JPH0460685B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a sieving device for papermaking raw materials. (Prior art) The pressure-type slit screen, which is conventionally well known as a sifting device for papermaking raw materials, is
As shown in the drawings and FIG. 27, a screen cylinder 1 (FIG. 29) having elongated slit-like holes is provided. The paper stock sent by the pump flows into the inlet section 2 and proceeds to the flow path 4 surrounding the outer periphery formed by the inner casing 3. Heavy foreign objects such as metal pieces and sand in the paper stock are removed from the inlet section. It is discharged from the system through a trap 5 provided in the tangential direction opposite to 2. The stock circulating in the flow path 4 enters the annular screening chamber 7 formed by the screen cylinder 1 and the bearing stand 6 from above in the direction shown by the arrow 8, and passes through the screen cylinder 1 in the process of flowing downward. It is filtered and sorted and discharged from the outlet section 9. On the other hand, foreign objects such as plastics, bundled fibers, and pieces of wood that are too large to pass through the screen cylinder 1 flow down the screening chamber 7 and are discharged from the retract outlet section 10. Also, an airfoil 12 (Figs. 33 and 34) suspended from the upper part of the main shaft 11 and driven by an electric motor 13 rotates continuously at high speed along the screen cylinder surface to remove paper stock. Stirring removes foreign matter that cannot pass through the screen cylinder surface and constantly cleans the screen cylinder.At the same time, strong stirring breaks down the fiber lumps that are generated by gathering together, and the fibers clean the screen cylinder. Facilitate flow through. Further, in FIGS. 29 and 30, taper rings 15 are attached to both ends of the cylindrical screen cylinder 1 with taper pins 16 to be attached to the main body of the screen device. The screen cylinder 1 is provided with a number of slit openings 19 arranged circumferentially approximately parallel to its axis. On the surface 17 of the screen facing the screening room 7,
There is a slit opening 19 which is straight in the thickness direction of the screen cylinder and consists of parallel walls spaced apart by a predefined dimension, and has a substantially right-angled entrance corner 21 where the surface of the screen cylinder and the parallel walls intersect. are doing. A relief groove 20 having a sufficiently larger opening size than the slit opening 19 is provided on the back surface 18 of the screen cylinder. FIG. 33 shows the structure of a conventional screen cleaning device, in which the airfoil section 12 is assembled using a spider 22 and a reinforcing cylinder 23, and is configured to move along a circular path across the surface of the screen cylinder. Installed. (Problems to be Solved by the Invention) However, in order to obtain the desired agitation and cleaning effect based on the principle of blades, the gap between the airfoil piece 12 and the screen cylinder must be extremely narrow, 1.5 to 2.5 mm.
It is necessary to drive the airfoils at high speeds of 10 to 30 meters per second. Therefore, additional support pieces and reinforcing pieces are required to ensure rigidity to withstand high-speed rotation, and advanced technology is required for assembly. Such supporting pieces and reinforcing pieces form surface areas that cause fibers in the paper stock to adhere and bind, resulting in large power loss, and have various drawbacks such as the need to take measures against pulsation. Ta. As mentioned above, the conventional pressure type slit screen operates on the principle of airfoils by moving the airfoil pieces 12 at narrow intervals along the surface of the screen cylinder 1 facing the screening chamber 7, as shown in FIG. This generates pulse pressure consisting of positive pressure and negative pressure to agitate the stock and prevent the screen plate from clogging. Therefore, although the airfoil piece 12 is rotated to obtain a predetermined pulse pressure, the stock liquid stirred by the airfoil is not limited to that between the airfoil and the screen cylinder 1; 1, even the stock liquid located further away from the blade in the radial direction is stirred. Therefore, power consumption for performing the required stirring on the surface of the screen cylinder is large. Although the power consumption is large as described above, the maximum agitation is performed near the blades, so the power efficiency for passing the stock decreases. To compensate for this,
An airfoil piece 12 is brought close to the surface of the screen cylinder 1. In this case, cylinder 1 due to runout
In order to prevent interference between the airfoil section 12 and the airfoil section 12, the airfoil section 12 is made sturdy. Therefore, if hard foreign matter enters the stock liquid and gets caught between the cylinder 1 and the airfoil 12, it can cause serious damage to both, especially the cylinder 1. As mentioned above, even though the airfoil piece 12 is provided near the surface of the cylinder 1, the agitation on the surface of the cylinder 1 is insufficient, and the fibers that should pass through the cylinder 1 flow out from the retract outlet 10. , fiber yield decreases. This tendency was more pronounced as the quality of the long fibers increased. The airfoil section 12 is continuous in the direction of its axis of rotation and passes intermittently near the stock outlet 9 or the inlet 2. At this time, when the pressure waves shown in FIG. 28 are propagated through the paper stock piping and reach the head box of the paper machine, a so-called pressure pulsation problem occurs, causing fluctuations in basis weight in the paper flow direction. In this case airfoil section 12
The greater the power required to drive the pressure pulsation, the greater the energy of the pressure pulsations, which increases the problem.
The drawback was that it was difficult to take measures to absorb pulsation. The present invention aims to solve the problems of conventional sieving devices, such as high power consumption and pulsation. (Means for Solving the Problems) Therefore, the present invention provides a sieving device having a pressure-type slit screen formed by combining a rotor and a screen cylinder, in which the rotor has a projection on its surface and the screen cylinder has a shaft. It has a slit opening elongated in the direction, and one or both sides of the entrance corner of the opening is chamfered, and this is used as a means to solve the problem. (Function) In the present invention, since the stirring by the rotor acts only on the paper stock in the thin annular stirring chamber formed by the surface of the screen cylinder and the rotor drum, the slit inlet opening is based on the swirling flow of the paper stock. It is possible to efficiently achieve strong stirring in the chamber and macroscopic stirring in the stirring chamber. In addition, in the present invention, one or both sides of the entrance corner of the slit opening, which is elongated in the axial direction, is chamfered, so that a strong stirring action of the paper stock based on the flow separation phenomenon is obtained, and the fibers are is never caught. Therefore, clogging can be prevented. (Example) Examples of the present invention will be described below with reference to the drawings. FIGS. 1 to 18 show examples of the present invention.
First, referring to FIGS. 1 and 2, the screen cleaning device has a rotor drum 24 that is concentric with the cylindrical surface of the screen cylinder 1, and has a protrusion 25 in order to stir the stock and generate a circular flow as it rotates. has been established. Note that parts 1 to 11 and 13 are the same as those in the conventional FIG. 27, so detailed explanations will be omitted here. Embodiments of the screen cleaning device of the present invention are shown in FIGS. 3 to 5. In the figure, the shape of the protrusion 25,
The size and position on the rotor drum surface should be determined based on factors such as ensuring that fibers are not caught, sufficient macroscopic agitation, sufficient swirling flow as the rotor drum rotates, and ease of manufacturing. It can be decided by In FIGS. 3 to 5, the shape of the protrusion 25 is exemplified as a cylinder, a square prism, or a triangular prism, but the shape of the protrusion is not limited thereto. Generally, both the rotor drum and the protrusion are made of a metal material such as stainless steel, and the protrusion 25 is attached to the rotor drum 24 by welding, as shown in FIG. With this method, if hard foreign objects such as metal pieces or gravel of the same size as the gap between the screen cylinder surface and the protrusion get mixed in and get stuck in the gap, or for some reason during operation, the protrusion and the screen If it comes into contact with the cylinder surface, serious damage will occur to the screen cylinder surface. In order to solve these problems, in the rotor of the present invention, the protrusions are made of an elastic material such as urethane rubber, and the protrusions are fitted onto the rotor drum as shown in FIGS. 11 and 12, and attached by adhesive or other means. can. This method completely prevents damage to the screen cylinder surface. Further, the rotor drum may be provided with openings 26, as shown in FIGS. 6 to 8. By providing this opening 26, the paper stock in the stirring chamber is locally exchanged with the supplied paper stock, which has the effect of promoting macroscopic stirring within the stirring chamber. Note that the shape, size, and number of the openings 26 are arbitrary. Next, the structure of a screen cylinder previously filed by the present applicant in Utility Model Application No. 1981-108190 is shown in FIGS. 13 to 16. First, as shown in FIG. 15, when the rotational movement of the paper stock as the rotor drum 24 rotates is in the direction of the arrow 27, the inlet corner on the downstream side of the flow is chamfered 28 as shown in FIG. 16. . The depth of the chamfer 28 in the thickness direction of the screen cylinder 1 and the angle of the chamfer 28 with respect to the normal line of the screen cylinder 1 are arbitrary.
8 such that the agitation area generated by 8 reaches the inlet of the screen opening 19. Note that if the chamfer is made too large, the agitation flow due to separation will be significantly attenuated at the entrance of the screen opening 19, which is not desirable. Another embodiment is shown in FIGS. 17 and 18. In the figure, when the trailing motion of the stock is in the direction of arrow 27, chamfers 28 and 29 are applied to the inlet corners on the downstream and upstream sides of the flow, respectively. Although the chamfers 28 and 29 are symmetrical along the center line in FIGS. 17 and 18, they may be asymmetrical. The depth and angle of the chamfers 28 and 29 are
Similar to the embodiments shown in FIG. 16 and FIG. 16, this is optional. In addition, in the structure of the pressure type slit screen, the main shaft 11 is a vertical axis in FIG. 2, but it may be a horizontal axis, and regarding the screen cylinder, in FIG. 2, the screen cylinder 1 is located outside the rotor drum 24. The stock is designed to pass from the inside to the outside, but on the contrary, a protrusion 25 is provided on the inner surface of the rotor drum 24, and a screen cylinder is provided inside the protrusion 25, so that the stock passes from the outside to the inside. You may let them. In addition, protrusions are provided on the inner and outer surfaces of the rotor drum,
Screen cylinders may be provided inside and outside. Next, to explain the operation of the embodiment configured as described above, as shown in FIG. It may peel off from the road surface, a phenomenon commonly known as delamination. In this separated part, a vortex flow in the opposite direction is generated on the surface of the flow path and has a strong stirring action, so it will be referred to as a stirring region here. In the present invention, whereas conventionally the paper stock is agitated by the airfoils 12 over the entire wide annular screening chamber 7, the agitation by the rotor is
As shown in the figure, a thin annular stirring chamber 3 formed by the surface of the screen cylinder 1 and the rotor drum 24
Since it acts only on the paper stock of 0, it is possible to efficiently realize the swirling flow of the paper stock and macroscopic stirring in the stirring chamber. In order to cause a separation phenomenon using this entangling flow, the entrance corner of the slit opening 19 is chamfered as shown in 28 in FIG. 16 or 28 and 29 in FIG. 18, and the slit entrance can be opened with low power consumption. The paper material is sorted by creating a strong agitation area in the slit opening 19, allowing the stock to pass through the slit opening 19, and not allowing foreign matter larger than the slit opening 19 to pass through. (Effects of the Invention) Since the present invention is configured as described above in detail, less power is required to prevent paper stock from clogging the surface of the screen cylinder. Figure 20 shows a comparative test between a conventional rotor and a rotor with cylindrical protrusions according to the present invention, with a screen diameter of 25 mm.
The results obtained using the model are shown below. Comparing the figures at a turning speed of 10 m/sec, it can be seen that the turning speed according to the present invention is reduced to about 1/3 compared to the conventional one. In the conventional combination of a screen cylinder and an airfoil, the leading edge has an angle of attack α as shown in FIG. 23, so that a hard foreign object 31 that is slightly larger than the gap As in, airfoil section 1
2 is continuous along the screen plate, any hard foreign matter that gets stuck must necessarily pass through the gap, which has the disadvantage of causing damage to the surface of the screen cylinder and the airfoil. On the other hand, in the combination of the screen cylinder and rotor of the present invention, as shown in FIGS. 24 and 25, since the protrusions are discontinuous, the hard foreign matter 31a, which is slightly larger than the gap Y, easily passes around the protrusions. do. Also, the gap X of the conventional type shown in Fig. 23 is 1.5.
~2.5mm, whereas in the present invention, the gap Y is 4.
It exhibits its performance even in cases as wide as ~5 mm, so the size of hard foreign objects that can be bitten becomes larger.
The probability of foreign matter contamination is also reduced. Therefore, it is possible to prevent damage to the screen cylinder surface due to hard foreign matter getting caught. Furthermore, by using an elastic material such as urethane rubber for the protrusion of the present invention, even if a hard foreign object gets caught in the gap Y for some reason, the elastic deformation of the protrusion will prevent damage to the screen cylinder surface. Completely preventable. In addition, the rotor protrusion made of an elastic material can be easily replaced by fitting or bonding as shown in FIGS. 11 and 12 to prevent wear and damage caused by long-term use. Further, in the present invention, one or both sides of the entrance corner of the slit opening, which is elongated in the axial direction, is chamfered, so that the clumps of fibers are agitated by the flow separation and are broken down before entering the slit. The slit entrance opening has a separation effect of the flow along the surface of the screen plate, so even if fibers are caught at the slit entrance opening, they will be swept in a different direction the next moment, so the fibers will not be torn off. As a result, the fibers cannot be caught in the slit opening. Therefore, clogging is prevented and the corners of the slit entrance opening where fibers were conventionally caught are eliminated, so the fibers move with the flow of the liquid and can easily pass through the slit. As a result, as shown in the test results in Table 1, the fiber yield is significantly improved. Comparative tests were conducted on a combination of a conventional screen cylinder with a screen diameter of 250 mm and an airfoil piece, and a combination of a rotor and a screen cylinder of the same size according to the present invention with a chamfer on the downstream side of the entangled flow. The results are shown in Table 1.

[Table] The test results are expressed as a percentage of the ratio of the supplied stock concentration to the accepted stock concentration, with the slit gap set to 0.3 mm, and roughly correspond to the fiber yield. From the results in Table 1, it can be seen that the present invention significantly improves the fiber yield from 75% to 95%, although there is some variation depending on the slit passing speed. Next, FIG. 21 shows the measurement results of pressure fluctuations of a rotor having cylindrical projections according to the present invention. In the figure, the fundamental frequency (1N component) determined by the rotor rotation speed and the number of protrusion rows is 21.7 Hz in this test, but
In FIG. 21, the peak of pressure fluctuation is unclear and at a low level, so there is no problem. In addition, clear peaks are observed in the high frequency components of 2N and 3N, but both are above 30 Hz, and because the frequencies are high, they are easily attenuated in the raw material piping. Therefore, in the rotor of the present invention, there is no need to take measures against pulsation caused by the pressure type slit screen.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional plan view of a sieving device showing an embodiment of the present invention, FIG. 2 is a partially sectional front view of the same,
Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8
9 and 9 are respectively perspective views of rotor drums showing embodiments of the present invention, FIG. 10 is a sectional view taken from XX in FIG. 9, and FIGS. 11 and 12 are elastic projections different from those in FIG. FIG. 13 is a perspective view of a screen cylinder showing an embodiment of the present invention; FIG.
The figure is a sectional view from A to A in Fig. 13, and Fig. 15 is a cross-sectional view of Fig. 14.
16 is an enlarged view of the part marked with ○ in FIG. 15, FIG. 17 is a sectional view from B to B in FIG. 14 of an embodiment different from FIG. 15, and FIG. 1
An enlarged view of the part marked with ○ in Figure 7, Figure 19 is a velocity distribution diagram in the stirring region, Figure 20 is a diagram showing the relationship between rotation speed and net power consumption in the present invention and the conventional technology.
FIG. 21 is a diagram showing the relationship between frequency and pressure fluctuation in the present invention, FIG. 22 is a front view showing a combination of a conventional screen cylinder and an airfoil piece, and FIG.
22 is a plan sectional view of the main part of FIG. 22, FIG. 24 is a front view showing a combination of a screen cylinder and rotor showing an embodiment of the present invention, and FIG. 25 is a plan sectional view of the main part of FIG. 24. Figure 26 is a partial cross-sectional plan view of a conventional pressure type slit screen, and Figure 27 is the same.
28 is an explanatory view showing the relationship between the screen cylinder and the airfoil piece in FIG. 27, FIG. 29 is a perspective view of the conventional screen cylinder, and FIG. 30 is A' in FIG. 29. ~A′ cross section, 3rd
1 is a sectional view from B' to B' in FIG. 30, FIG. 32 is an enlarged view of the part marked with ○ in FIG. 31, FIG. 33 is a perspective view of a conventional airfoil piece, and FIG. C~ in the diagram
It is a sectional view of C. Explanation of main parts of the figure, 1... Screen cylinder, 19... Opening, 24... Rotor drum, 2
5... Protrusion, 28, 29... Chamfer.

Claims (1)

[Claims] 1. In a sieving device having a pressure-type slit screen formed by combining a rotor and a screen cylinder, the rotor has a projection on its surface, the screen cylinder has a slit opening elongated in the axial direction, and the inlet corner of the opening A sieving device characterized by chamfering one or both sides of the screen.