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

Suction cups are by no means new. However, until recently they were all based on the same design principle. This changed when a new, multi piece suction concept was brought to the market. In a special study Schmalz compared the performance of single piece suction cups against multi part suction cups. The result: Single piece suction cups perform significantly better in many important respects.  Please join me as I discuss the study in detail in this first of a two part blog series.

Single piece suction cups consist of a single elastomer part. Every suction cup has a specific geometry, which is adapted during the development stage to meet the process requirements. Multi piece suction cups, on the other hand, are made up of different individual components such as a sealing lip and a base body. A large number of variants can thus be created using a small number of single components. Both concepts are available on the market, but which to choose?Single piece and multi piece suction cups

Multi piece suction cups can frequently be found in packaging processes. During testing we compared these with our own 1.5 bellows suction cups from the SPB1 series geared toward such applications in the industry. In a bid to determine suitability for use in the best possible way. The company examined performance features that are especially important in packaging processes, including dynamics, service life and ease of product selection. Extensive experiments enabled us to draw clear conclusions for and against the different suction concepts. When compared on the whole, single piece suction cups perform better with regard to all features – despite the wide choice of variants offered by the multi piece concept.

Efficient and dynamic

To evaluate the dynamics of the suction cups, test engineers concentrated on the holding power, shear force and relationship between suction cup stroke and height. Holding power is a pivotal factor that determines how many suction cups are needed for a handling task. This force is calculated from the vacuum level and the area that has been effectively evacuated. Essentially, the higher the vacuum level and the larger the effective vacuum area are, the stronger the holding power will be.

suction 2For applications in the packaging industry, the default vacuum level lies between -400 and -600 millibar. In the case of bellows suction cups, the internal diameter between the folds when suction is applied determines the holding force area. Because of the required plug connections, the internal diameter of multi piece suction cups was lower by an average of 40 percent in our tests. At a given vacuum level, the single piece suction cups achieved greater holding power by a factor of 272%.

High accelerations are needed in order to facilitate fast cycle times. In this respect, suction cups must be able to withstand the lateral forces that occur. On a suction-tight surface, the single piece suction cups that were tested achieved lateral forces up to 175 percent higher than comparable multi piece suction cups. For example, the 1.5 bellows Schmalz suction cup SPB1-25 in the test series showed a maximum lateral force of 23.4 newtons. The comparable multi piece suction cup achieved a maximum lateral force of 9 newtons. When subjected to higher lateral forces, in some cases the plug connections of the multi piece bellows suction cups actually came apart.

In my next blog I will introduce some discussion on service life and how easy it is to select the right product.

 

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