Rolling device

Abstract

A rolling device (1) is provided with: a pair of rolls (10) that face each other and roll a powder (A) supplied to a space (E) between the rolls; and a change mechanism (100) that changes an angle-of-bite (φ) between the rolls (10) and the powder (A).

Description

Rolling equipment

[0001] The present disclosure relates to a rolling mill.

[0002] For example, a rolling mill for rolling powder is known, as disclosed in Patent Document 1. This type of rolling mill includes a pair of rolls facing each other. The pair of rolls rolls powder supplied between the rolls.

[0003] Japanese Patent Application Publication No. 11-158510

[0004] The rolling mill rolls powder with a pair of rolls to obtain a plate-shaped rolled material. The thickness of the rolled material is largely determined by the outer diameter of the rolls. If the outer diameter of the rolls is small, the thickness of the rolled material will be small, and if the outer diameter of the rolls is large, the thickness of the rolled material will be large.

[0005] To roll a material to a desired thickness, it is sufficient to select a roll with a corresponding outer diameter. However, changing rolls every time the desired thickness of the material is required is cumbersome, costly, and unrealistic.

[0006] To address this issue, it is possible to change the rolling force applied to the powder by the rolls or to change the distance between the pair of rolls. However, the former method changes the density of the resulting rolled material. Alternatively, if the resulting rolled material is porous, the porosity of the rolled material changes. The latter method may cause the powder to slip through the gap between the pair of rolls, resulting in poor rolling.

[0007] An object of the present disclosure is to change the thickness of a rolled material without changing the density or porosity of the rolled material as much as possible in a rolling device that rolls powder to obtain the rolled material.

[0008] The rolling device according to the present disclosure includes a pair of rolls that face each other and roll powder that is supplied between the rolls, and a change mechanism that changes the angle of engagement between the rolls and the powder.

[0009] According to the present disclosure, in a rolling device that rolls powder to obtain a rolled material, the thickness of the rolled material can be changed while minimizing changes in the density or porosity of the rolled material.

[0010] FIG. 1 shows a front cross-sectional view of a rolling apparatus according to a first embodiment. FIG. 2 shows a plan cross-sectional view of the rolling apparatus according to the first embodiment. FIG. 3 schematically shows the bite angle between the roll and the powder. FIG. 4 shows a front cross-sectional view of a rolling apparatus according to a second embodiment. FIG. 5 shows a front cross-sectional view of a rolling apparatus according to a third embodiment. FIG. 6 shows a front cross-sectional view of a rolling apparatus according to a fourth embodiment. FIG. 7 shows the thickness of a rolled material according to an example. FIG. 8 shows the porosity of a rolled material according to an example.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0012] <First embodiment> (Rolling mill) A rolling mill 1 according to a first embodiment will be described. In the following description, the direction perpendicular to the plane of the paper in Fig. 1 will be referred to as the front-rear direction, the left-right direction in Fig. 1 as the left-right direction, and the up-down direction in Fig. 1 as the up-down direction. Fig. 1 shows the rolling mill 1 in a front cross-sectional view taken along line I. Fig. 2 shows the rolling mill 1 in a plan cross-sectional view taken along line II.

[0013] The rolling mill 1 rolls a continuously supplied powder A to obtain a rolled material B. The powder A is, for example, a resin powder or a metal powder.

[0014] The rolling apparatus 1 includes a pair of rolls 10, a hopper 20, a coating mechanism 30, a wiping mechanism 40, a scraper 2, and a receiver 3. The coating mechanism 30 and the wiping mechanism 40 constitute a change mechanism 100, which will be described later. In other words, the rolling apparatus 1 includes the change mechanism 100. The change mechanism 100 includes the coating mechanism 30 and the wiping mechanism 40.

[0015] The pair of rolls 10 are work rolls. The rolls 10 are cylindrical. The rolls 10 extend in the front-rear direction. When the rolling mill 1 is in operation, the pair of rolls 10 face each other in the left-right direction with a roll gap E therebetween. When the rolling mill 1 is in operation, the roll gap E is the gap between the pair of rolls 10. When the rolling mill 1 is initially set up, the roll gap E may be the contact area between the pair of rolls 10.

[0016] The left roll 10 rotates clockwise. The right roll 10 rotates counterclockwise. The rotation direction F of the rolls 10 is from top to bottom on the side between the rolls E.

[0017] The roll 10 is composed of a large-diameter barrel portion 11 constituting the middle portion, and small-diameter shaft portions 12 constituting both end portions. The barrel portion 11 rolls the powder A. The shaft portions 12 are supported by bearings 4 fixed to a housing (not shown).

[0018] Powder A is continuously supplied from above to below between the pair of rolls 10. The pair of rolls 10 rolls the powder A continuously supplied between the rolls E. When the powder A is rolled between the rolls E, a rolled material B is obtained. The rolled material B is transferred downward from the rolls E.

[0019] The hopper 20 is disposed directly above the gap E between the pair of rolls 10. The hopper 20 is a container. A large-diameter inlet is provided at the top of the hopper 20. A small-diameter outlet is provided at the bottom of the hopper 20. Powder A is fed into the hopper 20 from outside the hopper 20 through the inlet. Powder A is discharged from inside the hopper 20 to outside the hopper 20 through the outlet.

[0020] Powder A is stored in the hopper 20. The powder A is piled up in the hopper 20. The hopper 20 continuously supplies the powder A to a gap E between the pair of rolls 10.

[0021] There are two coating mechanisms 30. The coating mechanisms 30 are arranged on the left and right outer sides and below the roll 10. The coating mechanisms 30 extend in the front-rear direction along the roll 10. The coating mechanisms 30 are arranged upstream F1 of a gap E between the rolls in the rotation direction F of the roll 10.

[0022] The coating mechanism 30 is a nozzle. The coating mechanism 30 ejects liquid C toward the roll 10. The liquid C is, for example, water or an organic solvent. The coating mechanism 30 applies liquid C to the roll 10 on the upstream side F1 of a gap E between the rolls in the rotation direction F of the roll 10. The coating mechanism 30 imparts wettability to the roll 10.

[0023] There are two wiping mechanisms 40. The wiping mechanisms 40 are arranged on the outer left and right sides and above the roll 10. The wiping mechanisms 40 extend in the front-rear direction along the roll 10. The wiping mechanisms 40 are arranged upstream F1 of a gap E between the rolls in the rotation direction F of the roll 10 and downstream F2 of the coating mechanism 30.

[0024] The wiping mechanism 40 includes an endless belt 41, a pulley 42, and a heater 43. The endless belt 41 has no ends. When viewed in the front-to-rear direction, the endless belt 41 has an elliptical shape that extends obliquely relative to the left-to-right and up-to-down directions. The endless belt 41 is made of a highly absorbent material, such as cloth or sponge. The endless belt 41 is preferably made of a dust-free material that does not generate dust. The endless belt 41 contacts the roll 10. The endless belt 41 wipes the liquid C applied to the roll 10 by the application mechanism 30 from the roll 10. At this time, the liquid C is transferred from the roll 10 to the endless belt 41 and adheres to the endless belt 41.

[0025] There are two pulleys 42. The pulleys 42 are cylindrical. The pulleys 42 extend in the front-rear direction. The two pulleys 42 are arranged diagonally next to each other in the left-right and up-down directions. The pulleys 42 rotate the endless belt 41. The pulleys 42 are driven by a motor (not shown).

[0026] The heater 43 is disposed outside and above the endless belt 41 and the pulley 42 on the left and right sides. The endless belt 41 and the pulley 42 are disposed between the heater 43 and the roll 10. The heater 43 heats the endless belt 41. The heater 43 dries the endless belt 41. The heater 43 removes the liquid C from the endless belt 41 that has adhered to the endless belt 41 when it comes into contact with the roll 10.

[0027] In summary, the wiping mechanism 40 (endless belt 41, pulley 42, heater 43) wipes the liquid C from the roll 10 upstream F1 of the gap E between the rolls in the rotation direction F of the roll 10 and downstream F2 of the application mechanism 30.

[0028] There are two scrapers 2. The scrapers 2 are disposed below the rolls 10. The scrapers 2 extend in the front-to-rear direction along the rolls 10. The scrapers 2 are disposed downstream F2 of a gap E between the rolls in the rotation direction F of the rolls 10 and upstream F1 of the coating mechanism 30.

[0029] The scraper 2 comes into contact with the roll 10. The scraper 2 removes the powder A adhering to the roll 10 after rolling between the rolls E. The scraper 2 removes the liquid C remaining on the roll 10 before the coating mechanism 30, thereby initializing the wettability of the roll 10.

[0030] There are two receivers 3. The receivers 3 are disposed below the scraper 2. The receivers 3 extend in the front-to-rear direction along the roll 10. The receivers 3 receive the powder A and liquid C removed from the roll 10 by the scraper 2.

[0031] (Meaning Angle) Figure 3 shows a schematic diagram of the angle of meshing φ between the roll 10 and the powder A. The length of the part of the roll 10 that is in contact with the powder A is called the contact arc length L. The angle of meshing φ is the angle formed when connecting the center O of the roll 10 with both ends of the contact arc length L. The angle of meshing φ is also called the contact angle. The smaller the angle of meshing φ, the smaller the contact arc length L. The larger the angle of meshing φ, the larger the contact arc length L.

[0032] The bite angle φ is related to the thickness T (film thickness) of the resulting rolled material B, and is largely determined by the outer diameter D of the roll 10. If the outer diameter D of the roll 10 is small, the bite angle φ becomes small, the pressure (force per unit area) applied by the roll 10 to the powder A becomes large, and the thickness T of the resulting rolled material B becomes small. Conversely, if the outer diameter D of the roll 10 is large, the bite angle φ becomes large, the pressure (force per unit area) applied by the roll 10 to the powder A becomes small, and the thickness T of the resulting rolled material B becomes large.

[0033] In order to obtain a rolled material B with a desired thickness T, it is sufficient to select a roll 10 with a corresponding outer diameter D. However, replacing the roll 10 every time according to the desired thickness T of the rolled material B is cumbersome, costly, and not practical.

[0034] Therefore, it is conceivable to change the rolling force (pressure x area) applied to the powder A by the rolls 10 or to change the dimension of the gap E between the pair of rolls 10. However, the former method changes the density of the obtained rolled material B. Alternatively, if the obtained rolled material B is porous, the porosity (void fraction) of the rolled material B changes. The latter method may cause the powder A to slip through the gap E between the pair of rolls 10 and not be rolled properly.

[0035] In response to the above problem, the inventors of the present application came up with the idea of ​​changing the thickness T of the rolled material B by changing the engagement angle φ between the roll 10 and the powder A using the change mechanism 100 described below.

[0036] As described above, the application mechanism 30 and the wiping mechanism 40 constitute the change mechanism 100. The change mechanism 100 (the application mechanism 30 and the wiping mechanism 40) changes the meshing angle φ between the roll 10 and the powder A. The change mechanism 100 (the application mechanism 30 and the wiping mechanism 40) changes the contact arc length L between the roll 10 and the powder A.

[0037] The coating mechanism 30 applies the liquid C to the roll 10, thereby imparting wettability to the roll 10. The powder A becomes more likely to adhere to the roll 10 due to the liquid bridging effect, etc. The powder A becomes less likely to slide off the roll 10.

[0038] Increasing the amount of liquid C applied to the roll 10 by the application mechanism 30 increases the meshing angle φ between the roll 10 and the powder A. When the meshing angle φ increases, the pressure (force per unit area) applied to the powder A by the roll 10 decreases, and the thickness T of the resulting rolled material B increases.

[0039] Conversely, when the amount of liquid C applied to the roll 10 by the application mechanism 30 is reduced, the meshing angle φ between the roll 10 and the powder A is reduced. When the meshing angle φ is reduced, the pressure (force per unit area) applied to the powder A by the roll 10 is increased, and the thickness T of the obtained rolled material B is reduced.

[0040] By adjusting the amount of liquid C applied by the application mechanism 30, the bite angle φ can be adjusted.

[0041] When the wiping mechanism 40 wipes the liquid C from the roll 10, the meshing angle φ between the roll 10 and the powder A changes. Increasing the amount of liquid C wiped off by the wiping mechanism 40 reduces the meshing angle φ. Decreasing the amount of liquid C wiped off by the wiping mechanism 40 increases the meshing angle φ. The meshing angle φ can be adjusted by adjusting the amount of liquid C wiped off by the wiping mechanism 40.

[0042] To adjust the amount of liquid C wiped by the wiping mechanism 40, the contact pressure of the endless belt 41 against the roll 10 can be changed, the dryness of the endless belt 41 can be changed by changing the temperature of the heater 43, or the rotation speed of the endless belt 41 by the pulley 42 can be changed.

[0043] The bite angle φ must generally satisfy the following condition, where μ is the coefficient of friction between the roll 10 and the powder A: tan φ<μ.

[0044] When the change mechanism 100 changes the bite angle φ, the rolling force (pressure x area) applied to the powder A by the roll 10 changes slightly, but the effect of this rolling force (pressure x area) on the density and porosity of the rolled material B changes very little. Therefore, the density of the obtained rolled material B changes very little. If the obtained rolled material B is porous, the porosity of the rolled material B changes very little.

[0045] Even if the change mechanism 100 changes the bite angle φ, it does not change the dimension of the gap E between the pair of rolls 10. It is unlikely that the powder A will slip through the gap E between the pair of rolls 10.

[0046] (Effects) The rolling device 1 can arbitrarily change the bite angle φ between the roll 10 and the powder A by the change mechanism 100. By changing the bite angle φ between the roll 10 and the powder A, the thickness T of the resulting rolled material B can be changed.

[0047] When the change mechanism 100 changes the bite angle φ, the rolling force (pressure x area) applied to the powder A by the roll 10 changes slightly, but the effect of this rolling force (pressure x area) on the density and porosity of the rolled material B changes very little. Therefore, the density of the obtained rolled material B changes very little. If the obtained rolled material B is porous, the porosity of the rolled material B changes very little.

[0048] As described above, in the rolling mill 1 that rolls the powder A to obtain the rolled material B, the thickness T of the rolled material B can be changed while changing the density or porosity of the rolled material B as little as possible.

[0049] After the application mechanism 30 applies the liquid C to the roll 10, the wiping mechanism 40 wipes the liquid C from the roll 10. The amount of liquid C on the roll 10 is adjusted. The portion of the roll 10 where the amount of liquid C has been adjusted then enters between the rolls E and comes into contact with the powder A. By adjusting the amount of liquid C on the roll 10, the meshing angle φ between the roll 10 and the powder A can be adjusted.

[0050] For example, the amount of liquid C wiped off by the wiping mechanism 40 can be easily adjusted by changing the contact pressure of the endless belt 41 against the roll 10, changing the temperature of the heater 43 to change the dryness of the endless belt 41, or changing the rotation speed of the endless belt 41 by the pulley 42.

[0051] Second Embodiment A rolling mill 1 according to a second embodiment will be described. In the following description, the same components as those in the above embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted. Figure 4 shows a front cross-sectional view of the rolling mill 1.

[0052] The rolling device 1 includes a humidifying mechanism 50, a cooling mechanism 60, and a case 5. The humidifying mechanism 50 and the cooling mechanism 60 constitute a change mechanism 100. In other words, the change mechanism 100 includes the humidifying mechanism 50 and the cooling mechanism 60. The change mechanism 100 may further include a wiping mechanism 40. The humidifying mechanism 50 replaces the application mechanism 30.

[0053] The case 5 is box-shaped and houses a pair of rolls 10, a humidifying mechanism 50, a cooling mechanism 60, and a scraper 2. The hopper 20 and the wiping mechanism 40 pass through the upper wall of the case 5. The rolled material B passes through the lower wall of the case 5 and is transported downward.

[0054] There are two humidifying mechanisms 50. The humidifying mechanisms 50 are arranged on the left and right outer sides of the roll 10. The humidifying mechanisms 50 are nozzles. The humidifying mechanisms 50 humidify the air G around the roll 10 by discharging the liquid C. More specifically, the humidifying mechanisms 50 humidify the air G in the case 5 by discharging the liquid C.

[0055] A cooling passage 13 is provided inside the roll 10. The cooling passage 13 is annular when viewed in the front-rear direction. The cooling passage 13 extends in the front-rear direction. A cooling liquid M flows through the cooling passage 13. The cooling mechanism 60 is configured so that the cooling liquid M flows through the cooling passage 13 provided in the roll 10. The cooling mechanism 60 cools the roll 10.

[0056] The cooling liquid M in the cooling passage 13 and the air G (containing the liquid C) around the roll 10 exchange heat with each other. The air G (containing the liquid C) is cooled. The liquid C condenses on the roll 10. Conversely, the cooling liquid M is heated. The cooling liquid M is cooled by a cooling liquid cooler (not shown).

[0057] The wiping mechanism 40 wipes off the liquid C condensed on the roll 10 .

[0058] When the liquid C condenses on the roll 10, the meshing angle φ between the roll 10 and the powder A changes.

[0059] The amount of condensation of liquid C on the roll 10 can be adjusted by changing the amount of liquid C released by the humidifying mechanism 50, by changing the flow rate or temperature of the cooling liquid M in the cooling passage 13, or by changing the amount of liquid C wiped off by the wiping mechanism 40.

[0060] The other configurations are the same as those of the first embodiment.

[0061] The humidifying mechanism 50 and the cooling mechanism 60 can change the bite angle φ by condensing the liquid C on the roll 10 .

[0062] By accommodating the roll 10 in the case 5, it becomes easier to control the humidity of the air G around the roll 10 in the case 5.

[0063] The cooling mechanism 60 can be easily configured by providing the cooling passage 13 through which the cooling liquid M flows in the roll 10.

[0064] Third Embodiment A rolling mill 1 according to a third embodiment will be described. In the following description, the same components as those in the above-described embodiments will be denoted by the same reference numerals, and detailed description thereof will be omitted. Figure 5 shows a front cross-sectional view of the rolling mill 1.

[0065] The rolling device 1 includes a heating mechanism 70. The heating mechanism 70 constitutes the change mechanism 100. In other words, the change mechanism 100 includes the heating mechanism 70. The application mechanism 30, the wiping mechanism 40, the humidification mechanism 50, and the cooling mechanism 60 do not exist.

[0066] There are two heating mechanisms 70. The heating mechanisms 70 extend in the front-rear direction along the roll 10. The heating mechanisms 70 are arranged on the left and right outer sides of the roll 10. The heating mechanisms 70 are known heaters. The heating mechanisms 70 heat the roll 10. The amount of heat provided by the heating mechanisms 70 can be adjusted as appropriate.

[0067] Heating the roll 10 by the heating mechanism 70 changes the coefficient of friction of the roll 10. When the coefficient of friction of the roll 10 changes, the angle of engagement φ between the roll 10 and the powder A changes.

[0068] The other configurations are the same as those of the above embodiment.

[0069] The heating mechanism 70 heats the roll 10 to change the coefficient of friction of the roll 10, thereby changing the angle of engagement φ between the roll 10 and the powder A.

[0070] <Fourth embodiment> A rolling mill 1 according to a fourth embodiment will be described. In the following description, the same components as those in the above-described embodiments will be denoted by the same reference numerals, and detailed description thereof will be omitted. Figure 6 shows a front cross-sectional view of the rolling mill 1.

[0071] The rolling device 1 includes a hopper 20 and a pressurizing mechanism 80. The pressurizing mechanism 80 constitutes a change mechanism 100. In other words, the change mechanism 100 includes the pressurizing mechanism 80.

[0072] Powder A is stored in the hopper 20. The hopper 20 continuously supplies the powder A to a gap E between the pair of rolls 10.

[0073] The pressurizing mechanism 80 pressurizes the powder A stored in the hopper 20. Specifically, the pressurizing mechanism 80 supplies a gas J (e.g., air or an inert gas) into the hopper 20. The pressure of the powder A stored in the hopper 20 increases.

[0074] When the powder A is pressurized by the pressurizing mechanism 80, the normal force that the powder A exerts perpendicularly to the curved surface of the roll 10 between the rolls E increases. This increases the frictional force (normal force x friction coefficient) between the powder A and the roll 10. The energy required for the powder A to slide on the roll 10 increases, and the bite angle φ increases.

[0075] By changing the amount of pressure applied by the pressure mechanism 80, the frictional force between the powder A and the roll 10 can be adjusted.

[0076] Furthermore, by heating the roll 10 with the heating mechanism 70, the friction coefficient of the roll 10 can be changed, thereby adjusting the frictional force between the powder A and the roll 10.

[0077] The other configurations are the same as those of the above embodiment.

[0078] The pressure mechanism 80 applies pressure to the powder A stored in the hopper 20, thereby changing the frictional force between the powder A and the roll 10, thereby changing the engagement angle φ between the roll 10 and the powder A.

[0079] <Other Embodiments> Although the present disclosure has been described above with reference to preferred embodiments, these descriptions are not limiting and, of course, various modifications, substitutions, and combinations are possible.

[0080] The wiping mechanism 40 may simply be a pad that contacts the roll 10 .

[0081] The cooling mechanism 60 may externally cool the roll 10. The cooling mechanism 60 may be, for example, a known cooler such as a Peltier element.

[0082] The heating mechanism 70 may heat the roll 10 from the inside, for example, by hot water flowing through a heating passage provided inside the roll 10 .

[0083] The number and positions of each component are not limited to those described above.

[0084] Powder A may have any composition.

[0085] The present disclosure is applicable to rolling devices and is therefore extremely useful and has high industrial applicability.

[0086] Fig. 7 shows the thickness T of the rolled material B according to the example. Fig. 8 shows the porosity of the rolled material B according to the example. In Fig. 7, the horizontal axis indicates the measurement position [m] in the length direction of the rolled material B, and the vertical axis indicates the thickness T [μm] of the rolled material B. In Fig. 8, the horizontal axis indicates the measurement position [m] in the length direction of the rolled material B, and the vertical axis indicates the porosity [%] of the rolled material B. The length direction is the feed direction, which is the up-and-down direction in this example.

[0087] The measurement positions of the rolled material B where the numerical value is smaller are downstream (lower) in the feed direction of the rolled material B, and where the numerical value is larger are upstream (upper) in the feed direction of the rolled material B. In other words, the measurement positions where the numerical value is smaller are locations that were rolled earlier, and the measurement positions where the numerical value is larger are locations that were rolled later.

[0088] A rolling mill 1 according to the second embodiment was prepared. However, the rolling mill 1 does not include the change mechanism 100 (the humidifying mechanism 50 and the cooling mechanism 60).

[0089] The outer diameter D of the roll 10 was 60 mm. The width of the resulting rolled material B was 120 mm. The rolling force was 1 tonf. The production speed (feed rate) of the rolled material B was 1 m / min.

[0090] As an initial condition, the humidity inside the case 5 was set to 100%. As an initial condition, the temperature inside the case 5 and the surface temperature of the roll 10 were set to 25°C.

[0091] For the rolled material B obtained by rolling the powder A, the thickness T [μm] and porosity [%] measured every 1 m in the length direction were plotted.

[0092] Immediately after the start of rolling, the humidity inside the case 5 is 100%, so that a sufficient amount of liquid C is applied to the roll 10. Therefore, immediately after the start of rolling, the bite angle φ is sufficiently large, and the thickness T of the rolled material B is a large value of about 200 μm.

[0093] However, since there is no change mechanism 100 (humidifying mechanism 50 and cooling mechanism 60), no new condensation of liquid C occurs on the roll 10. Therefore, after a while has passed since the start of rolling, the amount of liquid C remaining on the roll 10 decreases, the bite angle φ decreases, and the thickness T of the rolled material B decreases to 120 μm.

[0094] On the other hand, the porosity of the rolled material B remains almost unchanged at about 65% to 68%.

[0095] The above facts suggest that the amount of liquid C remaining on the roll 10 affects the bite angle φ and, in turn, the thickness T of the rolled material B. The above facts also suggest that the amount of liquid C remaining on the roll 10 has almost no effect on the porosity of the rolled material B.

[0096] REFERENCE SIGNS LIST 1 Rolling device 2 Scraper 3 Receiver 4 Bearing 5 Case 10 Roll 11 Body 12 Shaft 13 Cooling passage 20 Hopper 30 Coating mechanism 40 Wiping mechanism 41 Endless belt 42 Pulley 43 Heater 50 Moisturizing mechanism 60 Cooling mechanism 70 Heating mechanism 80 Pressurizing mechanism 100 Change mechanism A Powder B Rolled material C Liquid D Outer diameter E Roll gap F Rotation direction F1 Upstream side F2 Downstream side O Center T Thickness φ Insertion angle L Contact arc length G Air M Cooling liquid J Gas

Claims

1. A rolling device comprising: a pair of rolls that face each other and roll powder fed between the rolls; and a change mechanism that changes the angle of engagement between the rolls and the powder.

2. A rolling apparatus according to claim 1, wherein the change mechanism comprises: an application mechanism that applies a liquid to the roll; and a wiping mechanism that wipes the liquid from the roll.

3. The rolling apparatus according to claim 2, wherein the wiping mechanism includes an endless belt that contacts the roll, a pulley that rotates the endless belt, and a heater that heats the endless belt.

4. A rolling apparatus according to claim 1, wherein the change mechanism comprises: a humidifying mechanism for humidifying the air around the roll; and a cooling mechanism for cooling the roll.

5. The rolling apparatus according to claim 4, wherein the humidifying mechanism humidifies the air within a case that houses the roll.

6. A rolling mill according to claim 4 or 5, wherein the cooling mechanism is configured so that a cooling liquid flows through cooling passages provided in the rolls.

7. The rolling apparatus according to claim 1, wherein the change mechanism has a heating mechanism for heating the roll.

8. A rolling apparatus according to claim 1, further comprising a hopper in which the powder is stored and which supplies the powder between the rolls, and the changing mechanism has a pressurizing mechanism which pressurizes the powder stored in the hopper.

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