HEICO-TEC tension nuts provide quick and easy preloading for particularly large bolted joints and are available in a wide range of standardised sizes. However, what happens if the standard does not fit? At the end of last year, HEICO Group faced a truly big and unusual challenge – manufacturing a special tension nut with an outer diameter of 620mm.
This gigantic tension nut was used to fasten a large hydraulic cylinder that is used in a mono pile rolling machine, which can produce large pipes and mono piles with a diameter of up to 12m. A conventional bolted joint of this size, with a thread diameter of 320mm, would theoretically require a tightening torque of more than 1.1 million Nm.
This special HEICO-TEC tension nut was designed to be able to create a pre-tension of 23,000kN, which corresponds to 2,300 tonnes.
“Considering that a vehicle with a conventional two litre petrol engine creates a torque of around 200Nm, approximately 5,000 vehicles with such an engine power would be needed to create the torque that produces the pre-tension force in a bolted joint of such dimension,” explains Sven Schierz, sales engineer for the HEICO-TEC division, who was responsible for this project.
Such enormous forces cannot be generated easily. The use of specially designed hydraulic tools that enable the preloading required can become expensive and also time-consuming – especially when a quantity of only one piece is required. An assembly in which the tied rod would be thermally heated is also a very time-consuming and work intensive method.
This is exactly where HEICO-TEC tension nuts make the difference. Two HEICO engineers took just 2.5 hours to assemble this giant tension nut. Pre-assembly of the 525kg tension nut colossus was completed in an upright position supported by a crane before the entire hydraulic cylinder, including the pre-assembled tension nut, was installed in the final upside down position in the machine.
Due to the special design of the tension nut, the force required for the pre-tensioning is distributed to 48 smaller pressure bolts of size M30. Each single pressure bolt was tightened with a tightening torque of approximately 1,080Nm. A conventional standard hydraulic tightening tool was all that was used by the HEICO personnel to complete the tightening process during assembly.
It is not just the unusually big size that makes this HEICO-TEC tension nut something special. To reduce stress on the bolted joint and increase the lifetime of the bolt, a so called ‘Niemann’ thread was applied on the main thread in this project.
“Tension nuts with these dimensions are rather out of the ordinary,” says Tobias Grobe, head of sales and marketing at HEICO Group. “However, we are very excited to see what extraordinary challenges our sales and development engineers will face in 2022.”
Having spent a decade in the fastener industry experiencing every facet – from steel mills, fastener manufacturers, wholesalers, distributors, as well as machinery builders and plating + coating companies, Claire has developed an in-depth knowledge of all things fasteners.
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