High-temperature silicone sealants were originally developed and are still used as seals or protective enclosures around heating elements and other industrial equipment likely to be exposed to temperatures in excess of 500° F. High-temperature silicone is specially formulated to withstand temperatures as high as 600° F, are resistant to aging, vibration, shock, and remains flexible even through repeated cycles of heating and cooling.
Silicone sealant is derived from a liquid form of adhesive, though in consistency and appearance it is more like a gel than a liquid. Silicone sealant differs in its chemical structure from other forms of more organic, polymer-based adhesive types. Unlike those other adhesives, silicone is resistant to chemical corrosion or deformation, and is also highly resistant to moisture and the effects of environmental exposure. It also retains a higher degree of elasticity and stability in extreme temperature variations.
Silicone sealants require curing after manufacture and before use. Curing typically takes place in a special curing oven, where finished silicone products are held for a period of time at a fixed temperature. Depending on the product, it can take anywhere from twenty-four to forty-eight hours to cure completely.
Industrial silicone is generally best used for applications requiring sealing an enclosure in order to ensure adequate climate control, or for use as a bonding agent between separate mechanical components. Silicone can be produced in a range of formulations with different properties, among them electrical grade, low-odor, paintable, and in the high-temperature variety that we mention above.
Silicone, regardless of its formulation, can be produced in a variety of types. A silicone formulation that is referred to as “high modulus” is more rigid and will tend to hold its shape better than other types. Low modulus silicone will be much more elastic. Other types include neutral cure and acetoxy cure, which are among the more commonly used types of silicone.
Neutral cure silicone takes longer to completely cure, but will be more adherent, and can be used in applications where it is required to stick to surfaces like those made of metal or glass. Acetoxy cure silicone releases acetic acid as it cures, which (because it evaporates quickly) means this type will cure faster. However, acetoxy cure silicone has poor adhesion, and will not stick to surfaces the way neutral cure silicone will.
High-temperature silicone is often used in automobiles, especially in the engine compartment, because it is ideal for use in an environment affected by the high heat of a running automotive engine. High-temperature silicone is typically used as sealant around components such as valve covers, axle housings, water and oil pump seals, timing chain covers, fuel pump covers, and solenoid covers. High-temperature silicones are called for in locations where the sealed joint or connection will be exposed to high heat.
High-temperatures silicone is also commonly used in industrial applications, such as appliance door gaskets, seals for humidifiers, around ductwork, in pump and compressor gaskets, for use in insulating wire and cable, and as furnace door gaskets, to name a few. Silicone sealant is used in a variety of craft projects because it is highly flexible.
Silicone sealant is often used in bathrooms and kitchens, because of its capability to provide a seal around sinks, showers, and bathtubs, which guards against the formation of mildew. It is also commonly used to seal windows and doors, as it provides an airtight barrier, eliminating air exchange, and is unaffected by exposure to the elements for very long periods of time.
To apply any kind of silicone sealant, including high-temperature variants, the surfaces it will be applied to should be clean and dry. If you are using a cartridge for application purposes, cut the nozzle tip at a 45° angle to obtain the optimum desired bead size. After application, the sealant should be tooled within a five- to ten-minute period.
Silicone sealant can also be applied to overhead areas or to sidewall surfaces without sagging, deforming, or running off. To bond materials, apply a bead of adhesive to one surface and immediately combine the two materials together. Apply pressure to ensure full contact between both surfaces, and allow the adhesive to dry.
Silicone sealant can be applied at temperatures as low as -85° F, provided the application surface is dry and free of frost. Applied sealant will generally be dry to the touch within thirty minutes, and will be fully cured within the first twenty-four hours.
The use of protective eye wear is always recommended when applying sealant, and sealant should never be combined with other chemicals. Care should be taken to prevent adhesive from coming into contact with skin, and the fumes should be avoided. After application, all equipment should be thoroughly cleaned with warm water, and any unused sealant should be stored in a cool, dry place.