FI117799B - chip screening - Google Patents

Description

117799 1

The present invention relates to an apparatus for removing oversized and thick chips from a chip stream, i.e. a chip screen.

Chip screening seeks to eliminate the amount of fine and large fractions (Oversized and Oversized) that are harmful to the process. In pulp production, chip thickness has been identified as a critical factor in optimizing the process. Various screens such as disc, roller and rod screens have been developed for thickness screening. Disc screens have been in use since the 1970s and have proven to be a reliable screening device. The screening efficiency of the wafer screens, which means the screening capacity relative to the screening area, is greater than that of the roller screens. Bar screens achieve the same efficiency as wafer screens, but the implementation of movable bar actuators is problematic.

A typical disk screen is formed by a plurality of parallel rotating shafts with discs. The axes are transverse to the transport direction, spaced apart. The shafts have · *: ·. at regular intervals, protruding discs. The shafts are arranged such that the disks of the two axles in succession in the conveying direction are overlapping to form gaps between the disks. The gap defines the thickness * · »smaller chips fall between the disks. Pieces larger than the desired thickness · · · pass over the wafer screen. A wafer screen is described, for example, in Fl 72271 (US 78190). A chip screening screening system is described, for example, in FI82719 (US5133507) and FI90019 (US5232097).

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• · • »♦ · · *: Typically, applicants are fed to a thickness hockey screen in a 10 to 20 cm thick as" mat "as possible. The thickness of the "mat" decreases as the chipping stream passes towards the end of the screen, since the majority of the chipping stream, i.e., accepted •: the fraction drops between the disks on the underlying conveyor. 1 i 117799 2 In addition, the diameter of the discs of the consecutive axes or of the discs mounted on the same axis may also vary. The eccentric discs are disposed in overlap, such as, for example, in US 3985233.

According to the present invention, a chip screen according to the invention consists of a plurality of parallel axes which are spaced substantially parallel to each other and are rotatable in the same direction, and are disposed perpendicularly to the axis, with the disk on the axis, the line perpendicular to the axes has a disk on substantially every other axis. It is characteristic of the chips screen according to the invention that at least every second disc spacing has a stationary planar surface extending from the axis to the adjacent axis at a screening clearance distance from each of the disks in the disc space.

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The planar surfaces perpendicular to the axes in the disc spacing are: * * formed as rod-like plates which pass in a uniform or accurate manner.

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: *] *: assembled in appropriate sections in the longitudinal direction of the sieve between the disks. The discs are spherical or elliptical, depending on the performance requirements of the screen, with the round discs possibly being eccentrically mounted on their axes.

The discs may, for example, be provided with a tooth pattern.

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With this structure, the opening forming the screening gap between the disk «and the solid structure is formed so that the openings have one side ··· live and the other solid. This prevents the openings from clogging even though • * · the disks of consecutive axes in the screen direction are aligned.

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The invention and its details will be described in more detail below with reference to the accompanying drawings, in which Fig. 117799 3 shows a structure of a typical prior art screen, Fig. 2 shows a side screen of Fig. 1, Fig. 3 shows a prior art disc screen with eccentric discs. Figure 5 shows section A-A of Figure 4, Figure 6 shows section B-B of Figure 5 with two parallel disks between the bars, the adjacent discs being eccentrically disposed on the shaft, Figure 7 illustrates the invention. and Figure 8 illustrates another alternative embodiment of the invention.

Y: The prior art chips screen with discs 1 shown in Figure 1 consists of parallel axes 3 rotated in parallel. The discs are mounted on discs 1 spaced apart · · · *: in the direction of the axes such that the discs of the next axis 3 ′ lie between the discs of the previous axis t ··: ... i. Adjacent (in the direction of sieve transport

there is an opening 4 having a width H of the discs on the consecutive axes

• *: Set according to acceptable chip thickness (screening clearance).

• · ·

In the screening of over-thick chips, the screening clearance, i.e. the size of the opening 4, is »generally 7-8 mm. In Fig. 1, the size of the openings relative to the thickness of the wafers is highlighted for illustrative purposes. The discs are generally provided with some kind of teeth 5 as shown in Figure 2. The teeth 5 * increase the carrying capacity and movement of the chips.

• ·; 117799 4

The shafts 3 and the discs 1 fixedly attached thereto rotate in the same direction indicated by the arrows shown in Fig. 2. The speed of rotation of the shafts can be selected freely. When the discs of successive axes are overlapped, the distance between the axes is Vi. By placing the discs 6 in the same line as in Fig. 3, the distance between the axes 7 is increased to V2. The clearance V2 is approximately the same regardless of whether the discs are mounted centrally or eccentrically to the shaft as in Figure 3.

As the clearance V is larger, the horizontal aperture surface area of the wafer screen relative to the total wafer screen surface area is also larger. This also allows for better throughput capacity.

When successive discs that are centrally attached to the axes are in alignment, the problem is the clogging of the disks between the discs attached to the same axis. The chips are easily trapped between parallel disks when there is no movement between the disks.

By positioning the discs 6 eccentrically and the parallel disks 6 'at different phase differences, the difference in motion is obtained over a wider range than the centrally mounted discs. However, there is still a small area 8 between the parallel disks 6, 6 ', which has no movement difference. "Dead area" is indicated by a dash 8 • «: in Figure 3.

Figures 4, 5 and 6 illustrate an embodiment of a disk screen · * '** according to the invention, wherein the phase difference between adjacent circular discs 6, 6' disposed eccentrically on the axes is 180 °. The width of the openings 9 is * *: highlighted in Fig. 4 for illustrative purposes.

* · · ...... · ·· · • φ • · ···. ·.

: j *: Eccentrically disposed discs require synchronized rotation of the shafts, for example by means of the sprockets 10 and the chain transmission shown in Fig. 4. The chain is represented by a dotted line 11.

·· ·: 117799 s

The screening is carried out between the surfaces moving relative to one another in the screen according to the invention. Between the disks 6, 6 'there is provided a rod 12 extending across the entire length of the disk screen, there is always a movement difference between the stationary rods 12 and the rotating discs 6, 6'. The openings 9 are live, so that the chipping of the chips into the openings 9 will not occur.

Figure 5 illustrates how eccentric discs effectively prevent wedge chips 20 from jamming between the rotating disk and the fixed rod 12. The discs rotate in the direction indicated by arrow R. The chip 20 tends to be wedged by the movement of the disc 21 between the disc 21 and the rod 12. After the discs rotate 180 °, the disc 22 is in the position indicated by the dashed line 23. The disc 22 is directed now to the chip 20 a force parallel to arrow G, to remove the chip between the wafer and the rod.

The clearance between the bar 12 and the discs is set, as shown in Figure 4, to a screening clearance K, which in normal thickness screening is approximately the same as H in Figure 1. K is approximately equal to the gap L between successive disks.

The bars 12 are mounted on the shafts as shown in Figure 5. The joint surface 13: V: with the shaft 7 is semicircular, on which the rod rests against the ♦ *: // axis. Rods can be easily replaced if needed. The rods can be supported: [**: from the beginning of the sieve, below the chips feed chute, to the sieve body. The rods can also be formed of several parts, whereby the different parts of the rods are connected to each other, for example, between each axis.

· ·: A single row of discs is generally disposed between the rods 12 as shown in Figure 4.

• · ·

On the other hand, the screen can also be constructed as shown in Figure 6, with two rows of disks between the rods 12 and a "dead zone" 8 as shown in Figure 3.

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In Figure 6, the shaft 7 is rotated 90 degrees relative to Figure 5 so that the eccentric mounting of the discs 6, 6 'on the shafts is visible. Between the rods and the disks 117799 6 there are sliding sleeves 14 mounted on the shaft and rotating with the shaft. The bar brush 16 is made ascending and descending so that the long straps hanging over the bar passes to the bottom of the brush. The lowest point of the brush can be provided with a sharp-edged wear-resistant carbide piece 17. The sharp edge 18 cuts or rubs the straps hanging over the rod, whereby they fall through the sieve.

In the disk screen of Fig. 6, adjacent discs 6 and 6 'are disposed eccentrically on the shaft at 180 °. This ensures that the shaft is in balance. The discs can also be positioned in three or four different stages, with phase differences between adjacent discs of 120 ° or 90 °.

The bars 12 'can also be applied to a wafer screen in which the wafer 1 is centrally located on the shafts 7 as shown in FIG. In this case, the wafer screen may also be inclined at an angle a other than horizontal to ensure transport capability.

Fig. 8 shows a wafer screen with successively placed elliptical disks 19.

: Y: There are rods 12 'between the disks. The advantage of the elliptical disk 19 is the chips that are twice upwardly moving during one revolution of the disk.

In the disc screen according to the invention, whether the discs are central * · 1 · 1 ... · 1 or eccentric, the discs may be provided with different teeth.

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Claims (6)

117799 7 A chopping screen consisting of a plurality of parallel axes (10) which are spaced substantially parallel to one another and are rotatable in the same direction, and are disposed perpendicular to the axis and rotatable with the shaft (6, 6). mounted on the axes such that the disk on the axis is perpendicular to the axes having a disk on substantially every other axis, characterized in that at least every second disk interval has a stationary bar (12) extending from the shaft to an adjacent shaft at a distance from each disk gap. Chip screen according to Claim 1, characterized in that the stationary bar (12) is located in each disc space. Chip screen according to Claim 1 or 2, characterized in that the discs (6,6 ') are eccentrically disposed on the shafts. Chip screen according to claim 3, characterized in that the discs (6,6 ') are round. Chip screen according to claim 1, 2 or 3, characterized in that the ··· disks (6,6 ') are elliptical. • · ♦ • · • · ♦ • · · ··· · Chip screen according to one of the preceding claims, characterized in that the bar (12) extending from the shaft to the shaft adjacent to it is provided with a sharpening at its upper edge for at least a part of its length. • · * • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •! 1 • Φ 117799 8