impact labor mgmt conference skidmore wilhelm presentation
TRANSCRIPT
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Torque vs. Tension
February 21, 2011
John O’Brien – Skidmore Wilhelm
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Overview - Tension vs. Torque Bolt Tension Calibrator (Skidmore) 4 Methods of Pre-Installation Verification
◦ Each method can be compromised without proper diligence
Best Practices (how to keep the inspector happy)
Outline
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What’s the difference between tension & torque?
Is it a big deal? 90% of torque overcomes friction (not tightening) Conditions outside control
of bolt manufacturer affects performance
Overview Tension vs. Torque
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What does a Skidmore do?◦ Simulates bolted joint◦ Measures Force in Lbs
How does a Skidmore work?◦ Hydraulic Load cell
Why is it used?◦ Test Bolts◦ Verify bolt tensioning
Bolt Tension Calibrator (Skidmore)
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Are bolts so different? Live Demonstration – Effect of Lubrication
Calibrator (continued)
Photo courtesy of Robert Shaw, President, Steel Structures Technology Center Inc.
Photo courtesy of Chris Curven, Vice President, Applied Bolting Technology
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Rusty bolts okay? Can’t I just lube them?
Calibrator (continued)
Photo courtesy of Chris Curven, Vice President,
Applied Bolting Technology
.
Photo courtesy of Chris Curven, Vice President,
Applied Bolting Technology
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Rusty bolts okay? Can’t I just lube them?
Calibrator (continued)
Photo courtesy of Chris Curven, Vice President,
Applied Bolting Technology
.
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Which bolts maintain lubricity?
Calibrator (continued)
Photo courtesy of Robert Shaw, President, Steel Structures Technology Center Inc.
Photo courtesy of Chris Curven, Vice President, Applied Bolting Technology
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Wrenches Compatible with Skidmore Units◦ Hand Torque Wrenches◦ Impact Guns◦ Electric Wrenches◦ Hydraulic Wrenches
Calibrator (continued)
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Turn of the Nut Calibrated Torque Wrench Direct Tension Indicators (DTI’s or “squirter
washers”) Tension Control Bolts
4 Methods of Pre-Installation Verification
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Turn of the Nut◦ Snug bolt◦ Mark bolt/nut/plate◦ Turn nut required amount– make sure
tension is at least 5% over required amount (see table)
◦ In structure bolt head must be prevented from turning
Turn of the Nut
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Turn of the Nut?
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Calibrated Wrench◦ Snug bolt◦ Tighten to tension plus 5%◦ Measure torque to move additional 5
degrees◦ Average 3 bolts assemblies
Calibrated Wrench
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Calibrated Wrench
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DTI◦ Snug bolt – Verify gaps with feeler gage◦ Tighten to tension plus 5%◦ Verify gaps with feeler gage◦ Squirter washers
Direct Tension Indicator
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Tension Control (TC) Bolt◦ Snug bolt◦ Tighten to spline break◦ Verify tension is correct
Tension Control Bolts
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Tension Control Bolts
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Proper setup of Skidmore◦ Seat parts◦ Proper Clamping◦ Oil Leaks (small leak okay…get fixed
when able) Spacers – Don’t stack washers!! Torque reaction arms? Spacer Bushings
Best practices (how to keep the inspector off your back!)
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Frequently Asked Questions◦ Temperature Effect◦ Calibrate the Skidmore? How often?◦ Is there a source for information on proper
bolting? www.boltcouncil.org Research Council Structural
Connections (RCSC) Structural Bolting Handbook – by SSTC
Questions?
Summary