How to improve machine reliability using threadlocking adhesives

Robert Dunkel PEng, Director of Technical Service at Henkel Corporation, explains how the use of threadlocking adhesives can dramatically improve the reliability of machines assembled using threaded fasteners, partly due to the way threadlockers prevent fasteners from loosening, and partly due to threadlockers acting as a lubricant during assembly and removing the variability that occurs when tightening as-received fasteners.

Root cause failure analysis is often employed when critical pieces of equipment fail. True root cause failure analysis forces you to ask 'why' five times. The fifth question sometimes identifies the mode of failure (a fastener loosened) instead of the root cause (insufficient clamp load).

Case studies and laboratory data provide new insights into the root cause of typical mechanical loosening and sealing failures. They explore the reasons why some of these root causes are most effectively addressed with non-traditional chemical solutions.

Bolted joints exhibit a very complex relationship between clamp load and the torque-tension relationship of threaded fasteners. A common perception is that a bolted joint produces consistent clamp load given a specified torque. However, load cell tests of identical bolts sourced from multiple manufacturers demonstrate that the actual clamp load, when torqued to a specification, can vary by over 20 per cent if used under as-received conditions. The use of a chemical thread treatment can dramatically reduce deviation and provide additional reliability benefits.

Gas and fluid leakage are common maintenance reliability issues. Root cause analysis has been applied to typical flange and threaded fittings configurations. The results identify several failure modes that can be countered with specific types of chemical sealants.

Machinery equipment reliability can be influenced by many factors. There were observed a number of factors that can influence this. Many are considered 'non-traditional' even though they have been around for many years.

True root cause of failure

Root cause failure analysis aims to break down a problem into the most basic elements and find the cause.

In a review of case studies, it was observed that the fifth question, or ultimate root cause, will often identify a loosened fastener or a leaky gasket. This fails to bring us down to the level of the assembly process to get to why this occurs and to prevent it from happening again. In examining either a loosened bolt or leaky gasket, a fastening system that has failed to provide adequate clamp force is often the true root cause - one that is avoidable with proper assembly techniques.

Mechanics of bolted joints

Image
A bolted joint is, in its most basic form, a wedge wrapped around a cylindrical part. As the bolt is turned, the threads effectively wedge the two parts together. The more the bolt is rotated, the more clamp load is achieved.

In a practical system, both the nut and the bolt have tolerances to ensure that they will not bind when assembled. By default, this means that a bolted joint will have variable gaps, depending on the combination of tolerances in the parts (see image, right).

The surface finish of bolts is related to how they are manufactured, the dies used to produce them, and the technology used to form the part. Though threaded fasteners conform to widely recognised standards, each manufacturer has slightly different processes that will lead to small, but ultimately significant differences in surface finish and under-head profile, with a resultant effect on the bolted system.

When a threaded system is assembled, the presence or absence of a lubricant will greatly change the lubrication co-efficient. Bolts procured from a vendor may have permanent coating or plating, residual cutting fluids, anti-corrosion oils or other substances. The challenge is that these are not documented and are often overlooked as to their influence on the bolted joint.

Most fasteners are used in dynamic systems subject to vibration. Though high vibration captures attention, even low-force vibration over time can cause issues. In the electrical industry, it is common for electrical panels to require re-torqueing of set screws due to the effect of the AC current over time.

A bolted system has variables that are difficult to model. As discussed, tolerances, surface roughness and surface friction all impact assembly and can lead to potential issues.

Vibration loosening

Image
This effect is tied to tolerance. Under vibration, a machine moves back and forth. Due to required manufacturing tolerances, the bolted assembly has empty space. In a simplistic manner, it is often assumed that if you tighten a bolted assembly properly, the friction of the surfaces will stop the assembly from loosening.

Under the constant vibration that machinery produces, the bolted assembly will eventually move relative to its components. The rate at which this occurs will vary, but disassembly can occur very rapidly if a harmonic is reached.

Returning to the description of the joint as a wedge, any movement back and forth is like standing on a ski slope and sliding back and forth. Under these conditions, you would tend to move downhill (the path of least resistance). On a bolted joint system, the tendency of a part is to come apart.

Image
Many methods of combating this are available on the market. One of the more effective means is to place a self-curing chemical into the joint to fill the machining tolerances and produce a solid filler. This addresses the root cause of the failure by eliminating the empty space in the threaded assembly (see image, right).

Mechanical systems for stopping vibration cover a wide spectrum of designs and effectiveness. Some mechanical systems actually speed up the rate at which fasteners come apart. The best of these work, but are very costly in comparison to chemical threadlocking systems.

Chemical threadlocking, despite being proven in over 50 years of service, is still considered a relatively new and unproven technology. Nevertheless, it provides a cost-to-benefit ratio that delivers high performance at a low cost.

Friction effect on clamp load

When a bolted system is assembled, the clamp load is generated by putting energy into the system, which stretches the bolt. The bolt stretch compresses the assembly to create the clamp load. The most commonly used method of achieving this is to apply a known torque that 'equates' to a certain clamp load. It is a common perception that with a specified assembly torque, a bolted joint produces consistent clamp load.

All nuts and bolts have a surface roughness that produces friction. This has implications when fastener systems are assembled using torque or energy input to correlate the clamp load generated to the amount of energy going into generating clamp load through bolt stretch.

Other methods of determining the correct bolt stretch exist, but have limitations in general use. One example is torque-to-yield bolts, which are commonly used in automotive cylinder head assembly. Another is the direct measurement of bolt stretch using a run-out gauge, which is commonly used in wind-tower base securing.

The following test was conducted to quantify this.

Bolt variability from different manufacturers

Knowledge within Henkel had long held that the surface finish, along with the variances in under-head bolt design, would produce a wide scatter when each bolt was torqued to the recommended amount.

As an experiment to verify this hypothesis, zinc-plated M16 bolts and nuts from five different manufacturers were used. Bolts were assembled with a 152Nm calibrated torque wrench.

Each bolt system was placed into a Skidmore-Wilhelm clamp load tester. When the bolted system was torqued, it compressed a hydraulic reservoir, producing a pressure that could be measured and directly correlated, thanks to the knowledge of the diameter of the piston, to the clamp load.

The first test utilised bolts in as-received condition to illustrate the variance in clamp load. Using bolts in the as-received condition is common. The table below illustrates how this produced a standard deviation in clamp load of 18 kN (21 per cent).

Image

In an era of cost avoidance, it is not uncommon for manufacturers to shop for interchangeable items based on cost. As a result, the clamp load generated can vary significantly, even using a properly calibrated torque wrench.

In the second part of the experiment, bolts were assembled from the same five manufacturers with a chemical threadlocker to observe the effect. The results shown in the graph below demonstrate a significant reduction in clamp-load scatter.

Image

In absolute values, the range of data dropped to 5.7kN of clamp-load difference, from highest to lowest values. Utilising a liquid threadlocker reduced the scatter of clamp loads from different bolt manufactures.

One of the most significant benefits of chemical threadlockers is their ability to reduce the variability of bolted assemblies. The consistent lubrication that results from specifying the material to be used as the assembly fluid is a major benefit. Chemical threadlockers not only stop vibration loosening, but also allow more consistent clamp load by removing variability from the system.

Non-traditional chemical threadlockers - alternative forms

One of the barriers to chemical threadlocking is that maintenance staff have found carrying liquid materials an issue due to the potential for spillage. One industrial company has been actively involved in trying to resolve this concern by introducing patented technology that allows for solid format, or 'stick', threadlockers.

This innovation was targeted at applications performed in the field or at the machine's location. The goal was to develop products that could easily go into a tool box, or even a pocket, for easy access. This stay-in-place format enables users to apply chemical threadlockers to all fasteners ahead of time, thereby accelerating re-assembly and providing an additional side benefit.

Non-traditional chemical threadlockers - primerless on inactive materials

A concern voiced by end users was the requirement for flammable primers on chemically inactive materials such as aluminium. Many plants and mines have banned their use for safety reasons.

Chemical threadlockers normally require free metal ions to cure. These are found on the surface of metals that corrode, such as steel. One industrial company has been active in developing materials that cure without a primer, which eliminates both a step and a flammable solvent from the workplace. These primerless materials are a large step forward in making this technology more accepted in the workplace.

More about anaerobic adhesives for threaded fasteners

Follow the link for more information about the Loctite Success Secured campaign; the microsite has customer case studies, videos, an adhesive selection 'wizard', webinars and a wealth of other useful information.

Henkel Ltd

Wood Lane End
Hemel Hempstead
HP2 4RQ
UNITED KINGDOM

+44 (0)1442 278000

technicalservice.loctite@uk.henkel.com

www.henkel.com

More from Henkel Ltd

Henkel’s Technomelt in a mould of its own

Posted 2 weeks ago

Fast and durable plastics bonding

Posted 1 month ago

Five day machine repair reduced to 8 hours

Posted 2 months ago

Threadlocker makes light work of solar panels

Posted 4 months ago

New repeatable threadlocking dispenser

Posted 4 months ago

Henkel Loctite highlights advantages of threadlocker

Posted 5 months ago

Dangers of vibrational fastener loosening

Posted 6 months ago

Beware of the gap when locking threaded fasteners

Posted 7 months ago

Loctite threadlocking webinar: 1100 GMT Tues 22nd September 2020

Posted 9 months ago

Quarry managers develop crush on LOCTITE

Posted 1 year ago

LOCTITE introduces larger adhesive pack size

Posted 1 year ago

Online support and CPD for users of threadlocking adhesives

Posted 1 year ago

Repair rubber components quickly and reliably

Posted 1 year ago

New packaging combats threat from counterfeiters

Posted 1 year ago

See Henkel's latest developments at Southern Manufacturing 2020

Posted 1 year ago

Pipe sealing products set to prove popular among plant engineers

Posted 1 year ago

See Henkel's latest developments at Southern Manufacturing

Posted 1 year ago

Epoxy coating suits abrasive and hot applications

Posted 1 year ago

Henkel offers free guide to leakage prevention

Posted 1 year ago

How to increase plant reliability and reduce operational costs

Posted 1 year ago

Henkel eShop is added-value resource for adhesives and sealants

Posted 2 years ago

Henkel opens European hub for 3D Printing technology

Posted 2 years ago

Henkel's Loctite 3D printing materials at Southern Manufacturing

Posted 2 years ago

Construction starts on Henkel's new Global Innovation Centre

Posted 2 years ago

Gasket sealant now available as a roller pen

Posted 2 years ago

Conveyor belts repaired in less than two hours

Posted 2 years ago

Cost-effective anti-spatter from Henkel

Posted 3 years ago

Henkel unveils Bonderite functional coatings website

Posted 3 years ago

Henkel to be global reseller of HP Multi Jet Fusion 3D printers

Posted 3 years ago

New hybrid, emergency repair adhesive for highly durable bonds

Posted 3 years ago

See Henkel LOCTITE at Southern Manufacturing 2018

Posted 3 years ago

Efficient sealing systems in fluid power applications

Posted 3 years ago

How to prove structural bonder's speed, strength and durability

Posted 3 years ago

Anaerobic sealants introduce new performance benefits

Posted 3 years ago

Hybrid structural bonder copes with heat and vibration

Posted 3 years ago

Loctite retaining compounds benefit from improved formulation

Posted 3 years ago

New hybrid adhesives for exceptional and safe performance

Posted 4 years ago

Remote assistance with internet-connected "˜smart' glasses

Posted 4 years ago

Loctite HY 4070 structural bonder for maintenance and repair

Posted 4 years ago

How to prevent threaded joints from working loose?

Posted 4 years ago

How can 3 grams of structural adhesive pull a 208 ton train?

Posted 4 years ago

New Universal Structural Bonders for dissimilar substrates

Posted 4 years ago

Featured application

Posted 4 years ago

Bonding systems: A track record of safety and success

Posted 4 years ago

Henkel innovations underpin automotive lightweighting

Posted 4 years ago

LOCTITE threadlocking adhesives better than ever

Posted 4 years ago

Ultra-safe, responsibly formulated hand cleaners

Posted 4 years ago

Lubrication - when is anti-seize the best choice?

Posted 4 years ago

Henkel launches dedicated YouTube channel

Posted 4 years ago

LOCTITE chosen for arduous, sub-zero conditions

Posted 4 years ago

See Henkel LOCTITE at Southern Manufacturing 2017

Posted 4 years ago

Rooflight manufacturer partners with Henkel

Posted 4 years ago

Henkel to present bonding products at K 2016

Posted 4 years ago

LOCTITE Maintenance Expert pocket guide is updated

Posted 4 years ago

Henkel equipment - the full works with upgraded website

Posted 4 years ago

Anti-seize in a stick - LOCTITE LB 8065

Posted 4 years ago

Henkel's LIS: fast and reliable fix for the automotive industry

Posted 4 years ago

Wider scope of application for gasketing adhesive

Posted 4 years ago

Henkel opens new composite test centre: The Composite Lab

Posted 5 years ago

Henkel Adhesives at the European Championship in soccer

Posted 5 years ago

Henkel practises what it preaches with pipe repairs

Posted 5 years ago

Henkel announces functional coatings "˜TechDay' in Birmingham

Posted 5 years ago

LOCTITE coating extends lifetime of flue gas duct

Posted 5 years ago

Be among the number: 1000 prizes & Henkel's "˜Grand Prize Draw'

Posted 5 years ago

Improved Loctite thread sealant resists higher temperatures

Posted 5 years ago

Henkel and the NextEV TCR racing team: Formula E hits Europe

Posted 5 years ago

Dual volumetric rotor pump for latest generation adhesives

Posted 5 years ago

Henkel's hotmelt restores the boy king's mask

Posted 5 years ago

Henkel webinar: how to seal your powertrain flanges

Posted 5 years ago

Free webinars: learn what you need to know about adhesives

Posted 5 years ago

Efficient sealing systems in fluid technology

Posted 5 years ago

Popular Loctite webinar series extends into 2016

Posted 5 years ago

Recognition worldwide for Henkel products

Posted 5 years ago

Henkel's adhesives experts help restore Pharaoh's mask

Posted 5 years ago

New Structural Bonding webinar added to Loctite programme

Posted 5 years ago

New Henkel literature and video for LOCTITE 4090

Posted 5 years ago

Adhesives cut costs and turnaround time, and improve aesthetics

Posted 5 years ago

Henkel at Southern Manufacturing 2016

Posted 5 years ago

Adhesives provide reliability despite repeated shock loading

Posted 5 years ago

Loctite adhesives bond 3D printed parts for immediate assessment

Posted 5 years ago

Henkel: recognising outstanding partnership

Posted 5 years ago

Threadlockers ensure reliability for specialist vehicles

Posted 5 years ago

Adhesive helps to improve lean manufacturing of valves

Posted 5 years ago

Explainer: threadlockers, sealants and anti-seize compounds

Posted 5 years ago

LOCTITE products foster success at companies in new campaign

Posted 5 years ago

LOCTITE Health & Safety adhesives continuously developed

Posted 5 years ago

New brochure explains benefits of adhesives for machine building

Posted 5 years ago

Furniture manufacturer exploits the benefits of Bonderite

Posted 5 years ago

Henkel expands expertise in surface treatment

Posted 5 years ago

Improve threaded fastener reliability with anaerobic adhesives

Posted 5 years ago

Instant adhesive is flexible and achieves excellent sealing

Posted 5 years ago

Loctite seminar and webinars in September

Posted 5 years ago

Movie of the month

Posted 5 years ago

Henkel to introduce extended Bonderite range at EMO Milano 2015

Posted 5 years ago

Workshop hand cleaner is now ultra-safe

Posted 5 years ago

Snow video conversion testbed

Posted 5 years ago

What can be achieved with instant adhesives today?

Posted 5 years ago

Henkel at Northern Manufacturing

Posted 5 years ago

Tips for using threadlockers and retaining compounds on machines

Posted 6 years ago

Featured webinars

Posted 6 years ago

Expert advice for students from Henkel

Posted 6 years ago

Adhesive technologies in LED lighting

Posted 6 years ago

New Henkel Loctite Success Secured webinar dates announced

Posted 6 years ago

Henkel unleash full potential of casting value chain expertise

Posted 6 years ago

Step-by-step concrete repair with Loctite Magna-Crete

Posted 6 years ago

Henkel to showcase thermal management expertise

Posted 6 years ago

Henkel adhesives, sealants and coatings for alternative engines

Posted 6 years ago

Henkel honoured with "Excellence Award in Supply"

Posted 6 years ago

Securing fasteners and interference fits on snowmobiles

Posted 6 years ago

Cutting fluids: decreasing process costs, increasing efficiency

Posted 6 years ago

Adhesive dispensing with high repetition accuracy

Posted 6 years ago

Henkel develops first-ever temperature-stable solder paste

Posted 6 years ago

Henkel introduces low-maintenance jet valve adhesive dispensing

Posted 6 years ago

Cost-effective, dependable curing of UV adhesives with LEDs

Posted 6 years ago

Adhesive dispensing with high repetition accuracy

Posted 6 years ago

The product guide with just a little bit more, from Henkel

Posted 6 years ago

Concrete repair that saves labour costs and downtime

Posted 6 years ago

Henkel at Southern Manufacturing 2015, Farnborough

Posted 6 years ago

Loctite - keeping the press rolling

Posted 6 years ago

New mobile maintenance app from Henkel

Posted 6 years ago

Loctite anaerobic adhesive performance further improved

Posted 6 years ago

Henkel announces Supplier Awards for outstanding partners

Posted 6 years ago

Henkel recognises students' adhesive-bonding applications

Posted 6 years ago

Henkel at Northern Manufacturing 2014 with LOCTITE

Posted 6 years ago

Henkel High Tech Adhesives and Coatings Academy

Posted 6 years ago

Henkel increases pipe lifetime by up to 20 years

Posted 6 years ago

New metal-free anti-seize for assembly and maintenance

Posted 6 years ago

Proven hand cleaner conforms to new EU cosmetic regulations

Posted 7 years ago

New generation of Loctite Threadlocker Sticks

Posted 7 years ago

Loctite 5189 sealant used for 1.0L EcoBoost "Engine of the Year"

Posted 7 years ago

Henkel sponsors world-class Formula Student racing team

Posted 7 years ago

Henkel showcases innovative products for industrial customers

Posted 7 years ago

Loctite retaining adhesives 638 and 648 upgraded

Posted 7 years ago

Find new Loctite products at Southern Manufacturing 2014

Posted 7 years ago

Loctite addition repels welding spatter and cuts costs

Posted 7 years ago

Loctite retaining adhesives go from strength to strength

Posted 7 years ago

Henkel claims world's first structural, instant adhesive

Posted 7 years ago

Why use a retaining compound?

Posted 7 years ago

Structural bonding for lighter-weight, energy efficiency robots

Posted 7 years ago

Henkel at Southern Manufacturing 2014

Posted 7 years ago

Crystal clear, high-temperature encapsulating compound

Posted 7 years ago

Adhesive bonding contributes to formula student success

Posted 7 years ago

Maintenance expert in your pocket

Posted 7 years ago

Loctite: the complete range for maintenance, repair and overhaul

Posted 7 years ago

Loctite Live - a nationwide tour

Posted 7 years ago

Loctite 5075 insulating and sealing wrap is multi-purpose

Posted 7 years ago

Ten things machine builders should know about adhesives

Posted 7 years ago

Ten things machine builders should know about adhesives

Posted 7 years ago

New customer web tool, much more than just online ordering

Posted 7 years ago

Health and safety flange sealant silicones

Posted 8 years ago

Perpetuum harvest the benefits of low-pressure moulding

Posted 8 years ago

New elastic adhesive allows instant handling

Posted 8 years ago

Composites help pump repairs to deliver rapid payback

Posted 8 years ago

Adhesives and sealants for equipment repairs

Posted 8 years ago

Henkel and Engineering Solution supply low-pressure mouldings

Posted 8 years ago

Van maker saves 30 per cent on pump energy costs

Posted 8 years ago

Cost-effective low-pressure moulding using Macromelt

Posted 8 years ago

New, simpler branding for Henkel industrial adhesives

Posted 8 years ago

New website for surface engineering products

Posted 8 years ago

Loctite instant adhesives at Southern Manufacturing 2013

Posted 8 years ago

Loctite engineering adhesives used in premium domestic stoves

Posted 8 years ago

Henkel helps Ford create stronger joints in engine parts

Posted 8 years ago

Non-hazardous engineering adhesives: no price premium

Posted 8 years ago

Improved low-bloom and low-odour instant adhesives from Henkel

Posted 8 years ago

Loctite anaerobic adhesives help bring in the harvest

Posted 8 years ago

Loctite 3090 instant adhesive fills gaps of up to 5mm

Posted 8 years ago

Loctite adhesives deliver the required safety standards

Posted 8 years ago

Loctite adhesives are temperature resistant to 120 degrees C

Posted 8 years ago

Comprehensive cleaning product range from Henkel

Posted 8 years ago

More bonding developments from Henkel with Loctite

Posted 8 years ago

Instant adhesives are temperature resistant to 120 degrees C

Posted 8 years ago

Free Loctite Industrial Selector Chart for maintenance products

Posted 9 years ago

Multan bactericide-free cutting fluids are cleaner and safer

Posted 9 years ago

Henkel features bactericide-free cutting fluid at MACH 2012

Posted 9 years ago

Improved threadlocking adhesives are more oil-tolerant

Posted 11 years ago

More technical articles