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.
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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.
First published in Bolted #2 2017.
You first worked with Superbolt tensioners at Diablo Dam in 1984. How did that come about?
“I was a machinist working at Seattle City Light, the electric utility for Seattle. We worked out of the machine shop down there, and we would go up and be labour support at Diablo Dam. In 1984, they were doing a stator-rotor inspection on the turbine, so they had to remove the rotor; that involves taking the thrust bearing apart, which is mounted on the turbine shaft. It is very important that the thrust block is perpendicular to the shaft within less than one-thousandth of an inch. Otherwise, it will have run-out and wobble.”
How did the Superbolt tensioners help with that?
“Back then, to get the right tension in the bolts, you had to heat the bolts so they would elongate, do the installation, and then wait for them to cool overnight. If the thrust bearing wasn’t sitting right on top of the shaft, you had to do it all over.
“The engineers at Diablo Dam had been in contact with Superbolt, and they modified the bolts so you didn’t have to go through this long process. Instead, we could tighten up those little bolts. If the thrust bearing wasn’t exactly perpendicular, you just tweaked the bolts on the opposite side. It was a very labour-saving modification.”
Today, you work at Wells Dam. What do you do there?
“I’ve been with the Wells Hydroelectric Project for about 17 years, managing and monitoring the project. What I’ve always enjoyed about my work is that every day there are new challenges or something that you’ve got to fix. We’ve got air systems, electrical systems, mechanical systems, hydraulic systems – all these different auxiliary systems that feed the turbines that run 24 hours a day.”
How has the dam been modernized over the years?
“One of the ways that it has been modernized is that we have installed PLCs on the majority of our alarm systems. Today, we have over 2,500 alarm points on different systems. This allows us to set more parameters for the alarm points, and we can also trend over time and compare with different machines. If something is starting to fail, you can set up a parameter to get an alarm so you can look into it before the failure actually happens.
“We are also using Superbolt tensioners when rebuilding our turbines. They’re being used in the load screws that hold the turbine bearing shoes in place, and in our turbine’s outer head cover, where you can’t access the bolts with a big wrench because it’s close quarters. They’re very reliable.”
FACTS: MIKE BRUNO
TITLE: Project Superintendent, Wells Hydroelectric Project, Douglas County Public Utility district
LIVES: Chelan, Washington
BACKGROUND: Has a degree in industrial technology from Shoreline College; also studied at Cogswell College. Worked at Seattle City Light as a hydro machinist and foreman until 1990, then as a mechanical supervisor for the Skagit River Hydroelectric Project until 2000. Since then with Wells Hydroelectric Project.
PASSION: Married with three grown daughters, two granddaughters. Enjoys bow hunting and playing golf.
First published in Bolted #2 2017.
SAFETY. The JFE Steel Corporation’s West Japan Works is one of the largest and most advanced steel mills in the world. Like all steel plants, the operating conditions are exceptionally demanding on machines and equipment, and potentially hazardous for personnel – especially the hot rolling mill, where molten steel is flattened and stretched into thin sheets. The temperature of the steel will reach at least 450°C (842°F).
Until recently, the fasteners that connected the decelerators and pinion stands on the hot rolling mill, were tightened using a 300-kg weight, which was suspended from the ceiling via a crane. The weight would be pulled from a makeshift scaffold, before letting it hit the wrench like a hammer. Overall, the procedure involved five people: three to pull the weight, one to fasten the wrench, and one to operate the crane. It took an hour to tighten each bolt, and the multiple safety risks for the personnel involved were considerable.
Switching to Superbolt multi-jack tensioners has turned one of the riskiest maintenance tasks in the plant into one of the safest. Each connection can now be secured by one person in just 15 minutes. With eight bolts on each mounted application, the overall reduction in downtime and increase in productivity is significant.
In fact, Superbolt multi-jack tensioners have proven so successful that they have been implemented in JFE Steel’s other hot rolling mills in Fukuyama and Chita.
First published in Bolted #2 2017.
SUPERBOLT has its origins in the US steel industry and has been providing a wide range of bolting innovations for a variety of industries since the 1970s. Its ongoing success within Nord-Lock Group’s portfolio is based on a knowledge of customer challenges and a commitment to supplying practical solutions to the market.
Launched in December 2016, HyFit and VersaTite tensioners continue Superbolt’s tradition of versatility. Superbolt multi-jackbolt tensioners have been on the market since 1984, allowing bolted joints to be tightened mechanically, without specialized skills or heavy tooling. HyFit is hydraulically actuated, while VersaTite uses both mechanical and hydraulic tightening. Easy to fit and remove, they are offering safe and efficient operations and increased uptime to customers worldwide.
“To have both mechanical and hydraulic options is a huge advantage in many industries,” says Steve Brown, Global Product Manager, Expansion Bolts. “HyFit is ideally suited for use on high-speed couplings on gas and steam turbines, and on marine propulsion drives. Traditionally fitted bolts must have a close tolerance. The fitting and removal of these are often problematic and can lead to damage of the couplings and costly downtime for customers.”
Both HyFit and EzFit (previously named EB, mechanical Expansion Bolt), are designed to offer a simple easy-to-fit solution that, once tightened, will provide a long and reliable lifespan.
VersaTite, as the name suggests, is a versatile tensioner that allows customers the flexibility of both hydraulic and mechanical tensioning and removal. Combining the speed of hydraulic tensioners and the accuracy of the Superbolt mechanical variant, it has been developed to improve operations in several industries since its launch at the Power-Gen International show in December 2016. “This type of ‘all-in-one’ technology represents the next step for Nord-Lock Group in terms of providing the market with a new generation of bolting solutions,” Brown says.
The 2017 September issue of Bolted magazine is available now! As with every issue we have filled the magazine with interesting cases and insights from the world of bolting.
In this edition, our theme article focus on lug wear which is a common issue for pivot joints. But why does it occur, what solutions exist and do they solve the root cause of the problem?
You will find out more about Expander System in our customer case, where we visited Danish company Viggo Benz who delivers solutions and equipment for crushing, demolition and sorting.
Also, see how Nord-Lock washers secure containers that transport radioactive substances, where there is no room for equipment failure.
Last but not least, don’t miss out on how and why we now offer lifetime warranty throughout our product range.
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Superbolt range of expansion sleeve coupling bolts offers a wide range of flexibility in application – suitable for through hole couplings, blind hole couplings – even applications requiring accurate location of components without axial load. The expansion bolts can be retrofitted to replace traditional interference and other types of coupling bolts most reliably and cost effectively.
The mechanical expansion bolt, now known as EzFit, is a long-established product with design capability for all types of couplings requiring truly fitted bolts, commonly used for Hydro turbines, Marine propulsion drive coupling, large motors and gear rings that require component location accuracy.
HyFit hydraulic expansion bolt is a newly advanced product that can replace all designs of coupling bolts. Main applications are found in power generation including conventional steam, high efficiency gas, hydro and wind turbines. With HyFit installed, customers benefit from both operation improvements in coupling performance along with saving time during plant maintenance periods. The innovative design features significantly reduce the risk of causing damage to the bolt or bolt hole, and address safety issues commonly experienced with alternative coupling bolt solutions.
The extensive product range of HyFit and EzFit expansion bolts provides the best options to fit your application. Furthermore, the unique features and advantages of both hydraulic and mechanical expansion sleeve coupling bolts can be combined to suit specific requirements.
First published in Bolted #1 2017.
ENERGY. With oceans covering more than 70 per cent of the earth’s surface, wave power is potentially a huge untapped source of renewable energy. The problem is that most wave energy converters are too large and costly to be commercially viable. Swedish company CorPower Ocean could have the answer.
The company’s compact Wave Energy Converter works by oscillating in resonance with waves, amplifying their motion and then converting that energy into power. CorPower Ocean founder, cardiologist Stig Lundbäck, invented the initial concept based on the pumping principles of the human heart. In the same way that a heart uses hydraulically stored energy to form back in place, the Wave Energy Converter uses a pneumatic pre-tension system to pull down the buoy after it has been lifted by a wave.
This allows for a relatively small device to harvest a large amount of energy. It is estimated that one buoy, eight metres in diameter, can generate around 250 kilowatts of power. That is enough electricity for around 200 homes.
“If you look at wave energy potential, somewhere between 10 to 20 percent of global electricity consumption could be provided by wave power,” says Patrik Möller, CEO, CorPower Ocean. “It has the potential to become the most competitive source of renewable energy. It offers five times more energy density than wind and ten times more than solar power. Waves have fewer variations and are more predictable than sun and wind, so you know a few days in advance what the energy flow will be.”
Currently, the Wave Energy Converter is undergoing tests with simulated wave loading, while a full-scale demonstration is being set up to begin in 2017. One of the key challenges has been keeping the buoy small and lightweight, while at the same time strong and durable enough to survive the toughest storms at sea.
This has presented a number of fastening challenges. On the mainframe inside the buoy, CorPower Ocean has elected to use Superbolt tensioners due to their lower torque requirements compared to a single bolt, which makes assembly far more manageable. Superbolt can also guarantee reliability over the buoy’s intended 20-year lifespan. At the base of the buoy, Nord-Lock washers are used, since they can maintain the correct tension over many load cycles over a long period of time.