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Description for Dow Dowsil 838 Silicone Adhesive Sealant
A one-part, white, non-flowing general purpose adhesive with good flame resistance, room temperature cure, high elongation.Brand Dowsil Application Type Bond, Sealant 1 Part or 2 Part 1-Part Material Form Pre-Cure: Paste, Post-Cure: Elastomer Substrate Ceramics, Glass, Many reactive metals, Plastics, Resins Industry Circuit boards, Light Emitting Diodes (LEDs), General purpose, PCB, Smart Meters, E-Mobility Solutions, Smart Home Devices, Power Tools, CRT module, Sealing in and around electrical leads, Electronic equipment, Electronics, LCD module, Sealing openings in modules, PDP module, Power supplies, PWBs Manufacturer Dow Chemistry Silicone elastomer Cure Method RTV, Moisture cure, Heat Cure, Room temperature cure Cure Temperature (°C) 20 to 25 Room temperature, 25, <60 Cure Time (min) 2,880, 1,440 to 4,320 Viscosity (cPs) Non-flowing Color White High Temperature Resistance (°C) 200 Low Temperature Resistance (°C) -45, -55 Volume Resistivity (O) 2.2E+15 (ohms/cm) Extrusion Rate (g/sec) 11,952 Key Specifications UL (Underwriters Laboratory), ULC (Underwriters Laboratories of Canada), NFPA (National Fire Protection Association): UL 94HB -
Technical Data for Dow Dowsil 838 Silicone Adhesive Sealant
Overview
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1 Part or 2 Part
- 1-Part
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Material Form
- Elastomer - Post-Cure: Elastomer
- Paste - Pre-Cure: Paste
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Industry
- LED (Light-Emitting Diodes) - Light Emitting Diodes (LEDs)
- Smart Meters
- Smart Home Devices
- E-Mobility Solutions
- Electronics - Circuit boards, CRT module, Sealing in and around electrical leads, Electronic equipment, LCD module, Sealing openings in modules, PDP module, Power supplies, PWBs
- Printed Circuit Board (PCB) - PCB
- Industrial - Sealing openings in housings, Yoke assembly
- General Purpose
- Power Tools
- Other - Sealing in and around wired
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Chemistry
- Silicone - Silicone elastomer
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Application Method
- Dispenser - Automated or manual needle dispensing systems
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Cure Method
- Room Temperature / Air Dry - Room temperature cure
- Moisture / Condensation Cure - Moisture cure
- Heat - Heat Cure
- RTV (Room Temperature Vulcanization) - RTV
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Color
- White
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Key Specifications
- UL (Underwriters Laboratory), ULC (Underwriters Laboratories of Canada), NFPA (National Fire Protection Association) : UL 94 HB - UL 94HB
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Brand
- Dowsil
Specifications
Cure Specs
Cure Temperature (°C) 20 to 25 Room temperature, 25, <60 Test Method Cure Time (min) 2,880, 1,440 to 4,320 Test Method Viscosity (cPs) Non-flowing Fixture or Handling Strength Time (min) 10 to 120 Tack Free Time (min) 46 Test Method Work / Pot Time (min) 60 Bond Strength
Shear Strength (psi) 140 Test Method Tensile Strength (psi) 270 Test Method Material Resistance
Flame Resistance Good Environmental Resistance Environmental resistance High Temperature Resistance (°C) 200 Low Temperature Resistance (°C) -45, -55 Moisture/Humidity Resistance Moisture resistance, Humidity resistance Conductivity
Dissipation Factor 0.00060, <0.00020 Test Method Dielectric Strength (V/mil) Good, Durable, 500 Dielectric Constant 2.64, 2.63 Test Method Volume Resistivity (O) 2.2E+15 (ohms/cm) Hardness
Shore A Hardness 31 Test Method Elongation (%) 430, High Flexibility Flexible Modulus (psi) 60 Test Method Other Properties
Extrusion Rate (g/sec) 11,952 Specific Gravity 1.020 Test Method Coefficient of Thermal Expansion (CTE) 375 (Linear (micron/m °C or ppm )) Business Information
Shelf Life Details Shelf life is indicated by the “Use Before” date found on the product label. For best results, Dow Corning RTV adhesives should be stored at or below 25°C (77°F). Special precautions must be taken to prevent moisture from contacting these materials. Containers should be kept tightly closed with head or air space minimized. Partially filled containers should be purged with dry air or other gases, such as nitrogen., DOWSIL 838 Silicone Adhesive Sealant should be stored at or below at or below room temperature (away from direct sunlight), maximum 25°C (77°F) in original, unopened containers.; Containers should be kept tightly closed with head or air space minimized. Partially filled containers should be purged with dry air or other gases, such as nitrogen. Shelf Life Temperature (°F) <90, 77 Shelf Life Type from date of manufacture Shelf Life (mon) 24 Not Good For
Don't Use For Polypropylene, Teflon®, Polyethylene Don't Use With Non-reactive plastic, Rubber substrates that are highly plasticized, Non-reactive metal, Plastic substrates that are highly plasticized, -
Best Practices for Dow Dowsil 838 Silicone Adhesive Sealant
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Surface Preparation
Preparing Surfaces All surfaces should be thoroughly cleaned and/or degreased with Dow OS fluids, naphtha, mineral spirits, methyl ethyl ketone (MEK) or other suitable solvent. Solvents such as acetone or isopropyl alcohol (IPA) do not tend to remove oils well, and any oils remaining on the surface may interfere with adhesion. Light surface abrasion is recommended whenever possible, because it promotes good cleaning and increases the surface area for bonding. A final surface wipe with acetone or IPA is also useful. Some cleaning techniques may provide better results than others
users should determine the best techniques for their particular applications.
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Testing
Due to the wide variety of substrate types and differences in substrate surface conditions, general statements on adhesion and bond strength are impossible. To ensure maximum bond strength on a particular substrate, 100 percent cohesive failure of the adhesive in a lap shear or similar adhesive strength test is desired. This ensures compatibility of the adhesive with the substrate being considered. Also, this test can be used to determine minimum cure time or can detect the presence of surface contaminants such as mold release agents, oils, greases and oxide films.
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Cure Temperature Test Methods
Cure Temperature | Cure Time Test Method |
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20 to 25°C Room temperature | |
25°C | |
<60°C | Mild heat |
Cure Time Test Methods
Cure Time | Test Method |
---|---|
2,880 min | |
1,440 to 4,320 min |
Tack Free Time Test Methods
Tack Free Time | Tack Free Temperature | Test Method |
---|---|---|
46 min | 25°C | Specification Writers: These values are not intended for use in preparing specifications. |
Tensile Strength Test Methods
Tensile Strength | Test Method |
---|---|
270 psi | Specification Writers: These values are not intended for use in preparing specifications. |
Shear Strength Test Methods
Shear Strength | Type |
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140 psi | Lap shear strength |
Dielectric Constant Test Methods
Dielectric Constant | Test Method |
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2.64 | 100 Hz |
2.63 | 100 kHz |
Dissipation Factor Test Methods
Dissipation Factor | Test Method |
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0.00060 | 100 Hz |
<0.00020 | 100 kHz |
Modulus Test Methods
Modulus | Test Method |
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60 psi | Tensile, Specification Writers: These values are not intended for use in preparing specifications. |
Shore A Hardness Test Methods
Shore A Hardness | Shore Hardness Test Method |
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31 | Durometer, Specification Writers: These values are not intended for use in preparing specifications. |
Specific Gravity Test Methods
Specific Gravity | Test Method |
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1.020 | Cured, Specification Writers: These values are not intended for use in preparing specifications. |

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