US3048874A - Doctoring devices - Google Patents

Description

Aug. 14, 1962 L MacDONALD DOCTORING DEVICES 2 Sheets-Sheet 1 Filed Jan. 6, 1960 fflz enfor [4N Mac Davao Aug. 14, 1962 l. J. M DONALD DOCTORING DEVICES 2 Sheets-Sheet 2 Filed Jan. 6, 1960 jrzv erzfor [4N Mm: flan/01.0

United States Patent Quebec, Canada Filed Jan. 6, 1960, Ser. No. 735 8 Claims. (Cl. 15-256.51)

This invention relates to improvements in doctoring means for the removal of deposits from the outer surface of a drum which is either wholly or partially immersed in a liquid suspension of particles of matter.

The conventional type of doctor employed for this purpose ususally consists of a long thin blade of suitable material which is secured in a framework so that one of its edges presses against the moving surface of a drum or cylinder, and so scrapes off any fibrous material which clings to the surface of the drum of cylinder. When high intensity of loading is required at the contact of the working edge of the doctor on the moving surface of the drum or cylinder, it is necessary to provide a rigid supporting frame which is usually massive in order to be capable of withstanding the forces involved without allowing defiections of the blade which would be undesirable because of the need for continuous and substantially uniform doctor blade loading for satisfactory performance.

The present invention proposes to overcome the difficulties and disadvantages inherent in the conventional type doctoring device. To this end it is an object of this invention to provide a means for doctoring the surface of a body having the surface contour of a solid of revolution, which gives a high doctor loading without recourse to a bulky supporting structure.

Another object is to provide a means for doctoring a drum surface which requires only tensile loading of the doctor' means to achieve loading of the doctor edge against the surface to be doctored.

A further object is to provide a means for doctoring of the character described which is readily adjustable to increase or decrease the loading of the doctor edge against the surface to be doctored.

A still further object is to provide a means for doctoring of the character described which is readily adjustable for quick and inexpensive replacement of a worn doctor.

Still another object of this invention is to provide a means for doctoring which has a minimum amount of a static surface area on which deposits may form.

I The above and other objects and characteristic features of this invention will be understood more readily from the following detailed description taken in connection with the accompanying drawings, in which;

' FIG. 1 is an elevational view of a drum and a doctoring means embodying this invention.

, FIG...2 is an elevational view of the drum and doctoring means at right-angles to the view shown in FIG. 1.

FIG. 3 is a plan view of same.

FIG. 4 is an enlarged fragmentary view showing one manner in which a doctoring means feeding reel is mounted.

FIG. 5 is a plan view of FIG. 4.

FIG. 6 is an elevational view illustrating modifications of the mounting of the doctoring means.

FIG. 7 is an elevational view illustrating further modifications.

FIGS. 8 to 12 are sectional views, greatly enlarged, illustrating modified forms of the doctoring means.

Referring more particularly to FIGS. 1 to 3 of the drawings, the invention in the embodiment immediately to be considered consists of a wire or tape 5 wound in a 3,94,874 Patented Aug. 14, 1%62 ice substantially helical form about the surface of a cylinder or drum 6 from one end to the other. The wire or tape, hereinafter referred to as a doctor 5, is fed through a clamping bar 9 on the end surface of a bracket 10 adjacent one end of the drum. The doctor is then helically formed about the surface of the drum to the opposite end thereof and from there it is passed through a second clamping bar 11 on the end surface of a second bracket '12.

The bracket 10 is an integral extension of a bearing block 14 and has its clamping end surface lying preferably in a plane tangent to the curved surface of the drum at the nearest point of contact of the doctor with the drum surface. The clamping bar 9 is provided with a pair of bolts 15 which straddle the doctor and are tightened to compress the bar 9 against the clamping surface of the bracket 10 with the doctor therebetween. The bearing block 14, which supports one journal 16 of the drum, is fixed by bolts 17 to two supporting channels 18 which are themselves supported by suitable means (not shown) in a vat or like container. The journal 16 is connectable to suitable driving means (not shown) which is located beyond the bearing block 14.

The bracket 12 is also an integral extension of a bearing block 20 and has its clamping end surface lying preferably in a plane tangent to the curved surface of the drum at the nearest point of contact of the adjacent end of the doctor with the drum surface. The clamping bar 11 is provided with a pair of bolts 21 which screw into the clamping end of bracket 12 to secure the doctor between the bar and the bracket end in the manner abovedescribed in relation to the clamping bar 9. The bearing block 2t), which supports the journal 22'on the opposite end of the drum, is shown to be fixed by bolts 23 to a mounting 24 at the bottom or a wall 25 of the vat.

The doctor 5 may be fed from a reel 8 to the clamping bar 9. As will be seen in FIGS. 4 and 5, the reel 8 is mounted on an axle 27 between two parallel arms 28 which are secured at their inner ends to two adjacent sides of bracket 10. The arms 28 extend outwardly from the sides of the bracket 10 and are laterally offset with respect to the axis of the drum at an angle predetermined bythe angle at which the doctor approaches the end of the drum. The angle at which the doctor approaches the drum according to whether the helix angle is small or large, as shown FIGS. 6 and 7, and the lateral offset of the real supporting arms 28 with respect to the axis of the drum will vary according-1y so that the doctor will be fed from the reel to the drum surface along a line at right angles to the axis of the reel.

FIGS. 6 and 7 show plan views of a doctor with a small helical angle, and of one'with a large helical angle, respectively. The version with the small angle would be more suitable for application to drums having convex surfaces, e.g. barrel shape, and the version employing the large angleto drums having concave surfaces, e.g.

hour glass shape.

FIGS. 6 and 7 also illustrate modified clamp supports. Here the clamping bars 9 and 11 are mounted on brackets 30 and 31 respectively which are secured to opposing sides 32 and 33 of the vat. The reel (not shown) may also be mounted on similar brackets carried by one side wall of the vat so that the axis of the reel is at right angles to the angle of the approach of the doctor to the adjacent end of the drum as predetermined by the helix angle of the doctor about the surface of the drum.

The doctor according to the present invention is quickly and easily replaced when worn. This is accomplished by loosening the clamping bars 9 and 11, then drawing the doctor from the end remote from the reel until a suflicient amount is withdrawn to replace the worn section of the 3 7 doctor. When the required amount is withdrawn from the reel the latter may be locked to prevent further unreeling by means of a locking member 35 which engages the reel axle 27. The clamping bar bolts are then screwed home. After suitable tension is applied along the length of the doctor, the clamping bolts are screwed home to secure the doctor in its taut condition at either ends of the drum.

FIGS. 8 to 12 inclusive show cross-sections of modified forms which the doctor may take. In FIG. 8 the doctor is in the form of a cylindrical wire. FIG. 9 shows the crosssection to be triangular. FIG. 10 shows the cross-section to be that of a broad band. FIG. 11 shows a modification of the band in which the edges are bevelled to provide a knife edge. FIG. 12 is a modification of the band shown in FIG. 11 in which the band is transversely curved to conform with the contour of the surface of the drum at the predetermined angle of helix.

This invention is intended to give high doctor loading, Without recourse to bulky supporting structure which interferes with stock flow and which would provide an undesirable static surface area on which fibre deposit could occur. In operation, the doctor and the drum surface have motion relative to one another. This results in an accumulation of tensile force in the doctor along its length, causing one end to pull more heavily against its anchor than the other, to an extent depending on the value of the static preload applied. The asymmetric loading of the doctor results in an asymmetric positioning of it, with a helix angle which increases from the slack end to the taut end of it.

In the present application of this invention the drum moves while the doctor is stationary. However, since only relative motion between the doctored surface and the doctor is required, the drum may be fixed and doctor may be anchored to supports which rotate about the axis of the drum to give the required relative motion.

While the invention is directed primarily to the prevention of the accumulation of wood fibres deposited on the surface of a steam heated cylindrical drum rotating vertically in a tank of paper making stock, it is by no means limited to such application. There are many other instances where a drum surface, cylindrical or otherwise, needs doctoring and in industries outside the field of pulp and paper. The doctoring device which constitutes this invention is as readily applicable to the drum surfaces employed in these other instances and other industries. The axis of the drum may be vertical, as described, or horizontal, or have any other attitude, without detriment to the action of the invention.

The combined flexibility and helical application of the doctor lends itself to eflicient use on convex and concave surfaces of a solid of revolution as well as to cylindrical surfaces. In the case of a concave surface the flexibility of the doctor will permit the doctor to lie along the surface when th helix angle is adjusted to suit the concave curvature provided that the degree of curvature is not too pronounced.

What I claim is:

1 1. The combination with a drum or cylinder of a flexible doctoring device extending substantially helically around the drum or cylinder in scraping contact therewith, means for effecting relative rotary movement between the doctoring device and the drum or cylinder whereby material adhering to the surface of the drum is doctored off, means for tensioning opposite ends of the doctoring device to cause the latter to engage firmly and continuously the drum or cylinder along the entire helical line of contact between the doctoring device and the drum or cylinder, a clamping means located outwardly of opposite ends of the drum and adapted to secure opposite ends of the doctoring device when the latter is under tension, said clamping means comprising a bracket having a clamping surface disposed to lie in a plane substantially tangential to the curved surface of the drum at the nearest point of contact of the doctoring device with the drum surface, a clamping bar mounted on the clamping surface of said bracket to straddle the doctoring device at right angles to the longitudinal direction of the doctoring device between the bracket and the first point of contact with the drum, and clamping bolts extending through said clamping bar and into said bracket at either side of the doctoring device.

2. The combination claimed in claim 1, in which the angle of the helix of said doctoring device is variable to compensate for the loading force to be applied by the doctor edge against the surface to be doctored.

3. The combination claimed in claim 1, in which the doctoring device is of an undefined length, a reel mounted at one end of said drum beyond said clamping means about which said undefined length of the doctoring device is coiled for intermittently feeding successive portions of the doctoring device helically across the drum surface as preceding portions become worn out;

4. The combination claimed in claim 3, in which the doctoring device consists of a length of wire.

5. The combination claimed in claim 3, in which the cross section of the doctoring device is triangular.

6. The combination claimed in claim 3, in which the doctoring device consists of a tape of flexible, wear-resistant material.

7. The combination claimed in claim 3, in which the doctoring device consists of a tape of flexible, wear-resistant material having at least one bevelled, longitudinal side edge.

8. The combination claimed in claim 3, in which the doctoring device consists of a tape of flexible, wear-resistant material having one surface concavely curved to conform with that portion of the drum surface along which the tape lies according to the predetermined angle of helix of said tape.

References Cited in the file of this patent UNITED STATES PATENTS 95,722 Pond. Oct. 12, 1869 2,392,490 Maruri Jan. 8, 1946 2,664,792 Cook Jan. 5, 1954 2,665,444 Nelson Jan. 12, 1954 FOREIGN PATENTS 695 Great Britain Mar. 7, 1872

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