The 2017 September issue of Bolted magazine is available now! As with every issue we have filled the magazine with interesting cases and insights from the world of bolting.
In this edition, our theme article focus on lug wear which is a common issue for pivot joints. But why does it occur, what solutions exist and do they solve the root cause of the problem?
You will find out more about Expander System in our customer case, where we visited Danish company Viggo Benz who delivers solutions and equipment for crushing, demolition and sorting.
Also, see how Nord-Lock washers secure containers that transport radioactive substances, where there is no room for equipment failure.
Last but not least, don’t miss out on how and why we now offer lifetime warranty throughout our product range.
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First published in Bolted #1 2017.
Q: What is clamped length?
A: Clamped length – LK – is the free length of a bolt that is stretched under tension, meaning:
It is also called “grip length” as the total thickness of clamped parts under compression.
To optimise a bolted joint, it is recommended to design the clamped length to at least 3 or 5 times the bolt diameter. Increasing the elasticity of the fastener greatly improves the properties of the joint, as it:
For stiff joints that don’t permit a long clamped length, it is possible to implement smart and effective solutions to avoid failure. Instead of using expensive and unattractive spacers, you can, for example, use:
First published in Bolted #1 2017.
ENERGY. With oceans covering more than 70 per cent of the earth’s surface, wave power is potentially a huge untapped source of renewable energy. The problem is that most wave energy converters are too large and costly to be commercially viable. Swedish company CorPower Ocean could have the answer.
The company’s compact Wave Energy Converter works by oscillating in resonance with waves, amplifying their motion and then converting that energy into power. CorPower Ocean founder, cardiologist Stig Lundbäck, invented the initial concept based on the pumping principles of the human heart. In the same way that a heart uses hydraulically stored energy to form back in place, the Wave Energy Converter uses a pneumatic pre-tension system to pull down the buoy after it has been lifted by a wave.
This allows for a relatively small device to harvest a large amount of energy. It is estimated that one buoy, eight metres in diameter, can generate around 250 kilowatts of power. That is enough electricity for around 200 homes.
“If you look at wave energy potential, somewhere between 10 to 20 percent of global electricity consumption could be provided by wave power,” says Patrik Möller, CEO, CorPower Ocean. “It has the potential to become the most competitive source of renewable energy. It offers five times more energy density than wind and ten times more than solar power. Waves have fewer variations and are more predictable than sun and wind, so you know a few days in advance what the energy flow will be.”
Currently, the Wave Energy Converter is undergoing tests with simulated wave loading, while a full-scale demonstration is being set up to begin in 2017. One of the key challenges has been keeping the buoy small and lightweight, while at the same time strong and durable enough to survive the toughest storms at sea.
This has presented a number of fastening challenges. On the mainframe inside the buoy, CorPower Ocean has elected to use Superbolt tensioners due to their lower torque requirements compared to a single bolt, which makes assembly far more manageable. Superbolt can also guarantee reliability over the buoy’s intended 20-year lifespan. At the base of the buoy, Nord-Lock washers are used, since they can maintain the correct tension over many load cycles over a long period of time.
First published in Bolted #1 2017.
The people of Nuremberg are proud of their underground system, which is among the most modern in Europe. The city, located in Bavaria, Southern Germany, has the only underground network in Germany where two of the three lines operate automatically, without train drivers. Nuremberg trains travel the equivalent of the circumference of the earth twice each day, carrying more than one hundred million passengers per year.
After 40 years of continuous use, it comes as no surprise that a renovation of the track beds is required to ensure passenger safety. The main beam, also known as a concrete stringer, which attaches the tracks to the tunnel floor, has simply sustained damage in too many places.
This is a daunting issue for the provider of the Nuremberg metro services, VAG (Verkehrs-Aktiengesellschaft Nürnberg). Normally, metro companies need to completely shut down a track for weeks during the renovation of such concrete stringers. Employing water pressure to remove the concrete, it is a time-consuming and extremely dangerous job, considering the many power lines inside the tunnel. Long delays caused by closed tunnels are costly for the track operators, adversely affecting train traffic and irritating passengers.
Coming to the rescue, a brand new innovation caught VAG’s attention just as they started planning the renovation. Local Nuremberg dowel and concrete bolt manufacturer TOGE Dübel won a railway innovation award for a new concept that enhances the sustainability of existing concrete bridges. Present in the audience, VAG representatives were intrigued and had the idea of trying the concept for the first time in an underground rail environment. Currently, work is under way at the first three stations: Bärenschanze, Gostenhof and Maximilianstrasse. Work on the second largest station in the network, the “Plärrer”, with 98,000 passengers daily, is planned for 2017.
Instead of complete reconstruction, concrete bolts measuring 36 centimetres and weighing 1 kilo are utilised as load-bearing components to improve the life span of the overall track bed construction. The bolts are fitted with a patented special thread that cuts into the borehole wall upon application. The force of the bolt is mechanically transferred to the anchor base and the concrete is fixed in place.
“Completely removing a concrete stringer and installing a new one could never be accomplished without service disruption,” says Waldemar Gunkel, Technical Director of TOGE and one of the two inventors of the new generation of concrete bolts.
“In Nuremberg, however, our system is only being installed between the hours of 23.00 and 04.00. By the morning, everything is running normally.”
During these working hours, only one track is shut down and trains are redirected via a single track, while the porous areas of concrete on each stringer are chipped away and replaced. Finally, the stringers are fixed into the ground utilising the concrete bolts. Since the bolts need to be drilled into the concrete, there is a risk of inclination as the drilling machine might not be positioned at an exact 90-degree angle. That’s why all concrete bolts that are being used in this first project are secured by Nord-Lock X-series washers. Their conical shape can compensate for the inclination, while the wedge effect prevents spontaneous bolt loosening due to vibration.
The Nord-Lock connection came via Deutsche Bahn – Germany’s national railway operator – where Nord-Lock original wedge-locking technology has long been prescribed as the standard.
Jochen Süssenbach, Nord-Lock Project Account Manager, sees great potential in this new approach to metro renovation. “We’re looking at a huge renovation of the tunnels that virtually doesn’t affect the timetable at all”, he says. “In terms of costs, it’s also a solution that beats any conventional method.”
So far, the renovation is running as planned. The first construction phase has even been completed a week ahead of schedule and the total time for construction carried out at all three metro stations will last six weeks instead of several months, which could have been the case with the previous method.
The concrete bolts themselves are designed to last for 50 years. No concrete will last that long, but further renovations will not be necessary for decades.
Describing TOGE’s Innovation Award-winning solution, Bavarian Interior and Transport Minister Joachim Herrmann said the following: “We have our fingers right on the pulse.” He hinted at the billion-dollar losses that Germany faces due to the poor condition of some 120,000 highway bridges and 30,000 railway bridges.
THE UNDERGROUND RAIL SYSTEMS are in a similar state. Just as in Nuremberg, most metro networks in Germany, as well as in the rest of Europe, were established in the 1970s. Gunkel thinks TOGE has found an important application for its concrete bolt: “This project gives us the boost to further drive our product development forward.”
Facts: The Nord-Lock Solution
Client: TOGE Dübel GmbH & Co.KG.
End customer: Metro services provider, Verkehrs-Aktiengesellschaft Nürnberg (VAG).
Location: Nuremberg, Germany.
Project: Renovating concrete stringers under metro tracks without affecting traffic.
Solution: Using concrete bolts with a patented special thread to reinforce the existing structure.
Nord-Lock Product: X-series multifunctional wedge-locking washers with enlarged outer diameter (NLX24sp)
First published in Bolted #1 2017.
How do you define ideal fastening, which you also covered in your book?
“Ideally, fastening should be based on the use of widely available, standardised fasteners, rather than specially designed parts. More importantly, ideal fastening should ensure a bolt fastening design that won’t lead to any kind of failure. The entire product design becomes invalid if a single failure occurs. You must pay attention to every aspect. I consider ‘evaluation without any omission’ most important.”
Is using lubricants an advantage in bolt fastening?
“Yes, if the fastened objects don’t slip against each other, lowering the friction coefficient is favourable in all aspects. If fastened objects are in a ‘loosening environment’, they are more likely to loosen if the friction coefficient is low, but it does not necessarily lead to loosening.
They are in a ‘loosening environment’ if they are repeatedly subject to slip against each other with a force exceeding a certain threshold.
How do external forces cause slip, based on shear direction, axial direction and torsion?
“If an external force is applied in the shear direction, it would cause slip. If it is applied in the axial direction, the fastened objects would separate from each other – separation. Under these conditions, the lower the friction coefficient, the more likely loosening is to occur.
When writing Bolted Joint Engineering – Fundamentals and Applications, I used the conventional view of the slip phenomenon, explaining the slip of fastened objects on the contact surface – so-called ‘macro-slip’. You can observe this with your eye, as this type of slip needs to be only 0.1 mm for visual confirmation. Around 1988, it was found that invisible ‘micro-slip’ actually occurs before the macro-slip and that it causes rotation, which is so micro that, whether turned in the direction of loosening or not, it can’t be confirmed with the naked eye. This phenomenon, ‘micro-slip’, gradually diminishes the axial force. It was introduced in an article in the Journal of the Japan Society for Precision Engineering.
“If fastened objects are in contact with each other, conventional experiments can’t measure the slip amount of a certain section of the contact surface or of other sections. But all of these values can be calculated using the finite element method, FEM. It has been used in the fastener industry since around 2000 and today most research on threaded fasteners utilises it. An article by Doctor Satoshi Izumi et al. in 2006 announced that gradual rotational loosening was found to occur with micro-slip (invisible minute slip)rather than macro-slip (clear, visible slip). I was shocked when I first read the article, which states that when micro-slip occurs repeatedly, it causes minute rotational loosening as small as 1 degree per 1,000 times or 1/1000 degree each time. A 1/1000-degree rotation is not at all observable to the eye. With the finite element method, it can be studied perfectly and it was demonstrated that micro-slip causes rotational loosening. I felt I was in trouble! [Laughs] The results drastically shook the concept of critical amount of slip.
I had thought that micro-slip would naturally lead to fretting wear, but didn’t consider that it could cause rotational loosening. I had no way of testing that at the time. It was an eye-opening experience.”
A slip not visible to the naked eye. Gradually diminishing the clamp force, it can ultimately lead to visible rotational loosening (macro-slip). Settlements and relaxation of the material can also decrease the clamp force. Nord-Lock Group has developed X-series washers that deal with both forms of slip. They counteract all kinds of clamp force losses with the spring effect, while the wedge effect prevents spontaneous bolt loosening.
Facts: Doctor Tomotsugu Sakai
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First published in Bolted #1 2017.
Customer: KTM Sportmotorcycle AG
Production: >160,000 motorcycles ANNUALLY (2015)
Number of world titles: 270
Company size: 2,900 employees, one billion Euro in revenue
Strongest motorcycle: KTM 1290 SUPER DUKE R, aka “The Beast” (177 HP, 1,301 cc, 144 Nm, 189 kilos)
Nord-Lock products: Nord-Lock washers for M6, M8, and a customized washer
Number of models: 45
Pick any of the world’s most exciting motor races and you will find the orange motorcycles by KTM, Europe’s largest manufacturer, among the top contenders.
Located in Mattighofen, Austria, close to both motorsport-crazy Italy and R&D stronghold Germany, KTM mixes influences from both countries with its own “never give up” attitude. After failing to cross the Dakar finishing line ten times, KTM turned failure into a winning streak that has lasted since 2001.
KTM is the only manufacturer that bolts the gearshift lever axially instead of clamping it, making it easier to access with tools. However, the bolt that attaches the conic gearshift lever to the shifter shaft was a weak spot on early pre-series bikes. Heavy washers combined with glue couldn’t prevent loss of preload during some of the most extreme jumps, where the riders land with their foot on the gearshift lever. The whole lever would come loose.
Standard Nord-Lock washers were either too large or too thick to solve the issue. However, Nord-Lock customized an NL6sp washer, with an outer diameter of 16.6 mm instead of 13.5 mm. Two years later, KTM hasn’t seen one single case of gear-lever bolt failure.
First published in Bolted #1 2017.
Market share, North America: 60% for mulching machines
Location: Factory in Quebec, Canada. HQ in South Carolina, USA
Products used: NL3/8″ & NL 20 washers
Applications: Mulching machines, bio-energy balers
The importance of sustainability in land clearing is reflected in the product range of North American company Gyro-Trac. With a 21-year history of manufacturing mulching machines, its focus is now also on creating bio-energy balers for easy packaging, transportation and storage.
As the mulching machines clear unwanted trees, this green technology leaves soil structures intact, eliminates erosion and run-off pollution. The machines can mulch trees to the ground, leaving the roots of neighbouring trees undamaged.
Nord-Lock has provided high-quality wedge-locking washers to Gyro-Trac for around 15 years. The washers maintain the balance of their mulching machines, extending the life cycle and sharpness of the teeth in the process.
The washers also play an important role in Gyro-Trac’s Bio-Baling System. The system involves compressing biomass in such a way that no compost is created and no burning is required. For Gyro-Trac’s customers, the added costs of hauling and dumping are eliminated, while onsite storage of the one-tonne bales promotes sustainable land use.
Daniel Gaudreault, owner of Gyro-Trac, says: “The teeth are the heart of the machines we produce. We have never had a problem with Nord-Lock washers and their reliability has been vital to our continued success.”
The March issue of Bolted magazine will be hitting the desks soon! As usual we invite you on a journey to explore interesting cases and insights from the world of bolting.
This edition’s theme article revolves around hydraulic torquing and tensioning. We play off one against the other in an attempt to answer which is the best method of tightening critical bolts.
In the process of creating this issue we have talked to many satisfied customers from around the world! We will take you to Nuremberg where we have a closer look at a better and more cost-efficient way to renovate track beds in their railway underground system, without weeks of construction and chaos caused by delays and diversions.
This issue also features sustainable mulching machines exposed to extreme vibration, KTM sports motorcycles solving issues with customized Nord-Lock products, and a customer who creates waves with a special buoy as a source of renewable energy.
At the same time we are glad to inform that this edition is also available in Spanish! Bolted magazine is now published in 9 languages: English, German, French, Swedish, Finnish, Japanese, Chinese, Korean and Spanish.
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