DRAFT INTERNATIONAL STANDARD© ISO 2019 – All rights reservedISO/DIS 22705-1:2019(E) 63Part 1: Cold formed cylindrical helical compression springsSprings — Measurement and test parametersRessort — Mesures et paramètres de test — Partie 1: Ressort hélicoïdal de compression cylindriques formé à froidSprings — Measurement and test parameters — Part 1: Cold formed cylindrical helical compression springsE2019-11-14(40) EnquiryISOISO/ International Standard 2019ISO 22705ISO 22705‑1ISO/DIS 22705-1 DIN Springs2 227 2Überschrift 2Überschrift 1 0 STD Version 2.9p40 4D:\3rd meeting - 2019-11-14 Nagoya\Draft\ISO_CD_22705-1_(E)_markup.docx ISO/TC 227 WG4 N25

Date: 2023-3-09

ISO/DIS 22705-3:2023(E)

Secretariat: JISC

Springs — Measurement and test parameters — Part 3: Cold formed cylindrical helical torsion springs

Ressorts - méthodes de mesure et d’essai - partie 3: Ressorts à torsion cylindrique, enroulés à froid

© ISO 2023

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Email: copyright@iso.org

Website: www.iso.org

Contents

Foreword vii

1 Scope 1

2 Normative references 1

3 Terms, definitions, symbols and abbreviated terms 1

3.1 Terms and definitions 1

3.2 Symbols and abbreviated terms 2

4 Environmental conditions 5

5 Qualifications of the person (s) performing the work 6

6 Geometries of guiding and supporting devices 6

7 Measuring and testing equipment 6

8 Measurement and test parameter for technical cold formed cylindrical torsion springs 6

8.1 Body length (L_B) 6

8.1.1 General 6

8.1.2 Type of characteristic 6

8.1.3 Measuring and/or testing equipment 7

8.1.4 Conditions of measurement and testing 7

8.1.5 Method of measurement and testing 7

8.1.6 Test location on the product 8

8.2 Outside diameter (D_e) 8

8.2.1 General 8

8.2.2 Type of characteristic 9

8.2.3 Measurement and/or testing equipment 9

8.2.4 Conditions of measurement and testing 9

8.2.5 Method of measurement and testing 9

8.2.6 Test location on the product 11

8.3 Inside diameter (D_i) 11

8.3.1 General 12

8.3.2 Type of characteristic 12

8.3.3 Measurement and/or testing equipment 12

8.3.4 Conditions of measurement and testing 12

8.3.5 Method of measurement and testing 12

8.3.6 Test location on the product 14

8.4 Spring leg length (l) 14

8.4.1 General 14

8.4.2 Type of characteristic 14

8.4.3 Measurement and/or testing equipment 15

8.4.4 Conditions of measurement and testing 15

8.4.5 Method of measurement and testing 15

8.4.6 Test location on the product 16

8.5 Number of coils (n) and coil direction 16

8.5.1 General 16

8.5.2 Type of characteristic 16

8.5.3 Measurement and/or testing equipment 17

8.5.4 Conditions of measurement and testing 17

8.5.5 Method of measurement and testing 17

8.5.6 Test location on the product 17

8.6 Bending radius on legs (r) 18

8.6.1 General 18

8.6.2 Type of characteristic 18

8.6.3 Measurement and/or testing equipment 18

8.6.4 Conditions of measurement and testing 18

8.6.5 Method of measurement and testing 18

8.6.6 Test location on the product 19

8.7 Angle of bend on legs (φ) 19

8.7.1 General 19

8.7.2 Type of characteristic 19

8.7.3 Measurement and/or testing equipment 19

8.7.4 Conditions of measurement and testing 20

8.7.5 Method of measurement and testing 20

8.7.6 Test location on the product 20

8.8 Spring pitch (p)/distance between the coils (u) 20

8.8.1 General 20

8.8.2 Type of characteristic 20

8.8.3 Measurement and/or testing equipment 21

8.8.4 Conditions of measurement and testing 21

8.8.5 Method of measurement and testing 21

8.8.6 Test location on the product 21

8.9 Spring torque (M) 21

8.9.1 General 21

8.9.2 Type of characteristic 22

8.9.3 Measurement equipment 22

8.9.4 Conditions of measurement 22

8.9.5 Method of measurement 22

8.9.6 Test location on the product 23

8.10 Free leg angle (α₀) 23

8.10.1 General 23

8.10.2 Type of characteristic 23

8.10.3 Measurement and/or testing equipment 23

8.10.4 Conditions of measurement and testing 24

8.10.5 Method of measurement and testing 24

8.10.6 Test location on the product 24

8.11 Shear-off burr 24

8.11.1 General 24

8.11.2 Type of characteristic 24

8.11.3 Test equipment 25

8.11.4 Conditions of testing 25

8.11.5 Method of testing 25

8.11.6 Test location on the product 26

8.12 Offset of leg (c) 26

8.12.1 General 26

8.12.2 Type of characteristic 26

8.12.3 Measurement and/or testing equipment 26

8.12.4 Conditions of measurement and testing 26

8.12.5 Method of measurement and testing 26

8.12.6 Test location on the product 26

Annex A (informative) Calculation of spring rate R_M 27

A.1 General 27

A.2 Type of characteristic 27

Annex B (informative) The design of the pins and the mandrels 28

Annex C (informative) Type of legs 29

Annex D (informative) Measurement of the length of leg l 30

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 227, Springs.

A list of all parts in the ISO 22705series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Springs — Measurement and test parameters — Part 3: Cold formed cylindrical helical torsion springs

This document specifies the measurement and test methods for general characteristics of cold formed cylindrical helical torsion springs made from round wire, excluding dynamic testing.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3611, Geometrical product specifications (GPS) — Dimensional measuring equipment: Micrometers for external measurements — Design and metrological characteristics

ISO 13385‑1, Geometrical product specifications (GPS) — Dimensional measuring equipment — Part 1: Design and metrological characteristics of callipers

ISO 16249, Springs — Symbols

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1.1

spring

mechanical device designed to store energy when deflected and to return the equivalent amount of energy when released

[SOURCE: ISO 26909:2009, 1.1]

3.1.2

torsion spring

spring that offers resistance to a twisting moment around the longitudinal axis of the spring

[SOURCE: ISO26909:2009, 1.4]

3.1.3

coil spring

coil-shaped spring

[SOURCE: ISO 26909:2009, 3.11]

3.1.4

helical torsion spring

torsion spring normally made of wire of circular cross-section wound around an axis and with ends suitable for transmitting a twisting moment

[SOURCE: ISO 26909:2009, 3.14]

3.1.5

cold formed spring

spring formed at ambient temperature

[SOURCE: ISO 26909:2009, 1.12]

3.1.6

free angle

relative angle between both ends of a helical torsion spring when no load is applied

[SOURCE: ISO26909:2009, 5.63]

3.1.7

torsional moment

torque

moment generated around the axis when external force is applied to a helical torsion spring

[SOURCE: ISO26909:2009, 5.11]

3.1.8

spring characteristics

relationship between the load applied to a spring and the deflection caused by the load

[SOURCE: ISO26909:2009, 5.1]

3.1.9

force

force exerted on or by a spring in order to reproduce or modify motion, or to maintain a system of forces in equilibrium

[SOURCE: ISO26909:2009, 5.2]

3.1.10

test parameter

parameter with a tolerance for which there is an immediate conclusion after test (OK or not OK)

Note 1 to entry: Test can be done without measurement (i.e., with go/no-go gauges)

Table 1 includes symbols, units and abbreviated terms in accordance with ISO 16249 and used throughout this standard.

Table 1 — Symbols and abbreviated terms

Figure 1 — Theoretical torsion spring diagram

Figure 2 — torsion spring with tangential ends

Figure 3 — torsion spring when loaded

The spatial distribution and equipment of the facility shall permit a reliable implementation of the measurement and test.

Measurements and tests should be carried out at ambient temperature in a normal workshop environment.

Special tests (e.g., in air-conditioned rooms or other special environments) shall be agreed upon between the manufacturer and the customer.

Measuring and testing equipment should be subject to regular inspection.

The measurements and tests shall be carried out by a person who has been instructed/trained in the use of the measuring and testing equipment, as well as regarding methods and test requirements.

The qualifications or additional knowledge and skills shall be documented in appropriate qualification or training documents, depending on the requirements.

If necessary, geometries of guiding and supporting devices (mandrels, guide sleeves, ring groove, etc.) shall be agreed upon between the manufacturer and the customer to include special cases such as snapping end coils, buckling, bulging, etc. The alignment of guiding and supporting devices is aimed to improve the reproducibility of the measures.

Suitable measuring equipment shall be selected. Measuring equipment shall conform to ISO standards, if such are available (e. g. ISO 3611 and ISO 13385-1).

If there is a customer requirement, the methods and measuring equipment shall be agreed on separately.

The body length L_B is a measurement and test parameter.

The body length L_B is the body length in axis direction (excluding legs) when no load is applied (see Figure 4); other case should be agreed upon between the manufacturer and the customer.

Figure 4 — Body length (L_B) of the unloaded torsion spring for open-coiled springs

The following measuring equipment can be used:

— micrometer gauge;

— height gauge;

— calliper;

— dial gauge/indicating calliper;

— electronic measuring sensor;

— manual/automatic force gauge;

— optical measuring instruments/measurement microscope/camera systems/projector.

In the case of attributive testing, the following testing equipment can be used:

— attributive gauges (“GO/NO GO” gauges).

The body length L_B shall be evaluated at ambient temperature as delivered.

The measurement can be carried out without contact using optical procedures, capacitive or electrically by contact (with minimal force) or by contact with the measuring surfaces (within tolerance/out of the tolerance/test gauges) (see Figure 5).

When there is a spring self-weight effect, the measurement of body length should be agreed upon between the manufacturer and the customer.

Figure 5 — Method of testing of the body length (L_B) with gauges (examples)

The test direction is in the axial direction to the finished spring. The measuring position is the distance between the tangent points of the two torsion legs and parallel to the axis of the spring body.

When measuring equipment is used that induces a measuring force then the applied force should not deflect and/or compress the spring.

When optical measuring equipment (camera systems) is used, the measurement axis is perpendicular to the spring axis.

The outside diameter D_e is a measurement and test parameter.

The outside diameter D_e is the value of the outside diameter through the whole spring body (see Figure 6). If legs are bent in the interior part of the spring body or the legs overlap the inner diameter, the legs have to be ignored.

Figure 6 — Outside diameter (De)

The following measuring equipment can be used:

— micrometer gauge;

— calliper;

— dial gauge.

Alternatively, optical measuring equipment can be used.

In the case of attributive testing, the following testing equipment can be used:

— test sleeve;

— special gauge (part-based):

— snap gauge.

The shape and dimension of all testing equipment shall be agreed upon between the manufacturer and the customer.

The outside diameter D_e shall be evaluated at ambient temperature as delivered.

a) Variable measurement (e.g., calliper) (see Figure 7)

The measurement is performed at several locations on the product, at least at the beginning, in the centre and at the end of the spring. In the case of no interference with the legs, the measurements at the end are performed in two perpendicular directions of the spring. Each measured value shall be within the tolerance. The maximum value shall be documented.

Key

Figure 7 — Method of measurement of the outside diameter De with calliper (example)

b) Variable measurement (e.g., dial gauge) (see Figure 8)

The measurements are to be carried out (0°-180°, 90°-270°). The measured values shall be within the tolerance. The maximum value shall be documented.

Key

Figure 8 — Method of measurement of the outside diameter D_e with dial gauge (example)

c) Attributive testing (within tolerance/out of the tolerance/test gauges) (see Figure 9)

The spring shall fall through the gauge due to its own weight at D_e,max.

The spring shall not fall through the gauge due to its own weight at D_e,min.

Figure 9 — Method of testing of the outside diameter D_e with gauges (examples)

a) Variable measurement

The measurement is performed at several locations on the product, at least at the beginning, in the centre and at the end of the spring with no load applied.

b) Attributive testing

The test is carried out over the entire length of the spring. The test sleeve length shall correspond to at least the clearance of 2 coils.

For the purpose of testing geometrical deviations (enveloping circle, curvature), a test sleeve with the length and diameter for cylindrical springs can be agreed upon between the manufacturer and the customer.

The inside diameter D_i is a measurement and test parameter.

The inside diameter D_i is the minimum value of the inside diameter through the whole spring body (see Figure 10). If legs are bent in the interior part of the spring body or the legs overlap the inside diameter, the legs have to be ignored.

Figure 10 — Inside diameter (Di)

The following measuring equipment can be used:

— calliper.

Alternatively, a micrometer screw or optical measuring equipment can be used.

In the case of attributive testing, the following testing equipment can be used:

— test pin;

— special gauge (part-based), e.g., GO/NO GO gauge.

The inside diameter D_i shall be evaluated at ambient temperature as delivered.

a) Variable measurement (e.g., calliper) (see Figure 11)

If the calliper jaws is greater than the spring body length, take only two measurements in perpendicular directions. For long length of spring body, the inside diameter is usually calculated indirectly by measuring the outside diameter. The measurement method of inside diameter can be agreed upon between the manufacturer and the customer. The measured values shall be within the tolerance. The minimum value shall be documented.

Key

Figure 11 — Method of measurement of the inside diameter (D_i) with calliper (example)

b) Attributive testing (within tolerance/out of the tolerance/test pin)(see Figure 12)

The spring shall fall over the test pin due to its own weight at D_i,min

The spring shall not fall over the test pin due to its own weight at D_i,max .

Both of the above-mentioned criteria shall be met, regardless of which side of the spring is attached to the test pin.

Figure 12 — Method of testing the inside diameter (D_i) with test pin (examples)

a) Variable measurement

Where the spring has legs, the measurement is carried out on the outside diameter and the value can be calculated by the following formula

Where d_wire is the wire diameter after coiling.

b) Attributive testing

The test is carried out over the entire length of the spring (L_B).

For the purpose of testing geometrical deviations (enveloping circle, curvature), a test gauge can be agreed upon between the manufacturer and the customer.

The spring leg length l is a measurement and test parameter.

The spring leg length l is the length of each leg segment when there is no load. Torsion springs can have legs with more than one leg segment (see Figure 13).

Figure 13 — Spring leg length (l)

The following measuring equipment can be used:

— calliper;

— electronic measuring sensor;

— optical measuring instruments/measurement microscope/camera systems/projector.

In the case of attributive testing, the following testing equipment can be used:

— attributive gauges (“GO/NO GO” gauges).

The spring leg length l shall be evaluated at ambient temperature as delivered.

In the case of tangential legs, the measurement is carried out indirectly using a calliper remembering to subtract half of the body outside diameter from the measurement.

The leg length l is the indirect measurement value. The measurement method is to measure the distance from the end of torsion leg to the outside of spring body minus half of the measured value of outer diameter of spring. According to the formula , , the measurement method is shown in Figure 14.

In the case of optical measurement, the wound body is deflected perpendicular to the measuring plane by means of a mandrel or fixations. If the wound body is parallel to the measuring plane, it shall be fixed in such a way that the legs to be measured are also parallel to the measuring plane.

Figure 14 — Method of measurement of the spring leg length (l) with calliper (examples)

Measurement takes place from leg end l₁/l₂ to the opposite facing spring body in one plane.

The test direction is in the axial direction to the spring legs. When measuring equipment is used that induces a measuring force, then the applied force should not deflect the spring.

When optical measuring equipment (camera systems) is used, the measurement axis is perpendicular to the spring leg.

The number of coils n and the coil direction are test parameters. All coils are active in the torsion spring.

Number of coils n is the number of wire rotations/coils around the spring axis, see Figure 15.

Key

Figure 15 — Number of coils (n)

The following measuring equipment can be used:

— visual inspection;

— test template;

— optical test;

— projector;

— measuring microscope;

— camera system.

The number of coils n shall be evaluated at ambient temperature as delivered.

All tests are carried out on the unloaded spring.

The wire coil rotations shall be counted from one end of the wire (spring body end) to the other.

The coil direction can be clockwise (right-handed) or counterclockwise (left-handed)(see Figure 16).

Figure 16 — Coil direction

The entire spring body shall be considered.

The bending radius on legs r is a measurement and test parameter.

The bending radius on legs r is the bending (inside) radius of bent or axially raised legs at the transition to the last turn, see Figure 17.

Figure 17 — Bending radius on legs (r)

The following measuring equipment can be used:

— visual inspection (e.g., radius gauge);

— optical test;

— radius gauge;

— optical measuring instruments/measurement microscope/camera systems;

— template.

The bending radius on legs r shall be evaluated at ambient temperature as delivered.

All tests are carried out on the unloaded spring. Figure 18 shows the schematic diagram of measuring with radius gauge.

In the case of optical measurements, the spring element shall be aligned perpendicular to the measuring plane using a mandrel or suitable fixings. If the spring body is parallel to the measuring plane, it shall be fixed in such a way that the legs to be measured are also parallel to the measuring plane.

Key

Figure 18 — Measuring the bending radius (r) of torsional leg with radius gauge (example)

When measuring equipment is used that induces a measuring force, then the applied force should not deflect the spring.

When optical measuring equipment (camera systems) is used, the measurement axis is perpendicular to the spring bend angle.

The angle of bend on legs φ are measurement and test parameter.

The angle of bend on legs φ is the angle between two adjacent leg segments, see Figure 19.

Figure 19 — The angle of bend on legs (φ)

The following measuring equipment can be used:

— template;

— projector;

— protractor;

— angle gauge;;

— optical measurement system;

— measuring microscope.

The angle of bend on legs φ shall be evaluated at ambient temperature as delivered.

All tests are carried out on the unloaded spring.

The measurement shall be performed without contact (optical) or with minimal force application without a deflection of the angle (manual check, see Figure 20).

For optical measurement, the spring body shall be aligned perpendicular to the measuring plane by means of a mandrel or suitable fixings. If the coiled body is parallel to the measuring plane, it shall be fixed in such a way that the legs to be measured are also parallel to the measuring plane.

Key

Figure 20 — Measuring the angle of bend on legs (φ) of torsional leg with template (example)

The measurement should be performed perpendicular to the spring legs.

The spring pitch p/distance between the coils u are measurement parameters.

The (functional) spring characteristic with the corresponding tolerances should be defined, rather than

specifying the spring pitch p/distance between the coils u.

The distance between two consecutive coils in the direction of the spring axis is u.

The spring pitch p can be calculated with the distance between coils u and the diameter of wire d_wire:

p = d_wire + u

Figure 21 illustrates the difference between distance between coils u and spring pitch p.

Key

Figure 21 — Difference between spring pitch and distance between the coils

The following measuring equipment can be used:

— calliper (with the corresponding dimension);

— optical test (identity check);

— sample rod;

— feeler gauge.

The spring pitch p/distance between the coils u shall be evaluated at ambient temperature as delivered.

The measurement can be performed without contact (optical) or with minimal force application (manual check).

The measurement should be performed perpendicular to the spring axis.

The test location is to be defined between the manufacturer and the customer.

The measuring point should be precisely defined, since there is partly different distance between the coils in the spring.

The spring torque M is a measurement parameter.

The spring torque M is a torsional load applied to the legs of the torsion spring with the loading pins in closing direction (see Figure 3).

The spring torques M₁, M₂... are the assigned spring torques to the rotation angles of the loaded spring α₁, α₂..._.

The following measuring equipment can be used:

— spring load tester (manual or powered);

— spring torque tester.

NOTE In most cases the torque is the required measurement parameter for testing torsion springs. In very rare cases, the force is requested when testing the springs. If the spring force is required, the geometries of guiding and supporting devices (e. g. test pins, guide bushings, ring groove) may be agreed upon between the manufacturer and the customer.

Before measuring the spring torque, the actual leg position is recorded.

The spring torque shall be evaluated at ambient temperature as delivered. Unless agreed with the customer, the spring should not be touched during testing and no additional lubrication should be used.

The spring shall be supported on a mandrel for its whole length and loaded using pins. The diameter of a torsion spring reduces as the spring is wound up, and the mandrel diameter should be smaller than the spring inside diameter at the maximum deflection (see Annex B).

It is recommended that the zero setting (α_h=0°) be made by moving the pins towards each other along the same circle (rewinding) until the torque to be measured is indicated on the machine. From this setting the spring as a whole to be turned.

If not specified one presetting, the torque measurement procedure should be as following: first load to α_n.; unload back to zero position then load again to _. while measurement of the torque and angle. The torque testing process is shown in the Figure 22.

Figure 22 — Torque test schematic diagram

Unless otherwise specified in the drawing, measuring conditions should be agreed upon between the manufacturer and the customer. The entire spring body shall be supported by the mandrel in the tester. The spring torque is measured at the points of the moment leg contact.

The free leg angle α₀ is a measurement and test parameter.

The free leg angle α₀ is the position angle between two legs when unloaded, see Figure 23.

Figure 23 — The free leg angle (α₀)

The following measuring equipment can be used:

— optical measuring device;

— projector;

— measuring microscope;

— camera system (without measuring force);

— protractor.

In the case of attributive testing, the following measuring equipment should be used:

— gauge.

The free leg angle α₀ shall be evaluated at ambient temperature as delivered.

The measurements and tests are carried out on the spring without load. The spring is aligned on a fixture on the diameter, perpendicular to the spring axis. An alignment is made from the first to the second leg. This test can also be carried out with a protractor, using the light gap method. It is also possible to check the leg position with a gauge.

The measurement should be performed perpendicular to the spring axis.

The shear-off burr is a test parameter.

The inspected property is the shear-off burr resulting from cutting off at both ends of the spring, see Figure 24.

Figure 24 — The shear-off burr

Evaluation is carried out by test. This test is the assessment of the sharp edge (subjective evaluation).

The following testing equipment can be used:

— test pin and test sleeve;

— calliper;

— gauge;

— magnifying glass;

— projector;

— stereoscopic microscope;

— camera.

Unless otherwise agreed between customer and manufacturer, assessment is done with naked eye.

The shear-off burr shall be evaluated at ambient temperature as delivered.

One of the following test methods shall be applied:

— visual inspection;

— magnifying glass test;

— projector test;

— stereoscopic microscope test;

— camera test.

The shear-off burr should be taken into account when testing with a mandrel or sleeve. The shear-off burr shall not exceed/undercut the tolerances of the inside and outside diameter.

Tests are carried out at the points where the wire is cut off/sheared.

The offset of leg c is a measurement parameter.

If one or both legs are not tangential because of a bend, the distance between the outer part of the leg to the outside diameter of the spring body is the offset of leg (see Figure 25).

Figure 25 — The offset of leg (c)

The following can be used as measuring equipment:

— calliper gauge (for tangential legs and depending on the dimensioning or customer agreement)

— optical measuring device/projector/measuring microscope/camera system

Test equipment should be agreed between the manufacturer and the customer.

The offset of leg c shall be evaluated at ambient temperature as delivered.

For measurement, the coiled body is to be aligned perpendicular to the measuring plane by means of a mandrel or suitable fixings (prism or similar). The leg to be measured is aligned with the measuring plane, the measuring device is zeroed and the length is moved to the spring body.

A measurement with a calliper gauge is also possible with a proper adapter.

The entire spring body shall be considered.

1. 
   (informative)
   
   Calculation of spring rate R_M
   1. General

The spring rate R_M [N · mm/rad , N · mm/degree] is a parameter and is determined by calculation.

To calculate the spring rate take two torque measurements at two agreed positions within the range of 30 % to 70 % of the safe deflection.

• 1. Type of characteristic

ΔM is the increase in torque corresponding to an increase in angle Δα .

The spring rate calculation is between two points only, and does not define the whole travel of the spring. Furthermore, the rate of the torsion spring will not be constant, especially near the delivery position and the maximum permissible end position.

1. 
   (informative)
   
   The design of the pins and the mandrels

Generally, the mandrel diameter should be decided by the specification or specified from the customer. Unless otherwise specified, the mandrel diameter D_d should be approximate 90 % of the inside diameter at maximum working torsional angle.

When,

Fixed pin and movable pin should be securely installed at the position decided by the specification or specified from the customer. Unless otherwise specified, the position of each pin should be approximate 70 % to 80 % of the length of each leg.

When,

NOTE During spring torque measurement, it is crucial to have a correct diameter of the pins and the mandrels in order to avoid both interference and too light (risk of bad positioning/movement of the spring during the test).

1. 
   (informative)
   
   Type of legs

Figure C.1 — Type of legs

1. 
   (informative)
   
   Measurement of the length of leg l

Each torsion leg can be idealized as a series of straight leg segments (l₁, l₂, ….) and bend segments, with each bend segment having a measurable inner bending radius (r₁, r₂, …) and angle of bend (φ₁, φ₂, ...).

When measuring the length of leg l, it is permissible to use other characteristics of the spring such as the wire diameter after coiling (d_wire), outside diameter (De) and bending radius (r₁, r₂, …), as long as the characteristics are used.

Figure D.1 — Measurement of the length of leg l

Bibliography

[1] ISO 3611, Geometrical product specifications (GPS) — Dimensional measuring equipment: Micrometers for external measurements — Design and metrological characteristics

[2] ISO 13385‑1, Geometrical product specifications (GPS) — Dimensional measuring equipment — Part 1: Design and metrological characteristics of callipers

[3] ISO 16249, Springs — Symbols

[4] ISO 26909, Springs — Vocabulary