1 609 929 M72 | (9.11.07) Bosch Power Tools
8 | English
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 dia-
gram, the result is the curve of a torque charac-
teristic. The height of the curve corresponds with
the maximum reachable torque, and the steep-
ness indicates the duration in which this is
achieved.
A torque gradient depends on the following fac-
tors:
– 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 con-
nection
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 duration, the maximum
torque is reached (steep characteristic
curve). Unnecessary long impact duration
only causes damage to the machine.
–A spring-loaded seat is given for metal-to-
metal screw applications, 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 wash-
ers or fiber washers as backing.
For a spring-loaded seat as well as for a soft seat,
the maximum tightening torque is lower than for
a hard seat. Also, a clearly longer impact duration
is required.
Reference Values for Maximum Screw/Bolt Tightening Torques
Calculated from the tensional cross-section; utilization 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.
Tips
Torque rods have shanks with precisely calibrat-
ed, reduced diameters. Thus, they act torque-lim-
iting. A torque rod is placed between the impact
wrench and the bit.
Rule of thumb for the application: Core diameter
of the screw/bolt = effective diameter of the
torque rod. The impact duration is to be deter-
mined through practical testing.
The thumbwheel 2 must be set to max. here.
For hanging up, a suspension hook 1 is mounted
at the machine's centre of gravity.
At temperatures below the freezing point, run
the machine for approx. 3 minutes at no-load to
improve its lubricating capacity.
Property Classes ac-
cording 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
M 6
2.71 3.61 4.52 4.8 5.42 6.02 7.22 8.13 9.7 13.6 16.2
M 8
6.57 8.7 11 11.6 13.1 14.6 17.5 19.7 23 33 39
M 10
13 17.5 22 23 26 29 35 39 47 65 78
M 12
22.6 30 37.6 40 45 50 60 67 80 113 135
M 14
36 48 60 65 72 79 95 107 130 180 215
M 16
55 73 92 98 110 122 147 165 196 275 330
M 18
75 101 126 135 151 168 202 227 270 380 450
M 20
107 143 178 190 214 238 286 320 385 540 635
OBJ_BUCH-546-001.book Page 8 Friday, November 9, 2007 8:43 AM
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