Title of Invention

AN IMPROVED ALUMINIUM ALLOY PISTON RING INSERT

Abstract

A process of manufacturing a top ring insert to be used in prstion or internal combustion engines, wherein the steel dies for centrifugal castings are heated to 300°C to 400°C, and given a dry coating of calcined alumina before pouring the molten metal, and after pouring the molten metal, the dies are rotated at 1400 rpm for a period of 2 to 3 minutes, wherein the constituent metals are melted in add lined 3000 cycles per second induction melting furnace and after melt down, the melt is inoculated with 0.75 stronitium bearing ferro silicon innoculant and the molten metal is raised to pouring temperature of 1350°C prior to pouring, characterized in that the constituent metal by weight comprises 7 to 10% manganese, 1 to 4.5% Nickel, 4 to 5.5% copper, 0.0 to 1.5% chromium, 1.5 to 2.5 silicon, a maximum of 3% carbon and the balance essentially iron.

Full Text

Purpose of Invention: High performance pistons used in high speed diesel engines require a top ring insert to withstand the high temperature and wear. This requirement is met by Niresist which has the expensive nickel as a major constituent. Extensive alloying with nickel is required for obtaining the austenitic structure but the point at issue is whether a less expensive element in combination with other additions will provide a comparable alloy at lesser cost. Published literature on the substitution of nickel with other elements, especially manganese is very inadequate and does not cover all aspects of composition properties, production techniques and applications. The development of a cost effective and yet performance oriented austenitic cast iron with manganese, copper and nickel is described here. As nickel can make contribution towards some oxdation or scaling resistance, an addition of 0.05% mischmetal has been made to improve oxidation resistance in the absence of substantial nickel. Consequently what is needed is an inexpensive alloy having good mechanical properties, high themial expansion, comparable thermal conductivity and elevated temperature properties. Although attempts have been made to develop such alloy, the author is not aware of any alloy which has been put successfully into commercial practice on an industrial scale. It is the object of this invention to provkle a new austenitic alloy with low nickel and the manufacturing process for the top ring insert used in aluminum pistons. Statement of Invention: A process of manufacturing a top ring insert to be used in pistons of internal combustran engines, wherein the steel dies for centrifugal castings are heated to 300C to 400'C, and given a dry coating of calcined alumina before pouring the molten metal, and after pouring the molten metal, the dies are rotated at 1400 rpm for a period of 2 to 3 minutes, wherein the constituent metals are melted in acid lined 3000 cycles per second induction melting furnace and after melt down, the melt is inoculated with 0.75 stronitium bearing fen-o silicon innoculant and the molten metal is raised to pouring temperature of 1350°C prior to pouring, characterized in that the constituent metal by weight comprises 7 to 10% manganese, 1 to 4.5% Nickel, 4 to 5.5% copper, 0.0 to 1.5% chromium, 1.5 to 2.5 silicon, a maximum of 3% carbon and the balance essentially iron. Abstract of Disclosure: An austenitic cast iron for application as top ring insert in pistons of internal combustran engines and containing, by weight, 7 to 10% manganese, 1 to 4.5% Nickel, 4 to 5 - 5.0% Copper, 0.0 to 1.5% Chromium, 1.5 to 2.75% Silicon, 3% Max Carbon and balance essentially iron. Also, disclosed is the process for manufacture of the alloy and castings. The physical and mechanical properties and the structure of the alloy are also disclosed. Introduction Cast austenitic cast irons are used in a variety of applications including automotive, chemical, petrochemical, food handling, marine, power plants, pulp and paper and fluid handling. Present production probably exceeds 30,000 tonnes per annum. The alloys are basically of different compositions with varying weight percentages of Nickel and other alloying elements. These alloys are a part of national and international specifications and come in the flake and spheroidal graphite varieties. Alloys with supplementary additions of elements for specifk: application requirements with enhanced properties have been developed as proprietary alloys. Niresist is the name applied to those family of alloy cast irons in which the presence of a substantial amount of Nickel along with smaller quantities of other elements like Copper, Chromium and Manganese has rendered the alloy, austenitic in structure. This structure and the alloying elements make the alloy superior to plain cast irons. The austenitic cast irons are extensively used for applications requiring resistance to corrosion in different environments, resistance to scaling at high temperatures and resistance to wear. The main uses include piston ring carriers in diesel engine pistons, pump and valves used in chemical/ petrochemical and for handling corrosive liquids and slurries. Niresist has a good resistance to corrosion in marine environment and is used for small propellers. Type of Austenitic Irons Available: The Niresist irons were first developed in 1927 and various grades were developed with nickel contents varying between 14% and 36% along with other elements. Later, the spheroidal graphite austenitic cast irons were developed with better mechanical and physical properties. The various grades of Niresist irons as specified by different countries are tabulated in Table I. The composition of the various grades are listed in Table 11 and typical properties are listed in Table III. Mechanical Properties: The mechanical properties vary slightly with varying Nickel contents as shown in Table III. The density of Niresist is about 7.31 gms / cc and is about 5% higher than plain cast iron. These alloys have good resistance to galling and wear in view of the graphite flakes and spheroids distributed in the structure and prevent metal to metal contact. The wear resistance can be further increased by increasing the hardness to 175 BHN. The wear resistance is superior to that of cast iron even at elevated temperatures. The Niresist irons are work hardening in the as-cast condition, which further improves wear resistance. Niresist irons have good ability to withstand a combination of erosion and corrosion especially in applkations wherein slun-ies are carried or pumped with high velocities. Austenitic cast iron has superior cavitation erosion property in pumps and impellers as compared to ordinary cast iron. Some of the other properties of interest are: Resistance to heat: The Niresist irons are superior to ordinary gray irons in growth and scaling resistance upto 650-700°C. The copper grade Niresist is unstable above 550°C. For applications such as manifolds, turbocharger castings, hot air valves etc., the low growth characteristics of Niresist is particulariy attractive. Thermal Expansion: The Niresist irons have been used for certain applications in view of their matching thenmal expansion with pistons of internal combustion engines. The use of grade 1 austenitic cast iron for top ring inserts in aluminum alloy pistons in diesel engines is one of the highest consumption applications in terms of tonnage. Thermal Conductivity: The thermal conductivity of Niresist irons is only slightly lower than that of ordinary cast irons. Magnetic Properties: The non-magnetic nature of Niresist alloys is controlled by nickel content or the magnetic chromium carbides in the structure. Austenitic cast iron can be mildly magnetic depending upon section thickness and chromium/nickel contents. Applications in Internal Combustion Engines: The austenitic irons have outstanding advantages in use in heavy duty diesel, petrol and natural gas engines used in heavy commercial vehicles and locomotives. Applications include manifods, valve guides, piston ring inserts, turbocharger castings, pistons rings, cylinder liners etc.. Ring Carrier bands for top ring groove in pistons of internal combustion engines is a very large application for Niresist alloys. These alloys have high expansivity and resistance to heat. Type I Niresist is the standard alloy for top ring groove where the effect of heat and wear is maximum. Life of pistons in heavy duty engines have increased dramatically through the use of specially bonded Niresist rings. This altoy has moderate heat and corrosion resistance, good wear and deformation resistance and good machinability. Alloy Composition: Only few elements like Carton, Manganese, Copper, Cobalt, Nickel and Nitrogen can extend the austenitic region in the Iron-Chromium system. However, only Nickel in contents around 18% or in combination with copper to obtain a total of 18% can provide the austenitic structure at room temperature. Attempts have been made in stainless steels to substitute nickel with nitrogen and few proprietary grades of stainless steels have been commercialised. The effect of carbon is to increase carbide precipitation, especially in Chromium containing grades. Manganese has an austenltising effect and is half as effective as nickel. Complete substitution of nickel with manganese is possible but the alloy becomes hard and difficult to machine. It is therefore possible to limit the manganese to 10% and add copper and nickel to obtain the austenitic structure and yet make the alloy machinable. In order to minimize the massive carbides, the chromium content was limited to 1.5% in the alloy. Table IV shows the composition of alloy selected for experimental purposes Table IV The optimum composition for RCI alloy was selected based on the major elements manganese, nickel and copper providing the structure, mechanical and physical properties of austenitic cast irons. A study of the ternary equilibrium diagrams for the major elements including carbon and the possible permutation combination of the proportbns of copper, manganese and nickel was arrived at. After examining the model from data, it was found that if we retain nickel at low contents for high temperature use ample manganese will be required. High manganese content (10-11.5%) results in considerable hardening and poor machlnability. A part of the manganese was substituted with copper. Within the range selected and with carbon and silicon at normal levels, the altoy provided a good combination of properties and machlnability. The high silicon has a graphitising effect and results in a lower proportion of (Fe Mn)3C carbides in the structure. Inhibiting carbide formation alloys manganese to remain in solid solution in the austenite. The additional manganese in the austenite matrix stabilizes it against transformation at fluctuating temperatures and makes it possible to lower nickel content. The oxdation resistance is maintained by the addition of small quantities of mischmetal (0.05%) and aluminum (0.5% max). Experimental Procedure: The alloy was produced under commercial conditions by melting in a 100 kg, medium frequency electric Induction furnace using relatively clean and analysed charge materials like Pig Iron, MS Scrap, high carbon ferromanganese, ferro-silicon, cathode copper and nickel squares. After meltdown, the melt was processed with mischmetal and inoculated with proprietory innoculant. The melt composition was analysed in a vacuum emmision spectrometer and poured in molds for various test castings. The test castings for the top ring piston inserts were centrifugally cast, under controlled condition, in steel molds. Production type heats were poured for bulk piston ring insert castings for manufacture of pistons of internal combustion engines and their testing under test conditions and for field testing. The following tests were made to assess the new alloy and the centrifugally cast insert rings: • Chemistry • Mechanical properties • Microstructure • Oxidation test • Sulphidation test • Lead corrosion test • Salt spray test • Wear tests The following physical and mechanical properties were evaluated: • Mechanical properties like ultimate tensile, strength, elongation, hardness, compressive strength, transverse strength and deflection and Impact. • Elevated temperature strength at 100°C, 200°C, 400°C, SOCC, 600°C and 750°C • Density • Coefficient of Thermal Expansion • Thermal conductivity • Magnetic Response • Linear contraction • Section Sensitivity • Machinability • Heat Resistance The mechanical properties were conducted on standard tensometer test pieces from centrifugal castings and from standard test bars. Oxidation resistance was assessed by heating machined 20 mm Dia x 25 mm length samples in refractory crucibles in a muffle furnace at 900°C for 24 hours. Specimen weight changes and detached scale weight were determined for each sample. The scales were detached by light brushing and with emery paper and hence the results are subject to some inaccuracy. Sulphidation test were carried out on machined samples of 10 mm diameter and 20 mm length, by passing Hydrogen Sulphide at 80°C for a period for 24 hours. More intensive sulphidation test was made on machined samples by immersing in a mixture of C-CaS04Na2S04at 870°C for 48 hours. Lead Corrosion test were carried out by immersing machined samples in a mixture of PbS04 and PbO at 290°C for 1 hour. Salt spray test was carried out on machined ring inserts in acid condition for 96 hours under standard test conditions. The section sensitivity of the alloy was analysed by pouring a step bar of 50 mm thick in step to 10 mm thick and tensometer test specimens machined for tensile testing. Metallographic specimens were prepared by polishing upto 320 grit paper and finally polished with levigated Alumina Suspension on polishing pads. Results Mechanical and Physical Properties: The mechanical and physical properties of the new RCI austenitic cast iron are given in tables VI & VII respectively. Tensile strength: The tensile strength is essentially related to the flake graphite present in the matrix and is comparable to that of Niresist Austenitk: Iron Type 1. All other mechanical properties of the new alloy RCI are comparable to that of the Niresist Iron type 1 alloys. Density: The density of the new alloy RCI is slightly less than that of Niresist Typel, as given in Table VII. With the comparable properties and an approximate 3% less density than Niresist Typel, the new RCI alloy is an attractive alternate for reducing weight of castings. Thermal expansion: From the Table VII it can be observed that the co efficient of themrial expansion of 18.49 between 20'C and 200°C is comparable to 19.3 of Typel Niresist. The expansion enables the new RCI alloy to be used in combination with a variety of alloys like Aluminum alloys, Copper, Bronze and austentitic stainless steels. This compatibility presents the distortion of the joint in the combined metals. This feature makes the RCI alloy very attractive application for the cast in ring inserts pistons of internal combustion engines. It is possible to slightly inaease the coefficient of thermal expansion by increasing the chromium content upto the top limit of the RCI alloy specification. Thermal Conductivity: The thermal conductivity as shown in Table VII is comparable to that of Niresist Type 1 alloy. Magnetic Properties: The new RCI alloy is non magnetic similar to Niresist Typel alloy. Its magnetk: response can be slightly increased by increasing chromium content within the specification. Linear Contraction: The contraction allowance for pattern or die design is generally 1.44% to 2.01% depending upon the design of the casting. These values of the contraction allowance for the new RCI alloy are also comparable that of Niresist Type 1 alloy. Wear Resistance: The new RCI alloy has excellent wear resistance as the graphite flakes are uniformly distributed in the matrix and makes the alloy highly resistant to wear under metal to metal contact conditions. In the hardness range of 130-180 Brinell, the new RCI alloy has god resistance to metal to metal wear. The adhesive wear test result on a 4.3 dia pin sample, shows that the wear resistance of the new RCI alloy is superior to that of Niresist Type 1 alloy. The wear resistance can be increased by increasing the chromium content within the specificatton to provide finely dispersed carbides in the matrix. The new RCI alloy has work hardening characteristic resulting in a work hardened glaze which develops good wear resistance. Heat Resistance: The heat resistance i.e., resistance to oxdation and scaling is comparable to that of Niresist Type 1 alloy. Table VIII gives the growth values and the weight bss of the new RCI alloy. The scale is adhearant in character and hence at elevated temperatures, the scale formed will not blow off, exposing fresh areas for oxidation. Table IX gives the tensile strength properties at elevated temperatures. The strength valves in the range of 100-750°C is comparable to that of Niresist Typel. combustion temperatures have been raised to improve the efficiency of engines and hence oxidation resistance is a aitical requirement especially for lead free gasoline engines. Corrosion: Sulphidation Resistance: In the combustion chamber of diesel engines, the sulphur contained in the fuels forms sulphates with alkali or alkali earth metal compounds added into lubricants. The mixture of sulphate and carbon free deposit causes serious sulphidation attack. Two tests have been done for sulphidation: • Weight loss in still Hydrogen sulphide gas at 80°C for 24 hrs. • Immersion test in a sulphate salt mixture which simulates the sulphidation attack in diesel engines. The results of the test are tabulated in Table X. the new RCI alloy has comparable resistance to sulphidation when compared to Niresist Type 1 alloy. Lead Oxide Corrosion: Leaded High Octane Gasolene contains Ethyl or Methyl lead which converts to PbO in the combustion gas mixtures of varying specifications. The resulting wet deposits of Pb PbSO4 corrodes severely. Tests conducted on machined samples by immersing in a PbO PbSO4 mixture at 290C indicates that the new RCI alloy and the Niresist Type 1 have comparable resistance. The tests were conducted at 290°C as the ring inserts reach 200-220C in actual practice in engine speek range of 1400 to 2000 rpm. The maximum temperature reached generally is in the range of 240-280°C. Atmospheric Corrosion: The new RCI alloy is comparable to Niresist Type 1 altoy when exposed to atmosphere. The new RCI alloy is also not rust free but shows very little staining after exposure for 120 days. Salt Spray Test: The results show that the new RCI alloy has a weight loss of 2.45% whereas Niresist Type I has weight loss of 1.98% which shows that the high Nickel Niresist Type 1 alloy is slightly superior to RCI alloy in marine atmospheric conditions. Section Sensitivity: The sectton sensitivity tests of the new RCI altoy showed that the alloy was not sensitive to section changes. The results are tabulated in Table XI. The slight differences can be attributed to the relatively low soundness of the thick sections. Machinability: The machinability of the new RCI alloy is comparable to that if Niresist Type 1 alloy. The machinability has been assessed by life of carbide cutting tool when machining RCI alloy and Niresist Type 1 alloy. Microstructure: The microstructure of the centrifugally cast rings show the following: The microstructure is comparable to that of Niresist Type 1 alloy. The carbide content is very low and can be expected to increase with increased chromium content. Conclusion: The results of the present work indicates that a cast iron about 4% nickel, 9% manganese, 5% copper is essentially austenitic in structure and has properties comparable to the more expensive, nickel rich, conventional austenitic cast irons. The RCI alloy of the present invention by virtue of its excellent properties and characteristics is suitable for use for a number of applications and especially for the top ring inserts for pistons of internal combustion engines. The major requirement of compatible coefficient of thermal expansion, good wear resistance and elevated temperature properties for the top ring inserts in piston is met with, in the RCI alloy. Thus, this invention has developed of melting and pouring centrifugal castings have been standardized for the production of defect free rings. The application of this invention can be extended to the manufacture of other automotive components like valve seat inserts and valve guides, manifolds etc.. Although the present invention has been described in conjunction with the preferred application, it is to be understood that modifications and variations to the alloy or process will be considered to be within the purview and scope of the present invention and claims. Brief description of the drawing: Fig 1 shows the flowchart for making improved top ring insert. Fig 2 shows a typical alloy Insert Ring made by the new alloy and in the process described. SI.NO.l indicates the thickness, SI. No.2 the outer diameter and SI. No.3 the bore. The dimensions depend upon the size of the diesel engine piston. The insert is placed in the piston die and pistons of internal combustion engines poured over it so that the insert gets bonded to the alloy. I Claim: 1. A process of manufacturing a top ring insert to be used in prstion or internal combustion engines, wherein the steel dies for centrifugal castings are heated to 300°C to 400°C, and given a dry coating of calcined alumina before pouring the molten metal, and after pouring the molten metal, the dies are rotated at 1400 rpm for a period of 2 to 3 minutes, wherein the constituent metals are melted in add lined 3000 cycles per second induction melting furnace and after melt down, the melt is inoculated with 0.75 stronitium bearing ferro silicon innoculant and the molten metal is raised to pouring temperature of 1350°C prior to pouring, characterized in that the constituent metal by weight comprises 7 to 10% manganese, 1 to 4.5% Nickel, 4 to 5.5% copper, 0.0 to 1.5% chromium, 1.5 to 2.5 silicon, a maximum of 3% carbon and the balance essentially iron. 2. A piston wherein the top ring is inserted in the manner as claimed in 1. 3. A process for making cast iron melt for pistons, wherein the melt comprises the metals in the ratio s claimed in claim 1. 4. A process for making novel austenitic cast iron top insert in pistons as substantially described and as illustrated in the accompanying drawings Figl & Fig2 respectivelly.

Documents:

0330-mas-2001 claims duplicate.pdf

0330-mas-2001 claims.pdf

0330-mas-2001 correspondence others.pdf

0330-mas-2001 correspondence po.pdf

0330-mas-2001 description (complete) duplicate.pdf

0330-mas-2001 description (complete).pdf

0330-mas-2001 drawings.pdf

0330-mas-2001 form-1.pdf

0330-mas-2001 form-19.pdf

0330-mas-2001 form-26.pdf