COIL OF TAPERED WIRE

Abstract: A coil of taper wire for forming coil springs, formed by winding substantially in concentric loops a quench-hardened and tempered taper wire having a successive arrangement of taper wire segments each consisting of a thick section (4), two thin sections (5) and two taper sections (6) connecting the thin sections to the opposite ends of the thick section, respectively. The taper wire is subjected to a preforming action immediately before being wound in loops on a winding drum, to form plastic bends in the thick sections and plastic bends of a radius (R₂) of curvature greater than (R₁) that of the plastic bends in the thick sections so that the taper wire is wound substantially uniform, concentric circular loops on a winding drum. When the taper wire is unwound from the coil and is subjected to a straightening process of a fixed straightening arrangement of a series of straightener rollers before being coiled in taper wire coil springs on a coil spring forming mill, the thick sections undergo a straightening action greater than that acts on the thin sections, so that the taper wire unwound from the coil of taper wire is straightened in a substantially straight taper wire and thereby the taper wire is coiled in taper wire coil springs having correct size and uniform shape.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a coil of taper wire for forming a coil spring, formed by coiling a taper wire continuously varying in section in substantially concentric loops Description of the Prior Art: Generally, the conventional coil spring is formed by coiling a wire having a fixed diameter through a cold working as illustrated in Figs. 3(1) and 3(2). A coil 21 formed by coiling a wire 25 having a fixed section substantially in concentric loops is mounted on a turn table 22. The wire 25 is pulled out from the coil 21 through a straightening unit 26 by the feed rollers 24 of a spring forming machine 23. The straightening unit 26 has an alternate arrangement of three fixed straightener rollers 26a and two movable straightener rollers 26b. The wire 25 is straightened by the straightening unit 26 so as to extend in a straight line in an unrestrained condition. The straightened wire 25a is subjected to the coiling action of coiling members 27 for cold coiling. The coiling members 27 need not necessarily be rolling members as shown in Figs. 3(1) and 3(2), but may be fixed dies. The degree of straightening action of the straightening unit 26 is regulated by varying the disposition of the two movable rollers 26b relative to the three fixed straightener rollers 26a. The respective numbers of the straightener rollers 26a and 26b need not necessarily be three and two, but may be optional numbers. In recent years, a coil spring continuously varying in section as shown in Fig. 4, namely, a taper wire coil spring 1 having nonlinear spring characteristics has progressively become used instead of a coil spring having a fixed section, to improve the riding comfort and to reduce the weight of automobiles and railway vehicles. Such a taper wire coil spring 1 is formed by coiling a taper wire 3 having a thick section 4, thin end sections 5 and 5′, and taper sections 6 connecting the thin end sections 5 and 5′ to the opposite ends of the thick section 4, respectively, as shown in Fig. 5. The diameter d₂ of the thin end section 5 and the diameter d₃ can be either d₂ = d₃ or d₂ ≠ d₃. In the following description, the thin end sections 5 and 5′ will be denoted inclusively by a reference numeral 5. Generally, the taper wire 3 is manufactured by using a swaging machine capable of high-speed forging or a peeling machine capable of high-speed peeling. The applicant of the present invention proposed previously a highly productive taper wire manufacturing process in Japanese Patent Provisional Publication Nos. 60-56416 and 60-56417. In this taper wire manufacturing process, a metallic material is fed at a fixed feeding speed into a heating furnace for softening, then the softened metallic wire is cooled, and then the cooled metallic wire is drawn at a regularly variable drawing speed so that the sectional area of the softened and cooled metallic wire is varied continuously to form a taper wire 3. The taper wire 3 is wound in a coil before being supplied to a spring forming machine 23. However, problem arises in winding the taper wire 3 in a coil. Since the thin end sections 5 are smaller than the thick section 4 in section, the thin end sections 5 are subject to plastic strain, so that the thin end sections 5 are liable to be bent sharply as shown in Figs. 6(1) and 6(2) when the taper wire 3 is wound in a coil. Therefore, the taper wire 3 thus wound in a coil assumes an unrestrained taper wire 3a as shown in Fig. 7 in an unrestrained state. That is, the unrestrained taper wire 3a has thin end sections 5 greater in plastic bend than the thick section 4, namely, R₁ > R₂, where R₁ is the radius of curvature of the thick section 4 and R₂ is the radius curvature of the thin end sections 5. A coiled wire having uniform section is uniform in plastic bend in an unrestrained state. The degree of plastic bend is dependent on the limit of elasticity and diameter of the wire, the diameter of the winding drum and the magnitude of back tension irrespective of position on the wire. To form a coil of the taper wire 3a having plastic bends as shown in Fig. 7, the taper wire 3a needs to be straightened by the straightening unit 26 in a manner as described with reference to Figs. 3(1) and 3(2) before coiling. However, the horizontal distance, the distance in a direction perpendicular to the sheet in Fig. 3(2), between the fixed straightener rollers 26a and the movable straightener rollers 26b is unavoidably fixed and hence the straightening action of the straightening unit 26 on the thick section 4 is more intensive than that on the thin section 5. Therefore, the thin section 5 cannot be straightened satisfactorily. Figs. 8(1) and 8(2) show modes of straightening operation of the straightening unit 26 with the fixed straightener rollers 26a and the movable straightener rollers 26b set in a fixed straightening arrangement, namely, with the center distance C₁ between the fixed straightener rollers 26a and the movable straightener rollers 26b for straightening a thicker wire 28a (Fig. 8(1)) and the center distance C₂ between the fixed straightener rollers 26a and the movable straightener rollers 26b for straightening a thinner wire 28b (Fig. 8(2)) equal to each other. As is obvious from Figs. 8(1) and 8(2), such an arrangement of the fixed straightener rollers 26a and the movable straightener rollers 26b is effective for straightening the thicker wire 28a, however, the same is unable to straighten the thinner wire 28b satisfactorily. When a taper wire 3 thus unsatisfactorily straightened on a straightening machine with the straightening rollers set in a fixed straightening arrangement is subjected to a coil spring forming process, the plastic bends of the thin sections of the taper wire 3 remains almost just as they are to form a taper wire coil spring 1′ having an irregular form as shown in Fig. 9. It is possible to straighten such a taper wire satisfactorily by automatically regulating the straightening arrangement of the straightener rollers according to the variable diameter of the taper wire and the degree of bends in the taper wire. However, such a straightening process needs a sophisticated control system including a detecting unit for detecting the continuously variable diameter and bends of the taper wire and a control unit capable of continuously controlling the straightening arrangement of the straightener rollers on the basis of information provided by the detecting unit. Accordingly, such a straightening process, in practice, is not readily feasible. It is also possible to form a uniform taper wire coil spring by continuously controlling the coil forming rollers so as to move radially of the taper wire coil spring in winding a taper wire having plastic bends in the thin sections 5. However, this process, similarly to the former process, needs a sophisticated control system and hence is not readily feasible. Therefore, according to the technical status quo, straight taper wire 3 having a fixed length is subjected to coil spring forming process, and hence coil springs cannot be formed continuously deteriorating the efficiency of the coil spring manufacturing process. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a coil of taper wire which enables winding a taper wire coil spring in normal size and shape without requiring the modification of the straightening unit and the coil spring forming machine. To achieve the object of the invention, the present invention provides a coil of taper wire, formed by winding substantially in concentric loops a taper wire 3 having a succe ssive arrangement of taper wire segments 3b each consisting of a thick section 4, thin sections 5 and taper sections 6 connecting the thin sections 5 to the opposite ends of the thick section 4, respectively, characterized in that the radius R₁ of curvature of respective plastic bends in the thick sections 4 in an unrestrained state is smaller than the radius R₂ of curvature of respective plastic bends in the thin sections 5 in an unrestrained state. Since the unrestrained plastic deformation of the thick sections 4 is greater than that of the thin sections 5, namely, since the radius R₁ of curvature of the thick sections 4 is smaller than the radius R₂ of curvature of the thin sections 5 in an unrestrained state, the taper wire 3 can be straightened satisfactorily even if the taper wire 3 is straightened on a straightening machine with a fixed straightening arrangement, because the straightening action of the straightener rollers on the thick sections 4 is more intensive than on the thin sections 5. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic side elevation of a wire winding equipment, by way of example, for carrying out the present invention; Figure 2 is a fragmentary view of a taper wire wound in a coil according to the present invention, showing the morphology of the taper wire in an unrestrained state; Figure 3(1) is a plan view of a coil spring forming mill; Figure 3(2) is a side elevation of the coil spring forming mill of Fig. 3(1); Figure 4 is a side elevation of a normal taper wire coil spring; Figure 5 is a fragmentary side elevation of a taper wire; Figure 6(1) is a cross-sectional view of a wire winding drum on which a taper wire is wound without forming plastic bends in the thick sections thereof; Figure 6(2) is a longitudinal sectional view of th wire winding drum of Fig. 6(1); Figure 7 is an illustration of a taper wire in an unrestrained state after wound on a wire winding drum without forming plastic bends in the thick sections of the taper wire; Figures 8(1) and 8(2) are schematic views of assistance in explaining respective modes of straightening a thicker wire and a thinner wire, respectively, under the same straightening arrangement of straightener rollers; and Figure 9 is a schematic view of an abnormal taper wire coil spring formed by coiling the taper wire shown in Fig 7. DESCRIPTION OF THE PREFERRED EMBODIMENT A coil of taper wire, in a preferred embodiment, according to the present invention will be described hereinafter in terms of a wire winding apparatus for winding a taper wire in such a coil of taper wire. Referring to Fig. 1, a wire winding apparatus has a winding drum 11 and a preforming unit 12 disposed before the winding drum 11. The preforming unit 12 comprises two fixed rollers 12a and a movable roller 12b movable relative to the fixed rollers 12a. The degree of preforming action of the preforming unit 12 is dependent on the relative disposition of the fixed rollers 12a and the movable rollers 12b. Naturally, the number of the rollers of the preforming unit 12 need not be limited to three, any preforming unit of suitable constitution may be employed. Indicated at 13 is a tempering furnace for continuously tempering a taper wire manufactured by a process disclosed in the previously cited Japanese Patent Application No. 60-56416 or 60-56417, at 14 is a cooling nozzle and at 15 are feed rollers. Since the taper wire manufactured through the manufacturing process of the cited Japanese Patent Application No. 60-56416 or 60-56417 is quenched, the taper wire is tempe red by the tempering furnace 13 to provide a tempered taper wire. Although an untempered taper wire manufactured on a swaging machine or a peeling machine can be wound in a coil by the wire winding apparatus of Fig. 1, it is more advantageous, from the viewpoint of manufacturing facility, to quench-harden and temper the taper wire before winding than to quench-harden and temper the taper wire after forming the same in a taper wire coil spring. That is, when a taper wire coil spring is subjected to hardening and tempering processes, the taper wire coil spring is liable to be strained and deformed and requires much work for correcting the deformation. The taper wire 3 delivered from the tempering furnace 13 is fed after being cooled to the preforming unit 12. Then, the taper wire 3 travels along a curved path formed between the fixed rollers 12a and the movable roller 12b. Then, the taper wire 3 is pulled by and wound up on the winding drum 11. The fixed rollers 12a and movable roller 12b of the preforming unit 12 are arranged so as to form a plastic bend (plastic deformation) of a fixed radius of curvature in each thick section 4 of the taper wire 3. Although dependent on the relation between the thick section 4 and the thin section 5 in diameter, a preferable radius of curvature of the plastic bend in the thick section 4, in general, is in the range of one to fifteen times the radius R of the winding drum 11 for winding the taper wire 3 without forming such plastic bends as shown in Figs. 6(1) and 6(2) in the thin sections 5. For the reasons as explained with reference to Figs. 8(1) and 8(2), the degree of plastic deformation of the thin sections 5 is less than that of the thick sections 4. The winding drum 11 is the same in construction as the conventional winding drum shown in Figs. 6(1) and 6(2); the winding drum 11 comprises a taper cylinder 11b and a flange 11a formed at one end of the taper cylinder 11b. The taper wire 3 provided large plastic bends in the thick sections 4 thereof is wound around the taper cylinder 11b from a position near the flange 11a toward the free end of the taper cylinder 11b, so that the loops of the taper wire 3 slide successively toward the tapered free end of the taper cylinder 11b. When the taper cylinder 11b is wound fully with the taper wire 3, loops of the taper wire 3 are bundled in a coil of taper wire, and then the coil of taper wire is removed from the winding drum 11 through the free end of the taper cylinder 11b. Ordinarily, the diameter of the winding drum 11 for winding a taper wire 3 having thick sections 4 of a diameter in the range of 10 to 15 mm is in the range of 1.5 to 2.0 m. The winding drum need not be of a horizontal type in which the coil of taper wire is removed from the winding drum 11 in the horizontal direction, but may be of a vertical type in which the coil of taper wire is removed from the winding drum in a vertical direction, namely, either upward or downward. Referring to Fig. 2, when unwound from the coil of taper wire of the present invention and left unrestrained, the taper wire 3 assumes the morphology of an unrestrained taper wire 3b having thick sections 4 each having a plastic bend of a radius R₁ of curvature smaller than the radius R₂ of curvature of the plastic bends in the thin sections 5. When this taper wire 3 is straightened on the straightening unit 26 of a coil spring forming mill, the taper wire 3 is straightened substantially in a straight shape by straightening only the plastic bends in the thick sections 4, because the straightening action of the straightening unit 26 on the thick sections 4 is more intensive than that on the thin sections 5 and, originally, only small plastic bends are formed in the thin sections 5. Basically, although R₁ < R₂, the taper wire 3 cannot be wound in circular loops on the winding drum 11 when R₁ is excessively small. Therefore, as mentioned above, a preferable value of R₁ is in the range of one to fi en times the radius of the winding drum 11. Thus, the taper wire wound in a coil of taper wire according to the present invention can be straightened substantially in a straight taper wire by the straightening unit 26 provided at the front stage of the coil spring forming machine 23, whereby the taper wire can be coiled easily in a taper wire coil spring having satisfactory size and shape. Examples: Concrete examples of the coil of taper wire will be described hereinafter. (1) Sample Taper Wire (Fig. 5): Quality: SAE 9254 (C: 0.55 wt%, Si: 1.43 wt%, Cr: 0.66%) Tensile strength (TS): 180 kg/mm² Dimensions: d₁ = 14 mm, d₂ = d₃ = 11 mm, ℓ₁ = 1000 mm, ℓ₂ = 200 mm, ℓ₃ = 600 mm The oil-tempered sample taper wire was passed through the preforming unit 12 and wound on the winding drum 11 of 1.5 m in diameter. The arrangement of the fixed rollers 12a and the movable rollers was varied to provide several sample coils of taper wire differing from each other in plastic bends in the taper wire. (2) Taper wires each having several taper wire segments each consisting of the thick section 4, the thin sections 5 and the taper sections 6 were sampled from the sample coil of taper wire, and then the radius R₁ of curvature of the thick sections 4 and the radius R₂ of curvature of the thin sections 5 were measured in an unrestrained state. The measured results are tabulated in Table 1. Sample taper wire No. 1 was wound on the winding drum 11 without subjecting to the preforming action of the preforming unit 12. Sample taper wires No. 1 and 2 has plastic bends in the thin sections 5. Sample taper wires No. 3 and 4 were sampled from sample coils of taper wire according to the present invention; these taper wires do not have any plastic bend in the thin sections 5. (3) Ten pieces of sample taper wires of each of the sample Nos. 1 to 5 were coiled on a coil spring forming mill to form cylindrical taper wire coil springs of 115 mm in target diameter and 300 mm in target height. The sample taper wires were straightened by the straightening unit 26 so that at least the thick sections are straightened. (4) The respective heights of the sample taper coil springs respectively formed of the sample taper wires of sample Nos. 1 to 5 were measured to determine the dimensional accuracy on the basis of the variation of the measured heights represented by the difference between the maximum height and the minimum height of the ten sample taper wire coil springs of each sample group. (5) As is obvious from Table 2, the dimensional variation of the taper wire coil springs formed of the taper wires unwound from the coils of taper wire according to the present invention is smaller than that of the rest of the taper wire coil springs, from which it was conformed that the coil of taper wire of the present invention enables forming taper wire coil springs of satisfactory quality. Thus, the coil of taper wire according to the present invention can be formed simply by forming plastic bends of a radius of curvature smaller than that of plastic bends in the thin sections in the thick sections of the taper wire, and the taper wire unwound from the coil of taper wire can be straightened satisfactorily even if only the thick sections are subjected to high straightening action of the straightener rollers; consequently, the coil of taper wire according to the present invention enables continuous and highly efficient manufacture of taper wire coil springs. Although the present invention has been described in its preferred form with a certain degree of particularity, it is to be under stood to those skilled in the art that many changes and variations are possible in the invention without departing from the scope and spirit thereo f.

Claims: 1. A coil of taper wire, formed by winding substantially in concentric loops a taper wire having a successive arrangement of taper wire segments each consisting of a thick section, two thin sections and two taper sections connecting the thin sections to the opposite ends of the thick section, respectively, characterized in that the radius of curvature of respective plastic bends in the thick sections in an unrestrained state is smaller than the radius of curvature of respective plastic bends in the thin sections in an unrestrained state. 2. A coil of taper wire as recited in Claim 1, wherein said taper wire having a successive arrangement of taper wire segments is a quench-hardened and tempered taper wire.

Inventors: KATSUBE, KOZO, KAWAGUCHI, YASUNOBU, KAWAKAMI, HEIJIRO, MURAHASHI, MAMORU, TAKADA, SUSUMU
Applicants: KABUSHIKI KAISHA KOBE SEIKO SHO ALSO KNOWN AS KOBE STEEL LTD.
Application year: 1987
Main classification: B21F35
IPC codes: F16F1, B21C47, B21F23, B21F3, B21F35, B65H55