GB2057934A

GB2057934A - Lining of cylindrical bores

Info

Publication number: GB2057934A
Application number: GB8028780A
Authority: GB
Original assignee: Cross Manufacturing Co 1938 Ltd
Current assignee: Cross Manufacturing Co 1938 Ltd
Priority date: 1979-09-07
Filing date: 1980-09-05
Publication date: 1981-04-08
Also published as: GB2057934B

Abstract

A method of lining a cylindrical bore e.g. of an internal combustion engine with a thin-walled liner. A length of strip material is selected such that when the strip is formed into a liner and pressed into the bore, it will be subjected to hoop- stress. The strip 17 is pressed into a semi-circular groove in a jig-plate 21 by a mandrel 25 on a plunger 24 and held in place by electromagnets 26A or suction. Jig cheek- pieces are moved over the groove which together with the groove define a bore the diameter of which equals that of the bore to be lined, the strip being enclosed and deformed to define a liner subjected to hoop-stress. The stressed liner is pressed into a slave sleeve also defining a bore of the same diameter as the bore to be lined. Subsequently, the stressed liner can be pressed out of the slave sleeve directly into the bore. <IMAGE>

Description

SPECIFICATION Lining of cylindrical bores This invention concerns methods of lining cylindrical bores, such as the cylinders of internal combustion engines. In particular, but not exclusively, the invention relates to a method of providing a cylindrical bore with a thin-walled liner formed from a strip of metallic material.

It is known, as has been described for instance in British Patent Specification No.

1237962 and the Patent-of-Addition thereto No. 1395220, in the name of Cross Manufacturing Company (1938) Limited, that advantageous properties can be realised when the cylinder of an internal combustion engine is lined with a relatively thin-wall liner formed from a strip of material deformed to define the liner. The insertion of such a liner has proved to be somewhat difficult, especially on a production basis: such a liner cannot, for instance, simply be pressed into the bore without internal support as is a conventional thick-walled liner, for the thin-wall liner exhibits insufficient strength to withstand the relatively large axial force required to drive the liner fully home.

It is an object of this invention to provide a method of lining a cylindrical bore, especially in the case of a thin-walled liner, which is relatively easy and reliable to perform, allowing mass production.

Accordingly, this invention provides a method of lining a cylindrical bore, which method comprises selecting a strip of lining material of such a length that when formed into a cylindrical liner for the bore and pressfitted thereinto the formed strip is subjected to hoop-stress, pressing the selected strip with a mandrel into a groove formed in a jig-plate which groove has an arcuate cross-section with a radius of curvature substantially equal to that of the unlined bore and which mandrel has a circular cross-section the diameter of which is substantially equal to that of the lined bore, retaining the partially-formed strip in the groove of the jig-plate whilst jig cheekpieces, each of which defines a part-circular groove of substantially the same radius of curvature as the groove in the jig-plate, are moved to a position in which the cheek-piece grooves and the jig-plate groove togetherdefine a cylinder of substantially the same diameter as that of the unlined bore thereby enclosing and deforming the strip to form a cylindrical liner which is subjected to hoopstress within the jig; and pressing the thusformed liner out of the jig into the cylindrical bore whilst maintaining the hoop-stress within the liner.

The various steps of the method just-described above will now be explained in greater detail and preferred aspects thereof given.

The length of the strip of lining material should be determined having regard to the thickness of the lining material and the diameter of the unlined bore into which the liner is to be inserted. Preferably, the length of the strip of lining material is cut slightly oversize, and is then ground to a finished length. For a mass production, several lengths could be cut, these then being clamped together and all ground simultaneously to the same finished length. The ground ends should be shaped so that an exact butt joint is formed therebetween on forming the liner from the cut and ground length, and consequently the ends should be ground dead square.

The material used should be selected having regard to the intended use of the lined bore, but for example in the case of an internal combustion engine, it has been found that flat, high carbon spring steel is suitable.

The steel should be fully heat-treated for this application, for example to specification EN 42G. A typical range of thickness for making thin-walled liners from such a material would be from 0.25 mm to 0.56 mm (approximately 0.010" to 0.022"), with a thickness control of approximately i 0.0076 mm (approximately 0.0003"). Other materials, such as aluminium alloy or bronze, could of course be used, as well as other thicknesses.

The mandrel used to press the lining material into the groove in the jig-plate preferably is of wholly circular cross-section, and is provided with a plunger extending radially from the side thereof opposed to the groove in the jig-plate, the plunger being slidably mounted to allow movement of the mandrel towards and away from the groove. Conveniently, means are provided on the jig-plate to locate the lining material so that the transverse centre line thereof overlies the centre of the groove in the jig-plate, prior to being pressed by the mandrel.

Once the mandrel has been pushed fully into the groove, thereby partially forming the lining material, the lining material should be held firmly in the groove to allow the next stage of the forming process. For example, in the case of a ferro-magnetic lining material, the jig-plate may support a plurality of electromagnets disposed both around and along the length of the groove, as appropriate, which electromagnets may be energised so as to clamp the partially formed lining material to the face of the groove. The mandrel may be non-magnetic to allow removal thereof, or could instead also be of a ferro-magnetic material, in which latter case the mandrel will be clamped to the jig-plate when electromagnets are energised.Another possibility is to use a vacuum-clamping technique, in which the groove in the jig-plate is provided with a network of relatively shallow and narrow grooves, or even discrete orifices, the grooves or orifices communicating with a vacuum pump and the pump being actuated once the mandrel has been pushed fully home, so that the reduced pressure serves to clamp the lining material to the groove.

Once the lining material has been held in the manner just-described, the mandrel could be removed and replaced by another not having a radially-extending plunger, to allow further forming of the lining material. Alternatively, the plunger may be removed from the mandrel, to allow the next stage of the forming operation. Yet another possibility is to provide a mandrel which is of a length greater than the groove in the jig-plate, the mandrel being carried by suitable driving means at its ends, for instance between the two arms of a yoke.The mandrel may then be driven into the groove by the yoke acting on the two ends of the mandrel, and provided that the driving means does not overlap the groove, then the driving means may also be employed to maintain the partially-formed lining material in the groove in the jig-plate, during the next stage of the forming operation, by maintaining a force on the driving means.

The groove in the jig-plate is preferably substantially semi-circular in cross-section, and conveniently two similar cheek-pieces are provided for use therewith, each defining a quadrant-shaped groove. The cheek-pieces are preferably slidably mounted on the jig-plate, for sliding movement towards each other in a direction lying within the plane containing the diameter of the semi-circular groove in the jigplate. Thus, as the two cheek-pieces are slid together, the free ends of the lining material will be formed by the grooves therein to butt one another. In the final stage of the movement of the cheek-pieces, and provided the length of the strip of lining material has properly been pre-determined, the completed liner will be subjected to hoop stress.When the cheek-pieces are moved to their final position, they should be locked together, by an appropriate means, thus completing the jig.

From the complete jig, the formed liner may be pressed either directly or indirectly into the cylindrical bore to be lined. For example, the jig could be positioned axially over the bore and in engagement therewith; if the mandrel has been left in position or replaced by another and provided that the mandrel has a flange thereon the radial extent of which is the same as the lining material thickness, the mandrel can be used to push the liner out of the jig and into the bore, whilst supporting the internal diameter of the liner during this -pressing operation. If no mandrel is present, a separate plunger may be used to press the liner out of the jig.

Another possibility is to use an indirect process, in which the liner is pushed out of the jig into a sleeve the bore of which is substantially the same as that of the cylindrical bore to be lined, a slave mandrel being provided within the slave sleeve to support the liner therewithin. Subsequently, the liner may be pushed out of the slave sleeve directly into the cylindrical bore to be lined, using the slave mandrel. The advantage of this latter process is that the slave sleeve may be relatively small as compared with the jig and thus much easier to handle and to align with the cylindrical bore to be lined. In addition, a batch of such slave sleeves and mandrels may be pre-loaded with liners prepared in the same jig, the slave sleeves and mandrels then being stored until required for use.

The invention extends to a cylindrical bore (for instance of an internal combustion engine) whenever lined with a thin-wall liner in accordance with a method of this invention, as described above.

By way of example only, two specific examples of methods of this invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a diagrammatic sketch of a machine for cutting lengths of lining material from a coil thereof; Figures 2A and 28 are sketches showing two views of a fixture allowing the finishgrinding of lengths of the lining material; Figure 3 shows diagrammatically the first step in a forming process for a liner; Figures 4 and 5 show further stages in the forming process; Figure 6 shows the insertion of a formed liner into a slave sleeve; Figure 7 shows the initial stage of the insertion of a liner into a bore in a cylindrical block, from a slave sleeve; and Figures 8 and 9 are respectively side and plan views of a second embodiment of jig plate having a semi-circular groove therein, for use in the forming of a liner.

Fig. 1 shows a cutting machine for cutting lengths of strip material from a coil 10, using a power driven slitting saw 11. The material is drawn from the coil 10 by means of driven feed rollers 12 until the material engages an end stop 13; then, the slitting saw is traversed to sever the material and the length cut off is ejected by means of an ejector pin 14 and driven ejection rollers 15, to a receptacle 16.

The cut off lengths are collated together and then held (for instance in batches of 100) in the fixture shown in Fig. 2. The stack of cut lengths 17 is clamped between two plates 18 and 19 of the fixture, and the fixture is then traversed beneath a surface grinding wheel 20, to finish-grind the ends of the cut-off lengths. This should provide dead square end faces precision ground to the required finish, each strip having precisely the same predetermined length. It is most important that the ends are ground properly, both to give the required degree of hoop stress in the finished liner and to prevent formation of a gas leakage path along the butting end faces when the formed liner is inserted into the bore of an internal combustion engine.

The cut and ground lengths of lining material are supplied one at a time to a jig having a base plate 21 (Fig. 3) to overlie a semicircular groove 22 formed in the base plate.

The base plate 21 also supports a pair of removable stops 23, between which the cut material is located. A non-rotatable plunger 24 is suitably mounted for sliding movement above the groove 22 and supports a a nonmagnetic mandrel 25 the axis of which extends parallel to the axis of the groove 22. As shown in Fig. 4, the mandrel is initially forced down towards the base plate 21, to form the lining material into a semi-circular shape with equal leg lengths extending upwardly from the groove 22. Electromagnets 26A, positioned within the base plate 21, (as shown in Fig. 4) are then energised, to hold the material in the groove 22 and prevent the material springing out of the groove, when the force is removed from the plunger 24.Next, the plunger 24 is removed from the mandrel 25, leaving the mandrel partially within the groove 22, and the stops 23 also are removed from the base plate 21.

A pair of cheek-pieces 26 (Fig. 5) are then slid towards each other along the top face of the base plate 21, each cheek-piece defining a quadrant shaped groove 27, the groove 22 and the two grooves 27 together defining a bore of circular cross-section when the cheekpieces are touching each other centrally over the groove 22. In reaching this position, the upwardly-extending legs of the partiallyformed liner are deformed around the mandrel 25, thereby completing the formation of a circular liner-and provided that the length of the material was properly pre-determined beforehand, the liner will be subjected to hoop stress as the cheek-pieces 26 move to their final position. A locking bar 28 is then used to hold the two cheek-pieces 26 together.

Next, the electromagnets in the base plate 21 are de-energised, leaving the liner fully supported externally by means of the base plate 21 and the cheek-pieces 26, with the mandrel 25 therewithin but free to be removed axially.

In the next operation (Fig. 6) the formed liner 39 is pushed out of the bore defined by the plate 21 and cheek-pieces 26, into a slave sleeve 29 (Fig. 6). This is performed by means of a guided linear actuator 30 supporting a slave mandrel 31 having a shoulder 32 at the end thereof adjacent the actuator 30, which shoulder has a radial extent equal to the radial thickness of the material of the liner. A plug 33 is provided at the opposite end of the slave mandrel and an appropriate supporting arrangement is provided for the slave sleeve 29, including an abutment bush 34 and alignment crotches 35. On operating the actuator 30, the mandrel 25 is pushed out of the formed liner by means of the plug 33 and eventually the shoulder 32 of the slave mandrel 31 engages the liner within the cylinder defined by the plate 21 and cheekpieces 26.Further operation of the actuator 30 pushes the liner into the slave sleeve, until both the liner and the slave mandrel 31 are located wholly within the slave sleeve 29.

Then, the apparatus of Fig. 6 may be dismantled, leaving the liner and slave mandrel within the slave sleeve, as shown in Fig. 7.

Also shown in Fig. 7 is the bore 36 of a cylinder block 37, and it can be seen that the top lip of the bore should be relieved as shown at 38, to allow relatively easy insertion of the liner 39 into the bore, when the slave mandrel 31 is pushed by means of a rod 40 engaged therewith. Once the liner 39 is fully home within the bore 36, the slave mandrel 31 may be removed therefrom.

Figs. 8 and 9 show an alternative embodiment of the base plate 21. Instead of the base plate being provided with electromagnets (as shown in Fig. 4), the groove 22 is instead provided with a matrix of relatively shallow and relatively narrow interconnected grooves 41, all of the grooves communicating with a duct 42 extending through the plate. This duct 42 can be connected to a vacuum pump, so that when the pump is operated, the lining material will be clamped to the semi-circular groove in the plate, in a similar way to that described above using the electromagnets. It is preferred for the vacuum pump to produce a depression of at least 712 mm Hg. Such a method is applicable for instance to nonmagnetic liner materials, such as bronze or aluminium alloys. The method could also be used for steel liners, such as liners made of high carbon fully-heat treated spring steel.

Claims

1. A method of lining a cylindrical bore, which method comprises selecting a strip of lining material of such a length that when formed into a cylindrical liner for the bore and press-fitted thereinto the formed strip is subjected to hoop-stress, pressing the selected strip with a mandrel into a groove formed in a jig-plate which groove has an arcuate crosssection with a radius of curvature substantially equal to that of the unlined bore and which mandrel has a circular cross-section the diameter of which is substantially equal to that of the lined bore, retaining the partially-formed strip in the groove of the jig-plate whilst jig cheek-pieces, each of which defines a partcircular groove of substantially the same radius of curvature as the groove in the jigplate, are moved to a position in which the cheek-piece grooves and the jig-plate groove together define a cylinder of substantially the same diameter as that of the unlined bore thereby enclosing and deforming the strip to form a cylindrical liner which is subjected to hoop-stress within the jig; and pressing the thus-formed liner out of the jig into the cylindrical bore whilst maintaining the hoop-stress within the liner.

2. A method as claimed in claim 1, in which the strip is pressed by the mandrel into a groove in the jig-plate which is substantially semi-circular in cross-section, and subsequently the strip is formed by two jig-cheekpieces each of which defines a substantially quadrant-shaped groove.

3. A method as claimed in claim 1 or claim 2, in which the strip is cut from a length of flat, high carbon spring steel.

4. A method as claimed in claim 3, in which the strip has a thickness in the range of from 0.25 mm to 0.56 mm.

5. A method as claimed in any of the preceding claims, in which the mandrel used to press the strip is of wholly circular crosssection, and is provided with a plunger extending radially from the side thereof opposed to the groove in the jig-plate the plunger being slidably mounted to allow movement of the mandrel towards and away from the groove.

6. A method as claimed in any of the preceding claims and wherein the strip is cut from a length of ferro-magnetic material, in which electromagnetic means associated with the jig-plate are employed to retain the partially formed strip in the groove once pressed thereinto by the mandrel.

7. A method as claimed in any of claims 1 to 5, in which means are provided to apply suction to the groove in the jig-plate, the suction being applied after the partially formed strip has been pressed into the groove by the mandrel to hold the partially formed strip therein.

8. A method as claimed in any of claims 1 to 5, and wherein the mandrel has a greater length than the axial length of the groove in the jig-plate, in which the mandrel is driven into the groove partially to form the strip by means acting on the ends of the mandrel beyond the axial extent of the groove, said means maintaining the mandrel in the groove whilst the jig-pieces are moved to complete the formation of the liner from the strip.

9. A method as claimed in any of the preceding claims, in which the liner formed from the strip is directly pressed into the bore to be lined by positioning the complete jig over the bore and then pressing the liner out of the jig into the bore.

10. A method as claimed in any of claims 1 to 8, in which the liner formed from the strip is indirectly pressed into the bore to be lined, by first pushing the liner out of the jig into a slave sleeve the diameter of the bore of which is substantially the same as that of the cylindrical bore to be lined, a slave mandrel being provided within the slave sleeve to support the liner therewithin, and subsequently pushing the liner out of the slave sleeve directly into the bore to be lined by using the slave mandrel.

11. A method of lining a cylindrical bore with a thin-walled liner substantially as hereinbefore described, with reference to the accompanying drawings.

1 2. A cylindrical bore whenever lined with a thin-wall liner formed from a strip of material appropriately formed by a method according to any of the preceding claims.