Finished for leak prevention

Paul Boughton

Seal and equipment manufacturers face unique challenges in high vacuum environments, or in those with explosive and toxic gases. However, a new surface finishing process now virtually eradicates leak paths

Leak paths can be a challenge in any sealing environment, reducing performance and sometimes leading to failure, replacement or redesign. But what about in applications where failure can have serious consequences?

Many existing surface finishing processes, though offering excellent leak-free operation in many applications, do not offer the levels of surface quality that vacuum and toxic gas operations require, and can often be unsuccessful on large diameter seals.

The height of flash is absolutely critical to tight sealing functionality and de-flashing procedures must not create scratches or holes on the seal surface.

“We noticed that certain applications, particularly those involving high vacuum processes and large diameter O- Rings, were not performing up to our expectations,” says Simone Frick, Product Manager O- Rings and Surface Finishing at Trelleborg Sealing Solutions. “The performance was usually acceptable, but we knew that a better solution could be found.”

Traditionally, tumbling and grinding methods are used to remove flash, frequently leaving minute scratches on the surfaces of the seals which can act as leak paths.

“We began research to determine a better way of providing a higher level of quality for large diameter seals, one that would be unmatched in the industry,” continues Simone.

Trelleborg Sealing Solutions research and development teams along with application engineers worked together globally to create a new surface finishing solution that outperformed existing methods.

“The result was Flexfinish, a special de-flashing method which results in the lowest possible flash height and an outstandingly even surface finish, especially when compared to the methods used on large diameter seals,” explains Simone. “We can offer flash heights down to ISO 3601-3, grade S or N, depending on the customer's requirements and the material chosen, while providing very high surface qualities depending on the material and production method.

“When combined with large diameter O-Rings produced by Trelleborg’s FlexiMold process, Flexfinish can result in cost-effective sealing solutions that can give outstanding leak-tightness when sealing in a vacuum or with gas,” concludes Simone.

Flexfinish is available globally for O-Rings with inside diameters greater than 200 mm/7.874 inches in FKM, NBR and EPDM materials and with other materials. O-Rings can be provided to standard cross-sections according to ISO 3601-1 with other sizes available on request.

Large diameter seals

O-Rings manufactured using the FlexiMold process offer the full visual and dimensional integrity of a moulded product and are available from 500 mm/20 inches to almost infinite diameters or in ISO 3601-1, AS568 and JIS B 2401 standard sizes.

When designed to a standard size, no additional tooling costs are charged. They are available in a wide variety of elastomer materials, including the proprietary Isolast FFKM range and high performance Resifluor fluoroelastomers.

The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies that establish technical committees which prepare international standards on a wide range of topics.

ISO 3601-3 describes the quality acceptance criteria for O- Rings as well as defining, classifying and providing acceptable limits for surface imperfections. Three grades exist to characterise acceptable limits for different application requirements.

Seals for mutual trust

Seals from Trelleborg must stand up to millions of cycles in Arburg injection molding machines. That’s one reason why Trelleborg’s production facilities are also home to a large number of Arburg machines.

A high-performance machine such as the hybrid all-rounders from the Hidrive series operating in the packaging industry might well complete 7.3 million production cycles a year. Needing to demonstrate the highest possible performance under these conditions, one of these high-tech machines might contain as many as 20 Trelleborg seals and guide strips.

Tests are currently being carried out with the new highperformance Turcon M12 sealing material. To do this, Arburg machines that are in production at the Trelleborg Sealing Solutions facility at Stein am Rhein, Switzerland, are equipped with seals in the new material.

“In this way we carry out our testing together, under real production conditions,” explains Theodor Mack, a sales representative at Trelleborg Sealing Solutions.

At Trelleborg’s Liquid Silicone Rubber (LSR) competence center in Stein am Rhein, Arburg’s green-and-yellow injection molding machines dominate the central production hall.

Wherever you look, the characteristic shudder of the hydraulic hoses and movement of the handling units indicate that production is under way.

“Our production is fully automated, and we have full confidence in the high efficiency of the Arburg machines,” says Jakob Bleiker, Technical Director of the Stein am Rhein facility.

Seals made by Trelleborg are also component parts for Arburg’s new freeformer, which heralded a new era in plastics processing when it was presented at the K 2013 trade fair, the international trade fair for plastics and rubber. It is likely that it won’t be long before the first of this newest generation of machines takes pride of place in a Trelleborg facility.

Arburg’s world premiere of the freeformer moves an unprecedented success story in the field of injection molding machines into a new, revolutionary process of additive manufacturing. The unique freeformer produces fully functional plastic parts using a new additive manufacturing technique – ARBURG Plastic Freeforming (AKF) – from 3D CAD files, standard granulates and without a mold. It therefore offers boundless freedom for the efficient production of individual parts and small-volume batches.

Trelleborg’s Turcon Roto Glyd Ring and Turcon Roto Glyd Ring D120 are used as internal seals while a Turcon Roto Glyd Ring seals externally.

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