Vacuum handling attachments are widely used for lifting large flat loads like panes of glass, aluminium plates or airplane wings – loads not readily suited to being wrapped in slings or attracted to magnets. However, they are also useful for the repetitive lifting of loads that may not necessarily be too heavy to lift manually, but the constant bending and lifting could injure the lifter.
The benefits of vacuum handlers go beyond the reduction or elimination of back injuries and improvement of working conditions, however. They can also increase productivity over manual handling by eliminating all the bending and stretching, and can be more efficient than hooks and hoists, since there is no time spent slinging and rigging. Vacuum handlers also they lend themselves to automated production. In addition to all this, they are likely to reduce or eliminate damage to the products being lifted.
In many countries there are regulations that govern what employers can and cannot expect their employees to lift manually. Andy Nicholson, an ergonomist with UK ergonomics and health and safety consultancy Hu-Tech, has helped draft two recent ergonomics standards: ISO 11228 and EN 1005. They say that, depending on a workplace’s circumstances, loads less than 15kg (33 lbs) may be handled without risk of injury. Loads between 15kg-25kg (33 lbs-55 lb) may be considered too heavy to lift by hand. Loads over 25kg are much more likely to be too heavy to lift and will require special factory planning.
These regulations have proved to be the catalyst for many workplaces to introduce some kind of mechanical handling.
The kinds of load that were previously lifted by hand lend themselves very well to a vacuum lifter, suspended either from a push-around light crane system or a jib crane. Moving boxes or sacks around, particularly into or out of pallets, is a classic application.
Albert Kilner, managing director of UK-based Kilner Vacuum Lifting, says that alternatives such as forklift trucks or conventional overhead cranes and slings are usually not appropriate. Vacuum lifters tend to be used in localised work stations or where the load does not lend itself to being picked in any other way. It would take a remarkably skilled forklift truck driver to lift a bag of fertiliser off a pallet, for example, without puncturing the bag. Where vacuum lifting is used, it seems, there really is no obvious alternative solution.
Vacuum lifting heads can be attached to wire rope and electric chain hoists as a simple alternative to
hooks and slings. Or they can be attached to a balancer or intelligent assist device, so the weight of the load is taken by the crane, but it can still be moved by hand. Often, particularly for handling sacks, bags or boxes rather than large panes of glass or metal sheets, the vacuum attachment head will be at the bottom of an extendible tube that controls vertical movement through the use of compressed air. Usually a handle will help the user to lower the vacuum head or heads onto the load and then lift it up. Lateral movement is provided by the jib or gantry system from which the tube is suspended.
For safety reasons, vacuum handlers are generally designed so that they cannot lift loads that are
too heavy for them to hold. In the event of power or air pressure cut-offs, a non-return valve ensures that the vacuum is retained so that the load can be lowered in a controlled manner.
According to US vacuum device manufacturer Anver, the lifting capacity of the device is proportional to the square of the cup diameter, and to the vacuum level. That means that the cup size is the most important factor in what the device can lift, but the strength of the vacuum is also important. The strength of the vacuum depends not only on the power of the pump, but also on the fit of the suction pad to the load.
Every load requires its own suction pad. With the wide range of packing materials used in such applications, different types of suction pads are needed. Materials may be airtight or porous, with smooth or rough surfaces, may be made of paper or plastic film and thus capable of supporting loads and withstanding mechanical stress, or may be flexible, as in the case of flat cardboard layers or flat-folded empty cardboard boxes. For each application, it is necessary to determine and select the best vacuum gripper head. For handling paper, cardboard boxes, plastic films, paper sacks, plastic sacks and other similar objects, suction pads need to be flexible to adapt themselves to fix securely to the material and surface finish of the objects being handled.
German supplier Schmalz’s standard suction pads are made of natural rubber and have a long, thin sealing lip, making them suitable for handling films and paper.
US’s Anver only recommends natural rubber cups for these applications. For general industry use, it advises suction cups made of neoprene, polyurethane and nitrile rubber.
Both companies recommend suction pads made of silicone for handling foodstuffs, where hygiene is crucial.
Probably the most common type of pads are proprietary formulations of plastics and rubbers, such as urethanes and polyurethanes, which offer greater durability and can withstand higher temperatures than other cups, though at a premium. Schmalz, for example, recommends pads made of Vulkollan, a polyurethane elastomer produced by Bayer, for handling cardboard sheets and boxes with rough surfaces.
Suction pads with foam-rubber seals are used for handling plastic bags and medium-sized sacks. They consist of an aluminium body and a foam-rubber seal and the inside of the suction pad has a supporting grid which can be adjusted depending on the size of the bag or sack.
