1、 Intentionally left blank AN AMERICAN NATIONAL STANDARD Class 5 Interference-Fit Thread ASME/ANSI B1.12-I 987 (REVISION OF ANSI B1.12-1972) The American Society of Mechanical Engineers 345 East 47th Street, New York, N.Y. 1001 7 - Date of Issuance: November 15, 1987 This Standard will be revised whe
2、n the Society approves the issuance of a new edition. There will be no addenda or written interpretations of the requirements of this Standard issued to this edition. This code or standard was developed under procedures accredited as meeting the criteria for American National Standards. The Consensu
3、s Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an oppor- tunity to participate. The proposed code or standard was made available for public review and comment which provides an opportunity for additional public i
4、nput from industry, academia, reg- ulatory agencies, and the public-at-large. ASME does not “approve,“ “rate,“ or “endorse“ any item, construction, proprietary device, or activity. ASME does not take any position with respect to the validity of any patent rights asserted in connection with any items
5、 mentioned in this document, and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable Letters Patent, nor assume any such liability. Users of a code or standard are expressly advised that determination of the validity of any such patent rights
6、, and the risk of infringement of such rights, is entirely their own responsibility. Participation byfederal agency representativek) or personk) affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard. ASME accepts responsibility for only thos
7、e interpretations issued in accordance with governing ASME procedures and policies which preclude the issuance of interpretations by individual vol- unteers. No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission o
8、f the publisher. Copyright 0 1987 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A. FOREWORD (This Foreword is not part of ASME/ANSI B1.12-1987.) Interference-fit threads are threads in which the externally threaded member is larger than the internally threaded me
9、mber when both members are in the free state and which, when assembled, become the same size and develop a holding torque through elastic compression, plastic movement of material, or both. By custom, these threads are designated as Class 5. Tentative Class 5 fit threads were first published by the
10、National Screw Thread Commission (1928), and alternate Class 5 appeared in the 1944 Handbook H28. These standards were helpful in stabilizing design; however, in spite of restrictive tolerances, loosening or breakage of externally threaded members has been all too frequent. Also, minimum and maximum
11、 torque values were established, the validity of which has been generally accepted. The tentative and alternate standards, which were based on National Bureau of Standards and industry research, testing, and field study, represent the first attempt to establish an Amer- ican standard for interferenc
12、e-fit threads. These specifications are published in Appendix A. In 1947, ASA Sectional Committee B1 on Screw Threads established Subcommittee 10 under the chairmanship of Harry Marchant to study the problems of interference fits. A subgroup of the subcommittee, chaired by W. S. Brown, conducted a c
13、omprehensive survey of design, production, and driving practices in the automotive, implement, railroad, and fastener indus- tries and found that all were experiencing difficulty. Typical problems were: (a) the variety of materials and heat treatments used for externally threaded members; (b) variat
14、ions resulting from rolling, cutting, or grinding external threads; (c) the huge variety of chemical analyses and physical and mechanical properties encoun- tered in the forged, cast, die cast, and rolled materials into which the externally threaded members are driven; (d) the widely varying effects
15、 of chemical coatings, platings, and lubricants; and (e) the inability to closely control sizes of tapped holes in various materials. It was impossible to establish a standard at that time, but it was agreed that interference-fit threads could not be eliminated in design of equipment and that a work
16、able standard was essential. In 1951, Subcommittee 10, later renumbered 12, established a research subgroup which conducted extensive tests under a variety of conditions. The work of this research subgroup and a report of subsequent research and field experience is described in the article “New Clas
17、s 5 Interference Fit Thread” by W. G. Waltermire, which appeared in the September 6, 1956 issue of Machine Design. This Trial American Standard was predicated on the following conclusions, which were drawn from the research and field experience for developing holding torque through plastic movement
18、of materials. (a) Materials of the external and internal interference-fit threads compress elastically and flow during assembly and when assembled. (b) During driving, plastic flow of materials occurs, resulting in either an increase of the external thread major diameter or a decrease in the interna
19、l thread minor diameter, or both. (c) Relieving the external thread major diameter and the internal thread minor diameter to make allowance for plastic flow eliminates the main causes of seizing, galling, and abnormally high and erratic driving torques. iii (d) Relieving the major diameter of extern
20、al threads and minor diameter of internal threads requires an increase in the pitch diameter interference in order to obtain driving torques within the range established. (In driving studs, it was found that the minimum driving torque should be about 50% greater than the torque required to break loo
21、se a properly tightened nut.) (e) Lubricating only the internal thread results in more uniform torques than lubricating only the external thread and is almost as beneficial as lubricating both external and internal threads. Some applications do not permit lubrication. (f) For threads having truncate
22、d profile, torque increases directly as the pitch diameter interference for low interferences, but torque soon becomes practically constant and increases little, if at all, with increases of interference. Obviously, for uniformity of driving torques, it is desirable to work with greater interference
23、s, resulting in plastic flow of materials. (g) Comparatively large pitch diameter interferences can be tolerated, provided the external thread major diameter and internal thread minor diameter are adequately relieved and proper lubrication is used during assembly. (h) Driving torque increases with t
24、urns of engagement, but levels off after the assembly is well advanced. (For thin wall applications, it may be desirable to use longer engagement and smaller pitch diameter interference to obtain desired driving torque.) (i) Studs should be driven to a predetermined depth. Bottoming or shouldering m
25、ust be avoided. Bottoming, which is engagement of the threads of the stud with the imperfect threads at the bottom of a shallow drilled and tapped hole, causes the stud to stop suddenly during power driving, thus inviting failure in torsional shear. Slipping clutches may permit transmis- sion of exc
26、ess torque. Bottoming can also damage parts having only a weak diaphragm at the bottom of the hole, through either mechanical or hydrostatic compression. Shouldering, which is the practice of driving the stud until the thread runout engages with the top threads of the hole, may create excessive radi
27、al compressive stresses and upward bulging of the material at the top of the hole. The torque, or stud holding power, produced by these radial compressive stresses is considerably relieved when the tensile load is applied to the stud, and may be inadequate to prevent backout in service. The Trial Am
28、erican Standard was issued in November 1959. On October 23, 1961, the subcommittee reviewed the standard and recommended republication, without technical change, as an American Standard. It was felt that the lack of adverse comment after 2 years existence as a Trial Standard, and the reception of fa
29、vorable comments of usage, warranted this step. On May 16, 1963, the standard was formally designated an American Standard. Several errors were discovered and B1.12 was rewritten. It was approved on September 5, 1972. The most recent research on interference-fit thread was conducted by the Portsmout
30、h Naval Shipyard on both hardened steel and nickel-copper-aluminum (K Monel) studs assembled in alloy steel (HY-80), corrosion resistant steel, nickel-copper (Monel), copper-nickel, and nickel-chromium (Inconel) internal threads, and on nonferrous studs in nonferrous internal threads. They modified
31、the B1.12 Class 5 specifications for plastic flow interference-fit threads when nickel-copper-aluminum external threads are assembled in many materials. They also provided more cavity space. A summary of their findings for developing holding torque through plastic flow and elastic compression of mat
32、erial follows. (a) Pitch diameter interferences specified in ANSI B1.12 were found to be too large, re- sulting in excessive failures. (b) Lead, flank angles, taper, straightness, and roundness are important. (c) Optimum surface roughness is 63 pin. Ra. (d) Difference between functional size and pit
33、ch diameter of both the internal and external threads are measured and may not exceed 50% of the pitch diameter tolerances. (One foreign standard specifies 25 % .) (e) Critical applications require selective fits, using measured pitch diameters on the ex- ternal and internal threads, to obtain a spe
34、cified interference when the external and internal threads are assembled. iv (f) Assembly torque cannot be continuous. Several waiting periods are required to let fric- tion heat dissipate. (g) Studs are indexed to monitor their movement. Assembly is considered a failure if there is stud rotation wh
35、en seating the prevailing torque nut or breaking it away. These Portsmouth Naval Shipyard thread specifications are published in Appendix Bfor elastic interference where permanent distortion is not desired and Appendix C for plastic flow interference with extra allowance at both the crest and root f
36、or K Monel. This Standard was approved as an American National Standard on July 13, 1987. Intentionally left blank ASME STANDARDS COMMITTEE B1 Standardization and Unification of Screw Threads (The following is the roster of the Committee at the time of approval of this Standard.) OFFICERS D. J. Erna
37、nuelli, Chairman H. W. Ellison, Vice Chairman C. E. Lynch, Secretary COMMITTEE PERSONNEL AEROSPACE INDUSTRIES ASSOCIATION OF AMERICA, INC. F. H. Cantrell, McDonnell Douglas Corp., St. Louis, Missouri H. Borrrnan, Alternate, Sperry Defense Electronics, Great Neck, New York AMERICAN MEASURING TOOL MAN
38、UFACTURERS ASSOCIATION P. F. Bitters, Greenfield, Massachusetts C. W. Jatho, Alternate, American Measuring Tool Manufacturers Association, Birmingham, Michigan AMERICAN PIPE FITTINGS ASSOCIATION W. C. Farrell, Jr., Stockham Valves and Fittings, Inc., Birmingham, Alabama DEFENSE INDUSTRIAL SUPPLY CEN
39、TER E. Schwartz, Defense Industrial Supply Center, Philadelphia, Pennsylvania F. S. Ciccarone, Alternate, Defense Industrial Supply Center, Philadelphia, Pennsylvania ENGINE MANUFACTURERS ASSOCIATION G. A. Russ, Cummins Engine Co., Columbus, Indiana INDUSTRIAL FASTENERS INSTITUTE R. M. Harris, Bethl
40、ehem Steel Corp., Lebanon, Pennsylvania K. E. McCullough, SPS Technologies, Inc., Newton, Pennsylvania J. C. McMurray, Russell, Burdsall the maximum torques establish a ceiling below which seizing, galling, or torsional failure of the externally threaded compo- nents is reduced. This Standard provid
41、es for the maxi- mum allowable interference. Appendices A, B, C, and D contain useful informa- tion that is supplementary to this Standard, such as re- prints of the obsolete tentative and alternate Class 5 standards, U.S. Navy ship specifications for elastic in- terference-fit coarse thread series
42、from 0.250 in. through 2.000 in., U.S. Navy ship specifications for Class 5 Modified which includes nickel-copper-aluminum al- loy external threads, and an interference metal compar- ison of standard to nonstandard interference-fit threads. 1.2 Field of Application Interference-fit threads provide a
43、 high degree of re- sistance against turning of studs when prevailing torque nuts are used and against loosening of studs caused by load cycling and vibration. These threads are not in- tended for use where regular removal for component maintenance is required. 1.3 Reference Documents ANSI B1.1 Unif
44、ied Inch Screw Threads (UN and UNR Thread Form) ANWASME B1.2 Gages and Gaging for Unified Inch Screw Threads ANWASME B1.3M Screw Thread Gaging Systems for Dimensional Ac- ceptability-Inch and Metric Screw Threads (UN, UNR, UNJ, M, and MJ) ANSUASME B 1.7M Nomenclature, Definitions, and Letter Symbols
45、 for Screw Threads ANSI B94.9 Taps-Cut and Ground Threads 1.3.2 Other References Standards and Dimensions. Cleveland, 1983. Metal Cutting Tool Institute. Taps, Ground nread, Society of Manufacturing Engineers.* Tool and Manu- facturing Engineers Handbook- Volume 1, Machin- ing. American Society for
46、metal. Metals Handbook-Vol- ume 3, Machining. Metal Cutting Tool Institute. Metal Cutting Tool Hand- book. Waltermire, W. G. “New Class 5 Interference Fit Thread.” Machine Design (September 6, 1956): 83- 96. 1.4 Acceptability Acceptability of product screw threads, based on the gaging method specifi
47、ed, shall be in accordance with ANWASME B1.3M. Gages and gaging are in accor- dance with ANSUASME B1.2 but with gaging dimen- sions as specified in Tables 11 and 12. See paras. 1 1.1.1, 11.1.2, and 11.1.3. 1.3.1 American National Standards. The latest 1230 Keith Building, Cleveland, Ohio 441 15-2180
48、. issues of the following standards form a part of this *One SME Drive, P.O. Box 930, Dearborn, Michigan 48128. Standard to the extent specified herein. 3Metals Park, Ohio 44073. 1 ASME/ANSI B1.12-I 987 CLASS 5 INTERFERENCE-FIT THREAD 1.5 Reference Temperature The reference temperature is 68F (20C)
49、for dimen- sions listed. 1.6 Units of Measure All dimensions and values are expressed in inches un- less otherwise noted. 1.7 Federal Government Use When this Standard is approved by the Department of Defense and federal agencies and is incorporated into FED-STD-H28/23, Screw Thread Standards for Federal Services, Section 23, the use of this Standard by the federal government will be subject to all requirements and limitations of FED-STD-H28/23. Appendices B and C are standard for U.S. Navy ship use. 2 TE
