Traditionally for sealing Face Joints a paper, asbestos or cork & rubber gaskets are used. But these have been found woefully inadequate for the modern-day auto aggregates. Leaky trucks and cars in the garage are no longer acceptable. Some of the reasons that such traditional gaskets are not suitable are:

1. The sealing depends on contact pressure or clamping load. This may be lost due to variety of reasons and the sealing ability of the gasket is compromised.
2. Over a period of time the gaskets acquire ‘compression set’ and lose their resilience. This then becomes a cause of leakage. (There is a method ASTM D 395 and D 1056 to measure such compression set.)
3. Compression set leads to loss of bolt tension. This leads to bolts further loosening tension rather easily and the loss of clamping. When this happens, the sealing is lost completely and we have a leaky joint.
4. Many such gaskets have ‘fibres’ which enable ‘sweating’ of media being sealed. This sweat attracts dust which can be seen along the joint interface. This also is not acceptable.

The solution to above problem has been found in Liquid Sealant s- which are also called ‘Formed-In-Place Gaskets ‘, FIPG.

1. What are they?
   1. Well as the name suggests they are applied as liquids to one of the faces, the faces are mated and bolted and then the liquid becomes a solid due to chemical changes – mostly polymerization reaction.
   1. Chemistry wise they are either Anaerobic Adhesives (Acrylic Chemistry), RTV Silicone (Silicon Rubber Chemistry), Rubber Solutions.
2. How do they work?
   1. They fill the gaps left after the faces are mated thereby blocking

the leakage path.

• Most importantly they do not prevent metal to metal contact unlike traditional gaskets. This enables proper bolt tensioning. In case of traditional gaskets this bolt tension is limited to the compressive strength of the gasketing material which can be far less than the tension that a bolt can develop.
  • They do not require any contact pressure. Remember that they are applied as liquids and as the faces mate they are displaced away and only remain in the gaps.
  • Because there is no pressure on them there is no phenomenon of ‘compression set’.
  • There is no loss of bolt tension due to compression set and consequent loosening leading to further leakage.

For Liquids Sealants to make a successful Face Sealant the property requirement will be:

1. The sealant should be able to resist the media it is sealing at all operating condition.
2. The Flexibility of sealant should be as per the requirement of the joint. Is the joint likely to flex, like vertical surfaces of a typical tractor aggregate, or there are micro movements due to thermal expansion and contraction- predominant when using Aluminium as a material of construction.
3. The gasket must have sufficient bond strength to the mating surfaces, but not too high to enable easy removal. This must be retained at all operating condition.
4. The bolt must be locked and the bolt tension must not come down throughout the working life. This is most critical.

Advantage of Liquid Gasket over Solid Gasket.

A lot of misconception is floating regarding the use of Fuji Film to measure contact pressure and its utility as tool for gasket selection.

1. Fuji film comes in 9 grades having different contact pressure range, from very low to very high.
2. It is a very useful tool in case of solid paper of Cork-Rubber gaskets. These owe their sealing ability to contact pressure being exerted on them. A higher gap means less pressure in that zone and less contact for the solid gasket. In such a case you have to go for higher thickness of the solid gasket.
3. A liquid sealant get displaced while the parts are being mated and clamped. It only fills the gaps that are left over. This could either be actual gap due to flatness error or due to peaks and valleys on the surface. Once in the gap it cures over a period of time give a seal. Since all the clamping load is transmitted through the metal-metal contact, there is no contact pressure on Liquid Sealant.