AU708508B2

AU708508B2 - Piston ring

Info

Publication number: AU708508B2
Application number: AU72760/96A
Authority: AU
Inventors: Norbert Feistel
Original assignee: Maschinenfabrik Burckhardt AG; Maschinenfabrik Sulzer Burckhardt AG
Current assignee: Burckhardt Compression AG
Priority date: 1995-11-17
Filing date: 1996-11-06
Publication date: 1999-08-05
Anticipated expiration: 2016-11-06
Also published as: PL181438B1; CA2237787A1; WO1997019280A1; DE59610335D1; ATE237083T1; NO982231L; SK61598A3; EP0861391B1; PL326701A1; RU2176043C2; NO982231D0; BR9611460A; EP0861391A1; AU7276096A; CZ151298A3

Abstract

The invention concerns a piston ring (10), in particular a piston ring for a reciprocating compressor, consisting of a first and a second annular element (10a, 10b) with a joint (10e, 10f), the rings (10a, 10b) being disposed concentrically about an axis C. The first ring (10a) has an essentially L-shaped cross-section, with a first arm (10h) extending parallel to axis C and a second arm (10g) extending radially outwards from axis C. The first arm (10h) has an inside surface (10n) and the second arm (10g) has an inside surface (10l), the inside surface (10l) of the second arm (10g) being inclined in the radial direction and the faces (10m, 10k) of the second ring (10b) which face towards the first ring (10a) physically locking with the inside surfaces (10m, 10l) of the first ring (10a).

Description

2 This object is satisfied in accordance with the features of claim 1 or claim 2. The subclaims 3 to 6 refer to further advantageous developments of the- invention.

The piston ring in accordance with the invention for a dry running piston compressor consists of two one-piece, ringlike bodies with ring gaps or butt joints, which bodies are designated in the following as rings. These rings are arranged to extend concentric to one another with respect to an axis C. The first ring has an essentially L-shaped crosssection with a first limb extending in the direction of the axis C and a second limb extending outwards radial to the axis C. The two limbs each have an inner surface, with the second ring being executed in such a manner that its surfaces facing the first ring lie in contact with the inner surfaces of the first ring in a form-fitted manner. The second limb, extending radially outwards from the axis C, has an inner surface which is inclined in the radial direction with respect to the axis C, with the angle of inclination being less than 900. The inner surface has a tangent extending in the radial direction, which tangent intersects the axis C at an acute angle. In an advantageous embodiment of the invention this inner surface is executed as a conical surface.

In dry running piston compressors there is no lubricant available in order to lubricate the piston rings of a piston and to additionally seal it. Accordingly metallic piston rings are unsuitable for such a dry running application. The dry running frictional pairings function as a result of solid lubricants which are contained in one of the frictional partners. The piston ring in accordance with the invention therefore consists of a plastic specially modified for dry running with solid lubricants such as PTFE, graphite or molybdenum disulphide.

3 Sealing elements with a very high sealing action are required above all when compressing very-light gases, such as hydrogen for example, to very high pressures in order to keep the leakage as small as possible. A good sealing action can be achieved for example by combining two sealing rings to a twin ring in such a manner that no through-going gaps or spaces result.

The self lubricating action of the dry running frictional seals has as a consequence that the piston rings which yield the lubricant gradually abrade away. Known twin rings of plastic have the disadvantage here that the two ring parts are displaceable with respect to one another in the radial direction. Since the pressure profile in the sealing subsurfaces of the two ring surfaces near the cylinder wall is not constant, the radial displaceability enables one of the two ring parts to abrade faster than the other. This unequal wear has the effect that the two ring parts no longer fully overlap and hence that gaps arise through which large amounts of leakage gas flow, in particular for very light gases under high pressure, which considerably reduces the amount of the gas forwarded by the dry running compressor.

The piston ring in accordance with the invention is especially suitable for the dry running compression of very light gases to high compression end pressure. The piston ring has the advantage that due to the construction of two ring parts or two ring-shaped bodies, their mutual slope and the form-fitting coupling of the two ring parts a uniform, harmonised wear of the two ring parts takes place during operation. The two ring parts are pressed against one another by the pressure of the fluid to be compressed, with no relative movement or only a slight mutual relative movement taking place due to the form-fitting coupling of the two ring parts, so that the sealing subsurfaces of the two ring parts 4 which, for example, face a cylinder wall, experience a uniform material abrasion. In this manner, no or only slight local leakage points can form, due to which the sealing effect of the piston ring remains approximately constant over a longer operating period in dry running piston compressors.

In the following the invention will be explained with reference to several embodiments. Shown are: Fig. 1 a longitudinal section through a piston with a cylinder; Fig. 2a a cross-section through a second ring; Fig. 2b a cross-section through a first ring; Fig. 3a a plan view of a second ring; Fig. 3b a plan view of a first ring; Fig. 4 a piston ring arranged in a one-piece piston; Fig. 5 two piston rings arranged in an assembled piston; Fig. 6a a cross-section through a further embodiment of a second ring; Fig. 6b a cross-section through a further embodiment of a first ring.

Fig. 7a a plan view of a second ring; Fig. 7b a plan view of a first ring.

5 Fig. 1 shows a longitudinal section through a dry running piston compressor with a cylinder 1 in which a piston 2 is arranged so as to be upwardly and downwardly movable. The lower end of the piston 2 merges into a piston rod 3 which is connected in a known manner, not shown, to a crank drive.

Above the piston 2 is a compression chamber 4 into which a gas to be compressed is drawn during the downward stroke of the piston 2 in a known manner, not shown. This gas is compressed on the following upward stroke and expelled from the compression chamber. The piston 2 has a rod-like extension 5 of the piston rod 3 over which a sleeve is placed bearing seven piston rings 10 placed one above the other. For an assembled piston 2 the individual parts of the piston 2 as well as the piston rings 10 are held together by a nut 7 screwed onto the upper end of the extension 5. Likewise shown is the central axis C of the piston 2.

The section A is shown magnified in Fig. 5, where two sections A are shown. The assembled piston is fabricated from individual parts and comprises the sleeve 6 extending in axial direction, the chamber rings 8a, 8b placed about the sleeve 6 as well as the piston rings 10 placed in the grooves. Each of the piston rings 10 consists of a first ring and a second ring 10b. The two rings 10a, 10b are executed in a mutually adapted manner such that the mutually contacting partial areas come to lie against one another in a form-fitted manner. Each of the rings 10a, 10b has areas facing the cylinder wall 1 which are slidingly moved upwards and downwards along the cylinder wall during the operation of the piston 2.

Fig. 4 shows a section A of a one-piece piston 2 with chamber ring 8 and a piston ring 10 consisting of the two rings placed in the groove. The first ring 10a is arranged in the cylinder 1 toward the pressure side, with the gas -6pressure 9 exerting forces on the first ring 10a acting in the axial direction 9a as well as in the radial direction 9b so that the entire piston ring 1-0 is firstly pressed against the inner wall of the cylinder 1 and secondly pressed in the axial direction against the boundary surface of the groove remote from the pressure side. In this way the sealing action of the piston ring is increased during operation and the two rings 10a, 10b are held in the groove and mutually formfitted without or with only a slight relative movement. This mutually form-fitted connection has the result that the subsurfaces 10c, 10d of the two rings 10a, 10b which slide along and rub against the cylinder wall la are uniformly worn away so that no local leakage point arises and the two rings 10b lie in contact with the cylinder wall la with the same effect over a longer operating period.

The piston ring 10 shown in Figures 4 and 5, comprising the rings 10a, 10b, is shown in detail in Figures 3a, 3b in a plan view and in the Figures 2a, 2b in cross-section. The two rings 10a, 10b extend circularly about a central axis C. Fig.

3b shows the first ring 10a of the piston ring 10, a ringshaped body of L-shape or nearly L-shape with a ring gap or butt joint 10e. This ring has two limbs 10g, 10h, a first limb 10h extending parallel to the direction of the axis C and a second limb 10g extending radially outwardly or approximately radially outwardly relative to the axis C. The width of the ring gap 10e is such that the first ring 10a is capable of a certain resilient movement in the peripheral direction.

A cross-section through the first ring 10a along the line A-A is shown in Fig. 2b. The first ring 10a, executed in L-shape, has a first limb 10h extending parallel to the axis C, which has an outer surface 10o as well as an inner surface 10n. The second limb 10g extending radial to the axis C has an outer 7 surface 10p extending perpendicular to the axis C. The inner surface 101 is executed to extend conically and subtends in the radial direction an angle a-to the normal to the axis C.

In the present embodiment the second limb 10g is executed in such a manner that, with respect to the direction determined by the axis C, it is made relatively narrow at the first limb and broadens in the direction of the periphery, i.e.

toward the surface 10d. The cross-section of the second ring which is shown in Fig. 2a, is shaped in accordance with the shape of the two inner surfaces 101, 10n. The ring body has four surfaces, the surface facing the cylinder wall the surface 10q facing the chamber ring 8, as well as the two surfaces 10m, 10k facing the first ring 10a. The two last named surfaces 10m, 10k are executed to be adapted with respect to the first ring 10a in such a manner that for rings 10b placed one within the other the surfaces 10m, come to lie in a form-fitted manner on the two inner surfaces 101, 10n. Therefore the surface 10k is likewise made conical, to extend radially to the axis C at an angle of inclination a.

Fig. 3a shows a plan view onto the second ring-formed body with ring gap or butt joint 10f, which body is designated in the following as a second ring 10b. The ring body 10i has the ring gap 10f at the one side and a protrusion projecting toward the axis C at the side opposite this ring gap 10f. In the assembled piston ring 10 the second ring is placed over the first ring 10a while retaining the position shown in Figs. 3a, 3b so that the protrusion comes to lie in the ring gap 10e of the first ring 10a. By this means the second ring 10b is secured with respect to the first ring 10a against mutual rotation since the protrusion and the limb 10h restrict their relative movement. The protrusion 10k is advantageously made narrower in the peripheral direction than the width of the ring gap 10e so 8 that the first ring 10a retains a certain mobility in the peripheral direction at the ring gap 10e. Figs. 7a and 7b show a further exemplary embodiment of an execution of the rings 10a, 10b for the mutual securing against a rotation.

A

cylindrical fixing pin 10r which extends in the vertical direction is arranged at the limb 10g on the side of the first ring 10a lying opposite the ring gap 10e. When assembling the piston ring 10 the second ring 10b is laid over the first ring 10a, while maintaining the position illustrated in Figs. 7a, 7b, so that the fixing pin 10r comes to lie between the ring gap 10f of the second ring whereby the second ring 10b is secured with respect to the first ring 10a against a mutual rotation. In the assembled state the rings 10a, 10b can be inserted into the groove of a one-piece piston 2 by simultaneous spreading apart of the two ring parts as shown in Fig. 4 or into an assembled piston 2 without spreading apart as shown in Fig. An advantage of the piston ring 10 in accordance with the invention is to be seen in the fact that the subsurfaces 101, 10k, 10m of the two rings 10a, 10b remain lying one upon the other in a form-fitted manner over long periods of time, even during the operation of the piston ring 10. The two rings 10a, 10b are executed in such a manner that a direct action of the gas 9 under pressure on the subsurfaces 101, 10k, 10m is prevented as far as possible. The gas pressure 9 acting on the rings 10a, 10b normally acts at the ring gap 10f and exerts a force acting in the peripheral direction of the first ring 10b, which, for an angle x= 0, could lead to a lifting off of the first ring 10b from the second ring 10a so that the gas pressure would act directly on the subsurfaces 101, 10n, 10k, 10m. Such a direct action of the gas pressure on the subsurfaces 10m, 10k of the second ring 10b would result in a relatively rapid wear of the second ring 10b. In order to avoid this effect the ring in 9 accordance with the invention is executed in such a manner that a lifting off of the first ring 10b from the first ring is prevented. In accordance-with Fig. 4 the piston ring is pressed in the axial direction against the chamber ring 8 by the action of the gas 9a and in the radial direction against the wall of the cylinder 1 by the action of the gas 9b. The first ring 10a subjected to this pressure exerts corresponding forces on the second ring 10b. Due to the conical execution of the subsurfaces 101, 10k the forces acting due to the gas pressure cause an increased mutual wedging together of the two rings 10a, 10b so that the subsurfaces 10k, 101, 10n, 10m are pressed against one another more strongly. A direct action of the gas pressure on the subsurfaces 10k, 101, 10n, 10m is thereby prevented, which leads to a low wear of the first ring 10b, and a uniform wear of the two rings 10a, 10b, in particular of the subsurfaces 10c, 10d, and thus to a long lifetime of the piston ring There is a great number of possibilities for the design of the subsurfaces 10k, 101, 10n, 10m in such a way that a mutual wedging together occurs between rings 10a, 10b placed together and loaded by gas pressure with the result that the subsurfaces 10k, 101, 10n, 10m in mutual contact are additionally pressed against one another. Figures 6a, 6b show a cross-section through a first ring 10a as well as a ring of a further exemplary embodiment. Here the two subsurfaces 10m, 10n are executed to extend cylindrically, parallel to the axis C. The further subsurfaces 101, 10k are executed to extend in curved form in such a manner that they come to lie against one another in a form-fitted manner in the assembled piston ring The inner surface 101, 10k has an inclination in the direction extending radially to the axis C, with the angle i 10 between a tangent to the inner surface 101, 10k and the axis C amounting to about 90° in the region of the surface 10d and becoming increasingly acute in the direction of the limb i.e. adopting an angle which becomes smaller than 900.

The rings 10a, 10b are formed of a plastic, in particular of plastics such as polytetraflouorethylene (PTFE), a modified high-temperature polymer such as polyetheretherketone

(PEEK),

polyetherketone (PEK), polyimide polyphenylene sulphide (PPS), polybenzimidazole (PBI), polyamidimide (PAI) or a modified epoxy resin. The high-temperature polymers are plastics which are not capable of dry running in pure form, so that the above named plastics are usually filled with additional solid lubricants such as e.g. carbon, graphite, molybdenum disulphide or PTFE.

11 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Piston ring for a dry running piston compressor, consisting of a first and a second ring-shaped body with ring gaps, said rings being arranged concentric to one another with respect to an axis C, with the first ring having an essentially L-shaped cross-section, with a first limb extending in the direction of the axis C and a second limb extending radially outwardly relative to the axis C, and with the first limb having an inner surface and the second limb having an inner surface, with the inner surface of the second limb having a slope in the radial direction, and with the surfaces of the second ring which face the first ring lying in contact with the inner surfaces of the first ring in a form-fitted manner, and with the inner surface of the first ring extending in the radial direction while subtending an acute angle, i.e. an angle less than 900, with the axis, and with the rings consisting of a material in the group: polytetraflouorethylene

(PTFE),

modified high-temperature polymer such as polyetheretherketone

(PEEK),

polyetherketone (PEK), polyimide polyphenylene sulphide (PPS), polybenzimidazole (PBI), polyamidimide (PAl) or modified epoxy resin, with the possibility of these materials containing additional solid lubricants such as e.g.

carbon, graphite, molybdenum disulphide or PTFE.

2. Piston ring consisting of a first and second ring-shaped body with ring gaps, said rings each having at least two mutually touching subsurfaces, being :II: arranged to extend concentric to one another with respect to an axis, with the touching subsurfaces being arranged to be mutually form-fitting, and with the subsurfaces of each of the rings meeting at an acute angle in order to effect an increased mutual holding of the rings at the touching subsurfaces by a fluid lying in contact with the piston ring under pressure during an operating state, and with the piston ring being constructed of a plastic.

3. Piston ring in accordance with claim 1 or claim 2 characterised in that the i e s inner surface of the first ring is executed as a conically extending surface.

o

Claims

4. Piston ring in accordance with claim 1 or claim 2 characterised in that the inner surface of the first ring is executed as a surface extending in a curve in the radial direction. Piston ring in accordance with one of the claims 1 to 4 characterised in that the second ring has a part protruding in the radial direction towards the axis which engages into the ring gap of the first ring in order to prevent a mutual rotation of the two rings.
6. Piston ring in accordance with one of the claims 1 to 6 characterised in that the first ring of the piston ring is arranged in a piston towards the pressure side.
7. Dry running piston compressor with a piston ring in accordance with one of the claims 1 to 6.
8. Piston ring for a dry running piston compressor substantially as hereinbefore described with reference to the drawings. DATED this 24th day of May 1999 MASCHINENFABRIK SULZER-BURCKHARDT AG *SS* WATERMARK PATENT TRADEMARK ATTORNEYS S290 BURWOOD ROAD S HAWTHORN VICTORIA 3122 AUSTRALIA IAS:JPF:VRH DOC 27 AU7276096.WPC S* S S S* Abstract of disclosure Piston ring in particular for a piston compressor, consisting of a first and a second ring-shaped body with ring gaps (10e, 10f), said rings (10a, 10b) being arranged concentric to one another with respect to an axis C, with the first ring (10a) having an essentially L-shaped cross-section, with a first limb (10h) extending in the direction of the axis C and a second limb (10g) extending radially outward from the axis C, and with the first limb having an inner surface (10n) and the second limb having an inner surface (101), with the inner surface (101) of the second limb (10g) having a slope in the radial direction, and with the surfaces (10m, 10k) of the second ring (10b) which face the first ring (10a) lying in contact with the inner surfaces (10m, 101) of the first ring (10a) in a form-fitted manner. (Figs. 2a, 2b, 3a, 3b)