GB2094928A - Plug assembly and method of plugging a passage - Google Patents

Abstract

An assembly for plugging a passage such as an oil gallery in a machine, comprises a sleeve 12 and a stem 14 which extends through the sleeve. The stem has a shank 26 one end of which projects from an end of the sleeve and the other end of which is attached through a breakneck 30 to an enlarged hollow head for expanding the sleeve. By pulling the shank while supporting the sleeve the head can be drawn into the sleeve (Figs. 7-9 not shown), expanding the sleeve into gripping and sealing engagement with the wall of a passage, the head undergoing wiredrawing if necessary until the breakneck reaches the first mentioned end of the sleeve. A head skirt can then be deformed outwardly into engagement with a shoulder 80 of the sleeve to prevent the head being removed in the opposite direction, and the breakneck can then be broken to allow removal of the shank, leaving the expanded sleeve with the head within it plugging the passage. <IMAGE>

Description

SPECIFICATION Plug assembly and method of plugging a passage The invention relates to a plug assembly for plugging a passage in a workpiece. The plug assembly is particularly although not exclusively suitable for plugging passages such as the openings of oil galleries of machines or passages for hydraulic fluid or gases in pneumatic apparatus where the installed plug assembly may be required to withstand considerable pressure from fluids contained within the plugged passage.

It is already known to provide a tubular sleeve of ductile material in combination with a solid tapering mandrel which can be pulled into the sleeve to expand the sleeve into frictional engagement with the walls of a bore or other passage to be plugged, the mandrel or more usually a part thereof being left plugging the bore of the sleeve so that, in combination, the sleeve and mandrel co-operate to plug the passage.

According to one aspect of the present invention, there is provided a plug assembly for installation in a cylindrical passage, which assembly comprises a stem and a tubular sleeve; the sleeve having a substantially cylindrical exterior capable of entering completely within the passage to be plugged, the sleeve having a bore throughout its length; and a stem having a shank which extends through the sleeve bore, and a head connected to the shank, the head being capable of radially expanding the sleeve, on being drawn into the bore; the stem head being formed with an internal cavity which has the effect of weakening the stem head around the cavity;; such that when, in use of the plug assembly, the assembly is inserted into a cylindrical passage of suitable diameter with the stem head leading and so that the sleeve lies entirely within the passage and the stem is retracted to draw the head into the bore of the sleeve whilst the sleeve is supported against axial movement, the stem head progressively enters the bore of the sleeve to radially expand at least part of the sleeve into contact with the passage wall whilst the internal cavity limits the amount of radially inward pressure required to cause deformation of the stem head, so that the stem head can collapse sufficiently to enter into the bore of the sleeve while resiliently exerting a radially outward pressure on the sleeve thereafter.

According to another aspect of the invention, there is provided a method of plugging a cylindrical passage by means of a plug assembly as hereinbefore defined, which method comprises the steps of: inserting the plug assembly into the passage with the stem head leading until the sleeve is completely within the passage; and supporting the sleeve against axial movement out of the passage and simultaneously retracting the stem with respect to the sleeve, and thereby causing the stem head progressively to enter the bore of the sleeve and expand at least part of the sleeve into frictional engagement with the wall of the passage.

An embodiment of the invention will now be described, by way of example, and with reference to the accompanying drawings, in which:~ Figure 1 is a side view of a plug assembly according to the invention; Figure 2 is an enlarged sectional elevation of a sleeve for use in forming the assembly of Figure 1; Figure 3 is an end elevation of the sleeve of Figure 2; Figure 4 is a fragmentary sectional elevation on an enlarged scale of a stem part of the assembly of Figure 1; Figure 5 is a part sectional elevation illustrating a first stage in the installation of a plug assembly in a workpiece; Figures 6-9 are views similar to Figure 6 showing successive stages in the installation of the plug assembly; Figure 10 is a sectional elevation showing a plug assembly completely installed in a passage of recommended minimum diameter; and Figure 11 illustrates the form of a plug assembly installed in a passage of recommended maximum diameter.

Referring first to Figures 1 to 4 of the drawings, a plug assembly 10 comprises a tubular sleeve 12 and an elongate stem 14. The sleeve is formed of ductile aluminium alloy and has a through bore 1 6. The stem 14 extends through the bore of the sleeve 12 and one end of the sleeve is crimped into engagement with the stem so that the stem is retained in the bore of the sleeve, thus constituting an assembly which is ready for use.

The sleeve 12 is initially formed of a tubular right cylinder through which the bore 1 6 extends axially, and both ends of the bore 16 are counterbored for a short distance at 18 and 20 to provide annular shoulders 22, 24 respectively adjacent to the ends of the sleeve. Thus, the sleeve 12 is initially symmetrical end to end and can be assembled to the stem either way round.

The stem 14 is made of 0.35% carbon steel, hardened and tempered, and is of circular crosssection. As shown in Figure 5 the stem comprises an elongate and generally cylindrical shank 26 and an enlarged head 28 which is attached to the shank through a narrow breakneck 30. The breakneck forms the root of an annular breaker groove 32.

The head 28 of the stem 14 comprises a first part 34 adjacent to the breaker groove 32 and of uniform external diameter, an annular retaining groove 36 of slightly smaller diameter than the first part 34, an intermediate tapering part 38 in which the diameter of the head increases progressively away from the breakneck at an included angle of 60O to a major diameter intermediate between the external and internal diameters of the sleeve. The major diameter is maintained throughout an elongate cylindrical portion 40 and at the end of the head remote from the breaker groove is an annular terminal rib 42 at which the external diameter of the head reaches a maximum slightly greater than that of the cylindrical part 40.The shank 26 of the stem has a plain cylindrical part 46 adjacent the breaker groove, and a ribbed and grooved gripping portion 48 which extends to the end of the stem remote from the head. The maximum diameter of the shank of the stem is such that the shank is a clearance fit in the bore of the sleeve 12. The first part 34 of the head has a diameter similar to that of the bore 1 6 of the sleeve 1 2 which it is just able to enter.

The sleeve 12 and stem 14 are assembled together by inserting the shank 26 of the stem into the bore 1 6 of the sleeve and passing the sleeve along the stem until it abuts the tapering part 38 of the head 28. As will be appreciated, in this condition the first part 34 of the head will have entered the bore 16 and the annular retaining groove will be within the counterbore at one end of the sleeve. This end of the sleeve is then crimped so as to force it into the annular retaining groove with the result that the sleeve and stem become mutually interengaged in the form of an assembly ready for use.

Referring now to Figure 4 of the drawings it will be seen that the first part 34 of the head has an inner core 54 adjacent to the breakneck 30, the core having a diameter the same as or very slightly greater than the diameter of the shank 26.

Surrounding the core 54 is a peripheral locking skirt 56, there being an annular cleavage 58 extending from the breaker groove and between the inner core and surrounding skirt. The skirt is integrally attached to the head at the end of the cleavage remote from the breaker groove.

The peripheral skirt and the inner core 54 of the first part of the head together present a common face which constitutes one side of the breaker groove 32.

A cavity 50 extends axially into the head 28 from the end face 52 remote from the shank 26.

The cavity 50 is in the form of a generally cylindrical bore which extends through the cylindrical part 40 of the head and into the tapering part 38. The shape and dimensions of the cavity 50 influence the behaviour of the head during installation of the plug assembly in a passage. In particular, the length and diameter of the cavity in a stem of given external dimensions governs the thickness of the surrounding wall. In general terms, the shape and dimensions of the cavity are chosen so that the stem head has, in the region peripherally of the cavity, a predetermined resistance to radially inward compression and also to ensure that the head will wiredraw when subjected, during installation, to a tensile force less than that required to break the breakneck.

In this embodiment, the inner end of the cavity is generally conical in form and is within the tapering part 38 of the head 28.

The installation and use of a plug assembly to plug a passageway will now be described.

Referring to Figure 5, a workpiece 70 has a passage 72 formed as a cylindrical bore in the workpiece by drilling. As will become apparent, plug assemblies according to the invention are capable of accommodating some variation in diameter as between one passage and another.

The plug assembly may be installed in the passage by means of a conventional pulling tool having a means for gripping and pulling the shank 26 of the stem 14 and an annular anvil 76 for abutting the sleeve 12. In this embodiment, the anvil is of the kind described in our British Patent No. 1 523 867.

The plug assembly 10 is first engaged with the pulling tool by inserting the shank 26 of the assembly through the annular anvil 76 and into engagement with the gripping and pulling jaws (not shown) so that the end of the sleeve 12 remote from the head 28 of the stem meets an annular abutment face 78 of the anvil. In this embodiment the anvil 76 has, peripherally of its central aperture, a rim 80 which projects forwardly of the abutment face 78 and enters into the counterbore 20. With the plug assembly thus engaged with the pulling tool, the assembly is then entered into the passage 72 in the workpiece, the head 28 of the stem leading, until the full length of the sleeve 12 has entered the passage and the abutment face 78 of the anvil has abutted the workpiece.It will be seen from Figure 5 that there is a small gap between the cylindrical external surface of the sleeve 1 2 and the wall of the passage 72.

The pulling tool is then actuated to pull the stem in a direction to draw the head of the stem towards the anvil 76 while the sleeve is supported by the anvil. The tapering part 38 of the head therefore begins to enter the crimped end of the sleeve 12, progressively expanding the crimped end radially outwardly into engagement with the wall of the passage 72. At the same time, the head exerts a compressive force on the sleeve in the axial direction and, as the sleeve is supported by the anvil, the compressive force causes the sleeve to undergo a radial expansion throughout substantially the whole of its length so as to fill the gap between it and the wall of the passage 72.

However, although the axial compression causes the external diameter of the sleeve to increase, the diameter of the bore throughout the length of the sleeve is not caused to alter to any appreciable extent. The stage thus reached is illustrated in Figure 6.

Once the sleeve fills the passage, the workpiece itself then resists any further radial expansion of the sleeve. Consequently, as the tool continues to pull the stem head further into the bore of the sleeve, the forces acting on both the head 28 and the sleeve 12 begin to cause plastic flow. Thus, in particular, the sleeve exerts a radially inward compressive force on the parts of the head of the stem which have entered the sleeve, and the head exerts a radially outward force on the sleeve.

These forces are resolved by the extrusion of the sleeve in a direction opposite to that in which the head is being pulled, so that the sleeve becomes elongated, and by wiredrawing of the head 28 with a consequent reduction in its external diameter.

The wiredrawing of the head occurs only in the region into which the cavity 50 extends. Thus the first part 34 of the head, being solid, resists the forces applied to it. However, once the hollow parts of the head enter into the sleeve and are subjected to the tensile and compressive forces, the wall peripherally of the cavity 50 begins to wiredraw and eventually to assume a waisted shape. Figure 7 shows an early stage in the wiredrawing of the head, where elongation of the tapering part of the head has taken place with some reduction in diameter in the region where the tapering part 38 joins the cylindrical part 40.

Eventually, the locking skirt 56 comes into abutment with the sloping front face of the rim 80 and is thereby deflected radially outwardly so as to fill the gap between the rim 80 and the shoulder 24.

Once this stage, which is shown in Figure 9, is reached, the force required to move the head nearer to the anvil increases abruptly to a value exceeding that which can be withstood by the breakneck. Continued pulling by the tool therefore causes the stem to break at the breakneck, leaving the head 28 in the bore of the expanded sleeve, and the shank of the stem being detached by the tool, to be discarded.

Thus, the concentric sleeve and head are left plugging the passage in the workpiece, with the sleeve frictionally engaging the wall of the passage and the tapering head 28 locked in the bore of the sleeve by, on the one hand, the interengagement between the shoulder 24 and the outwardly flared skirt 56, and, on the other hand, the interengagement between the sleeve and the waist 84 of the wiredrawn head.

Figure 11 illustrates, for comparison with Figure 10 (in which the passage 72 was of the recommended minimum diameterfora given diameter plug assembly), the effect of installing a plug assembly in a passage 90 of recommended maximum diameter.

Thus, it will be appreciated that, in the initial phase of installation in the passage 90, the sleeve required to be compressed axially to a greater extent than that in the passage 72 in order to expand it to fill the wider passage. It is, however, to be noted that in both cases the diameter of the bore 16 remains substantially constant during the axial compression. Consequently, in the larger diameter passage 90, the sleeve becomes shorter and thicker walled. Subsequently, as both the sleeve and the head elongate due to extrusion of the sleeve and the wiredrawing of the head, the head elongates to a lesser extent than the sleeve with the result that the terminal annular rib eventually enters the bore of the sleeve before the skirt 56 is fully deformed into locking engagement with the shoulder 22 and the shank breaks off.

In the case of the plug assembly installed in the smaller diameter passage 72 (Figure 10), the elongation of both the plug and the sleeve has been greater than of those of Figure 11. However the head has wiredrawn more in proportion to the elongation of the sleeve, with the result that the head has not entered entirely into the sleeve.

By reason of the cavity 50 within the head of the stem of the foregoing example, the head in the installed plug assembly shows a greater degree of residual elasticity or resilience to radially inward pressures. Consequently, the head exerts resiliently a radially outward pressure on the sleeve which tends to urge the sleeve more strongly than would a solid head into frictional engagement with the wall of the passageway in which the plug assembly is installed.

This residual elasticity of the head is also able to compensate for variations in diameter of the passage such as may arise from variations in temperature of the workpiece.

Furthermore, when used to plug passages containing pressurised fluids, such as oil in the oilways of engines or pneumatic or hydraulic fluids, the pressure of the fluid acting upon the surfaces within the cavity 50 tends to radially expand the head, and thus tends to expand the sleeve into more tightly fitting frictional contact with the walls of the passage. It will be appreciated that to some extent there is a correlation between the pressures acting on the plug assembly and the increase in friction between the assembly and the workpiece so that, as the pressure increases, the resistance of the plug assembly to ejection also increases.

Claims (10)

1. A plug assembly for installation in a cylindrical passage, which assembly comprises a stem and a tubular sleeve, the sleeve having a substantially cylindrical exterior capable of entering completely within the passage to be plugged, the sleeve having a bore throughout its length, and a stem having a shank which extends through the sleeve bore, and a head connected to the shank, the head being capable of radially expanding the sleeve, on being drawn into the bore, the stem head being formed with an internal cavity which has the effect of weakening the stem head around the cavity, such that when, in use of the plug assembly, the assembly is inserted into a cylindrical passage of suitable diameter, with the stem head leading, and so that the sleeve lies entirely within the passage, and the stem is retracted to draw the head into the bore of the sleeve whilst the sleeve is supported against axial movement, the stem head progressively enters the bore of the sleeve to radially expand at least part of the sleeve into contact with the passage wall whilst the internal cavity reduces the amount of radially inward pressure required to cause deformation of the stem head, so that the stem head can collapse sufficiently to enter into the bore of the sleeve and thereafter resiliently exert a radially outward pressure on the sleeve.

2. A plug assembly as claimed in Claim 1, in which the stem head is joined to the stem shank by a breakneck, and the arrangement is such that, when the stem head enters the sleeve as aforesaid, it can do so to such an extent that the breakneck is substantially level with the end of the sleeve remote from the initial position of the stem head.

3. A plug assembly as claimed in Claim 2, in which the stem head is provided with means adjacent the breakneck for lockingly engaging with the sleeve.

4. A plug assembly as claimed in Claim 3, in which the locking means comprises a part of the stem deformable radially outwardly.

5. A plug assembly as claimed in Claim 4, in which the said end of the sleeve is provided with a counterbore providing a shoulder for abutting the outwardly deformable part of the stem head.

6. A plug assembly as claimed in Claim 5, in which both ends of the sleeve are initially provided with a counterbore, and during assembly the portion of the sleeve around the counterbore at the end thereof adjacent the stem head is deformed inwardly to retain the sleeve assembled on the stem until use of the assembly.

7. A plug assembly as claimed in any of the preceding claims, in which, when the assembly is inserted into the passage and the stem retracted with respect to the sleeve as aforesaid, the stem head causes radial expansion of substantially the whole length of the sleeve into contact with the passage wall as aforesaid due to axial compression of the sleeve between the stem head and the support against axial movement, before the stem head has entered substantially into the shell.

8. A plug assembly substantially as hereinbefore described with reference to, and illustrated in, the accompanying drawings.

9. A method of plugging a cylindrical passage by means of a plug assembly as claimed in Claim 1, which method comprises the steps of: inserting the plug assembly into the passage with the stem head leading until the sleeve is completely within the passage, and supporting the sleeve against axial movement out of the passage and simultaneously retracting the stem with respect to the sleeve, and thereby causing the stem head progressively to enter the bore of the sleeve and expand at least part of the sleeve into frictional engagement with the wall of the passage.

10. A method of plugging a cylindrical passage, substantially as hereinbefore described with reference to, and illustrated in the accompanying drawings.