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The Cross SpiralockThread Insert
A Wire Thread Insert withextraordinary properties.
Piston rings made from coil
Ralph
Flower
The Spiralock thread
Tapped holeBolt
Cross Spiralock Insert wire section
Cross Spiralock Insert assembly
London Underground Central Line gearboxes
Blade attachment to main rotor head mast
Ralph
Flower
The Junkers Vibration Rig
Holding force
No loss of
bolt tension
Locking force
Bolt
tension
Number of vibrations
Peakpreload
Vibration start
The vibration test
Vibration endand removal ofbolt tension
• Spiralock taps• Prevailing torque inserts• Thin wall inserts• Spring washers• Schnorr safety washers• Nord-Lock• Loctite
Test other available Thread Locking Systems:
Spiralock Standard Thread (steel)
No loss ofbolt tension
Number ofvibrations
Bolt
tension
Spiralock standard thread (light alloy)
No loss ofbolt tensiononly at loweramplitudes
Number ofvibrations
Bolt
tension
Bolt
tension
Number of vibrations
Standard insert (non-locking)
Prevailingtorque
coil
Prevailing torque insert
Immediate loss ofbolt tension at thecritical amplitude
Bolt
tension
Number of vibrations
Prevailing torque insert
Bolt
tension
Number of vibrations
Cross spring washer (BS 2 SP.47)
Bolt tension ismaintained onlyunder less severeamplitude
Bolt
tension
Number of vibrations
Cross Grover washer
Bolt tension ismaintained onlyunder less severeamplitude
Bolt
tension
Number of vibrations
Commercial spring washer
Bolt tension ismaintained onlyunder very lowamplitude
Bolttension
Number of vibrations
Loctite 270 (studlock)
The studlock version ofthis threadlocker producesa ‘permanent’ bondbetween fastener and nut
At high amplitudesand high bolttensions, the onsetof fatigue is rapid -the fastener doesnot loosen
Due to the fatigueproblem, bolttension is onlymaintained atlower amplitudes
Loctite 268 (threadlock)
The ‘268’ version of thisthreadlocker is in the formof a ‘Pritt Stick’ – a self-feeding stick applicator
At high amplitudesand high bolttensions, the onsetof fatigue is rapid -
Bolttension
Number of vibrations
the fastener doesnot loosen
Due to the fatigueproblem, bolttension is onlymaintained atlower amplitudes
No loss of bolttension but boltfatigue problemsincrease
Bolt
tension
Number of vibrations
Schnorr Safety Washer
Nord-LockNord-Lock
No loss of bolttension but boltfatigue problemsincrease
Bolt
tension
Number of vibrations
No loss of bolttension but boltfatigue problemsincrease
Bolt
tension
Number of vibrations
Thinwall insert
No loss of bolttension plusimproved boltfatigue life
Number ofvibrations
Bolt
tension
Cross Spiralock Wire Thread insert
• What's the ideal bolt tension?• What happens if the tension is reduced?• Is the length of the thread insert significant to its
locking effect?• Do “base” materials alter the locking effect?• How many times can you “do and undo bolts”
and still get the locking effect?• How long do bolts stay locked?
What we needed to find out:
Insert re-use assessment
Multiple repeating of vibrationtest cycles
Bolt
tension
Number of vibrations…increasing number of cycles
Cross Spiralock Wire Thread insert
Repeat vibration tests – 75% Rp0.2
Vibration
test
1
Vibration
test
2
Vibration
test
3
Vibration
test
4
Bolt
tension
…more vibrations…more cycles…
Vibration
test
99
Vibration
test
98 100
Vibration
test
101
Vibration
test
102
Vibration
test
Cross Spiralock Wire Thread insert
Repeat vibration tests – 62.4% Rp0.2
Bolt
tension
…after 200 complete vibration tests
200
Vibration
test
197
Vibration
test
198
Vibration
test
199
Vibration
test
Cross Spiralock Wire Thread insert
Repeat vibration tests – 62.4% Rp0.2
Extended vibration testing
Continuous testing of a CrossSpiralock Wire Thread insert
Bolt
tension
Number of vibrations
Cross Spiralock Wire Thread insert
24 hour vibration test
No loss of bolttension and noindication offatigue problems
Bolt
tension
…further vibrations…
Cross Spiralock Wire Thread insert
24 hour vibration test
No loss of bolttension and noindication offatigue problems
Bolt
tension
Number of vibrations
Cross Spiralock Wire Thread insert
24 hour vibration testEnd of test
No loss of bolttension and noindication offatigue problems
1 million cycles
• Base materials
• Length of insert
• Finish of bolt
• Lubricant
• Long term
• Undoing & doing up
• Straight line relationships
• Bolt tension reduction
What have we found out about the locking effectof the Cross Spiralock Thread Insert?
No loss of
locking effect
Locking force
Bolt
tension
Number of vibrations
Peakpreload
Vibration start
The vibration test – reduced bolt tension
Vibration endand removal ofbolt tension
Holding force
Ralph
Flower
…better than we thought it would be…
Cross Manufacturing Co (1938) LtdMidford RoadCombe Down
BathBA2 5RR
01225 837000www.crossmanufacturing.com/spiralock
..……..…better than we thought it would be………….
Torque / preload relationships
• Frictional effects – underhead, thread, etc.
• Torsional effects – eg the release of storedenergy when vibration starts
• Embedding – interactions between fastener,insert, parent material, head and clampingmaterial and washer, etc.
Torque resistance (Tr)
Holding force
No loss of
bolt tension
Locking force
Bolt
tension
Number of vibrations
Peakpreload
Vibration start
The vibration test
Vibration endand removal ofbolt tension75% Rp0.2
The vibration test – hysteresis curve
Bolt tensionTorque
+
-
Peakpreloadand torque
Applicationof torque
Removal ofpreload
T = PDTr where
T = torque P = preload (bolt tension)D = fastener nominal diameter Tr = torque resistance
Application of a Universal Equation
Torque resistance (Tr)
Torque
Torque resistance
Constant bolt tension
Allfastener types,finishes,lubricant types
CMC research hasproved that thisrelationship iscorrect for…
Bolt
Tension
Reciprocal of torque resistance
Constant torqueCMC research hasproved that thisrelationship iscorrect for…
Allfastener types,finishes,lubricant types
No loss of
bolt tension
Locking force
Bolt
tension
Number of vibrations
Peakpreload
Vibration start
The vibration test – reduced bolt tension
Vibration endand removal ofbolt tension
Holding force
75% Rp0.2
No loss of
bolt tension
Bolttension
Number of vibrations
Peakpreload
Vibration start
The vibration test – minimum locking force
Vibration endand removal ofbolt tension
Holding force Minimum locking force
Minimum locking forces aslow as 25% Rp0.2
75% Rp0.2
50% Rp0.2
25% Rp0.2
• The minimum locking force is inverselyproportional to the torque resistance
• Fasteners having high values of torqueresistance lock at lower bolt tensions thanfasteners having a low torque resistance
The Blanchard Effect
Cross Manufacturing Co (1938) LtdMidford RoadCombe Down
BathBA2 5RR
01225 837000www.crossmanufacturing.com/spiralock
..……..…better than we thought it would be………….
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