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
  • 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
• • 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
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
  • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
  • C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
• • 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
  • C23C8/02—Pretreatment of the material to be coated
• • 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
• • 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
  • C21D2201/00—Treatment for obtaining particular effects
  • C21D2201/03—Amorphous or microcrystalline structure

Definitions

• the present invention relates both to a flexible steel ring according to the preamble of claim 1 hereinafter and to a method for producing such a ring.
• This type of ring is used as a component of a drive belt for a continuously variable transmission for, in particular, automotive use such as in passenger motor cars.
• the drive belt is typically composed of two sets of mutually concentrically arranged rings that are inserted in a recess of transverse members of the drive belt.
• the drive belt comprises a plurality of these transverse members that are arranged in mutual succession along the circumference of such ring sets.
• an individual ring normally has a thickness of only 0.2 mm or less, typically of about 0.18 mm.
• the drive belt is used for transmitting a driving power between two shafts, whereto the drive belt is passed around two rotatable pulleys, respectively associated with one such transmission shaft and provided with two conical discs defining a circumferential V-groove of the pulley wherein the drive belt is accommodated.
• the drive belt's radius at each pulley -and hence the rotational speed ratio between the transmission shafts- can be varied, while maintaining the drive belt in a tensioned state.
• This transmission and drive belt are generally known in the art and are, for example, described in the European patent publication EP- A-1243812.
• the performance of the drive belt is directly linked to not only the combined tensile strength of the ring sets, but to a large extent also the fatigue strength of the individual rings thereof. This is because, during rotation of the drive belt in the transmission, the tension and bending stress in the rings oscillate.
• the rings are core hardened and surface nitrided (i.e. gas-soft nitrided) in one or two heat treatment (s) that is/are part of the standing ring production process. More recently also stainless steels are being investigated as basic material for the manufacture of the ring.
• this parameter of the ring's performance can be improved upon by providing it with a so-called nano- crystalline surface layer, i.e. a relatively thin layer forming the outer surface of the ring wherein the metal crystals, i.e. the grains are particularly small. It was found that by such feature, in particular, the initiation of a fatigue fracture at the ring surface occurs only at considerably higher stress levels and/or only after more stress cycles have occurred.
• such nanocrystalline surface layer can be formed on steel products of varying composition by the mechanical deforma ⁇ tion thereof.
• plastic deformation processes of rolling, brushing and/or shot-peening the grain size of the steel is reduced, at least in the parts thereof that are plastically deformed in such process.
• a plastic deformation process must be selected that deforms only such thin surface layer of the product.
• the known rolling process will normally be less suited.
• the known shot-peening process can be appropriately arranged more easily.
• other suitable plastic deformation processes use fluid or gas (incl. plasma) as the medium to realize the deformation required for forming the nanocrystalline surface layer, e.g. ultrasonic- or laser- based processes.
• the said nanocrystalline surface layer of the ring is preferably formed prior the above-mentioned heat treatment of nitriding thereof. It was namely observed that with such nanocrystalline surface layer, the ring can be nitrided much faster than without. In other words, with nanocrystalline surface layer present, a desired thickness of the nitride layer of the ring is achieved in a favorably shorter (process) time and/or with a favorably lower concentration of ammonia gas in the process atmosphere.
• Figure 1 is a schematic illustration of a known drive belt and of a transmission incorporating such known belt.
• Figure 2 is a schematic illustration of a part of the known drive belt, which includes two sets of a number of flexible steel rings, as well as a plurality of transverse members .
• Figure 3 figuratively represents a known manufacturing method of the drive belt ring component that includes a process step of nitriding.
• Figure 4 is a schematic indication of a metal crystal structure including a nanocrystalline surface layer.
• Figure 5 is a photographic representation of a cross- section of the drive belt ring component revealing the crystal structure thereof including a nanocrystalline surface layer.
• Figure 6 figuratively represents a modification of the manufacturing method of figure 3 in accordance with the present disclosure.
• FIG 1 shows schematically a continuously variable transmission (CVT) with a drive belt 3 wrapped around two pulleys 1 and 2.
• Each pulley 1, 2 is provided with two conical pulley discs 4, 5, where between an annular, predominantly V-shaped pulley groove is defined and whereof one disc 4 is axially moveable along a respective pulley shaft 6, 7 over which it is placed.
• a drive belt 3 is wrapped around the pulleys 1, 2 for transmitting a rotational movement ⁇ and an accompanying torque T from the one pulley 1, 2 to the other 2, 1.
• Each pulley 1, 2 generally also comprises activation means that can impose on the said at least one disc 4 thereof an axially oriented clamping force directed towards the respective other pulley disc 5 thereof, such that the belt 3 can be clamped between these discs 4, 5. Also, a (speed) ratio of the CVT between the rotational speed of the driven pulley 2 and the rotational speed of the driving pulley 1 is determined thereby. This CVT is known per se.
• the drive belt 3 is made up of two sets 31 of mutually nested, flat and flexible steel rings 32 and of a plurality of transverse members 30.
• the transverse members 30 are arranged in mutual succession along the circumference of the ring sets 31, in such manner that they can slide relative to and in the circumference direction of the ring sets 31.
• the transverse segments 30 take-up the said clamping force, such when an input torque T is exerted on the so- called driving pulley 1, friction between the discs 4, 5 and the belt 3, causes a rotation of the driving pulley 1 to be transferred to the so-called driven pulley 2 via the likewise rotating drive belt 3.
• FIG. 3 illustrates a relevant part of the known manufacturing method for the drive belt ring component 32, as it is typically applied in the art for the production of metal drive belts 3 for automotive application.
• the separate process steps of the known manufacturing method are indicated by way of Roman numerals.
• a thin sheet or plate 11 of a maraging steel basic material having a thickness of around 0.4 mm is bend into a cylindrical shape and the meeting plate ends 12 are welded together in a second process step II to form a hollow cylinder or tube 13.
• the tube 13 is annealed.
• the tube 13 is cut into a number of annular hoops 14, which are subsequently -process step five V- rolled to reduce the thickness thereof to, typically, around 0.2 mm, while being elongated.
• the hoops 14 are usually referred to as rings 32.
• the ring 32 is subjected to a further, i.e. ring annealing process step VI for removing the work hardening effect of the previous rolling process step by recovery and re-crystallization of the ring material at a temperature considerably above 600 degrees Celsius, e.g. about 800°C.
• a seventh process step VII the ring 32 is calibrated by mounting it around two rotating rollers and stretching it to a predefined circumference length by forcing the said rollers apart.
• this seventh process step VII of ring calibration also internal stresses are imposed on the ring 32.
• the ring 32 is heat-treated in an eighth process step VIII of combined ageing or bulk precipitation hardening and nitriding or case hardening. More in particular, such combined heat-treatment involves keeping the ring 32 in an oven chamber containing a controlled gas atmosphere that comprises ammonia, nitrogen and hydrogen gas. In the oven chamber, i.e. in the process atmosphere, the ammonia molecules decompose at the surface of the ring 32 into hydrogen gas and nitrogen atoms that can enter into the metal lattice of the ring 32. By these interstitial nitrogen atoms the resistance against wear as well as against fatigue fracture is known to be increased remarkably. Inter alia it is noted that such combined heat-treatment can be carried out in the separate and subsequent stages of ageing and nitriding, which alternative process setup is known in the art.
• the eighth process step VIII of combined ring ageing and nitriding is carried out until a nitrided layer or nitrogen diffusion zone formed at the outer surface of the ring 32 is between 25 and 35 micron thick.
• a number of the thus processed rings 32 are assembled in to the ring set 31 by radially stacking, i.e. concentrically nesting these rings 32 with a minimal radial play or clearance between each pair of adjoining rings 32.
• radially stacking i.e. concentrically nesting these rings 32 with a minimal radial play or clearance between each pair of adjoining rings 32.
• the thus processed rings 32 show more or less correspondingly sized crystals/grains throughout the whole metal lattice thereof, i.e. also near the outer surface thereof.
• a typical, average grain size for such rings 32 is around 5 micron or more.
• the rings 32 are preferably provided with a surface layer of smaller sized, i.e. sub-micrometer sized grains, which feature was found to increase the fatigue strength of the rings 32 and which feature is schematically illustrated in figure 4.
• the presently, theoretically desired crystal structure of the ring 32 is indicated with smaller sized grains Gs at the surface of the ring 32 as compared to those grains Gb that are located more towards the bulk material of the ring 32.
• the smaller sized grains Gs at the ring surface are shown to define a layer of nano- crystalline ring material.
• Figure 5 illustrates the crystal structure of an actual ring 32 provided with a nanocrystalline surface layer NSL in accordance with the present disclosure.
• the crystals/grains of the ring 32 have been made visible by scanning electron microscopy (SEM) .
• SEM scanning electron microscopy
• the smallest grains at the ring surface are more than 100 times smaller than the largest grains in the bulk material of the ring 32.
• the grain size in the nanocrystalline surface layer NSL is about 50 nm on average, whereas in the bulk material of the ring the crystal grains are between 2 and 12 ⁇ wide in any direction.
• the nanocrystalline surface layer NSL is approximately 5 ⁇ thick.
• the above nanocrystalline surface layer NSL is preferably created by subjecting the ring 32 to a shot- peening process.
• shot-peening process is included in the above-described, known manufacturing method for the drive belt ring component 32 in between the seventh process step VII and the heat treatment of ring nitriding in the eighth process step VIII thereof, as is schematically illustrated in figure 6.
• the process step SP indicates the presently proposed shot-peening process, wherein the ring 32 is mounted and rotated around (for example) three mounting rollers and wherein two spray nozzles 70 spray (for example) miniscule glass beads onto at least the radially facing outer surfaces of the ring 32.
• the nitriding process By providing with a nanocrystalline surface layer NSL to the rings 32 before these are nitrided, the nitriding process, as such, is enhanced.
• the nano- crystalline surface layer NSL favorably allows for a reduction of either one or both of the duration and/or of the ammonia-concentration in the process atmosphere of the nitriding process that is/are required to provide the ring 32 with a nitrided layer of the desired thickness.

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

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• 2014
  • 2014-12-24 CN CN201480070855.XA patent/CN105849436B/zh not_active Expired - Fee Related
  • 2014-12-24 EP EP14830807.5A patent/EP3087293A1/de not_active Withdrawn
  • 2014-12-24 WO PCT/EP2014/079290 patent/WO2015097277A1/en not_active Ceased

Non-Patent Citations (1)

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