UBC International Training Fund

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UBC International Training Fund
Presents
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Computing Torque
PRESENTED IN COOPERATION WITH HYTORC
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• The following material is intended to make you
  awareof the currently acceptable and recognized
  methods of performing the tasks described in this
  presentation. However, every possible
  application of these methods cannot be foreseen
  and the following material is not designed to
  cover every potential application. Therefore,
  you must always follow all current procedures and
  safety regulations whenever you perform any of
  the tasks discussed in this presentation.

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HOW MUCH TORQUE IS RIGHT FOR A PARTICULAR BOLT?
In Your Work You Will Most Often Be Given Torque
Specifications In The Form Of A Torque Chart.
Behind The Numbers Are Factors Which Can
Change The Torque Values - Some Of The Major Ones
Are

• BOLT STRENGTH
• DESIRED TENSION
• BOLT DIAMETER
• LUBRICATION
• THREAD PITCH
• BOLT CONDITION

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FACTORS AFFECTING TORQUE
BOLT DIAMETER
Everything Else Equal, A Big Bolt Will Stand More
Torque Than A Small One
Pre-load ( Remember, This Is What We Really
Want) Is Measured In Pounds Per Square Inch
Radius ½ Diameter B 3.14 Area B (r2)
1 bolt .79 sq.in.
2 bolt 3.14 sq.in.
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FACTORS AFFECTING TORQUE
BOLT STRENGTH
A High Strength Bolt Will Stand More Torque Than
A Soft Bolt
S.A.E.
S.A.E.GRADE 7 115,000 P.S.I.
S.A.E.GRADE 8 130,000 P.S.I.
S.A.E.GRADE 5 90,000 P.S.I.
_______________________________________________
_______________________________________________
YIELD
CLASS 5.8
CLASS 8.8
CLASS 10.9
METRIC
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FACTORS AFFECTING TORQUE
DESIRED TENSION
Bolts Are Tightened To A Given Percent Of Their
Yield Based On The Engineered Requirements Of The
Job
50 Of Yield Means 50 Reserve Strength To
Withstand Dynamic Shock And Still Spring Back
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FACTORS AFFECTING TORQUE
Remember The Example Of The Pipe Flange
Pre-load Per Bolt _at_50of Yield 58,000 Lbs. 24
Bolts 1,392,000 Total Lbs. If The Pressure
Trying To Escape Is Less Than That Then The
Flange Will Seal
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FACTORS AFFECTING TORQUE
LUBRICATION
A Lubricated Bolt Will Turn Easier Than A Dry One
Friction (dry) 30 \ Friction (oil)
20 Friction (grease) 10 /
3 TIMES THE TORQUE (DRY VS. MOLY GREASE)
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FACTORS AFFECTING TORQUE
THREAD PITCH
It Makes A Difference Whether The Threads Are
Coarse Or Fine
But Almost Every Bolt You Will See Will Be
Standard 8 Threads Per Inch
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FACTORS AFFECTING TORQUE
BOLT CONDITION
New Turns Easier Than Old, Smooth Turns Easier
Than Rough
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SAMPLE TORQUE CHART SHOWING FACTORS AFFECTING
TORQUE PRE-LOAD STRESS _at_ 50 OF
MINIMUM YIELD STRENGTH (TORQUE IN
FT/LBS) THREADS HVY.HEX
S.A.E. GRADE 5
S.A.E. GRADE 8 STUD DIA. PER INCH. NUT
SIZE 45,000 P.S.I. AT THIS TORQUE
60,000 P.S.I. AT THIS TORQUE DRY
MCHN.OIL MOLY-DS DRY
MCHN.OIL MOLY-DS 1" 8 UNC 1-5/8" 533
361 172 800 542 258 1-1/4" " 2" 1023 693
330 1535 1040 495 1-1/2" " 2-3/8" 1817
1231 586 2725 1846 879 1-3/4" " 2-3/4" 2905
1968 937 4357 2952 1406 2" " 3-1/8" 4334
2936 1398 6501 4404 2097 2-1/4" " 3-1/2" 61
69 4179 1990 9254 6269 2985
2-1/2" " 3-7/8" 8457 5729 2728 12685 8593
4092 2-3/4" " 4-1/4" 10180 6896 3284 15271
10345 4926 3" " 4-5/8" 13522 9160 4362
20283 13740 6543 3-1/4" " 5" 16787 11372
5415 25180 17057 8123 3-1/2" " 5-3/8" 20953
14194 6759 31429 21291 10139
3-3/4" " 5-3/4" 25761 17451 8310 38642
26177 12465 4" " 6-1/8" 31248 21168 10080
46872 31752 15120
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Lets Try A Few Questions To Ensure We Understand
About Torque And Pre-load
(Quiz 2)
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The End