SPRINGS Design
Aims The aim of this document is to provide as much information as possible on spring design It is the result of work to which a large number of professions professions and functions have contributed: designers, material specialists, calculation engineers, buyers, suppliers The aim is to allow the designer to quickly identify best practices for spring design This guide aims at a large degree of openness. The aim is not to forbid but to specify.
Contents Spring design cycle Choosing the material Material correspondences Wire diameters Influence of temperature Choosing anticorrosion protection Stress level Stainless steels: stress corrosion Very stressed springs When must a spring be shot peened? Relaxation Fatigue, endurance Tolerances Spring packaging Information to be marked on the drawing
Compression Compressio n springs - Defin Definition ition Advice End geometry Setting Tangling Specification Control method Extension springs Extension springs - Definiti Definition on Advice Ends Loop radii Loop fatigue behaviour Initial tension Tangling of extension springs Specification Control method Torsion springs: Definition Advice Legs geometry Radial legs bending radius Polarisation of torsion springs Specification Control method
Spring design cycle Preliminary Design: functional needs, overall dimensions and environment known – feasibility study: dimensioning + material Proposal to the industrial supplier who checks the calculations, creates prototypes, makes proposals, etc. Validation of the drawing: the functional needs, tolerances, overall dimensions, environment and material are defined Qualification tests in product: corrosion withstand, temperature withstand, endurance in product, tolerances, efficiency of spring in product, etc. Validated spring
Choosing the material Choice of material depends on several criteria: Temperature withstand Corrosion withstand Mechanical withstand Spring cost Temperature withstand is an initial criterion allowing an initial sort to be made according to requirements Mechanical withstand for each material (resistance, relaxation, fatigue) is a second sort criterion Finally, when several solutions satisfy the functional needs, their cost will be a decisive factor in their choice
Choosing the material Material Carbon steel SM - SH - DH EN 10270 pt1 Hardened and tempered steel VDCrSi EN 10270 pt2 Stainless steel X10CrNi18-8 NS / HS EN 10270 pt3
Applications
All springs
Wire diameters
Temperature
0.05 to 20.00 mm < 80 to 100°C
Material Cost SM : + SH : ++ DH : +++
Compression
0.50 to 10.00 mm
< 200°C
++++
All springs
< 10.00 mm
< 250°C
NS : ++++ HS : +++++
Choosing the material On the initial consultation, material provides an indication: the spring manufacturer can then propose a material better suited to the functional needs, easier to supply or more economic As soon as the spring is validated, the material is defined once and for all. When choosing carbon steels, the SM or SH grades will be selected for applications not subjected to fatigue (<10 000 cycles) – the DH grade will be chosen for applications requiring fatigue behaviour (> 10 000 cycles) VDCrSi steel will mainly be used for compression springs. For extension springs, the loops will have to be added as this steel has a low tolerance to bending Caution: VDCrSi steel is expensive and few wire manufacturers propose it. It is not produced in Eastern Europe and is hard to find in Asia.
Choosing the material X10CrNi18-8 NS stainless steel is very easy to procure, which is not the case of the HS grade The commercial grades Sandvik 12R10 and 11R51 correspond to grades X10CrNi18-8 NS and X10CrNi18-8 HS respectively. As far as possible avoid specifying commercial grades on the drawings (Sandvik or other). Up to now, for wire diameters less than 1 mm, use of stainless steels was essential. This was due to the problem of implementing anti-corrosion surface treatments and to the risk of hydrogen embrittlement during electroplating. With the emergence of galvanised wires, steel wires with a diameter of less than 1 mm can be considered.
Mechanical properties: Rm mini 3000
C a r bo n s t e e l S M
2800
C a r bo n s t e e l S H - D H
2600
Hardened and tempe red steel VDC rSi
2400 2200
S t a i nle s s s t e e l X 1 0 C r Ni1 8 - 8 N S
2000
S t a i nle s s s t e e l X 1 0 C r Ni1 8 - 8 H S
) a P M (
m R
1800 1600 1400 1200 1000 0
1
2
3
4
5 d
6
7
8
9
10
Correspondences for EN - ISO ASTM - JIS EN
ISO
Carbon steel SM EN 10270 pt1
ISO 8458-2 SM 2002 (=)
Carbon steel SH EN 10270 pt1 Carbon steel DH EN 10270 pt1 Hardened and tempered steel VDCrSi EN 10270 pt2 Stainless steel X10CrNi18-8 NS / HS EN 10270 pt3
ISO 8458-2 SH 2002 (=) ISO 8458-2 DH 2002 (=)
ASTM ASTM A227/A227M 1999 Class II (>) ASTM A228/A228M 1993 (<) ASTM A228/A228M 1993 (<)
JIS JIS G 3521 SW-C 1991 (>)
JIS G 3522 SWPB 1991 (>)
ISO 8458-3 VDSiCr 2002 (<)
ASTM A877/A877M 1993 (=)
JIS G 3561 SWOSC-V 1994 (<)
ISO 6931-1 X9CrNi18-8 1994 (=)
ASTM A313/A313M 302 1995
JIS G 4314 SUS 302 1988 (<)
(=): Rm identical; (<) Rm less; (>) Rm more than the EN standard
Mechanical Resistance Comparison Carbon steels EN-ASTM-JIS 2900
C arbon steel SH - D H J IS G 3 5 2 2 S W P - B
2700
A S T M A 2 2 8 /A 2 2 8 M
2500 ) a P M (
2300 2100
m R
1900 1700 1500 0
1
2
3 d
4
5
6
Mechanical Resistance Comparison Hardened and tempered steel SiCr EN ASTM-JIS 2200
E N 1 0 2 7 0 -2 V D C rS i J IS G 3 5 6 1 S W O S C -V
2100
A S T M A 8 7 7 /A 8 7 7 M
2000
IS O 8 4 5 8 -3 V D S i C r
) a P M (
1900
m R
1800 1700 1600 0
1
2
3
4
5 d
6
7
8
9
10
Mechanical Resistance Comparison Stainless steels EN-ASTM-JIS 2400
E N 1 0 2 7 0 - 3 X 1 0 C rN i 1 8 -8 H S
2200
E N 1 0 2 7 0 - 3 X 1 0 C rN i 1 8 -8 N S J IS G 4 3 1 4 S U S 3 0 2 W P A
2000
J IS G 4 3 1 4 S U S 3 0 2 W P B
1800
) a P M (
A S T M A 3 1 3 /A 3 1 3 M 3 0 2
1600
m R
1400 1200 1000 0
1
2
3 d
4
5
6
Wire diameters There are no standards for wire diameters. Up to a diameter of 1 mm, we shall choose a wire diameter every 0.05 mm 0.10 0.60
0.15 0.65
0.20 0.70
0.25 0.75
0.30 0.80
0.35 0.85
0.40 0.90
0.45 0.95
0.50 1.00
0.55
As from 1 mm, we shall choose a wire diameter every 0.10 mm. 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9 00
1.10 2.10 3.10 4.10 5.10 6.10 7.10 8.10 9 10
1.20 2.20 3.20 4.20 5.20 6.20 7.20 8.20 9 20
1.30 2.30 3.30 4.30 5.30 6.30 7.30 8.30 9 30
1.40 2.40 3.40 4.40 5.40 6.40 7.40 8.40 9 40
1.50 2.50 3.50 4.50 5.50 6.50 7.50 8.50 9 50
1.60 2.60 3.60 4.60 5.60 6.60 7.60 8.60 9 60
1.70 2.70 3.70 4.70 5.70 6.70 7.70 8.70 9 70
1.80 2.80 3.80 4.80 5.80 6.80 7.80 8.80 9 80
1.90 2.90 3.90 4.90 5.90 6.90 7.90 8.90 9 90
Influence of temperature Temperature variations result in variation of rigidity modules (E, G) that will lead to variations in proportional loads.
n o i t a i r a v y t i d i g i R
T°C
Steel anticorrosion protection There are two main processes for anticorrosion protection of steel springs:
Lamellar zinc organo-metallic coating
Hot galvanised wire
Lamellar zinc organo-metallic coatings are produced after shaping of springs and are hot polymerised. The coatings are made by spraying or centrifugal process. A trade brand example: Delta Tone ®. In the process of qualification: Geomet®, Zintek ®. In some cases, this coating can be completed by an additional coloured coat for identification (trade brand example: Delta Seal) The hot galvanised wire is a wire on which either zinc only, or a zinc alloy + 5% aluminium is deposited at a high temperature (380°C). The galvanised wire can be re-drawn without damaging the protective coat. Trade brand example: Bezinal ® (Bekaert).
Electroplating is prohibited due to hydrogen embrittlement
