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Buffer springs

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Abbreviation Unit Term
F kN spring force
L mm spring lenght
s mm spring travel
h mm width of flat steel
Abbreviation Unit Term
b mm thickness of flat steel
d±x mm upper inner diameter
with tolerance range
D±x mm lower outer diameter
with tolerance range

The buffer spring

The conical, volute or buffer spring is a popular, widely used machine element made of wound flat steel wire. It is suitable for absorbing large forces within a small space at mostly small spring travels.
Before the winding, the spring leaf is rolled, tapered at the head and foot, and cut in such a way that the spring stands in an angular position. For convenience, the windings are normally wound on top of each other. As a result, the springs have more internal friction. In larger quantities and with correspondingly shaped tools, it is also possible to produce almost frictionless springs.

Due to the method of rolling and because of the internal friction, the calculation of the spring is complicated, so that it is advisable to select a tried and tested spring from the great number of possible variants in this catalogue.
This publication shows tried and tested springs in all sizes and strengths to provide an indication of the space required. As a matter of course, our product range also includes other types of buffer springs. Springs can be manufactured and delivered in accordance with various standards and lists.

Information and notes

Grade Standard Dimension
b (mm)
Note Comparison
with ISO 683
51 Si 7 Factory standard
(previously ISO 683/XIV-1973)
up to 20 Standard grade No 4
56 Si 7 EN 10089 3 to 10
61 SiCr 7 EN 10089 3 to 12 Standard grade No 7
51 Cr V 4 EN 10089 3 to 10 only in special cases No 13


Grade C %
min. / max.
Si %
min. / max.
Mn %
min. / max.
Cr %
min. / max.
V %
min. / max.
P + S %
51 Si 7 0.47 / 0.55 1.5 / 2.0 0.5 / 0.8 0.045
56 Si 7 0.52 / 0.60 1.6 / 2.0 0.6 / 0.9 0.025
61 SiCr 7 0.57 / 0.65 1.6 / 2.0 0.7 / 1.0 0.2 / 0.4 0.030
51 Cr V 4 0.47 / 0.55 0.15 / 0.4 0.7 / 1.1 0.9 / 1.1 0.1 / 0.2 0.030



The materials listed are suitable for producing buffer springs. We reserve the right to select the steel type as well as minor deviations of the diameters quoted in the tables.
The tempering hardness depends on the construction of the spring; the normal range is between 1350 N/mm2 and 1700 N/mm2. After tempering, the springs are pre-set until plasticization.
As a result, each spring is subject to a technological strength test. Proofs of the strength at the spring itself require a separate agreement.

The normal manufacturing tolerance is +30 % / -20 %; for higher demands, a separate agreement will be required.
Deviations < 20 % can be achieved in larger volumes (> 100 pieces) and with special tools.

Dimensional deviations / Tolerances

Manufacturing parameters: tolerances within the manufacturing process!

d ± x mm
Upper, inner
Tolerance range
from to from to
25 -1 +2
26 50 -1 +3
51 70 -2 +4
71 90 -3 +5
91 110 -5 +6
111 -5 +10
D ± x mm
Lower, outer
Tolerance range
from to from to
50 -2 +2
51 100 -4 +3
101 150 -6 +4
151 200 -8 +6
201 -10 +8
L0 mm
Tolerance range
from to from to
100 -5 +5
101 200 -5 +7
201 250 -5 +10
251 300 -10 +10
301 350 -10 +15

Characteristic curve and winding direction

Depending on the degree of rolling, the characteristic curve will be more or less progressive. The tables indicate two spring forces and their corresponding lengths, a normal operating load at approximately 0.5 to 0.7 of the possible spring travel, and a recommended end force beyond which the spring becomes highly progressive.
With our manufacturing facilities we can produce only right-wound buffer springs. However, the winding direction has no effect on the functioning of the spring.

Surface / Corrosion protection

Due to the internal friction, the springs should be kept well oiled or greased when in operation. Springs come standard with oiled surface. Rust protection with black colour, Luxoral Aqua, can be delivered on request.


On request, the springs are hot-stamped at the foot with the company logo and delivery year. Other markings, e.g. to differentiate between different types of springs or colour codes, can be agreed.

Static installation or infrequent operation

Buffer springs are well suited for this purpose. The average operating load should be between normal load and maximum load and may only occasionally reach maximum load (< 104 load changes). Example: preload springs; insulating springs; safety stop springs.

Frequent load changes

The buffer spring is not suited for vibration stress with an amplitude w > 0.1 of the total spring travel. For frequent use and an expected lifetime in the range of 104 to 106 load changes, a spring has to be selected carefully. The volume utilisation of a spring gives an indication here: Depending on the utilisation in the installation space, more and less frequently used springs can be distinguished. For this purpose, please make use of our consulting services. The less the full stroke is used, the longer will be the lifetime of the spring. Therefore, oversizing is required for vehicle suspension. The information provided here shall serve the purpose of avoiding grossly incorrect sizing and is not a general guarantee of suitability! The otherwise usual measures for lifetime extension cannot be applied to buffer springs. Therefore, we are unable to guarantee a certain lifetime. Examples: suspension of rarely used low-speed heavy-duty vehicles, impacts, heavy machinery, shock absorption, crane systems.

Setting, creeping

The springs are pressed to solid height several times and therefore have no significant loss of length at normal load. A small loss of length is to be expected at maximum load over a long period.

Operating temperature

The normal range is +80 °C to -30 °C. Setting losses may occur at above 80 °C with forces in the range of the maximum load. A stronger spring should be selected for higher temperatures, and it should be used for moderate loads. At below -30 °C, the materials will embrittle, although the Si-containing materials are well suited.
Also in this case, an oversized spring should be selected, whose strength can then be kept low. Please take advantage of our consulting services.

Activation transverse to the spring axis
(lateral suspension)

Normal buffer springs are not suitable for this purpose. In exceptional cases, springs with coil distance can be produced.

Quality assurance

Our buffer springs are manufactured within our documented and DIN EN 9001: 2000 certified quality management system.

Use Dimen-
Preload Normal
h x b mm d mm D mm L0 mm L1mm P1kN L2mm P2kN L3mm P3kN Ca. kg
U1 For draw hooks and locomotives CH
155×16 65+3 210-6 330+13/-6 288 10 175 120 158 210 28.7
U11 For draw hooks
according to UIC
UIC 155×16 65+3 195-6 250+10/-5 213 20 177 100 158 200 24.7
U2 For plunger buffers of the wagons CH
150×14,5 54+3 167-5 250+10/-5 230 10 168 100 155 170 17.0
U3 For tow hooks of the wagons CH
150×14,5 84+3 180-5 250+10/-5 220 10 165 90 155 160 17.0
U4 DIN 22473 for traction and buffer gear electric mine railway 120×10 54+3 165-5 230+10/-5 212 10 167 50 150 80 16.4
U5 DIN 5964 Bl.3 / F traction and buffer gear of light railway 150×8 48 130 200 195 5 172 35 160 52.5 10.2
U6 Conical spring for draw gear 155×9 60+3 175-5 268+10/-5 235 10 165 60 165 60 20.9

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*The technical characteristics of the spring remain unchanged within the dimension tolerances indicated.

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