Plugging the leaks

The Canmaker
July 2006

Cracked rivets are easy to detect. The challenge is to detect them in the conversion press and then refine the process to reduce spoilage. John Nutting reports

Much of Impress's easy-open food end manufacturing capacity is concentrated at its plant at Deventer in the Netherlands. For the past seven years it has been making steel ends for Heinz and other customers in increasingly reduced gauges.

Sophisticated process control has been a vital part of the operation of the conversion presses. The reduction in variability in the performance of the ring-pull and prevention of leakers are key to ensuring good customer service. Deventer's Tear Force Improvement programme has already been featured in The Canmaker (July 2001) but the detection of rivet failures has been a continuing project that goes back even longer.

Deventer project manager Henry Wiggers explained the reasons. "To safeguard against rivet failures all of the conversion presses from Service Tool have been equipped since 1996 with Brankamp- Prokos rivet detection systems," he said. "The PK500 processors are connected to a central PC over a dedicated serial bus which runs Brankamp DC5000 shop floor data collection software.

"Although the software can do a lot more, at Deventer it is only used to gather and store data such as stops and their causes for later analysis. In practice it may not be touched for weeks or months until we want to look back over a period of part of production."

Light testers aren't used to check ends for cracks from the conversion presses at Deventer, so the Brankamp system, allied with Tema vision inspection systems, forms the primary quality procedure. This employs load cells within each station of the press to measure forces. The forces form a curve during the process.

"Until we started testing with doublecurve functionality," said Wiggers, "all deviations outside the curve triggered a stop. The detected ends were reviewed before production was started.

"With the double curve it's possible to set two levels. We're gradually changing over the systems so the inner curve will trigger a reject and the outer curve will trigger a stop. This significantly improves quality and efficiency, and reduces waste.

"Overall we're pretty satisfied with the systems. The relationship with Brankamp, which is only a few hours drive away over the German border, and Prokos is excellent. System support and software maintenance is provided over a dial-up modem connection.

"We couldn't, and won't, run production without a rivet detection system. It can't be used for 100 percent rivet leak detection but it will detect many other problems in the rivet area that can't be found with a light tester. So far it has always saved us from delivery leakers to customers.

"Recently we had a very high level of non-metallic enclosures (NMIs) from our steel supplier. An NMI in the rivet area will cause a split which might not automatically result in a leaker. The PK system helped us identify the problem and determine the quality of the material, preventing a major quality drama.

"The biggest concern for us is to maintain a good balance between quality, the number of stops and spoilage. The system is pretty intelligent and in combination with the accuracy it can be too good. Not every deviation from the standard rivet force results in an incorrect rivet. If the sensitivity is set too high the level of false rejects is high. If it's set too low the chance is that the minimum deviation not being detected is too high. We have a periodic scheduled test to check the system for functionality, which is also a reasonable control for sensitivity levels."

Recent changes from single- to doublereduced tinplate have enabled significant downgauging for easy-open ends. The harder material demands improved rivet forming progression to maintain rivet thickness and strength. The availability of the Brankamp systems has enabled this to be carried out reliably, said Wiggers. "We've gone through this process of changes controllably," he said. "This also made us aware that we might have to reconsider the position of the sensors in the rivet progression system.

"As long as there's progress and development we will probably always be working on the conversion systems to stay ahead with the technology."

More information from
Brankamp System Prozessautomation GmbH,
Max- Planck-Str 9-13,
Erkrath,
D-40699, Germany.
T: 49 211 250 7645
F: 49 211 208 402.