1.2 Management of torgue and preload
1.2.1
Tightening test results
The basics of how to use the HARDLOCK Nut, after applying axial force
to the Convex Nut, use the Concave Nut to lock them together.
The Convex Nut should be tightened with the same axial force as a
general hex nut,the Concave Nut however, shall be installed with the
recommended torque set by HARDLOCK Industry Co., Ltd.
Below you can see the tightening test results of the HARDLOCK Nut
and standard double nuts
Tightning method of HLN convex nut
45 40 Bolt Preload [kN] 35 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 45 50 The convex nut was
tightened up to 70% of
the bolts yield
point,which is the
targeted axial force
Torque [N・m] Bolt Preload
[kN] Tightening method of HLN concave nut
45 40 35 30 Concave nut
tightened by hand Concave Nut one-side adhesion 25 The concave & convex
nut was tightened unti
one-sided adhesion.
There were no large
deviation in the initial
preload
20 The concave nut
was first tightened
by hand.
At this point there
was no change in
axial force
15 10 5 0 0 10 20 Torque 30 [N・m] 40 50 Reference Tightening Torque 1/4
Test Conditions
Speciemen
Bolt
：M12×70 Strenght Class 4.8, Surface treatment: Trivalent chromate
Nut
：Hexagon Nut (Class 1) 、Hexagon Nut (Class 3) 、HLN　Strenght Class 4
Surface treatment: Trivalent chromate
Lubricant
：Paste
Double Nut tightening method
Correct tightning method：Tighten the lower nut to 40% of the yield point
and the upper nut to 80% of the yield point
Double nut (Lower): Hexagon nut (Class 1) tightening method
45 Bolt Preload [kN] 40 35 30 凹ナット手締め 25 20 凹ナットを手で締
When
tightening double nuts
凹ナットと凸ナット
you should tighten the lower
の片面が密着するま
nut with 50% of the targeted
で締めました。 axial
force and the remaining
50% should be applied to the
upper nut. By doing this, the
bolt will be tightened to 40%
of its yield point
め込めるところまで
15 締めました。 この時点で軸力に
10 変化はありません。 5 0 0
10
20
Torque [N・m] 30
40
50
Reference tightening torque Double nut (upper): Hexagon nut (Class 3) Tightening method
By tightening the upper
nut, the preload is
increased immensely
45 Bolt Preload [kN] 40 35 30 25 20 15 Tighten the upper
nut until the
recommended
preload
10 5 0 0 10 20 30 Torque [N・m] 2/4
40 50 Hardlock Convex Nut: Tightening until damage on the bolts threads
Concave nut full adhesion Bolt damage condition Enlargement
The concave nut and
convex nut I was
tightened until
complete adhesion。
45 Tighten until shear
on the bolts threads
40 Bolt Preload [kN]
35 30 25 20 15 10 5 0 0 10 20 30 40 Torque [N・m] 50 60 70 Double Nut (Upper):　Tightening until damage on the bolts threads
Enlargement
Damage of the bolts threads Tightening until shear on the
bolts threads
。
45 40 Bolt Preload [kN] 35 30 25 20 15 10 5 0 0 10 20 30 40 Torque [N・m] 3/4
50 60 70 By observing the change in 2ghtening torque and axial force due to 2ghtening of the Concave Nut from Graph (1), there is no significant axial force change 2ghtening within the range of the recommended torque. Accordingly, in case of HARDLOCK Nut, the user can control the bolt axial force by 2ghtening the Concave Nut within the recommended torque range aQer 2ghtening the Convex Nut to the appropriate torque required for each individual applica2on. On the other hand, looking at Graph (4) for double nuts, the ini2ally set bolt axial force is increased when 2ghtening the upper nut. In other words, in prac2ce it is said to be difficult to control the bolt axial force when u2lizing dubbel nuts. Looking at Graph (5), you can see that the recommended 2ghtening torque for the Concave Nut is about half of the thread shear torque . From this fact, as long as the HARDLOCK Nut is installed correctly, you can see that there will be no shear on the threads from 2ghtening the Concave Nut. With this in mind, you can see that the HARDLOCK Nut is capable of bolt axial force control, there is no danger to reach the bolt breaking point even if slightly 2ghtening the Concave Nut beyond the recommended 2ghtening torque. Reference Case
In general, when comparing the breaking load of simply pulling the threads and twis2ng the threads by 2ghtening (torsion applied tensile breaking load) , the twis2ng is said to be about 85% of the bolts breaking load. As seen in the graph below, the hexagon thin nut (class 3) threads got damage aQer applying approximately 35kN. 85% of 35kN is around 30kN so the below thread destruc2on test results can be said to be accurate. 40 Hexagon thin nuts (class 3) was used 3 2mes in the tensile test Clamp Load [kN]
35 30 25 1st 2me
20 2nd 2me
15 Thread Shear 10 3rd 2me
5 0 0
2
4
6
8
Strokes [mm]
Test Conditions
Bolt　：M12×70　Strenght Class 4.8、Surface Treatment: Trivalent Chromate
(Same conditions as present test)
Nut: Hexagon Jam Nut (Class 3), Strenght Class 4, Surface Treatment: Trivalent Chromate
(Same conditions as present test) 4/4
10
12