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Renovating Nuremberg’s metro – without affecting the timetable

12 giugno 2018
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Testo: Linda Karlsson

foto: VAG/ Peter Roggenthin, 123rf

Renovating an underground railway system without weeks of construction and chaos caused by delays and diversions was previously unheard of. That is, until a unique concrete bolt emerged in Nuremberg.

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)
Benefits gained:

  • Reliability in different environments.
  • Safety under any dynamic load vibrations caused by trains.
  • Excellent partnership in which problems are solved quickly.

Far volare gli elicotteri senza il pilota

PRODOTTI PER OPERARE in alcuni fra i più difficili ambienti al mondo, gli elicotteri APID One, della società Svedese CybAero’s, possono essere adattati facilmente alle esigenze specifiche dei clienti.

 

L’idea si basa su quattro componenti principali: la piattaforma dell’elicottero, il carico utile, il collegamento ai dati e la stazione di terra. L’elicottero può essere dotato di vari sensori ed il design facilita il cambio veloce del sistema dei sensori stessi. I sensori includono videocamere, altoparlanti, proiettori, telecamere ad infrarossi, telecamere elettro-ottiche per il rilevamento della luce e radar ad apertura sintetica.

Questa modularità rende gli UAV (Unmanned Aerial Vehicles) adatti a molteplici applicazioni, come l’ispezione di linee elettriche, l’esecuzione di operazioni di ricerca e soccorso in cui il tempo è essenziale, così come le missioni di controllo alle frontiere. In questi ambienti non ti puoi permettere di prendere scorciatoie per la sicurezza. Per garantire che le rischiose missioni di volo si concludano senza intoppi, CybAero fa affidamento sulla tecnologia del Nord-Lock Group.

Dal 2009, Nord-Lock Group ha fornito le rondelle di serraggio a cuneo per il braccio di coda, per il sistema di scarico e per il mozzo del rotore principale dell’elicottero APID One. Si tratta di applicazioni in cui le singole parti subiscono un’elevata esposizione a vibrazioni, calore e forze estreme, che sono note per essere le principali cause di blocco e di svitamento dei bulloni.

“Abbiamo scelto la tecnologia Nord-Lock per le sue caratteristiche uniche a prova di vibrazione”, spiega Mikael Smith, CEO di CybAero. “Un performante giunto bullonato si traduce in una minore usura, che a sua volta prolunga la durata utile e riduce la probabilità di guasti, nonché la necessità di manutenzione”.

FACILE UTILIZZO

Per le applicazioni dove il tempo è un fattore fondamentale, spesso in aree inaccessibili, la maneggevolezza dell’elicottero APID One diventa essenziale. I mezzi per volare sono stati progettati per poter usufruire di un facile trasporto ed imballaggio, ma anche per avere una semplice manutenzione.

Utilizzando i prodotti Nord-Lock, CybAero ha allungato ulteriormente la vita utile dei propri elicotteri, riducendo la probabilità di guasti e la necessità di manutenzione.

Di seguito un’immagine della testa del rotore, assicurata dalle rondelle Nord-Lock.

 

COME SI COSTRUISCONO I BULLONI

I bulloni sono uno dei componenti base nell'ingegneria e nelle costruzioni, la loro produzione è però un processo avanzato, composto di diversi passaggi ad alta tecnologia. Scopriamo come l'acciaio grezzo viene trasformato in strumenti metallici altamente specialistici e precisi.

COME SI COSTRUISCONO I BULLONI

First published in Bolted #1 2018.

I BULLONI sono disponibili in un’ampia gamma di dimensioni e di forme, ma il processo di produzione di base rimane essenzialmente lo stesso per tutti. Inizia con lo stampaggio a freddo (o estrusione a freddo) della bobina d’acciaio nella giusta forma, che viene poi sottoposta ad un trattamento termico per migliorarne la resistenza e ad un trattamento esterno per migliorare la durevolezza. Tuttavia, per la realizzazione di bulloni tecnologicamente più performanti, il processo di produzione si avvarrà, ovviamente, alcuni passaggi aggiuntivi.

Il produttore svedese Bulten, uno dei principali fornitori fasteners dell’industria automobilistica, è un esperto in ogni fase ed aspetto della produzione di bulloni. “Non produciamo prodotti da catalogo – tutto ciò che produciamo è progettato su misura, secondo le specifiche del cliente”, afferma Henrik Oscarson, direttore tecnico dello stabilimento di produzione di Bulten a Hallstahammar, in Svezia. “A seconda di dove verrà utilizzato il sistema di bloccaggio, abbiamo diverse opzioni per produrre esattamente il bullone giusto.”

LO STAMPAGGIO A FREDDO INIZIA con delle grosse bobine di acciaio, che vengono srotolate e tagliate a misura.
La qualità dell’acciaio è standardizzata in tutto il settore, in base alla norma ISO 898-1. Usando utensili speciali, la vergella viene quindi stampata a freddo nella forma voluta. Fondamentalmente, questo è il momento in cui l’acciaio viene stampato, a temperatura ambiente, imprimendolo attraverso una serie di stampi ad alta pressione. L’attrezzatura stessa può essere piuttosto complessa e può contenere fino a 200 singole parti con tolleranze diverse, di pochi centesimi di millimetro. Una volta messa a punto, lo stampaggio a freddo consente di produrre i bulloni rapidamente, in grandi volumi e con elevati standard di uniformità.

Per la realizzazione di bulloni più complessi, che non possono essere sagomati tramite il solo stampaggio a freddo, potrebbero essere necessarie torniture o perforazioni aggiuntive.
La tornitura prevede che il bullone ruoti ad alta velocità mentre l’acciaio viene tagliato, in modo da ottenerne la forma e il design desiderati. Con la perforazione si praticano fori al bullone.
Se necessario, in questa fase del processo, ai bulloni possono essere collegate le rondelle.

IL TRATTAMENTO TERMICO È un processo standard applicato a tutti i tipi di bulloni, i quali vengono esposti a temperature estreme per indurirne l’acciaio.
La filettatura, sia per rullatura sia per asportazione di truciolo, viene solitamente creata prima del trattamento termico, quando l’acciaio è più morbido.
La rullatura funziona in maniera molto simile allo stampaggio a freddo e consiste nel far passare il bullone attraverso dei rulli filettati in modo da formare e modellare l’acciaio in filetti.
Con l’asportazione di truciolo, i filetti si formano attraverso tagli e rimuovendo fisicamente l’acciaio dai tagli.

Siccome con il trattamento termico si modificheranno le proprietà dell’acciaio per renderlo più resistente, è più facile ed economico creare prima la filettatura. Quest’ultima, comunque, avrà migliori prestazioni sotto sforzo dopo il trattamento termico.

“Il trattamento termico può causare segni e danni minori al bullone “, spiega Henrik
Oscarson. “Per questo motivo, alcuni clienti richiedono che la filettatura venga realizzata dopo il trattamento termico, in particolare per l’utilizzo tipo nei motori e nelle testate. È un processo più costoso dal momento che devi usare acciaio temprato, ma le filettature manterranno la loro forma ottimale. ”

Per i bulloni lunghi, la cui lunghezza è più di dieci volte il diametro del bullone stesso, il trattamento termico può far ritornare l’acciaio alla forma rotondeggiante della bobina originale. Pertanto, spesso è necessario aggiungere un processo di raddrizzamento.

LA SCELTA DEL trattamento superficiale è legata a dove il bullone verrà utilizzato e alle richieste particolari del cliente. Il rischio principale legato agli elementi di fissaggio è la loro effettiva resistenza alla corrosione, pertanto, una soluzione molto comune,  è un rivestimento zincato applicato mediante trattamento elettrolitico. Questo è un processo in cui il bullone viene immerso in un liquido contenente zinco, che viene elettrificato in modo che lo zinco si fissi come un rivestimento al bullone. Tuttavia, il trattamento elettrolitico aumenta il rischio che l’idrogeno renda più fragile il bullone. Un’altra opzione è la zincatura a lamelle, che offre una resistenza alla corrosione ancora più elevata, anche se ad un costo più alto.

QUANDO LA RESISTENZA ALLA CORROSIONE non rappresenta un problema, ad esempio se l’applicazione è all’interno di un motore o a contatto con il petrolio, l’utilizzo del fosfato risulta la scelta più economica. Una volta applicato il trattamento superficiale, i bulloni standard sono in genere pronti per essere imballati. Tuttavia, nei progetti più avanzati potrebbero servire alcuni passaggi aggiuntivi. Altri bulloni hanno anche bisogno di una specie di patch,  che può essere sia di chiusura sia liquido. Un patch di chiusura è composto da uno spesso strato di nylon sopra le filettature, che aiuta a migliorarne la presa. Un patch liquido aiuta, invece, a migliorare il momento torcente.

UNA VOLTA UTIMATI QUESTI PASSAGGI, il bullone è finito. L’ultima verifica che rimane da fare è quella di qualità, per garantire l’uniformità tecnica del prodotto, poi i bulloni possono essere imballati e spediti.

IL PROCESSO DI PRODUZIONE

1. BOBINA
Srotolata, raddrizzata e tagliata su misura.

2. STAMPAGGIO A FREDDO
L’acciaio viene stampato nella forma voluta a temperatura ambiente.

3. TESTA DEL BULLONE
Progressivamente ottenuta comprimendo l’acciaio in stampi ad alta pressione.

4. FILETTATURA
Le filettature si formano o per rullatura o per asportazione di truciolo.

5. TRATTAMENTO TERMICO
Il bullone è sottoposto a temperature estreme per indurire l’acciaio.

6. TRATTAMENTO DELLE SUPERFICI
Dipende da dove il bullone verrà applicato. La zincatura è quello più comune per aumentare la resistenza alla corrosione.

7. IMBALLO/STOCCAGGIO
Dopo il controllo di qualità i bulloni sono imballati e stoccati.

Read more: Top ten tips for secure bolting

SpaceX competition winners chose wedge-locking washers

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.

New issue of Bolted magazine out now!

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.

Bolted magazine is available in 9 languages – Read them now:
English
German
French
Swedish
Finnish
Japanese
Chinese
Korean
Spanish

Want to receive your complimentary copy of the Bolted magazine? Subscribe now!

Top tips from bolting expert

Bolted got a unique opportunity to meet ­Japan’s foremost expert in bolting, Doctor ­Tomotsugu Sakai. His book Bolted Joint Engineering – Fundamentals and Applications continues to receive an enormous amount of support as the definitive work on bolt fastening.

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.”

Facts: Micro-slip
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

  • 1941 – Born in Okazaki City, Japan
  • 1979 – After working for Toyota Motor Corporation, receives his doctoral degree in engineering, mainly engaging in the strength and durability testing, research and development of various automobile parts.
  • 2001 – Transfers to Toyota Techno Service Corp, engaging in education and technical consultation for threaded fasteners.
  • 2007 – Retires and establishes Sakai Consulting Office on Bolted Joint Engineering, where he provides education and technical consultation for bolt fastening to this day.

 

► Video: Multifunctional Nord-Lock X-series washers

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Washers triple-protect nuclear transports

23 febbraio 2018
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Testo: Ulrich Schamari

foto: ILLUSTRATIONS: Daher Nuclear Technologies

First published in Bolted #2 2017.

THE CHALLENGE

Daher Nuclear Technologies GmbH, located in Hanau close to Frankfurt am Main, Germany, develops containers for transportation of radioactive substances. For obvious reasons, these containers must be extremely safe.

Designing a new container for uranium hexafluoride transports, the company had to consider the very stringent international and national requirements, including the recommendations of the International Atomic Energy Agency (IAEA) for transport by road, rail and sea. A container that fulfils these requirements must, for example, be resistant to the mechanical and thermal loads that can occur in case of an accident.

These mechanical accident loads are defined by a sequence of tests that include a 120-centimetre fall, followed by a 9-metre fall, followed by a fall from 1 metre onto a spike. The container must remain sealed, so that the subsequent thermal test, a fire, doesn’t jeopardise the container’s safety.

THE SOLUTION

Daher set out to design the container locks so that the locking bolts would, under no condition, come loose or be lost during the loading of the container onto a lorry or during transport. The company’s intensive search for the optimal solution led to Nord-Lock wedge-locking washers of type NL16-254SMO. These safety washers are an important component in Daher’s triple-protected locking system: the lock is secured with a bolt, which in turn is locked in position by another bolt. The wedge-locking washers from Nord-Lock are located under the second of these bolts. Each container has six locks and each lock is equipped with a Nord-Lock washer pair.

THE RESULT

Thanks to the use of Nord-Lock wedge-locking technology, the locking systems on the Daher transport container for the nuclear industry can no longer be worn by vibrations or stress, but remain tightly and securely locked. Daher was also pleased to find how cost-effective the use of the Nord-Lock product is, and how easy the maintenance is. If needed, the wedge-locking washers can be replaced at any time to ensure that the transport containers remain in top condition. The containers have a service life of more than 30 years – something that the Nord-Lock washers contribute to.

The Experts: Improving fatigue resistance

First published in Bolted #2 2015.

A: The fatigue capacity of a bolted joint is very small, as compared to its static capacity. To improve fatigue resistance, designers can increase the thread capacity and decrease the alternating stresses at the threads.

To increase the thread capacity, it is recommended to use a rolled thread instead of a cutting process. To increase the bolted joint capacity, utilize multiple smaller fasteners instead of a single larger fastener.

The capacity is also increased by using an improved connector, such as a Superbolt MJT (Multi-Jackbolt Fastener) or Flexnut, which improves the load distribution in the threads and adds elasticity to the bolted joint.

The best way to improve fatigue resistance is to reduce the alternating stresses at the threads. There are three main ways of doing this: Assembly design, assembly tightening, and assembly security.

The assembly design process provides an opportunity for improvement of the load distribution on bolted joints and to reduce the level of external stresses supported by each joint. To facilitate that, keep these principals in mind:

1. Use the highest possible preload
2. Minimize the bolt to load eccentricity
3. Use the largest possible contact surfaces
4. Use the largest possible clamping lengths
5. In most cases, use a preload higher than the working load

Other assembly design options include the use of necked-down studs or bolts, and the use of elastic washers, which counter the effects of relaxation, creeping, and thermal differential elongation.

With regard to assembly tightening, achieving the necessary preload is the main factor in reducing alternating stresses. It is recommended to use calibrated tools with high accuracy. It is also recommended to use a proper lubricant to achieve preload accuracy, and to reduce the risk of seizing. A suitable tightening sequence should be used to mitigate the risk of un-evenly loaded bolts and to ensure overall bolted joint integrity.

Regarding assembly security, it is recommended to secure the bolted joint against loss of preload. Further, secure the assembly against environmental effects, such as corrosion that could initiate a fatigue crack. This may be done through the selection of suitable materials and/or coatings for parts and fasteners.

 

ASK THE EXPERTS
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Put the Nord-Lock experts to the test.
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