Extension springs in piano wire, electrogalvanised wire and stainless steel wire

Tech Drawing - Extension springs in piano wire, electrogalvanised wire and stainless steel wire

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With the help of our range sliders, we’ve made it quick and easy to navigate our range of standard extension springs in more than 3,000 different sizes.

We have everything from small extension springs to large extension springs used throughout industry and privately. The selection of standard extension springs is provided in lengths ranging from 6.35 mm to 377.00 mm (unloaded state).

The selection is produced in accordance with current DIN standards with the highest quality demands in Europe and America.

What is an extension spring?
 

An extension spring is used where traction is needed, for instance in industrial and agricultural machinery. Both large and small constructions.

An extension spring accumulates a force when the spring is pulled apart. The longer you stretch it, the more force is accumulated. The force is released when the spring is allowed to return to its original length. If an extension spring is designed and used correctly, it can be used for a prolonged period. For further information, see under “Service life” in the technical information below.

Piano wire: dry environment
 

Piano wire springs are recommended for use in dry environments. The material offers no protection against rust. Piano wire springs are approximately 10% stronger than stainless steel springs.

Electrogalvanised extension springs are made from piano wire, which is then electrogalvanised. This gives the extension springs an attractive, shiny surface. Electrogalvanisation only provides moderate corrosion resistance, but if the spring is used in a humid environment, the service life will be prolonged compared to the same spring made from piano wire without surface treatment.

Stainless steel wire: humid environment
 

For humid environments we recommend springs made from stainless steel wire. Stainless steel extension springs are approximately 10% weaker than piano wire springs.

If you use springs in environments where they are exposed to harsh chemicals or salt water, we recommend springs in a specific type of stainless steel (AISI 316). We do not keep these in stock, but we can custom-produce them on request. Contact us for further information.

Springs for cutting and testing
 

If you are unsure about the length/travel you need, we have springs in lengths of 300, 500 and 1,000 mm manufactured specifically to be cut to length and used for prototypes and testing. Sort by lengths using the slider below.

Note: These springs do not have loops. They must be bent up by the customer, following cutting to the desired length, if necessary. To extend the service life, we recommend that the bends are made as soft bends, not sharp bends or notches.

19-46655-description

Stainless steel 302

19-46095-description

Music wire

19-46719-description

Galvanised

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Shopping Options
d - Wire diameter (mm)
De - External diameter (mm)
Di - Internal diameter (mm)
L0 - Unloaded length (mm)
Ln - Max. loaded length (mm)
Sn - Maximum travel (mm)
Fn - Maximum load at Ln (N)
F0 - Initial force (N)
R - Spring constant (N/mm)
Lk - Spring body length (mm)
Range
Material

Items 1-10 of 2764

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Wire diameter (mm)
De
External diameter (mm)
Di
Internal diameter (mm)
L0
Unloaded length (mm)
Lk
Spring body length (mm)
Ln
Max. loaded length (mm)
Sn
Maximum travel (mm)
Fn
Maximum load at Ln (N)
F0
Initial force (N)
R
Spring constant (N/mm)
SKU Stock Tech Drawing Read More 3D CAD
Stainless steel 302 0.18 1.60 N/A 6.35 3.79 13.72 7.37 1.19 0.11 0.15 E00630070250S E00630070250S
Music wire 0.18 1.60 N/A 6.35 3.79 13.72 7.37 1.42 0.13 0.18 E00630070250M E00630070250M
Stainless steel 302 0.18 1.60 N/A 7.87 5.31 18.54 10.67 1.19 0.11 0.10 E00630070310S E00630070310S
Music wire 0.18 1.60 N/A 7.87 5.31 18.54 10.67 1.42 0.13 0.12 E00630070310M E00630070310M
Stainless steel 302 0.18 1.60 N/A 9.65 7.09 23.62 13.97 1.19 0.11 0.07 E00630070380S E00630070380S
Music wire 0.18 1.60 N/A 9.65 7.09 23.62 13.97 1.42 0.13 0.09 E00630070380M E00630070380M
Stainless steel 302 0.18 1.60 N/A 11.18 8.62 28.45 17.27 1.19 0.11 0.06 E00630070440S E00630070440S
Music wire 0.18 1.60 N/A 11.18 8.62 28.45 17.27 1.42 0.13 0.07 E00630070440M E00630070440M
Stainless steel 302 0.18 1.60 N/A 12.70 10.14 33.27 20.57 1.19 0.11 0.06 E00630070500S E00630070500S
Music wire 0.18 1.60 N/A 12.70 10.14 33.27 20.57 1.42 0.13 0.07 E00630070500M E00630070500M

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Music wire

The wire is certified in accordance with DIN 17223 Class C Wire WERKSTOFF NO. 1.1200 – EN Norm 10270-1
Working temperature between -30 ºC and +120 ºC
Recommended for use in dry environments.

Stainless steel

The wire is certified in accordance with DIN 17224 AISI 302 WERKSTOFF NO. 1.4310 – EN Norm 10270-3
Working temperature between -200 ºC and +250 ºC
Can be used in dry and humid or wet environments.

Galvanised

The wire is certified in accordance with DIN 17223 Class C Wire WERKSTOFF NO. 1.1200 – EN Norm 10270-1
Working temperature between -30 ºC and +120 ºC
Galvanised extension springs are made from piano wire, which is then electrogalvanised. Electrogalvanisation means that the extension spring is given a shiny, more corrosion-resistant surface.
Recommended for use in dry environments.

Tolerances

Series A and C: (See which series a spring belongs to in the “Series” column in the table).
All dimensions and forces in accordance with DIN 2097 (Grade 2). DIN 2097 defines the force as the determining parameter. The number of coils may therefore vary and will consequently not be stated for these series.

Series B: (See which series a spring belongs to in the “Series” column in the table).
See here for more information. (link to tolerances)

Series D: (See which series a spring belongs to in the “Series” column in the table).
The series is produced for use in testing and prototyping. There are therefore no tolerances for this series.

As this series is designed for testing, the cut spring’s coils will vary from spring to spring, and so the spring constant cannot be defined.

Datasheet and 3D CAD

If you want a PDF datasheet or a 3D CAD drawing of the spring in .step, .iges or .sat format, these can be downloaded for free by clicking on the 3D CAD symbol next to the item number in the table.

Terminology
Tech Drawing - Extension springs in piano wire, electrogalvanised wire and stainless steel wire
d
=
Wire diameter in mm
De
=
External diameter (Di + (d*2))
LK
=
Unloaded length of spring body in mm
L0
=
Free unloaded length. Lo is for guidance only. Lo can vary slightly.
L1
=
Loaded length in mm at F1
L2
=
Loaded length in mm at F2
Ln
=
Max. loaded length in mm (min. length/max. load)
F0
=
Initial force (N)
F1
=
Partial load in N (Newtons) at L1
F2
=
Additional load in N (Newtons) at L2
Fn
=
Maximum load in N (Newtons) at Ln (should not be used)
sn
=
Maximum travel in mm (Lo+Ln) (should not be used)
R
=
Spring constant in N/mm
LH
=
Internal loop height in mm
m
=
Opening (space) at loop in mm
x
=
Loop position
1 N
=
0,10197Kg
1Kg
=
9,80665N
Force calculation

The max. force in Newtons (Fn) for an extension spring in certified piano wire is approx. 10% higher than for the same dimensions in stainless spring steel.

Calculating initial tension (F0):
The initial tension (F0) of an extension spring is also called the initial force. This indicates how much force will be used to activate the extension spring.

Initial tension (F0) or initial force is for guidance only, as it can vary from batch to batch. As a rule of thumb, you can say that the initial tension (F0) corresponds to approx. 10-15% of maximum force (Fn).

Initial tension (F0) = Maximum force (Fn) - (Spring constant (R) x Maximum travel (Sn))

 

For example, the initial tension for stock number 32600 (Fn = 237 N, R = 2.67 N/mm and Sn = 75.70 mm) is calculated as:

237 N - (2,67 N/mm * 75,70 mm) = 35 N

The calculation of spring force at a given length:
If you want to know how much force an extension spring produces at a given length/travel, you can use the following formula:

Force at a given length (F1) = Initial tension (F0) + (Maximum travel (Sn) * Spring constant (R))

For example, stock number 32600, where R = 2.67 N/mm, where we want to know the force for a travel of 55 mm and F0 is approx. 35 N.

35 N + (55 mm * 2,67 N/mm) = 182 N

Design of loops

Series A: (See which series a spring belongs to in the “Series” column in the table).
German loops as per DIN 2097, random angle.

The loop position (X) is variable and the loops can therefore be turned in relation to one another. The external diameter of loops may well exceed the external diameter of the body.

German loop
German loop

Series A: Tolerance of loop width
The tolerance for deviations of loop width is determined based on the formula below. Note that you must use a value determined based on the spring’s coil ratio to be able to calculate the tolerance.

De (external diameter) + value from coil ratio table

Example: Stock number 32600 has a wire thickness (d) of 2.5 mm. The external diameter (De) is 18 mm, which produces a mean diameter (Dm) of 15.5 mm.

Based on the coil ratio table, we can therefore arrive at the value that needs to be added to the spring’s external diameter (De) to find the max. external diameter of the loop.

Coil ratio: 15,5 mm / 2,5 mm = 6,2 mm
Loop max. width: 18 mm + (1,5 * 2,5 mm) = 21,75 mm

Coil ratio table
Coil ratio: (dm/d)
Gütegrad 2
0 mm - 6 mm
d
6 mm - 12 mm
1,5 * d
12 mm +
The design of loops can be arranged on agreement.

Series A: - Tolerance of internal loop height
Tolerance of internal loop height (LH) is from 0,8 mm to 1,1 * Dm.

(E.g. Stock number 32600 has a mean diameter (Dm) of 15.5 mm.
Min. internal loop height = 0.8 * 15.5 mm = 12.4 mm.
Max. internal loop height = 1.1 * 15.5 mm = 17.05 mm.

Loop height (LH)
Loop height (LH)

Series B and C: (See which series a spring belongs to in the “Series” column in the table).
Loops in this range are German loops without a specific loop shape and with a random angle. Exceptions are stock numbers 503 and 503RF, which have English loops.

Every effort is made to keep the same external diameter for the loop as the spring body. However, the external diameter of the loop may vary. There are no tolerances for this series.

English loop
English loop

Series D: (See which series a spring belongs to in the “Series” column in the table).
There are no loops for this series. It is intended for testing and cutting. The customer must, therefore, create their own loops. To extend the service life of the spring, we recommend making loops in soft bends without notches. If the loop is bent too sharply, this may result in a weak point in the spring.

Series D have no loops
Series D have no loops

Service life of springs

The service life of a spring is generally very difficult to define. A large number of parameters come into play, and it is therefore impossible to define a service life.

Parameters with a significant influence on service life include: Installation, installation method, number of movements, vibrations, shocks, torsion, length of travel, non-axial travel, temperature, wear against other surfaces, environment of use, any cleaning agents, lateral impacts, etc.

Always dimension an extension spring so that it delivers the desired travel and force with as little exertion as possible. This will give the spring the longest possible service life.

Applying the maximum load to the spring or exceeding it will shorten its service life and may cause it to become permanently distorted.

Therefore we recommend that you do not use more than 75% of the maximum travel (Sn) of conical springs.

Winding direction

Usually right. The force and application is not affected by the direction of wind.

Standard extension springs are not defined with a specific direction of wind. Depending on production, the springs may be either right or left wound.

Misc.

If an extension spring with an exact value for one of the following parameters is required, springs must be custom-made:
- Loop type
- Loop height (LH)
- Loop position (X)
- Loop width (if the spring is to be incorporated into a tube)
- Opening at loop (m)
- Initial force (F0)

Safety requirements for extension springs in structures where a person is suspended from the spring, e.g. baby hammocks and baby bouncers

When using springs for baby hammocks or baby bouncers, for instance, or other structures where a person is suspended from a structure in some way, you must be aware of the following:

Spring deformities or breakages
A spring is a technical object that can be deformed, or that may break during use. There may be invisible defects in the alloy of a spring wire, and during the manufacture of the spring defects may also occur that can weaken the spring. Improper use of a spring can also reduce the service life of a spring and result in the spring becoming deformed or breaking.

A spring must always be dimensioned so that the spring always incorporates a safety factor that corresponds to the risk in use.

Safety device – IMPORTANT!
If a spring is to be used in a structure where a person is suspended in some way from the structure, and the spring will be a load-bearing element between the person and the structure, a separate appropriate safety device must be installed between the person and a fixed point. This ensures that the person cannot fall down if the spring becomes deformed or breaks.

It is always the user of a spring – in any structure where persons can fall or otherwise injure themselves – who is responsible for ensuring that the structure is correctly designed so that no personal injury can result if a spring becomes deformed or breaks.

Sodemann Industrifjedre A/S DOES NOT recommend the use of springs in structures where people are suspended from the spring.

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