US3535203A - Hole plate for one-sided inlet headboxes for paper machines - Google Patents

Description

Oct. 20, 1970 N. AKE NILSSON 3,535,203

HOLE PLATE FOR ONESIDED INLET HEADBOXES FOR PAPER MACHINES Original Filed Dec. 10. 1965 4 Sheets-Sheet 1 b INVENTOR NILS AKE NILS'SON HIS ATTORNEYS Oct. 20, 1970 N. AKE NILSSON 3,535,203

HOLE PLATE FOR ONE-SIDED INLET HEADBOXES FOR PAPER MACHINES Original Filed Dec. 10, 1965 4 Sheets-Sheet 2 Fig.2

HHIIHIIHIIIHHIlllllHHlllllllllllllllllllll o INVENTOR NILS AKE NILSSON HIS ATTORN EYS Oct. 20, 1970 N. AKE NILSSON 3,535,203

HOLE PLATE FOR ONESIDED INLET HEADBOXES FOR PAPER MACHINES I Original Filed Dec. 10. 1965 4 Sheets-Sheet 3 o lNVENTOR NILgYAKE NILSSQN HIS ATTORNEYS Oct. 20, 9 0 N. AKE NILSSON HOLE PLATE FOR ONEFSIDED INLET HEADBOXES FOR PAPER MACHINES 4 Sheets -Shee t 4 Original Filed Dec. 10, 1965 Fig.6

o INVENTOR NILgYAKE NILSSON |'-||s ATTORNEYS United States Patent 3,535,203 HOLE PLATE FOR ONE-SIDED INLET HEADBOXES FOR PAPER MACHINES Nils Ake Nilsson, Karlstad, Sweden, assignor to Aktiebolaget Karlstads Mekaniska Werkstad, Karlstad, Sweden, a Swedish company Continuation of application Ser. No. 513,044, Dec. 10, 1965. This application Feb. 27, 1969, Ser. No. 805,106 Claims priority, application Sweden, Dec. 23, 1964,

15,613/64 Int. Cl. D21f 1/06 US. Cl. 162343 12 Claims ABSTRACT OF THE DISCLOSURE A hole plate for a paper-making machine head-box or the like comprises a plurality of holes for conducting stock from a distribution pipe generally aligned with the plate to the head-box and a recess formed adjacent each hole in the surface of the plate and facing the distribution pipe. The recess for each hole merges at one end into the hole at its downstream end, relative to the direction of stock flow through the distribution pipe, and extends from the said downstream edge of the hole in a direction substantially aligned with the flow path of stock through the distribution pipe for a distance downstream of the hole substantially greater than the diameter of the hole. The downstream edge of the recess merges smoothly into the surface of the plate. The recess associated with each hole provides a stagnation point in stock flow that is located at a zone downstream from the edge of the hole so that there is no opportunity for obstruction of the hole and for formation of fiber bundles.

This is a continuation of application Ser. No. 513,044, filed Dec. 10, 1965, now abandoned.

The present invention relates to hole plates for onesided inlet headboxes for paper machines. One-sided inlet headboxes are usually at their inlet end provided with a distribution pipe, to which the pulp, i.e. the fibre suspension, is supplied from the one side in a direction substantially perpendicular to the flow direction of the pulp in the headbox. Between the headbox and the distribution pipe a perforated hole plate is arranged perpendicular to the flow direction of the pulp in the headbox and thus substantially parallel to the flow direction of the pulp in the distribution pipe. The object of this hole plate is to deflect the pulp flow about 90 and to distribute the pulp uniformly over the breadth of the headbox. Hole plates of this kind are provided with a large number of holes for the pulp uniformly spaced over the plate and these holes are often somewhat tapered at the surface of the hole plate facing the distribution pipe.

Prior hole plates of this kind are, however, aifected by certain severe difficulties, due to the fact that a stagnation point is formed in the pulp flow at the down-stream edge of each hole at the surface of the plate facing the distribution pipe. This stagnation point is caused by the division of the pulp flow at the sharp down-stream edge of the hole in one stream flowing into the hole and another stream passing the hole substantially parallel to the plate. In this stagnation point at the down-stream edge of each hole the velocity of the pulp flow is consequently substantially zero, which means that individual fibres in the pulp as Well as longer threads consisting of several twisted fibres will have a tendency to cling to the sharp down-stream edge of the hole right at stagnation point and to form a fibre bundle. This fibre bundle can become so substantial that it has a detrimental effect upon ice the flow through the hole and when it finally gets large enough to be pulled away from the edge of the hole, it will be carried by the pulp flow through the hole and the headbox out onto the wire of the paper machine and give cause to an uneven fibre distribution and thus a poor quality of the paper produced.

The principal object of the present invention is, therefore, to provide a hole plate of the above described type but of an improved design so that the above mentioned stagnation point at each hole is displaced to an even surface, whereby the above stated disadvantages with prior hole plates will be eliminated. With this object a hole plate according to the invention is provided with a recess, in conjunction with each hole in the plate, in the surface of the plate facing the distribution pipe, said recess being downstream from the hole and having a length in the flow directions of the pulp in the distribution pipe substantially exceeding the diameter of the hole. The bottom of the recess is either straight or smoothly curved and merges smoothly into the surface of the hole plate, whereby the stagnation point downstream of each hole will be located at a smooth surface spaced from the downstream edge of the hole. In this stagnation point there is no risk that a fibre bundle will accumulate as there is no sharp edge in this point, against which fibres and fibre threads can get sufiicient friction to adhere.

According to the invention the recess is in the surface of the hole plate facing the distribution pipe are preferably shaped to have a substantially trinagular cross section in planes perpendicular to the plate and parallel to the principal flow direction of the pulp in the distribution pipe. This triangular cross section is characterized by a mainly straight up-stream side approximately perpendicular to the plane of the plate and intersecting the surface of the plate at the up-stream edge of the hole, and by a mainly straight down-stream side forming an angle of at the most 30 and preferably between 10 and 15 with the plane of the plate. The downwards pointing apex of the traingular cross section, i.e. the lowermost point in the recess, lies at a depth below the surface of the plate of at least 25%, preferably between 50 and of the diameter of the hole, whereby the downstream side of the traingular cross section intersects the surface of the plate at an appreciable distance from the down-stream edge of the hole.

The holes in the plate are usually arranged in several rows extending across the plate perpendicular to the flow direction of the pulp in the distribution pipe, and accord ing to the invention the recesses at the holes in the surface of the plate facing the distribution are then preferably achieved by providing this surface, for each row of holes, with a groove having the above mentioned triangular cross section and extending parallel along said row of holes. When the recesses in the surface of the plate are formed by such grooves, it may also be advantageous to arrange the holes in the plate in rows extending across the plate obliquely to the direction of the flow in the distribution pipe, whereby also the grooves in the surface of the plate facing the distribution pipe will extend obliquely ot the direction of the flow in the distribution pipe.

In the following the invention shall be further described with reference to the accompanying drawing, in which:

FIG. 1 is a schematic side view of the headbox with the distribution pipe and the wet end portion of the Wire in a paper machine,

FIG. 2 shows schematically the headbox with the distribution pipe seen from above,

FIG. 3 is a cross section, perpendicular to the plane of the plate and parallel to the direction of the flow in the distribution pipe, of a hole plate of a prior design,

FIG. 4 is a corresponding cross section through a hole plate according to the invention, and

FIGS. and 6 are schematic plan views of two different designs of a hole plate according to the invention seen from the side of the plate facing the distribution pipe.

FIG. 1 shows the inlet end of a paper machine with the wet end portion of the wire 1 and a headbox 2 of conventional type. The headbox 2 is supplied with pulp introduced from one side through a distribution pipe 3 attached to the rear side (as viewed in FIG. 1) of the headbox. As shown in FIG. 2, the distribution pipe 3 extends over the whole width of the headbox 2 and is at its one end provided with an inlet opening 4 for the pulp. Between the distribution pipe 3 and the headbox 2 a hole plate 5 is mounted perpendicular to the flow direction in the headbox 2. The hole plate 5 is provided with a large number of holes 6 evenly distributed across the plate. The pulp flowing into the distribution pipe 3 through the inlet opening 4 will pass through the openings 6 in the hole plate 5 and flow into the headbox 2. The function of the hole plate 5 is thus to deflect the pulp flow about 90 and at the same time to distribute the pulp uniformly across the entire width of the headbox 2. The pul is supplied to the distribution pipe 3 in excess of that entering the headbox 2 and the pulp not passing through the hole plate 5 into the headbox leaves the distribution pipe 3 at its opposite end through an outlet Opening 7, from which the pulp is returned to the inlet 4. In this way a more favourable flow pattern is achieved at the end of the distribution pipe opposite the inlet opening 4.

As shown, the cross sectional area of the distribution pipe 3 decreases continuously from the inlet 4 to the outlet 7 in correspondence with the decreasing volume of the pulp flow. The pulp in the distribution pipe 3 has consequently a flow direction substantially parallel to the hole plate 5 except in the vicinity of the holes 6, where a deflection of the flow takes lace.

FIG. 3 is a cross section view through a hole plate of an exemplary prior art design. The cross section is taken perpendicular to the plane of the plate and parallel to the direction of the flow in the distribution pipe 3'. The holes 6' in the hole plate 5' are usually somewhat tapered at the surface 8' of the plate facing the distribution pipe 3'. At each hole 6 in the plate 5 some of the flow (arrows 9') in the distribution pipe will be deflected into the hole 6. The division of the pulp flow at a hole 6 in one portion flowing into and through the hole 6 and in one portion passing along the surface 8' of the plate 5 will with this design of the hole plate take place at the sharp down-stream edge 10 of the hole. At this edge a stagnation point in the pulp flow is formed, where the velocity of the pulp is zero. Due to this, individual fibres and twisted fibre threads in the pulp will have a tendency to cling to the down-stream edge 10 of the hole 6', whereby an accumulation of fibres 11' is formed on this edge. Due to the considerable friction existing between the sharp down-stream edge 10 of the hole 6' and the fibre accumulation 11' and due to the fact that the flow velocity of the pulp over this edge 10 is zero, this accumulation of fibres can become very large. It can even contain fibre threads having such a length that they extend from the down-stream edge 10' of one hole 6' along the surface 8' down stream of the hole all the way to and down into the next hole 6' in the plate 5'. Eventually a fibre accumulation formed in this way or parts thereof may be pulled away from the down-stream edge 10' of the hole 6' and be carried by the pulp flow through this hole or possibly through the next hole in the down-stream direction. This accumulation of fibres pulled away from the hole edge will be transported through the headbox as a fibre bundle out onto the paper machine wire, which results in poor quality of the paper produced.

This disadvantage is eliminated if the hole plate is designed according to the present invention. FIG. 4, which is a cross section corresponding to FIG. 3, shows a preferred design of a hole plate according to the invention. According to the invention the surface 8 of the plate 5 facing the distribution pipe 3 is recessed down stream of each hole 6 so that the down-stream edge 10 of the hole is disposed below the surface 8 of the plate and so that down-stream of the hole 6 a surface 12 is formed, which extends down-stream of the hole over a considerable distance as compared with the diameter d of the hole and which forms a small acute angle a with the surface 8 of the plate 5. With this design of the hole plate 5, the point in which the pulp flow 9 is divided into one portion flowing through the hole 6 and another portion flowing along the plate 5 will, as shown in FIG. 4 not be located at the sharp down-stream edge 10 of the hole but somewhere on the sloping surface 12. The unavoidable stagnation point 13 down-stream of each hole 6 will thus lie on the sloping surface 12 spaced from and down-stream of the sharp down-stream edge 10 of the hole 6. In this stagnation point 13 no large accumulation of fibres or fibre threads can be formed, as the friction between the fibres and the sloping surface 12 is much too small. Furthermore the stagnation point 13 will move back and forth along the sloping surface 12, whereby any fibres that may temporarily stop on the surface 12 will be carried on either into the adjacent hole 6 or further along the hole plate 5. No accumulation of fibres will be formed on the sharp down-stream edge 10 of the hole 6, as the velocity of the flow over this edge is high.

In the form of the invention shown by way of example in FIG. 4 the sloping surface 12 is straight. From an operational point of view, however, nothing prevents that this surface is somewhat curved, provided it does not have any pronounced edge, on which fibres can collect. From a manufacturing point of view, however, it is advantageous that the sloping surface 12 is straight. The angle a between the surface 12 and the surface 8 of the plate 5 should not exceed 30 and should preferably lie between 10 and 15. In FIG. 4 the angle a is 12.

As shown in FIG. 4, the recess in the surface 8 of the plate 5 at each hole 6 is preferably shaped so as to have a triangular cross section in a plane perpendicular to the plane of the plate and parallel to the principal direction of the flow in the distribution pipe 3. The up-stre'am side 14 of the recess can be approximately perpendicular to the plane of the plate and should intersect the surface 8 of the plate at the up-stream edge 15 of the hole 6, whereas the down-stream side of the recess forms the sloping surface 12 and thus the acute angle a with the plane of the plate. The largest depth b of the recess below the surface 8 of the plate should amount to at least 25% of the diameter d of the hole 6 and preferably lie between 50 and of this diameter. In FIG. 4 the depth b of the recess is /3 of the hole diameter d. As it is preferable from the manufacturing point of view to make the recess by milling, the sides 12 and 14 of the recess are preferably perpendicular to each other.

The surface 8 of the plate 5 facing the distribution pipe 3 can be provided with a separate recess for each hole 6, in which case each recess must have a width at least corresponding to the hole diameter d. From the manufacturing point of view and for other reasons, however, it is more advantageous to provide the recesses at the holes 6 in the surface 8 of the plate in the manner schematically shown in FIGS. 5 and 6. FIG. 5 shows a hole plate according to the invention seen perpendicular to the plane of the plate 5 from the surface 8 facing the distribution pipe 3. The holes 6 in the plate are arranged in several rows extending across the plate perpendicular to the direction of the pulp flow in the distribution pipe 3. The recesses at the holes 6 in the surface 8 of the plate 5 facing the distribution pipe 3 are here achieved in that the surface 8 for each row of holes is provided with a groove extending across the plate 5 parallel to the row of holes and having the cross section described above and illustrated in FIG. 4. The bottom of the groove, i.e. the intersection between the two sides 12 and 14 of the groove is preferably slightly rounded, whereby the manufacturing as well as the cleaning of the grooves is simplified. This rounded bottom in the grooves is, however, not essential for the operation of the plate. In the hole plate shown in FIG. the holes in the different rows of holes are somewhat displaced relative to each other, whereby a more uniform distribution of the holes over the plate is obtained.

Instead of arranging the rows of holes and thus the grooves in the surface 8 of the plate 5 facing the distribution pipe 3 perpendicular to the direction of the pulp flow in the distribution pipe 3, it can be advantageous, as is schematically shown in FIG. 6, to arrange the rows of holes and thus also the grooves in the surface 8 of the plate so as to extend obliquely across the plate relative to the direction of the pulp flow in the distribution pipe. In this case a flow component is obtained in the longitudinal direction of the grooves, whereby the fibres are prevented from collecting in the bottom of the grooves between the individual holes.

Other designs than those shown on the drawings are of course possible within the scope of the invention. Thus the sloping surface 12 down-stream of each hole 6 can, if preferred, extend all the way to the upstream edge 15 of the next hole.

I claim:

1. A hole plate for distributing stock in a paper-making machine or the like, comprising an elongated plate having a first lengthwise surface extending between a first end and a second end, means defining a plurality of holes extending through the plate substantially perpendicularly to the plane of the first surface for conveying stock through the plate, means defining a recess in the first surface adjacent each hole, each recess merging at one end into its adjacent hole at the edge of the hole nearest the said first end and having a base extending smoothly from the said nearest edge of the hole towards the said second end for a distance greater than the dimension of the hole lengthwise of the first surface and merging smoothly into the first surface at the other end of the recess, whereby the stagnation point of stock flowing over the first surface in a direction from the said first end to the said second end is located at a zone of the recess remote from the said nearest edge of the hole and whereby the stock is conveyed through the holes in a direction substantially perpendicular to the direction of flow of the stock over the first surface.

2. A hole plate according to claim 1, wherein the depth of the recess at the said nearest edge of the adjacent hole is not substantially less than one-quarter of the said lengthwise dimension of the hole.

3. A hole plate according to claim 1, wherein each recess is substantially triangular in section taken on a plane perpendicular to the first surface of the plate and extending lengthwise through the plate, the apex of the triangular section being recessed below the first surface a distance not less than one-quarter of the said lengthwise dimension of the adjacent hole, the apex being located in the region of the adjacent hole, and the base of the recess between the ends thereof forming an angle with the first surface of the plate of not substantially greater than 30.

4. A hole plate according to claim 1, wherein the recess merges at said other end thereof with the first surface of the plate at an angle of not substantially greater than 30.

5. A hole plate according to claim 1, wherein the edge of each hole nearest the said first end of the plate is substantially coincident with the edge of the adjacent recess nearest the said first end of the plate.

6. A hole plate according to claim 1, wherein the recess is defined by a smooth surface.

7. A hole plate according to claim 6, wherein the recess is defined by intersecting straight surfaces which are (a) aligned lengthwise of the plate, and (b) located in planes which are perpendicular to the lengthwise extent of the plate and angularly related to the plane of the first surface of the plate.

8. A hole plate according to claim 1, wherein the recess includes a wall at said one end forming a substantially right angle with the said base.

9. A hole plate according to claim 1, wherein the recess includes a wall at said one end intersecting the said base with a rounded wall part at the intersection.

10. A hole plate according to claim 1, wherein the holes are arranged on the plate in rows disposed transversely of the plate and the recesses are constituted by portions of continuous grooves in the plate extending parallel to the rows of holes.

11. A hole plate according to claim 10, wherein the holes are arranged in mutually parallel rows substantially perpendicular to the lengthwise extent of the plate.

12. A hole plate according to calim 10, wherein the holes are arranged in mutually parallel rows oblique to the lengthwise extent of the plate.

References Cited UNITED STATES PATENTS 3,098,787 7/1963 Sieber 162-343 X 3,216,892 11/1965 Wahlstrom et al 162-343 S. LEON BASHORE, Primary Examiner A. DANDREA, IR., Assistant Examiner U.S. Cl. X.R. 162338

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