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Quick Answer: A custom bonded seal is a metal washer with a molded rubber sealing lip, made to your required thread size, outside diameter, metal material, rubber material, and operating conditions. CORASEALS supplies custom bonded seals for bolt heads, drain plugs, filler plugs, and non-standard sealing points. Send us your thread size, ID, OD, washer thickness, metal material, rubber material, fluid, pressure, temperature, and quantity for a quotation.
A bonded seal has a metal outer ring and a rubber sealing element. The metal ring limits compression. The rubber lip seals against the seating face. Custom bonded seals are produced when a standard size is not available, or when the application requires a different metal grade, rubber compound, thickness, or outside diameter.
Dowty seal is a common trade name for this type of seal. CORASEALS uses the descriptive term bonded seal and treats Dowty as a third-party trade name.
Start with the thread size or bolt diameter. Measure the housing bore, seat diameter, and available outside diameter. Include the washer thickness and the rubber inside diameter if the hole must fit a specific bolt or plug. If the seat has a counterbore, include that diameter and depth.
Standard bonded seals are often referenced to DIN 7603. A custom bonded seal can use the same sealing principle with dimensions changed to match your housing and thread.
State dimensions in metric or inch units. Do not mix units. For example, a typical inquiry may state thread size M14, OD 20 mm, washer thickness 1.5 mm, and NBR rubber.
Common metal ring materials include carbon steel, 304 stainless steel, and 316 stainless steel. Common rubber materials include NBR, FKM, and EPDM. NBR is widely used for mineral oil and hydraulic oil. FKM is selected for higher temperature and chemical resistance. EPDM is used for water, steam, and brake fluid. The final material combination must match the fluid, temperature, pressure, and seat surface.
| Material Type | Common Grade | Common Use |
|---|---|---|
| Metal ring | Carbon steel | General hydraulic and lubrication systems |
| Metal ring | 304 stainless steel | Water, corrosion resistance, and general chemical exposure |
| Metal ring | 316 stainless steel | Seawater, chemical, and acid environments |
| Rubber | NBR | Mineral oil, hydraulic oil, and fuel |
| Rubber | FKM | Higher temperature and aggressive fluids |
| Rubber | EPDM | Water, steam, brake fluid, and weather |
Most bonded seals use rubber in the 70 to 90 Shore A range. The correct hardness depends on the seating face condition, pressure, and required compression.
Bonded seals work best in static threaded joints with a flat seat. The rubber lip must be compressed by the metal ring without being cut or extruded. Check the seat surface finish, bolt torque, thread clearance, and counterbore depth. A damaged seat or incorrect outside diameter can cause leakage.
To receive a quotation, send us the following information:
Send the same details to contact the CORASEALS team for standard or custom sizes. See our bonded seals product page for common sizes and material options.
What is the difference between a bonded seal and a Dowty seal?
Bonded seal is the descriptive name. Dowty seal is a trade name used for similar metal and rubber sealing washers. The function is comparable, but dimensions and tolerances should be checked before replacement.
Can CORASEALS supply custom bonded seals in stainless steel?
Yes. CORASEALS can supply custom bonded seals with 304 stainless steel or 316 stainless steel metal rings. The rubber compound is selected separately based on the fluid and temperature.
What is the typical rubber hardness for bonded seals?
Most bonded seals use rubber in the 70 to 90 Shore A range. Send us your operating pressure and seat condition to confirm the correct hardness.
What information do I need to provide for a custom bonded seal quote?
Send the thread size, ID, OD, washer thickness, metal ring material, rubber material, fluid, pressure, temperature, and required quantity. A drawing, photo, or sample is also helpful.
Does CORASEALS keep stock of custom bonded seals?
Custom bonded seals are quoted against your dimensions and quantity. Standard sizes can be checked on request.
