1 UBC International Training Fund Presents

Computing Torque

The following material is intended to make you aware of 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.

4 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

5 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 (r 2 ) 1” bolt =.79 sq.in.2” bolt = 3.14 sq.in.

6 FACTORS AFFECTING TORQUE BOLT STRENGTH A High Strength Bolt Will Stand More Torque Than A Soft Bolt 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. _______________________________________________ CLASS 5.8 S.A.E. METRIC CLASS 8.8CLASS 10.9 YIELD

7 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

8 FACTORS AFFECTING TORQUE Remember The Example Of The Pipe Flange Pre-load Per 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

9 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)

10 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

11 FACTORS AFFECTING TORQUE BOLT CONDITION New Turns Easier Than Old, Smooth Turns Easier Than Rough

12 SAMPLE TORQUE CHART SHOWING FACTORS AFFECTING TORQUE PRE-LOAD 50% OF MINIMUM YIELD STRENGTH (TORQUE IN FT/LBS) THREADSHVY.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-DSDRY MCHN.OIL MOLY-DS 1"8 UNC1-5/8" /4""2" /2""2-3/8" /4""2-3/4" ""3-1/8" /4""3-1/2" /2""3-7/8" /4""4-1/4" ""4-5/8" /4""5" /2""5-3/8" /4""5-3/4" ""6-1/8"

13 Let’s Try A Few Questions To Ensure We Understand About Torque And Pre-load (Quiz #2)

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