Bolt & Nut Tension, not bolt & nut torque (June 10, 2010)

Bolt & Nut Tension, not bolt & nut torque,Bolt pattern, Bolt Torque specification, Bolt Heater, Bolt grade, Shear bolt, High strength bolt, Stainless bolt, Aluminum bolt,Bolt gage,Bolt failures,Bolt tension,Flanges,Stress,SureBolt

 Bolt & Nut Tension, not bolt & nut torque
  
Which choice of: Bolt pattern, Bolt Torque specification, Bolt Heater, Bolt grade, Shear bolt, High strength bolt, Stainless bolt, Aluminum bolt? Why all these choices, just to get tension into a joint?

Engineers take classes on bolt & nut specs, so why do some bolts fail? Because getting the correct pre-load tension into a bolt and nut is even harder to implement, than it is to calculate.  And if you think calculating the correct torque is easy, just see either of these two web pages (no affiliation with FAST-DAQ or any bolt gage manufacturer), "nut factors" or "torque is not easy". With SureBolt, instead of calculating the torque to get you the correct tension, you just measure the tension directly. You can even use SureBolt to determine the torque and its variation in tension.

Verify your bolted joint design. Bolt and nut selection are affected by many factors:

1.   Friction. Engineers know that bolt and nut friction consume over 80% of the torque measurement.  But, how does the actual tension vary bolt to bolt?  What if you use the same type of bolt? It still varies more than 20% (flange bolts vary even more: see #7).

NDT Update says: 
" SureBolt outperformed the one-point bolt gauges on every bolt and every test in reliability and accuracy."

2.   Bolt failures. What do bolted joint designers say the number one reason, stated by bolting experts, for bolt failures? Lack of proper pre-load tension. What are some of the factors that cause pre-load tension errors? Why are the bolt torque specifications not enough? Can't I just choose a good wheel bolt pattern?

3.   Measure Tension errors. How can an engineer measure torque wrench errors?  Do these bolt tension errors matter? And If you think calculating the correct torque is easy, just see either of these two web pages (no affiliation with FAST-DAQ). Do you think nut factors or torque calculations are easy? With SureBolt, instead of calculating the torque, to get you the correct tension, you just measure the tension directly. You can even use SureBolt to determine the torque.

4.   Bolt gage. Your bolt's stress analysis can be verified using a bolt gage. What is an ultrasonic bolt gage?  See an animated demonstration of an ultrasonic echo inside of a bolt.  Mechanical engineering labs rarely have enough resources to let each engineer learn ultrasonics. Are bolt gages reliable? Are they easy to use? New patented technology has finally made ultrasonic bolt gages reliable and easy to use.

5.   Bolt tension, not bolt torque. Tension not torque. You want to put a known amount of tension into your nut and bolt combination, not just a known amount of torque. Your bolted joint design often relies on proper pre-load tension.

6.   Stress, strain & yield. A stress strain curve can be plotted using SureBolt.  Stress strain and yield.  SureBolt can help a engineer verify his bolted joint design.  Did his bolt reach yield?

7.   Flanges. Flange joints sometimes leak.  Why does the tension in a flange bolt vary so much, bolt to bolt?  Tightening one bolt loosens some others. No matter how many passes, the tension can vary over 50%.  How can you tighten each flange bolt to closer tolerances?  How can you use SureBolt on a flange? 
Notice the variation in bolt tensions on each of three passes with a torque wrench.

Credit Integra Technologies for this graph. They have taken data on 94 joints. They mislabeled the first pass (it should show 100 Pound-Feet instead of 200 Pound-Feet)
 
 X-axis = bolt position. 16 different bolts
Y-axis = bolt stretch (tension).
Large tension variations are typical with torque control. Notice the > 250% variations.

8.   SureBolt. How does SureBolt differ from any other ultrasonic bolt gauge? What is the difference between a one-point bolt gage and SureBolt's patented whole echo method? Are the prices similar? (Yes)

9.   Engineering. Some engineers use a strain gauge to measure bolt tension because they know a torque wrench is not directly measuring tension. This site is an engineering resource for torque versus tension in bolted joints. 

< Back >

Other News

New and Improved Sockets to Install Trident Nuts

HEX NUTS

Notes on Nuts and Bolts

Nuts and Bolts about Fasteners, Chapter Two - Nuts

Types of screws

High tensile bolts