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HM-AS38
Howell
3506100010
AS38 is supplied as a one-component, acid curing, high modulus silicone rubber and works as an acid gasket-free sealant. Elasticity and displacement deformation ability are good, adhesion to various building materials is good, and oil resistance together with high and low temperature resistance is excellent. Long-term working temperature spans -40°C to 240°C, short-term resistance reaches 280°C, the combination that makes it a gasket maker sealant for automotive engines, gearboxes and oil pans, and for chimney pipe bonding.
Good elasticity
Oil resistance
Good adhesion
Wide range of temperature
High-modulus
Good displacement deformation
Long-term working at temperature -40°C to 240°C
Fed from a one-component cartridge through a sealant gun, AS38 goes onto a substrate cleaned first: grime, oil, dust, damaged spots and the loose natural oxide film left by production and transportation are removed, the surface is roughened into a profile into which the mechanism can embed, and this helps both the surface chemistry and the way the bond holds up under stress and environmental factors.
Solvent choice normally falls on isopropanol, methyl ethyl ketone or xylene, wiped on with a white cotton cloth that is clean, soft and free of loose fiber. Under the double cloth wiping method the cloth is soaked, the substrate is wiped in a single direction only, and a second clean dry cloth takes the solvent off immediately, before it volatilizes. The soaked rag never goes back into the soaking container, and cleaning stays confined to whatever bonding and sealing area will be worked within 1 hour, so the cleaned surface is not left exposed to the air for too long.
Gluing begins by masking the area adjacent to the interface with plastic tape, which keeps the working lines of the seal perfect and neat. The hose nozzle is cut and the needle-nosed tube fitted, then trimmed to an angle of 45° sized to the caulking. Holding that same 45° angle, run the sealant gun along the gap so the rubber presses tightly against the substrate surface, passing several times if the seam width exceeds 15 mm. A knife then trims the surface, the excess rubber is removed, the tape comes off and a damp cloth wipes away stains.
A polyolefin, or a rod made from polyurethane of the open type or from closed-cell polyethylene foam, serves as padding, so the sealant cannot stick on three sides.
Restrictions on Use
◆ Structural assembly is not among its uses.
◆ Surfaces where plasticizers or solvents may leak out are to be avoided, since the sealant can be damaged there.
◆ A completely sealed space is unsuitable: without moisture the material cannot cure completely.
◆ Places that have been immersed in water for a long time are not recommended.
◆ Structural surfaces coming into direct contact with food are not recommended.
◆ Service as a medical device sealant is not recommended.
◆ Long-term duty stops below 240°C; 280°C belongs to short-term exposure.
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