Cure in place gasket – Choosing the right one.

As a new assembly technology, liquid gaskets were developed with the sealing & gasketing function and demonstrates many advantages over conventional gasket methods. That’s why in most industries, whether electronics to automotive or power generation, cure-in-place gasket is the high-performing and reliable gasketing sealant to keep processes running smoothly and prevent downtime and cost increasing.

What is Cure-in-place gasket (CIPG) ?

What to consider when choosing gasket?

Regardless of the gasket type, there are general factors to consider when choosing a gasket type:

1. Movement Capability should be determined by the ability of the joint to move either through external forces or natural forces such as thermal expansion and contraction. The movement capability of the gasket prevents it from being damaged when the joint is subjected to these forces. Gasketing sealants that set to a tough, inflexible compound, such as oil-based and oil and resin–based  sealants, have a low movement capacity. The development of synthetic sealants has improved  the movement capabilities of sealant formulations to new stature.

2. Mechanical Properties: Properties that are often of interest include hardness, modulus,  tensile strength, tear or abrasion resistance, and compressive strength and compressive set.

Hardness is the relative measurement of flexibility. As the hardness values increase, flexibility decreases. Hardness, by itself, is not an adequate property to use to select a sealant.

Modulus is related to the movement capability of the adhesive. In general, low or medium modulus sealants are able to accommodate much greater joint movement without putting large stress on either the sealant or the substrate surface. More  flexible sealants, which can stretch and return to their original shape in a short time, are preferred for dynamic loading conditions.

Tensile strength is needed in some degree to avoid cohesive failure of the sealant. However, a high degree of tensile strength is usually not necessary for most sealants. However, the  sealant should have internal strength necessary so that cohesive failure does not occur.

Compressive strength is the maximum compressive force that the sealant can withstand before physically deteriorating. Compression set is the inability of the sealant to  recover after prolonged compression. Compression set is usually caused by further curing  or degradation of the sealant by the service environment. It is very undesirable in a joint  that must expand and contract.

3. Adhesion: Adhesion is a measure of the ability of a sealant to adhere to a substrate. Adhesion must be  maintained even while the sealant material is being stretched. Adhesion is often a critical  requirement for most sealing applications. Loss of adhesion in a threaded or overlap joint  can result in the fluid wicking through the sealant-substrate interface, leading to increased  degradation of the sealant or corrosion of the substrate. Loss of adhesion can also allow vibration loosening of a threaded joint or loss of acoustical coupling in a sound deadening  sealant. Joint design, surface preparation, and primers are used to assure good adhesion.

4. Durability: The broad requirement of durability can be broken down into properties that are more  specifically related to the particular sealant application, such as thermal capability, chemical  resistance, chemical compatibility, permeability, weatherability.

Temperature affects gasketing sealants in different ways, these changes could include strength loss and embrittlement.

Chemical properties of concern in selecting sealants usually consist of resistance to fluids and other chemicals. As might be expected, chemical resistance varies considerably between sealant types and formulation.

A sealant’s reistance to the weather must include its resistance to water, heat, cold, cycling, ultraviolet and solar radiation.

5. Appearance: It must be determined whether the gasketing sealant causes dis-coloration of surrounding substrate ares and whether the sealant itself changes in appearance or color over masking

Type of Cure-in-place Gaskets (CIPGs)

Because of the compression requirements, only very soft types of sealants will work  well as cure-in-place sealants. The most common type of gasket materials include:

Silicone

RTV Silicones contain no solvent, are one-or two-component sealants that cure at room temperature, with heat or with UV light. They have the ability of gap-filling up to 6mm. Silicone adhere well to many surfaces without the need of a primer. RTV silicones can be used for extended periods at temperature from –70 to 260°C and  for shorter periods to 315°C. Even after thermal aging, the RTV silicone retains its good flexibility and  adhesion. Silicones are resistant to common oils and coolants, and they have excellent  resistance to weathering, vibration, moisture, and ozone. 

Some cure-in-place silicone sealant gaskets have a dual cure capability. The fast UV cure sets  the bead and provides sufficient strength and character for assembly. A moisture cure then  takes over, which continues even in shadowed areas to provide for optimal strength and  durability. This allows the sealant to cure in depths to 6mm.

The primary limitation of RTV silicones is their relatively poor resistance to fuel and  aromatic solvents. They are also not well suited to heavily stressed or high-pressure applications due to their relatively low tensile and shear strength. 

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Polyurethane

Polyurethanes are commonly used for cure-in-place gaskets. When mixed and cured, these two-part sealants form thick solids or foams with excellent excellent elongation and adhesion. They adhere well to many different substrates including metals, plastics, and composites. Polyurethane sealants resist dilute acids, bases, and light oils. The polyurethane sealants generally have a hardness rating of 20 (Shore 00)  to 60 (Shore A).

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▪ 2 component Polyurethane

▪ Fully automatic, flexible and safe process

▪ Low personnel expenses

▪ Short production cycles and high production speeds

▪ Reproducible quality of seamless, contour accurate foam seals

▪ Fast invisible self-levelling coupling point

▪ Cost-effective alternative, especially for complex component geometries.