GB2134819A - Magnetic collection of particles from a fluid - Google Patents

Abstract

A conduit along which a stream of fluid flows has a collector for collecting magnetic or magnetizable particles from the fluid. The collector comprises means 16 for applying a magnetic field M transversely to a magnetic collector strip or preferably an array of transversely spaced strips 18, preferably of paramagnetic material. The strips lie in a plane which is transverse to the streamflow direction A. The magnetic field converges on the strips and the magnetic field gradients around the strips are high. Magnetized particles in the fluid are strongly attracted to the strips. A region of stagnant or quiescent fluid forms downstream of each strip and particles can accumulate in these regions with a reduced likelihood of being removed by the fluid stream. The collector may be incorporated in a removable plug. For indicating the amount of particles collected, electromagnetic radiation is applied to the collector to excite the particles, which emit an odd harmonic of the exciting frequency. <IMAGE>

Description

SPECIFICATION Collection of particles from a fluid This invention relates to the collection of magnetic or magnetizable particles from a stream of fluid e.g. wear particles from circulating lubricant. The invention may be applied to probes for collecting a representative sample of particles, for inspection and/or analysis, and to filters designed to remove substantially all magnetic particles from a stream.

According to a first aspect of the present invention there is provided a collector for collecting magnetic or magnetizable particles from fluid flowing in a stream through a conduit, said collector comprising: an elongate magnetic or paramagnetic collector element supported within the conduit transverse to the fluid stream direction; and magnetic field-generating means for applying a magnetic field transverse to the collector element.

With this arrangement the magnetic field gradients are intense adjacent the element, because the magnetic flux converges towards the element. The element, thus in a strong field of high gradient, becomes an effective collector of magnetic or magnetizable particles.

Preferably the collector incorporates a plurality of collector elements, the collector elements being transversely spaced across the conduit.

The collector elements may lie substantially in a plane across the conduit, the magnetic fieldgenerating means being arranged to apply the magnetic field generally along the plane.

According to a second aspect of the invention there is provided a collector for collecting magnetic or magnetizable particles from fluid flowing in a stream through a conduit, the collector comprising: a paramagnetic collector element supported within the conduit transverse to the fluid stream direction, the collector element being so shaped as to engender a stagnant region in the fluid adjacent the downstream surface of the collector element; and magnetic fieldgenerating means for applying a magnetic field to the collector element.

The particles collect on the element in the stagnant region and are less likely to be swept off by the stream or by the scrubbing action of air bubbles entrained in the stream.

The collector element may be of circularly cylindrical section and its downstream surface may, under suitable stream conditions, still provide a stagnant region. Preferably, however, the downstream surface of the collector element is of generally flattened profile.

In this aspect of the invention, as in the first aspect, the collector may incorporate a plurality of elongate collector elements, the collector elements being tranversely spaced across the conduit, and the collector elements may lie substantially in a plane across the conduit with the magnetic field-generating means being arranged to apply the magnetic field generally along the plane.

The elements may be arranged in such an array as to cause turbulent flow adjacent the elements, whilst retaining the stagnant regions 'behind', i.e.

at the downstream surfaces of the elements. This arrangement serves to cause some eddies adjacent the elements, and increases the likelihood of particle collection. A suitable array may comprise two parallel but spaced apart planes which are transverse to the fluid stream direction, the collector elements of one plane being aligned with the transverse gaps between adjacent collector elements of the other plane.

A third aspect of the invention represents an advantageous combination of features of the first and second aspects. In the third aspect there is provided a collector for collecting magnetic or magnetizable particles from fluids flowing in a stream through a conduit, the collector comprising: a plurality of magnetic or paramagnetic collector strips supported within the conduit and transversely spaced across the conduit in a direction transverse to the fluid stream direction, each collector strip constituting a bluff obstruction to the fluid stream such that a stagnant region forms adjacent the downstream surface of each collector strip; and magnetic fieldgenerating means arranged to apply a magnetic field transverse to the collector elements.

Again, the elements (in this aspect, stripshaped) may be disposed in such an array as to cause turbulent flow between them. The strips may be arranged as an array comprising two parallel but spaced apart planes which are transverse to the fluid stream direction, the collector strips of one plane being aligned with the transverse gaps between adjacent collector strips of the other plane.

In all aspects of the invention the collector may further comprise: mounting means for removably mounting the collector element in the conduit and valve means for sealing the conduit against the escape of fluid when the collector element or set of collector elements is removed; and/or means for applying electromagnetic radiation to the or each collector element at a frequency to excite magnetic or magnetized particles attached thereto, and means for detecting an odd harmonic thereof. This harmonic detection technique may be used with the collector in situ. Alternatively the collector may be removed for analysis.

Although the use of ferromagnetic collector elements is within the scope of aspects of this invention the use of a paramagnetic element or elements has advantages in that magnetic particles may be readily removed from a paramagnet when the latter is magnetically isolated from magnetic flux e.g. to clean the element or elements and for subsequent analysis of the particles. Furthermore, the harmonic technique mentioned above is more sensitive to ferromagnetic particles retained on a paramagnetic element than to such particles on a ferromagnetic element. Whereas a paramagnetic element emits a weak odd harmonic signal the harmonic signal emitted by a ferromagnetic element is much stronger, due to its larger hysteresis loss, and the signal can swamp that of the wear particles attached to it.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is an inclined view of one embodiment of magnetic particle collector; Fig. 2 is an inclined view of a second embodiment of collector; Fig. 3 shows the collector of Fig. 2 in plane view with a flux shunt applied.

Fig. 4 shows a third embodiment of collector fitted into a plug for insertion into a socket in a wall of a lubricant conduit; Fig. 5 is a sectional view on the line AA of Fig.

4; and Fig. 6 shows the plug of Fig. 4 fixed in the socket.

The collector 2 shown in Fig. 1 comprises a support 4 of non-magnetic material. From one face 6 of the support 4 extends an array of paramagnetic stainless steel collector element strips 8. The strips 8 may be secured to or embedded in the support 4 in many standard ways. For example, the support may be of a suitable plastics material and the stainless steel strips may be fixed in the support during moulding.

The strips are parallel to one another and are arranged as three rows, each of four strips. Each strip is 3 mm by 1 mm in transverse cross section and is separated transversely from the next strip in the same row by 3 mm. The rows themselves are spaced at intervals of 5 mm. The strips of one row are aligned with the gaps between strips of the adjacent row or rows.

The collector 2 further comprises a button 10 of very strong magnetic material such as samarium cobalt, disposed on the same side of the support 4 as that from which the stainless steel strips 8 extend. The direction of magnetization of the button 10 is through the thickness of the button, in the direction of the arrow M in Fig. 1.

The button 10 may be secured to the support in any standard manner e.g. by fixing both the support and the button to a corner piece.

The collector 2 forms part of a probe which is plugged, in a sealtight manner, into a socket in a wall of a conduit in which lubricant flows, in a gas turbine aero engine. When the probe is in the socket, the strips 8 are in the lubricant stream, and extend substantially the whole distance across it.

The lubricant stream flows in the direction indicated by the arrow A in Fig. 1. The plane of each row of strips is perpendicular to the lubricant stream direction and the flattened downstream surfaces 12 of the strips provide stagnant or quiescent regions in the lubricant stream. The array of strips as a whole causes some eddies which assist collection.

The magnetic button 10 provides a magnetic field perpendicular to the length of the strips, which magnetizes the strips and converges on one edge and diverges from the opposite edge of each strip. The three rows of strips effectively form three preferential routes or channels along which the magnetic field between the poles of the button is concentrated. The field diverges between each adjacent strip in a row. Thus the field gradient adjacent each strip is high and when steel wear particles suspended in the lubricant are magnetized by the collector they are strongly attacted to the strips 8. Magnetic wear particles may then accumulated in the stagnant regions at the downstream faces 12 of the strips without substantial likelihood of being swept off by the lubricant stream or by the scrubbing action of air bubbles entrained in it.

The collector is provided with a soft iron plate 14 which may be slid between the button 10 and the strips 8 in the direction indicated by the arrow B in Fig. 1 when positioned between the button and the strips the plate 14 effectively short circuits the flux from the button to the strips, and demagnetizes the strips. The soft iron plate 1 4 is retracted from its short-circuiting position for particle collection but may be inserted into that position when it is desired to remove particles from the strips e.g. when the probe has been removed from the conduit and it is desired to remove and analyse the wear particles collected.

In this embodiment a third harmonic technique is used to analyse the collected particles whilst they are still attached to the strips 8. The probe is removed from its socket in the conduit and inserted into a similar socket in the analysis apparatus. The strips are excited by electromagnetic radiation at one frequency (e.g.

1000 Hz) the third harmonic of which is detected.

The third harmonic signal gives a sensitive indication of the amount of magnetic bearing material on the collector, since the paramagnetic stainless steel strips, having low hysteresis loss, emit weak third harmonic signals relative to the magnetic wear particles attached to them.

A particle size, distribution and material analysis could then be effected, following the magnetic isolation of the strips from the button 10 using the soft iron plate 14, and the removal of the collected particles.

In the second embodiment of collector shown in Fig. 2 the ferromagnetic button 1 6 provides the support for an array of stainless steel strips 18.

The strips may be embedded in the button 16 by force-fitting them in slots in the button.

In this embodiment two rows of stainless steel strips are provided and the strips of one row are aligned with the transverse gaps between the strips of the other row. When the collector is plugged into a socket in a lubricant conduit the strips are transverse to the lubricant stream direction A and each strip again constitutes a bluff obstruction to the stream, so that a stagnant region forms adjacent the downstream face of each collector strip.

The magnetic button 1 6 is magnetized along its length as shown by the arrow M, and thus the right-hand end, as shown in Fig. 2, is a North pole and the left-hand end, a South pole. Again, each row of strips serves to concentrate the magnetic flux and increase the field gradient adjacent each strip. The magnetic field provided is transverse to the collector strips and to the direction of lubricant flow A.

In this embodiment a third harmonic technique is used to provide a continuous read-out indicative of the wear of the bearings. An exciter winding 20 extends around the array of strips and provides a magnetic field alternating at 1000 Hz, parallel to the length of the strips. A detector winding 22 around the array acts as a seach coil for detecting the third harmonic signal of the exciting frequency, emitted by the collected particles. The windings may be secured on posts 24 extending from each corner of the button.

A soft iron flux shunt 26 is applied to the collector when it is required to magnetically isolate the magnetic button 1 6 from the paramagnetic strips 18. The flux shunt 26 is a U-shaped member and demagnetizes the strips when it is placed adjacent the button 16, on the opposite side of the button to the side from which the strips 1 8 extend, to form a magnetic circuit with the button. As is shown by the field lines 28, the magnetic field is shunted through the soft iron and away from the strips, which are thus no longer magnetized. Collected particles may then be easily removed from the strips, for further analysis if required, and to clean the strips.

A third embodiment of the invention will now be described, with reference to Figs. 4 to 6.

Fig. 4 shows a plug 30 about to be inserted into a socket 32 in the wall of an oilway 34.

The plug 30 comprises a stem 38, a head 40 and, between the head and the stem, a shoulder portion 42. The shoulder portion 42 is of larger diameter than the stem but smaller diameter than the head. The shoulder portion is fitted with two O-rings 44 and 46 and, between the O-rings and the head 40 is a bayonet pin 48.

The head 40 is provided with a knurled conformation or other suitable shaping to enable the operator to easily turn the plug.

The stem 38 is provided at its lower end with a magnetic particle collector 50. The collector 50 comprises an annular plastics member 52 in which a plurality of flat collector strips 54 are embedded. The strips are of stainless steel and may be formed for example as a unit by etching a foil of stainless steel. The strips are spaced transversely from one another and lie in a common longitudinal plane of the stem with each strip perpendicularly disposed to the axis of the stem.

The annular member 52 in which the strips 54 are mounted is force-fitted in a transverse through-bore 56 of the stem.

On either side of the annular member 52 and spaced axially along the stem 38 are permanent magnets 58 and 60. Each magnet is embedded in a plastics biock 62, 64 respectively, and each block is secured to the stem 38 e.g. by adhesive.

Each magnet is magnetized through its thickness and is disposed with its magnetic axis parallel to the stem axis. The magnetic field between the two magnets is thus transverse to each collector strip 54, and at least a portion of the field passes along the plane of the strips. The field converges in the region of the strips and high field gradients are provided around the strips.

An O-ring 66 is provided around the stem, above the collector 50.

The socket 32 is provided as part of fitting 67 which has, on both sides of the socket, conduit portions 68 and 70. The fitting 67 is welded into place in the oilway 34 by welding the conduit portions to the existing conduits 72 and 74, at positions 75. The fitting 67 including the socket 32 then forms a permanent part of the oilway 34.

The socket 32 extends from one side of the oilway 34 and comprises an upstanding circularly cylindrical wall portion 76 which is integral with the conduit portions 72 and 74. At the top of the wall portion, that is, at its end remote from the oilway, there is provided a bayonet socket 78 for engaging with the bayonet pin 48 of the plug 30.

The diameter of the bore 80 of the wall portion 76 is substantially equal to the width of the shoulder portion 42 of the plug 30.

At the bottom of the wall portion 76 is a circular opening 81 into the oilway and around the opening and within the oilway is provided an annular seating 82. Above the seating the internal surface of the wall portion is formed with an upwardly facing lip 84.

The socket 32 further comprises a spring loaded valve member 86 mounted for sliding movement within the bore 80 of the wall portion 76. The valve member resembles a circularly cylindrical cup in shape. It has a bottom sealing plate 88 which has an integral flange 90 extending beyond the wall 92 of the valve member and sealing against the seating 82 to close the opening 81 at the bottom of the wall portion 76.

At its top end the valve member has a ring 94 screwed to the outside of its wall 92. The ring serves as an outwardly directed flange. The ring is provided with an O-ring 96, which seals against the inner surface of the wall portion 76. Between the ring 94 and the lip 84 of the wall portion is retained a compression spring 98, which urges the valve member upwardly with respect to the wall portion, and therefore urges the bottom plate 88 of the valve member into sealing engagement against the seating 82.

The internal diameter of the valve member 86 is substantially equal to the width of the upper part of the stem 38 of the plug.

The valve member is provided with two opposed apertures 100 and 102 in its wall 92, the apertures both being substantially equal in diameter to the internal diameter of the oilway, to the diameter of the through bore 56 in the stem of the plug 30 and the diameter of the collector.

The assembly 67 has an outwardly extending wall portion 104 opposite the socket 32. The wall portion 104 is provided by a separate plate which is welded around its edge at 105 to the rest of the assembly 67. The wall portion 104 provides a recess 106 within the oilway for receiving the plate member 88 when the plug 30 is inserted into the socket.

Before installing the fitting 67 in the oilway the valve member 86, without the ring 94 secured to it, is first located in the wall portion 76, by inserting it through the hole between the conduit portions 68 and 70 over which the plate will be welded. The spring 68 is then dropped onto the lip 84 and the internally-threaded ring 94 is screwed onto the threaded outer surface of the wall 92 of the valve member. The plate is then welded around its edge at 105 to the rest of the assembly 67 and the assembly 67 can then be welded into place in the oilway.

To insert the plug 30 into the socket the stem 38 of the plug is slid into the valve member. On continued pushing of the plug the lower end of the stem 38 engages the upper face of the plate 88 and the valve member is depressed against the bias of the compression spring 98, causing the plate to leave the seating 82. At this point sealing of the oilway is maintained by the O-rings 66 and 96. On further depressing the plug the shoulder portion 42 engages the internal surface of the wall portion 76. Finaliy the bayonet pin 48 is engaged within the bayonet socket 78, and the collecting position shown in Fig. 6 is attained.

In the collecting position the plane in which the collector strips 54 lie is perpendicular to the lubricant stream direction S.

The collector 50 extends fully across the oilway, and lubricant flows through the upstream aperture 1 50 of the valve member 86, through the through bore 56 of the stem and thus through the collector, and thence through the downstream aperture 102. A stagnant region forms behind each collector strip.

The plug may be removed when required and the collector may simply be forced out of the stem for analysis, and replaced by a new collector, force fitted in the through bore 56. A third harmonic technique may again be used with advantage, either in situ or after removal of the collector.

Various other embodiments incorporating aspects of the invention will suggest themselves to those skilled in the art. Many other designs of collector to those described above are possible e.g. different shaped collector elements, different collector element materials, different arrays of collector elements, and different arrangements for providing a magnetic field.

For example, in one further embodiment two or more ring electromagnets are used. Successive ring magnets may give rise to oppositely aligned fields but the net effect can be arranged to provide a radial field. In this embodiment a paramagnetic collector element or elements adjacent or around the wall of the lubricant housing could be used.

Other embodiments of the invention may be designed to filter all magnetic particles from a lubricant stream. In such embodiments it may be preferred to use an electromagnet as the source of flux, instead of a permanent magnet, and it will often be advantageous to use a paramagnetic collector array in conjunction with a conventional paper filter.

It will be appreciated that an array of permanent magnets may be used as a collector in accordance with the invention, although the third harmonic technique described above will not be as sensititive as with paramagnets. The use of permanent magnets could be appropriate when a probe needs only visual inspection or else when a collector is being used to remove all magnetic particles from a lubricant stream.

Furthermore, other methods of analysing the collector to those described above will suggest themselves to skilled persons.

One alternative method of analysing a collector for magnetic material deposited on it is to use an inductance technique e.g. use the collector element, with and then without magnetic particles attached, as a core element of an inductance coil whose inductance is detected by a search coil. An in situ technique could compare the inductance of the coil around the collector in the fluid with the invariant inductance of a coil around a dummy collector which does not collect magnetic particles.

Another alternative method of analysing the collector in use is to moniter the pressure drop across it due to collected debris.

Claims (17)

1. A collector for collecting magnetic or magnetizable particles from fluid flowing in a stream through a conduit, the collector comprising: an elongate magnetic or paramagnetic collector element supported within the conduit transverse to the fluid stream direction; and magnetic field-generating means for applying a magnetic field transverse to the collector element.

2. A collector according to claim 1 including a plurality of collector elements, the collector elements being transversely spaced across the conduit.

3. A collector according to claim 2, wherein said collector elements lie substantially in a plane across the conduit, the magnetic field-generating means being arranged to apply the magnetic field generally along the plane.

4. A collector according to any preceding claim, further comprising mounting means for removably mounting the collector element or collector elements in the conduit and valve means for sealing the conduit against the escape of fluid when the or each collector element is removed.

5. A collector according to any preceding claim, further comprising means for applying electromagnetic radiation ot the or each collector element at a frequency to excite magnetic or magnetized particles attached thereto, and means for detecting an odd harmonic thereof.

6. A collector for collecting magnetic or magnetizable particles from fluid flowing in a stream through a conduit, the collector comprising: a paramagnetic collector element supported within the conduit transverse to the fluid stream direction, the collector element being so shaped as to engender a stagnant region in the fluid adjacent the downstream surface of the collector element; and magnetic field-generating means for applying a magnetic field to the collector element.

7. A collector according to claim 6, including a plurality of elongate collector elements, the collector elements being transversely spaced across the conduit.

8. A collector according to claim 7, wherein the collector elements lie substantially in a plane across the conduit.

9. A collector according to claim 8 wherein the collector elements are provided as an array comprising two parallel but spaced apart planes which are transverse to the fluid stream direction, the collector elements of one plane being aligned with the transverse gaps between adjacent collector elements of the other plane.

10. A collector according to claim 8 or 9 wherein the magnetic field-generating means is arranged to apply said magnetic field generally along the plane or planes.

11. A collector according to any of claims 6 to 10 wherein the downstream surface of the or each collector element is of generally flattened profile.

12. A collector according to any of claims 6 to 11 , further comprising mounting means for removably mounting the collector element or elements in the conduit and valve means for sealing the conduit against the escape of fluid when the or each collector element is removed.

13. A collector according to any of claims 6 to 12, further comprising means for applying electromagnetic radiation to the or each collector element at a frequency to excite magnetic or magnetized particles attached thereto, and means for detecting an odd harmonic thereof.

14. A collector for collecting magnetic or magnetizable particles from fluids flowing in a stream through a conduit, the collector comprising: a plurality of magnetic or paramagnetic collector strips supported within the conduit and transversely spaced across the conduit in a direction transverse to the fluid stream direction, each collector strip constituting a bluff obstruction to the fluid stream such that a stagnant region forms adjacent the downstream surface of each the means arranged to apply a magnetic field transverse to the collector elements.

1 5. A collector according to claim 14, further comprising mounting means for removably mounting the collector strips in the conduit and valve means for sealing said conduit against the escape of fluid when the collector strips are removed.

1 6. A collector according to claim 14 or 15, further comprising means for applying electromagnetic radiation to the collector strips at a frequency to excite magnetic or magnetized particles attached thereto, and means for detecting an odd harmonic thereof.

17. A collector according to any of claims 14 to 16, wherein the collector strips are provided as an array comprising two parallel but spaced apart planes which are transverse to the fluid stream direction, the collector strips of one plane being aligned with the transverse gaps between adjacent collector elements of the other said plane.

1 8. A collector substantially as hereinbefore described with reference to the accompanying drawings.