It’s late in the evening and heavily loaded lorries escorted by police cars, blue lights flashing, move through the sleepy town of Waren, north-eastern Germany. Yet the residents of the quaint little houses aren’t worried; they know it’s just another ship propeller about to leave town. Waren, with some 20,000 inhabitants, is home to Mecklenburger Metallguss GmbH (MMG) – a world leader in the design and production of propellers for large container ships. One of its crea-tions, a 131-ton, huge six-blade propeller for Maersk, holds the world record for the largest ship propeller.
It’s a tricky transport challenge. Hamburg, Germany’s largest sea-port, is more than 200 kilometres away and stopping on the autobahn is time-consuming for the convoy of long and heavy vehicles. Some years ago, a whole A-road, along with two railway tracks, had to be moved as the company grew and propeller transports kept jamming the traffic. So, what is an XXL ship supplier like MMG doing this far from the sea?
“We started manufacturing propellers 70 years ago, as the area was a Soviet occupation zone and the East German ship building industry had to be rebuilt after the war,” explains Jörn Klüss, Head of Design and Construction at MMG and a Waren native. “Back then, ship propellers were a lot smaller. Today, the know-how in the region is what makes us stay.”
CARGO CAPACITY has grown 1,200 percent over the past 40 years. Fifteen years ago, ships moved 5,000 TEU (twenty foot equivalent unit, a standard 6.1-metre shipping container). Today, ultra-large container ships load 22,000 TEU.
However, container demand collapsed during the financial crisis in 2009, and orders for new propellers stopped. “What saved us was our ‘Retrofit’ programme,” says Klüss, “a new generation of propellers that optimises efficiency in old ships.”
UNTIL THEN, propellers were built for ships operating at the highest possible speed. After the crisis, ships started slow steaming with engines running below capacity to cut fuel consumption. Ships that used to cross the oceans at 25 knots (46.3 km/h) slowed down to 18 knots (33.3 km/h) or less. “The slower an engine runs, the larger you can go on the propeller,” explains Klüss. “By analysing individual operating profiles, we adapt the number of blades and the diameter to determine the most efficient individual propeller.”
The company also analysed the propeller cap – the part of the propeller behind the blades that protects the steel components of the propeller shaft from seawater corrosion. It created a new energy saving cap (MMG-escap) with a new fin design that straightens the hub vortex, reducing the required torque and preventing wear on the rudder. These innovations made it possible to increase efficiency by up to 10 percent, sav-ing roughly EUR 200,000 for an Asia-Europe voyage.
MANY SHIPPING COMPANIES showed interest in upgrading old propellers with the MMG-escap, which alone increases propulsion system efficiency by up to 3 percent. Conventionally, propeller caps are fitted to the propeller with bolts secured by a chemical locking adhesive. But this requires the ship to dock for at least three days, incurring docking fees of about USD 15,000 per day, plus the cost of removing the ship from its sailing schedule. “We started thinking about attaching the new cap underwater, using divers,” says Klüss. “But that excludes the use of adhesives, which need oxygen to harden. That is how we found out about wedge-locking washers and the inventor of this technology – Nord-Lock.”
HOWEVER, the strictly regulated shipping industry relies on classification societies to ensure safety at sea and define technical standards for ship construction and operation. A ship cannot operate without classification, as it won’t get insurance or freight orders. The Nord-Lock washers hadn’t been tested and approved for use with the special copper alloy used in the propeller cap, so a certification that the washers efficiently secured the propeller cap was urgently needed. Every ship building country has its own classification organisation, and MMG works with all of them. In this case, they contacted DNV GL, one of the largest.
“If the shipping company and classification society agree, you may implement an application and perform a subsequent verification,” explains Klüss. “The Nord-Lock washers already had multiple certifications and DNV GL was motivated to test for another one due to our innovative steel-copper alloy combination.”
THE FIRST UNDERWATER ASSEMBLY of a propeller cap with Nord-Lock washers was carried out in 2014 on a large European container ship. Three divers only needed 1.5 days to do it during regular port time and without docking fees – a success. MMG, DNV GL and Nord-Lock met in September 2016. Less than a year later, the washers had been tested and approved.
“The shipping industry is very conservative,” says Klüss. “But we’ve convinced them of the diver solution’s merits, and Nord-Lock is now our new standard for all bolted joint applications.”
CUSTOMER: Mecklenburger Metallguss GmbH.
END CUSTOMERS: Shipping companies across the globe, ship yards mainly in Asia.
LOCATION: Waren (Müritz) in Mecklenburg-Vorpommern, Germany.
APPLICATION: Securing a ship propeller cap with Nord-Lock washers instead of adhesives.
NORD-LOCK GROUP SOLUTION: SMO washers for stainless steel bolts.
■ Excellent locking reliability.
■ Reduction of assembly errors thanks to ease of use.
■ Possibility to fix the propeller cap to an existing propeller under water.
What is the thinking behind 3D Hubs?
“The current value chain in which goods are manufactured produces a lot of waste. Many products have been produced in very high amounts for economies of scale, but roughly one third never get sold. What distributed manufacturing can bring is ‘on-demand manufacturing’, so goods are only produced the moment they’re sold. There’s no stock, no waste, and it can be done locally.
“3D printing is a new manufacturing technology, and in that it’s doing really well. The scepticism is based on the consumer market, where few people see anything happening. So that would be my message: it’s in the manufacturing sector.”
So, what benefits does 3D printing bring to manufacturing?
“For injection moulding, the most common process used for manufacturing in China, you need to build a mould first, and that means that there are a lot of up-front costs. Without moulds, 3D printing is very price competitive for small-batch production. It’s also on-demand, so if you upload a file now, we can start producing instantly. And because it’s additive, you can do highly complex geometries.”
Are there any specific industries or applications that benefit?
“3D printing is completely conquering the prototyping market. Then industries that need small-batch production of highly complex geometries, such as prosthetics, hearing aids and dental implants. There are already a lot of commercial aircraft with 3D printed parts in them. Replacement parts are also a very large business, which really leverages the on-demand aspect of 3D printing.”
What are the benefits for the fastener industry?
That’s an interesting case actually. As fasteners, almost by definition, are standardised parts, they are typically not suitable for 3D printing – simply not price competitive. However, in a wider context, from a value chain perspective – 3D printing can offer a lot in terms of replacement parts and ‘ondemand’ turn-around. Especially in the technical service branch, we see 3D printing used
a lot for these benefits, even for standardised parts. This is where I would see fasteners of any kind benefit as well.
FACTS: FILEMON SCHÖFFER
TITLE: Chief Marketing Officer, 3D Hubs, Amsterdam, The Netherlands.
BACKGROUND: I’m an industrial design engineer and physicist, so I know a lot about manufacturing, but I’ve always worked in ads and creative campaigning.
LIVES: Near the 3D Hubs office among the start-ups, galleries and hip bars of Amsterdam’s trendy Westerpark district.
PASSION: AFC Ajax.
INTERESTING FACT: Filemon’s ancestor Peter worked with Gutenberg in the 15th century. “3D printing has a lot of potential to localise manufacturing of lots of things, it distributes both skill and know-how, and I think that’s comparable to what the printing press did.”
NEARLY TWO YEARS AGO, US company All Energy Management (AEM) began developing retrofits and training com-panies that service a fleet of 1,000 wind turbines in the UK, the US, Canada and Italy.
When embarking on repair work, it was found that the pins attaching the turbine blades to the rotor were wearing prematurely, along with the rotor holes. Line boring and welding when up on the turbine tower was not possible due to weight and space constraints. The only solution was to replace the rotor and pins, which took roughly 10 working days and cost USD 15,000.
Subsequently, AEM began discussions with Expander about developing a solution that would increase speed, improve efficiency and maintenance safety, and ultimately reduce costs. AEM developed a system to bore the holes out before installing the pins to ensure a reliable connection. Sets of three pivot pins and three different oversized sleeve options were supplied by Expander, which fitted perfectly into the holes depending on the degree of wear.
Fewer parts meant faster and simpler installation, while the Expander System also provided a perfect fit into the borehole, eliminating further movement causing wear. AEM has now been using the solution for over a year and is delighted with the results. “Instead of taking three days with four workers onsite to repair a turbine, it now takes us less than a day with only two workers required,” says Ian Sleger, Operations Manager. “The guys at Expander are really accommodating and the solution has freed us up to concentrate on other matters.”
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 2018.
BOLTS can come in a wide range of different sizes and shapes, but the basic production process generally remains the same. It starts by cold forging steel wire into the right shape, followed by heat treating to improve strength and surface treating to improve durability, before being packed for shipment. However, for more advanced bolt designs, the production process can expand by a number of additional steps.
As one of the leading suppliers of fasteners to the automotive industry, Swedish manufacturer Bulten is highly proficient in every step and facet of bolt production. “We do not produce catalogue parts – everything we produce is custom-designed, according to the customer’s specifications,” says Henrik Oscarson, Technical Manager at Bulten’s production plant in Hallstahammar, Sweden. “Depending on where the fastener will be used, there are a number of different options for producing exactly the right bolt.”
COLD FORGING STARTS with large steel wire rods, which are uncoiled and cut to length. The grade of steel is standardised across the industry, according to the requirements of ISO 898‑1. Using special tooling, the wire is then cold forged into the right shape. This is basically where the steel is moulded, while at room temperature, by forcing it through a series of dies at high pressure. The tooling itself can be quite complex, containing up to 200 different parts with tolerances of hundredths of a millimetre. Once perfected, cold forging ensures bolts can be produced quickly, in large volumes, and with high uniformity.
For more complex bolt designs, which cannot be contoured through cold forging alone, some additional turning or drilling may be needed. Turning involves spinning the bolt at high speed, while steel is cut away to achieve the desired shape and design. Drilling can be used to make holes through the bolt. If required, some bolts may also have washers attached at this stage of the process.
HEAT TREATMENT IS a standard process for all bolts, which involves exposing the bolt to extreme temperatures in order to harden the steel. Threading is usually applied before heat treatment, either by rolling or cutting, when the steel is softer. Rolling works much like cold forging, and involves running the bolt through a die to shape and mold the steel into threads. Cutting involves forming threads by cutting and removing steel.
Since heat treatment will change the properties of the steel to make it harder, it is easier and more cost-effective to apply threading beforehand. However, threading after heat treatment will mean better fatigue performance.
“The heat treatment can cause heat marks and minor damage to the bolt,” explains Henrik Oscarson. “For this reason, some customers demand threading after heat treatment, especially
for applications like engine and cylinder head bolts. It’s a more expensive process since you need to form hardened steel, but the threads will maintain their shape better.”
For long bolts, where the length is more than ten times the bolt’s diameter, the heat treatment can have the effect of making the steel revert to the round shape of the original steel wire. Therefore, a process of straightening often needs to be applied.
THE CHOICE OF surface treatment is determined by the bolt’s application and the requirements of the customer. Often, the main concern for fasteners is corrosion resistance, and therefore a zinc-plated coating applied through electrolytic treatment is a common solution. This is a process whereby the bolt is submerged in a liquid containing zinc, and an electric current is applied so that the zinc forms a coating over the bolt. However, electrolytic treatment does come with an increased risk of hydrogen embrittlement. Another option is zinc flakes, which offers even higher corrosion resistance, albeit at a higher price.
WHEN CORROSION RESISTANCE is not an issue – such as inside an engine or an application that is regularly exposed to oil – using phosphate is a more cost-effective option. Once the surface treatment has been applied, standard bolts are typically ready to be packaged. However, more advanced designs may require some additional assembly, such as brackets. Other bolts will also require some form of patching, either a locking patch or a liquid patch. A locking patch consists of a thick nylon layer over the threads, which helps improve grip. A liquid patch will help improve thread-forming torque.
ONCE THESE STEPS are complete, the bolt is finished. Now all that remains is some form of quality control to ensure uniformity and consistency, before the bolts can be packaged and shipped.
THE PRODUCTION PROCESS
Uncoiled, straightened and cut to length.
2. COLD FORGING
Moulding the steel into the right shape at room temperature.
3. BOLT HEAD
Progressively formed by forcing the steel into various dies at high pressure.
Threads are formed by rolling or cutting.
5. HEAT TREATMENT
The bolt is exposed to extreme heat to harden steel.
6. SURFACE TREATMENT
Depends on the application. Zinc-plating is common to increase corrosion resistance.
After quality control to ensure uniformity and consistency, the bolts are packaged.
First published in Bolted #1 2018.
IN 2015, ELON MUSK, the billionaire behind the futuristic transport technology companies Tesla and SpaceX, launched the Hyperloop Pod Competition. It challenges university students to design the best transport pods for the Hyperloop– Musk’s dream where people will travel inside a pod that levitates on its tracks and races at almost supersonic speeds through a giant tunnel
network, which connects the major cities of the world.
During the 2017 competition, the WARR Hyperloop team from the Technical University of Munich was the one that finally raised the laser-sintered titanium trophy. During the competition, they broke a world-speed record for hyperloop pod travel, using Nord-Lock wedge-locking washers to secure each bolt of their pod.
THE 30-STRONG WARR Hyperloop team was divided into several sub-teams to manage areas ranging from CAD design and structure to procurement, finance and marketing. Sub-team leader for CAD design and structure, Florian Janke, says he was inspired by Musk’s vision for a superfast futuristic transport system, and especially the idea that people could one day travel from Munich to Berlin in just 30 minutes.
He says that, “When Musk launched his ‘SpaceX competitions’, I just had to be part of it. We did well in all the stages of the Hyperloop Pod Competition. In the last one, which focused on maximum speed, we achieved 324 km/h (210 mph).”
The WARR Hyperloop team’s lightweight pod smashed the previous 310 km/h (192 mph) record speed set by California-based Hyperloop One, whose pod reached this speed in a 500-metre tube. “There is obviously lots of acceleration and vibration when testing at such high speeds in a relatively short tube – 1.2 km (0.8 miles),” Janke explains. “It was essential that we had secure bolts, so we used Nord-Lock wedge-locking washers, which held the bolts firmly in place. They were perfect.”
The WARR team has registered for the next, third Hyperloop competition, and has already passed the first selection round. While some team members are active in the new, 2018 team, albeit in new roles and positions, most of the them are carrying on with their studies. A few are travelling from trade fair to trade fair showing the 2017 winning pod.
AS THE TEAM worked very closely with a lot of manufacturers in order to get financial backing and various parts, some team members have since had interviews with these companies, and are now considering working there.
The 2018 March issue of Bolted magazine is available now! As with every edition we have filled the magazine with interesting cases and insights from the world of bolting.
In this issue of Bolted, we take a closer look at what goes into the manufacturing process of traditional bolts – from raw steel to tailor-made applications.
We ask expert Filemon Schöffer about the potentials with 3D-printing, and we meet German company “MMG” who is a world leader in production of propellers for large container ships.
And of course a lot more.
Want to receive your complimentary copy of the Bolted magazine? Subscribe now!
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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