The Yanacocha Mine in Northern Peru is one of the largest gold mines in the world. As in any industry, downtime means lost productivity and – as a result – lost money. Keeping the operations running is always of the utmost importance.
Minimizing production shortfalls and lowering the life cycle cost of the machinery and equipment is a constant challenge for the service and maintenance crew.
The useful life of the conventional pins in the stabilizer linkage on CAT’s 793B fleet was calculated to be 5.000 hrs. The machine was then brought in for disassembly, line-boring and re-pinning as part of crew’s maintenance schedule.
In 2003 the decision was made to put Expander System to the test.
A mining truck was fitted with pivot pins from Expander System and they outlasted the conventional solution by four times. The Expander pivot pins were checked every 5.000 hours and were not replaced until the 20.000 hour maintenance check. During the replacement no line-boring was needed and the whole procedure was completed in a few hours instead of days as it would in case of the conventional solution.
The cost savings where Expander pins were fitted were calculated to be over $30.000. While the test was ongoing and proven successful, the Yanacocha Mine maintenance department decided to start using the Expander System in many other pivot applications on their haul truck fleet.
The Yanacocha Mine is also using the Expander System on several vital wear points on Motor Graders and Wheel Loaders.
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 of bolts 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 bolt 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.
Multi Stud Bolt Tensioner is designed to provide high and accurate preload within a minimum diameter envelope. Durable, lightweight and easy to use, these tools are ideal for use within the confined radial spaces typical to tower connections.
The video below demonstrates the tensioning process.
Click here for more information about Boltight.
First published in Bolted #2 2016.
Bolted joints are a key component of most machines, which make them essential to many of Japanese Sodick Corporation’s applications. The company manufactures industrial machines and machining tools as well as consumables and other products. Original research and development is a top priority, ensuring high-quality products that improve the customers’ manufacturing operations.
Sodick moulding machine engineers recently attended a seminar on solutions to the problem of loose bolts held by Ikeda Metals, a Nord-Lock Japan distributor. It touched upon exactly what they were struggling with.
Together with Ikeda Metals engineers, Nord-Lock engineers started searching for areas where they could help improve Sodick’s bolted joint design. They realized that in the Sodick moulding machines, the tie rod bolts were tightened by a traditional method. Tie rods are quite long, so if they are subject to torsion stress, and the machine is operating for a long time at the end-customer site, it is difficult to guarantee optimal performance. From the customer’s perspective, the ability to properly control the force on the joints becomes essential, because it is key to safe operation without costly downtime.
Superbolt was the perfect solution as it just has pure tension. It does not create any friction and therefore can control the force on the joints without giving off torsion stress. The people at Sodick were impressed by how diligently the Nord-Lock engineers worked at finding solutions that catered specifically to their application needs.
Superbolt tensioners are premium products and while there are cheaper alternatives in the market, Sodick firmly believes that the cost performance of the product makes it appealing. About half of Sodick’s products are sold overseas, and some big machines cannot be shipped assembled. It is essential that the moulding machine assembly and changing of parts can be carried out easily, quickly and safely at the end-customer site. Sodick is pleased to hear reports that their customers are satisfied with having smooth, speedy operations.
Operating for over 80 years, Boskalis Westminster is a leading global dredging and offshore contractor and maritime services provider. With safety and sustainability as their core values, the company has a long track record of successfully completing projects in different types of challenging offshore environments.
Among the multitude of machines and equipment Boskalis can boast, their fleet of dredgers is particularly impressive. In demanding offshore environments with limited MRO access, efficient and problem-free operations are crucial.
For one of their biggest dredgers – backhoe dredger Baldur – Boskalis has chosen Expander as their supplier of pivot pins.
Expander solutions are developed to function in extreme environments like the offshore industry, and Boskalis did not hesitate to put them to the test.
The pivot pin supplied by Expander for this project, mounted between the boom and dipper arm, is by far the largest that the company has designed and manufactured inhouse. The pin is 2230 mm long with a diameter of 320 mm and weights a whopping 1.5 tons. The sleeve alone weights 95 kg.
Downtime and production shortfalls due to pivot wear are no longer an issue for Boskalis. Expander’s design has prolonged the life span of their dredger fleet and improved their performance.
First published in Bolted #2 2016.
Project: San Francisco–Oakland Bay Bridge
Overall project cost: $6.4 billion
Application: Replacing the bridge’s east span
Boltight solution: Hydraulic bolt tensioning of cable band bolts
Contractors: American Bridge/Fluor
Engineering projects don’t get much bigger. A suspension bridge with only one tower, on limited bedrock, with ten lanes of traffic that has to be able to withstand the largest earthquake expected over a 1,500-year period.
In a 2006 joint venture contractors American Bridge and Fluor got the assignment to build the new eastern span of the San Francisco–Oakland Bay Bridge, the largest public works project in California’s history.
Most suspension bridges have multiple towers, explains Brian A. Petersen, Vice President – Western Region, American Bridge: “This bridge span only had a single tower and is essentially anchored on itself. The main cable is seated in the deck, which is an extremely involved structural engineering design achievement.”
A total number of 114 cable bands, secured around the main cable to keep the suspender ropes in place, needed to be bolted with exactly the right amount of tension. High-strength rods, which secured both the main tower as well as the bearings and shear keys at the bridge’s east end, required a high-capacity jacking system to obtain the large clamping force that the bolts were required to achieve. Over 2,000 fasteners were tensioned using the Boltight hydraulic bolt tensioners.
“Boltight’s system elongates the rod and tightens the nut, but never turns the rod, which was an important design requirement,” says Petersen. “Their equipment allowed us to properly tension the high-strength rods and bolts in a very limited space. The equipment had a high level of accuracy, and our workers could easily carry it around. No other manufacturer could meet our requirements.”
As the holiday season is upon us, the Nord-Lock Group would like to take this opportunity and wish everyone Merry Christmas and Happy New Year! With recent acquisitions and new technologies in our product portfolio it’s been quite a year for us all! We hope that 2016 has been just as memorable for you and everyone who has been helping us fulfil our mission of safeguarding human lives and customer investments.
This year the Nord-Lock Group is making a donation to Reach for Change charity on behalf of all employees. Reach for Change is an organization that finds exceptional social entrepreneurs – people that are passionate about creating a better world for children and who have an innovative idea on how to do it, and then helps them succeed. Read more at http://reachforchange.org/en/.
First published in Bolted #2 2016.
The development of new materials, for example glass-fibre reinforced plastic (GRP), has set new trends for the infrastructure of railway companies. Materials on the tracks, such as steel and timber, are increasingly being replaced by GRP for grates, walkways, bridge coverings, escape routes and service access ways. GRP makes these elements weather-resistant, slip-proof and thus safer.
Their simple, modular design, but also their low weight and high strength, make GRP profiles increasingly popular with railway operators for entire structures, such as railings, ladders, suspended stairways and work platforms. Another GRP advantage, compared to steel, is the fact that you don’t have to earth the entire structure, as the material is an electrical insulator. It is also resistant to corrosion, which significantly reduces the costs for maintenance.
Deutsche Bahn AG in particular has decided to make greater use of GRP in its infrastructure. This makes DB a trendsetter for Europe, since railway operators in neighbouring countries take cues from the continent’s largest railway industry company.
“This is a trend, because Deutsche Bahn has a complete understanding of this material’s advantages,” says Philipp Wilczek, Junior Partner and Sales Director at CTS Composite Technologie Systeme GmbH – a technology leader in the field of glass-fibre reinforced plastics. Products and structures made of GRP must be bolted together and these bolted joints can be problematic. To overcome this, CTS has decided to use the Nord-Lock X-series bolt-securing system. Maik Hartmann, Technical Director at CTS, explains: “Our material is low-maintenance in principle. However, in order to make the entire structure low-maintenance as well, we needed a solution for securing the bolts, so that we could expand the material’s advantages to the connecting elements as well.”
On or close to the tracks, shaking and vibrations from train traffic must always be expected. An increased loss of preload due to slackening (settlements and/or relaxation) should be considered when using new materials. Nord-Lock X-series washers combine the wedge-locking principle with a spring effect to prevent loosening caused by settlements and relaxation. This way, they enhance the advantages of CTS’s GRP products to offer the railway industry a safe option with many advantages.