Machine vision system helps eliminate equipment damage

Located on the shores of the St. Lawrence River in Québec, Aluminerie de Bécancour is an aluminum smelter that produces 400,000 metric tons of aluminum annually in the form of rolling ingots, T-ingots (pure and alloyed) and billets.

The ISO: 2000 and 14001 certified Aluminerie de Bécancour smelter, which is part of Alcoa Canada Primary Metals (ACPM), has been up and running since 1986.
Running most of the time, that is. Once or twice a day, production was interrupted by pieces of metal falling onto the line during a crushing process. That crashing debris significantly increased downtime and caused damage to equipment on the line.

A crushing problem
Smelting is an electrolytic reduction process that transforms the white powdery material — called “alumina” — that is produced from bauxite into aluminum. Alumina is dissolved in a cryolite bath inside large, carbon-lined cells called pots. When a powerful electric current is passed through the bath, aluminum metal separates from the chemical solution and is siphoned off.
After 21 days, the anode through which the current enters the pot reaches the end of its life. A crusher removes the used carbon attached to the anode frame. As crushing occurs, steel parts from the anode’s frame can fall on the conveyor and eventually damage equipment further down the process line. This can lead to costly equipment repair and replacement as well as production downtime.
Engineers at Aluminerie de Bécancour considered various ways to address this problem. Photoelectric sensors were considered but ultimately rejected because of the quantity of sensors that would be needed to perform the inspection. Due to product variations, machine vision was determined to be the simplest solution to the problem. Working with Groupe Rotalec, a distributor of high technology industrial automation products, product identification systems and mill products, Aluminerie de Bécancour engineers selected a new machine vision system that included a 640×480 monochrome camera.

Getting the big picture
The BOA from Teledyne DALSA is a fully-integrated machine vision system in an ultra-compact, designed for industry enclosure. Contained entirely within in a tiny (44 x 44 x 44 mm) industrial IP67 housing, the BOA is packaged complete with application software which contains a comprehensive library of tools and functions that can be readily applied to a wide range of manufacturing tasks.
At Aluminerie de Bécancour, every product is inspected by comparing three images. One BOA detects the anode’s frame geometry before the anode gets crushed. Using the same configuration, another camera detects the anode’s frame geometry after crushing. A “fail” occurs if one of the three images indicates that the geometry changed during crushing.
According to engineers at Group Rotalec, one major advantage of using the BOAs is the ease with which they and other operators can program and re-program the application.
“Because the process is pretty slow at only two parts per minute, we were triggering every 100ms, waiting for the perfect positions to apply the analysis tools,” says Alexandre Dargis, vision application engineer at Groupe Rotalec. “We overwrite all of our tools’ results using the BOA software’s custom scripting functionality. This scripting functionality allows us to write the communication I/Os whenever the picture is the one we’re looking for.”
Since much of the equipment on the line is original to the plant, there was no way to communicate through Ethernet. As a result, Groupe Rotalec used digital outputs from the expansion I/O breakout board (8 inputs & 10 outputs) to communicate with the PLC.
“The BOA is a simple and effective camera that meets Aluminerie de Bécancour’s inspection requirements,” Dargis said.
Since the BOA solution was installed at Aluminerie de Bécancour in November 2011, the company has experienced no downtime as a result of falling debris, and engineers are currently reviewing additional areas that would benefit from BOA vision system installations.

Steve Geraghty is vice president of U.S. Operations and director of Teledyne DALSA’s Industrial Products.