Designed for Differing Uses
|Cups with certain characteristics perform more ably when tasked with gripping contoured surfaces.|
Vacuum-cup families include two general design types: flat or bellows-style. A bellows-style vacuum cup resembles an accordion, making it more flexible and allowing for grasping of items without consistent shapes, or not well-aligned with the cup. In these instances, though, a higher vacuum flow is needed to remove the larger volume of air inside the vacuum cup. Flat vacuum cups require a lower volume of air to be evacuated, but these are not as pliable as their bellows-style cousins.
Cup Hardness Signifies Possible Applications
A durometer measures the hardness of a material —typically polymers, elastomers and rubbers. Most vacuum-cup suppliers test for this by using the Shore A hardness scale, which measures the hardness of flexible molded rubbers. These rubbers range in hardness from very soft and flexible, to medium and somewhat flexible, to hard with almost no flexibility. Higher numbers indicate harder materials. Here are some cup scale numbers and what they mean:
- 30—soft, ideal for use with contoured panels. A cup with this measure, however, exhibit a shorter lifecycle than a harder cup.
- 45—a medium-hard rubber that effectively seals and adapt to most contours, making it ideal for all-around usage. Such a cup generally has a longer operational life than a 30-durometer cup.
- 60—the hardest durometer measure, and a cup with this measure is effective for extremely oily, flat surfaces. It features a longer service life than a 45-durometer cup.
Some vacuum-cup suppliers color-code their products by durometer for simple identification, maintenance and replacement.
When choosing a durometer for the application, remember that contoured parts, or those with sharp corners or edges, need a softer durometer so that the vacuum cups can easily grip the contours. Flat surfaces are ideal for harder durometers because the vacuum cup has stronger holding properties.
Like the manufacturers of vehicle tires, all vacuum-cup suppliers have created their own unique tread pattern. The design of the tread pattern determines the holding power or grip of the vacuum cup on the surface of a part or sheet. What works in one application may not work in another, especially if a material surface is dry or oily. Some vacuum cups combine their unique treads with a range of durometers to help increase grip strength.
Match Mounting Type to Automation
A wide range of mounting types is available to manufacturers, including male/female, imperial NPT and metric-G threads, square T-mount, and quick-disconnect. New lightweight-plastic thread mounts also are available. Before choosing a mounting type, check on the type of automation system in use. If the vacuum cup can’t be placed on the mount, the system won’t operate.
If necessary, perform onsite tests to determine the right vacuum cup for an application. For example, while your first thought may have been that two large vacuum cups should work for an application, A test may show that six smaller vacuum cups perform more satisfactorily.
Beyond the type of material, consider the weight and size of the object to be lifted. A light sheetmetal automotive hood features an easy-to-grip flat surface, and while a single vacuum cup could accommodate the hood’s weight, something that large can fall out of balance when moved, causing a drop. In this case, using four or more vacuum cups can balance the load, thus further securing the transfer process.
Also, the importance of vacuum-cup size, tread pattern and durometer in high-speed, pick-and-place transfer applications cannot be stressed enough. The vacuum cup must grasp the panel during the most stressful points of the automation’s acceleration and deceleration phases—each and every time.
Specialized applications offer additional operational characteristics to be considered. For example, the hot-forming steel-stamping process requires lifting and transfer of steel sheets with temperatures exceeding 480 F. While some standard vacuum cups can tolerate such heat, in some instances a special high-temperature vacuum cup may be needed. MF
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