A forum about optimizing
bolt securing

Towering challenge for a giant crane

24 November 2015

Text: Claudia Flisi

photo: Terex CTL 650F


First published in Bolted #2 2015.

Challenges are nothing new to Terex Tower Cranes, an Italian-based manufacturer of cranes for construction and industrial use founded (as Comedil S.r.l) in 1962. It has been a part of Terex Cranes since 1998, and sells its flat top, luffing jib, hammerhead, and self-erecting tower cranes all over the world.

Recently, with an eye to the growing demand for tall, powerful cranes at large construction sites in the global market, Terex Cranes developed a new luffing jib tower crane with a maximum jib length of 75 metres, capable of handling a 66 tonne load. It is the largest tower crane ever built by Terex.

What eventually became the CTL 1600-66 presented a unique challenge: designing the coupling between the tower and the jib. Eight M100 bolts were needed for assembly, and a standard solution would have called for the use of a hydraulic torque wrench of 90 kilos to tighten them. This in turn would have required two workers to perform the assembly and a separate mini-crane to ­handle the weighty wrench, all in very limited space at high altitude.

While the standard solution was feasible, it meant modification of the crane’s design. Engineers working on the project were loath to make such changes because they were satisfied with the original plan. Their challenge was to ensure that the high-altitude assembly of the tower would be easy and safe for operators without altering their design.

Nord-Lock is one of Terex’s suppliers, and suggested an alternative solution – Superbolt multi-jackbolt tensioners. The Superbolt CY-M 100X6/W ensured the technical performance sought by the design team without the need for modification. Only a small amount of space is necessary because tightening requires only one worker, who can tighten the bolts to the correct clamp load using a simple torque wrench, instead of the 90-kilo hydraulic version.

The overall speed of operation is about 40 minutes, the same as the standard solution. Although each bolt can be tightened faster, there are eight per unit. However, speed was not a deciding factor. More important for this kind of application – very large cranes with long extensions – are the advantages of manageability, reduced space, safety, and the need for one worker rather than two.

The CTL 1600-66 made its market debut in 2014, so it is still too soon to evaluate customer reaction. But Terex is optimistic about the long-term prospects for its giant crane.

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.


Do you have a question about bolt securing?
Put the Nord-Lock experts to the test.
Email your questions about bolt securing to

Innovative wind turbine maker gets peace of mind with Nord-Lock

Quality and durability are Eastern Wind Power’s top priorities for its 50kW vertical axis wind turbines.

nord-lock on wind turbine

Cambridge, Massachusetts-based Eastern Wind Power (EWP) launched a wind turbine that could be spotted on roofs of urban high-rises, at remote industrial plants, or in developing countries, providing power for basic needs like drinking water and lighting.

Unlike the propeller-type horizontal axis wind turbines that are common in many parts of the world, EWP’s vertical axis wind turbine has three vertical six-metre high carbon fibre blades. The benefits of this vertical configuration include lower noise, less risk to birds, no gearboxes and their associated mechanical issues, and they can be erected closer together than traditional wind turbines.

Not satisfied with the bolt securing solutions they had used previously in their Sky Farm 50kW Vertical Axis Wind Turbine, EWP tried Nord-Lock wedge-locking washers and were amazed with the results. “We cannot afford failures,” says Linda Mongelli Haar, Chairman of Eastern Wind Power, Inc. “We wanted to make sure after all our design and development work that we didn’t lose the quality by putting on nuts and bolts that weren’t going to do the job. That is why we turned to Nord-Lock.”

EWP currently uses Nord-Lock NL8ss washers – 24 per turbine – to secure the blades to the struts. “If the bolts here are not properly secured you get the bolt backing out a little and it will start to vibrate,” says Jonathan Haar, President and CEO of EWP. “And even if it doesn’t back out all the way, it might snap the whole blade off because you’ve allowed enough space for vibration. That vibration can throw your whole turbine out of balance.”

EWP has attracted the attention of Siemens Industry Inc, one of the biggest players in the world wind power sector. “Siemens was looking to venture into ‘small wind’ and they wanted to prototype their inverters with a vertical axis turbine,” says Linda. “They interviewed a lot of companies and they selected us, which was a great vote of confidence.”

The project is in particular receiving a lot of interest from markets like Hawaii and the Caribbean where the energy prices are as high as the wind speeds. “We are also starting to get some interest from owners of high-rise buildings closer to home who understand that distributed energy will pay them back quickly and they will have a good 20 years of virtually free energy after a short break-even,” says Linda.

President of Nord-Lock Inc., calls EWP “a fantastic example of a progressive original equipment manufacturer (OEM)” in the wind power segment. “In the last four years Nord-Lock in North America has seen its OEM business grow as a result of companies like EWP focusing on innovation and safety – and safety of bolted joints is our primary mission,” he says. “We are rapidly becoming an industry standard in the wind power segment.”

“They didn’t think we could succeed”

12 November 2015

Text: Janna Thalén

photo: Sandra Lee Pettersson


First published in Bolted #2 2015.

If not for the big barn next to his grandparent’s home in Halabacken in Jämtland, in Sweden’s northwest, this story would probably have been completely different. The rather humble business that started here 55 years ago, in the middle of the woods with a backdrop of snow-clad mountains some 40 kilometres from the nearest town, has evolved into an international industrial company.

Kurt Persson has been with Nord-Lock (and its predecessor Nobex) for 50 years, and can these days be addressed as both Senior Advisor and senior citizen. He describes himself as a person who always looks forward and who never gives in.

“I finished school after nine years of compulsory schooling and since then it has been ‘learning by doing’.”

Nobex’ business sprang out of his father Bengt’s interest in technology. For a long period, the production focused on an innovative oil burner, which was later succeeded by mitre saws. These were produced until 2001. When Nobex acquired a company that produced locking washers in 1982, the seed was sown for Nord-Lock.

“For the first seven years of washer production we were in the red. We didn’t have a clue about what we were getting into. We have taken some pretty hard knocks, but have never doubted the longevity of the product.”

How did you solve the issues?

“The technology has always been good, but initially the product was not up to standard, and we more or less got thrown out of some large-scale Swedish companies when we tried to enter that world. We turned it around through continuous improvements of the wedge-locking system, design developments, and by making sure that we had technically skilled people in the sales organisation. Now we act as a partner to large international companies in a variety of sectors and fine-tune customer-specific solutions.”

What does the production look like?

“During the 33 years that we have produced our washers, production technology has changed immensely. We have roughly 350 variants of the wedge-locking system, but quite often get specific inquiries. A nuclear plant wanted a unique solution and we had to develop a special tool to produce the ten washers that they requested. It was not a cheap solution, especially as they only used two of the washers, but they were satisfied.”

Are there any decisive moments in the company’s history?

“One milestone was when we built the first real industrial building in Mattmar in 1980. The municipality supported us, but the county administrative board said no. They didn’t think we could succeed in this sparsely populated area. In the end we received the funding and were able to start construction, provided we put in ‘real doors, so that it at least can be used as a bus depot’.”

How do you feel about Nord-Lock’s future?

“It is incredibly satisfying to retire knowing that Nord-Lock is growing strongly and has a dynamic management team and wonderful employees.”

FACTS: Kurt Persson
Name: Kurt Persson.
Age: 66.
Title: Senior Advisor.
Background: started cleaning machines at the age of 4 at Nobex, Nord-Lock’s predecessor. Joined the family business aged 16 and has since worked as, for example, production technician, workshop manager and production manager. Nord-Lock CEO 1985–2010. Now works part time as Senior Advisor.

China: Opportunities on the coal market

10 November 2015

Text: Crystal Yan

photo: Wang Jing


First published in Bolted #2 2015.

The domestic coal market continues its downward trend since China implemented integration of coal resources in 2008. With coal mining output decreasing, coal mining enterprises are buying less mining equipment, forcing machine manufacturers to restructure and look for new opportunities in the industry. Xi’an Coal Mining Machinery Co. Ltd is an outstanding player in the pursuit of innovation and development.

Smart, customised, automatic, safe and reliable – these are the qualities that Xi’an Coal Mining Machinery aims to have embodied in its products. A coal shearer is a machine that operates in a harsh environment and frequently faces problems in terms of a poor clamping force of main joint parts and joint loosening easily under the impact load, which affects productivity and threatens the safety of the operators. At present, the company is preparing for the launch of its self-developed Shear MG1660, which allows automated production with unmanned operation. The MG1660 uses Nord-Lock washers and Superbolt tensioners on its joint parts to help improve the machine’s seal, anti-collision and vibration performance.

Moreover, Xi’an Coal Mining Machinery has established a Roadheader Machine Unit, reaching out to new markets. The company has approved Nord-Lock washers and Superbolt tensioners as specialised components for its shearers and roadheaders.

FACTS: Xi’an Coal Mining Machinery Co. Ltd
Established: 1951.
Employees: 1,500.
Capacity: 130 shearers and 40 roadheaders.
Applications: Shearer MG1660.
Mining height: 4 metres.
Power: 1,660 kw.

Meet the Nord-Lock Group at Power-Gen International 2015


The Nord-Lock Group will be exhibiting in Booth 3031 at Power-Gen International in Las Vegas, Nevada, USA. The booth will be hosted by Nord-Lock, Inc. / Superbolt, Inc., a division of the Nord-Lock Group. The show takes place from 8th-10th December 2015 at the Las Vegas Convention Center.

Visitors at Power-Gen International will be able to see a range of solutions from our Nord-Lock wedge-lock technology, Superbolt multi-jackbolt tensioners, and our newest member to the group – Boltight, the specialist hydraulic tensioning systems.

Introducing Boltight

Boltight hydraulic bolt tensioning systems have a global reputation for innovation and quality. The company’s products are used throughout the power industry for a range of critical bolting applications on steam, gas, diesel, nuclear, wind, hydro, and tidal power generation plant. A selection of tools and hydraulic nuts will be presented at the show, including the Closure System, the Typhoon® multi-stage range, the foundation bolt tensioners and more.

Catch our LIVE demonstration

Have you wondered how our technologies work? Check out the schedule below for your chance to see our engineers explain and demonstrate how each technology works.

December 8, Tuesday
13:00 – 13:30 | Boltight Hydraulic Tensioning
14:00 – 14:30 | Superbolt Tensioning
15:00 – 15:30 | Nord-Lock Junker Demonstration
16:00 – 16:30 | Boltight Hydraulic Tensioning

December 9, Wednesday
10:00 – 10:30 | Nord-Lock Junker Demonstration
11:00 – 11:30 | Boltight Hydraulic Tensioning
12:00 – 12:30 | Superbolt Tensioning
13:00 – 13:30 | Nord-Lock Junker Demonstration
14:00 – 14:30 | Boltight Hydraulic Tensioning
15:00 – 15:30 | Superbolt Tensioning
16:00 – 16:30 | Boltight Hydraulic Tensioning

December 10, Thursday
10:00 – 10:30 | Boltight Hydraulic Tensioning
11:00 – 11:30 | Superbolt Tensioning
12:00 – 12:30 | Nord-Lock Junker Demonstration

Do not miss our booth lucky draw!

We are giving away a brand new iWatch to one lucky winner. Visit our booth to find out more!

Have you registered for your visit? Follow this link for your complimentary visitor badge.

For more information on the exhibition, visit

Presenting the Expansion bolts product video

Superbolt Expansion Bolts Video

We are pleased to present our Expansion bolts product video. The video is available on the Nord-Lock Group YouTube channel and can be downloaded here.

The Expansion bolts video demonstrates the challenges that installers are faced with when working with critical flange couplings and our solution, the Superbolt Expansion bolts can help to save time, money and increase worker safety.

Find out more:


Ecuador’s new power

27 October 2015

Text: Ulf Wiman

photo: ČKD Blansko


First published in Bolted #2 2015.

Customer: ČKD Blansko Holding

Built: To be completed in 2015
Project: Toachi-Pilaton hydroelectric project
Capacity: 254.40 MW
Production: 1,090 GWh PER year
Application: Francis turbines, main inlet valves

Ecuador already meets 45 percent of its energy needs with hydroelectric power, but is aiming to increase this to 93 percent by 2016. The Toachi-Pilaton hydroelectric project, which includes the construction of the Sarapullo and Alluriquin power plants on the Toachi and Pilaton rivers, is one step closer towards meeting this goal.

ČKD Blansko Holding, the leading manufacturer of hydro-mechanical equipment in the territory of the former Czechoslovakia, specialises in the production of Francis and Kaplan turbines and closure valves for the power plants. The total power capacity of the company’s turbines installed in more than 30 countries is over 19 GW. ČKD ­Blansko Holding’s pipeline valves are connected to pipelines by means of bolted flanged connections. Due to the uneven distribution of load to the individual bolts, however, these connections must be very carefully dimensioned and inspected.

“We asked the manufacturer of Superbolt tensioners to provide material certificates and certificates for the applied anti-corrosion protection. We then carried out the FEM calculation in which we verified the uniformity of load distribution. The certificates and the results proved satisfactory,” says Josef Plch, ČKD Blansko Holding’s valve R&D Designer. “In recent time we have used Superbolt nuts and bolts – types MT, SB and SX – for six pieces of our butterfly valves at the ­Sarapullo and Alluriquin power plants in Equador. I ­really like the idea of Superbolt tensioners; the fact that somebody can come up with a new solution to something that already seemed perfect. The two main advantages of Superbolt tensioners are the simple tightening method and the uniform distribution of load on the individual threads.”

ČKD Blansko Holding therefore uses Superbolt tensioners in power plant projects all over the world.