how to eliminate mechanical, vibrational loosening, clampload & corrosion failures in your...
TRANSCRIPT
How to Eliminate Mechanical,
Vibrational Loosening, Clampload &
Corrosion Failures In Your Products
3
Before We Start
• This webinar will be available afterwards at
designworldonline.com & email
• Q&A at the end of the presentation
• Hashtag for this webinar: #DWwebinar
Paul Heney Design World
Doug Lescarbeau Henkel
Moderator Presenter
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How Non-Traditional Products Can
Improve Reliability:
Chemical Threadlockers Eliminate
the Root Cause of Threaded
Fastener Failure Doug Lescarbeau
Henkel Corporation
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Doug Lescarbeau
• North American Director of Technology Management for Loctite branded Anaerobic Products, Henkel Corporation
• Involved in Reliability Improvement programs for 30+ years
• Expert for product development and advancement in Anaerobic Technologies including threadlocking, thread sealing, retaining and gasketing products.
• Expert solution provider for market leading companies, including custom product development and R&D applied technology breakthroughs.
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Criteria for Bolted Joint Success
• Fastener delivers design clamp load
• Fastener maintains clamp load
• Fastener can be disassembled when required
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Root Cause Analysis
• Root Cause analysis often does not go far enough, often stopping when a bolt has failed.
• Failure can be either broken or yielded, or when clamp load is lost.
• Why do bolts break? Typically because clamp load is lost, bolts become loose, and then they get sheared.
• Need to go further and understand the mechanics of the bolted joint
• This will lead to true root cause analysis, the failure being a vibrational locking system was not employed, or not enough clamp load was delivered.
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Bolted Joint Mechanics
• A bolted joint is basically a wedge wrapped around a
cylindrical part.
• As the bolt is tightened, the threads effectively wedge
the two parts together.
• The more the bolt is rotated the more clamp load is
achieved on the assembly.
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Bolted Joint Mechanics
• Clamp load is generated by putting energy into the
system
• Most commonly by applying a set torque to the fastener,
to stretch the bolt.
• The bolt stretch compresses the assembly to create the
clamp load.
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Bolted Joint Mechanics
• Tolerances exist to allow the parts to be assembled
• Gaps allow side-to-side movement when the fastener is exposed to vibration or thermal expansion/contraction
• Air space is where corrosion will form. Leads to Seizure.
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Vibration Loosening
• Rate of movement will vary.
• Disassembly can be very rapid if a harmonic frequency is reached.
• Results are reduced clamp load. This ultimately causes the fastened assembly to fail.
• Most fasteners are subject to some level of vibration.
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Vibration Loosening • Consider the joint as a wedge
• Any back and forth movement tends to move components in the path of least resistance
• Downhill motion in a nut and bolt joint will result in disassembly.
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Traditional Systems
• Many mechanical methods are available to lock
threaded assemblies
Mechanical locking systems:
• They do not eliminate the gap from tolerance in
the threads, the root cause of the failure
• They rely on friction to stop motion
• Require extensive inventory to fit all shapes and
sizes.
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Spring washer Nut with nylon insert Castellated nut Tooth flanged bolt
Star washer Tab washer Lock nut Ramp Washers
Traditional Threadlocking Devices
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Performance Testing
Junkers Transverse Shock Tester
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Non-Traditional Solution • Chemical threadlockers address the root cause of the
loosening failure by eliminating the empty space in the threaded assembly.
• Simply put it unitizes the assembly by putting a solid chunk of plastic in the threads
• Physically prevents relative motion between the nut and the bolt.
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Performance Testing
Chemical Threadlocker
Locking Device Cost
Chemical Threadlocker $0.04
Ribbed flange bolt $0.50
Saw toothed flange nut $0.11
Elastic stop nut $0.08
Tooth lock washer $0.04
Spring washer $0.04
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Corrosion
• Traditional Locking Devices do not seal the thread
• Non-Traditional chemical threadlockers lock out moisture
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How is Corrosion a failure?
• Seizure failure mode resulted in a shaft failure.
• Root cause analysis would likely determine that there
was inadequate packing gland pressure and flow. Why?
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How is Corrosion a failure?
• The gland assembly couldn't be adjusted because the
nuts on the gland follower had seized in place
• Heat built up in the packing, expanded, choking the
gland of cooling water flow, thereby creating more heat
and expansion, thereby causing the packing to squeeze
against the shaft and wear it out.
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Non-Traditional Solution • Chemical threadlockers address the root cause of
corrosion by eliminating the empty space in the threaded assembly.
• It seals the assembly by filling the space with a chemical resistant thermoset plastic.
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Clamp Load
• The third mode of failure of a bolt is lack of adequate
clamp load on assembly
• Many variables involved in what clamp load delivers
• Lubricity is key to assembly, but not everything
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Traditional Approach Methods to precisely determine the correct bolt stretch
• Micrometer on a bolt, to directly measure bolt stretch. – Good for critical applications like wind tower bases, but is a slow
and delicate process.
• Torque to yield bolts used in the automotive cylinder head assembly. – Creates an even clamp load by permanently stretching, clamp
load a function of the steel metallurgy.
– Downside is bolts are single use only.
• The most common method remains a torque wrench
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Clamp Load Variables
Only a small amount of the energy from a torque wrench goes into stretching the bolt and producing clamp load. Significant amounts of energy are converted into heat through friction
• Tolerance
• Surface finish (roughness)
• Nut face profile
• Bolt size
• Surface coatings
• Cleanliness
• Thread lubrication
• Torque tool accuracy/calibration
These have a negative impact on reliability by affecting clamp load
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Bolted Joint Mechanics
• Friction can be controlled using lubricants.
• The presence or absence of a lubricant will greatly change the friction co-efficient by lubricating the joint.
• Bolts received from a manufacturer may have permanent coating or plating, residual cutting fluids, anti-corrosion oils, etc.
• The challenge is these are not documented, and often overlooked as to their influence on the bolted joint.
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Lubricity - Bolt Variability Study
• Experiment to verify if surface finish and under-head bolt design would produce a variance in torque
• Industrial distributors indicated that zinc plated steel was the most commonly supplied bolt material.
• As the zinc coating prevents rust, no oil film was observed.
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Lubricity - Bolt Variability Study • 5/8”-NC Grade 5 Zinc plated bolts and nuts from five
different bolt manufacturers.
• Bolts were assembled with a calibrated torque wrench to 112 foot-pounds (152 Nm), the standard SAE Grade 5 recommendations for steel bolts.
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Lubricity - Bolt Variability Study • Bolt system placed in Skidmore-Wilhelm clamp load
tester.
• Pressure measured and directly correlated by knowledge of the diameter of the piston to measure the clamp load.
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Lubricity - Bolt Variability Study • When the bolted system is torqued it squeezes a
hydraulic reservoir
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Lubricity - Bolt Variability Study • First study tested bolts in ‘as-received’ condition to
illustrate the variance in clamp load.
• Table 1 shows it produced a clamp load range of 4100 lbs (21%).
21% range
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Lubricity - Bolt Variability Study • In second study, same bolts from five manufacturers
• Using a chemical threadlocker
• Range dropped from 4100 to 1300 pounds of clamp load difference with chemical threadlocker.
12% range
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Bolt Variability Study • Liquid threadlocker reduced variability, by providing a
constant lubricity.
• Some variance remains, which is normal
12% range
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Friction Factor or K Value
• What is it?
• As joints have a large number of variables, all variables were wrapped up into one number.
• It is experimentally determined, not a calculation
• It is useful for approximations, but over time its actual meaning has become unclear to users.
• It is now common for end users to ask for the “K” value, as if it is an independently measurable value, not a collection of variables.
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Lubricity Factor or K Value • Tested a range of chemical and mechanical locking
systems in the Skidmore-Wilhelm tester.
• 5/8” bolts were utilized.
• Most standard values for K are calculated on 3/8” fasteners. Size changes value.
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Friction Factor or K Value • Goal of any material is to be repeatable and close to the
standard value.
• Good result is a K close to what an oiled bolt delivers.
• Lower K value (indicating higher lubricity) is acceptable, as long as the assembly torque is dropped to ensure bolts are not over tightened..
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Friction Factor or K Value • A higher K value (indicating lower lubricity) is a concern
• It means the correct clamp load will not be generated. The actual clamp load achieved is shown below
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Friction Factor or K Value • Mechanical locking device of two interlocking washers
with built in ramps was tested
• They require a lot of energy to overcome fiction and deliver a substantial increase in K value (higher friction)
• If the same torque specification used as an oiled bolt a significant drop in clamp load will result
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Non-Traditional Solution • Chemical threadlockers act as a lubricant during fastener
tightening.
• Not used for just threadlocking. Actually used to reduce variability of bolt tolerance
• K value achieved reasonably close to oiled values
• Allows applied torque to be converted into high clamp load instead of dissipating as friction or heat.
• Once cured, chemical threadlockers provide a reliable seal, preventing leaks, galling and corrosion that can seize threads and prevent disassembly.
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What is Failure in a Bolted Joint?
• Failure to maintain proper clamp load over time
– Vibration Loosening
• Failure to deliver adequate clamp load on assembly
– Lubricity key to assembly
• Failure to come apart when required
– Corroded assembly
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Summary
• Root Cause analysis can be taken to greater depth when
a fastener system fails.
• Exact mode of failure of fastener system needs to be
identified.
• Non-traditional solutions can be more effective at
resolving root cause of issue, versus treating symptom.
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Chemical Threadlocking Advances
• Concern about disassembly have been addressed with color defined strength controlled formulations
Low Medium High
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Chemical Threadlocking Advances
• Concern about process robustness has been addressed with primerless, oil tolerant cure chemistry
Performance on Oiled Substrates
Breakaway M10 black oxide
0
10
20
30
40
50
60
Hydrophobic (Evolution SXR
5W-30)
Emulsion (Aquasafe 21) Solvent based (SafeCoat DW
30 X)
Oil Type
Str
en
gth
Rete
nti
on
[%
]
Loctite 262 Control Loctite 271 Control Loctite 263
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Chemical Threadlocking Advances
Concern about migration and/or spillage has been addressed with innovative semi-solid stick and tape formats
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Chemical Threadlocking Advances
Concern about application control has been addressed with simple process equipment
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Extreme
Temperature
Military Specified Food Grade
Plastic Fastener
Low Halogen
Health & Safety
Chemical Threadlocking Advances
Concern about special performance characteristics has been addressed with specialized formulations
Rated to 650F
MSDS Health
Rating of 1
FDA Reg
Compliant
Purity
Certified
Certified
Performance
Multi substrate
Food Grade
FDA Reg
Compliant
Food Grade
FDA Reg
Compliant
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Questions
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Robert Dunkel
• Professional Engineer
• Based in Mississauga, Ontario, Canada
• Manager of Technical Call Center for USA & Canada
• Manage Technical Service for Canada
• Specialist in Loctite branded threadlockers
• Involved in Reliability Improvement programs for 10 years
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1-800-LOCTITE
www.loctitethreadlockers.com
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