Brand Silastic Application Type Mold-Making, Pot, Encapsulate 1 Part or 2 Part 2 Part Material Form Liquid Manufacturer Dow Chemistry Silicone rubber Cure Method Base/Curing agent Cure Temperature (°C) 25 Cure Time (min) 1,440 Viscosity (cPs) 92500 (mPa-s), Pourable Color Green Key Specifications FDA (U.S. Food & Drug Administration) and/or CFIA (Canadian Food Inspection Agency): FDA 21 CFR 177.2600
Technical Data for Dow Silastic L RTV Silicone Rubber
1 Part or 2 Part
- 1 Part or 2 Part - 2 Part
- Part A Name - Base
- Part B Name - Curing Agent
- Silicone - Silicone rubber
- 2-Part Cure - Base/Curing agent
- FDA (U.S. Food & Drug Administration) and/or CFIA (Canadian Food Inspection Agency): 177.2600 - FDA 21 CFR 177.2600
Cure Temperature (°C) 25 Test Method Cure Time (min) 1,440 Test Method Viscosity (cPs) 92500 (mPa-s), Pourable Test Method Work / Pot Time (min) 150 Test Method Mix Ratio 10:1 (by volume), 10:1 (by weight)
General Bond Strength (psi) High Tear Strength (piw) 60 (ppi) Test Method Tensile Strength (psi) 550 Test Method
Shore A Hardness 34, 35 Test Method Elongation (%) 350, High, Superior Test Method Flexibility Excellent Modulus (psi) Low
Specific Gravity 1.280 Test Method Flash Point (°F) 213.8
Shelf Life Details Silastic L RTV Silicone Rubber and its curing agent should be stored in closed containers at or below room temperature. The materials have a usable life of 12 months from date of manufacture. Refer to product packaging for “Use By” date. Shelf Life Type from date of manufacture Shelf Life (mon) 12
Best Practices for Dow Silastic L RTV Silicone Rubber
Certain contaminants sometimes used in moldmaking operations can prevent Silastic L RTV Silicone Rubber from curing. Patterns to be molded should be thoroughly cleaned to remove grease, oil and other surface contaminants. Care should also be taken to ensure that corners, crevices and draws are free of dirt or particles of foreign matter. A light “blow over” with compressed air is advised when the pattern has convoluted draws or undercuts. Then the original model or pattern should be placed in a light frame of cardboard, foil, wood or other material. There should be approximately 1/4-inch clearance on all sides and over the top of the pattern. The pattern should be attached securely to the bottom of the frame so it does not float. A pattern release agent should then be wiped or sprayed on the pattern. Spreading a light coat of release agent on the sides and underside of the top of the frame will facilitate release.
A good pattern release agent can be made by making a 5 percent solution of petroleum jelly in a suitable solvent. Either VM&P naphtha or mineral spirits can be used.
Silastic L RTV Silicone Rubber base and its curing agent are produced in matched lots
the two parts should be used in the kit form, as supplied. For the best curing results, use metal cans, clean glassware or unwaxed paper containers for mixing the base and curing agent. Silastic L RTV Silicone Rubber curing agent should be mixed into the base material just before use (with either manual or mechanical stirring) in the amount of one part curing agent to ten parts base by weight.
Inclusion of air during mixing may cause voids in the finished mold. Entrapped air may be removed by applying a vacuum of 28 to 29 inches of mercury. Under such a vacuum, the material will expand four to five times its original volume. As the froth collapses, the mixture will recede to its original volume. The vacuum should be held one or two minutes longer before releasing. Pressure casting may be substituted with equal success.
The cure of Silastic L RTV Silicone Rubber occurs by a reaction between the base polymer and the curing agent. This polymerization requires 24 hours after the addition of the curing agent at room temperature. This material will not revert or depolymerize, even under conditions of elevated temperature and confinement. Vulcanization can be accelerated by heating the catalyzed material. However, this will increase the shrinkage. The rate at which sections will set up depends on the size and shape of the piece. Vulcanization will not be accelerated at the center of the piece until the entire mass has reached the elevated temperature.
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Cure Temperature Test Methods
|Cure Temperature||Cure Time Test Method|
|25°C||CTM 0092A, Based on sample mass of one cubic inch.|
Cure Time Test Methods
|Cure Time||Test Method|
|1,440 min||CTM 0092A, Based on sample mass of one cubic inch.|
Viscosity Test Methods
|92500 (mPa-s)||CTM 0050, Brookfield Viscometer Model HAF, spindle #6 at 5 rpm.||25°C|
Work / Pot Time Test Methods
|Work / Pot Time||Test Method||Temperature|
|150 min||CTM 0092A, Time required to become nonflowable.||25°C|
Tear Strength Test Methods
|Tear Strength||Cure Time||Cure Temperature||Test Method|
|60 (ppi)||1,440 min||25°C||CTM 0159A|
Tensile Strength Test Methods
|Tensile Strength||Cure Time||Cure Temperature||Test Method|
|550 psi||1,440 min||25°C||CTM 0137A, Based on sample thickness of 125 mils, cured 24 hours at 25°C (77°F)|
Elongation Test Methods
|350 %||CTM 0137A, Based on sample thickness of 125 mils, cured 24 hours at 25°C (77° F).|
|High||Elongation Test Method|
|Superior||Elongation Test Method|
Shore A Hardness Test Methods
|Shore A Hardness||Shore Hardness Test Method||Hardness Temperature|
|34||Hardness/Durometer Test Method||25°C|
|35||CTM 0099, Based on sample thickness of 125 mils, cured 24 hours at 25°C (77° F).|
Specific Gravity Test Methods
|Specific Gravity||Temperature||Test Method|