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OBJ_BUCH-548-005.book Page 13 Wednesday, March 2, 2016 1:26 PM
Note: The consequences of excessive heating-up are high
wear of all hammer mechanism components and a high re-
quirement of lubricant.
The impact duration is to be determined for each required
tightening torque. The actually achieved tightening torque is
always to be checked with a torque wrench.
Screw Applications with Hard, Spring-loaded or Soft Seat
A test in which the achieved torques in an impact series are
measured and transferred to a diagram will produce the curve
of a torque characteristic. The height of the curve corre-
sponds with the maximum reachable torque, and the steep-
ness indicates the duration in which this is achieved.
A torque gradient depends on the following factors:
– Strength properties of the screws/nuts
– Type of backing (washer, disc spring, seal)
– 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 given for metal-to-metal screw applications
with the use of washers. After a relatively short impact du-
ration, the maximum torque is reached (steep characteris-
tic curve). Unnecessary long impact duration only causes
damage to the machine.
– A spring-loaded seat is given for metal-to-metal screw ap-
plications, however with the use of spring washers, disc
springs, studs or screws/nuts with conical seat as well as
when using extensions.
– A soft seat is given for screw applications, e. g., metal on
wood or when using lead washers or fibre washers as back-
ing.
For a spring-loaded seat as well as for a soft seat, the maxi-
mum tightening torque is lower than for a hard seat. Also, a
clearly longer impact duration is required.
Determining the Impact Duration
The diagrams (examples) indicate that the tightening torque
[Nm] depends on the impact duration [s]:
For a hard seat
For a soft seat.
The data are mean values and vary depending on the applica-
tion. As a control measure, always check the tightening
torque with a torque wrench.
Reference Values for Maximum Screw/Bolt Tightening Torques
Calculated from the tensional cross-section; utilization of the yield point 90 % (with friction coefficient μ
measure, always check the tightening torque with a torque wrench.
Property Classes
Standard Screws/Bolts
according to DIN 267
3.6
M 8
6.57
M 10
13
M 12
22.6
M 14
36
M 16
55
Bosch Power Tools
Diagram for GDS 24
[Nm]
The highest torque is achieved:
– for a hard seat after approx. 10 seconds of impact
– for a soft seat after approx. 22 seconds of impact
Diagram for GDS 30
[Nm]
The highest torque is achieved:
– for a hard seat after approx. 6 seconds of impact
– for a soft seat after approx. 26 seconds of impact
For reference values for the maximum tightening torques of
commercially available screw/bolts, see the following table.
4.6
5.6
4.8
6.6
8.7
11
11.6
13.1
17.5
22
23
26
30
37.6
40
45
48
60
65
72
73
92
98
110
= 0.12). As a control
total
High-strength Bolts
5.8
6.8
6.9
8.8
14.6
17.5
19.7
23
29
35
39
47
50
60
67
80
79
95
107
130
122
147
165
196
1 609 92A 2AT | (2.3.16)
English | 13
1
2
[s]
1
2
[s]
10.9
12.9
33
39
65
78
113
135
180
215
275
330
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