Bosch GDS 24 Notice Originale page 13

OBJ_BUCH-548-003.book Page 13 Wednesday, March 12, 2014 10:30 AM
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
When in a test, the achieved torques in an impact series are
measured and transferred into a diagram, resulting in 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
3 609 929 D00 | (12.3.14)
English | 13
1
2
[s]
1
2
[s]
10.9 12.9
33 39
65 78
113 135
180 215
275 330