1、t - MIL-HDBK-60 TH m 7777770 005L1364 4 MIL-HDBK-6 O 12 March 1990 MILITARY HANDBOOK THREADED FASTENERS - TI-NING TO PROPER TENSION Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-60 FORFGIORD 1. This military handbook is approved for use by
2、 all Departments and Agencies of the Department of Defense. 2. Benef Mal comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Avenue, Philadelphia, PA 19111-5096, by using the self-addressed Standardiza- tion D
3、ocurrient Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter. Appendix Al2 of FED-STD-H28, Screw-Thread Standards for Federal Services. Defense Industrial Supply Center, AiTN: DISC-ECF, 700 Robbins 3 The contents of this handbook replace the information contained
4、in ii Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-60 TH m 9779770 005Li36b A m MIL-HDBK-6Q CONTENTS PARAGRAPH 1 . SCOPE . 2 . Al?PLICA3rn lxxmmm 3 . EEFINITIQNS 4 . GEMERALI INFORMATION ON PRELQADS 4.1 Preload for bolts in axial loaded j
5、oints . 4.2 Preload for bolts in shear loaded joints . 4.3 Preloa for bolts in combined shear and axial Loaded joints . 5 . PRELOAD APPLICATION . 5.1. Preload application - general 5.2 Preload below yield point 5.3 Preload above yield pint 5.4 Preload limitation . 5.5 Preload adjustrrients 5.5.1 Tor
6、sion load compnent . 5.5.2 Preload relaxation . 5.5.3 Preload uncertainty 5.5.4 Temperature effects 5.6 5.4 Flange joint bolt tensioning . Back-turning following preload application . 6 . MFTHOS FOR CCNIROLLING BOLT TENSION 6.1 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.2.6 6.3 6.3.1 6.3.2 6.3.3 6.4 6.4.1
7、6.4.2 6.4.3 5,4.4 6.5 6. 6 6.6.1 6,6.2 6 . 7 Controlling bolt tension . general . Elongation measurement - stress below proportional limit Micrometer: method Modified micrometer method . Indicating bolt Turn-of-nut method . Ultrasonic method Strain gage method . Direct loading . Jacking methods Heat
8、ing-temperature control Heating-elongation control . Mechanical effect of load Washer or washer-face deformation Washer OK hex fastener tab fracture Conical spring nut . Change in sonic velocity under stress Yield pint tensioning . Torque control . Torque wrench Torque limiting fasteners 000.00000sB
9、.0600. Tbrcye-tension eompxison PACE 1 . 2 3 6 6 6 6 6 6 6 7 10 10 10 10 12 12 12 12 13 13 14 14 14 15 15 15 15 16 16 16 16 16 17 17 17 17 14 iii Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-60 TH W 7777770 005Ll3b7 T MIL-HBK-60 CONTEM3 -
10、 (Contd) FIGURES 1. Bolt load in joint with applied axial load * 2. Percent increase in tensile stress due to torsional load application; Unified screw threads 3. Percent increase in tensile stress due to torsional load application; UNJ screw threads . ; 4. Example of tightening order for pairs of f
11、lange bolts . 5. Effective length applicable in elongation formula . 6. Drilling for elongation determination when one end is not accessible . .o.eo. 7. through 9. (Part of Appendix A) 10. through 13. (Part of Appendix B) * TABLES I. Manualpreloading methods for bolts; accuracy and relative costs .*
12、 . II. (Part of Appendix B) A. Bolted joint behavior under applied load B. Bolt torque-tension relation pag13 - 5 8 9 11 13 13 21 I22 25 I 26 I 29 12 - 28 19 24 iV Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-60 TH W 7777770 0054368 I MIL
13、-HDBK-60 1. SCOPE 1.1 Scope. This document provides guidelines for the specification of proper bolt preloads and the selection of preload application methods. These guidelines may be used where no rules have been mandated either contractually or otherwise. Provided by IHSNot for ResaleNo reproductio
14、n or networking permitted without license from IHS-,-,-MIL-HDBK-60 TH 7777770 005LI3b7 3 MIL-HDBK- 60 2. AI?PLIcABU mNTs 2.1 Government documents. Unless otherwise specified, the following smcifications, standards and handbooks of the issue listed in the latest issue o? the Department of Defense Ind
15、ex of Specifications and Standards (DoDISS) are applicable to this document to the extent noted herein. MILITAFU SPECIFICATION MIL-S-8879 - Screw Threads, Controlled Radius Rmt with Increased Minor Diamter; General Specification for ETDERAI; STANDARD FE;D-STD-H28/1 - Screw-Thread Standards for Feder
16、al Services Section 1, Nomenclature, Definitions and Letter Symbols for Screw Threads MILITARY HANDBOOK MIL-HD3I-5 - Metallic Materials and Elements for Aerospace Vehicle Structures (Unless otherwise indicated, copies of federal and military specifications, standards, and handbooks are available frc
17、m the Naval Publications and Forms Center, AT“: NPODS, 5801 Tabor Avenue, Philadelphia, PA.19120-5099.) 2.2 ether publications. None. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-60 TH 9977970 005Li370 T MIL-HI=BK-60 3. DEFINITIONS 3.1
18、Screw thread definitions and symbols follow FED-STD-H28/1. Definitions and symbols for metallic material physical properties follow MIL-HDBK-5. Specific symbols used are defined in the applicable sections of this document. 3.2 Metric measurement units are shown in parenthesis after their respective
19、inch-pound measurement units. 3.3 The term “bolt“ is used for bolts, screws and studs in this document. 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I_ - - -_ MIL-HDBK-bO TH 7797770 005q37L I MIL-HDBK-60 4. GENERAC INFOIIMATICN ON PHELOADS 4.1 P
20、reload for bolts in axial loaded joints. As a general rule, applied bolt preroad should be sufficient to maintain joint members in contact and in compression. Loss of joint compression results in: a. Leakage of pressurized fluids past compression gaskets. b. Fastener loosening. a loss in bolt tensio
21、n. relatively small number of load applications. Joint load cycles which open the joint, cause Thus, only a minimal preload may remain after a c. F the amount depends upon friction under the bolt head or nut. or eliminated without loss of axial load. This reduces bolt stress which reduces creep and
22、fatigue. difficult so this method has limited use. Because of the small angles involved, it cannot be used for bolts which are relatively short. equal tension to each of the bolts in a flange joint, particularly if the joint includes a gasket. Unequal tension will result in leakage past the gasket.
23、The recommended procedure is to tighten in stages, following a pattern of tightening a pair of opposite bolts, then a pair of opposite bolts 90 away, followed by pairs of opposite bolts in between. An example of the order of tightening pairs of bolts is shown in figure 4. After tightening fully, a r
24、e- tightening several hours later will help to assure preload relaxation will not cause the joint to leak. if a compressed gasket is not used for sealing. Some of this With controlled back-turning, the torsional load may be reduced Calculation and control of the back-turn angle are 5.7 Flange joint
25、bolt tensioninq. It is important to apply approximately Following the above procedure is good practice even 10 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-bO TH 9999970 0054378 4 MIL-HDBK-60 Order of tightening: Pair of bolts in position
26、 1, Pair of bolts in position 2, Pair of bolts in position- FIGURE 4. Example of tightening order for pairs of flange bolts. 11 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-60 TH = 9797970 0054379 6 MIL-HDBK-60 6. METHOD3 FOR CUWROLLLING
27、BOLT TENCION 6.1 Controlling bolt tension - qeneral. The following are methods used for mntrollina initial bolt tension. There are other methods used which are not included accuracy and relative costs (courtesy of SPC Tec.mologies, Inc.) Preload Method Feel Torque wrench Turn of nut Preload indicati
28、ng washer Sensor wrench (computer controlled) - below yield using turn of nut - yield point sensing Bolt elongation Strain gages ad Accuracy - + 35% - + 10% + 25% 15% - + 15% - + 8% + 1% - + 3-5% .- this is the starting point. Nut turn angle wi-ll be different for each bolt size, length, material an
29、d thread lead and will vary with the properties of the clamped materials. Unless the deformation of the nut and joint materials under load is negligible compared to that of the bolt, a significant portion of the nut rotation will be absorbed other than in elongation of the bolt. nut turn angle would
30、 have to be determined empirically using a simulated joint and a tension measuring device as a standard. travel at the speed of sound for the bolt material, to the other end of the bolt, bounce off that end and return to the generator ina certain period of time. speed of sound varies with material,
31、temperature and stress level. An ultra- sonic control system generates a pulse and measures the tine for the pulse to travel the length of the bolt and return. computes the stress, load or elongation of the bolt at any time by comparing pulse travel time in the-loaded and unstressed conditions. cons
32、istent results, both ends of the bolt must be finished square to the bolt axis. In such a case, the above formulas will not apply so 6.2.5 Ultrasonic method. Sound pulse generated from one end of a bolt will This th is dependent upon the bolt length and the speed of sound; the Utilizing various inpu
33、ts the system To obtain 6.2.6 Strain qaqe nsethod. When a thin wire is bonded to a bolt, it stretches as the bolt elongates under load. electrical resistance of the wire which can be measured and correlated with bolt load. of the bolt or on the inside surface of a small axial hole where there is gre
34、ater protection. a plastic tube which is then bonded to the inside of a small axial hole in the bolt. This stretch causes a change in Strain gage wires or groups of wires may be bonded on the outside Another method uses mounting in recesses on the outside of 14 Provided by IHSNot for ResaleNo reprod
35、uction or networking permitted without license from IHS-,-,-MIL-HDBK-bo TH 9999970 0054382 b m MIL-HIBK-60 6.3 Direct loadinq. 6.3.1 Jackinq methods. Application of axial load to a bolt may be made using mechanical jacking or jacking powered by air; hydraulic or explosive gas pressure. to specially
36、designed nuts which incorporate jacking screws or pistons. The elongation of the bolt creates a gap which is filled by turning the nut down snugly or by a shim, spacer or other mechanical device. after this jacking force has been remved. Often, loads are applied to bolt threads extending beyond the
37、nut or Load is maintained 6.3.2 Heating-temperature control. When a hot bolt and nut in a joint are cooled, the bolt shrinks and tension is developed. used to calculate the temperature necessary to develop the required axial tensile stress in the bolt when the stress is below the elastic limit. The
38、following formula is Temperature, t = ft + to where ft = Axial tensile stress, psi e = Coefficient of linear thermal to = perating temperature, OF A steel bolt operating at 70% with an ini ia1 axial e = 6.2 x lO-f)J?. - E = Pbdulus of elasticity, psi Ee expansion /OF Example: tensile stres of 40,000
39、 psi. E = 30 x 10 i psi and t = 40,000 + 70 = 285% (30 x io6) x (6.2 x To provide bolt tension, the bolt and nut would be heated to a anperature slightly higher than the calculated temperature to allow for cooling prior to nut tightening. The nut would be tightened snugly and the assembly allowed to
40、 cool. This method can only be used where the bolt is accessible for heating and where the heating will not degrade joint material. Accuracy is limited by the ability to control bolt temperature and by any significant deformation of the joint materials. Tension would develop during cooling. 6.3.3 He
41、atinq - elongation control. Instead of using temperature controls ta set bolt tension as described in 6.3.2, accuracy can be improved by using controlled expansion of the heated bolt. The joint wuld be seated snugly as in 6.2.4 and heat applied to the bolt. When the bolt expansion, as indicated by a
42、 thickness gage inserted under the nut, is equal to the elongation calcu- lated as in 6.2.1 for the required axial stress, the nut would again be tightened snugly. approximately equal to the desired stress level. preload if there is an appreciable increase in temperature of the joint materials durin
43、g bolt heating. Upn cooling, the axial expansion in the bolt should be There will be come loss in 15 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a_ - - - - - - - MIL-HDBK-60 TH m 7997770 0054383 MIL-HIBK- 6 O 6.4 Mechanical effect of load. 6.4.1
44、Washer or washer-face deformation. a. One device consists of two concentric steel rings sandwiched between two close-tolerance, hardened steel washers. The inner ring is smaller in diameter and higher than the outer ring by a predetermined aniount. preload in the bolt is indicated when the inner rin
45、g is compressed and yielded, to the pint indicated when the outer ring can no longer be moved freely by means of a pin inserted into one of the peripheral holes. fastener beyond the first indication of correct tension will result in a significant increase in resistance. Additional rotation could res
46、ult in overtightening. reusable. A known Rotation of the Due to yielding of the inner ring, the washer assembly is not b. Other systems use calibrated deflection of a spring washer or deflection of projections on a washer or the bearing face of the fastener which flatten under axial load. The correc
47、t preload is indicated by checking the gap uner the bolt head or nut using a feeler gage or spacer which may be an inte- gral part of the joint. c. Still another type of system consists of a washer with either an integral tab or a separate member inserted into a radial groove on the fastener side of
48、 the washer. Under bolt preload, the tab or insert will deflect away from the joint to give an indication of the load. 6.4.2 - Washer or hex fastener tab fracture. a. A variation of the washer tab or insert system described in 6.4.1 uses fracture of the exposed tab or insert when a predetermined fas
49、tener load is achieved. b. Another device consists of a tab adhesively bonded to the outer edge of a washer or to one of the vertical faces of a hex nut or bolt head. The bottom surface of the tab is flush with the bearing surface and transmits a shear load to the adhesive as the fastener is tensioned. It
