JP2587478B2 - Press roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a press roll provided with a granite roll shell used in a paper machine, or a roll shell made of ceramics or glass having a small coefficient of thermal expansion. The present invention relates to a press roll such as a provided press roll.

[Conventional technology]

FIGS. 6 and 7 show press rolls used in a conventional paper machine.

1 is a roll shell made of natural granite. The press roll is assembled by a roll shell 1, a roll head 2, a center shaft 3, and a nut 4. Cement or the like is filled in a gap 6 between the roll shell 1 and the center shaft 3 so that an external force such as the own weight of the roll shell 1 or a nip pressure of a mating roll pressed against the main roll is transmitted to the center shaft 3 reliably. .

The reason why natural granite is used for the roll shell 1 of the press roll of this paper machine is that the wet paper adhering to the roll surface has good peeling properties (paper releasing property) and prevents breakage during paper making. This is because the roll itself retains its abrasion resistance and corrosion resistance.

However, the major disadvantage of rocks such as granite is that the tensile strength is extremely small compared to the compressive strength, probably because of the presence of minute defects inside (normal compressive strength = 16.62 kg / mm for granite)
² , tensile strength = 1.04 kg / mm ² ), cracks grow at high speed when exposed to water under tensile stress (10 ² to 10 ³ times faster in distilled water than in air with humidity of 40 to 60%) And there is data that a crack propagates), which means that it has stress corrosion cracking characteristics that eventually lead to severe fracture.

Therefore, in the conventional press rolls shown in FIGS. 6 and 7, in order to prevent the existence of tensile stress, the roll heads 2 attached to both sides of the center shaft 1 require 0.14 kg in an assembled state of the press rolls. The roll shell 1 is assembled by applying an axial compressive stress of / mm ² or more to the roll shell 1. (See U.S. Pat. No. 3,737,962). As a result, the roll shell 1 is always protected against bending stress due to nip pressure and the like.
The internal stress has been maintained within the compressive stress to prevent destruction.

[Problems to be solved by the invention]

However, the temperature of felts and wet paper webs recently increased to improve the dewatering efficiency of paper machines (for example, from 40 ° C to 65 ° C)
The serious destruction of the press roll accompanying it has occurred considerably all over the world. The following can be considered as causes of this destruction.

(1) Center shaft thermal expansion coefficient α ₁ (Steel 11
× 10 ^-6 ℃ ^-1 ) is larger than that of granite α ₂ (= 7 × 10 ^-6 ℃ ^-1 ), so that the compressive stress of the roll shell decreases or becomes zero due to temperature rise, and tensile stress is generated. The danger of destruction due to damage is significantly increased.

(2) When the feeding and heating of the raw material are stopped, the roll shell is cooled by the washing water. At this time, biaxial tensile stress substantially equal to the axial direction and circumferential direction of the roll shell is generated on the outer surface of the roll shell. In the axial direction, a compressive stress is added in advance as described above, and the tensile stress in the axial direction is offset by this compressive stress, but since such a pre-compressive stress is not added in the circumferential direction, A large tensile stress occurs in the circumferential direction. However, since the temperature of the washing water was not changed, as the roll temperature increased,
The tensile stress in the circumferential direction increases to promote fracture.

(3) A cement or the like having high rigidity is often filled in the gap 6 in FIGS. 6 and 7. In this case, when the temperature of the roll increases, the thermal expansion of the center shaft is larger than that of the granite. Due to the large size, an internal pressure is generated in the granite, and a tensile thermal stress is generated in the roll shell which causes the fracture.

Note that the above-mentioned phenomena (1) to (3) occur because the center shaft 3 is heated to almost the same temperature as the roll shell 1 because there is no cooling portion on the center shaft side of the roll.

As described above, the possibility of breakage when a tensile stress is generated in the granite roll shell 1 is large.
There is no data to prove whether this fracture originated on the center shaft side of the granite or on the outer surface in contact with the wet paper, but it is estimated that the outer surface is likely to be large based on the stress corrosion cracking characteristics of the rock in water Is done.

An object of the present invention is to solve the above-mentioned problems in a press roll having a roll shell made of a nonmetallic material having a smaller coefficient of thermal expansion than a center shaft such as granite.

[Means for solving the problem]

In the press roll of the present invention, a metal center shaft penetrates, and a pair of roll heads attached to both sides of the metal center shaft applies an axial compressive force, and has a thermal expansion coefficient higher than that of the metal center shaft. A small non-metallic roll shell was provided, and cooling means was provided inside the non-metallic roll shell.

[Action]

In the present invention, the cooling means is provided inside the non-metallic roll shell which is given a compressive stress in the axial direction and has a smaller coefficient of thermal expansion than the metal center shaft, and can exert the following effects.

(1) Since the center shaft is not thermally expanded by the cooling means, the axial compression stress of the roll shell is not reduced, and the generation of thermal stress in the circumferential direction due to the internal pressure of the roll shell is prevented.

(2) By providing a temperature distribution in which the temperature rises from the inside to the outside in the radial direction of the roll shell by the cooling means, the circumferential surface and the axial direction are formed on the outer surface of the roll shell.
The compressive stress of the shaft can be applied, and the tensile stress during rapid cooling of the outer surface of the roll shell due to washing water or the like can be reduced.

〔Example〕

A first embodiment as a press roll of the paper machine of the present invention will be described with reference to FIGS. 1 and 2. FIG.

Reference numeral 1 denotes a roll shell main body, which is made of a single piece of granite in terms of paper separation, abrasion resistance, and corrosion resistance. Reference numeral 2 denotes a metal roll head (material is SC46), and reference numeral 3 denotes a center shaft, in the center of which is provided a cooling hole 7 penetrating the center shaft through which water such as a cooling medium passes. The material of the center shaft 3 is 13Cr steel in consideration of corrosion resistance to water and the like. The roll shell 1 is supported so as to be sandwiched by a pair of roll heads 2 attached to both ends of a center shaft 3. The roll head 2 is tightened by a nut 4 after being inserted into the center shaft 3.
If the center shaft 3 has a large diameter and it is difficult to mechanically tighten the nut 4, the center shaft 3 is heated to 100 to 150 ° C. before the center shaft 3 is inserted into the roll shell 1 and the roll head 2. The nut 4 may be tightened while the center shaft 3 is extended, and the roll head 2 may be pressed against the roll shell 1 by cooling and shrinking the center shaft 3. As a result, a predetermined axial compressive stress is applied to the roll shell 1. After assembling the roll shell 1, the roll head 2 and the center shaft 3, cement is filled in a gap 6 between the roll shell 1 and the center shaft 3, and a force is transmitted from the roll shell 1 to the center shaft 3. Reference numeral 5 denotes a bearing for supporting the roll at both ends. Although not shown in FIGS. 1 and 2, a rotary joint is attached to both ends of the center shaft 3, and cooling water is introduced from outside via a rotary joint on one side to form a cooling hole 7. Then, it is discharged from the opposite side to cool the center shaft 3 and the inner surface of the roll shell 1. Since the purpose of cooling is to prevent the temperature of the center shaft and the inner surface of the roll shell from rising and not to remove the heat through the roll shell to cool the outer surface of the roll shell, the cooling water amount may be small. Further, if the temperature of the cooling water is lowered more than necessary, an extra high stress is generated in the roll shell.

The dimensions of this roll are, for example, 9
m, shell outer diameter 1220mmφ, shell inner diameter 360mmφ, center shaft outer diameter 250mmφ, cooling hole diameter 70mmφ.

The present embodiment is configured as described above. The compressive stress in the axial direction is given to the roll shell 1 made of granite by the center shaft 3 and the roll head 2, and even if bending stress due to nip pressure or the like is generated. The stress in the roll shell 1 is maintained within the compressive stress, thereby preventing the roll shell 1 from breaking.

Further, since the center shaft 3 is cooled by the cooling water flowing through the cooling holes 7, the temperature of the center shaft 3 having a large thermal expansion coefficient does not increase even when the temperature of the roll increases during the operation of the press roll. Therefore, even if the roll temperature rises, the above-mentioned compressive stress does not decrease, and an internal pressure is generated in the roll shell 1 due to the expansion of the center shaft, and the circumferential tension of the roll shell causing the roll shell breakage is pulled. No thermal stress is generated.

In addition, while the roll temperature rises during the operation of the roll, the temperature of the center shaft 3 does not rise, and the roll shell 1 has a temperature gradient in which the temperature rises from the inside to the outside in the radial direction. A biaxial compressive stress in the circumferential direction and the axial direction is applied to the outer surface of No. 1. Therefore, even when the outer surface of the roll shell 1 is rapidly cooled by the washing water or the like when the raw material is stopped or the heating is stopped, the biaxial shaft formed by the cooling of the outer surface of the roll shell 1 is cooled by the pre-applied compressive stress. Tensile stress can be reduced.

Furthermore, since the cooling water flows through the cooling holes 7 in the center shaft 3 and does not contact the granite roll shell 1, rapid growth of cracks under tensile stress can be avoided.

Further, when the roll is assembled, the center shaft 3 can be expanded by flowing the heating medium through the cooling holes 7 in the center shaft 3, thereby facilitating the assembly and improving the setting accuracy of the compressive stress. Can be.

A second embodiment of the present invention will be described with reference to FIGS.

The difference between this embodiment and the first embodiment is that the cooling holes formed in the center shaft 3 are different. In the case of the first embodiment, as described above, for example, the outer diameter of the center shaft is 250 mmφ, and the diameter of the center cooling hole is 70 mm.
φ, length (roll shell length) 9 m. As in this case, 70mm in the center of the long center shaft, 36 times the diameter
Drilling the φ cooling hole straight is an extremely difficult task. For this reason, it is necessary to adopt a method of performing forging and elongation with a hole at the stage of the steel ingot, and to modify the hole by machining, etc., but this processing requires time, Increases costs.

Therefore, the following configuration is employed in this embodiment. That is, a plurality of cooling passages 8 provided in the axial direction on the outer peripheral portion of the center shaft 3 except for both ends of the center shaft 3, the two cooling passages 8 being connected to both ends of the cooling passage 8 and not being applied with the force of the center shaft 3. An annular portion 8 "provided on the outer periphery of the portion in the circumferential direction, a hole 9 drilled at the center of the center shaft 3 from both ends of the center shaft 3 to a portion where the annular portion 8" is located, and the annular portion 8 " Holes 8 ′ are provided at four places on the center shaft 8 so as to connect the holes 9 with the holes 9 ′.

In this embodiment having the above configuration, the cooling passage and the like are formed as follows, for example.

(1) A plurality of grooves are formed in an axial direction on the outer peripheral portion of the center shaft 3 excluding portions where no force is applied at both ends of the center shaft 3, and portions of the both ends of the center shaft 3 where no force is applied are formed. An annular groove is formed by connecting to both ends of the groove in the circumferential direction.

(2) A hole 9 is formed in the center of the center shaft 3 from both ends of the center shaft 3 to a portion where the annular groove is present.

(3) Holes 8 'for connecting the annular groove and the hole 9 are formed at four locations in the radial direction on the bottom of the circular annular groove.

(4) A plurality of axial cooling passages 8 are formed to cover the plurality of grooves.

(5) An annular portion 8 "is formed at a portion where both ends of the center shaft 3 are not subjected to the force so as to cover the annular groove.

In this embodiment, the cooling water flows through the center shaft 1 through the cooling passage 8 through the hole 9 on one side, the hole 8 ', and the annular portion 8 ", and is discharged from the hole 9 on the other side. This cools the shaft 1. Therefore, this embodiment can provide the same operation and effect as those of the first embodiment.

In the first embodiment of the present invention, as described above, a thin cooling hole is made straight in the center of the long center shaft, which is extremely difficult work. As described in (5), the cooling passage and the like can be formed at low cost by simple machining.

In the case of the present embodiment shown in FIGS. 3 to 5, the dimensions and number of the cooling passages provided on the outer peripheral portion of the center shaft are as follows.
20mm width x 20mm height x 8 pieces.

In the first and second embodiments, as the cooling means, a cooling hole is formed in the center shaft so that the cooling water flows. However, as described below, the cooling means is provided inside the roll shell. May be provided.

(1) The structure is the same as in the first and second embodiments,
Oil or air other than water is used as the cooling medium.

(2) A heat pipe is incorporated in the center shaft, and heat exchange sections are provided at both ends of the center shaft to cool the center shaft.

(3) A cooling medium that does not have stress corrosion cracking characteristics for granite such as air or oil is used, and a passage is formed in a portion of cement between the roll shell and the center shaft for cooling.

In addition, the above embodiment relates to a press roll of a paper machine having a roll shell of granite, but the present invention can be applied to various presses having a roll shell having a low expansion coefficient such as ceramics and glass. .

〔The invention's effect〕

 The present invention has the following effects.

(1) Since there is no elongation of the center shaft, there is no decrease in the axial compressive stress applied to the roll shell by the center shaft and the roll head.

(2) Since the center shaft does not expand, no tensile stress is generated in the roll shell due to the internal pressure.

(3) The thermal stress of tension due to quenching of washing water or the like is proportional to the temperature of the outer surface of the roll shell before quenching, but a compressive stress that offsets this stress can be applied to the roll shell by cooling the inside of the roll. .

(4) Since the heat resistance limit of the roll is raised by the above,
The performance of the press roll can be improved.

[Brief description of the drawings]

1 is a longitudinal sectional view of a first embodiment of the present invention, FIG. 2 is a sectional view taken along line AA of FIG. 1, and FIG. 3 is a longitudinal sectional view of a second embodiment of the present invention. 4 and 5 are respectively BB line and C- line in FIG.
FIG. 6 is a longitudinal sectional view of a press roll of the conventional paper machine, and FIG. 7 is a sectional view along the line FF of FIG. 1 roll shell, 2 roll head, 3 center shaft, 4 nut, 6 gap, 7 cooling hole, 8 cooling passage, 8 ', 9 hole

Claims (1)

(57) [Claims] A metal center shaft has a lower thermal expansion coefficient than a metal center shaft through which a compression force in the axial direction is applied by a pair of roll heads attached to both ends of the metal center shaft. A press roll comprising a small non-metallic roll shell and cooling means provided inside the non-metallic roll shell.