US2278526A - Method of and apparatus for couching - Google Patents

Description

Inventor J. P. RICH METHOD OF AND APPARATUS FOR COUCHING Filed April 17, 1959 April 7, l1942.

Patented Apr. 7, 1942 UNITED STATES PATENT OFFICE.

METHOD F AND APPARATUS FOR COUCHING Y John r. nich, Nashua, N. ii., assignmtio nii-V proved Paper Machinery Corporation, Nashua, N. H., a corporation of Maine Application April 11, 1939, serial No. 268,355

(ci. zio-199) 4 Claims.

'Ihis invention relates to machines for removing solids from various liquids by theflltration process, and particularly to an improved means of removing these solids from the filter surface.

One conventional type of lter mechanism employs adrum or cylinder, the outside of which is covered with a fine wire screen or other ltering material. This y drum or cylinder is immersed in a tank .or vat containing the material to be filtered, the liquids of the material passing through the screen or filter surface, while the solids are retained on the filter surface.

'Ihe drum is preferably rotated at a speed to provide time for the solids to form in a mat on ,the lter surface, in sumcientthickness or degree so that they may be removed as a continuous web or sheet. Such removal can be simply accomplished by means of a conventional couch roll which is a cylinder or drum mounted above the -fllter drum and arranged to press against the mat formed on the filter drum, the mat adhering to the surface of the couch roll, enabling the removal of the mat from the filter surface. l

It is important that the couch roll travel at a predetermined rate of Vspeed relative to the sheet or mat on the filter surface, which it is desired to remove. If the couch roll is driven entirely by the friction between it and the sheet or mat on the filter drum, a certain amount of variable slippage o'r sliding may readily occur between the surface of the couch roll and the surface of the mat, due to the force required to turn the couch roll. This is particularly true if the couch roll is carried in or on bearings, and is pressed against the filter drum by means of weights. The friction of the doctor blade against the surface of the couch roll, for removal of the mat, also adds to the power necessary to keep the couch roll turning.

Not infrequently the couch roll is heldV from ever coming into direct contact with the filter drum by means of stops which are adjusted to provide a clearance between the couch roll and the filter drum when no mat is being formed. Under such conditions, while the filterdrum may be turning the mat may not touch theI couch roll which, therefore, will be at rest. A thick mat may then start to form on theiilter drum surface, and when it reaches the stationary cpuch roll, may jam or plug between the roll and the drum before the roll has time to get into motion.

The couch roll is sometimes driven directly from the filter drum by belts, chains, gearing or other suitable means in which case some definite relative speed of rotation can be xed between the two rotating members, and a definite relative lineal speed established between the surface of the filter drum and the surface of the couch roll. Y

In ordinary operation, however, of thickeners and lters employing couch rolls, varying conditions. of usevary the amount or. thickness of the mat through fairly wide limits. It is obvious that with a thin mat, where thecouch roll rests close to the filter surface, the relative lineal speed of the mat as it contacts the roll will be considerably less than the. surface speed of the mat were it considerably thicker, this added thickness having the effect of increasing the di- I ameter and the peripheral speed, even though the R. P. M. speed of rotation be the same.

These variations alone make it improper and undesirable to provide a fixed drive between the nlter drum and couch roll, such a drive providing only for a relative speed and R. P. M. between drum and roll, and in no way providing a relative lineal surface speed between the mat and the roll under varying conditions of operation. It is not only desirable, but frequently necessary to have a certain degree of exible control lbetween the relative'lineal speeds of the couch roll and the mat, to aid in the proper contact of .the roll on the mat, to express the water from the mat through the lter surface without injuring or crushing the mat itself. VShould the xed relative speed of the couch roll surface be adjusted to provide proper operation on a certain mat thickness, it is obvious that an increase in this mat thickness, automatically increases its lineal or surface speed, and

under these conditions there would be a retard- 1 ing or pushing back action as the mat contacts the roll surface, which may disrupt or crush the mat, and which condition is decidedly objectionable. Under such conditions, there may be a definite rubbing or abrasion occur between the mat and the filter surface of the drum, causing unnecessary wear on the filter surface, and a tendency to rub the mat into the surface, making it difilcult to remove cleanly; Under these conditions, the mat may tend to adhere to the drum sufficiently so that the roll will not remove it properly, and the disrupting of the mat surface by the roll may cause it to break up into sections or pieces rather than coming ofi?l as a complete sheet.

We have discovered that the provision of a couch roll drive which will turn the roll at a definite surface speed relative to that of the filter drum, while at the same time providing a .cer-

tain amount of flexibility or yield as regards the relative lineal speed of the roll and drum, greatly improves the contact between the couch roll and the mat, has less tendency to disrupt the mat or roll into the filter surface, reduces wear on lter wire and couch roll due to abrasion, and thereby effects an overall improvement in couch roll operation.

Reference is made to the following figures:

Fig. 1 is a vertical section through a conventional type of filter and couch roll, each being independently driven by means hereinafter described.

Fig. 2 is a section thru Fig. 1 on line 2-2.

Fig. 3 is a fragmentary vertical sectionshowing hand actuated pitch control.

In Fig. 1 a tank I is provided to hold the material to be ltered, this being supplied by any convenient means such as pipe 2 with a baille plate I to effect proper distribution of the materials supplied through pipe 2 throughout the area of vat I. Rotating in this vat I is a cylindrical drum-type filter or open cylinder mold 4 which may be made up of segmental drainage portions 5 or mere supporting members for filter medium, the surface of which is covered with a filtering medium l. This drum 4 may be mounted for rotation by any suitable means such as the shaft 1 journalled in the end tank walls in any well known and accepted manner.

Disposed above the filter drum 4 is a couch roll I, mounted on shaft i journalled in suitable bearings Il, which bearings may be arranged for motion about point II so that added pressure can be imposed on the filter drum by weight I2. Should it be desirable to reduce pressure to less than the weight of the roll 8, the lever and bearing I 0 can be extended beyond the fulcrum II so that counter-balance weights can be used, or, a spring or springs I3 could be used to support a part of the weight of roll t. The construction and arrangement of the filter drum and of the couch roll together with its mounting forms no part of this invention and any conventional or suitable arrangement may be employed.

According to my invention, the shaft 1 on which the filter drum 4 is mounted is rotated at a pre-determined and definite speed by an electric motor I4. Preferably, this is directly cony nected through reduction gearing to shaft 1, but for purposes of illustration we have shown this motor I4 connected to shaft 1 by means of a non-slip belt or chain I5, operating over a sheave or pulley Il. The characteristics of motor I4 are such that its speed varies only with the frequency changes of the electrical circuit supplying current to themotor. This motor I4 can be considered an alternating current moto;` operating at practically synchronous speed with the frequency of the electrical energy supply.

The couch roll l is driven by a second motor I1, this motor driving the couch roll shaft 9 through any convenient means such as a nonslip belt or chain operating over a pulley or sheave Il. 'I'his pulley or sheave I9 is adjustable as to its pitch or driving diameter, enabling the speed ratio between motor I1 and couch roll shaft 0 to be adjusted in increments as may be desired to meet the particular requirements of operation. Fig. 3 illustrates a simple and conventional form of speed ratio adjustment whereby a non-slip friction belt is used to drive the couch roll with means to adjust the driving diameter of sheave I9. As shown in this view, the

sheave I9 is formed into two halves, one of which 2i is keyed to the couch roll shaft l, and the other of which 22 is splined for adjustment longitudinally' of this shaft. A threaded adjusting nut and screw, indicated generally at 23, serves to move the adjustable portion 22 toward or from the xed -portion 2I of the sheave. Since the beit receiving groove 24 is tapered to receive a V-shaped driving belt 2l, it will be obvious that the effective diameter of the sheave I9 is decreased as the portions 2| and 22 are separated or increased -as they are brought together, forcing the belt inwardly or outwardly. as the case may be, thus varying the driving or driven speed of the sheave, and the couch roll shaft 9.

The method illustrated in Fig. 3 is simply one which might be utilized and is shown as illustrative of a method which may be employed. Once adjusted, a definite speed ratio is fixed between the motor I1 and the couch roll 8, subject, however, to the automatically controlled torque or driving eiort of motor I1.

The motor I1 is subject to the same electrical supply frequency change as the motor I4, and therefore its speed is affected by the current changesv in the same manner and in the same ratio. The motor I1, however, is especially constructed to provide only a small change in driving power through a limited range of speed change with the same electrical current supply. This special motor construction, therefore, provides a definite driving force, at the same time permitting the load on the motor to change its speed through a limitedrange, without materially changing the driving force or turning effort imparted to the couch roll itself. Thus, fc changes in the thickness of mat formed on the filter drum, which represents a small but definite changein surface or lineal speed of the mat relative to the couch roll, the driving force or wrque of the motor I1, at any one setting for the speed adjusting sheave Il can be considered virtually constant, so far as the contact between the couch roll and the mat is concerned whether the roll be tending to turn slightly faster, or slightly slower or substantially the same as its surface speed. It will thus be seen that the use of a specially constructed motor I1 automatically provides for the adjustment of couch roll speed to accommodate itself to different mat thicknesses and maintain relative positive, or negative or neutral surface. contact with the mat. The adjustable sheave i! enables the operator to vary or adjust the relative speed of the roll 8 and the motor I1 in order that the couch roll surface may tend to move at a slightly slower speed than the surface of the mat, or at substantially uniform or synonymous speed, motor I1 establishing automatically a denite torque or driving effort even though the speed in R. P. M. of the couch roll 8 may have to vary somewhat due to changes in mat thickness. This provides means for automatically varying the lineal or surface speed of couch roll 8 to accommodate different thicknesses of mat on the filter drum 4. It provides means whereby the relative surface speeds of the roll and of the mat may be practically identical, or produce a condition where the roll may have a certain denite and controlled effort to travel slightly faster than the mat, or slightly slower than the mat, the degree of change of relative speed being under control of the operator, and at no time sufficient to disrupt the surface of the mat, but rather to ald the couch roll to properly compress the mat and providing a surface thereon which will adhere to the roll.

Ordinarily the couch roll may be provided with some special surface materials of rubber, felt or other suitable material, which inherently tends to cause the mat to adhere to it, provided that the pressure on the mat is properly controlled, and the relative speed between the surface of the roll and the mat does not disrupt the mats surface. Under certain conditions. the mat may be reason,-

, ably iirm and smooth by the time it reaches the roll, hence all the roll is required to do is to contact the surface of the mat at as near the same lineal speed as possible, impress itself firmly on the surface so that the mat will adhere to the surface of the roll, and be readily removed from the surface of the lter drum. ditions, the surface` of the mat may be such that it would be desirable to have the couch roll surface tend to move slightly faster than the lineal surface of the mat, thereby having a tendency to draw and compress the surface structure of the mat more compactly and uniformly, thereby compressing the mat and reducing the liquid content by forcing it thru the filter surface.. Under other conditions, it may be .desirable that the couch roll lag very slightly over the surface speed of the mat to accomplish certain desirable results in compressing the mat and removing it vfrom the filter surface.

Heretofore, such highly desirable adjustments could only be accomplished approximately by any direct drive between the filter drum and the couch.

Under other conprising a lter drum on which a mat of semi solid material may be deposited, a couch roll adapted to compress this mat of semi-solid material, a driving motor of substantially fixed speed for all load conditions, for driving the filter drum, and a motor having a substantially constant torque and a variable speed range, for driving the couch roll with a substantially uniform driving torque over al denite speed variation range.

2. An apparatus of the class described comprising a filter drum, adapted to collect and retain a sheet or mat of semi-solid material on its surface, a motor of substantially fixed speed for driving' or rotating said drum, a couch roll, a constant torque, variable speed motor having a substantially uniform torque through a certain range of speed variation effective to drive said roll with a substantially uniform driving torque.

over a definite speed variation range, and means for manually adjusting the speed ratio between said second mentioned motor and said couch roll.

V3. Apparatus of the class described comprising a filter drum adapted for rotation in a vat containing solids in a liquid suspension, and to remove from said vat, a sheet or mat of semi-solid material on its surface, a motor of substantially fixed speed at all driving torques within its power range for driving or rotating saidiilter drum, a couch roll adapted to compress the sheet or mat formed on the filter drum, and a constant torque, variable speed motor having-a substantially uniform driving torque throughout a certain portion or degree of speed range effective to similar direct drive mechanical means were used. v

The result of using such an arrangement prevented the operator from obtaining optimum operating conditions, as no automatic means has heretofore been provided for maintaining a uniform torque or drive on the lter mat under rapidly varying conditions of mat thickness.

The foregoing discussion as to the characteristics ofimotors I4 and I1 have been based on the assumption that alternating electric current supply is used. Where direct current is available, it is, of course, obvious that relative speed adjustment of the two motors I4 and l1 can be even more readily accomplished by methods well known in the electrical art and which need not be elaborated on or herein described.

Having thus described my invention. what I claim is:

1. An apparatus of the class described comdrive said couch roll with a substantially uniform driving torque over a definite speed variation range.

4. Apparatus of the class described comprising a vat, means to introduce into said vat liquids containing solids in suspension, -a filter drum located within said vat and immersed in said liquid having a filter' surface thru which the liquids of said suspension will pass, leaving solids on the filter surface, means for rotating said lter drum in said vat at a substantially fixed speed, a couch roll mounted above said vat and adapted to contact the mat or sheet formed on said lter drum, and means, wholly independent of said Adrum rotating means, to rotate vor drive said couch roll to provide automatically a definite contact relationso far as relative surface speed of couch roll and mat are concerned regardless ot mat thickness, comprising a motor having a substantially constant torque and a variable speed range. Y

JOHN P. RICH.

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