GB2245680A

GB2245680A - Piston rings

Info

Publication number: GB2245680A
Application number: GB9014338A
Authority: GB
Inventors: Duncan Robert Bury
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1990-06-27
Filing date: 1990-06-27
Publication date: 1992-01-08
Anticipated expiration: 2010-06-27
Also published as: GB2245680B; GB9014338D0

Abstract

A piston ring 30 comprises discrete localised hardened areas 20, 22 on the face which will contact an associated cylinder wall. The localised hardened areas are produced by a high energy beam, (eg laser or electron beam) treatment of the input steel strip used to form the piston ring by wire bending. Due to the hardened areas being discrete and localised the strip is able to be formed without cracking or breaking. <IMAGE>

Description

Piston Rings The present invention relates to pison rings and particularly to a method of treatment of piston ring material to improve the wear resistance thereof.

It is known to treat the working faces of a piston ring to improve their wear resistance. Many such treatments form a hard, continuous and non-ductile surface and are usuallly applied to the finished piston ring. Such treatments include nitro-carburising and various other diffusion processes. These post-formation treatments are usually applied to piston rings which have been made by the method of casting individual ring blanks or of machining and slicing up of centrifugually cast cylinder.

One method which employs laser transformation hardening as a post-forming treatment, is described by McCormick in Us 4 299 401. The piston rings produced have a continuous band of hardened material running around each ring side face.

A more recent method of manufacturing piston rings is that of bending a strip of wire of the ring material with the aid of rollers or other guides into the final shape desired. It should be emphasized that the desired final shape of a piston ring in the free, unconstrained state is not a circle but a relatively complex shape.

It would be highly desirable to find a preforming treatment for the wire or strip rather than use a post-forming treatment since the treatment invariably causes distortion of the formed piston ring.

It is not possible to for a wire or strip which has been pre-treated by the known methods described above since the hard, continous surface layer either tends to spall or the wire cracks or breaks during bending.

A method of treating the input stock wire has now been found which overcomes the above disadvantages.

According to a first aspect of the present invention a method of rendering a piston ring more resistant to wear in service comprises the steps of treating an input strip of material with a high energy beam to produce discreat localised areas of hardening material along the length of the strip on the face which will contact an associated cylinder wall prior to forming into the piston ring shape.

The high energy beam may be either an electron beam or, more preferably, a laser beam.

The localised areas of hardened material may be formed alternately at each strip edge such that the areas overlap when presented to a cooperating cylinger wall and/or piston ring groove. Alternative 1 y, the hardened areas may be formed such that they lie substantially within the boundaries defined by the strip edges. Piston rings having a so called "barrelled face" where the cylinger wall contact face lies in the central region of the formed strip may be treated in this manner. The localised areas of hardened material are separated and/or surrounded by unhardened, ductile material which accepts the deformation during the ring forming operation.

After hardening and forming the piston rings may be subjected to a barrel lapping operation to achieve the desired surface finish.

In one embodiment of the method, using a laser beam the stip faces which will form the psiton ring side faces which cooperate with the associated piston ring groove may be hardened by laser transformation along or about the bending neutral axis ie at the point in the strip which receives zero or minimum deformation during bending.

Furthermore, side face hardening may be accomplished by using the same laser beam as for the cylinder wall rubbing face hardening and using beam splitting mirrors to direct the beam onto the side faces.

The laser beam may be either pulsed or continuous, the discreat areas in the latter case being formed by the use of masks over the wire, or by oscillating optical techniques.

According to a second aspect of the present invention there is provided a piston ring when made by the first aspect. In order that the present invention may be more fully understood it will now be illustrated by way of example only with reference to the accompanying drawings of which: Figure 1 shows a schematic view of a section through a wire inout strip having a laser beam applied to it; Figure 2 shows the wire of figure 1 in plan view after laser treatment; Figure 3 shows the wire of figure 2 looking in the direction of the arrow 'A' after bending; Figure 4 shows a plan view of a wire having a first alternative geometry of hardened areas; and Figure 5 shows a plan view of a wire having a second alternative geometry of hardened areas; Figure 6 shows a transverse section through the wire of figure 5; and; Figure 7 which shows a wire being hardened on the cylinder wall rubbing face and the side faces simultaneously.

Referring now to Figures 1, 2 and 3 where a wire input strip is indicated at 10 and corresponds to SAE 9254 composition having a carbon content of 0.45 to 0.53 wt%. A laser beam 12 is diverted into two alternately pulsed beams 14 and 16 by an oscillating mirror arrangement 18.

The wire 10 is fed at a constant speed beneath the beams 14 and 16 which results in transformation hardened areas 20, 22 being formed alternately on each edge of the wire.

When viewed in a direction normal to the wire axis 24 the hardened areas 20, 22 provide a continuous rubbing surface on an associated cylinger wall 26 by virtue of their overlapping geometry. The laser treated wire 10 remains ductile and thus formable, due to the matrix 28 being largely unaffected by the localised hardening. After laser treatment and subsequent forming the piston rings may be finished on the cylinger wall rubbing face 30 by a conventional operation such as barrel lapping.

Figure 4 shows a wire 40 having transformed regions 42 in the form of stripes across the cylinder wall rubbing face 44.

Figure boundaries formed by the wire edges 54, 56. In this type of ring which has a curved cylinger wall rubbing face 58, the areas 50, 52 overlap about both the wire centre line 60, which is parallel to the wire axis and about the direction normal to the wire axis and parallel to the cylinder axis (not shown). Since most of the rubbing wear is accommodated on the crown 62 of the curved face 58 a continuous hard surface is presented to the cylinder wall (not shown).

Figure 7 shows the wire side faces 70, 72 being hardened simultaneously with the areas 74, 76 of the cylinger wall rubbing face 78. Hardened areas 80, 82 are formed on the side faces by the laser beam 84 being split into three beams, 86, 88 90 by a slitter 92. The central beam 88 is also oscillated by a morror arrangement 94 to form the hardened areas 74, 76. Mirrors 96, 98 reflect the beams 86, 90 ont the side faces 70, 72 to form the hardened areas 80, 82. The mirrors 96, 98 may also be oscillated to vary the position and geometry of the areas 80, 82 on the side faces.

The laser bea 12, 84 may be either pulsed or continuous, the discreet areas in the latter case being formed by use of a mask, for example, of copper, or oscillating optical techniques.

Claims

1. A method of rendering a piston ring more resistant to wear in service, the method comprising the steps of treating an input strip of material with a high energy beam to produce discrete localised areas of hardened material along the length of the strip on the face which will contact an associated cylinder wall prior to forming into the piston ring shape.

2. A method according to claim 1 wherein the high energy beam is an electron beam.

3. A method according to claim 1 wherein the high energy beam is â laser beam.

4. A method according to any one preceding claim wherein the localised areas of hardened material are formed alternately at each strip edge.

5. A method according to claim 4 wherein the localised areas of hardened material overlap when viewed in a direction parallel to the piston ring axis.

6. A method according to any one of preceding claims 1 to 3 wherein the localised areas of hardened material lie substantially within the boundaries formed by the strip edge.

7. A method according to claim 6 wherein the localised areas of hardened material overlap when viewed in a direction parallel to the piston ring axis.

8. A method according to any one preceding claim from 1 to 3 wherein the localised areas of hardened material are in the form of bands, angled obliquely, with reference to the piston ring axis, across the face which will contact the associated cylinder wall.

9. A method according to any one preceding claim wherein the wire faces which will form the piston ring side faces are also treated to provide discrete localised areas of hardened material.

10. A piston ring when made by the method of any one of preceding claims 1 to 9.

11. A method for rendering a piston ring more resistant to wear in service substantially as herein described before with reference to the accompanying specification and drawings.

12. A piston ring substantially as herein described before with reference to the accompanying specification and drawings.