Fluid-operated percussion drill tool provided with a segmented ring mounting.

Abstract: The present invention relates to a segmented ring mounting (5) for retaining cylindrical components (2, 3) one within the other in a fluid-operated percussion drill tool, such as a downhole rock drill. However, the invention has application to other interengaging cylindrical components which are subject to heavy wear or pressure loading, such as compressors, pumps, borehole tools, casings and drillpipe mountings. The retaining ring (5) seats a smaller diameter cylindrical component (3) within a larger diameter cylindrical component (2), wherein one of the components is formed with a groove (12) or shoulder for seating the retaining ring in use, the ring being capable of radial compression and expansion so as to expand radially into the seating groove or shoulder for retaining the components one within the other in use. The retaining ring comprises at least three segments (7, 8, 9), which when touching end to end form a complete circle, and expansible holding means (11) such as an O-ring, for holding the segments together but allowing the segments to expand radially and move apart by a sufficient amount so as to seat the segments in the groove (12) or against the shoulder.

Description: FIELD OF THE INVENTION The present invention relates to a segmented ring mounting for retaining cylindrical components one within the other in a fluid-operated percussion drill tool, such as a downhole rock drill. However, the invention has application to other interengaging cylindrical components which are subject to heavy wear or pressure loading, such as compressors, pumps, borehole tools, casings and drillpipe mountings. BACKGROUND OF THE INVENTION Conventional fluid-operated percussion drill tools, such as that described in GB 2 296 731 of the present applicant, comprise an external cylinder or outer wear sleeve, within which is mounted an inner cylinder which in turn engages with a backhead assembly. A sliding reciprocating piston cooperates with the inner cylinder and backhead assembly, which when air pressure is supplied through the backhead assembly, acts with a percussive effect on a drill bit retained within a chuck on the outer wear sleeve. . In conventional arrangements, the inner cylinder is effectively suspended within the outer wear sleeve by means of a compressible retaining ring, such as a circlip, which has to be slid up the inner cylinder so as to seat against a shoulder or lip at one end thereof, being compressed when the inner cylinder is dropped down within the outer wear sleeve, and then expanding outwardly into a groove or shoulder formed on the inner diameter of the outer wear sleeve with a snap action. When in this position, the circlip seats within the groove and abuts against the lip of the inner cylinder, by which the inner cylinder is suspended within the outer wear sleeve. Compression of the circlip requires considerable force during this assembly operation. A disadvantage with the circlip mounting system is that the inner cylinder may move during operation because of vibration, and the lip may become deformed, and unevenly worn due to wear between the lip and the circlip. The circlip is not a complete ring and includes a gap, and there is therefore no wear on the lip above the circlip gap. The hardness of the steel from which the inner cylinder and the circlip are made may not be the same, which also contributes to wear between these two components. However, if the inner cylinder is removed from the outer wear sleeve for maintenance or inspection purposes, and then reassembled in the manner described above, the circlip is most likely to snap into place in the groove in the outer wear sleeve in a different position, i.e. the circlip gap is likely to be in a different position, so that wear between the circlip and the lip of the inner cylinder will be concentrated on a different portion of the lip. With continued wear, the result is that a slightly raised portion of the lip or lump will develop, and the presence of one or more lumps around the circumference of the lip caused by this uneven wear will result in poorer engagement between the inner cylinder and the outer wear sleeve, and even a skew or off-centre between the two cylindrical components, which will rapidly increase wear between the components and shorten the life of the downhole drill. The present invention seeks to provide a solution to the general problem of awkwardness and difficulty of assembly and reassembly of parts using a conventional circlip mounting, and furthermore to address the problems caused by uneven wear between the conventional circlip and the lip of the inner cylinder. SUMMARY OF THE INVENTION According to the present invention there is provided a retaining ring for seating a smaller diameter cylindrical component within a larger diameter cylindrical component, wherein one of the components is formed with a groove or shoulder for seating the retaining ring in use, the ring being capable of radial compression and expansion so as to expand radially into the seating groove or shoulder for retaining the components one within the other in use, characterized in that the retaining ring comprises at least three segments, which when touching end to end form a complete circle, and expansible holding means biassed to hold the segments together but of sufficient elasticity to allow the segments to expand radially and move apart by a sufficient amount so as to seat the segments in the groove or against the shoulder. Preferably, the segments are formed with an outer groove, and the holding means comprises an O-ring placed in the outer groove. Advantageously, the smaller diameter cylindrical component includes a lip for engagement with the retaining ring, and an inclined surface defined between the lip and an outer diameter of the said smaller diameter cylindrical component, which inclined surface causes the segmented retaining ring of the present invention to slide into abutting engagement with the lip and and causes it to expand into the seating groove or against the shoulder, when the smaller diameter cylindrical component is dropped inside the larger diameter cylindrical component during assembly of the two cylindrical components. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial cross-sectional view showing the inner cylinder, outer wear sleeve and backhead assembly and part of a piston of a downhole hammer drill, with a retaining ring according to the present invention shown in heavy black outline, Fig. 2 is a perspective view of the inner cylinder, and an exploded view of the three segments and O-ring of the retaining ring of the present invention, before assembly, Fig. 3 is a perspective view, similar to Fig. 2, with the retaining ring in place below the lip of the inner cylinder, but not yet expanded, and Fig. 4 is a perspective view, similar to Figs. 2 and 3, with the retaining ring seating against the lip of the inner cylinder in an expanded condition. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS The parts and functioning of the downhole hammer drill illustrated in Fig. 1 will not be described in detail, but the parts shown include a backhead assembly 1, an outer (larger diameter) wear sleeve 2, an inner (smaller diameter) cylinder 3, a piston 4, wherein the outer wear sleeve 2 includes a groove 12 cut on its inside diameter for seating a retaining ring 5, against a lip 6 of the inner cylinder. The invention relates to the novel retaining ring 5, which suspends the smaller diameter cylindrical component 3 inside the larger diameter cylindrical component 2. The retaining ring 5 of the invention comprises three identical arc-shaped segments 7, 8 and 9, each formed with an outer groove 10, for the purpose of seating an elastomeric O-ring 11, as shown in Fig. 3. It will be appreciated that when each segment is held tightly against the adjacent segment by means of the O-ring 11, no gaps are present between the adjacent segments, as shown in Fig. 3. In this position, the retaining ring is fully compressed and forms a complete circle. When the inner cylinder 3 is slid into position within the outer wear sleeve 2, the lowermost surface of the retaining ring 5 firstly seats against a shoulder provided by the base of groove 12, formed by an increase in the internal diameter of the outer wear sleeve. Continued downward pressure causes a taper or inclined surface 13 defined between the enlarged diameter overhanging lip 6 and the outer diameter of the inner cylinder, to bear against an inside edge of the segmented retaining ring, causing it to ride over the inclined surface 13 and expand radially, against the bias of the O-ring, thus causing small gaps between the segments 7,8,9, until the retaining ring is fully expanded and abutting against the overhanging lip 6, and seating fully into the groove 12, in the position as shown in Figs. 1 and 4. This mode of assembly and interengagement is achieved with a fraction of the force required to engage a conventional circlip. It will be appreciated that thr circlip is naturally biassed to flex forcibly towards an expanded condition. The ring of the present invention is naturally biassed with a much weaker force towards a compressed condition. Furthermore, the segments will expand evenly so that the gaps between them should be the same, when seated in place. It is only at these small gaps where less wear of the lip will occur, but this is minimised by the relatively small size of the gaps, relative to the single gap in a conventional circlip. In embodiments with more than three segments, the gaps between adjacent segments at full expansion of the ring when seated become even smaller. Because the retaining ring of the present invention most preferably comprises three segments, there will be three gaps with an equal distance between each gap around the circumference of the lip. If a small lump should develop on the lip above each gap, this will not cause a skew as tends to happen with the large single gap of the prior art circlip because of the equal distribution of the three gaps/lumps. In contrast, if a second lump develops with a circlip wear pattern, the two tend to be randomly spaced, and can still cause a skew. Furthermore, removal of the inner cylinder for inspection or maintenance during use and subsequent replacement of the retaining ring of the invention, even if in a different position, is still unlikely to cause any tendency for skewing or off-centering between the inner cylinder and outer wear sleeve. This is because any re-positioning of the retaining ring relative to the inner cylinder lip would result only in a multiplicity of small randomly spaced lumps on the lip. It will be appreciated that the O-ring only serves the purpose of holding the segments together during assembly and once seated firmly in place, the individual segments will not tend to move relative to each other because of the compressive forces acting on them when the drill is in use, and the tight interfitting of components when not in use. However, other means of holding and biassing the segments together, either temporarily during assembly of parts, or permanently during use in their seated arrangement, are also contemplated. The O-ring may provide a seal, but this is not essential.

Claims: A fluid-operated drill tool assembly, including a smaller diameter cylindrical component (3) suspended within a larger diameter cylindrical component (2), wherein one of the components is formed with a groove or shoulder for seating a retaining ring, the ring being capable of radial compression and expansion so as to expand radially into the seating groove (12) or shoulder for retaining the component one within the other, characterized in that the retaining ring comprises at least three segments (7, 8, 9), which when touching end to end form a complete circle, and expansible holding means (11) biased to hold the segments together but of sufficient elasticity to allow the segments to expand radially when the ring engages and rides over an inclined surface (13) defined between an enlarged diameter lip (6) and an outer diameter of the said smaller diameter cylindrical component, which inclined surface (13) causes the segments of the retaining ring to slide into abutting engagement with the lip and expand into the seating groove (12) or against the shoulder, when the smaller diameter cylindrical component is dropped inside the larger diameter cylindrical component during assembly of the two cylindrical components (2, 3), and wherein the segments are formed with an outer groove (10), for retaining the holding means. A retaining ring according to claim 1, wherein the holding means comprises an elastomeric O-ring placed in said outer groove. A retaining ring according to claim 1, comprising three segments (7, 8, 9).

Inventors: PURCELL JOSEPH, PURCELL, JOSEPH
Applicants: MINROC TECHN PROMOTIONS LTD, MINROC TECHNICAL PROMOTIONS LIMITED
Application year: 1999
Main classification: E21B4
IPC codes: F16B21, E21B4