What type of bolt is best for installing shaft couplings?
There are many components involved in wind turbine operation that must be joined safely, efficiently, and accurately. Shaft couplings is one of them.
These high-speed couplings often use fitted bolts. Tough demands are placed on the tolerances and surface finish of bores (precise holes in flanges) because torque transfer is dependent on their rigidity and strength. Even when the flanges are fitted together during assembly, the bores often require further rework. Wind is a challenging application for them because couplings can be difficult and expensive to install and remove.
One solution used in a variety of industries, including wind power, is an expansion bolt assembly. The design features multi-jackbolt technology combined with a split-tapered sleeve. The tensioners allow installing and removing the expansion-bolt assembly with only hand tools, alleviating the need for high-power tools.
The above photo depicts an expansion bolt assembly. In this configuration, a split-tapered sleeve (2) is first placed on a tapered stud (1) and inserted into the bore. The sleeve has a clearance fit and easily slides into the bore. The spacer (3) and multi-jackbolt tensioner (4) install on side A. The tensioner pulls the tapered stud into the expanding sleeve thus generating a radial force. The multi-jackbolt tensioner (5) is then installed on side B so it can pull the flanges together and generate an axial clamping force. This tensioner is also used in the removal process to release the tapered stud from the sleeve.
The design eliminates radial clearance and creates a radial pre-load. In operation, there is no one-sided lift-off of the tapered sleeve from the bore because the split-tapered sleeve remains in contact with the bore. The sleeve also increases the rigidity of the connection, eliminates harmful micro-movements in the split line, and compensates for wider tolerances of the bore.
What’s more, an expansion-bolt assembly offers substantial cost savings by eliminating destructive removal procedures and expensive repair of distorted bores. No honing or machining is required because the split sleeve compensates for small variations. Only line boring of the holes is necessary. Also, the expansion bolts are reusable because the split sleeve springs back to its original size after each removal. Lastly, the tensioners are installed and removed with only hand tools, which greatly increases worker safety.
What is a multi-jackbolt tensioner?
A “Superbolt” or “multi-jackbolt tensioner (MJT)” is a direct replacement for hex nuts, covered nuts, bolts, etc. They spin onto your existing bolt or stud and provide a better way to bolt up your joint. They consist of three components, shown to the left.
If you are tightening a nut greater than 1″ in diameter, you may find Superbolts useful, since the torque you need to tighten conventional nuts and bolts exponentially increases as the size increases. Our products solve this problem and only require hand/air tools to install or remove any size MJT. They eliminate the need for time consuming and unsafe bolting equipment such as sledgehammers, hydraulic wrenches and stud heaters.
Multi-jackbolt tensioners come in a variety of sizes and configurations. We have many stock items that are available for immediate shipment, and we are able to handle custom jobs quickly. If you are experiencing bolting problems such as leakage, thread galling, unsafe working conditions or are using expensive methods and find it difficult to properly bolt your joint, this bolting technology may be for you.
By Steve Busalacchi, Global Product Manager, Superbolt
Filed Under: Components, Featured, Turbines