Manufacturing procedure for a piston ring

Abstract: A wearing resistant piston ring, wherein said piston ring comprises a sintered alloy (2) having a superior wearing resistance and slidability with the thickness of more than 2 mm applied over the sliding surface of the piston ring, and wherein a metal which is arranged inside said sintered alloy so as to provide a piston ring body (1), and said two members are bonded together.

Description: SPECIFICATION 1. TITLE OF THE INVENTION Procedure for manufacturing a piston ring 2. FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a procedure for manufacturing a piston cylinder for use in an internal combustion engine such as diesel engines and the like. The typical example of the traditional type piston cylinder is represented by several products such as a cast iron ring, a chromium-plated ring having a sliding surface finished with the chromium-plating, and a WC sprayed ring etc., having the sliding surface sprayed with the tungsten carbide. Though the cast iron ring has been used for a long period so far, the cast iron ring is deficient in lacking desirable characteristics in wearing resistance. In contrast, the chromium-plated ring and the WC sprayed ring have been used lately in various fields, but they are also disadvantageous in several respects as described below. That is, while a procedure for manufacturing the piston ring utilizing welding and spraying process is easy to undertake, but they cannot ensure a production of a piston ring with a sufficiently long service life, since its coating thickness is reduced. The coating thickness is generally limited up to 0.5 mm, since the coating would be peeled off, or removed off, should the thickness be thicker than the above. On the other hand, the limit wearing amount of the piston ring is said to be approximately 2 mm (4 mm in diameter), and therefore the plated layer or the sprayed layer must have a wearing resistance characteristic approximately four times more superior to that of the traditional cast iron piston in order to enable the limit thickness of 0.5 mm of the plated or sprayed piston ring to cover such limit wearing amount. As a result, the need has arisen to develope a material which has a wearing resistance characteristics eight times and twelve times superior to that of the traditional material in order to provide a service life two time and three times longer than those of the traditional material respectively. However, it is considered difficult to achieve such improved characteristics, when various performances requirements for the piston ring are taken into accounts. French patent application FR-A-2 430 286 discloses a procedure for manufacturing a piston ring comprising steps of processing a groove circumferentially in the surface of a piston ring body material, filling a single or plurality of powders into said groove, applying an elevated temparature by means of a laser to said powder for causing the same to be sintered while simultaneously bonding the powder with said groove in the piston ring body material 1. The drawback of this known procedure is that only wear resistent layers of a limited thickness can be produced, due to the fact that during the bonding and sintering process no pressure can be applied to the powder in the non-sintered state. It is therefore an object of the present invention to improve said manufacturing procedure comprising the step of machining grooves into a piston body material so that pressure can be applied to the powder to be sintered, so that a piston ring is manufactured having a wearing resistent layer of a thickness which allows better wear and tear properties, by utilising a currently available high hardness material. From US-A-3,153,542 there is known a procedure to manufacture bi-metal piston rings using a cylinder, consisting of a layered bi-metal combination comprising a core of low alloy steel and a welded-on overlay of cast iron, which is severed into piston rings. Although the core of alloy steel of such a piston ring is relatively tough and resiliant the piston ring yielded by this known procedure is not sufficiently wear resistent, since the overlay of cast iron is relatively soft. It is therefore object of the present invention to provide a manufacturing procedure for a piston ring using a layered bi-metal combination cylinder which is severed into single piston rings, which allows use of a powder material, which is to be sintered and bonded to the core material to form the outer layer of material of the bi-metal combination cylinder, thereby providing an outer surface of a piston ring having a greater wear and tear resistence. The solution of these objects is described as far as the first object is concerned by the characteristic portion of claim 1, as far as the second mentioned object is concerned, by the characteristic portion of claim 2. The above and other objects and advantages of the invention will be more apparent from a perusal of the following specification. To accomplish the above objects, an embodiment of the present invention is devised such that a plurality of grooves is formed circumferentially in the upper surface of the piston ring body material made of an elongated cylindrical steel material, the grooves having width smaller than that of the piston ring and depth deeper than 2 mm, whereas a thin tubular steel material having a length substantailly equal with that of the piston ring body portion is provided, and said grooves are filled with a single or various types powdery material. After the opposite ends of the body material and the tubular steel material are welded together, sintering of the powders are effected by applying an elevated temperature and pressure while at the same time bonding the material with the groove of the piston ring body. After the outer tubular material is cut off for removal, the body portion between adjacent grooves is severed, whereby producing the piston ring of the invention. Another alternative embodiment of the invention is arranged such that the piston ring body portion made of elongated cylindrical steel material is provided with a tubular steel having a diameter larger than that of the piston ring by more than 4 mm, and one or more types of powder is/are filled in a space between the two members, and opposite ends of the body material and tubular steel material are welded together. Then, the above powdery material is sintered by applying an elevated temperature and pressure, while at the same time grasping the piston ring body, and after the outer tubular member is cut off for removal, different dual-layered members of are cut off into a ring-like configuration with a predetermined width, and whereby producing the piston ring. Since the present invention permits the production of the wearing resistant piston ring in accordance with the procedures of the invention, it may produce a piston ring easily having a wearing resistance layer on its sliding surface made of high hardness material and of the thickness more than 2 mm, and thereby ensuring an extended life span. Additionally, since any suitable material may be used to form the wearing resistant layer, as long as it is of a high hardness grade to permit it to be sintered at an elevated temperature and pressure, one can select a preferred material among a plurality of types of candidate materials, while also enabling one to select any suitable mixing ratio of such materials. Furthermore, a plurality of grooves of 2 mm or more in depth and a width narrower than that of the piston ring is formed in the piston ring which is produced in accordance with the second procedure of the invention, and a piston ring body made of steel materials is present on opposite ends of the sliding surface of the piston ring. Thus, there is no chance for the angular portion on the sliding surface to be notched, even when any material which is used to sinter the wearing resistant layer lacks viscosity. Besides, when the piston is made in accordance with the second procedure of the present invention, no grooves are required to be formed, and consequently such advantages may be derived as that a high hardness material may be used for the piston ring body and the powdery material may be inserted with ease. Moreover, when the HIP (Hot Isostatic Pressing) equipment is utilized to sinter the material under an elevated temperature and pressure, any shape can be selected relatively freely for the bonding portion, which is preferable when sintering the material in a complicated configuration and bonding, while permitting to apply steps of sintering the high hardness powdery material and of bonding the material with the piston ring body portion simultaneously, because the HIP equipment serves to substantially elevate the atmospheric gas pressure into an isotropic level. 4. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 through Fig. 8 illustrate one embodiment of the present invention, wherein; Fig. 1 is a perspective view of a piston ring body material; Fig. 2 is an enlarged view illustrating the portion A of Fig. 1; Fig. 3 is a view illustrating the HIP equipment while it operates to treat the material; Fig. 4 is a view illustrating the HIP equipment while it operates to treat the material; Fig. 5 is a view illustrating the piston which has been cut off in a ring-like configuration after the HIP equipment was operated to treat the material; Fig. 6 is a perspective view of the piston ring Fig. 7 is a cross-sectional view taken along a line VII - VII of Fig. 6; Fig. 8 is a view comparing a performance of the present invention with a prior art; Fig. 9 through Fig. 12 illustrate second embodiment of the invention, wherein; Fig. 9 is a view similar to Fig. 3; Fig. 10 is a view similar to Fig. 5; Fig. 11 is a view similar to Fig. 6; Fig. 12 is a cross-sectional view taken along the line XII - XII of Fig. 11. 5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS One embodiment of the present invention will be described in details hereinbelow by way of example, making reference to accompanying drawing illustrating the piston ring body material 1, which has a plurality of grooves 5 defined in the surface of the cylinder. The body material 1 is required to have an increased viscosity and preferably is made of an alloy steel and carbon steel rather than the cast iron. Fig. 2 is an enlarged cross-sectional view of the grooved portion A which has been machined in the surface of the Fig. 1, wherein the groove 5 is made smaller in width than the piston ring, and to have a depth of more than 2 mm in a trapezoidal shape. The shape of the grooves should not naturally be trapezoidal, but should avoid such a shape as may cause a stress concentration. Fig. 3 is a cross-sectional view illustrating the assembling state of the HIP equipment in a pre-treatment step, wherein a powdery material 2 with an increased hardness such as carbide is filled into a space between the piston ring body material and a tubular steel material 3 of reduced thickness. Lateral opposite ends of the material are covered with a lid 4 in a vacuum atmosphere and then an electronic beam welding (EBW) is applied to entrap the high hardness material 2 in the vacuum. The hardness level of the material with an increased hardness is preferably in the range of 500 - 1,000 HV, and the selectability of the material is rather limited because the material must possess superior slidablity and resistance to hardenability plus the wearing resistance characteristics. Tungsten carbide (WC) or chromium carbide (Cr₃C₂) are prospective materials, but the mixture of other various compositions is available to use in the procedure of the present invention. Fig. 4 is a view illustrating the HIP equipment while it is being operated, wherein the piston ring body material 1 is being treated with the HIP equipment under an elevated temperature and pressure. The pressure is approximately at 1,000 - 1,200 kgf/cm² , and the heating temperature is approximately at 1,000 - 1,200 °C. After the HIP equipment has been operated to treat the material, the tubular outer cylinder 3 of reduced thickness is removed by means of lathe, and then is severed into a ring-like configuration as illustrated in Fig. 5. The cutting is carried out in a position where the piston ring body material 1 occupies between adjacent very hard materials which have been welded. The piston ring which has thus been processed is further subject to the finishing process wherein its inner and outer diameters are finally defined, and then the piston ring flange is finally processed in the configuration as shown in Fig. 6. In Fig. 6, there are illustrated a piston ring body 1a and a very hard material 2a for forming the slidable surface. As described hereinbefore, the piston ring of the present invention is thus completed. Fig. 7 is a cross-sectional view taken along the line VII -VII of Fig. 6, wherein the piston ring comprises a piston ring body material 1a of increased viscosity and the sliding surface formed of high hardness material. The high hardness material 2a is hard and relatively fragile, but other portion than the sliding surface is in contact with the piston ring body. The bonding strength of the material is maintained invariably by means of the HIP treating equipment, and it is not possible that the end portion of the piston ring may be removed during use. Fig. 8 shows that the wearing resistant piston ring of the present invention has an extremly increased durability. Though a single groove is shown in Fig. 5 through Fig. 7, such grooves may also be formed in a plural numbers. Fig. 9 through 12 illustrates the second embodiment of the present invention. Fig. 9 is a cross-sectional view illustrating the assembling state of various members with the HIP equipment in a pre-treatment step. A powdery material 12 which is used to form a sliding portion of the piston ring is filled in a space between the piston ring body 11 and the steel outer tube 13 of reduced thickness. Lateral opposite ends are seal-welded by means of the lid 14 in a vacucum, and then the powdery material (wearing resistant material) 12 is sealed under a vacuum pressure. The powdery material 12 is preferably a material having hardness over 1,000 HV such as a carbide or a cobalt-alloy, but a mixture powder of the Mo powder having improved slidability and a powder with increased hardness is also effective, because the slidability and resistance to hardenability are required besides the wearing resistance characteristics. Fig. 4 illustrates the manner in which the HIP equipment is operated to process the piston under an elevated temperature and pressure, which is carried out in a similar manner for the previous embodiment. Generally, the pressure used is at around 1,000 - 1,200 kgf/cm² and the maximum heating temperature of approximately 1,200 °C Max. However, more elevated temperature and pressure may be applicable for special purpose. After the piston is processed by means of the HIP equipment, the lathe is utilized to remove the outer tube 13, and then is cut off in a ring-like configuration as illustrated in Fig. 10. Moreover, after the end flange trimming process is taken, the piston ring is completed with final dimensions in a ring-like configuration as illustrated in Fig. 11. Fig. 12 is a cross-sectional view taken along the line XII - XII of Fig. 11, wherein there are illustrated a piston ring body 11a and a wearing resistant material 12a which forms the slidable surface. Fig. 12 is a view illustrating the high hardness material 12a bonded with the entire surface of the ring body material 11a. In this embodiment, however, a substantial viscosity may be provided if the piston ring is produced using an utmost care so as to sure a proper mixing ratio of the sintering alloy which is applied by means of the HIP equipment so that the material may be diffused in an increased density, unlike the prior art rings with latings or spraying applied. Thus, the piston may be produced which can be satisfactorily used in an actual application even when it is used under the conditions as set forth in the present embodiment.

Claims: A procedure for manufacturing a piston ring, wherein said procedure comprises steps of processing at least one groove (5) circumferentially in the surface of a piston ring body material (1), filling a single or a plurality of powder(s) (2) said groove (5), and then applying an elevated temperature to said powder for causing the same to be sintered while simultaneously bonding the powder with said groove (5) in the piston ring body material (1), characterized in that the piston ring body (1) is made of an elongated cylindrical steel material, that said first step of processing at least one groove (5) in said material comprises furthermore processing of a plurality of grooves (5) having a depth greater than 2 mm, and that the procedure comprises furthermore the following steps: arranging a thin tubular steel material (3) around the outer circumference of said body material (1), said tubular steel material (3) having the length substantially equal to that of said piston ring body material (1), welding together opposite ends of said body material (1) and said tubular steel material (3), after said step of filling powder (2) in said grooves (5) has been completed, and then applying said elevated temperature and a pressure to said powder (2) for causing said powder (2) to be sintered and bonded, cutting off said outer tubular material (3) for removal, and severing the body material (1) at a portion between adjacent groove (5). A procedure for manufacturing a piston ring comprising the steps of arranging a tubular steel material (13) on a piston ring body material (11) made of elongated cylindrical steel material, said tubular steel material (13) having a diameter larger than that of said piston ring body material (11); welding opposite ends of said body material (11) and said tubular steel material (13) together; severing different dual layered members into a ring-like configuration having a predetermined width; characterised in that after said arranging step filling a single or a plurality of powder(s) (12) in a space between said two members (11,13) is performed and in that after said welding step applying of an elevated temperature and pressure to said powder(s) (12) for causing the same to be sintered while simultaneously bonding the powder(s) (12) with the piston ring body material (11) and the cutting off of said outer tubular material (13) for removal are performed. A procedure according to claim 1 or claim 2, characterized in that said powder(s) (2,12) is/are sintered alloy with superior wearing resistance and slidability with a thickness of more than 2 mm, and in that said piston ring body material (1,11) is a metal.

Inventors: KAMITO YOSHIMI C O NAGASAI TEC, KAWANAMI SHIZUO C O NAGASAI TE, KISHIKAWA RYOJI C O NAGASAI TE, KAMITO, YOSHIMI, C/O NAGASAI TECHNICAL INSTITUTE, KAWANAMI, SHIZUO, C/O NAGASAI TECHNICAL INSTITUTE, KISHIKAWA, RYOJI, C/O NAGASAI TECHNICAL INSTITUTE
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: F16J9
IPC codes: B22F7, B22F5, F16J9