ABB robots help reduce zinc ingot rejects by 60%.

2009-12-20 - Zinc smelter Nyrstar of Hobart Tasmania have installed a range of ABB robots to increase quality, productivity and improve working conditions for employees

Cleaner production
One of the toughest jobs in the Hobart plant is skimming the waste dross off molten zinc just poured into ingot mould. This was previously done by hand, with a rake, until four ABB industrial robots took over the work in 2008. Now the work of the 16 men, who sat beside the 600º C molten metal furnace around-the-clock in 30-minute spells, is totally automated - and Nyrstar is producing cleaner, smoother, more accurate zinc ingots with unprecedented consistency.

Nyrstar's Senior Project Manager , Michael Kupsch, led the 40-strong team, from Nyrstar and ABB integrator Lewis Australia, who installed the robot cells on four lines producing zinc alloy ingots.

“We make Special High Grade, 99.995 percent pure zinc and EZDA, a zinc alloy,” says Kupsch. “It’s used in galvanizing, alloying and die-casting, in battery casings, car panels - even zinc cream, to keep sunburn at bay. Most of the production now goes to China and India.”

Automation improves both quality and working conditions
Until robots were introduced a pneumatically controlled system poured just enough metal into each mould on a conveyor, and operators raked off the waste dross. Pouring speed could be changed, manually to improve consistency, but the process was complex. “Four full-time operators each shift just sat beside the conveyor, for 30 minutes at a time, in cocoons of safety clothing, (hard hats, face visors, hoods, gloves, coveralls) with a rake,” says Kupsch. “We got quite a bit of reject-weight zinc. Imagine pouring a 10 litre bucket of water into a mould in six seconds, repeatedly, without splashing. That’s quite difficult.”

Robotizing the process was “like putting an SL500 Mercedes engine into a Model T Ford,” he says. Each robotic cell comprises:

  • automated servo-control system for the pouring bowl;
  • ABB IRB 4400 robot, with 1.95 meter reach and 60 kilogram payload capacity;
  • a vibratory conveyor for the dross;
  • and lasers which check the zinc level in the moulds and adjust the pouring system.

"The project cost AUD 3 million, the robotic component about AUD 1 million", says Kupsch "and an awful lot of development and testing".

"Both the new and existing equipment in the plant communicate seamlessly through Devicenet" says Lewis Australia’s Senior Project Engineer, Graeme Little. “The existing Allen Bradley PLCs (Programmable Logic Controllers) and touch screens have been upgraded to run Contrologix Version 16. Each casting conveyor has a robot tracking system matched to the robot via an ABB IRC5 robot controller. This was a particularly complex robotics application,” says Kupsch. “Typically you do not have a moving target.”

Good experience with ABB
Two ABB IRB 6600 6-axis robots, with 200 kilogram payloads and 2.75 meter reach, were previously commissioned in Hobart in 2007, for stacking ingots. So familiarity was one driver for choosing ABB equipment, says Kupsch.

“Lewis Australia is one of ABB Robotics authorised partners ” says Little. “We tend to use a lot of their robots. They provide good service and our guys are familiar with them. We completed full workshop set up and testing at our base in Melbourne before we started bringing over the cells. The only thing we couldn’t test in our workshop was the molten zinc.”

The first new cell went in at Nyrstar in February, 2008, the last in mid July 2008. “It was a staggered process,” said Kupsch. “You can’t just walk into a hot zinc area whenever we like - there are permits, risk assessments, job safety analysis, a lot to get through. In fact, the installation window was only four days for each robot.” Nyrstar will do most ongoing work on the robotic cells itself, says Kupsch. “But for specific warranty on software and components, Lewis or ABB will be coming back in to do the work on those – depending on the component.”

60% improvement on rejects
Eliminating manual skimming was a key benefit in itself - but Nyrstar was also looking for quality gains, says Kupsch. “Overall, we’re seeing a 60 percent decline in reject-weight ingots and we’re aiming for the project deliverable target of 85 percent,” he says. “People who mind the stacking end now look after the pouring end as well,” Kupsch continues. “The new pouring bowl system prevents ‘flash’ – splashed metal which cools on the sides of moulds and interferes with the shape of the slabs. Now we have a clean, smooth consistent size product.”

"The robots will pay for themselves within 2 years" says Kupsch. “We’ve considered having the robots perform other functions, such as mould spraying and wire buffing, for example. We’ll discuss that in the second half of next year.”

Nyrstar at a glance
  • World’s biggest zinc producer, smelting more than a million tonnes, worth USD 1.8 billion, annually - and third largest lead producer
  • Created in September 2007, when Australian-based Zinifex’s and Belgium-based Umicore’s smelting operations merged
  • Operations in Australia, Belgium, China, France, Netherlands, Thailand and USA, employing 4000 people
  • Hobart smelter employs 500 people and produces 250,000 tonnes of zinc and zinc alloy, worth USD 450 million, plus sulphuric acid, copper sulphate and cadmium metal annually.

Lewis Australia Pty Ltd at a glance
  • Founded 1968 in Victoria, Australia
  • Industrial automation system and robotic cell specialist
  • Employs 26 people and has annual turnover around AUD 10 million
  • Projects in Australia, Asia and North America
    Robot advantages
    • Eliminated 16 of the dirtiest, riskiest jobs in the plant
    • Waste recycling reduced by 60 percent with 85 percent an achievable target
    • End-product shape, size and unit weight consistency - and transportability - all improved significantly

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      “Overall we’re seeing a 60 percent decline in reject-weight ingots" says Micheal Kupsch of Nyrstar.
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