Coefficient Of Friction For Different Coatings; Mechanical Properties Of Screws Used - Kohler SFGLD480 Operation & Maintenance Manual

Steel with cadmium
Cadmium with zinc
Cadmium with cadmium
Steel with phosphate
Phosphate with cadmium
Phosphate with zinc
Phosphate with phosphate
Steel with zinc
In any case, the normal coefficient of friction used is 0.14 for clean and non-lubricated steel-to-steel assembly. If
the screw and the mating threads are of steel, clean and lubricated, this coefficient is 0.1.
From a known coefficient of friction, it is possible to calculate the pre-stressing force using this formula.

S dn


M P [ (
v
4
To determine whether a screw will resist a pre-stressing force (as calculated from a known tightening torque and
coefficient of friction), it is necessary to know the mechanical properties of that screw. The following table shows
those properties.
GRADE
2
Tensile strength (N/mm
2
Yield strength (N/mm )
Extension to the breakage (%) min
2
Resilience (N.m/cm )
Hardness HRC
Table 3 – Mechanical properties of screws used
PRODUCT INFORMATION
IM-C-C-00-002e
TIGHTENING TORQUES FOR COMMERCIAL BOLTS & NUTS
Coating
Table 2 – Coefficient of friction for different coatings
 
. 0 58 df ) . 0 16
Min.
)
Max.
Min.
Max.
(acc. to DIN 267)
INDEX
B
Normal
0.07
0.1
0.1
0.11
0.11
0.11
0.12
0.14

df side diameter


The average coeficient


Coeficient
1


Coeficient
p ]
2

S Washer´s diameter

dn Screw nominal

p Screw pitch

P Pre - stressing
v
8.8
784
980
627
12
59
18
31
2.1.38
DATE
February 2012
O&M_2.002211.810_A_10_2016
Coefficient of friction
Lubricated
0.07
0.08
0.07
0.1
0.08
0.11
0.1
0.07
of friction of :
of friction between screw and
of friction in screw and part´s
diameter
force obtained with the torque
10.9
980
1176
882
9
39
27
38
Dep.2
part
thread
M
12.9
1176
1372
1058
8
29,4
34
44
2/3