Sealants compressive seals

Sealants basically seal by compression/repulsion. The sealing theory of a gasket is generally expressed by the following equation ... 

Compression Seals. These are preformed cellular elastomeric products available in either precompressed or uncompressed forms. The sealant may utilize external and/or internal adhesive elements. The seal is obtained by placing the preformed material in compression between the joining surfaces. Exact storage, handling, and application instructions must be followed. 

Intumescent sealants are widely used in expansion and compression joints, construction gaps, fire protection panels, fire doors and around cable and pipe penetration. They work with, or replace, fire stops and preformed seals in the creation of compartments which are essential to efficient fire protection. 

Compressible materials rarely have a good bond to the sides of the joint but, if installed under pressure, will expand to release that pressure if the joint opens, or squeeze together if it closes. Without a good bond to the joint sides, this type of filler is rather easily penetrated by contained liquids. It is, therefore, common practice to fill the joint to within V4 in. to Vz in. of the top with the compressible foam, then seal the top space with the deformable sealant, applied in putty or fluid form and bonded to the sides of the joint. It is important that the sides of the joint are truly vertical., at 90° from the floor surface, so that as the the joint opens or closes, the movement is at right angles with the sides. 

The compression set data, which we had obtained, reflect far poorer performances than we had anticipated on the basis of conversations with manufacturers of solar collector units and suppliers of sealants. A summary of thse data are presented in Table VIII. All three silicones, G, I, and J, tested exhibited compression sets of the order of 100% after only one day of aging at either 250°C or 225°C. (Compression set values greater than 100% are attributed to essentially complete loss of resilience by the specimen combined with an additional reduction in sample thickness due to shrinkage associated with thermal degradation). For example, the best of the three silicones, J, showed compression set values of 94% after one day at 225 C and 89% after 28 days at 175°C. We feel that a sealant should not exceed 50% in compression set if it is to retain good sealing ability. 

Apart from the poured joint sealants, particularly for the expansion type of joints, there are also preformed joint seals that are placed after compressing them into the expansion joint. These materials are such that they are always compressed, even when there is a complete expansion of the joint. The preformed joint seals should comply with specifications such as CEN EN 14188-3 (2006), ASTM D 2628 (2011), ASTM 1752 (2013), AASHTO T 42 (2010), AASHTO M 33 (2012), AASHTO M 153 (2011) or AASHTO M 213 (2010). 

Extrusion of the sealant may be caused by overfill sealing groove and lack of compressibility of the backer material (caulking strip), if used. 

Sealant materials could be hot applied (complying with CEN EN 14188-1 2004 or ASTM D 6690 2012), cold applied (complying with CEN EN 14188-2 2004 or ASTM D 5893 2010) or preformed joint seal material applied by compression (complying with CEN EN 14188-3 2006, ASTM D 2628 2011 or other specifications). When backer material is used, it should comply with ASTM D 5249 (2010) or any other specification. 

The compressive force in sealed joints is applied by means of bolts and the sealing material could be either a compressed foam or various forms of sealants and gaskets. 

Gasketing materials are generally preformed elastomers that are available as o-rings, rope, and other convenient shapes. Gaskets may also be cut from stock material such as thin sheet. However, sealants can be used to make formed-in-place gaskets. A ribbon of uncured sealant is applied to the flange area of the components to be sealed. On assembly of the components, the sealant is compressed to conform exactly to the mating surfaces. 

The fittings on CGA connections should not be lubricated nor should Teflon tape be used. In fact, it is not the thread itself that is making the seal, but the male and female end of the two parts that are connected. Sealants should also not be used on compression fittings (such as Swagelock fittings). In addition to other... 

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