FASTENERS FIRST LOOSEN WITHOUT TURNING!

Transcription

1 FASTENERS FIRST LOOSEN WITHOUT TURNING! "Settling down" is the term ESNA laboratory people use to describe a relaxation phenomenon that occurs at room temperature under static conditions. During the first few hours after a nut and bolt are tightened on an arbor, the fastener system has lost some of its pre-stress. The mechanical fits and finishes involved determine to a great extent how much initial clamping load will be lost. With precise, well-finished parts, this relaxation may be limited to 2 or 3 per cent of pre-stress. With rough surfaces, loose thread tolerances and lack of squareness, Schematic of all-metal fastener testing histories shows how bolt tension is lost first in the static condition and then, more rapidly, after vibration begins. The nut turns at a critical tension level. INITIAL BEST AIRCRAFT -QUALITY FASTENERS POOREST COMMERCIAL - QUALITY FASTENERS NUT DOES NOT TURN CRITICAL F _J w NUT ROTATES O FAILURE RANGE STATIC VIBRATION TESTING 13

2 as much as 1 per cent of the original loading may be lost. This stress relaxation is analogous to high-temperature creep. We suppose that it involves a gradual adjustment as localized zones stressed beyond the yield point transfer load to adjacent metal. Another mode of relaxation was observed by Professor Wright of the University of Illinois in connection with torque-tension studies of bolting for structural steel. He found that part of the pre-stress loss that occurred within a few hours after tightening was accounted for by rotation of one end of the bolt as it recovered from being twisted during tightening. When a retightened fastener system is subjected to a vibration test, loss of clamping force continues, but at a rate much slower than occurred initially. The nut does not turn on the bolt while that is happening. Nevertheless, bolt tension decreases as the vibration test progresses. The mechanism of loosening in this phase before any relative thread turning occurs is not known accurately. It is probably a combination of local yielding and wear. The vibrations tend to hammer down and wear away minute metal projections on all bearing surfaces. For any given nut type plain or self-locking intensity, resistance to loosening is influenced in at the start of the test. At the critical tension then comes off very soon. and a given level of vibration large measure by bolt tension level, the nut begins to turn, HIGH INITIAL BOLT TENSION z (7) z w MODERATE INITIAL BOLT TENSION CRITICAL LEVEL AT WHICH NUT BEGINS TO ROTATE ON BOLT _J CO LOW INITIAL BOLT TENSION VIBRATION TESTING 14

3 NAS NAS 333 thru NAS 34 1 Flush Head Bolt - Phillips Recess SPS Santo Ana, Calif. Only NAS 663 thru 668 Flush Head Bolt, Titanium Hi-Torque and Phillips Recess IIIIIIIIIII NAS 428 Crown NAS 673 thru 678, Titanium I o sal 16 NAS NAS 443 Internal Wrenching Nut 464 NAS :: ) S/S NAS 17 1 Flush Head Bolt I NAS 679 (96) Lightweight Sheet Metal Locknut NAS 679C, 9 F (97) NAS 68 and NAS 681 Nutt-Shel, Self-locking Plate Nut Two Lug SPS Santa. Ana, Calif. NAS 682 and NAS 683 Nuft-Shel Self-locking Plate Nut One Lug 1 NAS 6 Screw - Hi Temp 1 Flush Head 321 S/S, A286 or Inconel "X" as required NAS 684 and NAS 68 Corner 4 NAS 61 Spring Pin S/S and Carbon Steel NAS 686 Floating - Two Lug A1() NAS 63 thru NAS 72 NAS 687 Floating - One Lug NAS 83 thru NAS 9 1 Flush Head Hi-Torque Bolt 9, psi Min. SS NAS 696 Miniature - One Lug I CD NAS 67 Unbrako - Dowel Pin NAS 697 Nutt-Steel Self-locking Plate Nut Miniature - Two Lug n NAS 68 - NAS 69 Unbrako - Std. Socket Head Cap Screw NAS 624 thru NAS Point Bolt 41 NAS 63 thru NAS 68, Titanium NAS 698 Nutt-Steel Self-locking Plate Nut Miniature - Corner NAS 13 thru NAS 12 NAS 121 and NAS 122 Flexloc Nut - Self-locking Std. Regular Height and Thin Nuts

4 NAS continued NAS 123 and NAS 1 24 Two Lug NAS 11 1 Flat Fillister Head Screw, ', NAS 12 and NAS 126 One Lug NAS 127 and NAS 128 Nutt-Shel Self-locking Plate N'.t Corner NAS 131 Floating - Two Lug NAS 132 Floating - One Lug NAS 133 Floating - Right Angle NAS 167 Miniature - Modified Base NAS 168 Floating Miniature - Two Lug NAS 181 Hex Socket Set Screw - Self-locking o \1 I NAS Flush Head Screw, NAS 11 3 thru NAS 112 NAS 1121 thru 1128 Flat Fillister Close Tolerance Bolt NAS 1131 thru 1138 Pan Head Bolt, Close Tolerance, NAS 1131 thru 1138 (Titanium) Pan Head Bolt, Close Tolerance, NAS thru 1148 Brazier Head Bolt, Close Tolerance, NAS 11 1 thru Flush Head Bolt, Close Tolerance, NAS 183 thru Flush Head Bolt, Titanium Phillips and Hi-Torque NAS 11 1 thru 118 (Titanium) 1 Flush Head Bolt, Close Tolerance, NAS 196 Screw, Hex Head, Recessed Full Thread G NAS 1161 thru Flush Head Bolt, Self-locking, NAS 11 Pan Head Bolt, Alloy Steel and SPS Santa Ana, Recess A286 Calif. e NAS 1171 thru 1178 Pan Head Bolt, Self-locking, 17

5 AN737RM Radial-Machine Screw Type Clamp band is /8" wide and.2" thick for all sizes. The band is welded to the nut by certified spot-welding methods. This unit, when assembled to the bridge and its flexible bridge extender, provides a clamp which combines superior strength with uniform clamping action. Order by AN part number, per table below. Example: AN737RM22 is a single size, radial-machine screw type clamp having a minimum I.D. of 7/16". AN737 CLAMPS AN737 Hose Clamps are for use on fuel, oil and coolant lines. Installation can be made while hose is in place; clamps may be tightened repeatedly while in service. No lock wire needed. All parts of these clamps are made of stainless steel except the thumbscrews which are cadmium plated carbon steel. All clamps meet current MIL and AN specifications. AN737TW Tangential-Worm Screw Type The one-piece curved housing is spotwelded to the recessed band on certified equipment to form an integral unit. Contour serrations give greater band strength and are a perfect mate for the buttress thread of the screw for smooth clamping action. Order by AN part number per table below. Example: AN737TW22 is a single size, tangential-worm screw type clamp having a minimum I.D. of 7/16". Clamps are easily installed or removed with hose In place ORDERING TABLE AN737 Hose Clamps STRUT VALVES AN812-1 High Pressure Valve designed for shock struts and accumulators to permit inflation and gauging. Less AN89-1 core and AN813-1B valve cap. AN For use in high pressure shock absorber struts, hydraulic pressure accumulators, surge cylinders and high pressure pneumatic systems. Permits inflation, deflation and gauging of air cushions in these units. Supersedes the AN812.1 valve. Although not required on most aircraft, for design purposes it has been the current model since Consists of stainless steel stem, core, and MS cap. FOR 3 LB. SYSTEMS. MS Essentially the same as the AN strut valve. For design purposes, the MS superseded the AN in 19 and is functionally and dimensionally interchangeable with the AN with the exception of over-all and mounting base lengths. For, lb. systems. (AN-812-1) For pressures up to 1 p.s.l. (AN ) For pressures up to 3 p.s.l. DASH NO. MIN. I.D. OF CLAMP (INCHES) MAX. I.D. OF CLAMP (INCHES) FOR USE WITH HOSE I.D. NON SELF- SEALING 22 2/14 "A e 1/4 24 '/2 3/4 Vie 26 'A t "A. % 3 iiii, ' Vie 1/2 34 ' Yie 1 Vie % 38 ' Vie 1 Yls 3/4 SELF- SEALING 44 '1,44 1% % Yie t44 1 1/2 Vt 6 121,44 13/ % 1'14 11/4 66 1% 2 % e 1 1/2 1 Y /8 2 Y14 13/4 11/ /4 2 'A i ' Y % 3 Vie 21/ %2 3"3 2 21/ ya 3 VI. 3 NOTE: The above table shows only those Single Size clamps covered by the AN737 Standard Drawing. 89

6 FITTINGS AN standard fittings for use with aircraft tubing. Made in three basic types: flared, universal, and screw thread; and in combinations of these types. Flared tube fittings consisting of a nut, sleeve, and body form a leakproof connection... no soldering necessary. Screw thread fittings and universal fittings employ a soft brass or aluminum gasket to make a leakproof connection. Available in brass, steel, or aluminum alloy as indicated in the tables accompanying each illustration. Popular sizes only are listed on these pages. Most fittings can be ordered in larger sizes. Price and delivery information will be furnished on request. Order tube fittings by AN number plus dash number for size and material desired. Example: AN84- (Tee, 1a" tube size, steel )- AN86-4D (Plug, 1/4 " tube size, aluminum alloy) rn AN77 DASH NUMBER D 6D 8D -1D AN776 DASH NUMBER D -D 6D -8D 1D AN777 DASH NUMBER -4D 1/4" V, % " 1/2 1/4 I 6" AN77 BOLT \I\\Ii AN776 ELBOW, 9 AN777 ELBOW, 7 Shown here are those AN and MS fittings commonly used on aircraft. ro AN 77 AN 776 AN 777 AN z D 8D 1D AN778 DASH NUMBER 4D -D -6D 8-1D 3/4 " 1/2" /8" % " I 6 " 1/2 " AN778 ELBOW, 4 I MO H AN B4 AN 86 AN 87 AN 814 AN 81 AN 816 AN 817 AN 818 E11 MS2819 MI I I gall 11E1 AN 821 MS2822 MS2823 AN 824 MS282 MS2826 AN 827 AN 832 AN 833 AN CFIL AN 838 aann o=3 AN 837 AN 84 AN 842 AN 844 AN AN 871 AN 893 fir, AN 894 AN 91 AN 911 AN 912 MS2913 AN 914 AN 91 AN 916 AN 917 L 1 F- AN 918 AN "19 AN 924 AN 929 AN 937 AN 938 AN 939 AN 941 AN