First published in Bolted #2 2016.
Q: Can I re-use bolts?
A: Before you re-use bolts, you should always consider the security level of the assembly and economic factors. Operators often lack important information, such as if the assembly working load or working temperature have been exceeded. As fatigue cracks are difficult to detect, the use of a new bolt (screw, nut and washer) is often recommended for security and legal reasons.
You can re-use bolts:
Before re-using threaded fasteners, always make a visual inspection of the head and/or nut for signs of damage or corrosion. Check that the coating on coated fasteners is not damaged or worn away. Ensure that there is no permanent deformation of the threads by running a new nut over the thread engagement length of the screw. Inspect the fastener shank for signs of reduction in diameter “waisting”, indicating that the yield strength of the fastener has been exceeded.
Clean the internal and external threads and all contact areas. Using the same or similar tightening condition as on the initial installation – such as torque level, tool class or lubricant type – ensures that the same clamp load is achieved.
If the fastener is initially assembled un-lubricated, the surfaces of the bearing area and threads will degrade under pressure when untightening, increasing the coefficient of friction between these surfaces. Tightening on re-use to the initial torque value will result in a reduced clamp load, because of the higher coefficient of friction of these surfaces. Subsequent re-use will progressively reduce the clamp load and then be consistent at a low preload and a lot of problems could take place, such as fatigue, vibration or joint separation.
First published in Bolted #2 2016.
One way is adding excitement to the mix. Several universities are, quite literally, trying to accelerate student interest through extracurricular motorsports projects. Two American projects – Gator Motorsports at the University of Florida, Gainesville, and the Virginia Tech Baja SAE Team in Blacksburg – along with Dutch Forze Hydrogen Racing at Delft University of Technology are sponsored by the Nord-Lock Group.
These projects cover all steps, from design and development to assembly and racing the vehicles. Gator Motorsports highlights how students acquire technical skills while practicing teamwork and project management, which is beneficial for their transition into careers in the industry later on.
Gator Motorsports takes part in the yearly Formula Society of Automotive Engineers (FSAE) design competition in Michigan, USA. Here, they compete against more than 100 teams from all over the world with their high-performance Formula-style race car.
Combining motorsport with sustainable technology, Forze Delft focuses on race cars powered by hydrogen fuel cells. Their latest model, the Forze VI, is one of the first fuel cell system race cars globally, and the first and fastest hydrogen-powered race car ever measured on the Nürburgring Nordschleife in Germany. Recently, it broke the electric-lap record on Circuit Park Zandvoort in The Netherlands.
True to its “Fun, fast, dirty” slogan, the Virginia Tech Baja SAE Team has chosen to go off-road. Its single-seat vehicle competes each year in an international competition arranged by the Society of Automotive Engineers (SAE).
These student projects rely heavily on sponsors, but it is not all about getting free parts. “Networking with industry sponsors exposes us to engineering after college,” says Jess Barton of the VT Baja SAE Team. “We have the opportunity to learn from the companies, including how they operate and what they design and manufacture. Real-world skills and advice from sponsor companies make us great engineers and professionals.”
Johanna Persson, Sales and Marketing Director, Nord-Lock Group
1. What kind of student projects does the Nord-Lock Group sponsor?
“The projects that we select should resonate and align with our business and brand strategy. We wish to connect with future engineers, designers and innovators that will play an important part in developing solutions for both current and future challenges within our world.”
2. What are the long-term gains for the students?
“We want to help them to develop their creativity. We support thoughtful, innovative projects and programmes that build the capacity of students to succeed in a constantly evolving world.”
3. How do I get my student project sponsored?
“All student organisations are welcome to submit an inquiry through our website if they see a use for our products. We can’t support activities asking for a cash contribution, but we will support projects with knowledge and market-leading products.”
First published in Bolted #2 2016.
Couplings are as old as industrialisation itself with even early simple machines, such as cotton mills and windmills, needing some way of connecting shafts. However, ever since the invention of the steam turbine back in 1884, shaft couplings have become essential in the power generation and shipping industries. As both turbines and shipping vessels have increased in size, so too has the amount of power and torque that needs to be transmitted. This in turn has greatly increased the demands on shafts and couplings, and in the case of bolted couplings, on the bolts themselves.
“In the power generation and marine industries, couplings have always been there and they really haven’t evolved much,” says Martin Walsh, an engineer with over 30 years experience working with large-scale bolted couplings. “If you look at a coupling from 60-70 years ago, it is pretty much the same design and concept as today. However, the engineering behind them has evolved a lot. Bolts in particular is an area where couplings have become a lot more sophisticated and this has allowed smaller couplings to transmit more torque.”
One of the most important functions of a bolted coupling is to maintain shaft alignment. In marine applications, where shafts typically turn at low speed, any misalignment will cause vibration, which in turn puts unnecessary loading on the bearings. In power generation applications, where rotation can be as high as 3,600 rpm, even the slightest vibration or uneven loading is unacceptable and would severely limit the turbine’s ability to run at full power. For this reason, a lot of time and resources are invested in optimising shaft alignment.
“Once you’ve achieved the alignment, then the bolts need to hold it as it was set and maintain that alignment in service,” says Walsh. “At some point in the future, you will take those bolts out and disconnect the shaft. When you put it back together, you want it back to exactly where it was before because you’ve already invested a lot in getting the alignment right.”
For many years the most common bolting solution was standard through bolts, which are relatively cheap and readily available. A bolt is simply inserted through the bore and tightened with nuts on either end to create a friction connection. But the amount of torque that can be transmitted through friction is severely limited and excessive torque can lead to slippage and misalignment. The resulting micro movements and uneven loading can then lead to damaged bolts and bores. The coupling therefore needs to be rebuilt and shaft alignment re-established.
In theory, fitted bolts, which fill the bore, can offer greater torque capacity, since torque is then driven through direct shear across the cross-
section of the bolt. In practice it is difficult to achieve a truly fitted bolt, since the bolt’s diameter will reduce as it is tightened. This creates a gap between the bolt and the bore, leading to the same problems of slippage and bolt failure.
This need to establish and maintain shaft alignment, even after a coupling has been dissembled and reassembled again, has led to the increased use of expanding sleeve bolts. Since expanding sleeve bolts expand into the bore, they can ensure a truly fitted bolt and a far more even load distribution. This eliminates movement and slippage, so that shaft alignment should automatically be re-established once the expanding sleeve bolts are reinstalled.
“The expanding sleeve bolt has probably been the biggest single advance in accuracy over the past 30 years,” says Steve Brown, Global Product Manager – Expansion Bolts, Nord-Lock. “They offer many pros and little in the way of cons – ease of installation, accuracy of fit, ease of removal, regaining of alignment and with correctly prepared holes, regaining of concentricity and re-usability.”
A key factor driving the development of bolted couplings has been the evolution in engineering analysis. “70-80 years ago, couplings and bolts were over-engineered and bigger than they needed to be, as engineers erred on the side of caution,” says Walsh. “It was a situation that existed in many industries because the ability to do sophisticated calculations and simulations was not available.”
Now many OEMs have the ability to test the affects of temperature, different materials and operation conditions using computer modelling and simulations. Due to the complexity of rotating couplings, the finite element method (FEM) is becoming increasingly common for identifying weak points and torque tolerance of specific installations. Shear tests have also been used successfully to demonstrate the physical limitations of different bolting solutions.
“There is still scope for further analysis and it would be helpful to see exactly how the newer design of bolts with expanding sleeves compare to the older bolts when it comes to transmitting higher torque,” adds Walsh. “Having a full FE analysis could be a significant advantage since it shows the potential for reducing the number of bolts and size of the coupling, particularly in industries such as wind turbines, where they tend to avoid bolted couplings due to space restrictions.”
The need to design smarter and smaller couplings will continue to be important as turbines and shipping vessels keep on growing in size and output, and need to transmit even more torque.
C.A. PARSONS ”TURBINIA”
In 1884, British engineer Sir Charles Algernon Parsons invented the first steam turbine.
His first model only generated 7.5 kW of electricity, but it demonstrated huge potential for generating electricity and for powering ships. In 1893, the Parsons Marine Steam Turbine Company was set up and in order to demonstrate the capabilities of the new technology, began developing the experiential vessel Turbinia.
The new ship was equipped with three axial-flow turbines fitted to three shafts, with each shaft driving three propellers. On completion in 1894, the Turbinia was the fastest ship in the world reaching speeds of up to 34 knots (63 km/h) – in comparison the Royal Navy’s fastest vessels could only reach 27 knots.
In 1897, the Turbinia turned up unannounced to the Navy Review for Queen Victoria’s Diamond Jubilee, and in front of royalty and senior Navy figures, it was able to clearly demonstrate its superiority in speed and power. Within two years, Parson’s turbines were adopted by the Royal Navy and shortly afterwards used to power transatlantic passenger ships.
Sir Charles Algernon Parsons’ designs also saw steam turbines quickly scaled up, making it possible to generate cheap and plentiful electricity. In 1899 the first megawatt turbine was built in a power generation plant in Germany, and within Parsons’ lifetime, his invention was adapted by all major power stations in the world.
LET’S STICK TOGETHER
The need to assemble components in bolted joints goes way back. For long the through bolt was the standard threaded fastener. It is inserted through the bore and tightened with nuts on either end to create a friction connection. Excessive torque may lead to slippage and misalignment, which in turn can lead to damaged bolts and bores.
The expanding sleeve bolt is a more recent invention, which overcomes these problems. It expands into the bore and ensures a truly fitted bolt along with more even load distribution. It also simplifies installation and removal as well as retrofitting.
Boltight hydraulic tensioning system is engineered to accomplish a vast majority of bolt tightening work. Strong and robust designs ensure tools’ durability and long operating life. The tools operate quickly and safely to achieve high and accurate residual bolt stresses.
The video below demonstrates tightening with Boltight hydraulic tensioning system.
MINExpo is one of the largest mining shows on-and under-earth. Held every four years in Las Vegas, the fair is an excellent platform for bringing together mining experts from all over the globe, as well as showcasing everything what’s new in mining – from state-of-the-art products and services to innovative technologies.
Nord-Lock Group has a long track record of helping customers in the mining industry through safe and secure bolting solutions. “MINExpo was a great opportunity for us to see what is in the market place. The show was three days and within that time we never saw show traffic go down. We had a great presence keeping people engaged and a great turn out in attendees that visited us at the show.” – says Pam Corn, Marketing Manager at Nord-Lock, Inc. / Superbolt, Inc.
The main focus at this year’s MINExpo was the introduction of the Expander ® System to the Nord-Lock product portfolio. Acquired by the Nord-Lock Group in July, Expander ® System offers a modern cost-effective solution that stops pivot wear and eliminates line boring.
The solution is effective and reliable, with documented success in many industries, including mining. “MINExpo was my first opportunity to meet the people representing other technologies within the Group,” said Gene Roberts, Director of Business Development, Expander. “These are really great people and everyone was very excited about Expander coming on board. It is easy to see how each product offering complements the other, widening the solution opportunities for new and existing customers. As I visited each mine customer looking over the machines on display, it was easy to see opportunities for each technology. I went away from the show with positive feelings about the company, the people and the expanded product options we will now be working with.”
The Expander pivot technology further strengthens the total offer of the Nord-Lock Group, which also includes Nord-Lock wedge-locking washers, Superbolt™ multi-jackbolt tensioners and Boltight™ hydraulic tensioning. The combined range and the unique expertise vested within each technology brings tremendous opportunities for the future.
First published in Bolted #2 2016.
Customer: Ampegon Antenna Systems
Application: Gearbox in rotatable antenna
End customer: British Broadcasting Corporation (BBC)
Location: BBC Radio Transmitting Station, A’Seela, Oman
Product used: Superbolt CY-M36 x 4/W multi-jackbolt tensioners
Nord-Lock Superbolt tensioners came to the rescue when a windstorm damaged a broadcasting antenna structure in the Oman desert. German company Ampegon Antenna Systems were responsible for fixing the drive of a rotatable antenna, which is owned by the BBC.
Ampegon have over fifty years experience in providing high-performance antenna and mast systems for radio broadcasting. Their speciality is a rotatable short wave antenna system with a steel structure weight of 200 tonnes. One of these 80 metres high and 80 metres wide structures was installed on the BBC facility in Oman in 2000. In June 2010, a cyclone destroyed one of the gearwheels in the rotatable joint, which facilitates the rotation of one of the upper parts of the structure.
The antenna is an important part of the BBC’s broadcasting capabilities in Oman, allowing worldwide radio transmissions. However, a quick fix was to be delayed by lengthy legal and budgetary discussions. After finally starting the repairs, Ampegon looked to a solution for pre-tensioning the bolts, fixing the gearboxes to the tubular shaft without the temporary import of hydraulic tensioning equipment. It was then that they turned to Nord-Lock in Switzerland, who supplied Superbolt CY-M36x4/W multi-jackbolt tensioners. These were installed into replacement gearboxes at the site in May 2015.
According to Christoph Fischer, Ampegon’s Project Manager in Oman, the BBC are extremely happy with the Superbolt solution. “It was a complicated process to lift the gearboxes out of the steel tower and replace them. However, the Superbolt tensioners are high strength, reliable and were easy to install. The results of the project have been to everyone’s satisfaction.”
First published in Bolted #2 2016.
Customer: The Hoyer Group
Product used: Nord-Lock stainless steel and X-series washers
Number of tank containers: over 30,000 worldwide
Number of tank trailers worldwide: more than 2,000
Application: Tank containers for liquid transport
To avoid accidents that would put people and the environment in harms way, it is crucial that the transport of liquids is managed safely and efficiently.
Started in Hamburg more than 70 years ago, the Hoyer Group has vast experience in handling chemical products, foodstuffs, gas and mineral oil. Today this global market leader in moving liquids by road, rail and sea operates over 30,000 tank containers and over 2,000 tank trailers worldwide. On the recommendation of a customer, the Hoyer Group has started to employ Nord-Lock stainless steel washers on their tank containers used on the European continent.
Frits Bakker works at the Engineering department at Hoyer Nederland BV in Rotterdam. “We faced a problem with valves on gas containers,” he explains. “A customer advised us to try Nord-Lock washers. Using these washers and a different seal material solved the problem. After this, we started to fit them on the bottom valves of our tank containers.”
The Hoyer Group will be using the Nord-Lock stainless steel standard washer, as well as the X-series version. They have a standard guideline to fit them on particular parts during maintenance. According to Bakker, the Nord-Lock washers help the Hoyer Group to avoid critical situations. He says that, “Obviously on tank containers it is vital that leakages don’t occur. In this respect, the washers are very reliable.”
The September issue of Bolted magazine is out now! Prepare yourself on a reading journey to explore interesting cases and insights from the world of bolt securing.
In this issue, our theme article focuses on coupling challenges. Couplings are essential in the power generation and shipping industries, and are arguably the most demanding of all bolting applications. Learn what the bolting experts have to say about couplings.
Engineers from the Nord-Lock Group answer questions on how to get the most out of your fasteners and cover the key advantages of hydraulic tensioning.
We witness the largest public works project in California’s history, where Boltight tensioners are installed on the San Francisco-Oakland Bay Bridge. We then move on to Oman to find out how broadcasting antennas owned by the BBC are being secured against windstorms. Last but not least, we ride on the time machine as we simulate 20 years of wear and tear on a wind turbine in just a fraction of that time.
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