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Title:
MILLING DEVICE FOR EXCAVATING MINING MATERIALS
Document Type and Number:
WIPO Patent Application WO/2017/102070
Kind Code:
A1
Abstract:
A milling device (14) for excavating mining materials (260) is disclosed. The milling device (14) comprises a milling drum (15) rotatable about a drum axis (200); a first group of excavating heads (18, 18', 18") arranged around a periphery of the milling drum (15) and driven to rotate about a first rotational axis (210) extending substantially radially to the drum axis (200); and a second group of excavating heads (20, 20', 20", 20"') arranged around the periphery of the milling drum (15) and rotatable about a second rotational axis (212) extending substantially radially to the drum axis (200). The first group of excavating heads (18, 18', 18") includes a plurality of first excavating tools (60, 60') configured to perform a first, cutting operation, and the second group of excavating heads (20, 20', 20", 20'") includes a plurality of second excavating tools (267) configured to perform a second excavating operation different from the first, cutting operation.

Inventors:
RASCHKA, Joachim (Zur Waldschmiede 23, Bochum, 44805, DE)
BECHEM, Ulrich (Tiefendorfer Straße 87, Hagen, 58093, DE)
Application Number:
EP2016/002063
Publication Date:
June 22, 2017
Filing Date:
December 07, 2016
Export Citation:
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Assignee:
CATERPILLAR GLOBAL MINING EUROPE GMBH (Industriestraße 1, Lünen, 44534, DE)
International Classes:
E21C27/22; E21C27/24; E21D9/10
Domestic Patent References:
2012-11-22
2014-02-20
Foreign References:
US20140084667A12014-03-27
US20100001574A12010-01-07
US5234257A1993-08-10
US20150322644A12015-11-12
US2689117A1954-09-14
US5035071A1991-07-30
Attorney, Agent or Firm:
KRAMER BARSKE SCHMIDTCHEN PATENTANWÄLTE PARTG MBB (Landsberger Str. 300, Munich, 80687, DE)
Download PDF:
Claims:
Claims

1. A milling device (14) for excavating mining materials (260), the milling device (14) comprising:

a milling drum (15) rotatable about a drum axis (200);

a first group of excavating heads (18, 18', 18") arranged around a periphery of the milling drum (15) and driven to rotate about a first rotational axis (210) extending substantially radially to the drum axis (200);

a second group of excavating heads (20, 20', 20", 20"') arranged around the periphery of the milling drum (15) and rotatable about a second rotational axis (212) extending substantially radially to the drum axis (200); wherein

the first group of excavating heads (18, 18', 18") includes a plurality of first excavating tools (60, 60') configured to perform a first, cutting operation, and

the second group of excavating heads (20, 20', 20", 20"') includes a plurality of second excavating tools (267) configured to perform a second excavating operation different from the first, cutting operation.

2. The milling device (14) of claim 1, wherein the second excavating operation is a blunt compression operation acting against a tensile strength of the mining material (260).

3. The milling device (14) of claims 1 or 2, wherein the second excavating tools (267) include a disc-like shape with a blunt contact region (268) configured to perform the second excavating operation.

4. The milling device (14) of claim 3, wherein the blunt contact region (268) includes a conical cross-sectional shape in a plane including the second rotational axis (212), the conical cross-sectional shape further including

a radially outer face (270) with respect to the drum axis (200), a lateral face (272) having a diameter increasing in a radial outward direction with respect to the drum axis (200), and

a blunt edge (274) connecting the lateral face (272) and the radially outer face (270).

5. The milling device (14) of claim 4, wherein the radially outer face (270) includes a planar portion (276) at a radially inner side with respect to the second rotational axis (212), and a bevel portion (278) at a radially outer side with respect to the second rotational axis (212).

6. The milling device (14) of claim 5, wherein the second rotational axis (212) and a radial direction (220) of the drum axis (200) confine a first angle (a),

the bevel portion (278) and the planar portion (276) confine a second angle (β), and

the second angle (β) is substantially equal to the first angle (a).

7. The milling device (14) of any one of the preceding claims, wherein the first group of excavating heads (18, 18', 18") and the second group of excavating heads (20, 20', 20"') are alternately arranged on the periphery of the milling drum (15).

8. The milling device (14) of any one of the preceding claims, wherein, the first excavating tools (60, 60') include a first maximal radial distance (286) from the first rotational axis (210),

the second excavating tools (267) include a second maximal radial distance (284) from the second rotational axis (212), and

the second maximal radial distance (284) is substantially equal to the first maximal radial distance (286).

9. The milling device (14) of any one of the preceding claims, wherein,

the first excavating tools (60, 60') include a first maximal radial distance (282) from the drum axis (200),

the second excavating tools (267) include a second maximal radial distance (280) from the drum axis (200), and

the second maximal radial distance (280) is substantially equal to the first maximal radial distance (282).

10. The milling device (14) according to any one of the preceding claims, wherein the second group of excavating heads (20') includes a shaft carrier portion (265) disposed on a radially inner side with respect to the drum axis (200), and a tool carrier portion (266) disposed on a radially outer side with respect to the drum axis (200), the shaft carrier portion (265) being driven to rotate about the second rotational axis (212), the tool carrier portion (266) being configured to accommodate the second excavating tools (267), the tool carrier portion (266) further being rotatably mounted on the shaft carrier portion (265) and being rotatable about a third rotational axis (404), wherein the third rotational axis (404) is offset from the second rotational axis (212) by a predetermined value (406).

11. The milling device (14) of any one of claims 1 to 9, wherein

the first group of excavating heads (18") includes a plurality of slot cutting rings (600, 602, 604) arranged in an axial of the first rotational axis (210), each slot cutting ring (600, 602, 604) accommodating the plurality of first excavating tools (60, 60'), and

the second group of excavating heads (20'") includes a plurality of disc-shaped rings (606, 608, 6 0) arranged in an axial direction of the second rotational axis (212), each disc-shaped ring (606, 608, 610) accommodating the plurality of second excavating tools (267) and being configured to engage with slots (612, 614, 616) produced by the respective slot cutting ring (600, 602, 604).

12. The milling device (14) of any one of claims 1 to 6, wherein the first rotational axis (210) is identical with the second rotational axis (212), and the first excavating tools (60, 60') are arranged on a radially outer side with respect to the drum axis (200) and the second excavating tools (267) are arranged on a radially inner side with respect to the drum axis (200).

13. A method for excavating mining materials (260) with a milling device (14), the milling device (14) including a milling drum (15) rotatable about a drum axis (200), a first group of excavating heads (18, 18', 18") driven to rotate about a first rotational axis (210) and accommodating a plurality of first excavating tools (60, 60'), a second group of excavating heads (20, 20', 20", 20"') rotatable about a second rotational axis (212) and accommodating a plurality of second excavating tools (267) different from the first excavating tools (60, 60'), the first group of excavating heads (18, 18', 18") and the second group of excavating heads (20, 20', 20", 20"') being alternately arranged around a periphery of the milling drum (15), the method comprising: rotating the milling drum (15) about the drum axis (200) in a direction towards the mining material (260) thereby engaging the first excavating tools (60, 60') with the mining material (260);

concomitantly rotating the first group of excavating heads (18, 18', 18") about the first rotational axis (210) thereby performing a first, cutting operation with the first excavating tools (60, 60');

rotating the milling drum (15) further in the direction towards the mining material (260) thereby engaging the second excavating tools (267) with the mining material (260); and

performing a second excavating operation different from the first, cutting operation using the second excavating tools (267).

14. The method of claim 13 , wherein the first, cutting operation and the second excavating operation are perfonned in the same area of the mining material (260).

15. The method of claims 13 or 14, wherein the second excavating operation further includes

performing a blunt compression operation on the mining material (260), the blunt compression operation acting against a tensile strength of the mining material (260);

engaging the second excavating tools (267) with slots (302) generated in the mining material (260) during the first, cutting operation, and breaking out remaining mining material (310) by rotating the milling drum (15) further in the direction towards the mining material (260).

Description:
6 002063

Description

MILLING DEVICE FOR EXCAVATING MINING MATERIALS

Technical Field

[01 ] The present application relates to a milling device for mining

applications and, in particular, to a milling device for hard rock mining

applications.

Background

[02] Excavation of mining materials, in particular hard rock mining

materials, requires milling devices that are capable of performing sufficient impact on the mining material such that the mining material breaks and can be excavated. Milling devices, therefore, comprise a plurality of excavating heads usually arranged on a periphery of a milling drum. The plurality of excavating heads are equipped with a plurality of excavating tools that perform an

excavating operation on the mining material.

[03] The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior milling devices.

Summary of the Disclosure

[04] According to a first aspect, a milling device for excavating

mining materials is disclosed. The milling device comprising a milling drum rotatable about a drum axis; a first group of excavating heads arranged around a periphery of the milling drum and driven to rotate about a first rotational axis extending substantially radially to the drum axis; a second group of excavating heads arranged around the periphery of the milling drum and rotatable about a second rotational axis extending substantially radially to the drum axis. The first group of excavating heads includes a plurality of first excavating tools configured to perform a first, cutting operation, and the second group of excavating heads includes a plurality of second excavating tools configured to perform a second excavating operation different from the first, cutting operation.

[05] According to a second aspect of the present disclosure, method for excavating mining materials with a milling device is disclosed. The milling device includes a milling drum rotatable about a drum axis, a first group of excavating heads driven to rotate about a first rotational axis and accommodating a plurality of first excavating tools, a second group of excavating heads rotatable about a second rotational axis and accommodating a plurality of second excavating tools different from the first excavating tools. The first group of excavating heads and the second group of excavating heads are alternately arranged around a periphery of the milling drum. The method comprises rotating the milling drum about the drum axis in a direction towards the mining material thereby engaging the first excavating tools with the mining material;

concomitantly rotating the first group of excavating heads about the first rotational axis thereby performing a first, cutting operation with the first excavating tools; rotating the milling drum further in the direction towards the mining material thereby engaging the second excavating tools with the mining material; and performing a second excavating operation different from the first, cutting operation using the second excavating tools.

[06] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawings

[07] Fig. 1 shows an exemplary mining machine with a milling device;

Fig. 2 shows a cross-sectional part view through an exemplary milling device with an exemplary first group of excavating heads and an exemplary second group of excavating heads; Fig. 3 shows a cross-sectional part view through an exemplary milling device with another exemplary first group of excavating heads and the same exemplary second group of excavating heads as shown in Fig. 2;

Fig. 4 shows a cross-sectional part view through an exemplary milling device with the same exemplary first group of excavating heads as shown in Fig. 3 and another exemplary second group of excavating heads;

Fig. 5 shows a cross-sectional part view through an exemplary milling device where the first group of excavating heads and the second group of excavating heads are arranged on a same axis; and

Fig. 6 shows a cross-sectional part view through an exemplary milling device with yet another exemplary first group of excavating heads and a yet another exemplary second group of excavating heads.

Detailed Description

[08] The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as a limiting description of the scope of protection. Rather, the scope of protection shall be defined by the appended claims.

[09] The present disclosure is based in part on the realization that an excavation process with a plurality of excavating heads can cause vibrations on the mining machine and therefore adversely affect the performance of the mining machine.

[10] The present disclosure is based in part on the realization that the vibrations may arise when the excavating heads perform a plurality of excavating operations simultaneously. Because in this case, the disturbances arising from a -4- first excavating operation add to the disturbances arising from a second excavating operation, and so on and so forth. As a consequence, the disturbances from the various excavating operations superimpose each other and, as a result, may cause, for example, vibrations of the mining machine.

[11] According to the present disclosure, this superposition of

disturbances on the mining machine is prevented by providing a first group of excavating heads (first excavating heads) that include first excavating tools for performing only a first excavating operation, and a second group of excavating heads (second excavating heads) that include second excavating tools for performing only a second excavating operation different from the first excavating operation.

[12] Within the meaning of this disclosure, the first excavating

operation is a cutting operation. A cutting operation requires excavating tools with sharp edges such as a pin tip or the like. As the first, cutting operation is performed only by first excavating tools, first excavating tools include a shape with sharp edges or a sharp tip for performing the first, cutting operation. The first excavating tools are mounted on the first excavating heads which rotate about a first rotational axis. Upon rotation of the first excavating heads, the sharp edges of the first excavating tools pierce into the mining material, thereby generating micro-cracks and eventually slots, undercuts or the like in the mining material.

[13] Within the meaning of this disclosure, the second excavating

operation is a blunt compression operation. In contrast to the first, cutting operation, the blunt compression operation is not a piercing operation but an operation that applies an areal compressive strain on the mining material acting against a tensile strength of the mining material. As for mining materials, the resistance to compressive strain is only a fraction (between 5% to 20%) of the resistance to tensile strain, upon performing the blunt compression operation, the already cracked (pierced, half- fractured) mining material is subjected to an areal T/EP2016/002063

-5- compressive impact. This compressive impact works against the tensile strength of the mining material and weakens the mining material, thereby fracturing the mining material and, hence, improving the excavating performance of the mining machine.

Moreover, according to the present disclosure, the second group of excavating heads are freely rotatable about a second rotational axis. Hence, when the second excavating tools contact the mining material to perform the blunt compression operation, the second excavating tools roll over the mining material and thereby support a rotation of the milling drum. As a result, the second excavating tools can also stabilize the mining machine and thus can help to reduce vibrations of the mining machine.

The present disclosure is further based in part on the realization that, in some embodiments, the performance of the excavating process can be improved further, if the second excavating tools not only apply a compressive strain on the mining material, but transform this compressive strain into a tensile strain that additionally acts on the mining material. In some embodiments, the mining machine, therefore, includes second excavating tools which have a disclike shape with a blunt contact region. The blunt contact region creates an areal contact with the mining material during the second excavating operation and applies the compressive strain. To transform the compressive strain into a tensile strain, the blunt contact region includes a conical cross-sectional shape. The conical cross-sectional shape includes a radially outer face that is arranged radially outward with respect to a drum axis of the milling drum, and a lateral face. The lateral face has a diameter increasing in a radial direction outward with the respect to the drum axis and connects to the radially outer face via a blunt edge. By providing the described conical cross-sectional shape on the second excavating tools, the blunt edge can enter into slots generated during the first, cutting operation, engage with the slots and break out (lever out) remaining mining material. This "breaking or levering" of remaining mining material from the inside of the slot corresponds to a tensile strain acting upon the mining material. Accordingly, when the second excavating tools engage with slots, the second excavating tools transform compressive strain into tensile strain. As a result, the mining material is weakened further by the "levering effect" and the excavating performance of the mining machine can be increased.

The present disclosure is further based in part on the realization that, in some embodiments, the excavating process can be improved further when the second excavating tools apply a further impact on the mining materials additionally to the already explained compressive and/or tensile strain. In some embodiments, the second excavating heads, therefore, include a shaft carrier portion that is disposed on a radially inner side with respect to the drum axis and a tool carrier portion that is disposed on a radially outer side with respect to the drum portion. The shaft carrier portion is rotatably driven to rotate about the second rotational axis. The tool carrier portion accommodates the second excavating tools and is rotatably mounted on the shaft carrier portion. The tool carrier portion is further rotatable about a third rotational axis that is offset to the second rotational axis by a predetermined value. Hence, the tool carrier portion is freely rotatable about the third rotational axis but rotates about the second rotational axis offset from the third rotational axis. As a result, when the shaft carrier portion rotates about the second rotational axis, the tool carrier portion and therewith the second excavating tools hammer into the mining material. This "hammering" into the mining material adds to the already explained compressive and/or tensile strain applied to the mining material. Hence, the mining material is weakened further and the excavating process can be improved further.

Referring now to the drawings, Fig. 1 shows an exemplary mining machine 10. Mining machine 10 may be any type of mining machine used to excavate mining materials, such as a part- face heading machine or a mobile mining machine. Mining machine 10 includes an arm 12 connected to a chassis of mining machine 10. Arm 12 is pivotable and movable in vertical and 3

-7- horizontal direction, as indicated by arrows 38. Arm 12 is attached to a drum holder 13. Drum holder 13 serves to receive a milling device 14 and is pivotable, as indicated by arrow 39. Milling device 14 includes a milling drum 15, a first group of excavating heads (first excavating heads) 18 and a second group of excavating heads (second excavating heads) 20. First and second excavating heads 18, 20 are arranged on a periphery of milling drum 15. First excavating heads 18 and second excavating heads 20 are alternately arranged on the periphery of milling drum 15. Milling drum 15 may, for example, include between one and ten of first excavating heads 18 and, for example, between one and ten of second excavating heads 20. Mining machine 10 further includes track gears 11. Track gears 11 are configured to maneuver mining machine 10 and to advance milling device 14 into the mining material.

In some embodiments, mining machine 10 may include more than one milling drum 15 arranged in parallel to each other.

As shown in more detail in Fig. 1 , each first excavating head 18 includes a first rotational axis 210, a base member 24, a plurality of excavating tool support rings 40, a plurality of excavating tool carriers 50 attached to the plurality of excavating tool support rings 40, and a plurality of first excavating tools 60. Each first excavating tool 60 is rotatably supported by one of the plurality of excavating tool carriers 50. Excavating tool carriers 50 may be a splittable to allow for easy access to the first excavating tools 60.

As shown in Fig. 1 , first excavating head 18 exemplarily includes four excavating tool support rings 41, 42, 43, and 44. Excavating tool support rings 41, 42, 43, 44 are centrically disposed at the base member 24 with respect to first rotational axis 210. Each excavating tool support ring 41, 42, 43, 44 includes a diameter such that excavating tool support rings 41, 42, 43, 44 together form a cone-like shape. Excavating tool support rings 41, 42, 43, 44 may be welded or may be integrally formed on base member 24. First excavating head 18 may therefore also be termed "multi-row excavating head". Of course, first 2016/002063

-8- excavating head 18 may have a different number of excavating tool support rings, such as one excavating tool support ring. In these cases, first excavating head 18 may be termed "single-row excavating head".

[21 ] Base member 24 further includes a center bore 30 extending

through base member 24 along first rotational axis 210. Center bore 30 is configured to receive a drive bushing 32 (see Fig. 2) connected to a driven tool shaft (shown in Fig. 2) for rotating first excavating head 18 about first rotational axis 210. The driving mechanics of first excavating heads 18 will be described in more detail when referring to Fig. 2.

[22] As further shown in Fig. 1 , each first excavating tool 60 further includes a sharp tip 62. Tip 62 is configured to pierce into the mining material to generate cracks when first excavating head 18 rotates about first rotational axis 210. First excavating tools 60, therefore, perform a cutting operation on the mining material.

[23] Referring now to Fig. 2, a cross-sectional part view through

milling device 14 is shown. Milling device 14 includes the first excavating heads 18 and the second excavating heads 20 already explained in Fig. 1. As

mentioned, first excavating heads 18 and second excavating heads 20 are alternately disposed on the periphery of milling drum 15. Hence, in the cross- sectional part view shown in Fig. 2, an exemplary first excavating head 18 is shown on a top position of Fig. 2 and an exemplary second excavating head 20 is shown on a bottom position of Fig. 2. First excavating head 18 is schematically shown to be a multi-row excavating head as previously described with respect to Fig. 1. First excavating head 18 includes multiple rows of first excavating tools 60, indicated schematically by arrows 38. First excavating head 18 may also be a single-row excavating head.

[24] As can be seen in Fig. 2, milling device 14 includes milling drum

15. Milling drum 15 is formed by a first drum ring 15 A and a second drum ring 15B. Milling drum 15 includes a drum axis 200 disposed centrally in milling 16 002063

-9- drum 15. Milling drum 15 is rotatable about drum axis 200. Milling device 14 further includes a plurality of first tool shafts 34 arranged on a periphery of milling drum 15, and a plurality of second tool shafts 36 arranged on a periphery of milling drum 15. First and second tool shafts 34, 36 are arranged between first drum ring 15A and second drum ring 15B. Each first tool shaft 34 includes a first rotational axis 210 and each second tool shaft 36 includes a second rotational axis 212. First rotational axes 210 and second rotational axes 212 extend substantially radially with respect to drum axis 200.

[25] Within the meaning of this disclosure, "substantially radially with respect to drum axis 200" means that first rotational axes 210 and second rotational axes 212 extend at an angle a with respect to a radial direction 220 of drum axis 200. Angle a may be in a range between about 0 degree and about ±20 degrees, preferably in a range between about ±1 degree and about

±20 degrees, and more preferably in a range between about ±1 degree and about ±15 degrees.

[26] First tool shafts 34 are connected to first excavating heads 18 by first bearing bushes 230. Second tool shafts 36 are connected to second

excavating heads 20 by second bearing bushes 232. First and second bearing bushes 230, 232 are screwed in a circumferential end face of first and second drum rings 15 A, 15B by means of a plurality of fastening screws 234. Each first and second bearing bush 230, 232 is exchangeable in a cartridge- like manner and inserted into a drum chamber 236 via the fastening screws 234. Milling device 14 can also be converted into a configuration with first and second tool shafts 34, 36 extending perpendicularly to drum axis 200. In this configuration different first and second bearing bushes 230, 232 are used in which first and second tool shafts 34, 36 are arranged perpendicularly to drum axis 200.

[27] In each first bearing bush 230, a corresponding first tool shaft 34 is rotatably supported. In each second bearing bush 232, a corresponding second tool shaft 36 is rotatably supported. The rotatable support is achieved by means 02063

-10- of tapered roller bearings 238 arranged within first and second bearing bushes 230, 232, bearing rings 240 and shaft sealing rings 242.

[28] In the following the drive mechanism of milling device 14 is

explained.

[29] In milling device 14, there occur two forced rotations. A first

rotation is a rotation of milling drum 15 about drum axis 200. A second rotation is a rotation of first tool shafts 34 about first rotational axis 210.

[30] Rotation of milling drum 15 about drum axis 200 is performed via a first belt pulley 244. First belt pulley 244 is arranged on a right side of milling device 14. Rotation of first tool shafts 34 about first rotational axis 210 is performed by a second belt pulley (not shown). The second belt pulley is arranged on a left side of milling device 14 opposite first belt pulley 244 in a width direction of milling drum 15.

[31] First belt pulley 244 is connected to an input side of a first hub

gear 246, thereby driving first hub gear 246. The second belt pulley is connected to an input side of a second hub gear 248, thereby driving second hub gear 248. First hub gear 246 is mounted on a first fastening flange 250, whereas second hub gear 248 is mounted on a second fastening flange (not shown). Both fastening flanges are used to connect milling drum 15 to drum holder 13 shown in Fig. 1.

[32] First and second hub gears 246, 248 are driven by an engine such as an electric motor of mining machine 10. First hub gear 246 includes an output side 250 to which milling drum 15 is connected via its first drum ring 15 A.

Second hub gear 248 includes an output side to which a toothed crown gear 252 is connected. Toothed crown gear 252 is rotatably supported on second drum ring 15B via a bearing ring 254 and a shaft seal 256.

[33] Toothed crown gear 252 meshes with bevel gears 258. Bevel gears

258 are connected to first tool shafts 34. Because toothed crown gear 252 itself is driven by second hub gear 248 and because toothed crown gear 252 meshes with bevel gears 258, toothed crown gear 252 drives bevel gears 258. Moreover, toothed crown gear 252 can drive bevel gears 258 at a different rotational speed compared to a rotational speed of milling drum 15. Thus, a desired rotational speed ratio between milling drum 15 and first tool shafts 34 can be set using first and second hub gears 246, 248.

[34] As first excavating tools 60 are mounted on first excavating heads

18, operation of milling device 14 results in a rotation of milling drum 15 about drum axis 200 and in a rotation of first excavating heads 18 about first rotational axis 210. As a result, first excavating tools 60 are subjected to two rotational movements about two different rotational axes. First excavating tools 60 therefore describe a substantially cycloid path during operation of milling device 14. During operation of milling device 14, first excavating tools 60 engage into mining material 260, thereby causing cracks 261 in the mining material 260 and eventually create an undercut 262 or slot depending on the type of first excavating heads 18. Undercuts or slots are cut in an advancing direction of mining machine 10, as exemplarily indicated by arrow 264.

[35] Referring now to second excavating heads 20.

[36] As mentioned, second excavating heads 20 are connected to

second tool shafts 36. From Fig. 2 it can be seen that second tool shafts 36 do not contact toothed crown gear 252. Hence, during operation of milling device 14, second tool shafts 36 are not driven by toothed crown wheel 252. Because second tool shafts 36 are connected to second excavating heads 20, second excavating heads 20 are not driven either. Instead, second excavating heads 20 are freely rotatably about second rotational axis 212.

[37] Second excavating heads 20 include a shaft carrier portion 265 and a tool carrier portion 266. Shaft carrier portion 265 is connected to second tool shaft 36 and tool carrier portion 266 is connected to shaft carrier portion 265. Tool carrier portion 266 accommodates second excavating tools 267.

[38] Second excavating tools 267 have a maximal radial distance 280 from drum axis 200 that is substantially equal to a maximal radial distance 282 2063

-12- between first excavating tools 60 and drum axis 200. Moreover, second

excavating tools 267 have a maximal radial distance 284 from second rotational axis 212 that is substantially equal to a maximal radial distance 286 between first excavating tools 60 and first rotational axis 210.

[39] Each second excavating tool 267 further includes a substantially disc-like shape that is symmetrical about second rotational axis 212. The disc-like shape includes a blunt contact region 268. Blunt contact region 268 contacts the mining material 260 during operation of milling device 14. Blunt contact region 268 includes a conical cross-sectional shape in a plane including second

rotational axis 212. The conical cross-sectional shape includes a radially outer face 270 with respect to drum axis 200, and a lateral face 272. Lateral face 272 extends in radial direction with respect to drum axis 200 between shaft carrier portion 265 and radially outer face 270. Lateral face 272 includes a diameter that increases in radial direction from shaft carrier portion 265 to radially outer face 270. Blunt contact region 268 further includes a blunt edge 274. Blunt edge 274 connects lateral face 272 and radially outer face 270. Blunt edge 274 includes a predetermined radius in a range, for example, between about 2 mm and 10 mm.

[40] Radially outer face 270 further includes a planar portion 276 and a bevel portion 278. Planar portion 276 is disposed on a radially inner side with respect to second rotational axis 212. Bevel portion 278 is disposed on a radially outer side with respect to second rotational axis 212. Bevel portion 278 and planar portion 276 confine an angle β. Angle β is substantially equal to the angle a between radial direction 220 and second rotational axis 212.

[41] As maximal radial distances 280, 284 of second excavating tools

267 are substantially equal to maximal radial distances 286, 282 of first

excavating tools 60, upon operation of milling device 14, second excavating tools 267 contact the mining material 260 at the undercut 262 generated by the first excavating tools 60. During rotation of milling drum 15, second excavating tools 267, which are freely rotatable, contact the mining material 260 with their 3

-13- radially outer face 270 and roll over the mining material 260. This "rolling" over the mining material 260 generates a compressive strain on the mining material 260. The compressive strain is an additional impact on the cracks 261 previously generated by first excavating tools 60. The compressive strain, therefore weakens the mining material 260 further and supports the excavating process.

[42] Additionally, as angle a between radial direction 220 and second rotational axis 212 is substantially equal to angle β between planar portion 276 and bevel portion 278, bevel portion 278 contacts the mining material 260 about substantially its entire surface area. Hence, during rotation of milling drum 15, bevel portion 278 causes a lateral support for milling device 14. This lateral support also functions to limit a penetration depth of first excavating tools 60 in the mining material 260. Hence, second excavating tools 267 also function as a depth stop for first excavating tools 60. For example, a maximal penetration depth of first excavating tools 60 in the mining material 260 may be, for example, in a range between about 1 mm and about 5 mm for hard rock mining material and between about 5 mm and about 10 mm for soft rock mining material.

[43] Referring now to Fig. 3, a cross-sectional part view through

another exemplary milling device is shown. Compared to the example shown in Fig. 2, milling device 14 in Fig. 3 includes the same second excavating heads 20 as shown in Fig. 2, but different first excavating heads 18'. In the example shown in Fig. 3, first excavating heads 18' are slot cutting excavating heads. Compared to the already explained multi-row excavating heads of Fig. 2, slot cutting excavating heads 18' includes a single slot cutting ring 300.

[44] A top view of slot cutting ring 300 is shown in Fig. 3 indicated by

"X". As can be seen, slot cutting ring 300 includes a plurality of first excavating tools 60'. First excavating tools 60' are arranged in a saw tooth manner on an outer periphery of slot cutting ring 300. First excavating tools 60' have a cylindrical shape with sharp top and bottom edges and are made from carbide, diamond, or other hard materials. First excavating tools 60' include a diameter, for example, in a range between about 8 mm and about 20 mm.

Slot cutting ring 300 rotates in clockwise direction, as indicated by the arrow. During rotation of slot cutting ring 300, first excavating tools 60' engage their sharp edges with the mining material 260 and cut a slot 302 into the mining material 260 along advancing direction 264 of mining machine 10. Slot 302 may have an axial distance 304 with respect to drum axis 200, for example, in a range between about 5 mm and 20 mm and may have a radial distance 306 with respect to drum axis 200, for example, in a range between about 8 mm and 20 mm (not taking into account the slight inclination of first rotational axis 210 with respect to drum axis 200.

Second excavating heads 20 which are freely rotatable about second rotational axis 212 include second excavating tools 267. As mentioned, maximal radial distances 280, 284 of second excavating tools 267 are

substantially equal to maximal radial distances 286, 282 of first excavating tools 60'. Hence, upon operation of milling device 14, second excavating tools 267 engage with slot 302. Bevel portion 278 of radially outer face 270 contacts the mining material 260 at a radially outer side of slot 302 with respect to drum axis 200. Additionally, lateral face 272 contacts the mining material 260 at a radially inner side of slot 302 with respect to drum axis 200. As a result, second excavating tools 267 transform the compressive strain explained in connection with Fig. 2 into a tensile strain acting upon the mining material 260 from within slot 302. As a result, the mining material 260 in the vicinity of slot edge 308 is broken out.

By combining slot cutting excavating heads 18' with second excavating heads 20, the predefined slots 302 generated during the first, cutting operation are used to lever out remaining mining material 310. Moreover, by generating distinctly defined slots 302, a required overall cutting power of mining machine 10 decreases. 16 002063

-15-

Referring now to Fig. 4, a cross-sectional part view through another exemplary milling device is shown. Compared to the example shown in Fig. 3, milling device 14 in Fig. 4 includes the same first excavating heads 18' as shown in Fig. 3, but different second excavating heads 20'.

As shown in Fig. 4, second tool shafts 36 include bevel gears 400 that mesh with toothed crown gear 252. As a consequence, second tool shafts 36 are rotatably driven by toothed crown gear 252 and rotate about second rotational axis 212. Each second excavating head 20' includes shaft carrier portion 265. Shaft carrier portion 265 is fixedly connected to second tool shaft 36. Hence, shaft carrier portion 265 is also rotatably driven and rotates about second rotational axis 212. Each second excavating head 20' further includes tool carrier portion 266. Tool carrier portion 266 is rotatably mounted to shaft carrier portion 265 using bearings 402. Moreover, tool carrier portion 266 is freely rotatable about a third rotational axis 404. Third rotational axis 404 is offset to second rotational axis 212 by a predetermined value 406. Predetermined value 406 may be, for example, in a range between about 1 mm and about 10 mm.

With the second excavating heads 20' including third rotational axis 404 offset to second rotational axis 212, tool carrier portion 266 can freely rotate about third rotational axis 404 but is driven to rotate about second

rotational axis 212. As a result, when shaft carrier portion 265 rotates about second rotational axis 212, tool carrier portion 266 and therewith second

excavating tools 267 "hammer" into the mining material 260, as indicated by arrow 408. This "hammering" into the mining material 260 adds to the explained compressive and/or tensile strain applied to the mining material 260. Hence, the mining material 260 is weakened further and the excavating process of milling device 14 can be improved further.

Referring now to Fig. 5, a cross-sectional part view through another exemplary milling device is shown. In the exemplary milling device of Fig. 5, first excavating heads 18' and second excavating heads 20" are arranged on the same rotational axis. In other words, first rotational axis 210 and second rotational axis 212 coincide to rotational axis 500. Moreover, first excavating heads 18' are arranged radially outside with respect to drum axis 200, and second excavating heads 20" are arranged radially inside with respect to drum axis 200. As can be seen in Fig. 5, each first excavating head 18' and each second excavating head 20" are mounted together on a single tool shaft 502. In other words, first tool shafts 34 and second tool shafts 36 are combined to tool shafts 502. Tool shafts 502 are drivably connected to toothed crown gear 252 via bevel gears 258.

As can be further seen in Fig. 5, first excavating heads 18' are slot cutting excavating heads already explained in connection with Figs. 3 and 4. Second excavating heads 20" include shaft carrier portion 265 and tool carrier portion 266 already explained in connection with Fig. 4. Shaft carrier portion 265 is connected to tool shaft 502 and connects to slot cutting ring 300. Tool carrier portion 266 is rotatably mounted to shaft carrier portion 265 and freely rotatable about rotational axis 500 using bearings 402. First excavating heads 18' cut a slot 504 into the mining material 260 because first excavating tools 60' are driven to rotate about rotational axis 500. Second excavating heads 20 concomitantly widen slot 504 because second excavating tools 267 are freely rotatable about rotational axis 500 and engage with slot 504 from beneath first excavating tools 60'. Due to this combination of excavating operations, an excavating

performance of milling device 14 can be improved further.

Referring now to Fig. 6, a cross-sectional part view through another exemplary milling device is shown. In the exemplary milling device 14 of Fig. 6, first excavating heads 18" include a plurality of slot cutting rings 600, 602, 604. The plurality of slot cutting rings 600, 602, 604 are arranged in an axial direction of first rotational axis 210. Each slot cutting 600, 602, 604 ring includes a diameter. Between different slot cutting rings, the diameter of the respective slot cutting ring deceases with increasing radial distance from drum axis 200, 3

-17- such that slot cutting rings 600, 602, 604 form a first excavating head 18" with a cone-like shape.

[54] As can be further seen in Fig. 6, second excavating heads 20" ' include a plurality of disc-shaped rings 606, 608, 610. The plurality of discshaped rings 606, 608, 610 are arranged in an axial direction with respect to second rotational axis 212. Each disc-shaped ring 606, 608, 610 includes a diameter. Between different disc-shaped rings, the diameter of the respective disc-shaped ring deceases with increasing radial distance from drum axis 200, such that disc-shaped rings 606, 608, 610 form a second excavating head 20"' with a cone-like shape. Moreover, the diameters of the disc-shaped rings 606, 608, 610 are substantially equal to the diameters of the respective slot cutting rings 600, 602, 604. That is a diameter of smallest disc-shaped ring 606 is substantially equal to a diameter of smallest slot cutting ring 600, and so on and so forth.

[55] Hence, each slot cutting ring 600, 602, 604 cuts a slot 612, 614,

616 into the mining material 260, and each disc-shaped ring 606, 608, 610 engages into the respective slot 612, 614, 616, thereby creating a staggered levering effect on the mining material 260.

[56] By using a multi-row slot cutting excavating head 18" an

undercut depth, i.e. a distance 618 in radial direction with respect to first rotational axis 210, can be increased compared to a multi-row excavating head 18 shown in Fig. 2. Moreover, by generating a plurality of distinctly defined slots 612, 614, 616, a required overall cutting power of mining machine 10 decreases.

[57] Terms such as "about" and "substantially" as used herein when

referring to a measurable value such as a parameter, or an angle are meant to encompass variations of ±10 or less, more preferably ±5% or less, still more preferably ±1% or less of the specified value, insofar as such variations are appropriate to perform the disclosed invention. As already mentioned, the term "substantially radially to the drum axis" as used herein refers to the first and second rotational axes extending at an angle with respect to the radial direction of the drum axis in a range between about 0 degree and about ±20 degrees, preferably between about ±1 degree and about ±20 degrees, and more preferably between about ±1 degree and about ±15 degrees.

It is to be understood that the value to which the modifier "about" refers is itself also specifically, and preferably, disclosed. The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

Industrial Applicability

Exemplary mining machines suited for milling device 14 are, for example, part- face heading machines or mobile mining machines manufactured by Caterpillar Global Mining Europe GmbH. One skilled in the art will, however, appreciate that milling device 14 is suited for other mining machines as well.

In the following a procedure for excavating mining materials, in particular hard rock mining materials, is described in connection with the .

embodiments shown in Figs. 1 to 6.

To start with, milling drum 15 is rotated about drum axis 200 by first hub gear 246. Milling drum 15 is rotated in a direction towards the mining material 260, such that first excavating tools 60 engage with the mining material 260. Concomitantly, second hub gear 248 is operated and drives toothed crown gear 252 which meshes with bevel gears 258, thereby rotating first tool shafts 34 and therewith first excavating heads 18 about first rotational axis 210.

Then, upon rotation of first excavating heads 18, first excavating tools 60, 60' engage the mining material 260 and perform their first, cutting operation on the mining material 260, thereby creating an undercut 262, a slot 302 or a plurality of slots 612, 614, 616, depending on the type of first excavating heads 18, 18" used. Next, during the concomitant rotation of milling drum 15, second excavating tools 267 mounted on second excavating heads 20 engage with the mining material 260. As the maximal radial distances 284, 280 of second excavating tools 267 are substantially equal to the maximal radial distances 286, 282 of first excavating tools 60, 60', second excavating tools 267 engage in substantially the same area of the mining material 260 than first excavating tools 60, 60'. Hence, second excavating tools 267 perform their second excavation operation in substantially the same area of the mining material 260 as first excavating tools 60, 60' performed their first, cutting operation.

Second excavating tools 267 include a blunt contact region 268 that contacts the mining material 260 during rotation of milling drum 15. Because second excavating tools 267 do not include sharp edges as first excavating tools 60, 60', second excavating tools 267 perform a second excavating operation different from the first, cutting operation. Moreover, because blunt contact region 268 includes a bevel portion 278 extending at angle a with respect to planar portion 276 that is substantially equal to angle β between radial direction 220 and second rotational axis 212, bevel portion 278 contacts the mining material 260 substantially on its entire surface area. Hence, bevel portion 278 applies an areal compressive force on the mining material 260 which results in an areal compressive strain on the mining material 260. The second excavating operation is, therefore, a blunt compression operation that weakens the mining material 260 further by acting against the tensile strength of the mining material 260. In addition to the blunt compression operation, bevel portion 278 causes a lateral support for milling device 14. The lateral support reduces vibrations of mining machine 10 and also functions to limit a penetration depth of first excavating tools 60, 60' in the mining material 260, as already explained.

In cases where slot cutting excavating heads 18' are used (see Fig. 3), the second excavating operation is not limited to a blunt compression operation, but has additional effects on the mining material 260. For example, blunt contact region 268 is shaped such that radially outer face 270 and lateral face 272 engage with slot 302 generated during the first, cutting operation.

During the concomitant rotation of milling drum 15 towards the mining material 260, the engaged second excavating tools 267 act like levers from within slot 302, thereby transforming the compressive strain into a tensile strain acting on the mining material 260 from within slot 302.

[66] In cases where first excavating heads 18' and second excavating heads 20" are mounted on the same tool shaft 502, first and second excavating operations are concomitantly applied to the mining material 260.

[67] In cases where first excavating heads 18' and second excavating heads 20' are used (see Fig. 4), second excavating tools 267 are rotatably driven to rotate about second rotational axis 212. As a result, the second excavating operation additionally includes a "hammering" effect on the mining material 260.

[68] Generally, first excavating heads 18, 18', can be combined with second excavating heads 20, 20', 20" in any suitable way to improve the excavating process as long as an impact on the mining material 260 increases.

[69] Although each second excavating head 20, 20', 20" is shown to to include only a single second excavating tool 267, each second excavating head 20, 20', 20" may include a plurality of second excavating tools 267 such as in the case of multi-row excavating head 18. Hence, in some embodiments, second excavating head 20, 20', 20" may correspond to first excavating heads 18 but include disc-shaped second excavating tools 267 instead of sharp edged first excavating tools 60.

Although the preferred embodiments of this invention have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.