WO2012089228A1

WO2012089228A1 - Method and device for processing a metal ring, an annular metal band thus formed and a drive belt in which the annular metal band is used

Info

Publication number: WO2012089228A1
Application number: PCT/EP2010/007981
Authority: WO
Inventors: Paul VELTMANS; Johannes Adrianus Maria Vermeer; Koyama Satoshi; Wilhelmus Adrianus Antonius NELIS
Original assignee: Robert Bosch G.M.B.H.
Priority date: 2010-12-30
Filing date: 2010-12-30
Publication date: 2012-07-05
Also published as: JP5855125B2; MX2013007507A; JP2014506312A

Abstract

The invention concerns a method for treating a predominantly radially oriented side face (15) of a metal ring (14) by temporarily melting a lateral edge part of the ring (14), at least including a part of the side face (15), until the entire circumference of the ring (14) has been progressively melted and allowed to solidify again, wherein either the said part of the side face (15) is cleaned prior to the melting of the lateral edge part of the ring (14), or the said lateral edge part of the ring (14) is annealed after the melting thereof.

Description

METHOD AND DEVICE FOR PROCESSING A METAL RING, AN ANNULAR METAL BAND THUS FORMED AND A DRIVE BELT IN WHICH THE ANNULAR METAL BAND IS USED

The present invention firstly relates to a method for processing a metal ring, 5 as described, inter alia, in the preamble of claim 1. Further the invention relates to a

continuous or annular metal band that is formed from such metal ring.

Such an annular metal band is well-known from its application in a drive belt for a continuously variable transmission that typically comprises two sets of a number of such annular metal band in a mutually concentrically stacked arrangement, as well 10 as a number of plate-like transverse elements that are slideably mounted on such

arrangement and that form an essentially continuous row along the circumference thereof. A drive belt of this type, as well as the annular metal band used therein, is generally known, for example from European patent publication EP-A-0181670 in the name of applicant.

15 Hitherto, the annular metal band of this type, at least on an industrial scale, is

shaped by cutting off a ring section from a metal tube formed from a base material in sheet form, followed by plastically deforming such metal ring to produce the annular metal band with a desired radial thickness and tangential or circumferential length with the aid of a rolling process, optionally preceded and/or followed by one or more

20 heat treatments of the metal.

Before rolling, the metal ring is subjected to a combined edge deburring and shaping process such as stone-tumbling or edge melting, wherein at least the edges of the metal ring, but typically the entire axial or lateral side faces thereof, are shaped into more or less smoothly curved transition surfaces. The basic principles of the

25 latter process of edge melting have been described by applicant in the European

patent application EP-A-1939488.

It has, however, been found that when applying such edge melting process in the overall manufacturing process of the (end-product) annular metal bands, some of these thus formed bands show surface imperfections, which surface imperfections

30 can, i.e. depending on the size and/or the shape thereof, negatively influence the

fatigue strength thereof. Of course, such material property of fatigue strength is known to be a very, if not the most, important parameter for the presently considered drive belt application of the annular metal band.

Accordingly, it is an object of the present invention is to improve the surface

35 finish of the annular metal bands when processed according to a method including the step of edge melting of the metal rings.

According to the invention, such object may be achieved by applying the additional process step according to the characterizing portion of the Claim 1 and/or of the Claim 2 hereinafter.

The invention relies on the insight that, although the edge melting process step is advantageous in that it can provide the end-product annular metal bands with high quality transition surfaces, in some cases surface imperfections can still be formed. At the location of such surface imperfection that may become worse in a subsequent process step of rolling the metal ring, a fatigue fracture may initiate during use in a transmission of the end product annular metal band as part of the drive belt. Obviously, such fracture may provoke the undesired early failure of the drive belt.

In a first embodiment of the invention, the edge melting process is preceded by an edge cleaning process, wherein foreign particles are largely removed from the surface of the metal ring. It was determined that, as a result, no, or at least considerably fewer, surface imperfections will then be formed in the said edge melting process. Preferably, the metal rings are cleaned by treating them with dry ice or frozen carbon-dioxide, which cleaning process was found to provide a very good cleaning result and which cleaning process favourably avoids the need for water, and/or chemical solvents. More preferably, compressed air is used to carry and apply the dry ice to the surface of the metal ring. In particular, the metal ring is treated with dry ice only locally, i.e. only at the lateral side faces thereof.

Naturally, many more cleaning methods are known in the art that may likewise be suitable (in principle) to be applied in the above first embodiment of the invention.

In a second embodiment of the invention the edge melting process is succeeded by an edge annealing process, wherein at least the metal at the edges of the ring are re-crystallised to largely remove any internal stress that is caused by the said surface imperfections. As a result, the detrimental effect of these surface imperfections on the fatigue strength of the end-product annular metal band is largely mitigated. Preferably, the metal of the ring is heated inductively for such re- crystallisation. More preferably, an electrically energised wire coil is used for such inductive heating.

Naturally, many more annealing methods are known in the art that may likewise be suitable (in principle) to be applied in the above second embodiment of the invention.

In a third embodiment of the invention the edge melting process is both preceded by the above-described edge cleaning process and succeeded by the above-described edge annealing process for realising an optimum result in terms of the present invention.

The invention also relates to the devices for carrying out the above processes according to the invention.

The invention will be explained in more detail below on the basis of an example, in which:

Figure 1 is a schematic representation of a part of the well-known drive belt for a continuously variable transmission;

Figure 2 is a diagram representing a known sequence of process steps for manufacturing an annular metal band of a drive belt from plate-shaped base material;

Figure 3 provides a schematic side elevation of the very basics of a device for carrying out the process step of edge melting;

Figure 4 is a photograph of a cross section of the annular metal band obtained by the edge melting process to be used in a drive belt of a continuously variable transmission;

Figure 5 is a schematic representation of a first embodiment of the invention; Figure 6 is a schematic representation of a second embodiment of the invention;

Figure 7 is a schematic representation of a third embodiment of the invention; and

Figure 8 provides a schematic side elevation of the very basics of a device for carrying out the process steps within the scope of the present invention.

The known drive belt 3 that is schematically represented in part in figure 1 comprises two sets 31 of mutually nested, annular metal bands 32, as well as a several individual metal transverse elements 33, which transverse elements 33 are each provided with a recess 34 on either lateral side thereof wherein the band sets 31 are provided. In the known drive belt 3 the transverse elements 33 form a row that spans and essentially continuously fills the entire circumference of the band sets 31. During use in a transmission, the drive belt 3 is held between two transmission pulleys, whereby the band sets 31 of the belt 3 are tensioned such that the row of transverse elements 33 can transmit a drive force from one pulley to another while being guided by the band sets 31. Further during use, the drive belt 3 rotates causing the bands 32 of the band sets 31 thereof to also rotate, due to which rotation the bands 32 are subjected to oscillating bending and tensile stresses. As a result, the fatigue strength of the bands 32 typically determines the service life of the drive belt 3 in a given application of the transmission.

Figure 2 diagrammatically shows the major steps in a typical manufacturing process for forming the annular metal band 32. In a first process step I, a pre-cut plate 11 of base material having a thickness of between 0.250 mm and 0.500 mm is bended into a cylindrical shape and the meeting plate ends 12 are welded together in a second process step II to form a open cylinder or tube 13. In a third step III of the process the tube 13 is annealed in an industrial oven or furnace 16. Thereafter, in a fourth process step IV the tube 13 is cut into a number of metal rings 14, the lateral side faces 15 whereof which are subsequently -process step five V- melted by irradiation thus reshaping these. Then the metal rings 14 are rolled in a sixth process step VI to reduce the thickness thereof to less than 0.250 mm, typically around 0.185 mm, while being elongated. After rolling the rings 14 are referred to as annular metal bands 32 or bands 32 for short.

The bands 32 are then subjected to a further or band annealing process step VII for removing the work hardening effect of the previous rolling process (i.e. step five VI) by recovery and re-crystallisation at a temperature considerably above 600 degree Celsius, e.g. around 800 degree Celsius. Thereafter, in an eight process step VIII, the bands 32 are calibrated, i.e. they are mounted around two rotating rollers and stretched to a predefined circumference length by forcing the said rollers apart. In this eight process step VIII, also an internal stress distribution is imposed on the bands 32. Thereafter, the bands 32 are heat-treated in two separate process steps, namely a ninth process step IX of ageing or bulk precipitation hardening and a tenth process step X of nitriding or case hardening. More in particular, both such heat- treatments involve heating the bands 32 that is supplied with process gas that is typically composed of nitrogen and some, e.g. around 5 volume-% of hydrogen for ring ageing and of nitrogen and ammonia for ring nitriding. Both heat-treatments typically occur within the temperature range from 400 degrees Celsius to 500 degrees Celsius and can each last for less than 30 to over 120 minutes in dependence on the metal used for the bands 32 (i.e. typically a maraging steel alloy), as well as on the mechanical properties desired for the bands 32.

Finally, a laminated band set 31 of thus processed bands 32 is formed by radially stacking, i.e. nesting, a number of bands 32, as is further indicated in figure 3 in the last depicted eleventh process step XI. Obviously, the bands 32 of the band set 31 have to be suitably dimensioned, e.g. have to differ slightly in circumference length to allow the bands 32 to be closely fitted one around the other. To this end the bands 32 of the band set 31 are typically purposively selected from a stock of bands 32 of varying dimensions.

In figure 3, the basics of a exemplary device suitable for carrying out the process step V of edge melting are schematically indicated. The device contains an irradiation source in the form of a laser 63 that is mounted facing, i.e. aimed at, one of the lateral side faces 15 of the ring 14 that has been placed on a table 60. The table 60 is rotatable by means of an electric motor 62. During processing, i.e. when the process step V of edge melting takes place, the laser 63 locally irradiates the metal ring 14 to locally heat the ring material to beyond its melting point. At the same time the motor 62 is activated to slowly rotate the ring 14 and thus passing the entire lateral side face 15 through the laser beam B of the laser 63, until the entire circumference of the respective lateral side face 25 of the metal ring 14 entire side face 15 has been temporarily irradiated and melted. Alternatively, the laser 63 is moveable relative to the ring 14 capable of following the contour of the lateral side face 15 thereof. Then, the metal ring 14 is turned upside down and the respective other one side face 15 thereof is processed in the same way. Alternatively, the device may be equipped with two lasers 63 mounted on respective, mutually opposite axial sides of the metal ring 14 such that both lateral sides faces 15 thereof can be processed at the same time.

In the edge melting process step V any burrs resulting from the previous process step IV of cutting the tube 13 into rings 14 disappear and, moreover, due to the surface tension of the molten metal, the lateral side faces 15 of the metal ring 14 are shaped into a smoothly curved surface. Figure 4 provides a photographic cross- section of a lateral side part of the thus treated ring 14, showing its microstructure of the metal. In the cross-section of figure 4 both a first or outer zone MZ of ring material that has been melted and a second in between zone HAZ of heat affected ring material are discernable. The smoothly, convexly curved almost semi-circular shape of the side face 15 of the metal ring 14 obtainable with the edge melting process allows the end-product metal band 32 to be formed with a suitably high fatigue strength, as is highly preferred in relation to the intended application thereof in the drive belt 3.

According to the present invention it is highly favourable to avoid foreign particles to become embedded in the ring material when this is temporarily melted in the edge melting process step V, or at least to mitigate the disadvantageous effect of such embedded particles. In particular, the fatigue strength of the (end-product) annular metal bands 32 could be considerably improved thereby. More in particular the present invention provides for a novel process step to be included in the above- described overall manufacturing process for forming the annular metal band 32.

In a first embodiment of the invention that is illustrated in figure 5, the process step V of edge melting is preceded by a process step V-a of edge cleaning wherein dry ice or frozen carbon-dioxide is blown using compressed air through a nozzle 70 onto the side face 15 of the ring 14, thus at least largely removing the particles that may be present thereon. As a result no, or at least considerably fewer, particles can and do become embedded in the metal ring 14 in the subsequent process step V of edge melting.

In a second embodiment of the invention that is illustrated in figure 6, the process step V of edge melting is succeeded by a process step V-b of edge annealing by annealing at least the edges including the side face 15 of the ring 14 in a furnace 16.

In a third embodiment of the invention that is illustrated in figure 7 and to achieve an even better result than with the above-described first or second embodiments, the process step V of edge melting is both preceded by a process step V-a of edge cleaning and succeeded by a process step V-b of edge annealing.

It is noted that either one or both of said novel process steps V-a, V-b of edge cleaning and/or edge annealing can be favourably integrated in the edge melting device, i.e. in the device for carrying out the process step V of edge melting, as is schematically indicated in figure 8. Departing from the edge melting device illustrated in figure 3, the dry ice nozzle 70 can be included therein, preferably placed just in front of the laser 63, as seen in the direction of relative rotation between the table 60 and the laser 63, and/or, an electrically energised wire coil 71 can be included therein, preferably placed around the ring 14 just after the laser 63, as seen in the direction of relative rotation between the table 60 and the laser 63 (instead, in figure 3, the placement of the coil 71 is opposite the laser 63). By activating such coil 71 with an alternating current the material of the ring 14 can be locally, inductively heated to perform the said process step V-b of edge annealing.

Claims

1. Method for treating a predominantly radially oriented side face (15) of a metal ring (14) by temporarily melting a lateral edge part of the ring (14), at least including a part of the side face (15), until the entire circumference of the ring (14) has been progressively melted and allowed to solidify again, characterised in that, prior to the melting of the lateral edge part of the ring (14), at least the said part of the side face (15) is cleaned.

2. Treating method according to claim 1 , characterised in that, the said cleaning of the said part of the side face (15) is cleaned prior to the melting of the lateral edge part of the ring (14), but after any other process steps preceding the said melting have been performed.

3. Treating method according to claim 1 or 2, characterised in that, the said part of the side face (15) included in the said lateral edge part of the ring (14) is cleaned using frozen carbon-dioxide, which frozen carbon-dioxide is preferably carried and applied by compressed air.

4. Method for treating a predominantly radially oriented side face (15) of a metal ring (14) by temporarily melting a lateral edge part of the ring (14), at least including a part of the side face (15), until the entire circumference of the ring (14) has been progressively melted and allowed to solidify again, characterised in that after the solidifying thereof, at least the said lateral edge part of the ring (14) is annealed.

5. Treating method according to claim 4, characterised in that, the said lateral edge part of the ring (14) is annealed by inductively heating, e.g. by passing the ring (14) through a wire coil energized by an alternating electric current.

6. Method for treating a predominantly radially oriented side face (15) of a metal ring (14) by temporarily melting a lateral edge part of the ring (14), at least including a part of the side face (15), until the entire circumference of the ring (14) has been progressively melted and allowed to solidify again, characterised in that prior to the melting of the lateral edge part of the ring (14), at least the said part of the side face (15) included in the said lateral edge part of the ring (14) is cleaned, and in that, after the solidifying thereof, at least the said lateral edge part of the ring (14) is annealed.

7. Annular metal band (32) produced from a metal ring (14) treated in accordance with any one of the treating methods of claims 1-6.

8. Drive belt (3) provided with at least one set (31 ) of a number of mutually nested, annular metal bands (32) produced from a metal ring (14) treated in accordance with any one of the treating methods of claims 1-6.

9. Device for carrying out the treating method of claim 1 , 2 or 3. provided with a table (60) whereon the metal ring (14) is to be placed and with an irradiation source (63) that faces the table (60) for melting the said lateral edge part of the ring (14) including the said part of the side face (15), characterised in that, the device further includes a nozzle (70) for spraying a cleaning agent onto the side face (15).

10. Device for carrying out the treating method of claim 4 or 5, provided with a table (60) whereon the metal ring (14) is to be placed and with an irradiation source (63) that faces the table (60) for melting the said lateral edge part of the ring (14) including the said part of the side face (15), characterised in that, the device further includes an electrically energised wire coil (71 ) for inductively heating the ring (14).

11. Device for carrying out the treating method of claim 6, provided with a table (60) whereon the metal ring (14) is to be placed and with an irradiation source (63) that faces the table (60) for melting the said lateral edge part of the ring (14) including the said part of the side face (15), characterised in that, the device further includes both a nozzle (70) for spraying a cleaning substance onto the side face (15) and an electrically energised wire coil (71 ) for inductively heating the ring (14).