Vertical mill roller

Abstract

In grinding of a raw material by a vertical roller mill, highly-efficient grinding is performed irrespective of the type of the raw material, and the life of the mill roller is extended. In order to achieve these, in a grinding roller used in a vertical roller mill, an outer circumferential surface of the roller as a grinding surface is divided into a main grinding surface that mainly performs pulverizing and a grinding surface other than the main grinding surface. The main grinding surface is made smooth, and the grinding surface other than the main grinding surface is a raw material transfer surface in which slit grooves inclined at 90 degrees or an angle exceeding 45 degrees relative to a roller circumferential direction or screw grooves inclined at 45 degrees or smaller relative to the roller circumferential direction are formed.

Claims

1. A vertical roller mill comprising: a plurality of grinding rollers arranged on a rotating table so as to surround a rotational center line of the rotating table, wherein: each of the grinding rollers has a hybrid grinding surface structure, each grinding roller is a roller with a trapezoidal cross-section including a large diameter-side at one end and a small diameter-side at the other end, each grinding roller has a roller grinding surface formed of: a main grinding surface that is a smooth surface present only on the large diameter-side of each grinding roller and that mainly performs pulverizing, the main grinding surface extending around an entire circumference of the grinding roller on the large diameter-side; a grinding surface other than the main grinding surface that includes a plurality of slit grooves formed to intersect at an angle of 90 degrees relative to a roller circumferential direction or to be inclined at an angle less than 90 degrees but exceeding 45 degrees relative to the roller circumferential direction or a plurality of screw grooves formed to be inclined at an angle equal to or less than 45 degrees relative to each grinding roller circumferential direction; and an annular grinding part which is opposite the grinding rollers in the rotating table and whose entire surface is a smooth grinding surface or whose entire surface has a slit groove perpendicular to a rotation direction, wherein the plurality of grooves extends from the small diameter-side at the other end to an intermediate diameter area between the main grinding surface and the grinding surface other than the main grinding surface, and the main grinding surface extends from the intermediate diameter area to the large diameter-side at the one end.

2. The vertical roller mill according to claim 1, wherein: a direction of inclination of the screw grooves in each grinding roller corresponds to a raw material discharging direction of positively transferring a ground raw material toward an outer circumferential side in accordance with rotation and feeding the ground raw material onto the main grinding surface.

3. The vertical roller mill according to claim 1, wherein: an angle of inclination of the screw grooves is 5 degrees or larger relative to a roller circumferential direction.

4. The vertical roller mill according to claim 1, wherein: the main grinding surface is an outer circumferential surface of an area subjected to wear.

5. The vertical roller mill according to claim 1, wherein: the main grinding surface is an area that is 30 to 40% of a whole width of each grinding roller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1(a) and 1(b) are front views showing a trapezoidal roller as a vertical mill roller of the present invention in comparison with a conventional roller, FIG. 1(a) shows the conventional roller, and FIG. 1(b) shows the roller of the present invention.

(2) FIGS. 2(a) and 2(b) are front views showing a trapezoidal roller as another vertical mill roller of the present invention in comparison with a conventional roller, FIG. 2(a) shows the conventional roller, and FIG. 2(b) shows the roller of the present invention.

(3) FIGS. 3(a) and 3(b) are front views showing a tire convex roller as another vertical mill roller of the present invention in comparison with a conventional roller, FIG. 3(a) shows the conventional roller, and FIG. 3(b) shows the roller of the present invention.

(4) FIGS. 4(a) and 4(b) are front views showing another tire convex roller as still another vertical mill roller or the present invention in comparison with a conventional roller, FIG. 4(a) shows the conventional roller, and FIG. 4(b) shows the roller of the present invention.

(5) FIGS. 5(a) and 5(b) are front views showing a tire flat roller as still another vertical mill roller of the present invention in comparison with a conventional roller, FIG. 5(a) shows the conventional roller, and FIG. 5(b) shows the roller of the present invention.

(6) FIG. 6 is a configuration view showing an experimental compact grinder.

(7) FIG. 7 is a vertical sectional view showing the shape of a groove in a table.

BEST MODE FOR CARRYING OUT THE INVENTION

(8) An embodiment of the present invention will be described below with reference to the drawings.

(9) All of vertical mill rollers shown in FIGS. 1 to 5 are grinding rollers used for vertical mill roller.

(10) The vertical mill roller shown in FIG. 1 is a trapezoidal roller 10 used in the vertical mill roller called as Loesche mill. The trapezoidal roller 10 shown in FIG. 1(a) is a conventional roller, and a plurality of screw grooves 11A are formed in an entire outer circumferential surface 12 at regular intervals in the roller shaft direction. An inclined direction of the screw grooves 11A is a raw material discharging direction of actively transferring a ground raw material toward the outer circumference with rotation, and for its inclined angle, it is given that the inclined angle θ relative to the roller shaft is 67.5 degrees, and the inclined angle relative to the roller circumferential direction is 22.5 degrees.

(11) The trapezoidal roller 10 shown in FIG. 1(b) is a roller according to the present invention in which the outer circumferential surface 12 is broadly divided into a main grinding surface 12A on the large-diameter side, and the other part. The main grinding surface 12A is smooth. The plurality of screw grooves 11A are formed in the part other than the main grinding surface 12A at regular intervals in the roller shaft direction. The inclined direction of the screw grooves 11A is a raw material discharging direction of actively transferring the ground raw material toward the outer circumference with rotation and feeding the material to the main grinding surface 12A, and for its inclined angle, it is given that the inclined angle θ relative to the roller shaft is 67.5 degrees, and the inclined angle relative to the roller circumferential direction is 22.5 degrees.

(12) That is, the outer circumferential surface 12 of the trapezoidal roller 10 includes a smooth main grinding surface 12A on the large-diameter side and a raw material transfer surface 12B on the small-diameter side, in which the screw grooves 11A are provided in the raw material discharging direction.

(13) The main grinding surface 12A is defined as an area where the outer circumferential surface 12 of the roller is subjected to wear that is larger than two thirds of maximum wear, and a length of the main grinding surface 12A in the roller axial direction, that is, a horizontal width of the main grinding surface 12A in the trapezoidal roller is generally about 30 to 40% of the whole width of the roller.

(14) The vertical mill roller shown in FIG. 2, like the vertical mill roller shown in FIG. 1, is the trapezoidal roller 10 used in the Loesche type vertical mill roller. The trapezoidal roller 10 shown in FIG. 2(a) is a conventional roller, and a plurality of slit grooves 11B vertical to the roller circumferential direction are formed in the entire outer circumferential surface at regular intervals in the roller circumferential direction. In the trapezoidal roller 10 shown in FIG. 2(b), the outer circumferential surface 12 is broadly divided into the main grinding surface 12A on the large-diameter side and the other area, that is, a raw material biting surface 12C in which the plurality of slit grooves 11B vertical to the roller circumferential direction are formed at regular intervals in the roller circumferential direction.

(15) The vertical mill roller shown in FIG. 3 is a tire-type roller and a convex roller 20 having a small curvature (D/R=5). The tire convex roller 20 shown in FIG. 3(a) is a conventional roller, and a plurality of screw grooves 21A are formed in an entire outer circumferential surface 22 at regular intervals in the roller shaft direction. An inclined direction of the screw grooves 21A is a raw material discharging direction of actively transferring the ground raw material toward the outer circumference with rotation, and for its inclined angle, it is given that inclined angle θ relative to the roller shaft is 45 degrees, and the inclined angle relative to the roller circumferential direction is also 45 degrees.

(16) The tire convex roller 20 shown in FIG. 3(b) is a roller according to the present invention in which the outer circumferential surface 22 includes the central smooth main grinding surface 22A on the large diameter-side and raw material transfer surface 22B, 22B on both sides (small-diameter side) in which the screw grooves 21A in the raw material discharging direction are formed at regular intervals in the roller shaft direction. For the inclined angle of the screw grooves 21A, it is given that inclined angle θ relative to the roller shaft is 45 degrees, and the inclined angle relative to the roller circumferential direction is also 45 degrees.

(17) The vertical mill roller shown in FIG. 4, like the vertical mill roller shown in FIG. 3, is a tire convex roller 20 (D/R=5). The trapezoidal roller 10 shown in FIG. 4(a) is a conventional roller, and as opposed to the vertical mill roller shown in FIG. 4, slit grooves 21B in the raw material collecting direction are formed in the entire outer circumferential surface 22 at regular intervals in the roller circumferential direction. On the other hand, the tire convex roller 20 shown in FIG. 4(b) is a roller according to the present invention in which the outer circumferential surface 22 includes the central smooth main grinding surface 22A and the raw material transfer surfaces 22B, 22B on the both sides (small-diameter side), in which the slit grooves 21B in the raw material collecting direction are formed at regular intervals in the roller circumferential direction. For inclined angle of the screw grooves 21A, the inclined angle θ relative to the roller shaft is 45 degrees, and the inclined angle relative to the roller circumferential direction is also 45 degrees.

(18) The vertical mill roller shown in FIG. 5 is a tire-type flat roller 30 having a large curvature (D/R=4). The tire flat roller 30 shown in FIG. 5(a) is a conventional roller in which a plurality of screw grooves 31A are formed on an entire outer circumferential surface 32 at regular intervals in the roller shaft direction. An inclined direction of the screw grooves 31A is a direction of collecting back the ground raw material toward the center with rotation, and for its inclined angle, it is given that the inclined angle θ relative to the roller shaft is 67.5°, and the inclined angle relative to the roller circumferential direction is 22.5 degrees.

(19) On the other hand, the tire flat roller 30 shown in FIG. 5(b) is a roller according to the present invention in which the outer circumferential surface 32 includes smooth main grinding surfaces 32A, 32A on the small-diameter side, that is, the both sides, and a central raw material transfer surface 32B in which the screw grooves 31 in the raw material collecting direction are formed at regular intervals in the roller shaft direction. For the inclined angle of the screw grooves 31, it is given that the inclined angle θ relative to the roller shaft is 67.5 degrees, and the inclined angle relative to the roller circumferential direction is 22.5 degrees.

(20) A feature of the tire-type rollers shown in FIGS. 3 to 5 is that they can be horizontally flipped and used twice. In particular, in the tire flat roller 30 shown in FIG. 5, since grinding is performed near the small-diameter side, generally, the roller is horizontally flipped and used twice. In individual use, grinding is performed in the one main grinding surface 32A and a part 32B′ of the raw material transfer surface 32B. The horizontal width of the one main grinding surface 32A is generally 15 to 20% of the whole width of the roller, and the horizontal width of the total grinding surfaces 32A, 32A is about 30 to 40% of the whole width of the roller, which is the same as that of the trapezoidal roller.

(21) On the contrary, in the tire convex rollers 20 shown in FIGS. 3 and 4, since grinding is performed near the central large-diameter side, they cannot be often horizontally flipped. That is, in individual use, grinding is performed in the main grinding surface 22A and the one raw material transfer surface 22B, and in the horizontal flip, since the main grinding surface 22A overlaps and wear of the area extremely develops, horizontal flip becomes difficult. Like other rollers, the horizontal width of the main grinding surface 22A in this case is generally about 30 to 40% of the whole width of the roller.

EXAMPLE

(22) [Experimental Equipment]

(23) To estimate the effectiveness of the present invention, a Loesche type-like experimental compact grinder having the trapezoidal roller as a kind of the vertical roller mill was manufactured. As shown in FIG. 6, in this grinder, a grinding roller 2 is opposed to a surface of an outer circumference of a horizontal rotating table 1 as a base member. The grinding roller 2 is a vertical roller shaped like a truncated cone, and is arranged inclined such that the large-diameter side faces the outer circumferential side, the small-diameter side faces the center, and its surface opposed to a table 1 is horizontal. For purpose of a tester, the number of the rollers is one.

(24) The outer circumferential surface of the grinding roller 2 has a plurality of screw grooves 7. The plurality of screw grooves 7 discharge the ground raw material from the rotational center toward the outer circumference with rotation, and feed the material into a grinding chamber formed of the rotating table 1 and the grinding roller 2.

(25) In the rotating table 1, an outer circumferential part opposed to the grinding roller 2 is an annular grinding part 3, and for purpose of the tester, the annular grinding part 3 can be detached from a table body 4. As the grinding part 3, an interchangeable table, which had a flat surface and slit grooves vertical to the table rotating direction or grooves vertical to the limestone feeding direction, the edges of which inclined at 60 degrees (Japanese Unexamined Patent Application Publication No. 2009-142809), was prepared. The grinding roller 2 was attached to a supporting mechanism 5 rotatably and vertically movably such that clearance between the grinding roller 2 and the grinding part 3 could be freely adjusted. To apply predetermined pressure to the ground raw material, the grinding roller 2 is biased toward the grinding part 3 by a spring.

(26) With rotation of the rotating table 1, the rotating table 1 and the grinding roller 2 rotate relative to each other. In this test, to confirm the grinding property of the roller itself, a classifier by air of ground raw material was not provided. Accordingly, the ground raw material was discharged from the inside of the rotating table to the outside by the discharging capacity of the roller and the centrifugal force caused by rotation of the table. Thus, a collecting container 8 capable of completely collecting discharged limestone was provided outside of the rotating table.

(27) The Loesche type compact tester was designed such that a tire-type table could be also attached by detaching the table 4. As a matter of course, the grinding roller attached to the supporting mechanism 5 was designed so as to be exchanged with the tire-type grinding roller. It was designed such that one tester could test all of the rollers and table. Further details of the tester will be described later.

(28) [Ground Raw Materials]

(29) Using the compact grinding tester, it was cleared whether or not the amount of ground fine powder increased when the grinding roller including the grinding surface of the grinding roller divided into the main grinding surface and the raw material transfer surface was actually used, as compared with the conventional case where the slit grooves or the screw groove were formed in the entire grinding surface. As ground raw materials used in the test, following two types:

(30) 1) limestone having a high adhesiveness

(31) 2) coal having a lower adhesiveness than limestone were selected.

(32) [Limestone Grinding Test]

(33) When grinding limestone, screw grooves were formed to prevent adhesion of limestone to the roller surface. The screw grooves of 67.5 degrees as an intermediate inclined angle relative to the roller shaft in a range of 45 to 85 degrees were selected. When the slit grooves inclined at an angle less than 45 degrees were used for grinding of limestone, the slit grooves were excellent in collecting the raw material, resulting in that limestone adheres to the roller surface, making the grinding operation difficult. Thus, the screw grooves of 45 degrees or larger were formed. The screw grooves of 45 degrees or larger were poor in collecting the raw material, and were excellent in the transfer property of transferring the raw material. As the angle is larger, the transfer property is improved, thereby decreasing adhesion of limestone to the roller surface. Specifically, a large gradient of 67.5 degrees was assumed as the most excellent inclined angle.

(34) In this test, two types of rollers the trapezoidal roller shown in FIG. 1 and the tire flat roller shown in FIG. 5 (D/R=4) were employed. For grooves, the case where the screw grooves were formed on the entire roller grinding surface [FIG. 1(a), FIG. 5(a)] and the case where the main grinding surface was smooth and the screw grooves were formed in the other area [FIG. 1(b), FIG. 5(b)] were selected. Differences in the amount of ground fine powder under 200 meshes and power consumption of this grinding tester between the rollers were measured and the electric power consumption rate was compared, thereby comparing the effectiveness of both of the grinding surfaces.

(35) The shape of the slit grooves in the rotating table in this comparison test is shown in FIGS. 6 and 7. This groove shape is one of the shapes of the table grinding surface suitable for grinding of limestone, which are described in Japanese Unexamined Patent Application Publication No. 2009-142809. Size and grinding conditions of the trapezoidal roller and the tire flat roller are summarized as follows.

(36) Roller size:

(37) Trapezoidal roller large diameter: 200 mm, small diameter: 170 mm, width: 57 mm

(38) Tire flat roller (D/R=4) large diameter: 200 mm, tire R: 50 mm, width: 74 mm

(39) Table outer diameter:

(40) Trapezoidal roller outer diameter: 410 mm, inner diameter: 280 mm,

(41) Tire flat roller outer diameter: 420 mm, inner diameter: 220 mm, groove R: 60 mm

(42) Circumferential speed: 30 RPM (left rotation)

(43) Applied pressure: 23.5 kg

(44) Clearance between roller and table: 0 mm

(45) Test time: 30 minutes

(46) Time supplied amount: +/−1500 g/30 minutes

(47) Lime supplying method: continuous supply screw feeder method

(48) Temperature and humidity: 12 to 18° C., 60 to 89%

(49) Limestone used for the Test

(50) Grain size: 1 to 3 mm

(51) Grain size distribution (measured value after drying for 30 minutes)

(52) 10 meshes or more 46.0 g

(53) 16 meshes or more 44.0 g

(54) 30 meshes or more 9.0 g

(55) 60 meshes or more Tr

(56) P 0.5 g

(57) In the experimental grinder, the amount of limestone discharged to the outer circumference of the table, the amount of limestone remaining in the table, and the weight ratio of the grains passing through the 200 mesh screen and under 235 meshes to the total ground amount were examined. In this test, for convenience, only one grinding roller was used for grinding, two to four rollers were actually used, and the classifier for collecting fine powder was provided. Thus, numerical values of the amount of ground fine powder, which were obtained in the test, were different from those actually obtained. However, since the same tester is used, the findings are credible.

(58) In grain size measurement, after the grinding test for 30 minutes, all of limestone discharged from the table to a collector 8 and limestone remaining in the table were correctly collected. The weight of the collected limestone was measured and then, three samples for grain size measurement were taken from any position of the collected limestone. For purpose of accuracy, an average value of the three samples was adopted as a result of grain size measurement.

(59) The power consumption of the compact grinding tester was measured. A used power measuring device was “Cramp On Power High Tester 3168” manufactured by Hioki E.E. Corporation. The power consumption was an average value of numerical values measured in unit of second. In this test, an average value for 30 minutes was measured. This compact experimental grinder was 3-phase 220 V and has a power consumption of 750 W/H. A reason for measuring the power consumption is as follows. Although limestone was supplied to the mill with use of a screw feeder, the feeder often caused blockage, varying the supplied amount. When the supplied amount varied, the accuracy could not be ensured merely by comparison in the amount of ground fine powder under 200 meshes. Thus, the power consumption in each test grinding was measured, and the electric power consumption rate acquired by dividing the power consumption by the obtained ground amount of fine powder under 200 meshes was compared to ensure the accuracy.

(60) The total amount of ground fine powder under 200 meshes for the grinding test time of 30 minutes, as well as the power consumption (Wh) necessary for the grinding were measured, and a numerical value acquired by dividing the measured power consumption by the total ground amount of fine powder under 200 meshes was defined as the electric power consumption rate. The electric power consumption rates of various combinations of the roller and the table grinding surface were obtained and compared.

(61) [Comparison Test Results]

(62) Results of the case of using the trapezoidal roller as the grinding roller are shown in Table 1.

(63) TABLE-US-00001 TABLE 1 Collected amount Electric power Effective under 200 meshes Effective consumption rate of grinding Layer Supplied (g) and content consumed the amount under 200 Test surface area thickness amount ratio power meshes number (%) (mm) (g) (%) (Wh) (Wh/g) 1 85% 8 1530 281 g 120 0.43 18.4% 2 89% 6 1260 295 g 117 0.40 23.4%

(64) A test number (1) is a combination of the roller shown in FIG. 1(a) in which the 67.5 degrees screw grooves are formed in the entire grinding surface in the discharging direction (effective grinding surface area 85%), and a table with right-angled slit grooves having edges inclined at 60 degrees. A test number (2) is the same as the test number (1) except that the roller shown in FIG. 1(b) in which the main grinding surface on the large-diameter side is made smooth, and the screw grooves are provided only in the other grinding surface on the small-diameter side (effective grinding surface area 89%) is used. Of the whole width of the test roller of 57 mm, the width of the smooth surface as the main grinding surface was set to 20 mm (about 35% of the whole width). The screw grooves were formed in the other grinding surface. The amount under 200 meshes and the electric power consumption rate in both cases were compared.

(65) Table 1 shows comparison in the amount under 200 meshes and the electric power consumption rate (pressure applied to the roller is constant at 23.5 kg) between (1) the case where the screw grooves are formed in the entire grinding surface of the trapezoidal roller, and (2) the case where the main grinding surface is made smooth, and the screw grooves are formed in the other grinding surface.

(66) Since the amount of supplied limestone in (1) was larger than the amount in (2), the effective power consumption slightly increased. However, the amount of ground fine powder under 200 meshes in (2) slightly increased from the amount in (1). Accordingly, comparing in the electric power consumption rate, (2) saved energy from (1) by about 7%. Although there was no substantial difference, when (2) the roller grinding surface was divided into the main grinding area and the transfer area, as compared to the case where the screw grooves were formed in the entire grinding surface, the amount of ground fine powder under 200 meshes improved, and the electric power consumption rate lowered.

(67) Results in the case of the tire flat roller (D/R=4) as the grinding roller are shown in Table 2. Reasons for selecting the flat roller are as follows. The main grinding surface of this roller existed on the small-diameter side, and in the case of comparison at the same table rotating speed, the ground amount per unit time as well as the amount of ground fine powder in the flat roller were smaller than those of the convex roller. Accordingly, if a difference occurs in the state of a low ground amount of fine powder, the reliability of the present invention is considered to be high. As another reason, since the main grinding surface existed on the small-diameter side, it was easy to form the grinding surface.

(68) TABLE-US-00002 TABLE 2 Collected Raw material amount under Electric power Effective supplied 200 meshes Effective consumption rate of grinding Layer amount (30 (g) and consumed the amount under 200 Test surface area thickness minutes) content ratio power meshes number (%) (mm) (g) (%) (Wh) (Wh/g) 1 81 5 1640 164 g 112 0.68 10.0% 2 92 6 1590 186 g 107 0.58 11.7%

(69) A test number (1) is a combination of the roller shown in FIG. 5(a) in which the 67.5 degrees screw grooves are formed in the entire grinding surface in the collecting direction (effective grinding surface area 81%), and a table with right-angled slit grooves having edges inclined. A test number (2) is the same combination as the test number (1) except that the roller shown in FIG. 5(b) in which the smooth surfaces of the same width are formed on the both small-diameter sides and the 67.5 degrees screw grooves are formed inside it in the collecting direction (effective grinding surface area 92%) is used. In the test number (2), of the whole width of the roller of 74 mm, the width of the smooth surface as the main grinding surface was set to 25 mm (12.5 mm in width+12.5 mm in width, about 34% of the whole width).

(70) Table 2 shows comparison in the amount under 200 meshes and electric power consumption rate between the case where 67.5 degrees screw grooves are formed in the entire grinding surface of the tire flat roller (D/R=4) and the case where the smooth surface as the main grinding surface of the rollers is arranged on either side of the small-diameter side, and the 67.5 degree screw grooves are formed in the center. The screw grooves were formed in the direction of collecting the raw material to the inner side of the table.

(71) The test number (2) in which the main grinding surface was made smooth, as compared to the test number (1) in which the screw grooves were formed in the entire grinding surface, increased the ground amount by about 12% and decreased the electric power consumption rate by about 15%. The tire flat roller was superior to the trapezoidal roller both in the amount of ground fine powder and the electric power consumption rate. Reasons for this are as follows.

(72) In the trapezoidal roller, since the raw material was ground between the roller surface and the table surface, the highly adhesive material such limestone was adhered to the roller surface and the table surface more easily, and the gap between the roller and the table, and in turn, the production volume of fine powder decreased. As a result, a difference in the shape of the grinding surface did not clearly cause a difference in the amount of ground fine powder. On the contrary, in the tire-type roller that performed linear grinding and passed the ground raw materials, material is less likely to be adhered to the roller, as compared with the trapezoidal roller, the difference in the grinding surface clearly appeared as the difference in the pulverizing amount. For grinding of adhesive limestone, in both of the trapezoidal roller and the tire flat roller, when the main grinding surface was made smooth, the amount of ground fine powder slightly increased, and the electric power consumption rate decreased by about 7% in the trapezoidal roller and by about 15% in the tire flat roller.

(73) When limestone is ground by the vertical roller mill, it is highly difficult to increase the amount of ground fine powder under 200 meshes. Reasons for this are follows. Lime is easy to be adhered to the grinding roller, resulting in that the gap between the roller and the table, which is necessary for grinding, becomes small, and the biting amount at the gap lowers, thereby it is difficult to increase the amount of ground fine powder. Further, as limestone is finer, it is easier to be adhered again. As a result, the grains become large and are hard to be small. Even for such an adhesive substance, it is remarkable that when the main grinding surface is made smooth, the amount of ground fine powder increases. Thus, for the raw material having a low adhesiveness, it can be expected that the amount of collected fine powder dramatically increases.

(74) [Coal Grinding Test]

(75) Using the three types of rollers: the trapezoidal roller, the tire convex roller (D/R=5), and tire flat roller (D/R=4), as in limestone, a coal grinding test was made.

(76) Grinding conditions are summarized as follows.

(77) Used coal: steelmaking plant raw material coal

(78) Grain size range—G—: 7 mm×7 mm≧G≧0.5 mm×0.5 mm

(79) Initial grain size distribution:

(80) 20 meshes or more 40 g

(81) 60 meshes or more 34 g

(82) 120 meshes or more 3 g

(83) 200 meshes or more 13 g

(84) 235 meshes or more 2 g

(85) P 9 g

(86) Water content 5%

(87) Roller clearance: 0 mm

(88) Roller surface pressure: 23.5 Kg

(89) Table rotating speed: 60 RPM

(90) Coal supplied amount: 2530 to 2850 g/30 minutes

(91) Coal supply method: screw feeder continuous supply method

(92) Test temperature and humidity: 18 to 34° C., 62 to 78%

(93) The size of the trapezoidal roller and the tire flat roller is described in the paragraph of limestone and thus, description thereof is omitted. Details of only the tire convex grinding roller (D/R=5) will be described below.

(94) Roller size (D/R=5)

(95) Tire large diameter: 200 mm

(96) Tire R: 40 mm

(97) Tire width: 66 mm

(98) Rotating table size

(99) Outer diameter: 410 mm

(100) Inner diameter: 230 mm

(101) Groove R: 50 mm

(102) Table 3 shows comparison in the amount under 200 meshes and electric power consumption rate (pressure applied to the roller is constant at 23.5 kg) between different grinding surfaces in the trapezoidal roller. The tables combined with the trapezoidal roller are all smooth surface tables.

(103) TABLE-US-00003 TABLE 3 Effective Collected amount Effective Electric power grinding Layer Supplied under 200 meshes (g) consumed consumption rate of the Test surface area thickness amount and content ratio power amount under 200 meshes number (%) (mm) (g) (%) (Wh) (Wh/g) 1 100%  2 2770 1108 g 158 0.14 40.0% 2 85% 3 2850 1378 152 0.11 48.4% 3 89% 3 2800 1514 g 156 0.10 54.1% 4 86% 2 2800 1396 g 147 0.11 49.9% 5 91% 2.5 2770 1506 g 150 0.10 54.4%

(104) Test number 1. Smooth surface roller

(105) Test number 2. The 67.5 decrees screw grooves are formed in the entire grinding surface in the raw material discharging direction [FIG. 1(a)]

(106) Test number 3. The main grinding surface is made smooth, and the 67.5 degrees screw grooves are formed on the other grinding surface of the raw material discharging direction [FIG. 1(b)]

(107) Test number 4. The right-angled slit grooves are formed in the entire grinding surface [FIG. 2(a)]

(108) Test number 5. The main grinding surface is made smooth, and the right-angled slit grooves are formed in the other surface [FIG. 2(b)]

(109) Table 4 shows comparison in the amount under 200 meshes and electric power consumption rate (pressure applied to the roller is constant at 23.5 kg) between different grinding surfaces in the tire convex roller (D/R=5). The tables combined with the tire convex roller are all smooth surface tables. Of the whole width of the tire convex roller of 66 mm, the width of the smooth surface as the main grinding surface was set to 23 mm (35% of the whole width).

(110) TABLE-US-00004 TABLE 4 Effective Collected amount Effective Electric power grinding Layer Supplied under 200 meshes (g) consumed consumption rate of the Test surface area thickness amount and content ratio power amount under 200 meshes number (%) (mm) (g) (%) (Wh) (Wh/g) 1 100%  1 2780 1012 g 161 0.16 36.4% 2 83% 1 2790 1136 g 146 0.13 40.7% 3 93% 1 2760 1348 g 172 0.13 48.9% 4 93% 1 2770 1236 g 162 0.13 44.6%

(111) Test number 1. Smooth surface roller

(112) Test number 2. The grooves inclined at 45 degrees in the discharging direction of the raw material are formed in the entire grinding surface [FIG. 3(a)]

(113) Test number 3. The central main grinding surface is made smooth, and grooves inclined at 45 degrees in the discharging direction are formed in the other grinding surface [FIG. 3(b)]and

(114) Test number 4. The central main grinding surface is made smooth, and grooves inclined at 45 degrees in the collecting direction are formed in the other grinding surface [FIG. 4(b)]

(115) Table 5 shows comparison in the amount under 200 meshes and electric power consumption rate (pressure applied to the roller is constant at 23.5 kg) between different grinding surfaces in the tire flat roller (D/R=4). The tables combined with the tire flat roller are all smooth surface tables.

(116) TABLE-US-00005 TABLE 5 Effective Collected amount Effective Elecrric power grinding Layer Supplied under 200 meshes (g) consumed consumption rate of the Test surface area thickness amount and content ratio power amount under 200 meshes number (%) (mm) (g) (%) (Wh) (Wh/g) 1 100%  1 2840 716 g 151 0.21 25.2% 2 81% 1 2820 618 g 145 0.28 21.9% 3 92% 1.5 2850 826 g 146 0.18 29.0%

(117) Test number 1. Smooth surface roller

(118) Test number 2. The 67.5 degrees screw grooves in the direction of collecting back the raw material are formed in the entire grinding surface [FIG. 5(a)]

(119) Test number 3. The main grinding surfaces on both the small-diameter sides are made smooth, and the 67.5 degrees screw grooves are formed in the other central grinding surface in the raw material collecting direction [FIG. 5(b)]

(120) In coal grinding, by making the main grinding surface smooth in all of the three types of rollers: the trapezoidal roller, the tire convex roller and the tire flat roller, the amount of ground fine powder under 200 meshes greatly increased. By making the main grinding surface smooth, the electric power consumption rate representing the amount of energy necessary for grinding also exhibited a minimum value. By making the main grinding surface smooth surface, even when either of the right-angled slit grooves and 45 degrees slit grooves for collecting the raw material and the 67.5 degrees screw groove having the excellent transfer property of the raw material were formed in the other grinding surface, a pronounced effect was obtained. Importantly, even in the case where the right-angled slit grooves were formed in the trapezoidal roller, the amount of ground fine powder was the almost same as the case where the 67.5 degrees screw grooves were formed.

(121) In the trapezoidal roller, a difference between the effect of the 67.5 degrees screw groove having the excellent transfer property and the effect of the right-angled slit grooves having the excellent biting property was examined. The amount of ground fine powder of the roller in which the 67.5 degrees screw grooves were formed in the raw material discharging direction increased from that of the normal trapezoidal roller having the smooth surface by about 20%. The increase of the amount of ground fine powder was due to the biting property as a secondary function and the as material transfer property as a primary function of the 67.5 degrees screw grooves. By making the main grinding surface of the roller smooth, the amount of ground fine powder increased by about 9%. That is, the main smooth surface contributed to an increase of about 9%.

(122) In the trapezoidal roller, the amount of ground fine powder of the roller in which the right-angled slit grooves in parallel to the roller shaft are formed in the entire grinding surface increased from that of the normal smooth surface roller by about 21%. The increase of the amount of ground fine powder was due to the biting property of the right-angled slit grooves. By making the main grinding surface of the roller smooth, the amount of ground fine powder increased by about 7%. That is, the main smooth surface contributed to an increase of about 7%. It is assumed that the reason for a decrease from the former case by 2% is that the right-angled slits are inferior to the screw grooves in the transfer property.

(123) As a conclusion, it turned out that, in the trapezoidal roller, even when either of the right-angled slit grooves having the excellent biting property and the 67.5 degrees screw grooves having the excellent raw material transfer property were adopted, the almost same ground amount of fine powder could be obtained. Therefore, the right-angled slit grooves having the grinding edges directly engaged with the ground raw material straightforward should be applied to grinding of the soft raw material in terms of wear. Since the 67.5 degrees screw grooves were excellent in the function of smoothly feeding the raw material to the main grinding surface, the grooves should be applied to the hard raw material or moist raw material.

(124) For grinding of adhesive limestone and coal, it was proved that the grinding surface of the vertical grinding roller should be divided into the main grinding surface and the transfer surface transferring the raw material, which had different functions. Further, it was also proved that, by making the main grinding surface smooth, wear could be reduced and the amount of ground fine powder could be increased.

(125) Although the slit grooves and the screw grooves that have the biting property and the transfer property are mainly employed in this example, as a matter of course, protruding ribs in place of these grooves can achieve the same effect. However, in the case of the convex ribs, the height of the ribs is limited to the range of 5 to 20 nm. The reason is that the ribs directly face the ground raw material and thus, is greatly worn. Accordingly, the ribs are made of a material having a high wear resistance, but when the wear resistance is too high, the ribs tend to be broken by shock of the raw material.

(126) Although the slit grooves, the screw grooves, and the convex ribs are basically continuous in the longitudinal direction, they may be intermittently formed in the longitudinal direction, and such intermittent arrangement is especially suitable for the convex ribs.

(127) By setting up a hypothesis by theoretical deduction and supporting the hypothesis in the grinding tests, the perfect shape of the grinding surface of the vertical mill roller researched by the present inventors for a long time was established.

EXPLANATION OF REFERENCE NUMERALS

(128) 10 vertical mill roller (trapezoidal roller)

(129) 11A screw groove

(130) 11B slit grooves

(131) 12 outer circumferential surface

(132) 12A main grinding surface

(133) 12B raw material transfer surface

(134) 12C raw material biting surface

(135) 20 vertical mill roller (tire convex roller)

(136) 21A, 21B screw groove

(137) 22 outer circumferential surface

(138) 22A main grinding surface

(139) 22B raw material transfer surface

(140) 30 vertical mill roller (tire flat roller)

(141) 31 screw groove

(142) 32 outer circumferential surface

(143) 32A main grinding surface

(144) 32B raw material transfer surface