FR2730650A1 - Ultrasonic cleaning method for hollow body, such as pipe - Google Patents

Abstract

The ultrasonic cleaning method is designed for cleaning a hollow body(1) having a wall(2) made from a sensibly rigid material cable to which can be attached an ultrasonic vibration generator generating a set frequency. The operating frequency is set so as to generate surface waves in the bodies surface. For the case of an infinitely long tube, that is the length is greater than N times its diameter, at a point on the tube an exciting force is applied modelled by a sinusoidal wave characterised by the following equation: DELTA <2>(u) + 3 psi rho (1-v<2>)\/Eh<2>. delta <2>u\/ delta t<2> = 0 where DELTA <2>(u) is a mathematical operator. v is the Poisson coefficient of the wall material(2). E is the Young's Modulus of the wall material(2). h is the wall thickness. delta is a mathematical operator. t is time. u is the exciting force. rho is the volume mass of the wall(2).

Description

The invention relates to a method for cleaning hollow bodies by ultrasound.

The invention relates more particularly but not exclusively to a method for cleaning pipes by ultrasonic waves.

The term “cleaning” denotes essentially the operations for detaching particles that are sedimented or anchored to the surfaces of the bodies, with a view to their extraction from these bodies.

Known ultrasonic cleaning methods, such as those described in patents FR-A-2,549,745 and FR-A-2,549,746, aim at optimal application of a high power ultrasonic field to a liquid medium contained by a body. hollow.

The known methods make it possible to optimize the phenomenon of cavitation which generates the detachment of particles sedimented or anchored to the surfaces of the hollow body.

These known ultrasonic cleaning methods have essentially localized effects, that is to say practically limited to the envelope volume of an ultrasonic field which generates cavitation.

These methods must therefore be implemented on each site or at least in the immediate vicinity of these sites.

This therefore excludes the remote cleaning of sites at which the equipment for the implementation of the process cannot be installed.
- either because of a mechanical or architectural impossibility of access,
- or because the environment is harmful for the people who must intervene in the installation and use of said material.

This case is frequent, in particular, on the sites of use of nuclear energy.

The essential result which the invention aims to obtain is precisely an ultrasonic cleaning process which produces effects at a distance from the means for applying ultrasonic waves which it requires.

To this end, the subject of the invention is a method of the aforementioned type, in particular characterized in that the wall of the body is urged at a determined frequency in order to generate so-called surface waves at the level of the wall.

The subject of the invention is also the means for implementing the method.

The invention will be well understood with the aid of the description below given by way of nonlimiting example with reference to the appended drawing which schematically represents a hollow body subjected to the process of the invention.

Referring to the drawing, we see a hollow body 1 a wall 2 made of a substantially rigid material at at least one point of which is applied a device 3 generating ultrasonic vibrations of determined frequency.

The method of the invention is remarkable in that the wall 2 of the body 1 is urged at a determined frequency to generate so-called surface waves at the level of the wall 2.

Notably, in the case of a tube of infinite length, that is to say of length greater than N times its diameter, an exciting force is applied at a point of the tube, modeled by a sustained sine wave which corresponds to the equation 52 (U) + [3YP (l-vZ) / Eh21 2u / 6t2] = 0 in which equation - 52 (U) represents a mathematical operator, - u represents the POISSON coefficient of the material of the
wall 2, - E represents the YOUNG modulus of the material of wall 2, - h represents the thickness of wall 2, - 6 represents a mathematical operator, - t represents time, - u represents the exciting force, - p represents the density of the wall material 2
The means for implementing the method consist essentially, on the one hand, of a calculating means 4 with a view to determining the excitation frequency of the hollow body and, on the other hand, of a means 5 for controlling this frequency to the device 3. generator.

gs (#) = A sin (mi) + B cos (mi) concernant les ondes symétriques, et

gA(O) = A sin (m# + #/#) + B cos concernant les ondes asymétriques, les conditions aux limites (arr=O V# r=r1 r=r2 et {#r#}=0 quel que soit O r=r1 r=r2 nous donne donc les équations aux fréquences

a2=(C/cL) 2 2=(C/CT) 2 pour les ondes symétriques et

pour les ondes asymétriques.Preferably, we seek general solutions satisfying the equation of the form u = u (r, O) exp (jot-kz) with k = or by setting # scalar potential and # vector potential of solutions of the type # = f (rl, 0) exp (j # t - kz) w = g (rl, 0) exp (jot - kz) O these potentials verifying on the other hand the general wave equations either (## / # t) - (/ #) ## = 0; we will set / # = CT2 (62Q / 6t2) - (# + 2 / #) ## = O; we will set # + 2 / # = CL the general solution of (1) can be written u (r, 0) = sin me [A Jm (6r) + BIm (6r)] with Jm and 1m functions of
Bessel of order m of 1st and 2nd kind (6 = 2r1 / r1 + 1)
However in the case of a perfect geometry (not stiffened and not bent tube) one can find solutions by an integral method which leads to

gs (#) = A sin (mi) + B cos (mi) concerning symmetrical waves, and

gA (O) = A sin (m # + # / #) + B cos concerning asymmetric waves, boundary conditions (arr = OV # r = r1 r = r2 and {#r #} = 0 whatever O r = r1 r = r2 therefore gives us the equations at the frequencies

a2 = (C / cL) 2 2 = (C / CT) 2 for symmetrical waves and

for asymmetric waves.

From these equations whose only variables are the frequency oe and the speed c of the surface waves, we can for a given frequency (imposed by the stimulator) calculate the speed of the surface wave (when it exists).

The existence of this wave is conditioned by the speed of the wave solution of the equation to frequencies.

This surface wave will propagate along z (at infinity) if no damping).

In reality, and for a structural damping of 0.033 (K) [K stiffness of the tube, generally accepted value, one obtains a significant propagation over about ten meters.

The solution in O shows on the other hand that the whole of the tube will vibrate in a sinusoidal mode.

Claims (3)

1. Method for the ultrasonic cleaning of hollow bodies (l) to a wall (2) made of a substantially rigid material at at least one point from which a device (3) generating ultrasonic vibrations of determined frequency can be applied, this method being CHARACTERIZED in that the wall (2) of the body (1) is urged at a determined frequency to generate so-called surface waves at the level of the wall (2). 2. Method according to claim 1 characterized in that, in the case of a tube of infinite length, that is to say of length greater than N times its diameter, an exciting force is applied at a point of the tube, modeled by a wave. maintained sinusoidal which answers the equation (u) + [3yp (l-u2) / EhZ]. [62U / 8tZ = O in which equation - 2 (U) represents a mathematical operator, - u represents the POISSON coefficient of the material of the wall 2, - E represents the YOUNG modulus of the material of wall 2, - h represents the thickness of wall 2, - 6 represents a mathematical operator, - t represents time, - u represents the exciting force, - p represents the density of the wall material 2 3. Means for implementing the method according to claim 1 or 2 characterized in that they consist essentially, on the one hand, of a means (4) calculator for determining the excitation frequency of the hollow body and, d 'on the other hand, in a means (5) for controlling this frequency to the generator device (3).