LIEN, Odd (Holmavegen 5, Aardalstangen, N-6885, NO)
SKAAR, Knut (Almennhagen 2, Övre Aardal, N-6884, NO)
LIEN, Odd (Holmavegen 5, Aardalstangen, N-6885, NO)
Claims
1. Device for aligning anode studs (15-18) for electrolyses furnaces, including for the aluminium industry, for reuse of anode studs being bent due to multiple heating and cooling, wherein the apparatus comprises gripping means (36, 37) for gripping an anode stud and a pressure means (38) for exerting an aligning force with a power means, characterized in that the gripping means (36, 37) and the pressure means (38) are arranged on two mutually pivotal carrying structures (25, 28) with the power means (30) as an intermediate.
2. Device according to claim 1 , characterized in that the gripping means comprises two gripping members (36, 37) mutually restricting an opening (35) for the anode stud.
3. Device according to claim 2, characterized in that the gripping members (36, 37) have arced gripping beads (39, 40).
4. Device according to one of the claims 1 to 3, characterized in that the pressure means is a jaw (38) mounted on a pivoting arm (25), and that the gripping members (36, 37) are mounted in a carrying cassette (34) arranged between a pair of carrying arms (25, 28) pivoting on a shaft (29) and power transfer for aligning an anode stud.
5. Device according to claim 4, characterized in that the gripping members (36, 37) are arranged on opposite sides of the axis of the pivoting shaft (29), to grip the anode stud at the activating of the power means (30), to force the arms (25, 28) apart.
6. Device according to claim 5, characterized in that the pivoting arm comprises a pair of elements (28) and that the gripping members (36, 37) are mounted in a cassette (34) between the pair of elements, the axis of the pivoting shaft (29) of said pivoting arm extending through the cassette.
7. Device according to claim 6, characterized in that the pivoting arm (28) is suspended in a carrying structure of two sidewalls (25) being integrated with a cross girder (26, 27) at each end, said cross girder (27) adjoining the shaft (29) of the pivoting arm carrying the press jaw (38).
8. Device according to one of he claims 1 to 7, characterized in that it comprises sets of pivoting arms (28) with support (38) for concurrently aligning of between two and six anode studs, depending on the design of the anode yoke.
9. Device according to claim 8, characterized in that aligning sets are mounted in a structure corresponding to the design of the anode yoke. |
Device for aligning anode stubs for electrolytic furnaces
The invention relates to an apparatus as stated in the introductory part of claim 1 , for aligning anode studs for electrolytic furnaces.
Background
In electrolytic furnaces in an aluminium work, the current is supplied with anodes. The anodes comprises an aluminium rod which over a steel yoke with steel studs are moulded into an anode block. The aluminium works are striving to increase the current of the electrolytic furnaces, to increase the output and the efficiency. One of the measures for this purpose is increasing the cross section of the studs, to introduce higher current and deduct more heat. After a time in the electrolytic furnace, the anodes are removed, the residues of the anode block are removed and a new anode block is mounted.
Due to the different thermal expansion of steel and carbon, the studs will be bent over time, toward the centre of the anode block. The studs are bent 1 - 2 mm each time the anode is in the furnace. The studs are then turning bow-legged, which is called a "cowboy effect".
After some use, the studs are not fitting into the anode block. The size of the holes in the block is restricted, considering the contact between the steel and the carbon and the volume of the cast iron is too large. To increase the current, the diameter of the studs is increased, e.g. from 140 mm til 180 mm. No known prior art stub aligner is available for aligning this size of stubs. By increasing the stubs from a diameter of 140 millimetres to 180 millimetres, the forces for aligning the stub have to be increased from e.g. 36 ton to 72 ton, even when heating the stubs to 600 centidegree. Prior art comprises several machines for aligning stubs. From US patent specification 5,471 ,860 an apparatus is known for aligning stubs on an anode carrier. The stubs are positioned in the apparatus and the yoke is held by two press members on each side. The aligning is provided by a couple of annular members bending the stubs into a straight position. This design has restrictions in the appliance of force, particularly in regard of loading the yoke.
From US patent specification 5,268,083 a similar machine with corresponding drawbacks is known.
From J. H. Magnusson et al: Automatic stub straightening system for rod stubs, in Light Metals, 1995, it is known an apparatus for aligning anode stubs on an anode carrier is known, where hydraulic presses provides the straightening and where the outer stubs are heated close to the yoke by induction heating. Neither this apparatus has proved
satisfactory.
From US patent specification 4,667,501 an apparatus is known in which the anode stubs are held by V-blocks while being bent by a hydraulic cylinder pivoting in two arms. This apparatus has not been sufficiently effective for the anode stubs used in current aluminium works.
The main problem of current solutions is bending the stub in a way creating high forces acting on the yoke. This makes the yoke yield, creating two problems. One is the transfer of forces intended for the stub to the yoke, reducing the straightening effect. The second is that the yoke is gradually deformed, making the outer stubs "raised" over the intended level.
Object The main purpose of the invention is to provide an apparatus for aligning the anode stubs for making them useful until worn out. This is for reducing the maintenance cost currently encountered for changing anode studs. It is desirable to align anode stubs arranged in different assemblies and with different yoke designs.
An apparatus is needed, which will not introduce forces to the yoke, concentrating the forces on the anode stub, to align it.
Additionally, the apparatus should have a simple design.
The Invention
The invention is defined in claim 1. With this apparatus, the anode stubs are lowered into a nip consisting of two arced upper gripping members and a lower pressing jaw. With the apparatus in an idle position, the angle of the apparatus allows the stud to enter even if being oblique. In the example a 180 millimetre diameter stud may have a15 millimetre slanting and still enter the apparatus. The upper and inner gripping member relatively to the yoke will grip the upper or inner stud. The second gripping member will fasten on the outer side. Said gripping members will hold the stud while the cylinder moves the pressing jaw at the lower level and bends the stud. The gripping members are machined from hard steel and may be replaced. This will allow an apparatus to serve differently sized studs.
By making the straightening apparatus modularized, one design can be used for different shapes of anode hangers.
Further features of the invention are described in claims 2 - 9.
Example
The invention is illustrated in the drawings, wherein
Figure 1 shows a perspective view of an embodiment of an apparatus according to the invention, for aligning of a yoke with four anode studs side by side,
Figure 2 shows a sectioned side view of a hydraulic operated aligning arm, Figure 3 shows a part of the inner gripping member, Figure 4 shows a part of the outer gripping member, Figure 5 shows a part of the pressing jaw, while Figure 6 shows a power diagram for an anode stud being aligned.
In Figure 1 an embodiment of an apparatus 11 for aligning anode studs on a yoke with two or more anode studs are shown. The apparatus 11 is based on a boxlike frame structure 12 with rectangular base. The frame structure 12 accommodating two aligning modules 13, 14 designed and suspended for fitting four anode studs 15, 16, 17, 18 on a steel yoke 19 which is connected to an aluminium rod 20.
The aligning modules 13 and 14 each is suspended in two pair of links 21 connected to an upper girder 22 of the frame structure 12. Said modules are stabilized with individual links 23 to a central cross girder 24. Details of the aligning modules will appear from the Figures 2 - 5.
The embodiment of the example allows the aligning of two " anode studs at a time. On a yoke with four anode studs the aligning apparatus and the yoke has to be moved relatively and the studs aligned in two runs.
In Figure 2 an aligning module 13 with three main parts is shown: - A pair of carrying arms 25 connected with a cross girder 26, 27 at each end,
- A pair of aligning arms 28 journalled on a pivoting rod 29 between the carrying arms 25, and
- A hydraulic cylinder 30 which is operated to pivot the aligning arms 28 relatively to the carrying arms. The hydraulic cylinder 30 is carried between a piston rod bracket 31 between the carrying arms 25 and a cylinder bracket 32 on a web 33 at the free end of the aligning arms 28.
Between the suspended ends of the aligning arms 28, a cassette 34 with opening
35 for penetrations of an anode stud to be aligned, is supported. Central elements of the cassette 34 are an inner gripping member 36 (Figure 3) and an outer gripping member 37 (Figure 4) arranged in a larger distance from the yoke.
The gripping members 36, 37 are attached to the cassette 34 with bolts. Additionally, a pressing jaw 38 is arranged (Figure 5) on the cross girder 27, under the cassette, to engage an anode stud to be aligned.
In Figure 3 an arced inner gripping member 36 with a gripping bead 39 arced to match the engagement against a generally cylindrical anode stud. The bead is rounded to provide a distributed pressure against the cylinder, to avoid markings or scars in the stud. In Figure 4, an arced outer gripping member 37 with a gripping bead 40 is shown, being suited for engagement with an anode stud. This is also rounded for providing a firm grip without leaving markings in the stud. Both are arranged with the largest possible distance to provide the highest momentum for a firm grip on the stud.
In Figure 5 a design of the press.. 38 on the cross girder 27 is shown. The pressing jaw 38 has an arced face 41 of contact to press against one side of an anode stud. This will make the bending impact on the anode stud, and it is important to have highest force with highest momentum without leaving markings.
In Figure 6 the arrangement of the gripping beads 39 and 40 and the engagement face 41 in relation to an anode stud 35 and the pivoting axle 29 are shown. When the cylinder presses the aligning arms 25 and 28 apart, the forces are distributed on the pivoting axle 29. The gripping beads 39 and 40 are holding the anode stud at the upper end, while the pressing jaw 38 with the engagement face 41 is pressed with high force in the lower area. Increasing of the force on the pressing jaw 38, will increase the forces holding the stud in the upper part.
Due to the distance between the gripping beads 39 and 40, all forces applied over the pressing jaw 38 are absorbed in this area and no forces are transferred to the yoke. Due to the high forces needed for bending a stud with a diameter of 180 millimetre, the stud has to be heated to approximately 600 centidegree to reduce the forces. For this purpose, an induction heater may be utilized. This is heating the bending zone. This may vary from one design to another. For anode studs of the kind used at the Aluminium Works at Ardal, Norway, this zone will be approximately 30 millimetres from the inner end of the stud and 140 millimetres of width. This makes the engagement faces coldest and bending zone hottest.
To align the stud as desirable, a vision system is arranged, telling the bending of the anode stud. This is transferred to the control system of the apparatus. When a stud is in position, the cylinder is activated until a counterforce is established. The apparatus will then be ready for aligning. By using length monitoring in the cylinder, the desirable length can be determined.
Tests
To ascertain that the anode studs will stand the strain and have confirmed that the idea will function, an embodiment of the invention was built. This was mounted in a preliminary stand into which the anode hanger was transported with a forklift and was tested. For testing, a handheld induction heater EFD Type Minimax 50/80 was used. This had an output of 50 kW continuously and 80 kW for shorter intervals.
When carrying out the tests, various measures were made on the anode studs.
A = the distance between the anode studs, (prior to and after the aligning process (mm) B = the distance between the sides of the anode studs (prior to and after) (mm) C = the heating zone (from the lower edge to the zone where the heat was introduced) measured from the centre of the anode studs (mm) 11 = Indent in the anode stud at the top (mm) I2 = Indent central (mm) I3 = Indent at the lower end
It turned out that the anode studs being used in the electrolysis oven, had a reduced diameter. This varied from stud to stud. During the tests, the diameters of the anode studs were measured at each test.
Results
The test of the apparatus without loading the yoke was conducted under real conditions. A crane was used to install the anode holder to be aligned. This implied some additional time used and heat loss on the studs when transporting to the aligning apparatus and positioning the anode studs in the apparatus. Well warmed up studs maintained the temperature acceptable.
A simulating program was used for determining the time needed for heating to a
temperature of about 650 centidegree at the centre of the stud. In the simulating program, the anode stud diameter was entered at 180 millimeter. The heating time was 600 sec in all tests. Test 1 indicated that this allowed the aligning of bent studs. This corresponds to an outer temperature of 770 centidegree and 650 centidegree at the core of the anode stud.
When using a more heavy induction heater the heating time could be reduced.
As an important result, no damage was cause on the anode studs at the aligning, avoiding problems at removing cast iron in the next cycle.
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