Continuous Molding Enables Production of Large-Size Elastomer Seals

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Blog.

Continuous Molding - Vulcanization of Large Size O-RingsPrecision O-rings are manufactured by vulcanization in a closed mold using compression or injection molding. This makes it possible to produce O-rings in relatively small manufacturing tolerances and with good surface quality according to ISO 3601-1 and ISO 3601-3. Due to defined vulcanization parameters, precision O-rings exhibit consistently high mechanical properties across the entire circumference. This high quality level is an indispensable prerequisite for achieving consistently good sealing effects over a long period of time.

However, up to now, this production technology has been regarded in the sealing industry as not being economically feasible for O-rings in very large dimensions due to the enormous work and related costs involved in making extra-large molds. In addition, such large molds are extremely difficult to handle and therefore cannot be accomplished by many seal manufacturers.

Advantages of Continuous Vulcanization

The innovative manufacturing technology of continuous vulcanization used by Parker Prädifa, which does not involve failure-prone joints, enables the cost-efficient production of precision-quality O-rings with high mechanical load resistance in nearly any desired diameter. The technical properties of continuously vulcanized O-rings are comparable with those of O-rings produced by conventional compression molding. As a result of being molded, these XXL O-rings are quality products for challenging applications.

The surface qualities and tolerances correspond to those in ISO 3601:2012. However, this standard only covers cord thicknesses of up to 8.4 mm. To ensure that customers receive reliable and consistently high-quality O-rings where cord thickness is >8.4 mm, Parker Prädifa has developed an in-house standard based on ISO 3601:2012.

Customer-specific geometries for static and dynamic applications
In addition to precision-quality XXL O-rings, Parker Prädifa offers the development and production of customer-specific geometries in large diameters. A wide range of materials is available according to the application requirements.

Case study: Sealing solution for centrifuge (pharmaceutical industry)

Continuous Molding - Vulcanization of Large Size O-Rings

The challenge >> In the large-scale industrial production of semi-synthetic antibiotics, up to 500,000 liters of antibiotics are produced per batch. For such large-scale production to be economically feasible equipment of corresponding dimensions is required. In addition to large fermenters with diameters of several meters in which the biotech antibiotic is bred, centrifuges of similar dimensions are utilized to separate the antibiotic from process agents. Leakage must be prevented at all cost for safety and economic reasons. A leaking centrifuge might contaminate the antibiotics, resulting in high financial losses or, worse yet, in health and environmental hazards.

The solution >> Parker Prädifa was involved in the project at an early stage to develop a reliable sealing solution. The utilization of continuously vulcanized, i.e. jointless precision O-rings ensures the requisite reliability. Besides the seal design, the compound properties, particularly temperature and media resistance, play a key role. In addition to permanent temperatures of 250 °C, the seal has to withstand the aggressive media used in antibiotics production. The Parofluor® (FFKM) compound V8920 was selected as the suitable material for this application.

Case study: Lip seal ring for lithography system (semiconductor industry)

Continuous Molding - Vulcanization of Large Size O-Rings

The challenge >> The development of a new lithography system for semiconductor manufacturing posed the challenge of sealing two halves of a housing. Due to the tolerance situation in producing the respective housing halves, there was a risk of a gap of up to 0.5 mm occurring between the two halves in the assembled housing.

The solution >> In sealing technology, the gap dimensions to be bridged are typically between 0.05 mm and 0.25 mm. As larger gap dimensions available for sealing in the groove in this application could not be reliably sealed, or only by entailing a higher risk of leakage, with a solid seal such as an O-ring, a conventional O-ring sealing solution was not selected here, but a profile seal featuring a lip design. This seal was developed using Finite Element Analysis (FEA) to ensure reliable sealing of large gaps and tolerance variations in the seal groove between the two halves of the housing. In addition, the shape of the seal prevents twisting during installation and reduces the required assembly forces.
In the selection of the seal compound, high purity requirements had to be considered. Due to specific post-curing processes, the FKM compound V0747 with low outgassing properties achieves outstanding results.

More information
EMG Report 07/2017, Page 22
Brochure: XXL Size Seals and Molded Parts

This article was contributed by Stefan Reichle, Market Unit Manager Indsutry, Engineered Materials Group Europe, Prädifa Technology Division.