Flexible Expander Seal Tolerances

In advanced manufacturing environments precision is often critical, but flexibility can be just as important. This is increasingly the case in the sealing of fluid ports. Expansion-style plugs are replacing traditional sealing methods – such as cup plugs, pin plugs and ball plugs – in many production environments. Often the flexibility of these plugs is key to the total value, or “tolerance stack-up,” and makes these solutions best-in-class.

MB 850 Koenig Expander Plug
Indicated in green, push-style plugs support tolerances of +0.1 mm (0.004”) and pull-style plugs support tolerance of +0.12 (.005”), which can provide greater flexibility and savings for manufacturers.

SFC KOENIG® solutions have become the preferred expansion seal for many engine applications. With tolerances +0.1 mm (0.004”) for their push-style plugs and +0.12 mm (.005”) for pull-style plugs, the liberal tolerance allowances of KOENIG EXPANDER® seals are a key consideration for many manufacturers.

“With more than 5 billion parts installed and failure rates less than one part per million, we know that our reliability and flexible tolerance allowances provide enormous value in today’s high-speed production environments,” noted Tom Ryan, Head of Product Management at SFC KOENIG. “Customers don’t have to implement as many process controls, and the cumulative effect of our parts is greater reliability, reduced costs and lower risk.”

Larger tolerance allowances are often extremely valuable in part installation. Misalignment is a common problem for many common seal types, which can lead to system failure or the need to remove and reinstall mis-seated plugs. Even slightly mis-calibrated cup seal or ball plug installation can result in labor-intensive fixes. These errors also increase scrap rates, further adding to costs.

Ball plugs require tight tolerances by design, as only a small “ring” – the outer diameter – of these components makes contact with the bore wall. Smaller contact area means a smaller sealing surface and increases the difficultly of properly mating the ball and the base.

KOENIG Expander Sealing Plugs
KOENIG EXPANDER® plugs support the same flexible tolerances across its product line, which is maintained on parts as small as 3mm.

As the potential risk of seal failure increases, it directly correlates to an increase in the risk for system damage, safety concerns and warranty costs.

Notably, in the case of the KOENIG EXPANDER, tolerance allowances are not related to the size of the plug diameter – so +0.1mm or +0.12mm tolerance flexibility is supported across the entire SFC KOENIG® expansion plug line, even on sealing components as small as 3mm. The company’s advanced manufacturing processes precisely control production, reliably maintaining tolerance allowances across large run volumes. This flexible tolerance can be extremely valuable when sealing small fluid ports.

Many seals – such as cup plugs, ball plugs, pin plugs and even other expansion style plugs – require additional machining processes, such as reaming, to properly prepare the hole. This adds to process and labor costs. Additionally, smoother finishes negatively impact pressure limits in harder materials. KOENIG EXPANDER seals require no additional reaming, further increasing their total value.

Some plugs increase their tolerance allowance by relying on chemical sealants. However, chemical sealants pose significant risks, including contamination, and eventual break-down of the seal barrier over time when exposed to heat and vibration. KOENIG EXPANDER plugs create a secure, metal-to-metal seal, with no sealants or additives.

metal to metal seal tolerance
Cup plugs rely on sealant, which can break down or cause contamination, eventually leading to failure – KOENIG EXPANDER® plugs create a secure metal-to-metal seal with no sealant required.

Additionally, one-piece seals – such as the KOENIG EXPANDER – provide added value beyond seating and sealant. Compared with most pin plugs, which require the assembly of two pieces in their installation, KOENIG EXPANDER plugs are faster, more reliable and eliminate errors associated with plug assembly.

Even in modern, CNC controlled manufacturing environments, advanced operations benefit from liberal bore tolerances and product flexibility. While every step in production requires control – from forming the raw material to precision machinery to the speed at which the line can run – by utilizing a sealing solution with flexible tolerances, engine manufacturers are able to reduce costs and improve results.