Drawn and Ironed: Container Producer Makes the Cut with Help from Vacuum Pressure

Value creation
North America

Next time you open a can of fruit, vegetables or soup, give a nod of thanks to Napoleon Bonaparte. Metal cans used to store and transport food trace their roots to 1795 when the French government, then led by Napoleon, offered a substantial cash prize to whoever invented a method of preserving food for the army and navy.

High angle view of lots of cans
The prize of 12,000 francs went to Nicolas Appert in 1809. The next year, a patent was granted for the idea of preserving food in tin cans and it wasn’t long before food canning became a commercial enterprise. Two centuries later, the basic concept of a food can is the same, although a great deal has changed in the way cans are made. Today, high speed production facilities, including at Silgan Containers in Edison, New Jersey, use advanced manufacturing technologies to make cans…a lot of cans. “We make over 4 million food cans a day,” according to Dave McCarren, Plant Engineer-Manufacturing for Silgan Containers. “In this facility, we make cans from steel using the drawn and ironed process.” Silgan Containers is a pioneer in the drawn and ironed (“D&I”) manufacturing method and operates more D&I production lines than any other food can producer in the world. Rapid production speeds, efficient metal utilization and a one-piece can bottom are major benefits of D&I-produced cans. The manufacturing process works like this:
  • Steel coil is fed into a cupping press and the initial cup is drawn.
  • The cup is then conveyed into a body maker where a die punches it through a series of rings to form the can bottom.
  • As the bottom passes through each ring, the can walls are progressively thinned (“ironed”) to achieve a predetermined can height.
  • The formed can base is trimmed, beaded and coated, then sent to final inspection.
After finished can bases are filled at a food packaging plant, they are sealed with can tops, known in the industry as ends. “Silgan makes two kinds of ends for D&I cans,” says McCarren. “There is a traditional end that you open with a can opener, and an easy-open end that you pop open. More companies are going with the easy-open variety as a value-added convenience for the end user.” Throughout the various manufacturing steps, much of the conveying and positioning of a steel can is accomplished with magnetic force, but at Silgan Containers in Edison one step employs vacuum positioning. “We have 22 machines involved in the trimming process,” McCarren explains. “Vacuum pressure sucks each can tightly onto a holder so it can be trimmed with rotating carbide knives that spin around the top of the can at high speed to slice it off. It has to be a perfect cut all the way around with no slivers, and vacuum pressure helps ensure that happens.” To generate the required 22 inches of vacuum pressure, Silgan had two 100 horsepower fixed speed vacuum pumps. “We would run one of our fixed speed vacuum pumps flat out all the time and the other was a spare,” says McCarren. “The cutting machines turn on and off continuously. Some days we may need all 22 of our cutting machines working and other days only 12. Our vacuum load is constantly changing, and we simply can’t be without vacuum. When one of our pumps failed I needed a replacement. I started fishing for alternatives, and that’s when I talked to Larry.” Larry Emmolo, B.S.M.E., Systems Specialist with Airmatic Compressor of Carlstadt, New Jersey for 23 years, introduced McCarren to Atlas Copco’s new GHS VSD+ Series vacuum pump. “Efficiency for a vacuum pump is different than for an air compressor,” says Emmolo. “A fixed speed compressor running at maximum speed is at its most efficient, so if you have multiple compressors, you base load your fixed speed units and trim with a variable speed compressor. But with multiple vacuum pumps, you get your best energy efficiency when they’re all variable speed drive.” Emmolo explains the problem with using a traditional fixed speed pump in Silgan’s variable demand scenario. “Silgan needs 22 inches of vacuum pressure, but their system would dictate the vacuum level because it ran constantly at the same capacity. As demand dropped, the fixed speed pump just pulled a deeper vacuum through the system. It was wasted energy because the power consumption wouldn’t drop at all. Now Silgan gets a constant 22 inches of vacuum. The set point control of the GHS VSD+ lets you lock into whatever vacuum level you need, and then the pumps speed up or slow down automatically as required to maintain it.” Andy Nezelek, Regional Sales Manager Industrial Vacuum for Atlas Copco, says that the GHS 900 VSD+ vacuum pumps at Silgan are the state of the art in vacuum pump technology. “Atlas Copco variable speed pumps are so much more energy efficient than traditional fixed speed pumps that the equipment cost is quickly recovered through lower energy cost,” Nezelek explains. “Silgan also has less total horsepower now with three variable speed pumps each running at a maximum of 20 horsepower versus the one pump that was running 100 horsepower all the time. Atlas Copco’s Elektronikon controller automatically synchronizes and optimizes Silgan’s pumps and even rotates them so they operate the same number of hours.” The new variable speed drive vacuum pumps provide additional operational savings. “These Atlas Copco pumps are air cooled,” Nezelek explains, “so Silgan doesn’t need water to cool them like they did with the old pumps. That’s saving hundreds of dollars a month in water cost alone.” McCarren included this extra savings as part of the justification for the capital budget to fund the project. Factoring in reduced energy consumption, his projected payback is less than two years. The new GHS VSD+ pumps also operate at dramatically reduced noise level. “In a plant where hearing protection is required most everywhere, it’s a small extra benefit,” says McCarren, “but they really are much quieter than the old pumps.”
Studio shot of arrangements of cans for the food industry.Lighting from bottom of Frosted glass with wire mesh as a base with soup can arrangement in dramatic blue light.
The new GHS VSD+ pumps also operate at dramatically reduced noise level. “In a plant where hearing protection is required most everywhere, it’s a small extra benefit,” says McCarren, “but they really are much quieter than the old pumps.” Since Silgan has three lines running 24/7, planned shutdowns for maintenance must be carefully scheduled and executed. “We typically shut down one line every six weeks for maintenance,” McCarren explains. “Because we’re a high speed, low margin business, unplanned downtime is unacceptable, so I’m working with Larry now on acquiring a fourth vacuum pump so we always have a dedicated backup.” McCarren emphasizes the good relationship he has had with Emmolo and Airmatic Compressor. “They have been servicing our compressors for over 20 years,” McCarren says. “We got our first Atlas Copco compressors from Larry about 10 years ago and still use both the GA315 and GA315VSD. Now we’ve got the variable speed drive vacuum pumps and they’re working well for us. The equipment is good and our local vendor’s done a good job. We go with what works.” Steel food cans are the most recycled food package in the U.S. and steel is the most recycled material in the world. What is the result of all that recycling? Less pollution, reduced costs and a steady supply of resources for years to come—the very definition of sustainability. By focusing on the sustainability of its products and operations, Silgan Containers seeks to strengthen its standing as a market leader and trusted partner.

Boyle’s Law, in a Vacuum

One thing you may remember from high school chemistry class is Boyle’s Law: for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional. Boyle’s Law also applies to vacuum systems: as system pressure decreases, the volume of air flow increases. In most manufacturing environments, the demand encountered by a utility vacuum system varies even though the level of vacuum required for manufacturing processes is ideally held constant. But when a vacuum pump running at fixed speed pulls a deeper vacuum in response to decreased demand, energy is wasted. Atlas Copco’s GHS VSD+ vacuum pump with Variable Speed Drive eliminates this wasted energy. Rather than letting the system dictate the level of vacuum, the GHS VSD+ utilizes precise set point control and automatically adjusts pump speed to keep the vacuum level constant. The system operates at the required vacuum level, never deeper, which optimizes energy efficiency.

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