Type of washer used to create a seal around a screw or bolt

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In mechanical engineering, a bonded seal is a type of washer used to provide a seal around a screw or bolt. Originally made by Dowty Group, they are also known as Dowty seals or Dowty washers.[1] Now widely manufactured, they are available in a range of standard sizes and materials [2][3][4]

A bonded seal consists of an outer annular ring of a hard material, typically steel, and an inner annular ring of an elastomeric material that acts as a gasket. It is the compression of the elastomeric part between the faces of the parts on either side of the bonded seal that provides the sealing action. The elastomeric material, typically nitrile rubber, is bonded by heat and pressure to the outer ring, which holds it in place. This structure increases resistance to bursting, increasing the pressure rating of the seal. Because the bonded seal itself acts to retain the gasket material, there is no need for the parts to be sealed to be shaped to retain the gasket. This results in simplified machining and greater ease of use as compared to some other seals, such as O-rings. Some designs come with an additional flap of rubber on the internal diameter to locate the bonded seal at the centre of the hole; these are called self-centring bonded washers.[5][6]

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Bonded Seals Overview

The Bonded Seal was originally designed to replace copper type washers in high-pressure systems. Often used as bolt seals in hydraulic equipment, today bonded seals (commonly known as Dowty Seals) are finding usage in many and varied applications throughout various industries.

The Bonded Seal comprises a metal washer and an elastomeric ring bonded inside the diameter. The metal washer prevents over-compression and limits deformation of the elastomeric ring.

All size ranges and material combinations are available. This same basic concept can be used to produce customized shapes for specific applications in any of the combinations of rubber to metal or plastic bonding.

Bonded Seals are available with or without the self-centralizing lip.

*Not a stock item. Factory minimums apply.*

Bonded Seal Advantages:

• Reliable low and high pressure sealing
• High and low temperature capabilities
• Bolt torque is reduced with no loss of tightening load

Bonded Seal Materials:

Elastomer component is available in:

• NBR 70 (Standard)
• NBR 90
• FKM (Viton®) 75
• EPDM 70

Washer component is carbon steel, zinc/yellow zinc plated or stainless steel (on request). For more information or to request a quote on bonded seals, please give us a call at 832-448-5550 or submit the Product Inquiry Form.

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