ULTRASONIC IN-SITU INSPECTION FOR SLEWING BEARINGS

Abstract: A bearing comprises two opposite rings, at least one row of rolling elements which are in rolling contact with the raceways of said rings, and at least one ultrasonic scanning device carried by one of the rings for scanning specific areas of the other ring upon relative rotation of the rings. The ultrasonic scanning device is oriented in such a way that the ultrasonic waves emitted thereby generate surface waves in said specific area, which surface waves, upon encountering a surface defect in said area, are at least partly reflected for detection by the scanning device.

Description: Ultrasonic in-situ inspection for slewing bearings The invention is related to a bearing comprising two opposite rings, and at least one row of rolling elements which are in rolling contact with the raceways of said rings, at least one ultrasonic scanning device carried by one of the rings for scanning specific areas of the other ring upon relative rotation of the rings. In particular, the invention is related to the field of inspection of bearings, in particular the in-situ inspection for slewing bearings. Bearings such as a slewing bearing or a pivot bearing are operated in harsh environmental conditions, and subjected to intensive loadings. The bearings in question are often used in offshore crane applications, which are exposed to extreme weather conditions and extreme shock or peak loadings. Other applications, such as in heavy earth moving equipment, are conceivable as well As a result of these conditions, it is required to inspect the slewing bearing frequently. These inspections are aimed at the early detection of defects, such as raceway pitting or cracks in highly loaded areas. Thereby, sudden premature failure is to be avoided. Frequently, the problem arises thereby that the slewing bearings in question are hardly or not accessible. They are situated in a cumbersome place, such as on top of a pedestal, and are covered by the crane structure on top. A solution to this problem has been proposed in EP-B-228731. In that case, one of the rings of the slewing bearing has been equipped with an ultrasonic probe, which upon relative rotation of the rings scans critical areas in the other ring. Thereby, surface defects, cracks, etc. in specific highly loaded areas can be detected in-situ. This brings the important advantage that bearing inspection can be carried out without dismantling the entire arrangement in which the bearing is installed. Said slewing bearing has highly loaded areas on both sides of a nose, which nose has three raceways for a corresponding number of rows of rollers. Furthermore, in Dutch patent application 1005088, which is not an earlier published application, ultrasonic probes are applied for scanning specific areas, e.g. the raceway, of a slewing ring having a series of balls. Although both approaches offers satisfying results, it still appears to be difficult to scan for areas which are more or less shielded with respect to the ultrasonic waves. This shielding effect may for instance occur in the ball bearing mentioned before. The ultrasonic probes are arranged somewhat sideways of the raceway, and cannot scan for the deepest or lowest area of the raceway. Likewise, dependent on the position and orientation of the ultrasonic probes in the slewing bearing according to EP-B2228731, specific areas, e.g. in the shoulder of the nose, are difficult to scan for. The object of the invention is therefore to provide a solution for this problem, allowing the inspection of all relevant, critically loaded areas of a bearing. This object is achieved in that the ultrasonic scanning device surfaces are oriented in such a way that the ultrasonic waves emitted thereby generate surface waves in said specific areas, which surface waves, upon encountering a surface defect in said area, are at least partly reflected for detection by the scanning device. The approach of scanning of specific bearing areas according to the invention relies on the insight that not only longitudinal or transverse ultrasonic waves can be used to achieve said goal, but also surface waves or Rayleigh waves. Such surface waves propagate in solid materials along the bounding surface thereof. They are constrained to lie near such surface, and hence propagate in only two dimensions. Away from the boundary surface into the interior of the body, such waves are quickly damped out. As a yardstick, generally the decay is complete at a depth of about a single wavelength. It should furthermore be observed that the three different modes of propagation of an ultrasound wave in solid material have different velocities. When the incidence angle of the ultrasound wave is not normal, refraction or reflection occurs, as well as conversion from one propagation mode to the other. According to the invention, by allowing an ultrasonic wave to impinge upon a surface of the bearing ring in question at a not perpendicular incidence angle, controlled angles and propagation modes are generated. Because an ultrasound wave beam generally is not fully parallel, but spreads out somewhat like a cone, transverse waves will impinge on a surface at many different angles. At a specific angle of about 67,7°, transverse waves in steel material are partly converted in surface waves. Such surface waves follow the contours of the surface in question, even around corners and radii and hence are able to scan areas which where hitherto thought to be impossible to reach due to shielding effects. The surface waves are eventually reflected by surface defects, cracks, etc. whereby they are returned along the same path that they arrived along. Once the point is reached where the original surface wave was generated by the incident transverse wave, the reflected surface way is converted back into a reflected transverse wave. Said reflected transverse wave can subsequently be detected by the ultrasonic probe, as an indication of the surface defect in question. According to the invention therefore, the ultrasonic waves emitted by the ultrasonic scanning device are oriented at such angle with respect to the surface of said other ring, that said ultrasonic waves, upon impingement on said surface, are converted in surface waves. In particular, the ultrasonic waves emitted by the ultrasonic scanning device impinge upon said surface of the other ring at an angle of about 67,6°. As referred to before, the invention is in particular fit for scanning areas which are shielded, e.g. by curved contours, etc. Thus, according to the invention, at least one of the rings may have a cross-sectional shape with at least one boundary contour having at least a curved portion, the ultrasonic scanning device being situated at a surface portion at a distance from said at least one boundary contour such that the ultrasonic waves impinge on said boundary contour according to an angle to said contour so as to form surface waves following at least said curved portion of said boundary contour. Such curved contour is e.g. to be found near the raceways of a slewing ball bearing. Said raceways are, in cross section, formed by arc of about 180°. According to the invention, also the intermediate area of said arc at about 90° can now be scanned reliably. The invention is furthermore related to a method for scanning, comprising the steps of emitting ultrasonic waves in said ring such that surface waves are generated, and scanning for reflected ultrasonic waves resulting from surface waves which have hit a surface defect or surface crack. Subsequently, the invention will be described further with reference to the embodiments shown in the figures. Figure 1 shows a four-point contact ball slewing bearing. Figures 2a, b show a detail of figure 1. Figure 3a, b show a corresponding detail of a three row roller bearing. Figure 1 shows a four-point contact ball slewing bearing having an outer ring 1, an inner ring 2 and a series of balls 3 supporting these rings 1 and 2 mutually. The balls 3 are contained in the raceway 4 of the outer ring and in the raceway 5 of the inner ring. In service, the outer ring 1 is connected to a supporting structure, such as the pedestal of a crane. Onto the inner ring 2, the crane structure itself is mounted. To that end, holes 6 are provided in the inner ring which may accommodate mounting bolts. Also, the inner ring on its inner circumference is provided with a tooth rack 7, which can cooperate with a pinion for rotating the crane structure. As is common practice, seals 8, 9 have been provided in order to seal the bearing space between the rings 1, 2. According to the invention, two ultrasonic scanning devices 10, 11 have been inserted in radial holes 12 in the outer ring. The devices 10, 11 comprise a housing 13, a shaft 14, as well as a means 15 for fixing the shaft 14 in a certain position within housing 13. The other end of the shaft 14 is supplied with a means for pressing the ultrasonic scanning probes 17 against the outer circumference 18 of the inner ring 2 or inner circumference of the outer ring 1. The devices 10, 11 have been directed in such a way, that the path of the ultrasonic waves emitted thereby is oblique, as indicated by lines 19. These paths of the ultrasonic waves impinge upon the raceway 5 of the inner ring 2. In particular, they impinge upon the points 20, 21, which are the most highly loaded areas of a four-point ball bearing. By means of the ultrasonic probes 17, it is therefore possible to obtain a very accurate assessment of the area of the raceway 5, and of the underlying structure of the inner ring 2 which is subjected to the highest stresses. The path 19 of the ultrasonic waves intersect each other at a spot 22 lying beyond the raceway 5. Thereby, also this rather highly loacj&ed area can be scanned accurately. Although the figure shows two devices 10,11 which are able the scan the inner ring. It is of course also possible to insert ultrasonic devices in the inner ring for detection of corresponding areas in the outer ring. As shown in figure 2a, b, the ultrasonic wave 19 emitted by the devices 10, 11 is in the form of a cone-shaped bundle 34. Said cone- shaped bundle hits the raceway surface 5 at various angles. In particular, part 30 of said cone bundle hits the raceway surface 5 at an angle of about 67,6° with respect to the normal line on said surface, whereby the transverse waves, emitted by the ultrasonic scanning device 17, are converted into surface waves 31 at spot 33. Said surface waves 31 are confined to the boundary of the curved raceway surface 5, and thereby to the cross-sectional contour thereof. While following said contour, the surface wave 31 will reach a surface crack 32 which is shielded with respect to the transverse waves which travel along a straight path. As a result, said surface wave is ref1ected . Subsequently, the reflected surface waves travel back to the spot 33 where they were generated, as a result of the transverse waves impinging at the proper angle of 67,6. At the spot 33 in question, the surface waves are converted back into transverse waves, which finally travel back over the same path along which they arrived. Subsequently, the thus reflected transverse waves are detected by the ultrasonic scanning device 17, which is thereby able to establish the presence of the crack 32. The embodiment of figures 3a, b is a three-row roller bearing, ocmprising an outer ring 1, an inner ring 2 having a nose 50, and rows of rollers 41, 42 and 43 which engage the raceways 44. In the outer ring 1, two ultrasonic scanning devices 10, 11 carrying ultrasonic probes 17 have been inserted. The probes 17 each emit a cone-shaped bundle 46 of ultrasonic waves, part of which hits the raceway 44 or the neighouring surface thereof, at an angle of about 67.6°. The transverse ultrasonic waves 47 in question are thereby converted in surface waves 48 which follow the curved boundary contour of the area in question. Thus, in a way analogous to figures 2a, b, the crack 49 is detected. Although in the description, reference is made to the embodiment shown, the outer ring of which is connected to a supporting structure, an alternative embodiment with the inner ring connected to the supporting structure is also possible. In that case, the tooth rack will be located on the outer circumference of the outer ring. It is also possible that the tooth rack can be located on the non-rotating ring.

Claims: Claims 1. Bearing comprising two opposite rings (1, 2), at least one row of rolling elements (33, 41, 42, 43) which are in rolling contact with the raceways (4, 5, 44) of said rings (1, 2), and at least one ultrasonic scanning device (17) carried by one of the rings (1, 2) for scanning specific areas of the other ring (1, 2) upon relative rotation of the rings (1, 2), characterized in that the ultrasonic scanning device (17) is oriented in such a way that the ultrasonic waves (34, 46) emitted thereby generate surface waves (31, 48) in said specific area, which surface waves (34, 48), upon encountering a surface defect (32, 49) in said area, are at least partly reflected for detection by the scanning device (17). 2. Bearing according to claim 1, wherein the ultrasonic waves emitted by the ultrasonic scanning device (17) are oriented at such angle with respect to the surface of said other ring (1, 2), that said ultrasonic waves (30, 47), upon impingement on said surface, are converted in surface waves (31, 48). 3. Bearing according to claim 1 or 2, wherein the ultrasonic waves (30, 47) emitted by the ultrasonic scanning device (17) impinge upon said surface of the other ring at an angle of about 67,6° with respect to the normal line on said surface. 4. Bearing according to any of the preceding claims, wherein at least one of the rings (1, 2) has a cross-sectional shape with at least one boundary contour (5, 51) having at least a curved portion, said ultrasonic scanning device (17) being situated at a surface portion (18, 52) at a distance from said at least one boundary contour (5, 51) such that the ultrasonic waves impinge on said boundary contour according to an angle to said contour so as to form surface waves (31, 48) following at least said curved portion of said curved boundary contour. 5. Method for scanning a specific area of a bearing ring (1, 2) of a bearing by means of an ultrasonic scanning device (17), comprising the steps of emitting ultrasonic waves (34, 46) in said ring (1, 2) such that surface waves (31, 48) are generated, and scanning for reflected ultrasonic waves resulting from surface waves which have hit a surface defect or surface crack (32, 49).

Inventors: BOURGEOIS-JACQUET PIERRE, HANDS GODFREY, BOURGEOIS-JACQUET, PIERRE, HANDS, GODFREY
Applicants: BOURGEOIS JACQUET PIERRE, HANDS GODFREY, SKF IND TRADING & DEV, BOURGEOIS-JACQUET, PIERRE, HANDS, GODFREY, SKF INDUSTRIAL TRADING & DEVELOPMENT COMPANY B.V.
Application year: 1997
Main classification: G01N29
IPC codes: F16C19, G01M13, G01N29