Definition

It is a dynamic type of Joint of which the goal is to prevent the passage of a liquid or a gas but where the contact between the joint and the parts of the envelope to be sealed cannot come into contact in way permanante, because they are moving relative. Wear would deteriorate the joints of contact. To carry out the sealing, the parts are rapporchées to the maximum and the passage of gas is made most difficult possible by obstacles leaving of spaces extremely fine or leading to skirtings.

Examples

One counts in this family:

• Labyrinth seal
• Joined to brush
• joined to coating abradable

Applications in the bearings

In the Bearings, the rotation movement between the ring outside and the interior ring is not favorable to the presence of a rubbing joint when large speed are reached. The elements rolling however require to be lubricated, one often uses the labyrinth seal in order to avoid a lubricant escape out of the bearings.

Applications in the axial turbines and compressors

In the Compressing axial Turbines or , the play between the mobile wings and the casing of gas control must be at least reduced to increase the effectiveness and the output by it. However high speeds and the important modifications of geometry under operation make that one needs seals without contact. They owe, moreover, being conceived to resist the possible contacts between fixed parts and revolving parts, without causing damage with the various parts of the mechanism. One thus employs:

• of the labyrinth seals for the parts where the sealing is paramount and tangential speeds weak (close to the rotor)
• of the brush joints (under same the conditions)
• of the joints with coating abradable when energies of impact are important, in end of revolving paddle in particular, but also between the vanes and the stator, coupled to a labyrinth seal. The Revêtement abradable reduces the wear of the wings to the minimum.

Industrial development

Many industrialists of the air transport air made development of seals without contact in partnership with research laboratories in mechanics.

Among the motor mechanics and their subcontractors working on this subject, one counts:

• Snecma (of the group Safran)
• Rolls Royce
• General Electric
• Volvo

Notes and references of the article

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