Schnorr Disc Springs
Disc Spring EngineeringMaximum load - minimum space - maximum flexibility
Figure 1 - click to enlarge
Symbols and Units
Symbols
Unit
Designation
D_{e}
mm
Outside diameter
D_{i}
Inside diameter
D_{w}
Diameter at the root of slots in a disc spring
D_{o}
Diameter of centre of rotation
E
N/mm^{2}
Young’s modulus
F
N
Spring force of a single spring
F_{1}, F_{2}, F_{3}
Spring force for deflections s_{1}, s_{2}, s_{3}
F_{c}
Calculated spring force of a single spring when flat
F_{ges}
Spring force of a spring set or stack
ΔF
Force lost in setting
K_{1}, K_{2}, K_{3}, K_{4}
Constants for calculations
L_{O}
Unloaded length of the spring stack or spring sets
L_{1}, L_{2}, L_{3}
Length of the loaded spring stack or spring set for forces F_{1}, F_{2}, F_{3}
L_{c}
Calculated length of the spring stack or set when springs are flat
Number of cycles to failure
R
N/mm
Spring rate
W
Spring work
h_{o}
Cone height of an unloaded single spring (calculated h_{o} = l_{o} – t)
h_{o}'
Cone height of an unloaded spring with reduced thickness t’ (and contact flats, calculated h_{o}=l_{o}– t)
i
No. of single springs or sets in series in a stack
l_{o}
Height of an unloaded spring stack
n
No. of parallel springs in a set
s
Deflection of a single spring
s_{1}, s_{2}, s_{3}
Deflections relative to loads F_{1}, F_{2}, F_{3}
s_{ges}
Deflection of a spring set or stack
t
Thickness of individual
t'
Reduced spring thickness for springs with contact flats (group 3)
W_{M}, w_{R}
Friction factors
δ= D_{e}/D_{i}
Diameter ratio
µ
Poisson’s ratio (for spring steel = 0.3)
σ
Calculated stress
σ_{OM}, σ_{l}, σ_{ll}, σ_{lll}, σ_{lv}
Calculated stress at points OM, I, II, III and IV as per figure 1
σ_{o}
Calculated maximum stress for springs with dynamic loads
σ_{u}
Calculated minimum stress for springs with dynamic loads
σ_{h}
Stress range for the working stroke of dynamically loaded springs
σ_{O}
Maximum stress for fatigue resistance
σ_{U}
Minimum stress for fatigue resistance
σ_{H} = σ_{0} - σ_{U}
Permissible stress range for fatigue resistance