Extreme Temperature Range Seals
Silicone (VMQ) oil seals provide the widest operating temperature range of any standard sealing elastomer: -65°F to 350°F. The compound also tolerates dry running better than other elastomers and is compatible with food-grade applications. Specialty Durus sizes available for specific temperature-critical applications.
What Is a Silicone Oil Seal?
Silicone (VMQ) is an inorganic-backbone elastomer based on silicon-oxygen chains rather than the carbon chains of NBR, Viton, and Polyacrylate. The inorganic backbone gives silicone exceptional temperature stability - both at extreme cold (-65°F, below which other elastomers stiffen) and continuous high heat (350°F). Silicone also has good biocompatibility, making it the elastomer of choice for food, pharmaceutical, and medical applications.
When to Specify Silicone
- Extreme cold service below -40°F - Silicone remains flexible to -65°F where NBR and Viton stiffen
- Wide temperature swings - Outdoor equipment that sees both arctic cold and summer heat
- Dry running or intermittent lubrication - Silicone has self-lubricating properties superior to other elastomers
- Food, pharmaceutical, or medical contact - Silicone compounds available in FDA-compliant grades
- Compressed air systems - Silicone tolerates the oil-free environment of pneumatic actuators
When NOT to Use Silicone
Silicone has significant limitations and is not a universal upgrade:
- EP gear oils - Silicone swells in EP additives; use Polyacrylate (ACM) instead
- Fuels and hydrocarbons - Silicone has poor fuel resistance; use Viton
- Mineral oils with high shaft speeds - Silicone's low abrasion resistance limits dynamic sealing in standard oil applications; use NBR
- Hydraulic fluids - Limited compatibility with hydraulic system fluids; use NBR or Viton
Silicone's strength is temperature range and biocompatibility, not general industrial oil sealing. Use silicone where the temperature or food-grade requirement actually drives the selection - not as a default upgrade from NBR.
Temperature Range vs Other Compounds
| Compound | Low Limit | High Limit | Range Span |
|---|---|---|---|
| NBR (Buna-N) | -40°F | 250°F | 290°F |
| Viton (FKM) | -40°F | 400°F | 440°F |
| Polyacrylate (ACM) | -25°F | 300°F | 325°F |
| Silicone (VMQ) | -65°F | 350°F | 415°F |
Related Materials
Frequently Asked Questions
What is the temperature range for Silicone oil seals?
Silicone (VMQ) oil seals operate from -65°F to 350°F continuous - the widest temperature range of any standard sealing elastomer. Silicone's inorganic silicon-oxygen backbone resists both extreme cold (stays flexible to -65°F where NBR and Viton stiffen) and continuous high heat (350°F). Short excursions to 400°F are tolerable. The combination makes silicone the compound of choice for outdoor equipment exposed to wide seasonal temperature swings.
When should I use Silicone instead of Viton?
Use silicone when the operating temperature drops below -40°F - silicone's lower temperature limit of -65°F handles extreme cold where Viton stiffens. Also choose silicone for food, pharmaceutical, or medical contact applications where FDA-compliant elastomers are required. For high-temperature petroleum oil sealing above 200°F where temperatures stay above 0°F, Viton is generally the better choice due to better dynamic sealing performance.
Can Silicone oil seals be used with gear oil?
No - silicone is not recommended for EP gear oils. The sulfur and phosphorus additives in modern API GL-5 gear oils cause silicone to swell and lose mechanical properties. For gear oil applications, specify Polyacrylate (ACM) which is engineered for EP additive compatibility. Silicone is appropriate for non-EP applications: clean compressed air, dry-running shafts, and food-grade petroleum oils.
Are Silicone oil seals food-grade compliant?
Silicone compounds can be manufactured in FDA-compliant grades suitable for incidental food contact. However, not all silicone elastomers meet FDA requirements - confirm the specific compound and certification when food-grade compliance is required for your application. Durus offers food-grade silicone in select sizes; contact Texas Belting at (888) 203-2358 to confirm certification documentation for a specific part number.
Why is Silicone not a universal upgrade from NBR?
Silicone has excellent temperature range but limited fluid compatibility. It performs poorly with fuels, hydrocarbons, EP gear oils, and hydraulic fluids - all common industrial sealing applications. Silicone's mechanical properties are also softer than NBR, leading to faster wear in high-speed shaft applications. Silicone is the right choice for specific applications (extreme cold, dry running, food contact) - not a general-purpose upgrade. For most industrial mineral-oil applications below 250°F, NBR provides the best cost-performance balance.
Cross-reference from any CR, SKF, National, Federal-Mogul, or Timken part number. Houston, TX warehouse stocks the full Durus catalog with same-day shipping for in-stock items.
Call (888) 203-2358 or email sales@texasbelting.com with your existing part number, equipment make/model, or shaft and bore measurements.
