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Cleaning-up one of Tassies dirtiest jobs

ABB Australia installs four industrial robots to clean-up one of Tasmania’s dirtiest jobs — zinc smelting at the Nyrstar plant in Tasmania.

Overview of the project:

* 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.

Zinc smelting began in 1917 on the site of Nyrstar’s Hobart plant in Tasmania, Australia. For generations it has involved hard, dirty and risky jobs.

One of the toughest jobs – skimming the waste ‘dross’ off molten zinc just poured into ingot molds – was done by hand, with a rake, until four ABB industrial robots took it over in 2008.

Now the work of 16 men, who sat beside the 600ºC molten metal around-the-clock in 30-minute spells, over four shifts, is automated and Nyrstar is producing cleaner, smoother, correct weight ingots with unprecedented consistency.

Nyrstar Senior Project Manager Michael Kupsch led 40 people, from Nyrstar and systems integrator Lewis Australia, who installed the robotic cells on four lines producing 25 kilogram zinc and 9 kilogram zinc alloy ingots.

“We make Special High Grade, 99.995 percent pure zinc and EZDA, a zinc alloy,” he said.

“It’s used in galvanizing, alloying and die-casting, in battery casings, car panels – even zinc cream [to keep sunburn at bay]. Most now goes to China and India.”

In Australia, Nyrstar also operates a smelter at Port Pirie, South Australia, and is by far the biggest zinc producer — with only one, smaller, competitor.

The process

Molten metal from the furnace is first pumped into pouring bowls on the four casting lines.

Until robotisation, a pneumatically controlled system then poured just enough metal into each mold on a conveyor, and operators raked off the waste ‘dross’, for re-processing.

Pouring speed could be changed, manually, to improve consistency, but the process was complex.

“Four fulltime 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 liter bucket of water into a mold in six seconds, repeatedly, without splashing. That’s quite difficult.”

Robotising the process was “like putting an SL500 Mercedes engine into a Model T Ford,” he says.

The project

Each robotic cell comprises: an automated servo-control system for the pouring bowl; an ABB ARB4400 robot, with 1.95 meter reach and 60 kilogram payload; a vibratory conveyor for the dross; and lasers which check the zinc level in the molds and adjust the pouring system and testing.

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

“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.”

Kupsch said: “This was a particularly complex robotics application. Typically, in the robotics industry you don’t have a moving target.”

The installation

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

“Also, we are a partner with ABB,” 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 molten zinc.”

The first new cell went in at Nyrstar in February, 2008, the last in mid-July.

“It was a staggered process,” said Kupsch.

“You can’t just walk into a hot zinc area whenever we like – there’s 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.”

The benefits

Eliminating manual skimming was a key benefit in itself – but Nyrstar also was looking for quality gains, says Kupsch.

“Overall, we’re seeing a 60 per cent decline in reject-weight ingots and we’re aiming for the project deliverable target of 85 per cent.

“People who mind the stacking end now look after the pouring end as well.

“The new pouring bowl system prevents ‘flash’ — splashed metal which cools on the sides of molds and interferes with the shape of the slabs. Now we have a clean, smooth consistent size product.

“The robots will pay for themselves within two years.

“We’ve considered having the robots perform other functions, such as mold spraying and wire buffing, for example.

“We’ll discuss that in the second half of next year.”

Contact ABB Australia;


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