JP2009539619A - Manufacturing method for making thin metal rings - Google Patents

Abstract

The present invention comprises a thin metal ring (16), such as a push belt (1) comprising at least one such ring (16) and a number of transverse metal elements (3). With regard to a method for manufacturing, the method comprises: cutting the plate section (12) from the total length (L) of the elongated steel plate (11); bending the plate section (12) into a cylindrical shape; Welding the adjacent ends (13) of the section (12) to form a tube (14), and processing steps (III, IV, Vl), wherein the plate section (12) is bent into a cylindrical shape as described above In processing step (III), the plate section (12) is bent in a direction essentially perpendicular to the overall length (L) of the elongated steel plate (11), ie along its width (W).
[Selection] Figure 6

Description

  The present invention relates to a manufacturing method for making a thin metal ring for use in a stacked set of endless rings of push belts as defined by the preamble of claim 1 below. Such a push belt is generally known in the art and is described in detail, for example, in Patent Document 1. This belt is mainly used as a means for power transmission between two adjustable pulleys in known continuously variable transmissions applied to automobiles.

  Known push belts consist of a number of relatively thin transverse metal elements slidably provided along one or two of such stacked sets of rings. These rings are usually manufactured from precipitation hardened steel compositions, such as maraging steels, which can be relatively advantageous for processing it from raw matrix towards the desired shape and properties of the ring. And the importance of the properties of high tensile strength and resistance to tensile and bending stress fatigue.

In a typical manufacturing method for this type of ring, the following processing steps are included:
-Preparing an ingot of a metal composition required as a base material of the ring;
Rolling the ingot in several stages into an elongated (rectangular) steel plate having a minimum thickness for its width and length dimensions;
-Cutting the plate-section shaped steel plate at right angles to the length direction of the elongated steel plate, the length direction of which coincides with the rolling direction of the previous processing step;
-Bending the plate into a cylindrical shape along the length of the elongated steel plate;
-Welding adjacent plate edges to form a tube;
-Detaching the ring section from the tube.

  Typically, the rings thus formed are subjected to a number of further processing steps, as illustrated, for example, in US Pat. Is realized. In this push belt, a plurality of such rings are radially nested inside each other, i.e. stacked concentrically with a defined radial play provided between adjacent rings, Forming each pair of rings.

  In the above-mentioned previous and universally applied manufacturing methods, the tube has its circumferential direction and thus also the circumferential direction of the ring separated from it, the longitudinal direction of the elongated steel plate, i.e. the rolling direction of the previous processing step. Formed to match. This particular orientation of the tube associated with the elongated steel plate from which it is formed has been considered an inevitable fundamental aspect of the fabrication process from the start of commercial push belt manufacturing in the 1980s to today. This type of belief is that many of the currently relevant properties of metals used as ring materials, including their fatigue properties and impact strength (the latter parameter indicates their resistance to fatigue failure), are certainly present and Similarly, when non-metallic inclusions are included in the material, it is based on previous and generally well-known insights in that the rolling direction is much better in the direction directed perpendicular thereto. In fact, there are many publications that convey this kind of common technical insight.

  References to illustrate the above are Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 as a recent confirmation. These three publications, however, serve only as random examples of widely known technical knowledge. Based on this widely practiced insight, the push belt manufacturing process described above has been arranged so that the circumferential direction of the ring coincides with the rolling direction in previous processing steps since the beginning of the 1980s.

  Also, in the known manufacturing method described above, the ring has different perimeters by simply increasing the diameter of the tube, i.e. the length of the plate section cut from the elongated steel plate, in order to produce push belts of different lengths. Can be provided.

Next, despite the existing knowledge and preferences described above, Applicants performed a basic mechanical property test with a ring material while loading it perpendicular to the rolling direction. Surprisingly, these tests are performed at least in any direction where the fatigue strength of the material of the elongated steel plate is applied in almost any direction, i.e. whether the fatigue load is applied in the longitudinal direction of the steel plate or perpendicular thereto. Clarified that they are the same. This type of conclusion has been drawn at least for the currently investigated push belt. Obviously, some aspect of the material of the present application, its treatment in the overall fabrication process, and / or its specific composition, ie, about 18 parts nickel, 9 parts cobalt, 5 parts molybdenum, 0.5 parts by weight Maraging steel with titanium and a balance of iron invalidates, at least, inapplicability to the dominating technology insights. However, the decisive aspect has not yet been clearly identified.
EPA 1 403 551 European patent application EPA 1 055 738 G. The paper by Fowler, entitled “Effects of non-metallic inclusions on threshold behavior in fatigue”, Materials Science and Engineering Journal, Vol. 39 (pages 121-126), 1979, 1996 ASM Handbook, Volume 19: “Fatigue and Fracture Properties of Structural Steels”, “Fracture Toughness” and “Fatigue Crack Growth” chapters, Y. Furuya et al., “Inclusion Controlled Fatigue Properties of 1800 MPA Class Spring Steel”, Metallurgical and Materials Transactions, Volume 35A (pages 3737-3744), December 2004.

  In accordance with the invention, it is therefore also possible to bend a section of a sheet cut from an elongated steel sheet in its width direction, i.e. without obviously affecting its fatigue strength, in order to form a tube. Although this novel feature of the manufacturing method may not seem very noteworthy or advantageous as such, it will be understood that it is the overall manufacturing process and thereby manufactured. Certainly provides a noticeable improvement in both rings.

  In known manufacturing methods, the axial tube dimensions and thus the number of ring segments that can be separated therefrom is determined by the width of the elongated steel plate, so that theoretically, a wider steel plate is less than required. It provides a more efficient and economical manufacturing process through plate cutting, pipe bending, welding and processing operations. However, as a practical matter, the width of the sheet is limited to specific dimensions. First, because the thickness of the sheet varies along its width due to the technical limits of the immediately preceding rolling stage, the thickness variation increases from a certain point, i.e., to the sheet width, as the sheet becomes wider. It grows so that it exceeds the dimensional tolerance values of the current ring fabrication process for push belts. Second, the small ingot matrix generally provides more advantageous material properties with respect to optimal homogeneity and purity, eg, defined by the number and size of non-metallic inclusions contained therein. That is, the larger the ingot, the more difficult and / or more expensive it is to control this kind of homogeneity and purity, so that the dimensions of the steel sheet, including its width, can It should be noted that it is related to and limited by the dimensions of For a particular ingot size, i.e. sheet width, it is no longer-economically-to achieve the material properties required for the final product ring, which prefers a homogeneous and pure matrix to achieve its optimum fatigue properties. Not possible. As an example of this kind of material properties required for push belt ring components, reference is made to European Patent Application Publication No. EP-A-1 243 812, which further discusses its mechanism of fatigue failure in detail.

  However, with this novel manufacturing method, the axial tube dimensions are no longer limited to the width of the elongated steel plate. Here, a very efficient and more economical ring fabrication process can be realized, and by increasing the axial tube dimensions over what has been achieved previously, plate cutting and tube bending and welding The number of times the processing steps are performed can be advantageously minimized. In this novel manufacturing method, the width of the elongated steel plate is determined by the perimeter of the ring piece cut from it, which is typically about 250 to 350 mm, i.e. advantageously applied to the maximum in conventional manufacturing methods. Reach only half of the sheet width that can be done. With this kind of relatively limited width of the elongated steel plate, extremely high precision ring thickness and material homogeneity and purity can be achieved at a relatively low cost.

(Brief description of the drawings)
The above basic features of the present invention will now be described by way of example with reference to the drawings, in which:
FIG. 1 is a schematic view of a push belt of the present invention and a transmission to which this type of belt is applied.
FIG. 2 is an illustration of how the stacked tensioning means and the transverse elements are directed towards each other in the push belt.
FIG. 3 diagrammatically represents the currently relevant processing steps in a known method for manufacturing thin metal rings used in stacked sets of endless rings for push belts.
FIG. 4 is a photograph of the microstructure of the cold rolled maraging steel.
FIG. 5 shows the measured fatigue strength of various specimens made from materials for push belt ring components. and,
FIG. 6 schematically represents a method for manufacturing a thin metal ring for a push belt of the present invention.

  FIG. 1 schematically shows a continuously variable transmission (CVT) with a drive belt 1 wound around two pulleys 4 and 5, the belt 1 being thin and endlessly nested in concentric circles. Consists of two sets 2 of metal rings 16 and a basically continuous arrangement of transverse elements 3 that are attached along the circumference of the sets 2 of ring 16 and that can slide freely along them. Is done. This type of drive belt 1 is generally referred to as a push belt 1. Both the push belt 1 and the continuously variable transmission as a whole are well known.

  FIG. 2 represents a front view of the transverse element 3 and a sectional view of the set 2 of rings 16 in the longitudinal section of the belt 1. The transverse element 3 shows the side 6 sideways, by which it engages the conical mesh wheel of the transmission pulleys 4, 5. The ring 16 is made of high quality steel, such as nitrided and precipitation hardened maraging steel, typically having a thickness of about 0.18 mm, a width of about 10 mm, and a perimeter of about 500 to 750 mm. .

  In FIG. 3, the separate processing steps for creating the stacked ring set 2 of the push belt 1 are shown schematically and identified as Roman numerals.

  In a first processing step I, the slab 10 is cast, wrought, and possibly cut to dimensions that deviate from the desired steel alloy ingot. This slab 10 is subsequently rolled in a second processing step II to form an elongated steel plate 11 having a minimum thickness for its width W and length L dimensions. For ease of transport, the steel plate 11 is often coiled in the longitudinal direction into a spiral shape (not shown). Thereafter, in a third processing step III, the plate section 12 is cut off from the stretched-out steel plate 11, which is subsequently bent into a cylindrical shape in the longitudinal direction L of the elongated steel plate 11, And adjacent plate ends 13 are welded together in a fourth processing step IV to form a tube 14. Therefore, the tube axis is directed along the width W of the steel plate 11. In the fifth processing step V, the tube 14 is annealed. Then, in a sixth processing step VI, the tube 14 is cut into a plurality of annular strips or rings 16, which are then rolled to the processing step 7 VII-required perimeter length and / or radial thickness. And stretched so that the axial width of the ring 16 is only slightly affected. After rolling, the ring 16 becomes considerably more flexible, especially in the circumferential direction. The rolled ring 16 is subjected to a further annealing step VIII in order to remove internal stresses introduced during rolling, and in the ninth processing step IX the ring 16 is calibrated, ie usually determined individually. Is stretched longitudinally to a predefined perimeter, which in this example is achieved by mounting a ring around two rotating rolls separated radially. In the next tenth processing step X, the ring 16 undergoes a heat treatment. Typically, the heat treatment comprises at least two stages, in which the ring 16 is precipitation hardened, i.e. aged (indicated by the letter “A”) in the first stage, and in the second stage the ring 16 is nitrided ( The added hardness is applied to the outer surface layer of the ring 16 as well as compressive stress (indicated by the letter “N”).

  From a plurality of such treated rings 16, the ring set 2 stacks a plurality of intentionally selected rings 16 radially, ie, nested, as further shown in FIG. Is formed by. In order to obtain the required number of rings 16 suitable for forming one set 2, the representative dimensions of each processed ring 16, for example its perimeter, are measured in the eleventh processing step XI. The ring 16 is then sorted and stored by this type of length. Thereafter, in the twelfth and final processing step XII, the set 2 of rings 16 is obtained by nesting together the required number of appropriately sized rings 16 from this type of inventory of sorted rings 16. Assembled.

In currently applied maraging steels containing approximately 0.3-0.6 parts by weight titanium, as shown in FIG. 4, the titanium nitride (TiN) inclusions are a series of extremely dense, substantially uninterrupted series. It exists in the form of a so-called string of inclusions in an elongated steel plate. Generally, these strings have a length of about 100 to 300 micrometers and a width of about 10 to 30 micrometers, and are oriented in a straight line in the length direction L of the thin plate 11 for the reason , Because larger TiN inclusions are formed when they break down into a plurality of smaller pieces smeared in the rolling direction in the second processing step II above under the influence of rolling force. . These inclusions ultimately limit the functional life of the push belt due to one fatigue failure of the endless ring, which failure is usually of this kind due to its well-known local stress-increasing action. Begins at or near the object. In this respect it focuses on this phenomenon
Is referenced again.

  Due to the anisotropic nature of the inclusions, i.e. their occurrence as strings oriented in the rolling direction, the fatigue strength of the ring material has always been regarded as optimal in the rolling or longitudinal direction. For push belt applications, this means that according to existing technical insights, the circumferential direction of the ring should coincide with the rolling direction.

  However, recent studies by the applicant have shown that, at least for the currently investigated materials, there is no significant difference in fatigue strength between the rolling direction and the direction oriented perpendicular to it. Do not. In this regard, reference is made to the diagram of FIG. 5 in which the measured fatigue strength of a plurality of specimens is plotted on a logarithmic scale with respect to the amplitude of the applied periodically varying tensile stress. Here, the fatigue strength is quantified by the number of stress cycles until failure of the specimen, while the stress amplitude is defined as the maximum tensile stress applied to each cycle minus the minimum tensile stress, which stress is − Satisfy the constraint that the ratio (ie, its quotient) between the underlying fatigue tests is constant.

  In FIG. 5, each (white circle) circle represents the test result obtained when tensile stress is applied in the rolling direction in the second processing step II, while each (blackened) square represents the rolling The test result obtained by the tensile stress applied to the direction orthogonal to a direction is represented. What can be evident from FIG. 5 was that it could be demonstrated that there is no noticeable difference in fatigue strength between the two test directions.

  Thus, according to the present invention, the efficiency of the known ring manufacturing method is achieved by bending the plate section 12 in the width direction W of the elongated steel plate 11 to form the tube 14 in the third processing step III described above. The push belt 1 can be improved without loss to the final fatigue strength, and a novel setup of this process is illustrated in FIG. The tube axis is thus along the length L of the steel plate 11. By this measure, the axial dimension of the tube 14 can exceed the width of the elongated steel plate 11, i.e. the plate section 12, so that advantageously less plate cutting operations (processing step III), tube bending and welding operations (processing). Step IV) needs to be performed on the number of rings 16 to be created.

  Furthermore, it is noted that in the novel setup of the ring manufacturing method according to the invention, the ring is rolled in the second direction at the seventh processing step VII, which is the first of the second processing step II. It is directed at right angles to the rolling direction. As a result of this, it is possible to expect that the inclusion strings formed in the first rolling direction by the shearing force in the previous rolling treatment step II will be caused by the shearing force exerted in this seventh treatment step VII. , In any stretch that is broken in the second direction at right angles to it. The novel ring manufacturing method can thereby reduce the inclusion-strand stress-increasing action and thus improve the resistance of the ring 16 to fatigue failure. In this way, the present invention unlocks the possibility of being unknown and even difficult to reach before improving the fatigue strength of the push belt end product.

  In order to be able to manufacture rings 16 of different perimeter lengths in the process according to the invention, avoiding having to prepare separate steel plates 11 of different width dimensions to create tubes 14 of different diameters. Instead, it is presently proposed to change the thickness of the elongated steel plate 11 instead, preferably in direct proportion to this type of perimeter. This thickness can be advantageously and easily controlled within the scope of the above manufacturing method in the last rolling stage of its existing second processing step II. Of course, the thicker the elongated steel 11- and the ring 16- disconnected therefrom, the longer these rings 16 are after rolling to their final thickness in the seventh processing step VII, And vice versa.

  In accordance with a further independent aspect of the present invention, the above-described strategy of changing the thickness of the elongated steel plate 11 with respect to the perimeter required for the ring 16, preferably in direct proportion, is further dependent on the conventional manufacturing method described above. It can also be applied effectively in By applying this measure, the plate section 12 can be cut from the elongated steel plate 11 with a fixed length, i.e. irrespective of the circumferential length of the ring 16 made therefrom. This means that this type of plate is a bend and the diameter of the welded tube 14 also has a constant value, the characteristics of which are particularly simplified, ie less complicated product handling and / or From the point of view of skillful handling, it brings considerable advantages. As an example for this, the machine no longer has to deal with tubes 14 of different diameters, which can be advantageously simplified, in step III plate bending, in step IV tube welding, and in step VI. Reference is made to the design of the manufacturing machine and tool used for the ring detachment. In particular, a single tube mounting a fixed diameter yoke can be used in process steps IV and VI, and furthermore, the welding torch and ring cutter used in these process steps IV and VI are fixed in a radial position. Can be designed to engage the tube 14. As far as processing step III is concerned, it can be obvious and, in this case, a less flexible and therefore more basic and simpler tool is needed to process a plate 11 of varying dimensions. In comparison, it may be advantageous and sufficient to successfully process a plate 11 having the same length and width dimensions.

  Of course, this latter measure in accordance with the further independent aspect of the present invention certainly requires the additional effort of having to change the sheet thickness with respect to the ring circumference. However, as described above, such thickness is only a minor effect since the sheet thickness is easily controlled in the final rolling stage of the second processing step II.

It is the schematic of the transmission of the push belt of this invention, and this kind of belt is applied. FIG. 4 is an illustration of a method in which stacked tensioning means and transverse elements are directed toward each other in a push belt. FIG. 2 diagrammatically represents currently relevant processing steps in a known method for manufacturing thin metal rings used in stacked sets of endless rings for push belts. It is a photograph of the microstructure of cold-rolled maraging steel. FIG. 3 shows the measured fatigue strength of various specimens made from materials for push belt ring components. and, Fig. 2 diagrammatically represents a method for producing a thin metal ring for a push belt according to the invention.

DESCRIPTION OF SYMBOLS 1 Push belt 2 Ring 16 set 3 Transverse element 4 Pulley 5 Pulley 11 Steel plate 12 Plate section 14 Tube 16 Ring

Claims (8)

A method for manufacturing a thin metal ring (16), in particular for a push belt (1) comprising at least one such ring (16) and a number of transverse metal elements (3), comprising: The method is
-Separating the plate section (12) from the total length (L) of the elongated steel plate (11);
-Bending the plate section (12) into a cylindrical shape;
-Welding adjacent ends (13) of said bent plate section (12) to form a tube (14);
Detaching the ring (16) from the tube (14) and processing steps (III, IV, Vl),
In the processing step (III) in which the plate section (12) is bent into a cylindrical shape, the plate section (12) is basically perpendicular to the full length (L) of the elongated steel plate (11). A bending along its width (W).   A method for manufacturing a thin metal ring (16) according to claim 1, wherein the axial dimension of the tube (14) formed therein is the width of the elongated steel plate (11). A method characterized by exceeding (W).   3. A method for manufacturing a thin metal ring (16) according to claim 1 or 2, wherein the method reduces the thickness of the ring (16) by rolling in the circumferential direction. (VII) The method characterized by the above-mentioned.   In particular for a push belt (1) comprising at least one such ring (16) and a number of transverse metal elements (3), as claimed in any of claims 1, 2 or 3. A method for manufacturing a thin metal ring (16), the method comprising at least two processing steps (II, VII), wherein the thickness of the material for the ring (16) is In the two processing steps (II, VII), the shearing force is reduced in the directions (L, W) that are basically perpendicular to each other. A method characterized by being demonstrated above.   Method for manufacturing push belts (1) of different perimeter lengths, said push belts (1) each comprising a number of relatively thin transverse metal elements (3), At least one thin metal ring (16) manufactured according to the manufacturing method according to 2, 3 or 4, wherein the thickness of the elongated steel plate (11) is equal to the peripheral length of the push belt (1). A method characterized by being changed in relation to   A method for manufacturing a push belt (1) according to claim 5, characterized in that the width (W) of the elongated steel plate (11) is essentially constant.   7. A method for manufacturing a push belt (1) according to claim 5 or 6, wherein the method reduces the thickness of the ring (16) by rolling in the circumferential direction thereof. (VII), wherein all of the rings (16) comprise essentially the same thickness.   Push belt (1) comprising a thin metal ring (16) manufactured according to the manufacturing method according to any of claims 1, 2, 3 or 4.

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