Windpower Engineering & Development

  • Home
  • Articles
    • Most recent posts
    • News
    • Featured
  • Resources
    • Digital issues
    • Podcasts
    • Suppliers
    • Webinars
    • Events
  • Videos
  • 2025 Leadership
    • 2024 Winners
    • 2023 Winners
    • 2022 Winners
  • Magazine
  • Advertise
  • Subscribe

Many Jackbolts Make Lighter Wind Work

By Windpower Engineering | March 1, 2011

Allan Steinbock

Allan Steinbock, VP – Sales, Superbolt Inc.,www.superbolt.com

multi-jackbolt tensioner

The cutaway of a multi-jackbolt tensioner shows how tightening the jackbolts puts the main bolt in pure tension

Nuts and bolts may be the most common elements in any piece of machinery. They’ve been around so long the average person doesn’t give the technology much thought. Engineers, however, know better.

The wind industry presents several bolting challenges. It’s critical to get tower and turbine joints tightened correctly and in the safest, most economical way possible. But it’s not always easy.

The problem is that the amount of torque required to attain a given preload increases exponentially with bolt diameter. As a result, special tooling, such as hydraulic wrenches, is usually needed to generate a required preload. For wind turbines, this means lugging expensive and heavy tooling up to some pretty interesting places. Such methods can also cause problems with joint integrity, or do not provide consistent bolt load across the bolted surface. The bottom line: It’s no small task to generate preloads on large diameter, hex-head bolting with conventional hex nuts.

Low Torque graph

One alternative to using high-powered tools on existing nuts and bolts is the Multi-Jackbolt Tensioner (MJT). Rather than turning one large nut or bolt to obtain preload, MJTs use a number of smaller jackbolts threaded through the tensioner body. The benefit is that any size MJT tensioner can be installed and removed using a hand-held, electric or air-powered torque wrench. This is a huge advantage in wind turbine work because towers and nacelles makes it difficult to use heavy tooling.

Part of MJT

A multi-jackbolt tensioner consists of a nut body, several jackbolts, and a hardened washer.

How they work

The MJT consists of three components – a hardened washer, a tensioner nut body, and jackbolts. The jackbolts thread through the round tensioner body, or bolt head, and thrust against the hardened washer to stretch the stud/bolt and generate clamping force.

The torque needed to tighten each jackbolt tends to be small and easy to generate, thus enabling use of hand tools. The preload generated is directly proportional to the size and number of jackbolts used.

Benefits

There are several benefits when using MJTs. Besides increased worker safety and smaller tooling, the tensioners improve the entire bolting system. For instance, torquing conventional nuts and bolts can twist the main bolt, adding unwanted internal stresses and reducing its load capacity. MJTs tighten in pure tension, so there is no torsion on the main bolt. Also, because the main thread does not slide under load, there is no thread galling or seizing.

Another problem with hex nuts and bolts is that there’s a high stress concentration found on the first few threads. By comparison, the jackbolts in the MJT system create hoop stresses in the nut body, so the nut flexes out slightly at the bottom and in slightly at the top. This flexing distributes load throughout the entire thread engagement and adds elasticity, which means short, stubby bolts are much less likely to break from fatigue stress.

JackboltOne possible drawback to the MJT system seems to be the number of jackbolts that need tightening. One might think they would result in longer installation and removal times. Surprisingly, the opposite is true. The MJT system has been proven to reduce installation and removal times. For example, a 1.5-in. tensioner can be installed and tightened in about 1 min. 29 sec, while a 2-in. tensioner would take about 1 min. 33 sec.

So, if you are having problems bolting a critical wind turbine joint, or want to make bolting easier and safer for workers, the Multi-Jackbolt Tensioner system could be a viable alternative.


Filed Under: Components, Turbines
Tagged With: Fastening/Joining, Wind Turbine Design
 

Related Articles Read More >

GE expands New York wind turbine factory, creating 200 new jobs
Richardson Electronics unveils new line of pitch energy modules for wind turbines
GE supplying turbines for 200-MW South Dakota wind project
Leeward completes 3rd wind project in Colorado county

Podcasts

Wind Spotlight: Looking back at a year of Thrive with ZF Wind Power
See More >

Windpower Engineering & Development Digital Edition

Digital Edition

Browse the most current issue of Windpower Engineering & Development and back issues in an easy to use high quality format. Clip, share and download with the leading wind power engineering magazine today.

Windpower Engineering & Development
  • Wind Articles
  • Solar Power World
  • Subscribe to Windpower Engineering
  • About Us/Contact Us

Copyright © 2025 WTWH Media LLC. All Rights Reserved. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media
Privacy Policy | Advertising

Search Windpower Engineering & Development

  • Home
  • Articles
    • Most recent posts
    • News
    • Featured
  • Resources
    • Digital issues
    • Podcasts
    • Suppliers
    • Webinars
    • Events
  • Videos
  • 2025 Leadership
    • 2024 Winners
    • 2023 Winners
    • 2022 Winners
  • Magazine
  • Advertise
  • Subscribe