JPH086274B2 - Stock screen - Google Patents

Description

TECHNICAL FIELD The present invention relates to a stock screen for removing contaminants from a pulp suspension or stock.

<Prior Art and Problems Thereof> A screen is used to remove coarse plastics, stones, and other contaminants from a suspension of pulp or waste paper (hereinafter referred to as paper stock). An example of the sealed screen is shown in FIGS. 4 and 5. Incidentally, FIG. 5 is a view taken along the line VV of FIG. In the figure, 1 is a casing,
2 is a stock material inlet chamber, 3 is an accept chamber, 4 is a screen cylinder, 5 is a rotor, and usually 3 or 4 blades 5a are attached. 6 is a reject room.

The screen cylinder 4 is formed by forming a metal plate into a cylindrical shape and forming a large number of perforations. The perforations include round perforations having a diameter of 1 to 3 mm and slits having a width of 0.1 to 1.0 mm. The slit holes are usually formed in parallel with the cylinder axis of the screen cylinder. The rotor 5 is a blade that is supported by a cylindrical body 5c that is rotationally driven by a pulley 5b via a belt from an electric motor (not shown), and an arm 5d that projects radially from the cylindrical body 5c.
It consists of 5a. As shown in FIG. 5, the blade 5a has a jewel-shaped cross section, and rotates along the inner surface of the screen cylinder 4 with a slight distance from the inner surface of the screen cylinder 4. Therefore, the screen cylinder 4 is prevented from being clogged by generating a positive pressure at and a negative pressure at the trailing edge. Also, as shown in the figure, some are vertical and others are slightly inclined by about 10 °. Paper charges from entrance 2a to paper entrance room 2
It enters inside and descends from there inside the screen cylinder 4. Since there is a required differential pressure between the inner and outer surfaces of the screen cylinder 4, the pulp fibers pass along with the water, and the impurities that do not pass through the eye holes descend along the surface of the screen cylinder 4 into the reject 6 chamber, and the reject 6 chamber is rejected. It is discharged to the outside from the discharge port 6a. The paper material that has passed through the screen cylinder 4 is discharged to the outside from the accept chamber 3 through the accept outlet 3a.

With the above-mentioned stock screen, the stock density is 0.3-
It must be used at about 1%, and if it exceeds that amount, the screen will be clogged and it will become unusable, so the processing amount will be small,
Power consumption is also high. In order to process high-concentration stock material, the peripheral speed of the blade has been increased to about 10 to 12 m / s, and the distance between the blade and the screen plate has been increased from 1 to 2 mm to 3 to 3. It was proposed to make it 10 mm (Japanese Patent Publication No. 56-1479).
No. 3), 2 to 4% of stock can actually be processed,
The throughput was greatly increased.

On the other hand, in the screen as shown in FIG.
Since the fibers 8 flow in the circumferential direction by the action of, the fibers 8 are parallel to the inner surface of the screen cylinder 4 and are oriented in the direction perpendicular to the eye holes 4a, so that it is difficult to pass through the eye holes 4a of the screen cylinder 4 and the processing amount It is considered that the amount of water is small, and it has been proposed to install a bar 7 on the inner surface of the screen cylinder 4 as shown in FIG. 7 so as to block the flow in the circumferential direction (Japanese Patent Publication No. 45-36958). Since the flow is blocked by 7, the fibers 8 are oriented in the direction of the eye holes 4a.
The screen throughput increases because the flow rate through the eye holes increases due to the pressure increase on the upstream side of the bar 7 due to the blocking.

In the above description, the screen in which the amount of paper flows from the inside of the screen cylinder 4 to the outside has been described, but there is also one in which the blades rotate outside the screen cylinder to allow the stock to flow from the outside to the inside.

Focusing on the above-mentioned facts, the inventors used a screen cylinder having a projection as shown in FIG. 7 on the inflow side surface, and used the blades as described in JP-B-56-14793. An experiment was conducted on the assumption that the processing amount would be further increased by rotating at high speed. In the experiment, the blades are not parallel to the cylinder axis, that is, vertical blades as shown in FIG. 4, but the blades whose upper ends are inclined forward by about 10 ° with respect to the lower ends are used. However, it was found that when the blades were rotated at high speed, violent vibration and noise were generated and the driving power became excessive.

 The cause is considered as follows.

That is, since the blades 5a have a function of rapidly pushing the flow of the stock blocked by the bar 7 toward the screen surface when passing through the bar 7, this causes a rapid pulse-like pressure increase, which causes such a pressure increase. Therefore, it is considered that the screen plate 4 vibrates and the rotation resistance increases.

<Experimental Results> The inventors further conducted experiments under the idea that if the angle at which the protrusions and the blades intersect is increased, the above-mentioned pulse-like pressure increase should be reduced and vibration should be reduced. The experimental results are shown in Table 1 below.

<Consideration of Experimental Data> (1) The motor load decreases as the blade tilt angle increases.

(2) However, the pressure difference between the inlet and outlet is the lowest at the crossing angle of 30 °, and increases when it exceeds 30 °. It is considered that this is because if the angle is too large, the original function of the blade is to weaken the hole cleaning action of the screen plate. From the values in the table, 45 ° is considered to be the maximum practical angle.

(3) The sound is abruptly quieter than 20 °. It is considered that this is because the blades intersect two or more protrusions at the same time, and because the intersecting angle is large and the pressure rise escapes in the vertical direction, the pulse-like pressure rise is small.

(4) The fact that the reject rate is high means that the proportion (%) of contaminants in the inlet stock is equal in each experiment number, which means that the proportion of good-quality pulp in the reject is high. . When the blade tilt angle is increased, the rejection rate decreases. The effect of the blade tilt angle is that the paper stock in the stock material inlet chamber 2 is rapidly pushed down to the reject chamber 6 along the inner surface of the screen cylinder. Upflow occurs near the center. That is, it is considered that the circulation occurs between the stock material inlet chamber 2 and the reject chamber 6, and the stock material is subjected to the screening action a plurality of times before being discharged as a reject, and the proportion of the high-quality pulp in the reject is reduced. The reason why the reject rate increases when the tilt angle exceeds 30 ° is considered to be that the above-mentioned circulation amount becomes excessively large.

(5) Overall, practically, the blade crossing angle is within the range of 20 ° to 45 °, and the optimum angle is considered to be 30 °.

<Objects of the Invention> The present invention has been devised in consideration of the above experimental results. By improving the shape of the blade, the throughput is large, the power consumption is small, and the problem of vibration does not occur. It is intended to provide a screen.

<Means for Solving Problems> In order to achieve the above object, the stock screen of the present invention comprises:
A cylindrical screen cylinder having a large number of holes and a plurality of projections provided on the inflow side surface in parallel with the axis and spaced in the circumferential direction, and the screen cylinder. A paper stock screen having a plurality of blades rotating at a peripheral speed of 17 to 25 m / s along a surface on the inflow side, the blades advancing in the rotation direction on the paper stock inlet chamber side,
It has a spiral shape in which the side of the reject chamber recedes in the direction of rotation, and the angle intersecting with the above-mentioned projections is within the range of 20 ° to 45 °, and at the same time it always intersects at least two projections during rotation. On the inflow side of the screen cylinder, the stock liquid, which has been swept away from the stock inlet chamber side by the blade in the direction of the reject chamber along the screen cylinder by the blades, moves from the reject chamber at a position away from the inflow side surface of the screen cylinder. A stock screen having a space serving as a circulation channel in a stock inlet chamber.

<Operation> The blades are spiral, and the angle of intersection with the protrusions on the inner surface of the screen is in the range of 20 ° to 45 °, which is a relatively large angle. Since it can be easily escaped, it is slight, and since it constantly intersects with two or more protrusions during rotation, the pulse-like pressure rise is almost eliminated. Therefore, the screen cylinder does not vibrate and the sound is quiet. Moreover, the spiral-shaped blades push the stock solution along the inner surface of the screen cylinder. The inside of the blade (a position away from the surface on the inflow side of the screen cylinder) has a space that serves as a flow path, so that circulation of the stock occurs between the stock inlet chamber and the reject chamber, and the stock in the reject chamber enters the inlet chamber. It is returned to and is subjected to the screen action multiple times. Therefore, the proportion of good quality pulp in the reject chamber decreases, the reject rate decreases, and the yield increases.

<Example> An example of the screen of the stock material of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a paper stock screen of the present invention, FIG. 2 is a view taken along the line II-II of FIG. 1, and FIG.
The figure is a partial development view along the screen cylinder surface. 1 to 3, 1 is a casing, 2 is a stock material inlet chamber, 3 is an accept chamber, 4 is a screen cylinder, 5
Is a rotor, 6 is a reject chamber, 10 is a protrusion attached to the inner surface of the screen cylinder, and 11 is a blade. The difference between the screen of the present invention and the conventional screens shown in FIGS. 4 and 5 is that in the present invention, the projection 10 is provided on the inner surface of the screen cylinder in parallel to the axial direction, and
Since the shape of 11 is a spiral shape and the intersecting angle between the blade 11 and the projection 10 is in the range of 20 ° to 45 °, the same reference numerals are used for the same components as the conventional one,
Description is omitted. The blade 11 is supported by an arm protruding in a radial direction from the cylindrical body as shown in the drawing, has three or four blades, has a spiral shape that advances in the traveling direction with respect to the upper end or the lower end, and has a protrusion 10 The intersection angle α with
It is in the range of 20 ° to 45 °, preferably 30 °. The crossing angle and the pitch of the protrusions 10 are set so that the blades 11 always intersect with two or more protrusions 10 during rotation. The gap between the blade 11 and the tip of the protrusion 10 is 2 to 5 mm, and the blade 11 is 17 to 25 m / s.
It is rotating at the peripheral speed of. The protrusions 10 are provided on the inner surface (inflow side surface) of the screen cylinder in parallel with the axis and at equal intervals in the circumferential direction. The protrusion may be formed by welding a square bar on the cylinder surface, or may be formed by cutting off the other portion while leaving the protruding portion from the thick cylinder. The shape of the eye of the screen cylinder 4 may be a slit hole or a round hole. Further, as shown in FIG. 8, the inflow side surface of the screen cylinder 4 may be the outer surface.

 Next, the operation will be described.

The flow of the stock material in the stock material inlet chamber 2 is made to spiral down along the inner surface of the screen cylinder 4 by the action of the blade 11. At this time, since the inclination angle of the blade 11 is large, the downward component of the flow is large. On the other hand, since the flow rate from the reject discharge port 6a is narrowed and there is a space inside the blade (a position away from the inflow side surface of the screen cylinder) with the cylindrical body, the paper amount liquid from the reject chamber 6 is Ascend the space as indicated by arrow A. Thus, circulation of the stock occurs between the stock inlet chamber 2 and the reject chamber 6. Therefore, the stock solution is subjected to the screening action a plurality of times, the proportion of the high-quality stock in the reject chamber is reduced, and the proportion of foreign substances is increased, so that the reject amount is reduced. An example will be described.

FIG. 9 shows the flow balance of the conventional screen, and FIG. 10 shows the flow balance of the screen of the present invention. As shown in FIG. 9, in the screen without circulation between the stock material inlet chamber 2 and the reject chamber 6, the stock material liquid containing 3% of foreign materials (that is, the foreign material T = 3 to the high quality pulp P = 97). The ratio of good quality pulp and contaminants in the reject chamber is 50:50, and if the reject rate is 6%, the amount of good quality pulp discharged as rejects is 3 and the quality obtained as accept Fiber is 94. On the other hand, considering the case where the circulation amount is the same as the inlet flow rate under the same inlet conditions as shown in Fig. 10, the ratio of high-quality pulp and contaminants in the reject chamber is 25:75, so the stock inlet chamber 2 Since the circulation amount is 100, 122 (= 97 + 2) for good quality pulp.
5), the amount of impurities is 78 (= 3 + 75). Under this condition, the rejection rate is 4%, and the quality pulp material discharged during the rejection is 1 and the quality pulp of accept is 96.

On the other hand, the blade has a spiral shape and the crossing angle with the protrusion 10 is
There is no vibration or noise because it is over 20 ° and always intersects with two or more protrusions.

<Effects of the Invention> As described above, the screen of the stock material of the present invention has the following effects.

(1) Protrusions are provided on the inflow side surface of the screen cylinder in parallel with the axis and at intervals, and the intersection angle with the protrusion is 20 ° ~
The 45-degree spiral blades rotate at high speed along the inner surface of the cylinder, resulting in a large amount of screen processing and less vibration and noise.

(2) Circulation occurs inside the screen due to the spiral blades, which reduces the reject rate and increases the yield.

[Brief description of drawings]

1 is a cross-sectional view of the paper stock screen of the present invention, FIG. 2 is a view taken along the line II-II of FIG. 1, and FIG. 3 is a partially developed view along the screen cylinder surface of FIG. 1, FIG. Is a cross-sectional view of a conventional stock screen, FIG. 5 is a view taken along the line VV of FIG.
The figure is an explanatory view showing the behavior of fibers near the screen surface,
FIG. 8 is an explanatory view showing the behavior of fibers when a projection is provided on the screen surface, FIG. 8 is a partial cross-sectional view when the inflow side surface of the screen cylinder is the outer surface, and FIG. 9 is a conventional stock material screen. FIG. 10 is a flow balance of the screen of the stock material of the present invention. 4 …… Screen cylinder 4a …… Eye hole 10 …… Protrusion 11 …… Blade

Claims (2)

[Claims] 1. A cylindrical screen cylinder having a large number of perforations and a plurality of projections provided on an inflow side surface extending in parallel with an axis and spaced in a circumferential direction. , 17-25 along the inflow side surface of the screen cylinder
A paper stock screen having a plurality of blades rotating at a peripheral speed of m / s, in which the paper feed inlet chamber side is advanced in the rotational direction and the reject chamber side is retracted in the rotational direction. It has a spiral shape and the angle at which it intersects with the above protrusions is
It is in the range of 20 ° to 45 °, and it always intersects with at least two projections during rotation. On the inflow side of the screen cylinder, along the screen cylinder from the stock inlet chamber side by the above-mentioned blades. Stock screen having a flow passage for circulating the stock liquid swept away toward the reject chamber from the reject chamber to the stock inlet chamber at a position away from the inflow side surface of the screen cylinder. . 2. The paper stock screen according to claim 1, wherein an angle at which the blade and the projection intersect is approximately 30 °.