WO1993009642A1

WO1993009642A1 - Sealing of flextensional transmitter

Info

Publication number: WO1993009642A1
Application number: PCT/SE1992/000684
Authority: WO
Inventors: Göran Engdahl; Gunnar Molund
Original assignee: Abb Atom Ab
Priority date: 1991-10-31
Filing date: 1992-09-30
Publication date: 1993-05-13
Also published as: SE9103191D0; SE9103191L; SE469310B; CN1073569A

Abstract

Sealing of a flextensional transmitter which comprises a shell (1), an end plate (2) and an inner end lid (5) fixed to the end plate and wherein the seal, among other things, consists of an annular cloth (6) of a flexible material which is sealingly fixed to the end surface (7) of the shell and the outer contour of which coincides with the outer contour of the shell and wherein the radially inner part of the cloth is formed with a flange (8) which is adpated to a slot (9) in the inner lid. The axial thickness of the cloth at the flange is dimensioned so that it will be attached between the inner end lid and the end plate.

Description

Scaling of flextensional transmitter

Flextensional transmitters with a high output power, that is₇ high intensity sound sources which send out sound waves under water, are used together with hydrophones, among other things to communicate with objects within a wide circum¬ ference around the transmitter and to study the earth crust below the sea bed.

In a very commonly used embodiment of a flextensional trans¬ mitter, the transmitter has a flexible shell of cylindrical shape with a near elliptic cross section, the end surfaces of the cylinder being covered with end plates. The sound waves are generated by the arrangement, inside the trans- mitter, of driving elements which act in the same direction as the major axis of the elliptic cross section. The driving elements are connected to end beams in the shell at the ends of the major axis. When activating the driving elements, the shell in the direction of the major axis and the shell between the end regions will move to keep pace with this activation. The greatest amplitude of oscillation of the shell occurs at the minor axis of the elliptic cross section.

The driving elements inside the shell are often electrically controlled. Because of the relatively great movement of the shell and because the transmitter operates under water and, at times, at great depths with high water pressures, high demands are placed on the seal between the oscillating shell and the end plates. The relative motion between the shell and the end plates may amount to several millimetres. In addition to there being placed demands on watertightness, the seal should therefore also make it possible for the shell to move relatively freely, which means that insigni- ficant forces are transferred to the end plates.

The present invention relates to a seal which has proved to fulfil the above-mentioned high demands. The embodiment is clear from the accompanying figure. The seal comprises an annular cloth of a flexible material, which is sealingly fixed to the end surface of the shell so that its outer contour coincides with the outer contour of the shell. The seal also comprises means for protection against penetra¬ tion, etc.

The oscillating shell is shown at 1 and and end plate is shown at 2. An end beam 3 transmits the force, developed by a driving element 4, to the shell. To make the seal accor¬ ding to the invention function in the intended way, an inner end lid 5 is connected and fixed to the end plate, the lid being arranged such that an open space is created between the inner cylindrical surface of the shell and that surface of the inner end lid which faces the shell. Both the end plate and the inner end lid are fixed to an internal fixing device (not shown) to which also the driving elements are fixed. As mentioned above, the seal comprises an annular cloth 6 of a flexible material which is fixed to the end surface 7 of the shell. Otherwise, the radial length of the annular cloth is adapted so as to extend well inside the inner cylindrical surface of the shell. At its inner part the annular cloth is provided with a flange 8, extending to the inner periphery of the cloth. The inner end lid is shaped such that a slot 9 for the flange 8 is formed. The depth of the slot is adapted to the axial thickness of the annular cloth at the flange in such a way that the cloth is effectively clamped between the end plate and the inner end lid. Otherwise, the end plate is formed such that a clearance is created between the outwardly-facing surface of the cloth at the end surface 7 of the shell and the end plate. The embodiment of this part of the end plate will be described in greater detail below in connection with the description of a preferred embodiment.

Between that side of the annular cloth which faces the end plate and the end plate opposite the flange 8, a sealing strip 10 of a plastic teflon material is applied. When the shell moves in relation to the end plate fixed to the inner fixing device and the inner end lid, the annular cloth, which is fixed to the end surface of the shell, will be stretched substantially only in a radial direction on that part which is located between the inner cylindrical surface of the shell and the attachment between the end plate and the inner lid. By a suitable internal gas pressure in the flextensional transmitter and a suitable embodiment of the surface of the annular cloth, that part of the cloth which is attached between the end plate and the inner end lid will only be subjected to insignificant friction while at the same time the sealing strip 10 ensures that satisfac¬ tory sealing is obtained. By making the distance between that part of the cloth which is fixed to the shell and that part of the cloth which is fixed between the end plate and the inner end lid relatively large and choosing a relatively small thickness of the rubber cloth, the forces acting between the shell and the end plates/the inner end lid can be made very small.

In a preferred embodiment of the seal, the end plate is also provided with a slot 11 which is placed so as to cover the inner part of the shell and extends to the edge of the inner end lid. In this slot there is placed a damping material 12, preferably of silicone caoutchouc, which will then rest against the ouwardly-facing surface of the annular cloth.

As penetration protection, the seal may comprise a silicone rubber joint 13 which (a) fills up an outer slot 14 in the end plate, (b) connects with the outwardly-facing surface of the annular cloth at the end surface of the shell, and (c) connects with the outer free surface of the shell.

The seal according to the invention comprises several zones with different tasks:

The silicon rubber joint 13 and the slot 14 form a penetration protecting zone. Between the two slots 11 and 14 a near elliptic ring 15 is formed in the end plate. This ring is dimensioned with respect to the shell so as to form a certain play between the ring and the rubber ring 6. This results in the forma- tion of- a shock-absorbing zone.

The slot 11 with damping material 12, which makes contact with the outwardly-facing surface of the annular cloth, forms a flexible zone since this is the point where the movement of the shell is substantially absorbed.

The inner part of the annular cloth, which also comprises the flange 8, forms a sealing zone between the annular cloth and the sealing strip and the surrounding end plate and the inner end lid. Also the above-mentioned sealing attachment of the annular cloth to the end surface of the shell serves as a sealing zone.

Claims

1. Sealing of a flextensional transmitter which comprises a shell (1) with a cylindrical shape with a near elliptic cross section, an end plate (2) , and a inner end lid (5) which is fixed to the end plate and which is arranged such that an open space is created between the inner cylindrical surface of the shell and that surface of the inner end lid facing the shell, the seal being characterized in that it comprises an annular cloth (6) of a flexible material which is sealingly fixed to the end surface (7) of the shell and the outer contour of which coincides with the outer contour of the shell, and that the radially inner part of the annu¬ lar cloth is formed with a flange (8) which is adapted to a slot (9) in the inner end lid and that the axial thickness of the annular cloth at the flange is so dimensioned that- it will be attached between the inner end lid and the end plate and that the end plate is shaped such that a clearance is created between the outwardly-facing surface of the annular cloth at the end surface of the shell and the end plate.

2. Sealing of a flextensional transmitter according to claim 1, characterized in that a sealing strip (10) of a plastic teflon material is arranged between that side of the annular cloth which faces the end plate and the end plate opposite the flange.

3. Sealing of a flextensional transmitter according to claim 1, characterized in that in the end plate, substantially outside that part of the annular cloth which covers the open space between the inner contour of the shell and that contour of the inner lid which faces the shell, there is provided a slot (11) in which there is arranged a damping material (12) which rests against the outwardly-facing surface of the annular cloth.

. Sealing of a flextensional transmitter according to claim 1 and 3, characterized in that the damping material (12) is of silicone caoutchouc.

5. Sealing of a flextensional transmitter according to claim 1, characterized in that in the radially outer part of the annular cloth there is arranged a device (13) protecting against penetration, said device being adapted such that it fills up an outer slot (14) in the end plate, such that it connects with the outwardly-facing surface of the annular cloth at the end surface of the shell, and such that it connects with the outer free surface of the shell.

6. Sealing of a flextensional transmitter according to claim 1 and 5, characterized in that the penetration protection device is formed from silicone rubber.