Paper Machine Foil Support Having Controlled Deflection

Abstract

A dewatering foil for positioning beneath a traveling Fourdrinier wire of a paper making machine having a supporting beam pivotally mounted at its ends with the beam constructed relative to the foil so that in all positions of support it has a vertical downward component of deflection due to the force of the friction of the wire against the foil.

Description

BACKGROUND OF THE INVENTION

The invention relates to improvements in supports for foils in paper making machines. The foils are generally of the nature shown in U.S. Pat. No. 3,377,236 assigned to the assignee of the instant application. In this type of foil, the foil generally has a leading edge which makes line contact across the traveling fourdrinier wire, and has a planar offrunning surface which forms a small diverging angle with the wire, so that as the wire passes the foil, water will emerge from the web through the wire and flow onto the upper surface of the foil and downwardly off the trailing edge to dewater the web. The wire travels at a relatively high rate of speed and in the dynamic operation of dewatering, changes in the frictional force of the wire on the foil occur. These frictional forces while varying in small amounts can change very rapidly, and it has been found that with foil supports of conventional construction vibration and chattering occur resulting in unstable operation and non-uniform dewatering that can cause non-uniform fiber arrangement and result in non-uniformity of the web on the wire. One of the reasons for this vibration has been discovered to be the stubbing effect between the foil and the wire which resembles a stick - slip type of vibration which occurs approximately at the maximum natural frequency of the foil support about its vertical axis. Foils and their supports have been generally designed to obtain maximum strength to accommodate static forces or vertical forces of the wire on the foil and have been designed to accommodate other factors without recognition of the vibration caused by variations in the frictional force caused by rubbing of the wire on the foil blade.

Designs heretofore available have also been constructed with the support for the foil being located so that its center of gravity is generally vertically directly beneath the foil. It has been discovered that this type of construction also causes vibrations and disturbing effects to the web formation inasmuch as this excites a torsional natural frequency. This is particularly true with open sections of construction such as those employed with double deflectors beneath the wire.

Accordingly, an object of the present invention is to provide an improved foil support having construction which helps eliminate the vibrations and chatter between the foil and the wire due to variances in frictional force which result during high speed dynamic operation.

A more specific object of the invention is to provide a support wherein momentary increase in frictional force between the wire and foil results in a downward deflection of the foil thereby tending to compensate for the increase or, in other words, decrease the frictional force and thereby tend to obtain a stable running condition.

Another object of the invention is to provide a foil support wherein the structural positioning between the foil and its support are such that torsional natural frequency vibrations due to reaction between the foil and the support are avoided.

Other objects and advantages will become more apparent with the disclosure of the preferred embodiments of the invention in the specification and drawings in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a support beam for a foil, with portions omitted, constructed in accordance with the present invention; and

FIG. 2 is a detailed vertical sectional view taken substantially through line II--II of FIG. 1 and illustrating schematically the unique construction and location of the elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 2, a traveling fourdrinier wire W is located in a fourdrinier section of a paper making machine and travels over dewatering elements including a foil 9. The foil has a leading edge 10 at which it forms substantial line contact with the wire W, and has a trailing planar surface 11 which forms a small angle 12 of divergence with the wire W for removing water from the web through the wire. The small angle of divergence preferably is in the range of 0.degree. to 3.degree. and this is adjustable to accommodate variations in running conditions by the support structure which will be described. The foil is rigidly mounted on a support beam B with a gib connection 13 on a plate 19 secured on the beam B. The beam and the foil extend in a cross-machine direction beneath the wire, and the beam is supported on its ends. At the ends are trunnions 14 and 15 which are adjustably mounted on the frame of the machine to pivot the beam to obtain the desired offrunning angle 12 between the foil and the wire. Various suitable locking structures which permit angular adjustment may be obtained, and need not be shown in detail since they will be fully appreciated by those skilled in the art. A split collar arrangement which can be locked by tightening the parts in the collar is a conventional structure which may be employed.

The beam preferably is constructed in an open box shape with the walls of the box shown at 18, and cross reinforcing webs 17 extend across the box beam B. At the ends of the beam are plates 16 to which the trunnions 14 and 15 are attached.

As shown in FIG. 2, the support beam has a first principal axis Y which is substantially vertical and a second principal axis X which is substantially horizontal (the axes are not exactly horizontal or vertical and their principal location will become clear in the following description).

The vertical axis X is the axis of the maximum moment of inertia and the horizontal axis Y is the axis of the minimum moment of inertia of the beam construction. The center of gravity of the beam is shown at C.G.

As the wire travels over the foil, a frictional force is caused by the rubbing of the wire on the foil. This force, as it acts on the center of gravity of the beam, is shown by the arrowed vector F. For this analysis the weight of the wire on the foil need not be taken into account since it is substantially static.

As shown in FIG. 2 the X and Y components of the force F are shown at F.sub.x and F.sub.y.

Plotting the deflection of the beam in the X direction, the force F.sub.x and from the minimum moment of inertia I.sub.y will result in a deflection .DELTA.X.

The deflection along the Y axis is shown as .DELTA.Y which is obtainable from the force F.sub.y and the maximum moment of inertia I.sub.x.

The beam is designed with the X axis being the maximum moment of inertia and the Y axis being the minimum moment of inertia so that F.sub.x is greater than F.sub.y and accordingly .DELTA.X is much larger than .DELTA.Y.

.DELTA. is the vector addition of .DELTA.X and .DELTA.Y and is the resultant deflection of the beam B. Therefore, it will be apparent that the deflection .DELTA. has a downward component with respect to the direction of the wire, and the deflection .DELTA. is at an angle .alpha. with respect to the wire.

The result of this construction is that if a variation occurs in the frictional force between the wire and the foil, for example, an increase in .DELTA.F will cause the beam to deflect downwardly causing the foil to move in a direction away from the wire to decrease the normal force (shown by the arrowed line 20) and thereby decrease the frictional force. Accordingly, a decrease in the frictional force .DELTA. will cause the beam to move slightly upwardly tending to increase the normal force 20 and thereby increase the frictional force. This will achieve a condition of stability.

It has been discovered in practice that the angle .alpha. (which is the angle between the resultant deflection vector and the wire) should be between 0.degree. to 5.degree.. This results in the vertical axis Y of the moment of inertia being near the full vertical position to minimize static beam deflection. Because of the possibilities of inaccuracies of construction, the positive angle should be maintained and designed to insure that an actual angle of 0 degrees or more will result.

It has been further discovered that to avoid exciting a torsional natural frequency in the beam it is important to position the leading edge 10 of the foil 9 beyond a minimum angle .beta. . This is the angle of measurement between a line 21 normal to the wire, and a line 22 drawn through the center of gravity C.G. and the leading edge 10 of the foil. It has been discovered that an optimum angle for .beta. is substantially 45.degree., and between 40.degree. and 50.degree. is desirable. The 30.degree. angle is critical and if .beta. falls lower than this torsional vibration, with its disturbing effect on web formation will tend to occur.

As will be apparent from the foregoing disclosure and the illustration of FIG. 2, a positive angle .alpha. can be obtained by construction and design both in the tilted position of the beam relative to the foil and the strength of the moment of inertia along its vertical axis Y relative to the strength of the moment of inertia along its horizontal axis X.

Thus, it will be seen that there has been provided an improved foil and support therefor which achieves the objectives and advantages above set forth which improves stability of operation and results in improved paper web formation particularly in high speed operating machines.

Claims

I claim as my invention:

1. In a dewatering foil structure for the fourdrinier section of a paper making machine, the combination comprising:

a dewatering foil having an upper planar surface for close running relation with a fourdrinier wire and positioned at an angle thereto to aid in removing water from a web on the wire and having a leading edge contacting the wire;

a rectangular hollow fabricated beam supporting the foil beneath the wire;

end support means for the beam;

the beam having a width substantially wider than said foil surface; said beam constructed to have a moment of inertia with a first principal axis which is generally vertical and a second principal axis which is generally horizontal;

said beam tilted with respect to the wire at a substantially greater angle than the angle between the foil surface and the wire so that the resultant beam deflection due to frictional force of the wire acting on the foil has a downward component whereby running variations of the frictional force of the wire on the foil will vary the deflection of the beam in a downward direction avoiding vibration of the beam through such frictional variances, said foil mounted on the upper leading corner of said beam and projecting a substantial distance ahead of the beam with said contacting leading edge being ahead of the beam.

2. In a dewatering foil structure for the fourdrinier section of a paper making machine constructed in accordance with claim 1, the combination comprising:

said end support being located directly below the contacting leading edge of the foil.

3. In a dewatering foil structure for the fourdrinier section of a paper making machine constructed in accordance with claim 1, the combination comprising:

said contacting, leading edge located relative to the center of gravity of the beam to form an angle of more than 30.degree. with a line normal to the wire extending through said center of gravity.

4. In a dewatering foil structure for the fourdrinier section of a paper making machine constructed in accordance with claim 3:

wherein said angle between the contacting leading edge and the center of gravity of the beam is between 40.degree. and 50.degree. .

5. In a dewatering foil structure for the fourdrinier section of a paper making machine constructed in accordance with claim 3:

wherein said angle between said contacting leading edge and the center of gravity of the beam is substantially 45.degree. .