WO2012085870A1 - Method of manufacturing sealing rings for combustion engine pistons - Google Patents

Method of manufacturing sealing rings for combustion engine pistons Download PDF

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Publication number
WO2012085870A1
WO2012085870A1 PCT/IB2011/055879 IB2011055879W WO2012085870A1 WO 2012085870 A1 WO2012085870 A1 WO 2012085870A1 IB 2011055879 W IB2011055879 W IB 2011055879W WO 2012085870 A1 WO2012085870 A1 WO 2012085870A1
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WO
WIPO (PCT)
Prior art keywords
semi
finished product
stock
profile
machining
Prior art date
Application number
PCT/IB2011/055879
Other languages
French (fr)
Inventor
Lauro Mariani
Original Assignee
Sarl Maritime Trading Company
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Publication date
Application filed by Sarl Maritime Trading Company filed Critical Sarl Maritime Trading Company
Publication of WO2012085870A1 publication Critical patent/WO2012085870A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16J—PISTONS; CYLINDERS; SEALINGS
    • F16J9/00—Piston-rings, e.g. non-metallic piston-rings, seats therefor; Ring sealings of similar construction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
    • B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
    • B23P15/06—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass piston rings from one piece

Definitions

  • the present invention relates to a method of manufacturing sealing rings, such as compression piston rings and oil scraper rings for combustion engine pistons.
  • a machining step foresees providing a galvanic coating on at least part of the outer side profile of the rings, which must then be subjected to later grinding.
  • Said coating is intended to define in use the sliding surface of the rings themselves.
  • the sliding surface engages in use the cylinder sleeve once the sealing rings are in place in their seats on the piston.
  • said galvanic coating once ground, should provide a thickness as precise and uniform as possible, remaining within very limited machining tolerances both dimensional and geometric. With current machining methods, however, said tolerances can be met only with very high production costs and with operational complications, however, that do not mitigate the problem of the high number of rejects.
  • the aim of the present invention is to overcome the drawbacks of the prior art, in particular by providing a method to produce piston rings for large engines, marine engines in particular, that is of easy and fast execution, which allows a significant decrease of the production costs and above all, guarantees obtaining narrow tolerances corresponding particularly to the galvanic coating, thus drastically reducing the number of rejects.
  • the method of the invention starts from a semifinished product obtained from fusion, which is mechanically machined by stock-removing.
  • the method of the invention differs from the known art, for the combination of a series of specially selected machining steps.
  • the first semi-finished product is subjected to a first step of mechanical machining by stock-removing at both the outer and inner side walls to obtain at least a second semifinished product consisting of an inner central core of the first semi-finished product, which is revealed by said machining, and which has a predetermined circumferential profile in radial section; at the end of said first step of stock-removing machining, respective reference surfaces are further obtained, at opposite ends of the second semi-finished product ;
  • a second step of stock-removing machining during which a profile is obtained in the axial direction on said wall, which is adapted to define the radially outermost profile of a plurality of sealing rings to be obtained, axially arranged side by side, substantially equally spaced out with respect to one another by means of segments of the second semi-finished product having a smaller transversal size;
  • an inner side wall of the second semi ⁇ finished product is subjected to a third step of stock- removing machining during which a profile is obtained in the axial direction on said wall, a profile adapted to define the radially innermost profile of a plurality of sealing rings to be obtained, and mating with the previously obtained . profile on the outer side wall of the second semi-finished product.
  • the centering of the second semi-finished product is obtained by using the same previously obtained reference surfaces as locators, which are preserved intact during all said machining steps .
  • the second semi-finished product is cut in the longitudinal direction (if not already done) in order to provide the required tangential load and in the direction perpendicular to the side walls thereof and at said segments of smaller transversal size thereof, thus obtaining a plurality of sealing rings. These are then subjected only to a finishing operation.
  • the second semi-finished product is forced to take and/or maintain a cylindrical shape, and a predetermined axial pressure is applied thereto, by preferably acting upon the reference surfaces.
  • FIG. 1 illustrates a starting semi-finished product used by the method according to the invention and a first step, preferred but optional, of the method itself;
  • Figure 2 illustrates in Figure 2a a second step of the method of the invention and in Figure 2b the final result of the step itself in case piston rings are to be produced;
  • FIG. 8 and 9 illustrate the same step of the method according to the invention, to be carried out after the step of Figures 6 and 7, in the case of producing piston rings and oil scraper rings, respectively, and
  • FIG. 10 schematically illustrates a final step of the method according to the invention.
  • the method according to the invention has the aim of creating in a simple, rapid and economical, but nevertheless highly accurate way, sealing rings 1 for pistons of large internal combustion engines, marine engines in particular (known and not shown for simplicity) .
  • the sealing rings 1 may consist of piston rings lb, which are characterized by a particular circumferential profile, or of oil scraper rings lc, which, instead, present a circular circumferential profile. According to the known art, said rings are obtained by casting and mechanical machining, individually.
  • the sealing rings 1 are, instead, produced in groups, starting from a single semi-finished product 2 ( Figure 1) , which is obtained by static or centrifugal casting of cast iron, lamellar or spheroidal in the form of an annular cylindrical bushing having a maximum size in the direction of a symmetry axis thereof, referred to as A, equal to a relatively large multiple (e.g. 10 or more times) of the height/thickness (measured/or in the direction of axis A) of the sealing rings to be obtained.
  • Figure 1 which is obtained by static or centrifugal casting of cast iron, lamellar or spheroidal in the form of an annular cylindrical bushing having a maximum size in the direction of a symmetry axis thereof, referred to as A, equal to a relatively large multiple (e.g. 10 or more times) of the height/thickness (measured/or in the direction of axis A) of the sealing rings to be obtained.
  • the bushing forming the first semi-finished product 2 is defined along a direction parallel to the A axis by opposite side walls, a radially inner wall3 and a radially outer wall 4, respectively, having in the non limitative example shown cylindrical symmetry.
  • said semifinished product 2 is obtained by a method described in the Italian patent application entitled "MANUFACTURING METHOD OF SEALING RINGS FOR COMBUSTION ENGINE PISTONS" deposited on the same date by the same Applicant.
  • First of all the semi-finished product 2 is subjected to a first step of mechanical machining by stock-removing, turning in this case, illustrated schematically in Figure 2, at its outer side 4 and inner side 3 walls to obtain, in the end, a second semi-finished product 5, shown hatched in Figures 1 and 2a, consisting of an inner core of the semi-finished product 2, which is revealed by said first turning machining.
  • the metal material (cast iron) forming the inner core when the semi-finished product 2 is obtained by centrifugal casting, presents a very high purity, which as a start already contributes to significantly raise the quality of the semi ⁇ finished product 5 upon which the next machining takes place.
  • the semi-finished product 5 so obtained presents, in radial section, a predetermined circumferential profile; said circumferential profile, if the object is to obtain sealing rings made by oil scraper rings lc, is substantially circular, conversely, if the sealing rings to be obtained are piston rings lb, a semi-finished product 5b (Figure 2b) is obtained, whose predetermined circumferential profile, shown in radial section in Figure 2b, has the same ovaled heart-like shape that is typical of the piston rings and that may already be present in the semi-finished product 2, or that is obtained, starting from the walls with cylindrical symmetry, by eccentrically turning the semi-finished product 2 in a known way for the skilled in the art, for example, by using a lathe whose respective turning tools 9, 10 are coupled to a cam that reproduce the profile to be obtained.
  • the semifinished product 5 always presents a tubular sleeve shape, and is therefore delimieted by an outer side wall 23 and by an inner side wall 24; just in case of semi-finished products 5b said side walls 23 and 24 are not of perfectly cylindrical shape, while they are in the case of semi-finished products 5 destined to obtain oil scraper rings lc.
  • a through radial slot 12 (i.e. that breaks the circumferential continuity of the semifinished product 5) is produced by means of a suitable cutting tool 11, , said slot being of prefixed circumferential width in order to obtain the required tangential load.
  • said slot 12 can also be practiced later, as it will be seen.
  • the semifinished product 2 before performing the first step of machining by stock-removing can be cut in half or into several parts, perpendicularly to its side walls 3 and 4, using a tool 12, in order to divide it into two or more semi-finished products (2' and 2" mirror image identical, in the example shown) .
  • respective grooves 15 are obtained (of which only one, on the end 13, is illustrated in Figure 1) adapted to receive during the first step of machining by stock-removing shown in Figure 2, a respective support equipment 16.
  • the equipment 16 is adapted to overhangingly receive, as non limitatively shown in Figure 2a, each half 2', 2" of the semi-finished product 2.
  • the first step of machining by stock-removing, of figure 2 is performed in sequence on both halves 2' and 2"; in Figure 2a is shown for simplicity only the machining of the first half 2", being identical to the machining of the half 2'.
  • the machining step of Figure 2a is carried out on the inner semi- finished product 2 retained by equipment 16 at both opposing ends 13, 14 provided with grooves 15.
  • respective reference surfaces 20, 21 and 22 are obtained, according to a fundamental aspect of the invention, at the opposite ends 18, turning, which reference surfaces are shown in Figures 3 and 4, in relation to a semi-finished product 5b obtained from the half 2' ( Figure 3), the semi-finished product 5b obtainable from the half 2" being machined in an identical way and, therefore, not shown for simplicity; and in relation to a semi-finished product 5 obtained from a semi-finished product 2 uncut, respectively.
  • a second machining step by stock-removing is carried out, in this case by turning by means of a tool 25, during which a profile 26 is obtained on the wall 23, operating progressively in axial direction, which profile is adapted to define the sequence of radially outer profiles of a plurality of sealing rings 1 to be obtained, axially arranged side by side and substantially equally spaced out with respect to one another by means of segments 27 of the semi-finished product 5 having transversal size (i.e., measure perpendicular to the axis A) lower than those of the rest of the semi-finished product 5 itself.
  • a step of depositing a galvanic coating 28 of a hard metal or metal alloy (preferably chrome) on the profile 26 is carried out, covering also the segments 27.
  • Said step which is carried out in a substantially known way, electrically and mechanically connecting the semi- finished product 5 to a metal counter electrode made of a support plate 30 connected through a circuit 31 to a didposable electrode 32, is carried out, according to an aspect of the invention, centering the semi-finished product 5 on the respective support equipment, consisting of plate 30 and of a sleeve 33 integrally and axially overhangigly held by plate 30, by the same reference surfaces 20, 21 (or 22) obtained during the machining step of figure 2.
  • care must be taken to protect the reference surfaces 20, 21 (or 22) from being affected by the coating 28 through at least one appropriate masking, in the case shown offered by the sleeve 33, which is purposely built in a non- conductive material, such as a synthetic plastic material.
  • Figure 5 shows this step with respect to the semi-finished product 5b of figure 3, but it is clear that the above applies identically to the semi-finished product 5 of Figure 4, simply referring to the conical reference surfaces 22, instead of the flat reference surfaces 20, 21.
  • a grinding step is carried out ( Figures 6 and 7) wherein the semi-finished product 5 or 5b is centered on the grinding axis by means of equipment.66 (semi-finished product 5) or 60 (semi-finished product 5b) , as will be described in more derails below, equipment that couple with the reference surfaces 20, 21 (equipment 60) or 22 (equipment 66) ; during said step, the galvanic coating 28 is removed. Is removed, in particular, the galvanic coating from over the whole profile 26, with the exception of respective crests 34 thereof designed in use to define the sliding surfaces of the sealing rings 1 to be obtained.
  • the inner side wall 24 of the semi-finished product 5 is subjected to a third step of machining by stock-removing, in thecase shown consisting of a boring, illustrated schematically in Figures 8 and 9, both in the case of semi-finished products 5b obtained from the half 2', for obtaining piston rings lb, and in the case of semi-finished products 5 obtained from semifinished products 2 uncut, for obtaining oil scraper rings lc.
  • a profile 36 is obtained in the axial direction on the wall 24, which profile isadapted to define the sequence of radially inner profiles of a plurality of sealing rings 1 to be obtained, profile 36 which mates with the profile 26 previously obtained on the outer side wall 23.
  • sealing rings 1 to be obtained are already all present, all attached one another, as a block, by segments 27, and should receive just the normal final finishing step.
  • the centering of the semi-finished product 5 is obtained on the respective machining equipment, by using, as locators, always the same reference surfaces 20, 21 and 22 previously obtained, which are kept intact during all said machining steps.
  • said reference surfaces 20, 21 and 22 are also used for centering the semi-finished product 5 during the galvanic coating of figure 5. In this way, the dimensional accuracy with which the coatings 28 are obtained on the crests 34 is very high with a guarantee of uniformity in the thickness of the coating 28.
  • sealing rings 1 To complete the machining of sealing rings 1, at this point, it is sufficient to cut, at the end of the third machining step by stock-removing of Figures 8 and 9, the semi-finished product 5 in a longitudinal direction to obtain also a slot 12 thereon (if not done previously) , in order to obtain the required tangential load, and, then, cut both the semifinished product 5 and 5b in the direction perpendicular to the side walls 23 and 24 at segments 27 of lower transversal size, obtaining a plurality of sealing rings 1, separated one from the other that, successively ( Figure 10) are only subjected to a finishing machining, consisting of a centerless grinding and/or lapping, executed by traditional techniques.
  • a finishing machining consisting of a centerless grinding and/or lapping
  • the high precision and the high speed processing obtainable on the final product (ring 1) are essentially due to the described "block" machining technique.
  • This technrque is feasible, according to the invention, because, at least during the second machining step by stock-removing of Figures 3 and 4 and .
  • the grinding step of Figures 6 and 7, the semi-finished product 5b is forced to take a cylindrical shape and because on both semi-finished product 5, 5b, a predetermined axial pressure P is applied (indicated by the arrow in the figures cited) , preferably acting upon the reference surfaces 20, 21 (semi-finished product 5b) and 22 (semi-finished product 5) .
  • the semi-finished product 5b instead shows in the radial cross-sectional the profile of Figure 2b; the semi-finished product 5b is therefore forced to take a cylindrical shape during all the steps of machining by stock- removing and grinding circumferentially forcing the same, or at least its opposing ends (18 and 50, in the example shown in non limitative way in Figures 3 and 6) , within respective tubular cylindrical equipments 60 ( Figures 3 and 6) and 61 ( Figure 8) of such a diameter to reduce the circumferential width of the slot 12 so as to lead the circumferential profile of the semi-finished product 5b, by elastic deformation, to abandon the ovaled heart-like shape and take a circular shape.
  • the force applied to the semi-finished product 5b is such that the circumferential size of the slot 12 remains between 2 and 3 tenths of mm and respective longitudinal edges 62 of the slot 12 remain parallel to each other.
  • the axial pressure P is applied by way of tie rods 65 and the equipments 60 consist of cup-shaped bodies adapted to receive the ends 18 (or 19) and 50, the latter being formed by the cut area through which the semifinished product 2 has been divided into semi-finished products 2', 2" which then give rise to the semi-finished products 5b.
  • equipment 66 are used, consisting of discs with a conical surface, which are centered on the conical surfaces 22.
  • the semi-finished product 5 (5b) is forced to take (or keep) a cylindrical shape and to it is applied, in particular at least at one end thereof, a predetermined axial pressure P also during the third step of machining by stock- removing performed on the wall 24 ( Figures 8 and 9) .
  • the semi-finished product 5b is inserted from the side of the profile 26 already completed, within a tool 61, formed by a tubular sleeve longitudinally opened, which, at a lower (in Figure 8 the axis A is arranged vertically) end thereof rests in part on a shoulder 70 obtained on the end (18 in this case shown) provided with the reference surfaces 20, 21 and in part on a tool 72 consisting of a annular plate with radial L section, which surrounds the end 18 and is centered on the surface 20; the opposite end of the bushing 61 is pressed by an annular counter-plate 74 with radial L section, which is connected to the plate 72 by a tie-rod 75 for the application of the axial pressure P to the semifinished product 5b and, in particular, at its lower end (the end 18 in the case illustrated) through the relative flat reference surface 21.
  • a tool 61 formed by a tubular sleeve longitudinally opened, which, at a lower (in Figure 8 the axis A is arranged vertical
  • the semi-finished product 5 (5b) is kept at the reference surfaces 20, 21 or 22; this is at the opposing ends 18, 19 thereof during the second step of machining by stock- removing of figures 3, 4 and the grinding step of figures 6, 7, applying to both ends of the semi-finished product (18, 19 for the semi-finished product 5, 18 - or 19 - and 50 for the semi-finished product 5b) , the axial pressure P.
  • the semifinished product 5 (5b) is overhangingly held at a single end, respectively, 18 (in the example shown in Figure 8) or 19 (case not shown for simplicity and in any case dual of that shown in Figures 8 and 9) , always applying a respective axial pressure P to the reference surfaces 21 (semi-finished product 5b) and, respectively, 22 (semi-finished product 5) of said end.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Sealing Devices (AREA)
  • Compressor (AREA)
  • Pistons, Piston Rings, And Cylinders (AREA)

Abstract

Method for obtaining sealing rings (1) such as piston rings and engine oil scraper rings: a first annular cylindrical semi-finished product (2) obtained by centrifugal casting of cast iron is cut in half or into several parts, perpendicularly to its side walls (3,4), is turned on said walls and at its opposite ends (13,14) to obtain a second semi-finished product (5) consisting of an inner central core of the first and having in radial section a predetermined profile, provided at its opposite ends (18,19) with respective reference surfaces (20,21;22) in the case of piston rings, the predetermined radial profile is obtained by eccentric turning and has an ovaled heart-like shape and on the entire length of the second semi-finished product a radial through slot (12) is obtained; always using the same reference surfaces (20,21;22), obtained previously, for centering and imparting to the second semi-finished product (5) a cylindrical shape while applying an axial pressure (P), an outer side wall (23) thereof is turned, chrome-plated and ground and, successively, an inner side wall (24) thereof is also machined, finally the second semi-finished product (5) is cut in a direction perpendicular to its side walls (23,24) obtaining a plurality of sealing rings (1) that are subjected to finishing.

Description

"METHOD OF MANUFACTURING SEALING RINGS FOR COMBUSTION ENGINE PISTONS"
TECHNICAL FIELD
The present invention relates to a method of manufacturing sealing rings, such as compression piston rings and oil scraper rings for combustion engine pistons.
BACKGROUND ART
It is known that such mechanical parts are nowadays made of cast iron, by so-called "cluster" casting, obtaining individual rings joined by a single riser to form, in fact, a "cluster" of ring-like semi-finished products and substantially already having the profile of the sealing rings to be obtained, and then by machining, which takes place individually, ring by ring.
This method, if on one hand allows forming the rings destined to form the piston rings of the engine already with the particular circumferential "ovaled heart-like shape" profile that characterizes them (instead of a circular profile) , a profile that will allow the rings to later assume, in use, a substantially circular shape but remaining elastically preloaded, however, presents several drawbacks, such as long execution times, high operational complexity and, above all, considerable difficulty in maintaining a uniform standard of quality, which leads to a relatively high number of rejects, which significantly raise the final product cost.
In particular, a machining step foresees providing a galvanic coating on at least part of the outer side profile of the rings, which must then be subjected to later grinding. Said coating is intended to define in use the sliding surface of the rings themselves. The sliding surface engages in use the cylinder sleeve once the sealing rings are in place in their seats on the piston. To ensure good performance of the rings in use, said galvanic coating, once ground, should provide a thickness as precise and uniform as possible, remaining within very limited machining tolerances both dimensional and geometric. With current machining methods, however, said tolerances can be met only with very high production costs and with operational complications, however, that do not mitigate the problem of the high number of rejects.
DISCLOSURE OF INVENTION
The aim of the present invention is to overcome the drawbacks of the prior art, in particular by providing a method to produce piston rings for large engines, marine engines in particular, that is of easy and fast execution, which allows a significant decrease of the production costs and above all, guarantees obtaining narrow tolerances corresponding particularly to the galvanic coating, thus drastically reducing the number of rejects.
According to the invention is thus provided a method for producing sealing rings for pistons of large combustion engines, particularly marine engines, as defined by claim 1.
In particular, the method of the invention starts from a semifinished product obtained from fusion, which is mechanically machined by stock-removing.
The method of the invention, however, differs from the known art, for the combination of a series of specially selected machining steps.
First of all, starting from a single first axially developing semi-finished product equal to a considerable multiple (e.g. ten or more times) of the height of the piston rings to be obtained, rather than from a plurality of ring-like semi- finished products, as in the known art, which single semifinished product is obtained by centrifugal casting, or by static casting of cast iron in the form of an annular bushing having cylindrical or ovaled heart-like shape, and having a maximum size in the direction of one of its axis of symmetry parallel to which the bushing forming the first semi-finished product is delimited by opposite, radially inner and radially outer side walls, respectively.
Then the first semi-finished product is subjected to a first step of mechanical machining by stock-removing at both the outer and inner side walls to obtain at least a second semifinished product consisting of an inner central core of the first semi-finished product, which is revealed by said machining, and which has a predetermined circumferential profile in radial section; at the end of said first step of stock-removing machining, respective reference surfaces are further obtained, at opposite ends of the second semi-finished product ;
Then, subsequently and sequentially subjecting an outer side wall of the second semi-finished product to:
- a second step of stock-removing machining, during which a profile is obtained in the axial direction on said wall, which is adapted to define the radially outermost profile of a plurality of sealing rings to be obtained, axially arranged side by side, substantially equally spaced out with respect to one another by means of segments of the second semi-finished product having a smaller transversal size;
- a step of depositing a galvanic coating of a hard metal or metal alloy upon said profile;
- a step of grinding during which part of said galvanic coating is removed.
Still successively, an inner side wall of the second semi¬ finished product is subjected to a third step of stock- removing machining during which a profile is obtained in the axial direction on said wall, a profile adapted to define the radially innermost profile of a plurality of sealing rings to be obtained, and mating with the previously obtained . profile on the outer side wall of the second semi-finished product. According to the main aspect of the invention, during at least the steps of stock-removing machining and grinding, the centering of the second semi-finished product is obtained by using the same previously obtained reference surfaces as locators, which are preserved intact during all said machining steps .
Finally, at the end of the third machining step by stock- removing, the second semi-finished product is cut in the longitudinal direction (if not already done) in order to provide the required tangential load and in the direction perpendicular to the side walls thereof and at said segments of smaller transversal size thereof, thus obtaining a plurality of sealing rings. These are then subjected only to a finishing operation.
According to another aspect of the invention, moreover, at least during the second step of mechanical stock-removing machining and the step of grinding, the second semi-finished product is forced to take and/or maintain a cylindrical shape, and a predetermined axial pressure is applied thereto, by preferably acting upon the reference surfaces.
In this way, high precision can be obtained, particularly in correspondence with the galvanic coating, remaining easily within tolerances well below a tenth of mm. In addition, the machining sequence and the various processing steps, are greatly simplified compared to the known art, so leading, together with a drastic reduction of waste, to a significant reduction of production costs.
BRIEF DESCRIPTION OF THE DRAWINGS Additional features and advantages of the present invention will appear clear from the description that follows of a non- limitative embodiment thereof, carried out with reference to the figures of the attached drawings, wherein:
- Figure 1 illustrates a starting semi-finished product used by the method according to the invention and a first step, preferred but optional, of the method itself;
Figure 2 illustrates in Figure 2a a second step of the method of the invention and in Figure 2b the final result of the step itself in case piston rings are to be produced;
- Figures 3 and 4 show the same step of the method according to the invention in the case of producing piston rings and oil scraper rings, respectively;
- Figure 5 schematically illustrates a further step of the method according to the invention;
- Figures 6 and 7 illustrate the same step of the method according to the invention, to be carried out after the step of Figure 5, in the case of producing piston rings and oil scraper rings, respectively;
- Figures 8 and 9 illustrate the same step of the method according to the invention, to be carried out after the step of Figures 6 and 7, in the case of producing piston rings and oil scraper rings, respectively, and
- Figure 10 schematically illustrates a final step of the method according to the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to Figures 1 to 10, the method according to the invention has the aim of creating in a simple, rapid and economical, but nevertheless highly accurate way, sealing rings 1 for pistons of large internal combustion engines, marine engines in particular (known and not shown for simplicity) . The sealing rings 1 may consist of piston rings lb, which are characterized by a particular circumferential profile, or of oil scraper rings lc, which, instead, present a circular circumferential profile. According to the known art, said rings are obtained by casting and mechanical machining, individually.
According to a first aspect of the invention, the sealing rings 1 are, instead, produced in groups, starting from a single semi-finished product 2 (Figure 1) , which is obtained by static or centrifugal casting of cast iron, lamellar or spheroidal in the form of an annular cylindrical bushing having a maximum size in the direction of a symmetry axis thereof, referred to as A, equal to a relatively large multiple (e.g. 10 or more times) of the height/thickness (measured/or in the direction of axis A) of the sealing rings to be obtained. The bushing forming the first semi-finished product 2 is defined along a direction parallel to the A axis by opposite side walls, a radially inner wall3 and a radially outer wall 4, respectively, having in the non limitative example shown cylindrical symmetry. In particular, said semifinished product 2 is obtained by a method described in the Italian patent application entitled "MANUFACTURING METHOD OF SEALING RINGS FOR COMBUSTION ENGINE PISTONS" deposited on the same date by the same Applicant.
First of all the semi-finished product 2 is subjected to a first step of mechanical machining by stock-removing, turning in this case, illustrated schematically in Figure 2, at its outer side 4 and inner side 3 walls to obtain, in the end, a second semi-finished product 5, shown hatched in Figures 1 and 2a, consisting of an inner core of the semi-finished product 2, which is revealed by said first turning machining. The metal material (cast iron) forming the inner core, when the semi-finished product 2 is obtained by centrifugal casting, presents a very high purity, which as a start already contributes to significantly raise the quality of the semi¬ finished product 5 upon which the next machining takes place.
At the end of this first machining step shown in Figure 2, in addition, the semi-finished product 5 so obtained presents, in radial section, a predetermined circumferential profile; said circumferential profile, if the object is to obtain sealing rings made by oil scraper rings lc, is substantially circular, conversely, if the sealing rings to be obtained are piston rings lb, a semi-finished product 5b (Figure 2b) is obtained, whose predetermined circumferential profile, shown in radial section in Figure 2b, has the same ovaled heart-like shape that is typical of the piston rings and that may already be present in the semi-finished product 2, or that is obtained, starting from the walls with cylindrical symmetry, by eccentrically turning the semi-finished product 2 in a known way for the skilled in the art, for example, by using a lathe whose respective turning tools 9, 10 are coupled to a cam that reproduce the profile to be obtained. In all cases, the semifinished product 5 always presents a tubular sleeve shape, and is therefore delimieted by an outer side wall 23 and by an inner side wall 24; just in case of semi-finished products 5b said side walls 23 and 24 are not of perfectly cylindrical shape, while they are in the case of semi-finished products 5 destined to obtain oil scraper rings lc.
Moreover, after completing the first step of machining by stock-removing, and thus, obtaining the desired profile, on the entire length of the semi-finished product 5 (5b in the case illustrated in Figure 2b) a through radial slot 12 (i.e. that breaks the circumferential continuity of the semifinished product 5) is produced by means of a suitable cutting tool 11, , said slot being of prefixed circumferential width in order to obtain the required tangential load. In the case of walls 23, 24 with cylindrical symmetry (semi-finished product 5 destined to obtain oil scraper rings), said slot 12 can also be practiced later, as it will be seen. Preferably, as shown schematically in Figure 1, the semifinished product 2, before performing the first step of machining by stock-removing, shown in Figure 2, can be cut in half or into several parts, perpendicularly to its side walls 3 and 4, using a tool 12, in order to divide it into two or more semi-finished products (2' and 2" mirror image identical, in the example shown) .
At the same time with the above cutting operation, or as an alternative thereof, on respective opposite ends 13 and 14 of the semi-finished product 2 respective grooves 15 are obtained (of which only one, on the end 13, is illustrated in Figure 1) adapted to receive during the first step of machining by stock-removing shown in Figure 2, a respective support equipment 16. In the event in which the semi-finished product 2 is cut in half (or several parts) , the equipment 16 is adapted to overhangingly receive, as non limitatively shown in Figure 2a, each half 2', 2" of the semi-finished product 2. In this case, the first step of machining by stock-removing, of figure 2 is performed in sequence on both halves 2' and 2"; in Figure 2a is shown for simplicity only the machining of the first half 2", being identical to the machining of the half 2'. Obviously, if the semi-finished product 2 is not cut, the machining step of Figure 2a is carried out on the inner semi- finished product 2 retained by equipment 16 at both opposing ends 13, 14 provided with grooves 15.
At the end of the first step of mechanical machining by stock- removing, of figure 2, in addition, also those that were the opposite ends 13, 14 of the semi-finished product 2 are cut with a tool 17, so as to expose the corresponding opposite ends 18, 19 of the semi-finished product 5.
Again at the end of said first step of Figure 2, respective reference surfaces 20, 21 and 22, are obtained, according to a fundamental aspect of the invention, at the opposite ends 18, turning, which reference surfaces are shown in Figures 3 and 4, in relation to a semi-finished product 5b obtained from the half 2' (Figure 3), the semi-finished product 5b obtainable from the half 2" being machined in an identical way and, therefore, not shown for simplicity; and in relation to a semi-finished product 5 obtained from a semi-finished product 2 uncut, respectively. In particular, in the case of obtaining piston rings lb the next machining step is carried out as shown in Figure 3, proceeding in sequence on semi-finished products 5b obtained from both halves 2' and 2", obtaining on the ends 18 (figure 3) and 19 (for the semi-finished product 5b obtained from the half 2", not illustrated) annular reference surfaces 20 and 21 arranged at 90° with respect to each other, obtained on the outer side wall 23 of the semi-finished product 5 and on the front face thereof delimiting the respective end 18, 19. In the case of obtaining oil scraper rings lc, instead, respective reference surfaces 22, annular and conical, are obtained, on both ends 18, 19,, by turning the ends 18, 19 at the inner side wall 24 of the semi-finished product 5. At this point, the outer side wall 23 of the semi-finished product 5 is subjected, subsequently and sequentially, to the following machining steps.
First of all (Figures 3 and 4) a second machining step by stock-removing is carried out, in this case by turning by means of a tool 25, during which a profile 26 is obtained on the wall 23, operating progressively in axial direction, which profile is adapted to define the sequence of radially outer profiles of a plurality of sealing rings 1 to be obtained, axially arranged side by side and substantially equally spaced out with respect to one another by means of segments 27 of the semi-finished product 5 having transversal size (i.e., measure perpendicular to the axis A) lower than those of the rest of the semi-finished product 5 itself. Successively, (Figure 5) a step of depositing a galvanic coating 28 of a hard metal or metal alloy (preferably chrome) on the profile 26 is carried out, covering also the segments 27. Said step, which is carried out in a substantially known way, electrically and mechanically connecting the semi- finished product 5 to a metal counter electrode made of a support plate 30 connected through a circuit 31 to a didposable electrode 32, is carried out, according to an aspect of the invention, centering the semi-finished product 5 on the respective support equipment, consisting of plate 30 and of a sleeve 33 integrally and axially overhangigly held by plate 30, by the same reference surfaces 20, 21 (or 22) obtained during the machining step of figure 2. In addition, in said step, care must be taken to protect the reference surfaces 20, 21 (or 22) from being affected by the coating 28 through at least one appropriate masking, in the case shown offered by the sleeve 33, which is purposely built in a non- conductive material, such as a synthetic plastic material.
Figure 5 shows this step with respect to the semi-finished product 5b of figure 3, but it is clear that the above applies identically to the semi-finished product 5 of Figure 4, simply referring to the conical reference surfaces 22, instead of the flat reference surfaces 20, 21. Finally, a grinding step is carried out (Figures 6 and 7) wherein the semi-finished product 5 or 5b is centered on the grinding axis by means of equipment.66 (semi-finished product 5) or 60 (semi-finished product 5b) , as will be described in more derails below, equipment that couple with the reference surfaces 20, 21 (equipment 60) or 22 (equipment 66) ; during said step, the galvanic coating 28 is removed. Is removed, in particular, the galvanic coating from over the whole profile 26, with the exception of respective crests 34 thereof designed in use to define the sliding surfaces of the sealing rings 1 to be obtained.
Next, completed the machining of the outer side wall 23, the inner side wall 24 of the semi-finished product 5 is subjected to a third step of machining by stock-removing, in thecase shown consisting of a boring, illustrated schematically in Figures 8 and 9, both in the case of semi-finished products 5b obtained from the half 2', for obtaining piston rings lb, and in the case of semi-finished products 5 obtained from semifinished products 2 uncut, for obtaining oil scraper rings lc. During said boring step with a tool 35, a profile 36 is obtained in the axial direction on the wall 24, which profile isadapted to define the sequence of radially inner profiles of a plurality of sealing rings 1 to be obtained, profile 36 which mates with the profile 26 previously obtained on the outer side wall 23.
Practically, at the end of the boring machining step, sealing rings 1 to be obtained are already all present, all attached one another, as a block, by segments 27, and should receive just the normal final finishing step.
According to the main aspect of the invention, during at least the steps of machining by stock-removing of figures 3, 4 and 8, 9 and of grinding of Figures 6 and 7 the centering of the semi-finished product 5 is obtained on the respective machining equipment, by using, as locators, always the same reference surfaces 20, 21 and 22 previously obtained, which are kept intact during all said machining steps. As already seen, said reference surfaces 20, 21 and 22 are also used for centering the semi-finished product 5 during the galvanic coating of figure 5. In this way, the dimensional accuracy with which the coatings 28 are obtained on the crests 34 is very high with a guarantee of uniformity in the thickness of the coating 28.
To complete the machining of sealing rings 1, at this point, it is sufficient to cut, at the end of the third machining step by stock-removing of Figures 8 and 9, the semi-finished product 5 in a longitudinal direction to obtain also a slot 12 thereon (if not done previously) , in order to obtain the required tangential load, and, then, cut both the semifinished product 5 and 5b in the direction perpendicular to the side walls 23 and 24 at segments 27 of lower transversal size, obtaining a plurality of sealing rings 1, separated one from the other that, successively (Figure 10) are only subjected to a finishing machining, consisting of a centerless grinding and/or lapping, executed by traditional techniques.
The high precision and the high speed processing obtainable on the final product (ring 1) are essentially due to the described "block" machining technique. This technrque is feasible, according to the invention, because, at least during the second machining step by stock-removing of Figures 3 and 4 and . the grinding step of Figures 6 and 7, the semi-finished product 5b is forced to take a cylindrical shape and because on both semi-finished product 5, 5b, a predetermined axial pressure P is applied (indicated by the arrow in the figures cited) , preferably acting upon the reference surfaces 20, 21 (semi-finished product 5b) and 22 (semi-finished product 5) .
In particular, while the semi-finished product 5 already has a cylindrical shape, which must simply be maintained by way of appropriate equipment, the semi-finished product 5b instead shows in the radial cross-sectional the profile of Figure 2b; the semi-finished product 5b is therefore forced to take a cylindrical shape during all the steps of machining by stock- removing and grinding circumferentially forcing the same, or at least its opposing ends (18 and 50, in the example shown in non limitative way in Figures 3 and 6) , within respective tubular cylindrical equipments 60 (Figures 3 and 6) and 61 (Figure 8) of such a diameter to reduce the circumferential width of the slot 12 so as to lead the circumferential profile of the semi-finished product 5b, by elastic deformation, to abandon the ovaled heart-like shape and take a circular shape. In addition, during at least the second step of machining by stock-removing of figure 3 and the grinding step of Figure 6, the force applied to the semi-finished product 5b is such that the circumferential size of the slot 12 remains between 2 and 3 tenths of mm and respective longitudinal edges 62 of the slot 12 remain parallel to each other.
In the schematic figures which in a non limitative way illustrate the invention, the axial pressure P is applied by way of tie rods 65 and the equipments 60 consist of cup-shaped bodies adapted to receive the ends 18 (or 19) and 50, the latter being formed by the cut area through which the semifinished product 2 has been divided into semi-finished products 2', 2" which then give rise to the semi-finished products 5b. On the semi-finished products 5 derived from the uncut semi-finished product 2, equipment 66 are used, consisting of discs with a conical surface, which are centered on the conical surfaces 22.
Preferably, the semi-finished product 5 (5b) is forced to take (or keep) a cylindrical shape and to it is applied, in particular at least at one end thereof, a predetermined axial pressure P also during the third step of machining by stock- removing performed on the wall 24 (Figures 8 and 9) . In this case, the semi-finished product 5b is inserted from the side of the profile 26 already completed, within a tool 61, formed by a tubular sleeve longitudinally opened, which, at a lower (in Figure 8 the axis A is arranged vertically) end thereof rests in part on a shoulder 70 obtained on the end (18 in this case shown) provided with the reference surfaces 20, 21 and in part on a tool 72 consisting of a annular plate with radial L section, which surrounds the end 18 and is centered on the surface 20; the opposite end of the bushing 61 is pressed by an annular counter-plate 74 with radial L section, which is connected to the plate 72 by a tie-rod 75 for the application of the axial pressure P to the semifinished product 5b and, in particular, at its lower end (the end 18 in the case illustrated) through the relative flat reference surface 21.
Vice versa (Figure 9) , in the case of the semi-finished product 5 for obtaining the rings lc, the end 18 is centered on a plate with a conical edge 80 and is pushed against the same with pressure P, in particular at the reference surface 22, by way of an L bracket 81 provided with a special tie-rod 82, wghich said tie-rod binds the bracket 81 to a work platform 83 of the boring machine.
Thus, in all machining steps, whether grinding, boring or turning steps, the semi-finished product 5 (5b) is kept at the reference surfaces 20, 21 or 22; this is at the opposing ends 18, 19 thereof during the second step of machining by stock- removing of figures 3, 4 and the grinding step of figures 6, 7, applying to both ends of the semi-finished product (18, 19 for the semi-finished product 5, 18 - or 19 - and 50 for the semi-finished product 5b) , the axial pressure P.
Instead, in the final machining on the wall 24, the semifinished product 5 (5b) is overhangingly held at a single end, respectively, 18 (in the example shown in Figure 8) or 19 (case not shown for simplicity and in any case dual of that shown in Figures 8 and 9) , always applying a respective axial pressure P to the reference surfaces 21 (semi-finished product 5b) and, respectively, 22 (semi-finished product 5) of said end.

Claims

1. A method of manufacturing sealing rings (1), such as piston rings (lb) and oil scraper rings (lc) for combustion engine pistons, from at least one semi-finished product (2) which is mechanically machined by stock-removing, characterized in that it comprises, in combination, the steps of:
- starting from a single first semi-finished product (2), which is obtained by static casting or, preferably, by centrifugal casting of cast iron in the form of an annular cylindrical bushing having maximum dimension in the direction of a symmetry axis thereof (A) , parallel to which the bushing forming the first semi-finished product is delimited by opposite cylindrical side walls (3,4), radially inner and outer side walls, respectively;
- subjecting the first semi-finished product (2) to a first step of mechanical machining by stock-removing at both of the outer and inner side walls (3,4), to obtain at least a second semi-finished product (5) consisting of an inner central core of the first semi-finished product, which is revealed by said machining, and which has a predetermined circumferential profile in radial section; at the end of said first step of stock-removing machining, respective reference surfaces (20, 21; 22) being further obtained at opposite ends (18,19) of the second semi-finished product;
- making a longitudinal opening defined by a radial slot (12) adapted to obtain the required tangential load;
- subsequently and sequentially subjecting an outer side wall (23) of the second semi-finished product to a second step of stock-removing machining, during which a profile (26) is obtained in the axial direction on such a wall, which is adapted to define the radially outermost profile of a plurality of sealing rings (1) to be obtained, axially arranged side by side, substantially equally spaced out with respect to one another by means of segments (27) of transversal size smaller than that of the second semi-finished product (5); to a step of depositing a galvanic coating (28) of a hard metal or metal alloy on such a profile; and a step of grinding during which part of said galvanic coating (28) is removed;
- subjecting an inner side wall (24) of the second semifinished product to a third step of stock-removing machining during which a profile (36) is obtained in the axial direction on such a wall, which profile is adapted to define the radially innermost profile of a plurality of sealing rings to be obtained, mating with the previously obtained profile (26) on the outer side wall of the second semi-finished product;
- during at least said steps of stock-removing machining and grinding, obtaining the centering of the second semi- finished product (5) by using the same previously obtained reference surfaces (20,21;22) as locators, which are preserved intact during all these steps of machining;
at the end of the third step of stock-removing machining, cutting the second semi-finished product (5) in the direction perpendicular to the side walls (23,24) thereof and at said segments (27) of smaller transversal dimension thereof, thus obtaining a plurality of sealing rings (1).
2. A method according to claim 1, characterized in that said sealing rings (1) obtained at the end of the step of cutting the second semi-finished product are then subjected to a finishing operation only.
3. A method according to claim 1 or 2, characterized in that at least during said second step of mechanical stock- removing machining and the step of grinding, the second semi¬ finished product (5) is forced to take and/or maintain a cylindrical shape, and a predetermined axial pressure (P) is applied thereto, by preferably acting on said reference surfaces (210;22) .
4. A method according to claim 3, characterized in that if the sealing seals to be obtained are piston rings (lb), said predetermined circumferential profile of the second semifinished product (5b) is obtained by eccentrically turning the first semi-finished product (2); said profile being made with an ovaled heart-like shape and, at the end of the first step of stock-removing machining, said radial slot (12) being made over the whole length of the second semi-finished product, over a predetermined circumferential width; said second semi- finished product (5b) being forced to take a cylindrical shape during the subsequent steps of stock-removing machining and grinding by circumferentially forcing it, or at least the opposite ends thereof, within respective tubular cylindrical equipments (60,61) of such a diameter to reduce the circumferential width of the slot (12) so as to lead the circumferential profile of the second semi-finished product (5b) , by elastic deformation, to abandon the ovaled heart-like shape and take a circular shape.
5. A method according to claim 4, characterized in that at least during the second step of stock-removing machining and the step of grinding, the force applied to second semifinished product (5b) is such that the circumferential size of the slot (12) remains between 2 and 3 tenths of mm and respective longitudinal edges of the slot remain parallel to each other.
6. A method according to one of the preceding claims, characterized in that the second semi-finished product (5b) is forced to take a cylindrical shape and a predetermined axial pressure is applied to at least one end (18,19) thereof, even during said third step of stock-removing machining.
7. A method according to one of the preceding claims, characterized in that said step of depositing of a galvanic coating (28) of a hard metal or metal alloy is a step of chrome-plating which is carried out on the profile (26) obtained on the outer side wall (23) of the second semifinished product (5,5b) by centering the latter on a respective support equipment (30,33) by means of the same reference surfaces (20, 21; 22) obtained during the first step of stock-removing machining, and being careful to protect the same from said coating by means of a least one appropriate masking ( 33 ) .
8. A method according to one of the preceding claims, characterized in that said steps of stock-removing machining are carried out by turning or boring, by holding said second semi-finished product (5,5b) at said reference surfaces (20,21;22), at both opposite ends (18,19) thereof during the second step of stock-removing machining and the step of grinding, by applying said axial pressure (P) to both ends; and by overhangingly holding the second semi-finished product (5,5b), at a single end (18;19) thereof, again by applying a respective axial pressure (P) to the reference surfaces (21;22) of such an end, during the third step of stock- removing machining.
9. A method according to one of the preceding claims, characterized in that said first semi-finished product (2), before carrying out the first step of stock-removing machining, is cut in half or into several parts; perpendicularly to its inner and outer side walls (3,4) and on respective opposite ends (13,14) thereof, grooves (15) are obtained which are adapted to receive a respective support equipment (16) for overhangingly supporting of each half (2' , 2") of the first semi-finished product (2) during the first step of stock-removing machining.
10. A method according to one of the preceding claims, characterized in that at the end of said first step of stock- removing machining, those which were the opposite ends (13,14) of the first semi-finished product (2) are cut so as to expose said opposite ends (18,19) of the second semi-finished product (5, 5b) .
11. A method according to one of the preceding claims, characterized in that during the step of grinding, the galvanic coating (28) is removed from over the whole profile (26), except for respective crests (34) thereof intended to define in use the sliding surfaces of said sealing rings (1) to be obtained.
PCT/IB2011/055879 2010-12-21 2011-12-21 Method of manufacturing sealing rings for combustion engine pistons WO2012085870A1 (en)

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ITTO2010A001032A IT1403413B1 (en) 2010-12-21 2010-12-21 METHOD FOR REALIZING SEALING RINGS FOR PISTON OF ENDOTHERMIC MOTORS
ITTO2010A001032 2010-12-21

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114346618A (en) * 2022-01-19 2022-04-15 哈尔滨汽轮机厂有限责任公司 Method for machining sealing ring with triangular cross section

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0436996A1 (en) * 1990-01-09 1991-07-17 Ae Piston Products Limited Piston Rings
WO1997005985A1 (en) * 1995-08-08 1997-02-20 Martin James Quinney Manufacturing piston rings

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0436996A1 (en) * 1990-01-09 1991-07-17 Ae Piston Products Limited Piston Rings
WO1997005985A1 (en) * 1995-08-08 1997-02-20 Martin James Quinney Manufacturing piston rings

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114346618A (en) * 2022-01-19 2022-04-15 哈尔滨汽轮机厂有限责任公司 Method for machining sealing ring with triangular cross section

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