ABB robots clean up one of Tasmania’s dirtiest jobs

The project involved:

• Elimination of 16 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 tough processes involved skimming the waste ‘dross’ off molten zinc just poured into ingot moulds which 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. Kupsch said that Nyrstar make Special High Grade, 99.995 percent pure zinc and EZDA, a zinc alloy.

It is used in galvanising, alloying and die-casting, in battery casings, car panels even zinc cream, to keep sunburn at bay. Most of it now goes to China and India. In Australia, Nyrstar also operates a smelter at Port Pirie, South Australia.

The process of the project included:

• 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.
• Robotising the process was like putting an SL500 Mercedes engine into a Model T Ford, Kupsch added.

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
• Lasers which check the zinc level in the moulds and adjust the pouring system and testing

Kupsch also said that the project cost A$3 million, the robotic component about A$1 million, with lot of development and testing.

According to Graeme Little, Lewis Australia’s Senior Project Engineer Graeme Little, the new and existing equipment in the plant communicate seamlessly, through Devicenet. 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 through an ABB IRC5 robot controller.

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, Kupsch stated.

Graeme Little said that Lewis Australia are partners with ABB and they tend to use a lot of their robots.They provide good service and the team at Lewis Australia is familiar with them.

Lewis Australia have completed full workshop set up and testing at their base in Melbourne, before they have started bringing over the cells. The only thing we couldn’t test in Lewis Australia workshop was molten zinc. The first new cell went in at Nyrstar in February, 2008, the last in mid July.

Kupsch stated that it was a staggered process and one cannot just walk into a hot zinc area whenever –as 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.

The benefits:
Kupsch said that eliminating manual skimming was a key benefit in itself but Nyrstar also was looking for quality gains. Overall, Nyrstar are seeing a 60 percent decline in reject-weight ingots and Nyrstar are aiming for the project deliverable target of 85 percent. 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 Nyrstar have a clean, smooth and consistent size product.The robots will pay for themselves within 2 years. Nyrstar have considered having the robots perform other functions, such as mould spraying and wire buffing. This will be discussed in the second half of next year.