New Brunswick Power Belledune Generating Station has been using Superbolt products since the mid 2000’s in their steam turbine for valves bolting.
In this video we show how EzFit expansion sleeve coupling bolt was able to solve a problem when standard fitted coupling bolts were causing severe damage on the turbine couplings.
Find out more:
First published in Bolted #2 2013.
Q: When and why does galling and seizing appear?
A: Galling is caused by a combination of friction and adhesion between metallic surfaces during sliding. When galling occurs material is adhesively pulled from one surface leaving it stuck on the other in the form of a lump. This process spreads rapidly as the built up lumps induce more galling.
The tendency of material to gall is affected by the material’s ductility. Typically, softer materials are more prone to galling while harder materials are more resistant.
In bolting, thread galling appears during fastener tightening as pressure builds up between the contacting and sliding thread surfaces. Thread galling commonly occurs with fasteners made of stainless steel, aluminium, titanium, and other alloys.
In extreme cases galling leads to seizing – the actual freezing together of the threads and bolt lock-up. Continued tightening may lead to the breakage of the fastener or result in torn off threads.
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.
Q: What is clamped length?
A: Clamped length – LK – is the free length of a bolt that is stretched under tension, meaning:
It is also called “grip length” as the total thickness of clamped parts under compression.
To optimise a bolted joint, it is recommended to design the clamped length to at least 3 or 5 times the bolt diameter. Increasing the elasticity of the fastener greatly improves the properties of the joint, as it:
For stiff joints that don’t permit a long clamped length, it is possible to implement smart and effective solutions to avoid failure. Instead of using expensive and unattractive spacers, you can, for example, use:
First published in Bolted #1 2017.
Starting with ROLLING STOCK some 20 years ago, Nord-Lock wedge-locking washers are now found in all safety-related areas of the railway industry, such as bogies, coupling devices, brake systems, rail dampers, housing, and many more.
Nord-Lock washers ensure the functionality of bolted joints, even at the highest levels of vibration caused by rail traffic. One example is in railway switches, highly complex structures that must be used as long as possible with minimal maintenance, while exposed to the elements and to considerable stress.
Nord-Lock steel construction washers (NLSC) help railway companies avoid operational downtime, thus saving money. When renovating or replacing old bridges, small temporary bridges are assembled on site with a bolt preload of 100 percent to achieve secure bolted joints. However, these bolt connections can only be used once. Using Nord-Lock washers, the preload can be reduced.
Overhead line masts and signal masts must cope with severe dynamic loads caused by passing trains. Given the large number of masts, reliable bolt connections are crucial to reducing maintenance costs. With their special geometry, Nord-Lock X-series washers increase security, including on bolted joints with short clamp length, as well as in softer materials.
A recent application for the Nord-Lock X-series is noise-absorbing walls, which cope with extreme vibrations from passing trains. In Germany alone, 3,000 km of noise-absorbing walls are to be installed by 2030. A combination of concrete bolts and X-series washers is used to attach noise-absorbing barriers on existing bridge decks, many of which were not designed for noise barriers.
First published in Bolted #1 2017.
What is Expander’s business?
“Our patented Expander System is a state-of-the-art, cost-effective solution that permanently ends pivot wear in construction, forestry, mining and other heavy machinery. Fitted in the pivot, a double-locking expanding pivot pin assembly increases stability and safety and eliminates welding and line boring of worn-out pivot lug ears. The system has been field-tested for over 50,000 hours without failure.”
How did the company start?
“My father, Everth, and his twin brother Gerhard, did road work in the 1950s, starting out with one bulldozer. Machinery joints and pivots are prone to wear and tear, leading to expensive downtime and repairs, but they came up with a makeshift solution, knocking a rusty nail into the lughole to eliminate the gap. This worked surprisingly well, which inspired them to start developing the technology.”
When did you get involved?
“I learned about their ideas and immediately saw the potential. My father and I founded the company in 1986. At quite an early stage we got involved with computer engineers in the development of a parameter-controlled CAD system. This is an invaluable tool, as each Expander System is custom made to fit customer-specific applications.
In the 1990s we expanded geographically. North America is a huge market and in 1997 I moved there to get a business foothold. The launch was successful and in 2006 we established our own production facility in North America.”
Why did you sell the company?
“Enormous markets, such as South America, are starting to develop, but you need local presence. It was about either setting up my own network or selling to someone that already had a global subsidiary and distributor network. We already collaborated with Nord-Lock and after several discussions with Ola Ringdahl, CEO, Nord-Lock Group, I was sure that the Nord-Lock Group was a perfect fit.”
What does Expander bring to the Nord-Lock Group?
“There has been a major change in how people view repair and maintenance, which makes the market potential for the Expander System huge. We’ve only scratched the surface.
Also, we and the Nord-Lock Group have often shared customers, but solved different problems. Bringing our solutions together – and cross-fertilising them – will make our portfolio and product range so much stronger, which will benefit the customers.”
Facts: Roger Svensson
Role: Founder and former CEO, Expander System Group.
Lives: Sedona, Arizona, USA.
Background: Studied Economics/Political Science at UCLA (double major). Member of the UCLA team that won the prestigious NCAA swimming championships in 1982. Held a couple of positions with other companies before starting Expander with his father in 1986. “I have always been an entrepreneur.”
Passion: Music: sings, plays guitar and writes his own songs. Is currently working on his debut album. Also paints and likes to write.
First published in Bolted #1 2017.
Nearly everyone has tightened a nut at some point in their lives and can understand the basic concept of torquing. It is the oldest, simplest, and for most non-engineers, the only method of tightening bolted joints.
Whether by hand or hydraulics, compared to other methods, simple to understand basics of torquing make it overall a far more cost-effective option. This does not dismiss the need for training and understanding of the key factors in torque tightening.
“With one torque wrench and a range of sockets, you can tighten quite a wide range of nuts and bolt sizes,” says Robert Noble, Technical Director, Asset 55. “It offers quite a bit of flexibility, and it’s easy to explain to a technician how to use torque equipment.”
Given that it will be effective in the majority of applications, it is clear why it is often the default first choice.
Hydraulic torquing has its limitations, particularly friction, which Noble labels, “the number one enemy of torque.” Typically, friction accounts for 90 percent of the torque applied to the nut, which means only a small portion of torque will translate into useful bolt load. Because torquing is an indirect way of loading, it is difficult to predict the exact bolt load. Many factors should be taken into consideration, in particular the lubricant used, the need to avoid possible contamination and a good surface finish on the nut bearing surfaces. This must be overcome to ensure reasonable accuracy when using torque to produce preload and can be a significant disadvantage in critical joints.
Noble stresses that with good procedures, calibrated equipment and competent personnel, torque tightening can be used successfully on most joints. Much is made of bolt scatter, which will see the achieved preload on an individual bolt within +/– 25 percent of target, but on a flange with multiple bolts the usual result is to achieve an average bolt load within close range of target (providing good practice is followed and the coefficient of friction is assessed). “This is accurate enough for the majority of gasketed flange joints, so torque remains a very viable technique,” Noble says.
Hydraulic tensioning began in the 1970s, pioneered in part by British engineer Fred Heaton, who would go on to found companies Hydratight and Boltight. Over the next 20 years it gradually became more common and is now becoming the preferred method for tightening large critical joints in many industries, such as oil and gas, wind, subsea, or power generation.
Compared to hydraulic torquing, it is a more complex procedure that involves more specialised equipment. In certain applications tensioning can offer greater accuracy and control, as well as speed of assembly. It is particularly advantageous on flanges with multiple bolts. Using conventional torque, each bolt is tightened one-by-one in a pattern, which must be applied carefully to avoid the risk of putting too much load on one side of the gasket or flange. By attaching multiple tensioners, it is possible to tighten a number of bolts simultaneously for an even compression of the gasket.
“This is essentially where hydraulic tensioning came from,” says Nitin Patel, Projects and Commercial Manager, Boltight. “It allowed people to control the clamping force and if you could do it all in one go, around the whole circumference, that would be much better for the gasket, much better for the joint, and you could actually predict the load that is in that joint.”
Another perceived advantage of tensioning is improved accuracy, but as Noble points out, it’s not always that simple. “Unfortunately, the industry tries to use simple one-size-fits-all rules but they do not apply to the torque and tension criteria,” he explains. “Where the conditions are right, tensioning can become very accurate. Typically, that would be for bolts with a high length-to-diameter ratio – long, thin bolts – and where you have high bolt loads. In these applications tensioning is more accurate than torque. But conversely with short, fat bolts and low bolt loads, tensioning becomes less accurate.”
Tensioning also has its disadvantages, namely load loss, which occurs when the tensioner is released and the load transfers to the nut. To compensate for this, the load loss is estimated and the technician applies the expected load loss in advance. This means that the bolt, gasket and flanges are subjected to greater stress than the targeted assembly stress. This has to be taken into consideration either at the joint design stage or prior to using the tooling. An alternative is to repeat the tensioning procedure to compensate for the settlements.
Hydraulic tensioning can also have practical and logistical drawbacks. Since it requires more equipment and specialised tools, it can be significantly more expensive. “Tensioning is not easily understood, other than by those who tension regularly,” says Noble. “You need specific tension tools and it’s difficult to design a tensioner range with the same flexibility as a torque wrench.”
So the truth is that there is no simple answer to which one is better, torquing or tensioning. It is best decided on a joint-by-joint basis.
“Blanket policies result in a lot of technical queries and in some cases the need to compromise on bolt load. Instead you need to do what is best for that specific joint,” Noble says and concludes: “Sometimes it comes down to looking at the application with open eyes, considering how you will actually get the equipment out to the site, the location where it has to be used and how it is going to fit into the application.”
Did you know that…
Friction typically accounts for 90% of the torque applied to the nut during hydraulic torquing?
For bolted joints, several factors must be considered before choosing between torquing or tensioning.
First published in Bolted #1 2017.
Look up into the sky in the coastal city of Miri, in north-eastern Sarawak, Malaysia, and you may see Nord-Lock washers in action: inside a radio-controlled aircraft. These hobby airplanes are sold by Byond Horizon, a business that otherwise uses drones to take aerial photos and videos for companies.
“Unlike our drones, these recreational aircraft use gasoline-powered engines,” says Mr. M. Fadzly of Byond Horizon. “These engines cause a vibration problem. Since the frame is made of wood, which is soft, and the engine and its mounting are made of steel, the bolts holding them together can come loose after only four or five flights.”
Fadzly says that it can be difficult to access the plane’s engine, so the loosening is a real problem. A friend of Fadzly’s, however, works at Mayura Engineering and is a supplier of Nord-Lock washers.
“I ordered a box, tried them out, and now I recommend them to all of my customers when we are assembling their airplanes,” says Fadzly. “The Nord-Lock washers never need to be retightened, and they also make sure the engine stays in place. It would be quite dangerous if the engine were to fall out during flight.”
Fadzly not only sells the radio-controlled airplanes, he flies them himself. “I’ve been doing it since 1997,” he says. “It’s a passion, and a fun thing to do on the weekend. It gives you the feeling of flying a real airplane.”