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– Strength properties of the material being screwed/bolted
together
– Lubrication conditions at the screw/bolt connection
The following application cases result accordingly:
– A
hard seat
is a metal-to-metal screw application which
uses washers. After a relatively short impact duration, the
maximum torque is reached (steep characteristic curve).
Unnecessary long impact duration only causes damage to
the machine.
– A
spring-loaded seat
is also a metal-to-metal screw ap-
plication but uses spring washers, disc springs, studs or
screws/nuts with conical seats. It is also called a spring-
loaded seat when extensions are used.
– A
soft seat
is a screw application of e.g. metal on wood or
a screw application that uses lead washers or fibre wash-
ers as backing.
For a spring-loaded seat as well as for a soft seat, the max-
imum tightening torque is lower than for a hard seat. Also, a
clearly longer impact duration is required.
Determining the impact duration
The diagrams (examples) show the tightening torque [Nm]
depending on the impact duration [s]:
❶
for hard seat
❷
for soft seat.
The values provided are average values and differ depending
on the application. As a control measure, always check the
tightening torque with a torque wrench.
Diagram for GDS 24
[Nm]
[s]
1
2
The maximum torque is achieved:
– After an impact duration of approx. 10 seconds for a hard
seat
– After an impact duration of approx. 22 seconds for a soft
seat
Diagram for GDS 30
[Nm]
[s]
1
2
The maximum torque is achieved:
– After an impact duration of approx. 6 seconds for a hard
seat
– After an impact duration of approx. 26 seconds for a soft
seat
Guide values for maximum screw/bolt tightening torques of
commercially available screws/bolts can be found in the fol-
lowing table.
Guide values for maximum screw tightening torques
Figures given in Nm; calculated from the tensional cross-section; utilisation of the yield point: 90% (with friction coefficient
µ
total
= 0.12). As a control measure, always check the tightening torque with a torque wrench.
Property classes
according to DIN
267
Standard screws/bolts
High-strength bolts
3.6
4.6
5.6
4.8
6.6
5.8
6.8
6.9
8.8
10.9
12.9
M8
6.57
8.7
11
11.6
13.1
14.6
17.5
19.7
23
33
39
M10
13
17.5
22
23
26
29
35
39
47
65
78
M12
22.6
30
37.6
40
45
50
60
67
80
113
135
Bosch Power Tools
1 609 92A 4R3 | (28.02.2019)
