip end. The tapered first and second tip ends facilitates fitting, production of the tip and prevents chipping of the tip. The first angle can be e.g. between 20 and 60 degrees. The second angle can be e.g. between 5 and 45 degrees.
The various aspects of embodiments herein, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:
a,
6
b and 6c illustrate cross sectional views of the cutting tool according to some embodiments.
Embodiments herein will now be described more fully with reference to the accompanying drawings. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.
The shank 50 can be attached e.g. to a complementary shaped attachment portion of a tool holder of a rotatable drum or the like. The shank 50 can comprise one or more notches, flanges 51, protrusions or similar which may be used for securely attaching the shank 50 to a tool holder of any kind, such as the aforementioned rotatable drum. In some embodiments the shank 50 is arranged to be attached to a sleeve or collar which in turn is attached to the tool holder. The shank 50 can be attached to the tool holder in a fixed or rotatable manner. The body 30 and the shank 50 can be integrally formed or may in some embodiments be separately formed and then attached to each other.
In the embodiment of
In
The tip 20 is made of a hard metal, such as a carbide alloy. For example, the tip 20 is made of cemented carbide, tungsten cemented carbide, silicone carbide, cubic carbide, cermet, polycrystalline cubic boron nitride, silicone cemented diamond, diamond composite or any other material with a hardness of at least 1300 HV50. HV50 is hardness measured by Vickers hardness test and is commonly used for hard material-testing. Since hardness of a material can be measured by different kind of tests, it is understood that the tip 20 is made of a material with a hardness of at least 1300 HV50 or a corresponding hardness measured by other tests. The tip 20 can have a toughness of at least 11 K1c. The toughness, also referred to as fracture toughness, can e.g. be measured by the Palmqvist method as described in US20110000717A1.
Preferable, the ISO standards ISO 3878:1983 (Vickers hardness test for Hard Metals) and ISO 6507:2005 (Vickers hardness test Metallic Materials) are be used for hardness measurements. If measurements have been done according to another established method conversion tables according to ISO 18265:2013 (Hardness conversion Metallic Materials) for metallic materials may be used. For toughness measurements the ISO standard ISO 28079:2009 (Palmqvist test for Hard Metals) is preferably used.
The body 30 is made of a steel alloy with a hardness of at least 450 HV30 or a corresponding hardness measured by other tests. HV30 is hardness measured by Vickers hardness test and is commonly used for testing hardness of steel alloys etc. The body 30 can for example be made of steel, such as of steel comprising about, in weight-percent: 1% Cr, 0.2% Mo, 0.8% Mn, 0.4% C, 0.3% Si, 0.025% P and 0.035% S. The tip 20 can for example comprise 5-7% Co and 93-95 WC, such as about 6% Co and 94% WC. The hardness depends e.g. on the Cobalt content and the particle size of the material.
The below charts illustrate test result from tests where different cutting tools with different tip hardness and body hardness have been tested. The hardness of the tip is measured with HV50 and the hardness for the steel body is measured with HV30. With reference to chart 1 below, cutting tool “G” is an example of a cutting tool 10 according to claimed embodiments herein. Cutting tools A, B, C, D, E and F are other tested cutting tools according to the state of the art. Cutting tools E and F are variants of the cutting tool G with corresponding geometrical shapes but different combinations of hardness. As illustrated below relative service life for cutting tool G is much larger than for cutting tools E and F.
Chart 2 below illustrates test results for the cutting tools A-G after the cutting tools have been tested. During this test the cutting tools were attached to a rotary drum and used for milling a distance of 2000 meters. During approximately 1000 m of the distance, the cutting tools were milling asphalt. Moreover, during approximately 1000 m of the distance, i.e. the remaining portion of the distance, the cutting tools were milling concrete. The milling depth was 3-5 cm and the ambient temperature was about 5° Celsius.
Relative service life is defined as inverted wear compared with the best prior-art-cutting tool, i.e. in this test cutting tool “B”. As an example, relative service life for cutting tool A in Chart 2 is thus 4.5 mm/7.5 mm=0.6. Relative service life for cutting tool G in Chart 2 is thus 4.5 mm/3.5 mm=1.29.
A second test with deeper depth of cut was also performed. Chart 3 below illustrates test results for the cutting tools A and G after the cutting tools have been tested. During the second test the cutting tools were attached to a rotary drum and used for milling a distance of 1300 meters. The cutting tools were milling asphalt. The milling depth was 5-10 cm and the ambient temperature about 8° Celsius. As above, relative service life is defined as inverted wear compared to best prior art cutting tool, in this case bit A.
Several tests were performed. The above charts illustrate some examples of results achieved during the tests. The entire hardness ranges of the claimed embodiments performed very well and had longer relative service life, i.e. a longer amount of time before it was worn out, than cutting tools according to the state of the art. As indicated from the tests, cutting tools according to embodiments herein proved to be very durable and efficient throughout the tests as compared to cutting tools according to the state of the art.
A major part of the cutting tool 10 can have a shape that is substantially rotational symmetric with reference to the longitudinal axis A of the cutting tool 10. Thus, when the tip 20 is retained within the recess 33 a longitudinal axis of the tip 20 substantially coincides with the longitudinal axis of the body 30. The longitudinal axis A is then a longitudinal centre-axis for the entire cutting tool 10, i.e. for the tip 20, for the body 30 and for the shank 50.
In some embodiments, the first tip end 21 comprises a chamfered or tapered portion 22. The shape of the first tip end 21 can then be seen as substantially frustoconical. A surface of such tapered portion can extend e.g. with an angle 20-60 degrees relatively the longitudinal axis A.
As illustrated in
In
In some embodiments, a first body radius 41, which is a radius of the body 30 adjacent to the first periphery radius 38, is between 1.1 and 1.8 times the recess radius 40, preferably about 1.3-1.6 times the recess radius 40. According to a first example, the recess radius 40 may be about 5.5 mm and the first body radius 41 may be about 8.5 mm. The first body radius 41 is then about 1.55 times the recess radius. According to a second example, the recess radius 40 may be about 5.5 mm and the first body radius 41 may be about 7.25 mm. The first body radius 41 is then about 1.32 times the recess radius.
In some embodiments, a second body radius 42, which is a radius of the body 30 at approximately half the depth of the recess 33, is between 1.5 and 2 times the recess radius 40. According to some embodiments the second body radius 42 is 1.2-1.7 times the recess radius 40. The recess radius 40 is, when a tip is tightly mounted in the recess, also referred to as a tip radius. The tip radius is illustrated in
According to some embodiments the third body radius 43, which is a radius of the body 30 at a bottom of a cylindrical portion of the recess 33, is 1.6-2.2 times the recess radius 40. In some embodiments a third body radius 43, is between 1.2 and 1.6 times the recess radius 40. According to an example embodiment the recess radius 40 can be about 5.5 mm and the third body radius 43 can be about 10 mm. The third body radius 43 is then about 1.82 times the recess radius.
In some embodiments the bottom portion of the recess 33 is substantially flat. In the embodiment illustrated in
In some embodiments a ductile plate (not shown) is arranged between a mounted tip and the bottom of the recess 33. Such a ductile plate may be made of cupper or other ductile material.
In
As mentioned above, the tip 20 is tightly fitted into the recess e.g. by shrink-fitting. A tip radius 23 is therefore substantially equal to the radius of the recess into which the tip 20 is fitted, i.e. the recess radius 40 discussed in conjunction with
As illustrated in
As used herein, the term “comprising” or “comprises” is open-ended, and includes one or more stated features, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions or groups thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1550578-7 | May 2015 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2016/050404 | 5/3/2016 | WO | 00 |
