Schaaf GmbH Hydraulic Bolt Tensioning Technology The advantages of generating pure axial pre-tension using pressures up to 4000 bar (SSV and HM) Torsion-free generation of tension force – Economical use of bolt material capacity A bolt is designed to hold two or more components together. Axial bolt elongation is the only force at work here. Torsion, which is generated, due to friction in the threads and in the support surface, by using torque wrenching methods, means only unnecessary weaking of the components. This requires stronger bolt connections. This disadvantage is no longer existing when using SCHAAF SSV and HM to generate the axial pre-tension. This increases the economic utilisation factor. Axial tension force has been attained by using SCHAAF SSV and HM for bolts with a thread diameter from 8 mm to over 800 mm. Maximum accuracy Since the pre-tension is purely axial and only varies by -4% maximum, bolts can be tightened up to the yield strength of the material used. An integrated displacement transducer even allows tensioning beyond the elastic limit. Increased safety Due to the purely axial bolt tensioning force applied and as the safety factors given in bolt calculation instructions come down to a minimum, bolts can be higher tensioned for the same bolt thread cross section. The connection is more secure. Frictionless application of tensioning force Due to the purely axial bolt tensioning force applied, the main nut (SSV) or the locking nut (HM) can be threaded without effort or friction up to the flange. This completely eliminates the problem of chewing of the threads with a fine pitch or of bolt connections made of austenitic steel. For large bolt connections the calculated total torque is dependant, by more than 90% on the amount of friction. Estimated coefficients of friction for torque from µ = 0.08 to µ = 0.35 (a tensioning difference of around 400%) are now a thing of the past. Capability to start simultaneous tensioning at multiple points „Crossover-tightening“ of several bolts at several points is no longer necessary, since SCHAAF SSV and HM offer the possibility of tightening all the bolt connections simultaneously with exactly the same tensioning force. This also applies when increasing the tensioning force. Start of tensioning independently of tensioning path As opposed to thermal screw starting procedures, SCHAAF SSV and HM make it possible to eliminate different gaps between individual components. Each bolt can be tensioned with exactly the same force and not over the same distance! Quickest test capability at any time SCHAAF SSV and HM make it possible to apply a residual tensioning force by means of test force stress application in order to determine if any settling of the screw may occur, and if so, to eliminate it. Universal application With a compact unit and the ability to interchange the component parts relating to the size of the bolt, SCHAAF SSV can also be used for other thread sizes. Saving of time SSV and HM will dramatically save time required for tensioning applications. This effect increases for higher tensioning forces, larger bolt thread diameters and also the installation of several SCHAAF SSV or HM. Time savings up to 99% are possible! It is no longer necessary to apply large torque by hand. There is a number of handling features available, designed to make work easier with SCHAAF Bolt Tensioners and Hydraulic Nuts, especially when it comes to large dimensions.

1. Advantages of hydraulic
tightening for bolt
connections
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

2. Purpose of a bolt
Connect at least 2 parts
dismountable together
glueing,
welding, Friction µ
riveting
Prevent take-off by elongation
of the bolt and compression
of the parts
Sealing effects
Transmitting shear-forces by friction
Weight-reduction:
Use of high-strength bolts with
high and exact pretensioning force
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

3. Different models
Screw-head forms
default values for pretensioning force
Thread-size + pitch
Standard series, fine series…
Thread forms
metric, buttress,
trapezoidal, round…
Strength categories:
8.8, 10.9, 12.9
Surface treatening
Friction coefficient
Forms
Necked down bolts – large
elongations for only little
loss of pretensioning!
Shoulder studs
Special bolts
….
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

4. Bolt loads
Axial operating force
Optimum load: Only axially
Shear-force
Bending moment
Torque
Exspecially during mounting
Partly during operation
Often pretensioning to
90% of yield stress for
highest load capacities of
bolts
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

5. Tightening methods I
method advantages disadvantages Tighten-
ing
factor
Tightening by cheap, available Large deviations in pretensioning force 2,5-4
hand (socket everywhere Inapplicable for large thread-sizes
wrench)
Torque-controlled Little more expensive Smaller deviations, inknown influence 1,7-2,5
with torque wrench Available of friction
Inapplicable for large thread-sizes
Thermical with Very precise Only for large clamping length and 1,05-1,2
measuering of special screw forms (flat heads)
elongation Ultrasonic measuring or exact length
(Ultrasonic) measuring for each bolt
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

6. Tightening methods II
method advantages disadvantages Tighten-
ing
factor
Controlled by precise, Extensive equipment necessary 1,2-1,4
yieldstress of Almost independent
torque-angle from friction
Impact wrench Applicable for large Large deviation in tightening torque due 2,5-4
(electric/air driven) sizes to design
Adjustment is inaccurate, requires
measurement of Actual pretensioning
force
Counter-torque has to be taken by user
or external support
hydraulic High forces achievable Accessories needed (Pump/Hose…) 1,2-1,6
Detection of actual
force possible
Tensioning several
bolts at a time
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

7. Tightening Factor
Tightening Factor kA according 1
to SCHAAF
remaining clamping relation K
By Changing the flux of 0,8
forces during
pressurization and 0,6
releasing pressure a loss of
force takes place 0,4
Depending on clamping
length relation l / d 0,2
Depending on thread-
0
pitch p 0 2 4 6 8 10 12 14 16 18 20
clamping length relation l/d
→ kA = 1 / K ≈ 1 - 2 large pitch small pitch
(Empirical data)
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

8. Calculation base
Precondition for exact
dimensioning is the
notice of operational
FB
loads!!
FV
Tensioning diagram:
Calculate pretensioning force
from operational loads
Compression and
elongation
Clamping force
has to be > 0 during
operation
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

9. Calculation base
Depending on tightening method the mounting
force can be determined:
FVM= kA x FVmin
kA = tightening factor (1,05-4)
FVmin = Min. pretensioning force
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

10. Calculation base
Thread-Friction
Head-Friction
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

11. Calculation base
Torqueing methods lose a lot of torque for
overcoming friction inside the thread and below
the head:
MA=FVM x (d2/2 x tan (φ+ρ‘) + µk x dk/2)
Thread-friction Head-friction
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

12. Example
Using a torqueing method: Thread Pitch Torque MA Friction Tensionin
transforming torque to size D P [Nm] coeff. µ g force
FVM
axial force by means of [mm] [mm] [-]
[kN]
inclined plane 36 4 2000 0 3142
Due to friction only little (100%)
axial force
Friction coefficient has 0,08 522
to be estimated (17%)
Additional torque load
inside th screw 0,25 188
(6%)
Result: 120 6 64500 0 67500
Little transforming rate from (100%)
torque to pretensioning force
(abt.. 90% loss) 0,08 5510
For large sizes the torque can (8%)
not be reached by hand Abt. 300%
difference
0,25 1870
Large deviations when fricition
is unknown (3%)
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

13. Preconditions for hydraulic tightening
Thread-size and pitch
are known
Protruding bolt end is
long enough
Design is modified for
little losses:
Only few separation planes
No washers necessary.
If necessary: place tool
directly on washer
Large clamping length
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com

14. Conclusion
Advantages of using hydraulic tightening
methods
Friction coefficient has not to be estimated
Only axial load can be set to the bolt – no torque load due to
friction
Bolt size can be reduced
Force depends only on the piston area and pressure of the
tensioning device – no inaccuracy
Special solutions possible
schaaf_englisch_schraubenverbindung_kat6.ppt · 12.07.2007 www.schaaf-gmbh.com