Brand Silastic Application Type Mold-Making 1 Part or 2 Part 2 Part Material Form Liquid Manufacturer Dow Chemistry Silicone rubber Cure Method Heat, Base/Curing Agent Cure Temperature (°C) 25 Cure Time (min) 1,440 Viscosity (cPs) 55000 (mPa-s), Pourable Color White 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 E RTV Silicone Rubber
- Casting / Moldmaking - Mold-Making
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) 55000 (mPa-s), Pourable Test Method Linear Shrinkage (%) 0.10 Test Method Work / Pot Time (min) Long, 120 Test Method Mix Ratio 10:1 (by volume), 10:1 (by weight)
General Bond Strength (psi) High Tear Strength (piw) 110 (ppi), Tear Resistance Test Method Tensile Strength (psi) 800 Test Method
Shore A Hardness 37, 35 Test Method Elongation (%) 350, High Test Method Flexibility Flexible
Specific Gravity 1.140 Test Method Flash Point (°F) 212.0
Shelf Life Details Silastic E RTV Silicone Rubber and its curing agent should be stored in closed containers at or below room temperature. The materials have a shelf 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 E RTV Silicone Rubber
Patterns to be molded should be thoroughly cleaned to remove grease, oil and other surface contaminants. Certain contaminants sometimes used in moldmaking operations can prevent Silastic E RTV Silicone Rubber from curing. 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 place the original model or pattern in a light frame of cardboard, foil, wood or other material. Allow approximately 1/4-inch clearance on all sides and over the top of the pattern. Attach the pattern securely to the bottom of the frame so that it does not float. A pattern release agent should then be wiped or sprayed on the pattern. A light coat of release agent on the sides and underside of the top of the frame will facilitate release.
Silastic E 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 E 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. Note: Varying the ratio of the Silastic E RTV Curing Agent will not hasten or slow the rate of cure. However, it will result in lowering the physical properties of the cured rubber.
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.
With the curing agent added, 0.45 kg (1 lb) of Silastic E RTV Silicone Rubber will produce 409.7 cubic centimeters (25 cubic inches) of rubber.
The cure of Silastic E 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 thick sections will set up depends on the size and shape of the piece.
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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.|
Linear Shrinkage Test Methods
|Linear Shrinkage||Test Method||Temp|
|0.10 %||CTM 0157, 7 days, Based on sample thickness of 125 mils, cured 24 hours at 25°C (77°F).||25°C|
Viscosity Test Methods
|55000 (mPa-s)||CTM 0050, Brookfield Viscometer Model HAF, spindle #6 at 5 rpm., As Catalyzed – 10:1 Ratio, by weight||25°C|
Work / Pot Time Test Methods
|Work / Pot Time||Test Method|
|120 min||CTM 0055, Time required to double initial catalyzed viscosity.|
Tensile Strength Test Methods
|Tensile Strength||Cure Time||Cure Temperature||Test Method|
|800 psi||1,440 min||24°C||CTM 0137 A|
Tear Strength Test Methods
|Tear Strength||Cure Time||Cure Temperature||Test Method|
|110 (ppi)||1,440 min||24°C||CTM 0159 A, Die B|
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|
Shore A Hardness Test Methods
|Shore A Hardness||Shore Hardness Test Method||Hardness Temperature|
|37||Hardness/Durometer Test Method|
|35||CTM 0099, Based on sample thickness of 125 mils, cured 24 hours at 25°C (77°F).||25°C|
Specific Gravity Test Methods
|Specific Gravity||Temperature||Test Method|
|1.140||25°C||CTM 0022, Based on sample thickness of 125 mils, Based on sample thickness of 125 mils, cured 24 hours at 25°C (77°F).|