Vacuum Technology Design – Single Piece Cup or Modular? (Part Two)

In part one of the blog series I talked about the dynamics of single piece or modular suction cups.  In part two we will continue our discussion.

Suction cups that don’t come apart during the higher accelerations that are needed to facilitate fast cycle times can be attributed to the physical properties of single piece suction cups optimized for packaging applications. A thin sealing lip and a reinforced bellows guarantee maximum stability when suction is applied. During pick-up, a special suction cup geometry causes the bellows and sealing lip to interlock. Lastly, the suction cup material Elastodur ED-65 shows high friction values despite its special elasticity. What this means in practice is that single piece suction cups allow significantly higher speeds without causing the gripped piece to slip.

The lower a bellows suction cup operates, the greater its stability is. Therefore, when suction is applied, the fewest possible layers of elastomer should lie on each other, and these layers should be as thin as possible. As a rule of thumb, the thicker the walls are and the greater the height is, the more unstable the suction cup will be when operated. If, due to the nature of the work piece and its surface, a bellows suction cup with a large stroke is needed, this must be attached so that the folds completely cushion one another to ensure product stability. “In the size range that was examined between 25 and 50 millimeter diameters, the single piece suction cups developed by Schmalz boast a relationship between suction cup stroke and size that is greater than multi piece suction cups by a factor of over 200% on average,” notes Kilb. The lesser ratio achieved by multi piece suction cups is due to their mechanical interfaces, which lead to additional height but do so without improving the stroke properties.

Long service life equals high process reliability

Abrasion and adhesion tendency are two factors that have a significant impact on the service life of suction cups. In a test involving 1,000,000 pick-up cycles, Schmalz determined the service life of suction cups with similar shore hardness by applying them to a suction tight surface and pulling them off under vacuum to simulate the maximum load imaginable in practice. The single piece Schmalz suction cup SPB1 showed slight abrasion at the end of the test series but remained fully operational. “Our endurance tests established a maximum service life of only 800,000 suction cycles for the multi piece suction cups,” says Kilb. After this, as a result of abrasion, increased adhesion tendency and the rapid disappearance of the multi piece suction cup sealing lip, a reliable suction process is no longer possible. In addition, clear signs of abrasion were visible on the mechanical plug connection between the bellows and the sealing lip.

How easy is it to select the right product?

Single piece suction cups are developed for industry-specific handling tasks. This defines the number of variants required. Combining every series, the Schmalz product range includes 19 types of packaging suction cups that cover all common packaging process applications. Multi piece suction cups, in contrast, allow a considerably higher number of variants. “The series examined allows several thousand suction cup combinations for designers and buyers to choose from,” explains Kilb. These also cover all common packaging processes. Since the single piece suction cups that were examined manage with far fewer variants, the process of product selection is faster and less prone to error, saving both time and money.

Dynamics, service life, and ease of product selection – when these core requirements in the packaging industry are taken into consideration, the following is certain: Multiple piece allows for more variants, but to achieve maximum performance a suction cup must be matched perfectly to a specific application. Single piece suction cups are clearly the winners in this regard.

Thank you for the opportunity to discuss suction cup design technology with you.  Please feel free to contact me with any specific questions.