When it comes to locking mechanism solutions, Nord-Lock Group is at the forefront of the industry, having engineered a range of innovative products including the Nord-Lock wedge-locking washers that prevents bolts from loosening, the popular Expander System, which eliminates the need for line boring, and the extended downtime associated with the process.
The company also designed the Superbolt mechanical tensioner which is a safer, more reliable method of bolting large parts in heavy machinery together and Boltight hydraulic bolt tensioners and hydraulic nuts which are great for bolts on cutters and conveyors.
Australian Mining Review spoke with Nord-Lock Oceania general manager Jeff Jared about the innovative technologies, as well as other solutions the company offers in the way of locking mechanisms.
Expander System Pivot Pin Technology
All heavy mining equipment with parts that pivot undergo inevitable wear. Since the pivot pins are typically harder than the lugs and play is needed between the parts to mount the pin, the lug will undergo deformation and damage due to heavy impact associated with the harsh conditions of a mining environment.
The typical remedy for this is to park the machine up, drill the damaged lugs round, weld new metal into the lug lining and then re-bore the hole again to re-establish a tight tolerance between pin and lug.
This process is known as line boring and causes significant reduction to a machine’s availability.
“Not only is line boring with welding an expensive process but the downtime for the machine is significant.
For them to be shipped off site for line boring, they can be out for up to a week!” Jared said.
“A normal axle or pivot pin is just a straight bar and as it moves due to the needed mounting play, the pressure from the pin permanently deforms the lugs.
“Our system, the way it is designed, has a tapered pin on both sides with a sleeve. So, when you torque the axle along with the sleeve, it will fill in all the gaps of the lug eliminating the movement, thereby preventing any future lug wear. It will never wear out the lug.”
The Expander System’s versatility with the expanding sleeves eliminate the need for line boring of a lug that is slightly worn.
“And if you have a lot of wear you can simply drill the lug hole larger and use an oversized sleeve, no need for welding or tight tolerances,” Jared said.
The ingenuity of the Expander System is such that it is a simple swap-out process that significantly reduces the machine downtime.
“We had a case in Queensland where we went on site, knocked out the pin, put the Expander System in within 30 minutes and the machine was up and running again,” Jared said.
The high-quality steel used in the Expander System ensures a long-lasting life which contributes to the increased availability of the machine. Nord-Lock Group designs and manufactures just about any size, diameter and length of pin. The designs can be adapted to the needs of the applications such as space constraints, single side mounting or flush mount.
“We’ve had a customer test our Expander System in one location for longer than 50,000 hours, after which they stopped the test since it had already passed their traditional straight pin test time multiple times over,” Jared said.
“We currently have a database of about 70,000 pin designs, all made to order. The production time is anywhere between two to five days and then we ship them over from Sweden.
“Anything that has a pivot, we can design it to suit. The customer can also use our online portal, look up the make and model of the machine, find the pin location and say, ‘Yep that’s the one I want!’ And in 2021 the customer will be able to go online and order the part they need directly from the portal.
“We’ve produced a product for a Terex MT4400 Truck in WA which was made to order – it’s a really massive size pin and we’re currently doing the installation.
“As far as credibility goes for the Expander System – they’ve been specified as both first fit and repair solutions by most OEMs within mining, construction and forestry heavy machinery.”
Superbolt Mechanical Tensioners
A typical nut and bolt combination is used to join parts together – however, for bolt diameters over one inch, it becomes increasingly difficult to create enough bolt load using typical torque-tightening methods (for example, heavy torque wrenches, and in some cases large spanners and sledgehammers) to tighten or loosen the bolts.
A variety of bolting methods are available today, though many of these methods can lead to worker injury, strain injuries, inaccurate preloads, thread galling, difficulty removing the bolt, high equipment costs and excessive downtime.
Nord-Lock Group’s Superbolt mechanical tensioners allow the fitter to achieve high preloads while only using simple hand tools.
They are designed for direct replacements for hex or other standard nuts and bolts and offer a significant mechanical advantage. Since only hand tools are required, worker safety is greatly increased.
Instead of applying a torque to the bolts, the Superbolt Tensioners stretch the bolt using pure tension.
“A heavy hydraulic tensioner uses a hydraulic pump to create the tension, whereas the Superbolt uses mechanical tensioning,” Jared said.
“The way the mechanical tensioning works is a similar concept, but without requiring a hydraulic pump.
“You just hand-tighten a nut onto the spot face where several jackbolts get torqued up; then the Superbolt nut gets pushed against a hardened washer which then stretches the bolt or stud using torque from the jackbolts.
“Superbolt uses our mechanical Multi- Jackbolt Tensioning (MJT) technology and creates a massive clamping force with very little torque requirement.
“Hypothetically – for a 6” bolt with 1.2m lbs of load, you’re looking at about 55,000 ft- lbs of torque. Using Superbolt, you can achieve that same load with only 189 ft-lbs of torque.
“Usually, when dealing with huge threads, installers typically apply heat and then screw down the nut, or they will use a hammer and a spanner, in which case they have no idea what kind of load they’re applying to the joint.
“Alternatively, they might utilise massive, expensive hydraulic torque wrenches to apply the necessary torque.
“Whereas with Superbolt, all you need is a hand tool to individually tighten the jackbolts.
“For example, a 2-inch thread on a mining truck application contains 12 bolts. Prior to the Superbolt, they were using a 25kg hydraulic torque wrench in a very confined space with two people holding the torque wrench in place to torque up this bolt.
“It would take around 16 hours to do the install. We introduced the Superbolt technology to our customers, which improved the installation time of our mining strut application to under four hours.
“The other advantage created because we’re using pure tension instead of torque, is that the strut assembly spot face is getting a much more reliable joint connection.
“When they take the strut assembly off, there’s not a lot of shearing or spot face damage that is created from the joint, which reduces downtime when they’re ready to put on a new assembly, it’s a simple swap.
Whereas prior to the Superbolt, it would require machining and all sorts of repairs.
“It’s a huge time-saver and massive safety advantage because they’re no longer lugging around a 25kg torque wrench or using sledgehammers to tighten the bolts.”
Boltight Hydraulic Tensioners
Nord-Lock Group’s Boltight hydraulic bolt tensioning tools are used extensively across many industries where bolt load accuracy is critical. As bolts increase in size, the load critically increases, and operators are faced with the challenge of ensuring bolt load accuracy.
“When tightening a bolt by any method, the operator is aiming to achieve the correct bolt elongation. Due to friction, this can be difficult to accurately control when using traditional torque tightening methods,” Jared said.
“Using high pressure hydraulics and a predetermined pressure, Boltight hydraulic bolt tensioners axially stretch the bolt. The nut is then rotated down the joint face, accurately locking in the bolt load.
“Preload is accurate, and can provide an enormous amount of load into a joint with a lot less effort involved. You eliminate pinch points and don’t have to lift heavy hydraulic torque wrenches, which can weigh up to 20kg-30kg, so there is a safety benefit.”
There are many advantages to using hydraulic bolt-tensioners, including speed of tightening. Multiple bolts can be tightened simultaneously by using sequential tensioning such as 100%, 50% or 25% of the total bolts in a flange.
Underground mining applications such as longwall shearers are difficult to get to the coal face due to their size: they are built in sections and each section is bolted together normally with grade 10.9 bolts from M24 to M48 depending on the size of the shearer.
On average each section will have 12 bolts and a typical shearer will have five sections, making a total of 60 bolts. Due to space restrictions these bolts are generally tensioned using specially designed hydraulic nuts.
It is also common for the shearer to be bolted to an under frame and again these bolts are quite frequently tensioned with hydraulic nuts.
Other applications are the continuous miner, the road header, armored face conveyor, crushers and sizers which also suffer from enormous forces on main joints which can lead to joint separation and potential bolt failure due to fatigue.
So why use hydraulic tensioners and hydraulic nuts on these types of application?
There are longer sustained production periods, and less maintenance time is needed attributed to the fact the hydraulic nuts hold joints together preventing adverse vibration forces being transmitted.
When blades need replacing on cutters the hydraulic nuts can all be removed and replaced simultaneously.
Boltight hydraulic tensioners ensure a high and evenly distributed bolt load is achieved significantly reducing premature joint failure. This improves coal production and reduces maintenance costs.
Nord-Lock Wedge-Locking Washers
Nord-Lock Group’s Wedge-Locking Washers are another locking mechanism designed to reduce the impact of vibration creating more reliability in the bolted joint.
Wedge-locking washers utilise tension instead of friction to secure bolted joints exposed to vibration and dynamic loads. Since friction is not a reliable locking method, the bolts require retightening at regular intervals to prevent downtime or incident.
Wedge-locking washers create a wedge effect whereby the cam inclination is greater than the pitch of the thread of the bolt, which lock together and prevent any rotation in the nut.
“Nord-Lock Wedge-Locking washers are a well-proven method effective in the securing of bolted joints, verified by test institutes like DNV, TUV and others. Once correctly installed no amount of vibration will be able to make the joint loosen,” Jared said.
“The washers have cams on one side and radial teeth on the other. They are installed as pairs, cams against cams. The key to this solution is the cam angle of the washers.
“The cam angle alpha is larger than thread angle beta. Due to the difference in these angles, if the bolt or nut should rotate in the loosening direction, it would have to take the washer with it, and climb the slopes of the cams. Instead of loosening, a wedge effect is created making the joint tighter.
“There is no need to use any glue when Nord-Lock washers are used. The wedge-locking function of the Nord-Lock washers is so effective that the washers can be used in critical applications, even for joints immersed in oil since the washers do not rely on friction to secure.”
Nord-Lock wheel nuts incorporate a pair of captivated washers with cam faces on one side and radial teeth on the other.
When the wheel nut is tightened, the radial teeth on the lower washer are embedded into the mating surface.
The wedge-effect is similarly created, allowing movement only across the cam faces. Any rotation of the wheel nut is blocked by the wedge effect of the cams.
“Nord-Lock safety wheel nuts are easy to install, and you only need to retorque once after installing, they never come loose unintentionally,” Jared said.
“So costly downtime and safety risks are significantly reduced. And these wheel nuts are reusable, offering an extended lifetime over conventional wheel nuts.”
When the Nord-Lock wedge-locking washers are tested using the Junker Test (a mechanical test designed to test bolt load response to vibration), results show that the clamping load of all solutions (e.g., no washer, plain washer, adhesive, spring washer, tab washer, locking wire, nylon insert nuts, and double nuts) drops dramatically apart from the Nord-Lock washers.
A second pass of the Junker test shows that the wedge-locks do not require retightening even after additional dynamic load is applied, illustrating the additional safety and reliability gained through the simple yet effective geometric design.
Find out if your selected bolt securing solution is securing your equipment here: https://www.nord-lock.com/campaign/bolt-securing-options
Nord-Lock Group has been providing customers with high quality, safe and innovative bolting solutions since 1982.
Nord-Lock is able to service customers all over the globe including Europe, the Americas, Asia and Australia, through the use of its comprehensive network of local sales offices and authorised distributors.
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