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Schnorr Disc Springs

Disc Spring Engineering
Maximum load - minimum space - maximum flexibility

DIAGRAM OF A DISC SPRING

Figure 1 - click to enlarge

 

Symbols and Units

Symbols

Unit

Designation

De

mm

Outside diameter

Di

mm

Inside diameter

Dw

mm

Diameter at the root of slots in a disc spring

Do

mm

Diameter of centre of rotation

E

N/mm2

Young’s modulus

F

N

Spring force of a single spring

F1, F2, F3

N

Spring force for deflections s1, s2, s3

Fc

N

Calculated spring force of a single spring when flat

Fges

N

Spring force of a spring set or stack

ΔF

N

Force lost in setting

K1, K2, K3, K4

Constants for calculations

LO

mm

Unloaded length of the spring stack or spring sets

L1, L2, L3

mm

Length of the loaded spring stack or spring set for forces F1, F2, F3

Lc

mm

Calculated length of the spring stack or set when springs are flat

N

Number of cycles to failure

R

N/mm

Spring rate

W

N/mm

Spring work

ho

mm

Cone height of an unloaded single spring (calculated ho = lo – t)

ho'

mm

Cone height of an unloaded spring with reduced thickness t’ (and contact flats, calculated ho=lo– t)

i

No. of single springs or sets in series in a stack

lo

mm

Height of an unloaded spring stack

n

No. of parallel springs in a set

s

mm

Deflection of a single spring

s1, s2, s3

mm

Deflections relative to loads F1, F2, F3

sges

mm

Deflection of a spring set or stack

t

mm

Thickness of individual

t'

mm

Reduced spring thickness for springs with contact flats (group 3)

WM, wR

Friction factors

δ= De/Di

Diameter ratio

µ

Poisson’s ratio (for spring steel = 0.3)

σ

N/mm2

Calculated stress

σOM, σl, σll, σlll, σlv

N/mm2

Calculated stress at points OM, I, II, III and IV as per figure 1

σo

N/mm2

Calculated maximum stress for springs with dynamic loads

σu

N/mm2

Calculated minimum stress for springs with dynamic loads

σh

N/mm2

Stress range for the working stroke of dynamically loaded springs

σO

N/mm2

Maximum stress for fatigue resistance

σU

N/mm2

Minimum stress for fatigue resistance

σH = σ0 - σU

N/mm2

Permissible stress range for fatigue resistance

 

 

 

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