Cured-In-Place-Gasket (CIPG)

A cured-in-place gasket – CIPG for short, also referred to as a formed-in-place applied seal – is a seal that is applied directly onto the component to be sealed and subsequently vulcanised in place. The seal is therefore not produced as a separate part and then fitted, but is formed and cured on the carrier part itself. The result is a component-integrated seal that adheres captively and passes into the further manufacturing process as a completely pre-assembled unit.

The CIPG principle differs clearly from conventional profile or moulded seals: the geometry and positioning of the seal are not determined by a tool, but by the application system and the design of the sealing point.

Materials and application process

The sealing compounds used are predominantly RTV silicone types (RTV-1 and RTV-2), and in certain applications also polyurethane (PUR). RTV stands for "Room Temperature Vulcanizing" – cross-linking can take place at room temperature or with the input of heat, and subsequent tempering is generally not required.

The process sequence in practice: the sealing compound is applied to the component as a bead in a liquid-to-pasty state via a mixing and metering unit. Application is carried out fully automatically – by robot or coordinate table – with high repeat accuracy. The bead is then vulcanised in a drying oven or IR channel. After vulcanisation, the seal adheres firmly to the carrier part on one side and can be built in together with it.

Whether the seal adheres durably to the carrier part depends decisively on the latter's surface. Oil, release-agent residues or low-energy plastics such as PP prevent reliable adhesion – in these cases the RTV silicone finds insufficient adhesion and peels off during handling or assembly. Depending on the surface of the carrier part, surface pre-treatment by cleaning, plasma, flame treatment or primer is imperative. The bond strength must be demonstrated as part of the process qualification.

Design of the sealing point

With the CIPG, the sealing effect is created by partial compression when the components are joined – the compression is typically around 25–35 %. Since silicone rubber is elastic but practically incompressible, the material displaces sideways into the groove when compressed.

The groove must offer sufficient displacement space for this: at a fill level above 80–85 %, uncontrollably high forces build up when the housing is closed – the housing distorts or the seal is damaged. This gives rise to specific design requirements:

• Groove width: approximately 1.3 to 1.4 times the bead width
• Bead cross-section: the applied bead will be wider than it is high; the width-to-height ratio is approximately 1 : 0.6–0.8
• Bead geometry: a round application is not possible for process-related reasons; the cross-sectional profile is flat-oval

These characteristic values are decisive for a reliable sealing effect and must be taken into account when designing the seat geometry. Since solid silicone rubber is physically incompressible, sufficient displacement space must be available for the material yielding sideways when joining. If the groove is dimensioned too narrow, uncontrollably high forces build up when the housing is closed – the housing distorts or the seal becomes dysfunctional. As a guide value, a groove fill level of no more than 80–85 % applies, so that the displaced material has room without placing a load on the structure.

Strengths and limits of the process

The CIPG process offers significant advantages in series production:

• Fully automatic application directly at the system supplier – no separate assembly step for the seal
• Captive adhesion to the carrier part, thereby ensuring safe handling and logistics
• Repeated dismantling possible without destroying the seal – relevant for maintenance concepts
• Simple groove design without complex profile geometry
• With appropriate design, additional sound and noise decoupling between the joining partners

At the same time, there are clear limitations that play a role in the design decision:

• The baseline mechanical properties of RTV silicone do not reach the level of synthetic rubbers such as NBR or FKM, or FPM – under high dynamic loads or extreme media requirements, CIPG seals reach their limits
• A specific profiling of the seal – as with moulded seals or profiles – cannot be realised for process-related reasons
• In the event of a repair, the seal must be renewed completely; a simple replacement as with an O-ring is not possible
• The most critical quality parameter in the application process is the start-stop overlap: at the point where the metering robot sets down and lifts off the bead, local thickenings or tapers frequently arise. In practice, this junction is the most common cause of leakage – its definition, positioning and monitoring must be explicitly regulated within the manufacturing process.

Typical applications

CIPG seals are particularly well established in vehicle and engine construction, where a high degree of manufacturing automation, component-integrated sealing functions and compact installation spaces come together:

• Water pumps and thermostat housings
• Radiator connectors and radiator seals
• Intake manifolds and valve covers
• Housing lids and unit seals in general mechanical engineering