When it comes to sealing joints, liquid gaskets can offer many benefits. Bob Orme from Henkel looks into the technology
To ensure the integrity of a seal, gaskets must remain in place and prevent leaks, no matter how demanding the prevailing conditions become. But while compression gaskets – paper, rubber, metal, cork and so on – are a traditional method of sealing joints, these can suffer from practical disadvantages.
Firstly, there is a requirement for an initial compressive load in order to deform the gasket into the surface irregularities. Too much deformation, however, can cause the gasket material to lose its elastic properties, with the result that compression set occurs. The consequence is bolt clamp load loss – a condition that can result in leakage.
Furthermore, gaskets need to conform exactly to the contours of the surfaces to be sealed; and these contours can be quite complex, with inherent surface irregularities as well as shapes that might incorporate curves, oilways, ‘T’ joints and bolt holes. Producing, and then positioning, compression gaskets that match such contours can be both time-consuming and costly.
The use of liquid gasketing materials to provide seals between mating parts can not only eliminate these problems, but offer other distinct advantages.
Prior to component assembly, a sealant is applied to one of the mating surfaces. No matter how complex the shape of the parts, as they are brought together the product spreads across both faces, filling all surface irregularities, such as voids, scratches and gaps.
Once assembled, the sealant cures to form a durable gasket of just the right shape and size – enabling the mating surfaces to be fully, and reliably, sealed.
The liquid gasket allows metal to metal contact which means, in turn, the seal can withstand higher external loads. In addition, because fewer bolts are required and ‘T’ joints are possible, lighter weight assemblies can be produced. Furthermore, one container of liquid sealant can meet every conceivable shape and size of flange – removing the need for a large inventory of different sized rigid gaskets.
Two adhesive technologies are available for gasketing. Where rigid joints are involved, an anaerobic product should be employed. For applications that require a flexible seal, the preferred technology is silicone. Rigid flanges are designed to create optimum stiffness between mating components, while minimising relative movement.
Gaskets need to conform exactly to the contours of the surfaces to be sealed; and these contours can be quite complex, with inherent surface irregularities as well as shapes that might incorporate curves, oilways, ‘T’ joints and bolt holes
Liquid anaerobic adhesive sealants allow tolerances to be accurately maintained, as no allowance is needed for gasket thickness. Also, this close contact ensures the correct clamp load is maintained, and no re-tightening of the bolts is necessary.
Anaerobic products offer a high shear strength that prevents movement due to side loading, the ability to seal scratches and scored surfaces without prior treatment, and a reduction in surface finish and flatness requirements.
Because anaerobic gasket materials only cure in the absence of air and when trapped between metal surfaces, excess (and therefore, uncured) material can be readily wiped from exterior surfaces or flushed away from interior faces.
In addition, anaerobics can be easily integrated into production lines through the use of automated robotic dispensing or screen printing systems.
For sealing flexible joints, high performance silicone products are the answer. In order to overcome the effects of micro-movement, these sealants are formulated to cope with a high degree of elongation. Just as important, they can seal gaps up to several millimetres, and are effective within a wide operating temperature range of -70°C to +315°C, with intermittent exposure up to 350°C for some grades.
Like their anaerobic counterparts, silicones will achieve metal to metal contact of the mating parts and therefore also eliminate bolt relaxation and allow tolerances to be maintained.
Liquid gasket materials provide an excellent seal, and the process of applying the gasket can be easily automated.
Other advantages include: these are generally a single component, and easy and clean to apply; they effectively fill voids; there’s no need for re-torquing; an instant seal is created; high resistance to solvents; and liquid gaskets resist high pressure when fully cured.
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