Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/001—Heat treatment of ferrous alloys containing Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
  • C22C38/105—Ferrous alloys, e.g. steel alloys containing cobalt containing Co and Ni
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding of ferrous surfaces
• • 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
  • F16G—BELTS, CABLES, OR ROPES, PREDOMINANTLY USED FOR DRIVING PURPOSES; CHAINS; FITTINGS PREDOMINANTLY USED THEREFOR
  • F16G5/00—V-belts, i.e. belts of tapered cross-section
  • F16G5/16—V-belts, i.e. belts of tapered cross-section consisting of several parts

Definitions

• the present invention relates to a manufacturing method for a metal ring to be used in a drive belt, more in particular a heat treatment process part thereof as defined by the preamble of the following claim 1.
• the drive belt is typically used as the means for power transmission between two adjustable pulleys of the well-known continuously variable transmission that is mainly applied in motor vehicles.
• EP-A-1 403 551 is composed of a multitude of relatively thin transverse metal elements that are slideably incorporated on two laminated endless tensile means that are each composed of a set of mutually nested flat metal rings, alternatively denoted endless bands or hoops.
• Such rings are typically produced from a precipitation hardening steel, such as a maraging steel, that combines a/o the properties of great tensile strength and good resistance against tensile stress and bending fatigue with a relatively favourable possibility to process the steel from sheet material towards the desired shape and material characteristics of the end-product rings, which, preferably, should not vary along the circumference of the rings.
• the present invention in particular relates to the range of maraging steel alloys having a basic composition with 17 to 19 mass-% nickel, 4 to 6 mass-% molybdenum, 8 to 18 mass- % cobalt, possibly with small amounts of other alloying elements such as less than 1 mass-% titanium and/or of impurities and with balance iron.
• These desired material characteristics comprise a fair hardness of the ring core material for combining the properties of a great tensile strength together with sufficient elasticity to allow longitudinal bending of the ring and an extremely hard outer surface layer of the ring to provide wear resistance. Additionally, the outer surface layer is provided with a residual compressive stress to provide a high resistance against metal fatigue, which is a significant feature of the rings because of the numerous numbers of load and bending cycles the rings are subjected to during the service lifetime of the belt.
• the basics of the known manufacturing method for such rings have become well known in the art and are, for example, described in the European patent publication EP-A-1753889.
• the rings are formed out of a sheet base material, which is bent and welded into a cylindrical shape, or tube, which is heat treated, i.e. annealed, to restore the original material properties, i.e. to largely remove changes therein that were introduced by the bending and welding.
• the tube is then cut into a number of hoops, which are subsequently rolled and elongated to a required thickness, which is typically about 0.185 mm in the end product. After rolling the hoops are usually referred to as rings or bands.
• the rings are subjected to a further annealing step to remove the internal stresses introduced during rolling. Thereafter, the rings are calibrated, i.e. they are mounted around two rotating rollers and stretched to a predefined circumference length.
• the rings are subjected to a heat treatment process that includes both, i.e. that combines, the heat treatments of precipitation hardening, i.e. ageing or core hardening, and of gas soft-nitriding, i.e. of case hardening by insertion of Nitrogen atoms, in an ammonia-containing process atmosphere.
• This known combined process lasts for 45 up to 65 minutes at a temperature of 440 up to 480 degrees Celcius and in an atmosphere containing at least 10 volume- % ammonia.
• the known combined heat treatment process is very cost effective in relation to the more conventional, sequential heat treatment processes that are, for instance, described- in EP-A-1055738.
• the process temperature is increased to speed up the heat treatment, the known phenomenon of compound layer formation can occur that unacceptably reduces the (metal) fatigue strength of the rings.
• the present invention aims to improve the standing combined heat treatment process in the sense that the process time thereof is shortened, in particular without detriment to the fatigue strength of the drive belt rings produced thereby.
• the above aim can be realised with the improved combined heat treatment process according to claim 1 hereinafter.
• the invention counter-intuitively, applies a lower ammonia content of/concentration in the process atmosphere to accelerate the combined heat treatment process.
• Such lower ammonia content was found to effectively allow the comparatively high process temperature of 500 degrees Celsius or more to be applied to speed up the combined heat treatment, while largely avoiding the formation of the compound layer that is detrimental to the fatigue strength of the drive belt ring component.
• the invention favourably allows the combined heat treatment process of the drive belt ring component to be performed in less time and with less ammonia gas as compared to the standing process. More in particular, it was found that with the above particular setup of the combined heat treatment process, i.e.
• the process time could be reduced to anywhere between 15 and 45 minutes depending on the actually applied temperature and ammonia concentration, as well as on the thickness of the case hardened surface layer to be formed.
• the process gas supplied to the process atmosphere i.e. to the heat treatment room or oven, is composed of the said ammonia gas and nitrogen gas only, whereby it is noted that due to the chemical processes in the heated process atmosphere a substantial amount of hydrogen gas will be present as well.
• process settings were determined to be a process temperature of 500 degrees Celcius, a process gas ammonia concentration of 3 vol.-%, mixed-in with 97 vol.-% nitrogen, and a process time of 30 minutes.
• Figure 1 is a schematic illustration of the drive belt the present invention relates to and of the transmission in which such belt is applied.
• Figure 2 is an illustration of the manner in which a laminated tensile means and a transverse element are mutually oriented within the drive belt.
• Figure 3 figuratively represents the known manufacturing method of a metal ring applied in the endless tensile means of the drive belt that includes the process step of combined ageing and nitriding.
• Figure 4 illustrates the process settings of the temperature T in °C and of the ammonia NH 3 concentration in vol.-% in the process gas supplied to the process atmosphere during the combined ageing and nitriding of the ring in accordance with the invention.
• FIG 1 shows schematically a continuous variable transmission (CVT) with a drive belt 1 wrapped around two pulleys 4 and 5, which belt 1 is made up of a laminated tensile means 2 in the form of two sets of mutually nested endless thin and flat metal rings 14 ( Figure 2), alternatively denoted bands 14 and an essentially continuous array of transverse elements 3, alternatively denoted transverse elements 3, which are mounted along the circumference of the tensile means 2 and which may freely slide there along.
• CVT continuous variable transmission
• Figure 2 depicts a front view of a transverse element 3 and a cross section of the laminated tensile means 2.
• the transverse element 3 laterally shows a side face 6 by which it rests against the conical face of one sheave of either a drive or a driven pulley.
• the rings 14 of the tensile means 2 are produced of high quality steel, e.g. maraging steel.
• a typical thickness of the rings 14 ranges from 0.15 to 0.25 mm, a typical width thereof ranges from 8 to 35 mm and a typical circumference length thereof ranges from 500 to 1000 mm.
• Figure 3 illustrates the presently relevant part of the known manufacturing method for the above described belt 1 , in particular for the rings 14 thereof, as is practised since the early years of metal push belt production.
• a sheet of base material 11 is bent into a cylindrical shape, whereby the sheet ends 12 that meet each other are welded together in a second process step II to form a tube 13.
• the tube 13 is annealed at a temperature of more than 800 °C in an inert process atmosphere such as a vacuum or nitrogen gas N 2 .
• the tube 13 is cut into a number of hoops 14, which are subsequently -process step five V- rolled and elongated to a thickness.
• the hoops 14 After rolling the hoops 14 are usually referred to as rings 14 or bands 14.
• the rings 14 are subjected to a further annealing process step VI to remove the internal stresses introduced during rolling. Thereafter, in a seventh process step VII, the rings 14 are calibrated, i.e. they are mounted around two rotating rollers and stretched to a predefined circumference length. In this seventh process step VII, also an internal stress distribution is imposed on the rings 14, which defines the so-called curling radius of the respective ring 14.
• the rings 14 are heat treated for 60 minutes and at 460 °C in a combined heat treatment process step of ring core hardening or ageing and of ring case hardening or gas soft-nitriding.
• the process atmosphere in the combined heat treatment process is supplied with process gas that is predominantly composed of inert gas, i.e. nitrogen gas "N 2 ", but also comprises 10 volume-% ammonia gas "NH 3 ".
• the tensile means 2 is formed by nesting a number of purposely selected rings 14, i.e. concentrically placing the rings 14 one around the other, as is also indicated in figure 3, whereby only a small positive or negative play is allowed between the adjacent rings 14 of the tensile means 2.
• the above known manufacturing method at least the combined heat treatment process step thereof may be significantly improved in terms of a shortening of the required process time by applying a specific and unexpected combination of the process parameters of processing temperature, time and process gas, an example whereof is illustrated in the figure 4.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Engineering & Computer Science (AREA)
• Heat Treatment Of Articles (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

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Citations (7)

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• 2010
  • 2010-12-20 JP JP2013545054A patent/JP5784144B2/ja not_active Expired - Fee Related
  • 2010-12-20 WO PCT/EP2010/007783 patent/WO2012083974A1/en not_active Ceased

Patent Citations (7)

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