Engineers at Boltech Mannings, West Newton, Pa, suggest a better way to tighten a nut or tension a bolt. Traditional methods of tightening nuts, bolts, and studs such as slugging, hand wrenching, or impact wrenching, says the company, are often inefficient and dangerous. Accurate and dependable axial loading is difficult with traditional methods. Measuring torque is an unreliable method for determining bolt load, because tighten a threaded fastener wastes up to 80% of the energy required to overcome friction. Hydraulic tensioners may be the better way. The firms says advantages include:
Safer operation because hydraulic tools minimize exposure to hazardous environments. Safety is more assured by eliminating the “hot bolting” methods that introduce a fire risk and can break bolts.
Better accuracy comes from tightening a bolt after directly applying the tension load, as opposed to a twisting force (torque) on the nut. The effects of friction are negligible when the bolt is tensioned first.
Uniformity comes by ganging several hydraulic tensioners for simultaneous bolt tightening. This eliminates uneven bolt loads and produces a reliable seal. Leak-free connections call for uniformity in gaskets pressure.
Shorter work cycles result when tightening many bolts simultaneously. This reduces assembly time for multibolted connections. Most hydraulic tensioners can be used with minimum effort and maximum safety.
Hydraulic devices are compact and versatile. Hydraulic tensioners are easily used where space limits traditional tightening methods. The tool is relatively light and simple to install. Any type of thread can be used and a variety of pulling heads are available.
Closer look at the tool
A hydraulic bolt and stud tensioner is a simple tool with four primary parts. A nut retaining disk, the first part applied, slides over the nut. Holes in it allow turning it with a device called a tommy bar. A bridge then keeps the entire tensioner just hovering above the nut and around the bolt/stud. Next, a hydraulic load cell attaches to the bridge and surrounds the bolt or stud. With the socket, bridge, and load cell in place, a worker screws down a puller into the load cell and onto the bolt or stud. The tensioner is completely attached and ready for service.
How it works
High-pressure fluid from the company’s TP30K pump pressurizes the hydraulic load cell which creates force that lets the tensioner stretch the stud. Doing so also lifts the nut off the flange. A worker turns the nut retaining disk with a tommy bar to return the nut to its seated position.
With the nut tight against the flange, pressure in the load cell is released and the stud remains stretched with the load locked in.
Bolttech says its Delta Series of bolt tensioners maximize efficiency and minimize size for specific single stud size applications. A few features include a patented high pressure and low-friction seals that outlast competitive brands and provide accuracy within 0.5% with a calibrated pumping unit. What’s more, Delta Series Hydraulic Nuts replace existing hexagon nuts for quickly placing an accurate and uniform bolt load to any bolted joint. The company offers a method of tensioning multi-bolt assemblies (such as a flange) which greatly improves the joint integrity. The speed at which joints can be tensioned and detensioned allows spending significantly less time than conventional detachable bolt tensioning systems.