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Powerful Anode Positioning
Screw Jack Ltd has been involved in anode positioning ever since the very first commercial primary aluminium smelters were established in the 1940’s.
Screw jacks are the tried and accepted method for the lowering, precise positioning of the anodes and anode beams in the vast majority of smelters. They are also used for “high jacking” of frozen pots. The same method is used in both Søderberg smelters and Prebaked Anode smelters although jack styles and configurations vary depending on the technology employed. The screw jacks are mechanically linked and through a combination of gearboxes and electric or air motor drives, anodes are positioned via an electronic control system monitoring the potline efficiency.
The company has supplied numerous jacking systems (including jacks, bevel gearboxes, speed reducers, shafts, couplings, electric and air motors) to smelters around the world including the UK, US, New Zealand, South Africa and most notably Dubai where 5 of the pot-lines utilise Screw Jack products on the reduction cells. Screw Jack estimates that the capital investment in pot-room jacking equipment at Dubal over the past 25 years is in the region of £6million. Annual spare requirements represent less than 1/10th of 1% of the investment and this bears testimony to the quality and reliability of our products.
Unlike our competitors, we are a screw jack company first and foremost - screw jacks are not just a sideline of our business. This is important as we can dedicate all of our resources into the design and manufacturing of jacking systems that will give a smelter at least 3040 years of trouble-free operation. Over 60% of the products we ship, to an endless variety of industrial positioning applications, are customised in some way. This ability for customisation and design is particularly important in the smelter business where the jacks have to be incorporated into different types of reduction cell technology.”
For jacking in aluminium smelters a standard screw jack is modified to cope with the harsh operating environment. Larger gears of a special bronze alloy, heat-treated steel alloy worm-shafts and large taper roller bearings all ensure durability. The lifting screw is specially forged to incorporate the clevis-end for added strength and heavy-duty seals protect the gear-set from abrasive alumina dust”. One of Screw Jack strengths is that all the jacks, bevel gearboxes and shafts are manufactured in-house speeding up lead times.
Among the jacking systems provided are fixed position jacks (used extensively in Kaiser technology and similar technologies derived from Alcoa) that are robust enough to allow for a certain amount of side-loading stresses caused thermal expansions. Where side loading is very high, a swivel-jack is employed. Invented the company back in the 1960s and used extensively in end-to-end pre-bakes, these jacks allow for 3-degree movement in the lifting screw from the vertical. Virtually every smelter has different jacks although the principle is basically the same.
It is interesting that anode jacking in the aluminium industry has not developed significantly over the years despite the improvements and changes that have occurred in Prebaked Anode smelters. Amperages have increased significantly since commercial smelters began and the carbon area has increased with the use of larger anodes. Typical anode beam lifting systems were designed in the '40s when the current levels were around 100kA, now they exceed 300kA. Perhaps there is an understandable reluctance to move away from tried and tested methods. Screw Jack believes however that as many smelters constructed in the '60s and '70s will need to replace their anode positioning systems over the next few years, new technology can offer the industry greater positional accuracy that could lead to significantly reduced running costs.
In pre-bakes, the anode-cathode interface should ideally remain constant at a level where the voltage maintained is as close as possible to the theoretical tension imposed the electrochemical reaction and the Faraday efficiency is highest. If the interface is too high, Joule effect causes higher heat losses in the bath. If too short, the same occurs in the anode and stem, and cathode. Traditional jacking systems can periodically adjust the interface lowering the anode system. This frequency in a pre-bake is generally much lower than the alumina feed frequency, which itself provokes a change in bath resistance and justifies an adjustment. This is especially true with the point feeder technology that is now widespread.
A new design of anode jacking system developed Screw Jack can offer both high positional accuracy, speed variation and continuous duty cycles enabling the anode to be adjusted in conjunction with the alumina feed to allow consistent optimum production. Screw Jack is interested in talking to smelters willing to act as partners for testing the new technology.
In addition to new systems, the company offers retrofit or repair of all existing screw jacks in the field whatever the origin. The need to eliminate downtime is recognised Screw Jack and the company will work with smelters to offer fast repairs and to establish annual spares requirements. Most Søderbergs could benefit immediately from a simple redesign of their anode and sleeve lifting system, resulting in immediate Faraday improvement. Screw Jack recently committed to fund equity in VSFb, Mini-Smelter Inc, the Development Corporation that will promote future green fields and conversions of existing smelters to Vertical Stud Soderberg.
Click here to download Screw Jack Aluminium Applications brochure. 
