AU598686B2

AU598686B2 - A rake arm

Info

Publication number: AU598686B2
Application number: AU19725/88A
Authority: AU
Inventors: David Taylor
Original assignee: Supaflo Pty Ltd
Current assignee: Supaflo Technologies Pty Ltd
Priority date: 1987-07-23
Filing date: 1987-07-23
Publication date: 1990-06-28
Anticipated expiration: 2008-07-22
Also published as: AU1972588A

Description

i9 8 6 8 6 £1O1EN 1Q CnMMPLETE SPECIFI ~QJi g-l~;lbDL-n= ~QB~Q~QCiLU~i Class Int.Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: 0 0 Sa o Priority: o'Related Art: t 0 Name of Applicant: o "Address of Applicant: *6 LAROX PTY, LTD..

18/1 Short Street, Chatswood, New South Wales 2067, Australia David Taylor Actual Inventor: Address for Service: SHELSTON WATERS, 55 Clarence Street, Sydney Complete Specification for the Invention entitled: "A RAKE ARM" The following statement is a full description of this invention, including the best method of performing it known to us:- 1 Complete of PI 3294 dated 23rd July, 1987 SOc3i ISO 22/07/83 This invention relates to thickeners of the kind used to separate liquid from a pulp. More particularly the invention relates to rake arms used in such thickeners and a method of fabricati~ng rake arms. Thickeners of this type are used in fields such as mining, food processing, and sugar refining.

Hitherto most thickeners which employed rakes used trusses for the rake arms since these gave high strength at minimum cost. These designs have proven satisfactory for thickeners in which only the blade attached to the bottom of the rake arm is submerged in the pulp. However, in so called high rate thickeners in which both the rake arms and attached blades are submerged in the pulp the truss rake arms have proven to be unsatisfactory. In particular the drag on the truss rake arms results in high torque loading on the driving machinery and the truss rake arms tend to move the entire pulp bed around with the rake thus reducing the. effectiveness of the directing blades.

These problems are partly due to the greater viscosity of 02do flocculated pulps which are used almost exclusively in high rate thickeners. The problem of truss rake arms moving the whole pulp bed particularly arises if the pulp is over flocculated.

It is therefore an object of this invention to provide a rake arm which will overcome or substantially ameliorate these disadvantages. It is also an object of this invention to provide a method of fabricating such a rake arm.

-2 Accordingly, this invention consists in a rake arm of the kind for submerged use in a thickener to extend from a central driven hub and carry a plurality of rake blades at spaced intervals along its length characterised in that the arm is a single member having a relatively sharp leading edge and a streamlined cross-sectional profile with the distance between the leading edge and trailing edge being greater than the height of the profile, For preference the area of the cross-sectional profile gradually decreases towards the remote end of the 0 a arm.

The trailing edge of the rake arm is also preferably relatively sharp.

o",O It is also preferred that the distance between the leading edge and the trailing edge is greater than twice 0 o0 the height of the profile. That is, the cross-sectional o o width of the arm is greater than twice the crosssectional height of the arm.

S'o' In a preferred embodiment the cross-sectional profile is triangular and disposed such that one of the corners of the triangle forms the leading edge. The triangular cross-section preferably has two corners with included angles of about 30° which respectively form the leading and trailing edges of the arm.

In a second aspect the invention consists in a method of fabricating a rake arm of the kind described above, said method comprising the steps of forming two or more elongate plates each with a transverse profile 3 corresponding to part of said stream lined crosssectional profile and joining said plates along the respective longitudinal edges to form said arm.

Preferably one of the plates is formed substantially flat.

In the preferred embodiment the arm has a triangular cross-sectional profile and is formed from two elongate plates. A first plate is bent to form a generally V-shaped transverse profile and is joined to a second substantially flat elongate plate along the respective longitudinal edges. It is preferred that the plates are 0 0 steel and are joined by electric arc welding.

The rake arm of this invention produces significantly less drac; than previously known arms when moving through o o pulp due to the relatively sharp leading edge. In 0 addition the decreasing size of the arm along its length reduces the drag further toward the outer end of the arm thus decreasing the torque loading on the hub. The i preferred form of the invention in which the arm has a 0 2d' relatively sharp trailing edge provides an additional advantage. In this regard it is sometimes necessary to reverse the direction of rotation of the rakes in a high rate thickener if they become bogged. The relatively short trailing edge provides the advantage of low drag during such reversing.

One embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings in which: 4 Figure 1 is a plan view of an assembly of four rake arms according to this invention; Figure 2 is a part elevation of the arrangement shown in Figure 1; Figure 3 is a cross sectional view of one of the arms in the arrangement of Figure 1 toward the outer end thereof; Figure 4 is a cross-sectional view similar to Figure 3 toward the inner end of the arm; Figure 5 is an enlarged plan view of part of the arrangement shown in Figure 1 illustrating the connection of one of the rake arms to the central hub; and Figure 6 is an end elevation of the arrangement shown in Figure Referring to the drawings Figures 1 and 2 show an assembly of four rake arms 10 of the kind for submerged use in a thickener (not illustrated). The rake arms extend from a central hub 11 which is driven in rotation in the conventional manner by a hydraulic or electric motor (not illustrated). Each rake arm 10 carries four rake blades 12 spaced at intervals along the length of the arm in the known manner. The depth of successive rake blades 12 preferably decreases toward the outer end of the rake arm 10. As best seen in Figures 5 and 6 the rake arms 10 are secured to a flange 13 forming part of hub 11 by means of a plate 14 which is bolted to the flange 13 and welded to the rake arm The rake arms 10 are inclined as shown in Figure 2 5 and each is held in this position by a strut 15 of adjustable length. The ends of the strut 15 are secured to lugs 16, 17 respectively welded to hub 11 and rake arms Adjustable tie rods 18 extend between adjacent rake arms 10 to rigidify the structure.

As best seen in Figures 3 and 4 the rake arms 10 are a single member of triangular cross-section which gradually decreases in size toward its free end. The arm is formed with two corners 19, 20 of the triangular cross-section having included angles of approximately 300 and these corners form the leading and trailing edges of the arm. In this way a comparatively sharp edge is presented to the pulp to reduce drag.

The rake arm is constructed from steel plate. This is done by bending or folding an appropriately shaped top plate 21 to a suitable angle (approximately 1200) and welding the V-shaped plate 21 to a shaped flat bottom plate 22 at corners 19, 20 to form the triangular cross-section. That is to say V-shaped plate 21 and plate 22 are joined along respective longitudinal edges.

Strengthening plates (not illustrated) can be placed within the triangular section if necessary.

The rake arm according to this invention has been found to produce considerably less drag than previously used truss type arms in submerged rake arm thickeners thus reducing the driving torque and allowing smaller drive components such as motor and gearboxes to be used.

The foregoing describes only one embodiment of this 6 invention and modifications can be made thereto without departing from the scope of the invention. For example, the rake arm can be formed from two bent plates welded at respective edges to result in a diamond shaped cross-sectional profile. Alternatively, one or more plates with a smoothly curved profile can be used to form an arm with a cross-sectional profile in the nature of an aerofoil. In all cases it is strongly preferred that the cross-seczional width of the arm is greater than twice the height.

rJ o -7- 7

Claims

2. A rake arm as claimed in claim 1 wherein the area of the cross-sectional profile gradually decreases toward the remote end of the arm.
3. A rake arm as claimed in claim 1 or claim 2 wherein the distance between the leading edge and trailing edge is greater than twice the height of the profile.
4. A rake arm as claimed in any one of claims 1 to 3 wherein the included angle of the profile at the leading edge is about 300. i 5. A rake arm as claimed in any one of claims 1 to 4 wherein the trailing edge of said arm is relatively sharp.
6. A rake arm as claimed in any one of claims 1 to 4 wherein said cross-sectional profile is triangular and is disposed such that one of the corners of the triangle Sforms the leading edge.
7. A rake arm as claimed in claim 6 wherein the triangular cross-section has two corners with included angles of about 30 which respectively form the leading and trailing edges. 8
8. A method of fabricating a rake arm as claimed in any one of claims 1 to 7, said method comprising the steps of forming two or more elongate plates each with a transverse profile corresponding to part of said streamlined cross-sectional profile and joining said plates along the respective longitudinal edges to form said arm.
9. A method of fabricating a rake arm as claimed in claim 8 wherein one of said plates is formed substantially flat. A method of fabricating a rake arm as claimed in claim 6 or claim 7, said method comprising the steps of forming a first elongate plate with a generally V-shaped transverse profile and joining a second substantially flat elongate plate thereto along respective longitudinal edges to form said arm"with a triangular cross-sectional profile.
11. A rake arm substantially as herein described with reference to the accompanying drawings.
12. A method of fabricating a rake arm substantially as herein described with reference to the accompanying i drawings. I DATED this 22nd day of JULY, 1988. J LA-ROX LTD-. Attorney: LEON K. ALLEN Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS -9-