# Patent

## Title
Method of manufacturing a separation fence and separation fence

## Abstract

In a method for fabricating a separation fence (1) to be used in a hydrometallurgical liquid-liquid solvent extraction settler, the fence is manufactured of polymer resin. The fence (1) is manufactured as a shell-like integral piece by rotational molding. The fence (1) is a rotationally molded shell-like integral piece.

## Background
This is a national stage application filed under 35 USC 371 based on International Application No. PCT/FI2013/050636, filed Jun. 12, 2013 and claims priority under 35 USC 119 of Finnish Patent Application No. 20125716 filed Jun. 26, 2012.
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a separation fence to be used in a hydrometallurgical liquid-liquid solvent extraction settler. Further, the invention relates to a separation fence.
BACKGROUND OF THE INVENTION
Separation fences are used in a hydrometallurgical liquid-liquid solvent extraction settler to enhance coalescence of the dispersion. In the VSF® technology (stands for Vertical Smooth Flow) developed by the applicant the separation fences are so-called DDG® fences (Dispersion Depletor Gate) (disclosed e.g. in document U.S. Pat. No. 7,517,461).
In prior art, the separation fence is typically manufactured of a fibre-reinforced plastic composite (FRP) by hand laminating. The fence fabricated by hand lamination has many disadvantages. Hand lamination makes the surfaces of the fence, which are in contact with the liquid flow, rough and the edges sharp so that vortices and dead areas are created in the flow. Sharp edges cause unwanted eddies, spouts and jets. This causes scale build-up on flow patterns and the fence is trapping crud. The cleaning of the fence is time-consuming and cumbersome. The liquid flow on the rough surfaces and sharp edges of the fence also causes electrostatic charging which may cause igniting of the flammable atmosphere in the settler. Ignition of the volatile organic compounds (VOC), which are released from the hydrocarbon based solvents, can occur if sufficient electrostatic energy is released in a static discharge. As a manufacturing method of the fence, hand lamination is slow, costly and vulnerable to poor craftsmanship. In hand lamination, also air bubbles may easily remain inside the structure, weakening the fence structure.
OBJECT OF THE INVENTION
The object of the invention is to eliminate the disadvantages mentioned above.
In particular, it is an object of the present invention to provide a method of manufacturing a separation fence and a fence which enable a remarkable reduction in fabrication costs of the fence.
It is also an object of the present invention to provide a method of manufacturing a separation fence and a fence which enable minimizing the local production of unwanted vortices, eddies, dead areas, spouts and jets in the flow when it contacts the surfaces of the fence.
It is also an object of the present invention to provide a method of manufacturing a separation fence and a separation fence which enable minimizing the scale build-up and trapping of crud in the fence, thus also minimizing the time needed for maintenance.
It is also an object of the present invention to provide a method of manufacturing a separation fence and a fence which enable minimizing the VOC emissions and electrostatic charging of the solvents, thus preventing fires in the solvent extraction plant.
SUMMARY OF THE INVENTION
According to a first aspect, the present invention provides a method for fabricating a separation fence to be used in a hydrometallurgical liquid-liquid solvent extraction settler. In the method, the fence is manufactured of a polymer resin material. In accordance with the invention the fence is manufactured as a shell-like integral piece by rotational moulding.
According to a second aspect, the present invention provides a separation fence to be used in a hydrometallurgical liquid-liquid solvent extraction settler, which fence is made of a polymer resin material. In accordance with the invention the fence is a rotationally moulded shell-like integral piece.
Rotational moulding is an established mass-production method which is much more economical than hand lamination. In rotational moulding the manufacturing is performed in a mould. The surfaces of the mould can be made very smooth and all the edges can be rounded so that the fence gets similar characteristics. Therefore, the smooth surface and rounded edges contacting the solvent flow minimize local production of vortices, eddies, dead areas, spouts and jets in the flow when it contacts the surfaces of the fence. Scale build-up and crud trapped in the fence are minimized, as well as the time needed for maintenance. VOC emissions and electrostatic charging of the solvents are minimized, thus minimizing the risk for fires in the solvent extraction plant.
In one embodiment of the method, the method comprises: fabricating a mould composed of two mould halves, comprising a first mould half and second mould half, said mould halves having walls, the inner surface of which corresponds to the outline of the fence; supporting the mould to be rotational about two perpendicular axes; pouring a charge of a polymer resin material powder inside the first mould half; installing the second mould half on the first mould half to close the mould; rotating the mould around the two perpendicular axes; heating the mould while it is rotating around the two perpendicular axes to melt the polymer resin material and to disperse and stick it to the wall of the mould as a layer having a substantially even thickness and forming the fence; stopping the heating of the mould; cooling the mould; opening the mould by separating the mould halves and removing the fence from the mould; and, if needed, performing finishing operations for the fence.
In one embodiment of the fence, the fence has a general shape of a flat rectangular casing having a hollow inner space.
In one embodiment of the fence, the fence comprises a vertical front wall, a vertical rear wall, two vertical side walls, a top wall and a bottom wall. “Front” and “rear” relate to the orientation of the fence when it is installed in the settler in relation to the direction of flow of solvents. The front wall is the wall facing the flow and the rear wall is the trailing wall.
In one embodiment of the fence, the front wall comprises an inlet opening located at the lower part of the front wall, said inlet opening being, in operation, adapted to receive a flow of dispersion to enter the inner space between the front wall and the rear wall, and an outlet opening located at the rear wall at an elevated level in relation to the inlet opening so that, in operation, the dispersion is forced to flow vertically in the inner space between the front wall and the rear wall and out trough said outlet opening.
In one embodiment of the fence, the fence comprises through-channels extending through the fence at the upper part of the fence at a level above the outlet opening.
In one embodiment of the fence, at least one of the front wall and the rear wall comprises outwardly directed bulges extending horizontally along the width of the fence, the bulges thus forming complementary recesses at the inner surfaces of the fence facing the inner space.
In one embodiment of the fence, the polymer resin material comprises carbon fibers. The addition of carbon fibers reinforces the structure and reduces the static electrical charging.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:
FIGS. 1 to 5 illustrate steps of the rotational moulding of the separation fence in accordance with one embodiment of the invention,
FIG. 6 shows an axonometric view of a separation fence according to one embodiment of the invention seen from the front side and obliquely from above,
FIG. 7 shows an axonometric view of the separation fence of FIG. 6, seen from the rear side and obliquely from above, and
FIG. 8 is a cross-section VIII-VIII of FIG. 6.



DETAILED DESCRIPTION OF THE INVENTION
In the method for fabricating a separation fence 1 to be used in a hydrometallurgical liquid-liquid solvent extraction settler, the fence 1 is manufactured as a shell-like integral piece by rotational moulding.
A mould 2 composed of two mould halves 21, 22 comprising a first mould half 21 and second mould half 22 is manufactured. The mould halves 21, 22 have walls, the inner surface of which corresponds to the outline of the fence 1. Preferably, the mould halves 21, 22 are made of sheet metal, and thus they have a thin metal wall with a good thermal conductivity.
As shown in FIG. 1, the mould 2 is supported in a rotation moulding machine so that the mould is rotational about two perpendicular axes. A charge of a polymer resin material powder 3 is poured inside the first mould half 21. The polymer resin material powder 3 may include suitable additives, such as carbon fibers.
As shown in FIG. 1, the second mould half 22 is installed on the first mould half 21 to close the mould 2.
As shown in FIG. 3, the mould 2 is placed into an oven wherein the mould 2 is heated while it is rotating around the two perpendicular axes. The heat melts the polymer resin material. Due to the rotational movement, the melted polymer resin material disperses and sticks to the wall of the mould 2 as a layer having a substantially even thickness and forming the fence 1.
As shown in FIG. 4, after heating, the mould 2 is placed into a cooling station wherein the mould 2 is cooled by spraying a cooling fluid.
As shown in FIG. 5, after cooling, the mould 2 is opened by separating the mould halves 21, 22 from each other. The fence 1 is removed from the mould.
If needed, finally, finishing operations, such as machining, may be performed on the fence 1.
FIGS. 6 to 8 show a separation fence 1 to be used in a hydrometallurgical liquid-liquid solvent extraction settler, which fence is made of a polymer resin material.
The fence 1 is a rotationally moulded shell-like integral piece that has a general shape of a flat rectangular casing having a hollow inner space 4. The fence 1 comprises a vertical front wall 5, a vertical rear wall 6, two vertical side walls 7, 8, a top wall 9 and a bottom wall 10.
The front wall 5 comprises an inlet opening 11. The inlet opening 11 is located at the lower part of the front wall 5. In operation, the inlet opening 11 receives the flow of the dispersion which enters the inner space 4 between the front wall 5 and the rear wall 6 and is forced to flow upwards to an outlet opening 12 which is located at the rear wall 6 at an elevated level in relation to the inlet opening 11. In operation, the dispersion is discharged from the inner space trough said outlet opening 12.
At the upper part of the fence 1, at a level above the outlet opening 12, the fence 1 comprises through-channels 13 extending through the fence.
The front wall 5 and the rear wall 6 both comprise outwardly directed bulges 14 extending horizontally along the width of the fence 1. The bulges 14 form complementary recesses 15 at the inner surfaces of the fence facing the inner space 4. In operation, these recesses 15 enhance coalescence of the dispersion.
It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead, they may vary within the scope of the claims.

## Claims

1. A method for fabricating a separation fence capable of being used in a hydrometallurgical liquid-liquid solvent extraction settler, in which method the fence is manufactured of a polymer resin material and has a front wall and a rear wall, at least one of the front wall and rear wall defining outwardly directed bulges extending horizontally along the a respective width of the fence, to form complementary recesses on at least one respective inner surface of the fence, characterized in that the fence is manufactured as a shell-like integral piece by rotational molding.

2. The method according to claim 1, characterized in that the method comprises
fabricating a mold composed of two mold halves, comprising a first mold half and second mold half, said mold halves having walls, the inner surface of which corresponds to the outline of the fence,
supporting the mold to be rotational about two perpendicular axes,
pouring a charge of a polymer resin material powder inside the first mold half,
installing the second mold half on the first mold half to close the mold,
rotating the mold around the two perpendicular axes,
heating the mold while it is rotating around the two perpendicular axes to melt the polymer resin material and to disperse and stick it to the walls of the mold halves as a layer having a substantially even thickness and forming the fence,
stopping the heating of the mold,
cooling the mold, and
opening the mold by separating the mold halves and removing the fence from the mould.

3. The method according to claim 2, including the step of performing finishing operations on the fence.

4. A separation fence capable of use in a hydrometallurgical liquid-liquid solvent extraction settler, which fence is made of a polymer resin material, characterized in that the fence is a rotationally molded shell-like integral piece and has a front wall and a rear wall, at least one of the front wall and rear wall defining outwardly directed bulges extending horizontally along a respective width of the fence, to form complementary recesses on at least one inner surface of the fence.

5. The fence according to claim 4, characterized in that the fence has a general shape of a flat rectangular casing having a hollow inner space.

6. The fence according to claim 5, further comprising two vertical side walls, a top wall and a bottom wall.

7. The fence according to claim 6, further comprising
an inlet opening located at the lower part of the front wall, said inlet opening being, in operation, adapted to receive a flow of dispersion to enter an inner space between the front wall and the rear wall, and
an outlet opening located at the rear wall at an elevated level in relation to the inlet opening so that, in operation, the dispersion is forced to flow vertically in the inner space between the front wall and the rear wall and out through said outlet opening.

8. The fence according to claim 7, characterized in that the fence comprises trough-channels extending through the fence at the upper part of the fence at a level above the outlet opening.

9. The fence according to claim 7, characterized in that the polymer resin material comprises carbon fibers.

10. The fence according to claim 8, characterized in that the polymer resin material comprises carbon fibers.

11. The fence according to claim 4, characterized in that the polymer resin material comprises carbon fibers.