An evenly tensioned series of bolted joints is critical to the safe, low maintenance and cost-efficient assembly and disassembly of many types of equipment used throughout the mining industry, Technofast says.

Secure tensioning of a series of bolts on equipment such as comminution machinery, gearboxes, motors, vibrating screens and turbines is critical, because bolted joints are designed so the individual fasteners apply a collective compressive load greater than the working forces, which try to separate the components. Any under-tensioned bolt sheds excessive load onto nearby fasteners, which may be overstressed and fail, thereby causing loss of mechanical integrity and severe damage.

Second and conversely, if bolts are overtightened, then the elastic limit of their steel material may be exceeded and lead to premature failure. Additionally, the area under the bolt head or the nut could be crushed with resulting damage to the joint components.

The ideal means of tightening a bolted joint is to energise all the fasteners simultaneously using a bolt tensioner or hydraulic nut. As these can be connected in a ‘daisy chain’, force is applied evenly and equally to each via the increasing hydraulic pressure applied from a single point source.

“Whatever the reason for unevenly tensioned bolts, the outcome is never good. The fault ultimately affects machinery reliability, maintenance downtime – and potential risk to people working around them,” John Bucknell, CEO of Technofast precision engineered solutions, said.

Different versions of Technofast’s hydraulically-actuated EziTite® hydraulic nuts and CamNut® tensioning systems provide solutions to such issues where they are used to speedily apply and release bolted joints. Technofast’s bolting products are used to accelerate and make safer assembly and disassembly of machinery in applications in mining, particularly those production-critical applications under high pressure or heat, or those subject to intense vibration, Bucknell says.

Applications include machinery used globally across extractive industries including those for coal, copper, gold, iron ore, nickel, aluminium, bauxite, potash, silver, lead, uranium, ilmenite, zinc, zircon, lithium as well as quarries for sand, gravel, road base and construction materials.

“Rather than tightening the bolts by torque methods – that is rotation of the nut by hammering or use of torque wrenches, or alternatively, by using bolt heating methods – Technofast CamNut and EziTite HT hydraulic nuts use hydraulic force to stretch multiple bolts axially,” Buckell said. “They achieve exact tensions across a series of bolts by exerting the exact amount needed for the particular application on all of them simultaneously. They are then locked with their individual screwed Lock Rings to achieve reliable, even and precise tensioning the first time. Up to 100% of all the fasteners used in a particular daisy chain can be precisely fastened or released simultaneously.”

This type of speed and safety offered by standard and custom-made EziTite hydraulic nuts and CamNuts is valuable on mine sites, as shown by an application involving Newmont’s Boddington gold mine in Australia, which is one of the world’s largest gold mines.

Newmont’s particular high-stress application involved gearbox couplers on Polysius-Polycom PM8-24/17M high-pressure grinding roll machinery. Originally, installation was performed with two hydraulic bolt tensioners that required multiple passes of the bolts (40 in total).

Removal was then carried out with the use of a hydraulic torque wrench, which, in this application, was an extremely time-consuming process in a difficult and confined location.

“There was also the issue of inconsistent bolt loads in this application, plus the occupational health and safety issues with the use of hydraulic torque wrenches in this tough and time-consuming operation, which involved 10-12 hours and a team of six personnel,” Bucknell said.

The solution to the time, efficiency and safety issues involved a series of special M48 x 3.0 ultra-high tensile EziTite hydraulic nuts linked together over the 40 nuts involved.

Benefits borne out by this application included easy installation, as well as removal for maintenance (installation and removal are by the same method). In addition to fewer handling and fewer occupational health and safety issues, precise bolt loads were achieved across all the fasteners involved and installation and removal times improved dramatically, according to Technofast.

Bucknell said: “Compared with the 10 hours and six personnel involved previously, the new technology resulted in installations involving just three hours and three personnel. This radically improved time efficiency and costs, while substantially increasing safety, because the tensioning and release process was carried out remotely, simultaneously and immediately under precisely controlled conditions.

“The Technofast team working with the client in this application designed a special nut to achieve required size and particular strength requirements. Project management staff commented on the ease of fitting and the fact that the tensioning has reduced the overall time by two thirds and personnel from six to three. They said the implementation of the new setup allowed them to achieve the timelines required for shutdowns on these machines.

“These are typical benefits of Technofast hydraulic bolt tensioning over many installations and many countries, including those organised by our US office in conjunction with our global headquarters in Brisbane, from where we service Australia, Asia, Africa and Europe.”

Complementing Technofast’s EziTite hydraulic nuts, the CamNut system is designed for applications where longer bolts for standard bolt tensioners are not available or desirable, and for situations with elevated operational temperatures, such as pumps and steam valves.