ADVANCED TECHNOLOGY FROM BROCHOT
A PROVEN SOLUTION FOR ANODE SLOT CUTTING
the build-up of a layer of gas increases the cell resistance. The distance needed by a gas bubble to escape from the underside of the anode is a determining factor in the development of the layer thickness and basically, the shorter the escape distance the lower the resistance created by the gas layer will be. As anode sizes grow, the problem of the gas layer increases. The introduction of slots into the anode therefore simulates, for as long as the slot exists, the effect of using a smaller anode by providing an escape path for the gas bubbles formed on the underside of the anode. Slot configurations Brochot anode slot cutting machine during workshop testing The French based company : Brochot is a well-established supplier of production process equipment to the non-ferrous metals industry. The company is represented on a worldwide basis with offices in Canada, China, Russia and Middle-East and 3 workshops in Quebec, France and China. The company’s portfolio is extensive and increasing, in particular with the addition of recent equipment supply to the copper and zinc industries by the Brochot Hydromet division. Brochot’s principal activity remains the design, development, manufacturing and supply of equipment for the primary aluminium sector. In this sector Brochot is well known for supply of individual machines and complete turnkey projects for anode rodding shops and anode handling installations. A recent successful installation is the supply of an anode slot cutting machine to the NALCO plant in Angul, India. This machine is part of an ongoing development of the Brochot anode slot cutting design, which seeks to improve and adapt the design to the
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varying criteria of individual smelter sites. Brochot continues to invest in the development of new and revised designs for its slot cutting machine, and future orders will incorporate a number of improvements to cycle times and adaptations to client slotting requirements Advantages of slotted anodes The use of slotted anodes is now well established in aluminium smelter pot lines. The slotting of anodes is known to give improvements in pot efficiency by reducing the formation of bubble films (which create higher electrical resistance), reducing anode cracking and allowing use of increased pot currents. The cost of aluminium production is highly dependent on the cost of energy used in the reduction process and efficiency gains from slotted anodes have a direct cost benefit. Studies have shown that a large part of the gases (mostly carbon dioxide and carbon monoxide) generated by the reduction process are formed on the underside of the anode block and
Anode slotting arrangements have existed in two configurations – lengthwise slots and transverse slots. These slots can be formed in two ways – by moulding during the formation of green anodes or by machining the slots in baked anodes. It is accepted that the longitudinal slot configuration delivers the greatest benefit and the Brochot slot cutting machine produces slots in this direction. The use of moulded slots has a number of disadvantages compared to machined slots. Slot forming plates introduced in green anode moulds can affect the paste distribution and compaction around the slots. The slots are wider than machined slots and they can become clogged with packing coke at the anode baking stage. The wider slots also reduce the overall mass of carbon consequently reducing the life of an anode. Such slots create more fragile green anodes and increase rejection rates during the green anode forming, cooling and transportation stage. These problems are exacerbated with increases in the slot depth which would be potentially useful in maintaining the slot through a greater part of the anode life.
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We emphasize that Brochot is manufacturing its own in-house blade, which is designed for the specific application of each customer. The stability of the slot cutting discs is very important for reliable operation of the slot cutting machine. Disc diameters for deep slots become very large compared to the disc section. One of the objectives of slot cutting is to create a significantly smaller slot than in a moulded anode. The disc stability is related to its thickness, materials, detail design and fixing arrangements.
Anode slot cutting in progress
Machine installation and construction The Brochot slot cutting machine is intended to be used as an integrated part in the anode handling system. The machine is integrated into the anode conveying lines, receiving anodes from the baked anode storage areas and cutting the slots before transfer to the anode rodding shop. At NALCO the Brochot machine was integrated as a retrofit into the existing conveyor line just before feeding the anode rodding station. The machine installation was adapted to the existing slope of the conveyor and the machine integrates the possibility of changing its configuration to allow a ‘pass through’ condition. Space restrictions in this plant do not allow the use of a by-pass conveyor. The basic elements of the machine are a strong, rigid frame which supports an anode transport carriage and anode lifts, a powerful gearmotor which directly drives the shaft mounted cutting tool discs, entry and exit roller conveyors, and a fully enveloping enclosure to retain carbon dust within the machine, whilst assuring operator safety.
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Slot parameters The machine delivered to Nalco can cut a variety of slot configurations, including horizontal slots and sloped slots up to 450mm deep. In this machine the slot cutting unit is in a fixed mounting configuration. Brochot, as mentioned below, can deliver other slot dimensions as well. This simple and robust solution. is well adapted to the clients needs. Brochot can also offer machine configurations with mobile slot cutting unit mountings, where the position of the cutting discs can be raised or lowered. The position of the slots in the anode is normally predefined by the client, but nevertheless, the distance between the slots may be modified by changing the disc mounting spacers. To aid the exit of gas bubbles from the slots, the top of the slot is often inclined. This parameter can be quickly and easily changed in the Brochot machine by the addition or removal of spacers on the anode support pads of the transport carriage. This operation inclines the anode, relative to the machine chassis, so that the depth of cut is greater at one end of the anode than at the other.
ANODE PLANT TECHNOLOGY
Any run-out in the cutting discs will cause premature wear to cutting tools, creates localised tool heating and slots that are wider than desired. The design of the Brochot disc ensures excellent stability of the disc with respect to the mechanical loads and the thermal variations caused by cutting anodes which are still at a high temperature, particularly in the core of the anode. For NALCO, Brochot has produced tooling which produces an 11.5mm inclined slot with two slots per anode. Brochot can also offer machines with slot capacity up to 450mm with small slot widths.
Brochot slot cutting unit
The machine offered by Brochot is a fully automated process machine where the type of product to be treated is defined by the requirement of a particular smelter or anode production unit. Within the limitations of the machine sizing determined at the outset, the machine can be adapted to accommodate changes in slot dimensions (depth, length, slope, fully traversing or partially traversing slots, distance between slots) when production parameters change.
Tooling life Operating costs of slot cutting machines are largely related to the life of the cutting tools. Brochot has worked over a number of years to choose and refine the specification of the cutting tools in order to achieve long life and reliability. A single set of tool tips can reliably achieve a life of 40000 anodes (Customer reports achievement of 45000 anodes) and by indexing the tool tips the life of the tools can be doubled. The Brochot tooling design uses special tool holders carrying diamond tip tools which are alternately mounted on either side of our tool carrying discs. Brochot supplies the complete machine and tooling package with after sales service, giving full support for supply of consumables and replacement parts.
Brochot anode transport carriage
In any slotting operation the rigid mounting of the anode is essential to avoid problems of vibration during the machining operation. The Brochot machine has a rigid anode transfer carriage equipped with strong pneumatic anode clamps. The anodes are delivered to the machine by a motorised roller conveyor and placed above an anode lift. The lift raises the anode allowing the transfer carriage to position itself around the anode. The lift retracts lowering the anode onto the anode support pads, and the carriage anode clamps fix the anode securely in place. The carrier advances the anode and the discs cut the slots in the anode as the carriage advances. After exiting the cutting, the anode clamps are released and the exit lift lowers the anode onto the outlet roller
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conveyor. During the cutting, a new anode is loaded and lifted ready for the return of the anode carriage. The slot inclination and the orientation of the slot are determined by the height of the anode support pads, the anode being inclined in the carriage during the slotting operation. The quality of the cutting operation and the control of vibration are well understood by Brochot, allowing reliable calculation of the parameters for disc rotation speed and anode advance. This ensures good prediction of cycle times for new projects, which is essential to the sizing of equipment in new and existing installations. Dust control One constraint of the slot cutting method is the creation of carbon dust during the process. To control the dust, Brochot supplies a complete dust extraction and filtration system along with the slot cutting machine and works together with our clients to create the best package for the site installation. A fully enclosing housing is supplied for the machine providing dust control and safety protection. The housing is in two parts, retractable to allow maintenance access into the machine. The lower part of the machine is formed by a dust collection hopper which feeds a screw conveyor. During the cutting, the larger carbon particles fall into the hopper and are extracted by a screw conveyor to a collection bin. Periodically this bin is emptied to the carbon recycling system.
Brochot slot cutting machine during installation at Nalco
and drive system) to allow multiple anode slotting with a single cutting unit. Other improvements include new dust collection and extraction systems, tool life optimisation and automation of pass-through systems to facilitate anode transfer without slotting. The reliability of the equipment is of primary importance, since downtime of the slot cutting machine can quickly lead to supply problems for the rodding shop operations. The current Brochot slot cutting machine delivers a reliable performance at around 45 anodes/hour depending on anode dimensions. The next generation of equipment will maintain current reliability levels while increasing this to a rate of around 60 anodes/hour. Backed up by its commercial and engineering resources across several continents, Brochot is already replying to client requests for the next generation of slot cutting machines and has the intention to remain a leading player in this market.
Ongoing developments Capitalising on our experience at NALCO and at other sites, current design developments at Brochot are focused on providing cost optimised designs with higher capacity, and reducing cycle times whilst simultaneously increasing the depth of slot. New designs optimise the use of the cutting unit (discs
Author: Philip Dunabin, Brochot Engineering Department Manager
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BROCHOT, YOUR PARTNER IN THE LIGHT METAL INDUSTRY ĞƐŝŐŶ͕ DĂŶƵĨĂĐƚƵƌĞ͕ ^ƵƉƉůLJ͕ /ŶƐƚĂůůĂƟŽŶ Ăƚ ƐŝƚĞ ŽŶ Ă ƚƵƌŶŬĞLJ ďĂƐŝƐ
ALUMINIUM
Special vehicles
Potrooms • Electric pot ramming machines with paste feeding
machines and/or data box
• Anode raising beam
On a single machine delivery or on a turnkey basis :
Carbone plant • Full anode handling system and rodding shop
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ANODE PLANT TECHNOLOGY
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