Dow 93-076-1/2 Aerospace Sealant

Surface Preparation

DOW CORNING 93-076 Aerospace Sealant adheres well to primed surfaces of most materials used in the aerospace and aircraft industries. Typical materials include glass, cured silicone rubber, cork, phenolic, polyester, epoxy, silicone resin laminates and most metals including stainless steel, titanium and aluminum. It may not adhere well to polyethylene or certain plastics and organic materials (including rubber), which bleed or exude plasticisers. Stronger and more uniform bonds are obtained by preparing metal and plastic surfaces with DOW CORNING® 1204 Primer. For best results: Clean the surface with a chlorinated solvent (see Handling Precautions) and a slightly abrasive pad or a coarse lint-free cloth.

Rinse cleaned surface with acetone or methyl ethyl ketone.

Apply a thin coat of primer by dipping, brushing or spraying.

Allow the primer to dry for at least 1 hour, according to relative humidity.

Silicone rubber surfaces should not normally be primed, but only roughened slightly with abrasive paper and rinsed with acetone.

Mixing

The catalyst is added in a ratio of 10 parts of base to 1 part catalyst by weight. For best results the base should be thoroughly de-aired in standard vacuum equipment for 2 hours at greater than 650mm of mercury vacuum. The catalyst may then be added to the base in an air free mixer, such as a Semco® Pressure Mixer, model S-1350 or S-1378. Hand mixing may also be used if, after mixing, the product is de-aired in vacuum for about 30 minutes.

Curing

DOW CORNING 93-076 Aerospace Sealant is specially compounded to assure deep section curing. Like all tin-catalysed silicone rubbers, DOW CORNING 93-076 Aerospace Sealant may depolymerise in thick section when overheated in total confinement. To minimise this effect, encapsulations which must operate for extended periods in total confinement at elevated temperatures must be given a graduated post cure to allow volatiles to escape. During the graduated post cure, the temperature should be increased approximately 25°C per hour, depending upon the thickness of the potted sections. A final bake of 4 hours at 50°C above the maximum operating temperature of the device is recommended. To eliminate all the possibilities of depolymerisation, contact Dow Corning for alternate product recommendations.