Custom-Made Beats Universal

25.01.2012

In a study, Schmalz compared the performance of single-component suction pads against multi-part suction pads. The result: Single-component suction pads perform significantly better in many important respects.

Single-component vs. multi-component
Single-component suction pads consist of a single elastomer part. Every suction pad has a specific geometry, which is adapted during the development stage to meet the process requirements. Multi-part suction pads, on the other hand, are made up of different individual components such as a sealing lip and 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?
Multi-part suction pads can frequently be found in packaging processes. During testing, therefore, Schmalz compared these with the 1.5 bellows suction pads 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.

Efficient and dynamic
To evaluate the dynamics of the suction pads, test engineers concentrated on the holding power, shear force and relationship between suction pad stroke and height. Holding power is a pivotal factor that determines how many suction pads 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. For applications in the packaging industry, the default vacuum level lies between -400 and -600 millibars. In the case of bellows suction pads, the internal diameter of the folds when suction is applied is crucial. “Because of the required plug connections, the internal diameter of multi-part suction pads was lower by an average of 40 percent in our tests,” Kilb explains. At a given vacuum level, the single-component suction pads achieved greater holding power higher by a factor of 2.72.

High accelerations are needed in order to facilitate fast cycle times. In this respect, suction pads must be able to withstand the lateral forces that occur. On a suction-tight surface, the single-component suction pads that were tested achieved lateral forces up to 175 percent higher than comparable multi-part suction pads. For example, the 1.5 bellows suction pad SPB1-25 in the test series showed a maximum lateral force of 23.4 newtons. The comparable multi-part suction pad achieved a maximum lateral force of 9 newtons. “When subject to higher lateral forces, in some cases the plug connections of the multi-part bellows suction pads actually disconnected,” comments Kilb, chief test engineer.
This result can be attributed to the physical properties of single-component suction pads optimized for packaging applications. A thin sealing lip and reinforced bellows guarantee maximum stability when suction is applied. During pick-up, a special suction pad geometry causes the bellows and sealing lip to interlock. Finally, the suction pad material Elastodur ED-65 shows high friction values despite its special elasticity. What this means in practice is that single-component suction pads allow significantly higher speeds without causing the gripped piece to slip.

The lower a bellows suction pad 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 these 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 pad will be when operated. If, due to the nature of the workpiece and its surface, a bellows suction pad 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 millimeters, the single-component suction pads developed by Schmalz boast a relationship between suction pad stroke and size that is greater than multi-part suction pads by a factor of 2.08 on average,” notes Kilb. The lesser ratio achieved by multi-part suction pads is due to their mechanical interfaces, which cater for additional heights 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 pads. In a test involving 1,000,000 pick-up cycles, Schmalz determined the service life of suction pads 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-component suction pad SPB1 showed slight abrasion at the end of the test series but remained fully operational. “Our endurance tests established a maximum service life of 800,000 suction cycles for multi-part suction pads,” says Kilb. After this, as a result of abrasion, increased adhesion tendency and an advanced reduction in size of the multi-part suction pad, 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 sealing lip.

Eeasy suction pad selection
Single-component suction pads 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 pad that cover all common packaging process applications. Multi-part suction pads, in contrast, allow a considerably higher number of variants. “The series examined allows several thousand suction pad combinations for designers and buyers to choose from,” explains Kilb. These also cover all common packaging processes. Since the single-component suction pads 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 parts allow for more variants, but to achieve maximum performance a suction pad must be matched perfectly to a specific application. Single-component suction pads are clearly the winners in this regard.

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J. Schmalz GmbH Customer Center Aacher Straße 29 D-72293 Glatten	Tel.: +49 (0)7443 2403-105 Fax: +49 (0)7443 2403-9105 kundencenter@schmalz.de

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