1 Scope
This part of ISO 8458 specifies requirements for cold-drawn non-alloy steel wire for the manufacture of mechanical springs for static duty and dynamic duty applications, complying with the general requirements of ISO 8458-1.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of ISO 8458. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of ISO 8458 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
ISO 7989:1988, Zinc coatings for steel wire
ISO 8458-1, Steel wire for mechanical springs – Part 1: General requirements
ISO 16120-1:2001, Non-alloy steel wire rod for conversion to wire一Part 1: General requirements
ISO 16120-2:2001, Non-alloy steel wire rod for conversion to wire – Part 2: Specific requirements for general purpose wire rod
ISO 16120-4:2001, Non-alloy steel wire rod for conversion to wire- Part 4: Specific requirements for rod for special applications
3 Classification and designation
The wire diameter ranges and tensile strength grades normally available for static duty and dynamic duty are shown in Table 1.
Table 1一Tensile strength grades and diameter range
4 Dimensions and supply conditions
4.1 Dimensional tolerances
The dimensional tolerances on wire diameters shall be in accordance with ISO 8458-1.
4.2 Welds
The wire of a unit coil shall consist of one single length of wire originating from only one heat.
For coiled and cut lengths of wire, welds prior to the last patenting operation are allowed. All other welds shall be removed or, if so agreed, properly marked.
4.3 Cast of the wire
4.3.1 The wire shall be uniformly cast.
4.3.2 By agreement, for sizes up to 5 mm, the cast requirements may be considered as being fufilled if the following statement is satisfied.
An individual ring taken from the coil and freely hung on a hook may show an axial displacement,f, at the ends of the ring (see Figure 1).
This displacement,f, shall not exceed a value given by the fllowing inequality:
where
f is the axial displacement in millimetres;
D is the diameter of a free ring in millimetres;
d is the nominal diameter of the wire in millimetres.
4.4 Straightness of cut lengths
For the straightness of cut lengths, the following requirements apply.
For 500 mm test lengths – 0,5 mm maximum deviation from straightness;
For 1 000 mm test lengths – 2 mm maximum deviation from straightness.
NOTE 1 000 mm test lengths are recommended for wire diameter above 6 mm and 500 mm test lengths for those below.
5 Requirements
5.1 Material
5.1.1 General
Spring wire shall be made from steel complying with ISO 16120-1.
For grades SL, SM and SH the steel shall comply to ISO 16120-2.
For grades DM and DH the steel shall comply with ISO 16120-4.
5.1.2 Chemical composition
The steel is characterized by the heat analysis, which shall be in accordance with the values of Table 2. The permissible deviation of the product analysis from the heat analysis shall be in accordance with ISo 16120-2 or iso 16120-4.
Table 2 – Chemical composition, % (m/m) (heat analysis)
5.2 Coating and surface finish
5.2.1 The spring wire may be supplied lime coated, borax coated or phosphate coated, and may be produced by either dry drawing or wet drawing.
A metallic coating, where required, be it copper, zinc or zinc/aluminium alloy, shall be applied to the wire.
Other coatings may be agreed upon between the purchaser and the manufacturer.
If no specific surface finish is nominated, it shall be at the manufacturer’s discretion.
5.2.2 In the case of zinc and zinc/aluminium alloy coated spring wire, the mass of zinc or zinc/aluminium alloy coating shall satisfy the minimum values specified in Table 3.
Table 3一Minimum required zinc or zinc/aluminium alloy coating mass
Other levels may be agreed upon between supplier and manufacturer. The adherence of the coating shall be tested by a wrapping or bend test (see ISO 7989).
NOTE The usual coating processes may alter the properties of the steel wire. The ductility and endurance of the wire may thereby be reduced so that one cannot guarantee for zinc coated or zinc/aluminium alloy coated spring steel wire the same torsion values or expect the same dynamic performance (DM and DH) as for the respective uncoated material.
5.3 Surface quality
5.3.1 Surface quality tests shall be applied to wires intended for use in dynamic duty spring only (DM and DH).
The radial depth of seams or other surface discontinuities shall be not greater than 1 % of the nominal diameter of the wire.
5.3.2 For spring wire grade DH and DM, the cross-section shall show no completely decarburized layer and partial decarburization shall not have an average radial depth greater than 1,5 % of the nominal diameter of the wire.
5.4 Mechanical properties
The tensile strength of the wire shall be in accordance with Table 4 for the appropriate tensile strength grade, nominal wire diameter and type of spring use.
Table 4- – Tensile strength requirements
5.5 Technological properties
5.5.1 Wrapping test
The wrapping test may be applied to wires with a nominal diameter of less than 3 mm.
he wire shall not show any sign of fracture when closely coiled for at least four turns around a mandrel of diameter equal to that of the wire.
5.5.2 Torsion test
5.5.2.1 The torsion test shall be applied to wires with nominal diameter from 0,70 mm to 6,00 mm, and subject to negotiation for wires with nominal diameters over 6 mm and up to and including 10 mm.
5.5.2.2 The wire shall withstand being twisted, without failure, the number of turns given in Table 5, on a gauge length equivalent to 100 wire diameters.
For sizes over 3 mm, other gauge lengths may be used, in which case the number of twists shall be adjusted in praportion to the gauge length.
Table 5 – Torsion test requirements
5.5.2.3 The test shall be continued until fracture, wherein the primary fracture shall be perpendicular to the axis of the wire and the surface shall not be split. During fly-back of the wire, secondary fractures may occur and these shall be ignored.
5.5.3 Bend test
Where requested, the bend test may be applied to wires with nominal diameter greater than 3 mm.
The wire shall not show any sign of fracture when bent through an angle of 180° to form a U around a mandrel of diameter equal to twice the wire diameter for sizes above 3,0 mm to 6,5 mm, and equal to x 3 the wire diameter for sizes above 6,5 mm.
5.5.4 Coiling test
The colling test may be applied to wires with nominal diameter not greater than 0,7 mm.
The test piece shall exhibit a defect-free surface without splits or fracture, a uniform pitch of the turns after coiling and a dimensional regularity of the coil.
6 Inspection and testing
6.1 Test methods and other requirements
Test methods and other requirements shall be in accordance with ISO 8458-1. See Table 6.
Table 6- Summary of the information on test methods and requirements
6.2 Extent of testing
The extent of testing shall be in accordance with Table 7.
Table 7一Acceptance unit and number of samples and test pieces
