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Vacuum carburizing of ferrous workpieces is performed at low pressure in a vacuum furnace using a napthene hydrocarbon as the carburizing medium. The furnace is constructed to be generally transparent to the napthene so that cracking tends to occur at the workpiece which functions as a catalyst to m

Vacuum carburizing of ferrous workpieces is performed at low pressure in a vacuum furnace using a napthene hydrocarbon as the carburizing medium. The furnace is constructed to be generally transparent to the napthene so that cracking tends to occur at the workpiece which functions as a catalyst to minimize carbon deposits. The napthene is supplied in liquid form to fuel injectors which inject the liquid napthene as a vapor at duty cycles and firing orders to produce a uniform dispersion of the hydrocarbon gas about the work resulting in uniform carburizing of the workpieces. An in-situ methane infrared sensor controls the process. Hydrogen is added to the napthene to either assure full carbon potential and produce methane or to perform variable carburizing.

대표청구항 ▼

What is claimed is: 1. In a method for vacuum carburizing wherein ferrous workpiece(s) are heated to a carburizing temperature in a furnace pressure chamber that is maintained at a vacuum while a carburizing gas within said furnace chamber disassociates to produce carbon absorbed into the surface o

What is claimed is: 1. In a method for vacuum carburizing wherein ferrous workpiece(s) are heated to a carburizing temperature in a furnace pressure chamber that is maintained at a vacuum while a carburizing gas within said furnace chamber disassociates to produce carbon absorbed into the surface of said workpiece to produce carbon in solution and Fe 3C, the improvement comprising the step of: metering a naphthene cyclic hydrocarbon into said furnace chamber wherein said naphthene hydrocarbon is said carburizing gas. 2. The improved method of claim 1 wherein said naphthene is selected from the hydrocarbon group comprising 5 and 6 sided carbon rings. 3. The improved method of claim 1 wherein said naphthene is selected from the group consisting of cyclohexane, including variations thereof such as methylcyclohexane, ethyl cyclohexane, dimethyl cyclohexane, trimethyl cyclohexane, and cyclopentane, including variations thereof such as methylcyclopentane, ethyl cyclopentane. 4. The improved method of claim 1 further including the steps of providing said naphthene in liquid form and metering said naphthene in liquid form into said furnace chamber whereupon said naphthene hydrocarbon is vaporized into gas from the heat and pressure of said furnace chamber. 5. The improved method of claim 4 further including the steps of providing a fuel injector in sealed fluid communication with said furnace chamber and injection pulsing said naphthene into said furnace chamber by said fuel injector. 6. The improved method of claim 5 wherein said step of injection pulsing is fixed or variably set for pulse time and pulse width during the time said naphthene is metered into said furnace chamber. 7. The improved method of claim 6 further including the step of vaporizing said liquid naphthene in an expansion chamber downstream of said fuel injector and upstream of said furnace chamber, said vacuum chamber in direct fluid communication with said furnace chamber. 8. The improved method of claim 7 further including the step of externally heating said expansion chamber. 9. The improved method of claim 7 wherein a plurality of fuel injectors are circumferentially spaced about said furnace chamber and the firing order of said injection is fixed or variably changing. 10. The improved method of claim 9 wherein said naphthene is selected from the hydrocarbon group comprising 5 and 6 sided carbon rings. 11. The improved method of claim 9 wherein said naphthene is selected from the group consisting of cyclohexane, including variations thereof such as methyl cyclohexane, ethyl cyclohexane, dimethyl cyclohexane, trimethyl cyclohexane, and cyclopentane, including variations thereof such as methylcyclopentane, ethyl cyclopentane. 12. The improved method of claim 5 wherein said injection pulsing continues until a set volume of said naphthene liquid has been injected into said furnace chamber while a vacuum is maintained in said chamber and thereafter said chamber is maintained at a set vacuum and temperature for a set time to allow said carbon to diffuse into the case of said workpiece and form Fe3C along the way. 13. The improved method of claim 7 wherein said furnace chamber is provided with deflecting surfaces about said workpiece and said injectors are orientated within said furnace chamber to direct said naphthene towards said deflecting surfaces which, in turn, direct said naphthene towards said workpieces, said deflecting surfaces being substantially transparent to said naphthene hydrocarbon so that said naphthene hydrocarbon tends to catalytically react only with said workpiece. 14. The improved method of claim 3 wherein said surfaces are formed or coated with material selected from the group consisting of molybdenum alloys with iron content less than about 5%, silica, graphite and ceramics coated with carbon to produce a graphite like surface. 15. The improved method of claim 5 wherein said naphthene hydrocarbon is supplied as a liquid feedstock having at least a 99% content of naphthene hydrocarbon(s) and the balance comprising different hydrocarbons. 16. The improved method of claim 5 further including the step of simultaneously metering hydrogen into said furnace chamber during the time said naphthene hydrocarbon is introduced into said furnace chamber. 17. The improved method of claim 16 wherein said naphthene is selected from the hydrocarbon group comprising 5 and 6 sided carbon rings. 18. The improved method of claim 16 wherein said naphthene is selected from the group consisting of cyclohexane, including variations thereof such as methyl cyclohexane, ethyl cyclohexane, dimethyl cyclohexane, trimethyl cyclohexane, and cyclopentane, including variations thereof such as methylcyclopentane, ethyl cyclopentane. 19. The improved method of claim 16 wherein said hydrogen is metered with said naphthene at quantities sufficient to allow saturation of carbon into the iron at the surface of the workpiece. 20. The improved method of claim 16 further including the step of continuing the injection pulsing of said naphthene with said hydrogen until a set carburization level is reached whereupon the pressure in said furnace chamber is returned to atmospheric so that a separate diffusion step does not occur. 21. The improved method of claim 20 further including the step of measuring the concentration of methane present inside said furnace chamber and stopping or reducing the injection of said naphthene when a set level of methane is detected. 22. The improved method of claim 20 further including the step of providing a plurality of said fuel injection circumferentially spaced about said fuel chamber and a plurality of hydrogen inlets to said furnace chamber and maintaining flow of hydrogen through said hydrogen inlets while said injectors are activated in a sequence. 23. The improved method of claim 22 wherein said hydrogen flows into said furnace chamber at a volumetric flow rate at least twice that of the volumetric flow rate of said naphthene. 24. The improved method of claim 16 wherein the quantity of said hydrogen and the quantity of said naphthene introduced into said workpiece is set as a function of the surface area of said workpiece, the depth of desired penetration of carbon into said workpiece, and the temperature, pressure and size of said furnace chamber to produce a workpiece surface where the quantity of carbon in solution formed in the workpiece is controlled at set levels. 25. The improved method of claim 5 wherein said temperature is between 1500째 to 1900째 F. and said pressure is between 1 to 100 torr. 26. The improved method of claim 25 wherein said temperature is between 1700째 to 1800째 F. and said pressure is between 7 to 10 torr. 27. The improved method of claim 26 wherein said naphthene is selected from the hydrocarbon group comprising 5 and 6 sided carbon rings. 28. The improved method of claim 26 wherein said naphthene is selected from the group consisting of cyclohexane, including variations thereof such as methyl cyclohexane, ethyl cyclohexane, dimethyl cyclohexane, trimethyl cyclohexane, and cyclopentane, including variations thereof such as methylcyclopentane, ethyl cyclopentane. 29. The improved method of claim 5 wherein said furnace chamber is of cold wall design having an interior casing surrounded by an exterior casing to define a cooling chamber therebetween, said process further including the step of providing a coating over said inner casing in the form of insulating board, insulation foil or otherwise having or containing graphite therein whereby reaction of said naphthene and said casing is minimized. 30. The improved method of claim 5 wherein said furnace chamber is of hot wall design having a single furnace casing with insulation attached thereto, said process further including the step of providing a coating over the interior of said casing which is substantially graphite. 31. The improved method of claim 5 wherein said furnace chamber further includes a cathode and anode connected to a power supply for generating a plasma, one of said cathode and anode connected to the furnace hearth through hearth supports and said cathode, anode and said hearth supports having a substantially graphite surface. 32. A heat treating process for carburizing the case of a ferrous workpiece(s) which is subsequently case hardened comprising the steps of: a) providing a furnace having a vacuum tight furnace chamber containing said workpiece; b) drawing a vacuum in said furnace chamber; c) heating said workpiece to a carburizing temperature; d) admitting a naphthene hydrocarbon into said furnace chamber forming carbon in solution in the case of said ferrous workpiece while maintaining a vacuum in said furnace chamber and said workpiece at said carburizing temperature; and, e) stopping the flow of said naphthene into said furnace chamber when a set quantity of carbon has been produced in said case. 33. The method of claim 32 further including the steps of providing a fuel injector having an outlet in fluid communication with said furnace chamber and an inlet in fluid communication with source of pressurized liquid naphthene; and, pulse injecting said liquid naphthene into said furnace chamber whereupon said liquid naphthene is vaporized. 34. The method of claim 33 further including a plurality of fuel injectors circumferentially spaced about said furnace chamber and said method comprising the steps of sequentially actuating each injector in a fixed or variable sequence and actuating each injector with a fixed or variable pulse width. 35. The improved method of claim 34 wherein said naphthene is selected from the hydrocarbon group comprising 5 and 6 sided carbon rings. 36. The improved method of claim 34 wherein said naphthene is selected from the group consisting of cyclohexane, including variations thereof such as methyl cyclohexane, ethyl cyclohexane, dimethyl cyclohexane, trimethyl cyclohexane, and cyclopentane, including variations thereof such as methylcyclopentane, ethyl cyclopentane. 37. The method of claim 34 further including the steps of injecting a fixed volume of said naphthene hydrocarbon over a set time and thereafter stopping said injection while maintaining said furnace chamber at a vacuum so that said carbon can diffuse from the surface of said workpiece throughout the case of said workpiece and form Fe3 C as said carbon travels through the case. 38. The method of claim 34 further including the step of metering hydrogen into said furnace chamber while said naphthene is injected therein. 39. The method of claim 38 wherein said vacuum is removed when said injectors stop pulsing so that carburizing is completed without holding said vacuum chamber at a set vacuum to allow diffusion of said carbon into the case of said workpiece. 40. The method of claim 39 further including the step of sensing the presence of methane in said furnace chamber and stopping or reducing the injection of said naphthene when the concentration of methane in said furnace reaches a set level. 41. The method of claim 40 wherein said hydrocarbon flows into said furnace chamber at a volumetric flow rate which is at least twice the flow rate of said naphthene. 42. The improved method of claim 41 wherein said naphthene is selected from the hydrocarbon group comprising 5 and 6 sided carbon rings. 43. The improved method of claim 41 wherein said naphthene is selected from the group consisting of cyclohexane, including variations thereof such as methyl cyclohexane, ethyl cyclohexane, dimethyl cyclohexane, trimethyl cyclohexane, and cyclopentane, including variations thereof such as methylcyclopentane, ethyl cyclopentane. 44. The method of claim 34 further including the steps of directing the principal flow of said naphthene vapor against deflecting surfaces in said furnace chamber which are generally transparent to said naphthene and redirecting said flow by said deflecting surface to said workpiece. 45. The method of claim 44 wherein said deflecting surfaces are, or are coated with graphite, ceramics which have been exposed to hydrocarbon gas to develop a graphite type surface, or molybdenum alloys having an iron content less than about 5%. 46. A method for controlling a vacuum carburizing process wherein carbon is absorbed in the case of a ferrous workpiece comprising the steps of: a) heating a vacuum sealable furnace chamber to a carburizing chamber; b) drawing a vacuum in said furnace chamber sufficient to remove substantially all atmospheric gases initially present in said furnace chamber; c) metering inside said furnace chamber a hydrocarbon carburizing gas while maintaining said furnace chamber at a set vacuum level; d) measuring in-situ the concentration of methane inside said furnace chamber; and, e) maintaining the metering of said carburizing gas to assure the concentration of said carburizing gas in said furnace chamber, wherein said carburizing gas is a naphthene cyclic hydrocarbon. 47. The method of claim 46 wherein said naphthene is a 5 or 6 sided carbon ring naphthene. 48. A method for vacuum carburizing a ferrous workpiece wherein carbon is absorbed onto the surface and diffused into the case of a ferrous workpiece comprising the steps of: a) providing a furnace having a vacuum sealable furnace chamber containing said workpiece; b) heating said workpiece to a carburizing temperature; c) drawing a vacuum in said furnace chamber; d) providing a liquid source of naphthene cyclic hydrocarbon as a carburizing medium; e) injecting the hydrocarbon in liquid form into said furnace, said hydrocarbon vaporizing into a gaseous hydrocarbon before or at the time it enters said furnace chamber; and, f) stopping the injection when a set quantity of Fe3 C has been produced on the furnace of said workpiece by said hydrocarbon. 49. The method of claim 48 further including the step of pulsing discrete quantities of said liquid hydrocarbon into said furnace at set time intervals. 50. The method of claim 49 further including the step of providing a fuel injector, said fuel injector pulsing said liquid hydrocarbon at set pulse widths and frequencies. 51. The method of claim 50 wherein said pulse widths and frequencies are varied during the time said hydrocarbon is injected into said furnace. 52. The method of claim 50 further including the step of providing a plurality of fuel injectors in fluid communication with said furnace chamber at set spaced distances about said furnace and firing each injector at a set time in relation to the other injectors. 53. The method of claim 52 wherein the firing order of said injectors is varied. 54. The method of claim 53 wherein said pulse widths and frequencies are varied during the time said hydrocarbon is injected into said furnace. 55. The method of claim 54 wherein said frequency of said pulses, said pulse widths and said firing order are varied in a manner which simulates a random flow path of said hydrocarbon gas in said furnace. 56. The method of claim 50 further including the step of providing an expansion chamber downstream of said injector and upstream of said furnace chamber and causing said liquid hydrocarbon to vaporize into a hydrocarbon gas in said expansion chamber. 57. The method of claim 50 wherein said naphthene is a 5 or 6 sided carbon ring naphthene. 58. A method for carburizing the surface of a workpiece in a furnace chamber comprising the steps of: a) heating said workpiece to a carburizing temperature; b) drawing a vacuum in said furnace chamber; c) maintaining said furnace chamber at a set vacuum while metering into said furnace chamber hydrogen and a hydrocarbon carburizing gas; and, d) setting the ratio of quantities of hydrogen gas to said carburizing gas admitted to said furnace chamber to produce a set quantity of iron carbide at the surface of said workpiece up to the saturation limit of carbon on the surface of said workpiece; wherein said process is complete when metering of said hydrogen and said carburizing gas stops whereby a diffusion step in said process normally required to enhance diffusion of carbon into the case of said workpiece is not required; and further including the step of case hardening said workpiece; wherein said carburizing gas is a naphthene cyclic hydrocarbon. 59. The method of claim 58 wherein said naphthene is a 5 or 6 sided carbon ring naphthene. 60. In a method for vacuum carburizing wherein ferrous workpiece(s) are heated to a carburizing temperature in a furnace pressure chamber that is maintained at a vacuum while a carburizing gas within said furnace chamber disassociates to produce carbon absorbed into the surface of said workpiece to produce carbon in solution and Fe 3C, the improvement comprising the step of: metering a naphthene cyclic hydrocarbon into said furnace chamber, said cyclic hydrocarbon being a gas in said furnace chamber. 61. The improved method of claim 1 wherein said naphthene cyclic hydrocarbon comprises a blend of naphthenes. 62. The improved method of claim 1 wherein said carburizing medium is a blend and said naphthene hydrocarbon comprises at least 50% of the carburizing medium metered into said furnace chamber. 63. The method of claim 1 wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 64. The method of claim 63 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 65. The method of claim 63 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 66. The method of claim 63 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 67. The method of claim 32 wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 68. The method of claim 67 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 69. The method of claim 67 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 70. The method of claim 67 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 71. A method for controlling a vacuum carburizing process wherein carbon is absorbed in the case of a ferrous workpiece comprising the steps of: a) heating a vacuum sealable furnace chamber to a carburizing chamber; b) drawing a vacuum in said furnace chamber sufficient to remove substantially all atmospheric gases initially present in said furnace chamber; c) metering inside said furnace chamber a naphthene cyclic hydrocarbon carburizing gas while maintaining said furnace chamber at a set vacuum level: d) measuring in-situ the concentration of methane inside said furnace chamber: and, e) maintaining the metering of said carburizing gas to assure the concentration of said carburizing gas in said furnace chamber, wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 72. The method of claim 71 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 73. The method of claim 71 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 74. The method of claim 71 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 75. The method of claim 48 wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 76. The method of claim 75 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 77. The method of claim 75 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 78. The method of claim 75 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 79. A method for carburizing the surface of a workpiece in a furnace chamber comprising the steps of: a) heating said workpiece to a carburizing temperature; b) drawing a vacuum in said furnace chamber; c) maintaining said furnace chamber at a set vacuum while metering into said furnace chamber hydrogen and a naphthene cyclic hydrocarbon carburizing gas; and, d) setting the ratio of quantities of hydrogen gas to said carburizing gas admitted to said furnace chamber to produce a set quantity of iron carbide at the surface of said workpiece up to the saturation limit of carbon on the surface of said workpiece; whereby no sooting occurs in said furnace chamber due to the presence of said hydrocarbon carburizing gas, wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 80. The method of claim 79 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 81. The method of claim 79 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 82. The method of claim 79 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 83. The method of claim 79 wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 84. The method of claim 83 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 85. The method of claim 83 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 86. The method of claim 83 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 87. The method of claim 60 wherein the method includes at least a further step of adding a source of monatomic nitrogen into the furnace chamber. 88. The method of claim 87 wherein the source of monatomic nitrogen comprises at least one of ammonia or at least one ring hydrocarbons which contains monatomic nitrogen. 89. The method of claim 87 wherein the source of monatomic nitrogen comprises at least one cyclic hydrocarbon having at least one NH, NH2, or NHCH3 groups attached to any of the carbons in the ring. 90. The method of claim 87 wherein the source of monatomic nitrogen comprises at least one of cyclic hydrocarbons including aniline, methylpiperidine, piperidine, speridine, cyclohexylamine, aminocyclohexane and cyclohexanamine. 91. The method of claim 46 wherein said controlling step is used to maintain the flow of said carburizing gas when a set methane concentration is reached or to verify that a set quantity of Fe3 C has been absorbed on the surface of said workpiece at the completion of a timed cycle. 92. The process of claim 46 wherein said controlling step maintains the composition of the gas in said furnace chamber during metering of said carburizing gas in accordance with the concentration of said methane gas in said furnace chamber. 93. The process of claim 46 further including the step of reducing the metering of said carburizing gas to converse said carburizing gas when a set quantity of carbon has been absorbed by said workpiece and maintaining a set vacuum in said furnace chamber for a set time to allow carbon diffusion into the case of said workpiece. 94. The process of claim 46 further including the step of metering a desired concentration of hydrogen gas into said furnace with said carburizing gas and controlling the flow rates of either said hydrogen gas or said carburizing gas or both in accordance with the concentration of methane sensed in said furnace chamber, said metered concentration of hydrogen gas being sufficient for part brightness. 95. The method of claim 94 further including sensing in-situ the concentration of said hydrogen gas in said furnace and varying the flow of either said hydrogen gas or said carburizing gas or both in accordance with the sensed concentration of said hydrogen and said methane gas. 96. The method of claim 94 wherein said carburizing gas and said hydrogen gas is metered into said furnace chamber at controlled flow rates such that Fe3C fails to saturate the surface of said workpiece while said carburizing gas is being metered into said furnace chamber. 97. The method of claim 95 wherein said carburizing method is completed at the conclusion of said metering step without further diffusion of carbon into the case of said workpiece.