by Josef Karbassi, VP Automation Division, Piab AB
It may seem like a small thing — a bag of candy dropped on the floor in a plant’s packaging area. Or a bag of frozen peas deformed from its original square shape into a messy plastic package with an ugly cone-shaped suction mark. But these are symptomatic of bigger design issues faced by manufacturers wishing to use a vacuum-based automated system to handle bags, regardless of whether these contain candy, peas or something entirely different.
Traditionally, vacuum-based bag handling systems have been so marred by problems that some manufacturers have found it almost impossible to use them. Getting the suction right for the job is a delicate balancing act.
However, innovative technology is available that enables the safe, secure and efficient operation of automated bag handling systems. Here are a few tips on what to look for.
The right cup keeps a tight hold
The suction cup is a vital component of any vacuum-based materials handling system, but its quality and materials characteristics are of particular importance when handling bags. It is essential that the right cup is used for the specific job and there simply isn’t one cup or a system of cups that will fit all types of bags, contents or weights. On the contrary, the suction cup system needs to be tailored to suit specific bags.
The design of the suction cup, internal cleats and the hardness of the lip are crucial. Suction cups with soft, high friction, highly flexible silicone lips and stable polyurethane (TPU) bellows are able to keep a tight hold on bags, yet not damage them. The latest soft and durable lips have excellent sealing capacity and can control how the bags wrinkle to provide an even tighter seal. Combined with stable bellows or bodies, these can provide a firm grip.
Use durable and configurable cups
The cup’s durability and wear are other important factors for the engineer to keep in mind. As the friction between the suction cup and the surface itself is of vital importance, use suction cups capable of handling shear forces from rapid acceleration and deceleration.
High quality liquid-silicone has better abrasion and tear resistance than conventional silicone rubber, as well as greater load bearing capacity and exceptional elastic memory. For bags containing food, it is important to look out for cups made from materials compliant with specific regulations (from the U.S. Food and Drug Administration, for example).
As it is, the lip, particularly soft lips, will suffer the most wear, so going with a configurable cup system will help keep costs down. Look out for suction cups that allow for just the lips to be replaced. A soft lip may need to be replaced every two weeks, whereas the bellow may last considerably longer than that.
Balance the flow and the release
For bag handling, a vacuum system with a well-balanced flow is particularly important. A decentralized vacuum system is more suitable and easier to balance for secure bag handling. To avoid bags being deformed by the suction in the cups, vacuum levels need to be kept between 40 and 50%. Some systems use advanced vacuum regulators to adjust and balance the vacuum.
The vacuum system also needs to have an appropriate and efficient release mechanism, so that the bags are released quickly and safely. A passive release mechanism simply acts as a door that is opened and closed. For a faster release, such “doors” need to be placed as close to the suction cup as possible.
Some bags may require an active release mechanism that allows compressed air to blow through the suction cup. As the active system will use more energy, it is critical to optimize this type of release mechanism. Less than one second of compressed air—rather than one or two seconds of compressed air—may be sufficient.
It’s all about configuration
Knowing how to configure the best bag handling system can be tricky. Determining the number of suction cups required for certain bags, contents and weights, as well as the positioning of these cups, is not always a straightforward task. Experienced suppliers will be able to assist. They may provide specialized configuration tools online or even offer testing facilities or labs in which their equipment can be test-run with the customers’ bags.
It is also worth noting that any vacuum system is made up from more than good components. Even if you have acquired the best components on the market, these need to be put to work in an optimized system by competent engineers. And what’s more, once the system is up and running, it needs to be operated by personnel that understand and know how to use it. If your supplier offers training, make sure to take full advantage of it.