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Distributor's Link Magazine Spring 2019 / Vol 42 No2

116 THE DISTRIBUTOR’S

116 THE DISTRIBUTOR’S LINK BRUNO MARBACHER TECHNICAL BRIEFING: NUTS from page 32 Tests and calculations have shown that the first 4 nut threads support up to 40% of the entire load. After the 6th thread, the flank load in the normal thread becomes so low that it no longer contributes to the stripping resistance. The proper nut height was investigated by ISO (International Organization for Standardization). Tests showed that when the yield-tightening method was applied, nuts with 0.8 height would strip. This led to an increase of nut height, slightly higher than DIN nut heights. It should be noted that the yield-tightening method is essentially only applied to load critical bolted joints such as connecting rod bolts in engines. For a standard Inch nuts per ANSI, the height to thread diameter ratio is about 0.8 to 0.85 Mechanical Property Inch Nuts come in various grades. Metric nuts in various property classes. One can pair a nut with a higher grade /property class, with a bolt of a lower grade/ property class, but not the other way around. Proof load for nut M10 Class 05 29000 N Class 5 34200 N Metric nuts may also be marked with a “clock marking”. A dot at 12 o’clock, a dash at 8 o’clock, indicates class 8. Metric nuts come in 2 styles, style 1 and 2 , the nut height of style 2 is slightly higher. Heavy hex nuts have a more robust body, they are higher and have larger width across the flats. They are only covered by ANSI standards. Higher nuts could be used for bolted joints, where the nut has to be over-tapped to accommodate thicker coatings (hot dip or fluorocarbon coatings). Over-tapping may weaken the load capacity, the extra height will compensate. Manufacturing Of Nuts First, the nut blank is cold formed in several subsequent steps. The common grades are: Grade 2, 5, 8 The common property classes of regular metric nuts are: Class 5, 8, 10, 12 For jam nuts Class 04 and Class 05 *Since jam nuts have a lower proof load, a zero is put in front of the number indicating lower load capacity. The Wire is cut-off then Upset (cold formed) in 4 stages with final hole punching. The nut blanks are fed from the top. Spinning taps cut the threads into the blanks. Unlike regular tapping (tapping and backing out) nuts are tapped in a continuous process, using special nut taps. The tap is kept and centered in a sleeve by the already tapped nuts. They are fed on the frontside of the machine move along on the tap, they are ejected on the opposite side. Now you have it… that is the story of the nut. BRUNO MARBACHER

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