1、BRITISH STANDARD OBSOLESCENT MARCH 1986 BS 2693-2: 1964 Incorporating Amendment No. 1 Specification for Screwed studs Part 2: Recommendations for high grade studs UDC 621.882.626BS2693-2:1964 This British Standard, having been approved by the MechanicalEngineering IndustryStandards Committee and end
2、orsed by the Chairman ofthe Engineering Divisional Council, was published under theauthority of the General Council on 19August1964 BSI 12-1999 The following BSI references relate to the work on this standard: Committee references MEE/60 and MEE/60/8 ISBN 0 580 34069 4 Co-operating organizations The
3、 Mechanical Engineering Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: The Government departments and scientific and industrial organizations
4、marked with an asterisk in the above list, together with the following were directly represented on the committee entrusted with the preparation of this standard: Associated Offices Technical Committee Institute of Marine Engineers Association of Consulting Engineers Institute of Petroleum Associati
5、on of Mining Electrical and Institution of Civil Engineers Mechanical Engineers Institution of Gas Engineers British Chemical Plant Manufacturers Institution of Heating and Ventilating Engineers Association Institution of Mechanical Engineers British Compressed Air Society Institution of Mechanical
6、Engineers British Electrical and Allied (Automobile Division) Manufacturers Association* Institution of Production Engineers* British Gear Manufacturers Association Locomotive and Allied Manufacturers British Internal Combustion Engine Association of Great Britain* Manufacturers Association* London
7、Transport Board British Iron and Steel Federation* Machine Tool Trades Association* British Mechanical Engineering Federation* Ministry of Defence, Army Department* British Railways Board* Ministry of Defence, Navy Department* Crown Agents for Oversea Governments Ministry of Labour (H.M. Factory Ins
8、pectorate) and Administrations Ministry of Power D.S.I.R. National Engineering Laboratory Ministry of Public Building and Works Electricity Council, the Generating Board and Ministry of Transport the Area Boards in England and Wales National Coal Board Engineering Equipment Users Association* Nation
9、al Physical Laboratory (D.S.I.R.)* Gas Council Radio Industry Council High Commission of India* Royal Institute of British Architects Agricultural Engineers Association Council of British Manufacturers of Petroleum Association of Hydraulic Equipment Equipment Manufacturers Electronic Engineering Ass
10、ociation Bright Bolt although the absence of adverse comment and reception of favourable reports have now led the Committee responsible to confirm it, without technical change, as an American Standard, users in the U.S.A. are still urged to report on the results, whether good or bad, of applying its
11、 requirements. Information gained from such experience will be taken into account when considering any future amendment or revision of the standard. These Recommendations are issued on the same basis and users are most strongly requested to advise the British Standards Institution of the results the
12、y obtain. In this way it is hoped ultimately to be able to specify a series of stud fits which have been proved by practical experience. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application
13、. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 10 and a back cover. This standard has been updated (see copyright date) and may have had amendment
14、s incorporated. This will be indicated in the amendment table on the inside front cover.BS2693-2:1964 BSI 12-1999 1 Introduction (From the introduction to American standard ASAB1.12) Interference fit threads are threads in which the externally threaded member is larger than the internally threaded m
15、ember when both members are in a 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 Class5. HandbookH28, “Screw thread standards for Federal Services” has
16、for several editions published specifications for tentative Class5 and alternate Class5 fits. 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. HandbookH28 has also establis
17、hed minimum and maximum torque values, the validity of which has been generally accepted in service for the past twenty years. The present standard, which is based on ten years of research testing and field study, represents the first attempt to establish an American standard for interference fit th
18、reads. A comprehensive survey of design, production and driving practices in the automotive, implement, railroad, and fastener industries begun in1947 showed that all were experiencing difficulty. Typical problems were: i) The variety of materials and heat treatment used for externally threaded memb
19、ers; ii) Variations resulting from rolling, cutting or grinding external threads; iii) The huge variety of analyses and physical and mechanical properties encountered in the forged, cast, die cast and rolled materials into which the externally threaded members are driven; iv) The widely varying effe
20、cts of chemical coatings, platings and lubricants; and v) The inability to control closely sizes of tapped holes in various materials. It was impossible to establish a standard when the results of this survey were first available, but it was agreed that interference fit threads could not be eliminat
21、ed in design of equipment and that a workable standard was essential. In1951 a research sub-group was established and conducted extensive tests under a variety of conditions. The work of this research sub-group and a report of subsequent research and field experience is described in the article “New
22、 Class5 Interference Fit Thread”, by W. C. Waltermire, which appeared in the September6, 1956, issue of “Machine Design”. The standard is based on the following conclusions which have been drawn from the research and field experience: i) Materials of the external and internal interference fit thread
23、s compress elastically during assembly and when assembled. ii) During driving, plastic flow of materials occurs, resulting in either an increase of the external thread major diameter or a decrease in the internal thread minor diameter or both. iii) Relieving the external thread major diameter and th
24、e internal thread minor diameter to make allowance for plastic flow eliminates the main causes of seizing, galling and abnormally high and erratic driving torques. iv) Relieving the major diameter of external threads and minor diameter of internal threads requires an increase in the effective diamet
25、er interference in order to obtain driving torques within the range established by HandbookH28. (In driving studs, it was found that the minimum driving torque should be about50 per cent of the torque required to break loose a properly tightened nut.) v) Lubricating only the internal thread results
26、in more uniform torques than lubricating only the external thread and is almost as beneficial as lubricating both external and internal threads. vi) For threads having truncated profile, torques increase directly as the effective diameter interference for low interferences but torques soon become pr
27、actically constant and increase little, if at all, with increases of interference. Obviously, for uniformity of driving torques, it is desirable to work with greater interference. vii) Comparatively large effective diameter interference can be tolerated provided the external thread major diameter an
28、d internal thread minor diameter are adequately relieved and proper lubrication is used during assembly. viii) Driving torque increases directly with turns of engagement. (For thin wall applications, it may be desirable to use longer engagement rather than large effective diameter interference to ob
29、tain desired driving torque.)BS2693-2:1964 2 BSI 12-1999 ix) As interference on the flanks of the threads is guaranteed even with minimum metal conditions, studs can be driven to a predetermined depth. it is not necessary as in Part1to lock on the thread run-out which, for high duty applications, ma
30、y be undesirable due to possible creation of excessive radial compressive stresses, causing upward bulging of the material at the top of the hole. The American Committee is continuing its study with a view to (1) extending sizes downward to No.6, (2) going to sizes above1 1 / 2in and(3) including ad
31、ditional sizes of the8-thread series and perhaps sizes of the fine pitch series.BS2693-2:1964 BSI 12-1999 3 Figure 1 BS2693-2:1964 4 BSI 12-1999 Section 1. General 1 Scope These Recommendations provide dimensional tables for external and internal interference fit (Class5) threads of modified Unified
32、 form, in the Coarse thread series, sizes 1 / 4in to 1 1 / 2in. It is intended that designs conforming to this standard will provide adequate torque conditions which fall within the limits shown inTable 3. These limits are taken from HandbookH28(1957)“Screw thread standards for Federal Services” Par
33、tIII. The minimum torques are intended to be sufficient to ensure that externally threaded members will not loosen in service; the maximum torques establish a ceiling below which seizing, galling or torsional failure of the externally threaded components is unlikely. SeeFigure 1 for conditions of fi
34、t. 2 Material It is essential that the studs should have a minimum tensile strength of50 tonf/in 2and with mechanical properties equal to those for grade S bolts in BS1768 1) . NOTEThe length of engagement, depth of thread engagement and effective diameter inTable 1, Table 2 andTable 3 are designed
35、to produce adequate torque conditions when using heat-treated studs with a tensile strength of50tonf/in 2minimum. These Recommendations are not intended to cover the use of studs made of stainless steel, silicon bronze, brass or similar materials. Where such materials are used, the dimensions given
36、here will probably require adjustment based on pilot experimental work with the combination of materials in question. 3 Tables Table 1 andTable 2 of the standard are based on engagement lengths, external thread lengths, and tapped hole depths specified inTable 3 and in compliance with the recommenda
37、tions for conditions of use and inspection given in Section2. a) External threads.Table 1 contains maximum and minimum dimensions for external threads. i) For each size, it contains one set of effective diameter limits regardless of material involved. The minimum effective diameter is larger than th
38、e basic effective diameter of comparable UNC series threads. ii) For driving into brass and into ferrous materials having hardness under160HB, the length of engagement is1 1 / 4D. For driving into other non-ferrous materials, the length of engagement is2 1 / 2 D. In both cases the minimum major diam
39、eter limit is approximately that of the minimum major diameter for Class2A. iii) For driving into ferrous material of160HB and harder, the length of engagement is1 1 / 4 D; however, the maximum and minimum major diameter limits are reduced to permit plastic flow and to reduce and stabilize driving t
40、orque. b) Internal threads. Table 2 contains the minimum and maximum dimensions for internal threads. i) One set of effective diameter limits is maintained for each size regardless of material. ii) The tapped hole minor diameter limits are Class3 for all sizes in nonferrous materials and for sizes u
41、p to and including 3 / 8inch in ferrous materials. For 7 / 16in and larger sizes in ferrous materials, the minor diameters have been enlarged slightly in order to reduce driving torques and tolerances have been adjusted. c) Interferences and engagement lengths. Table 3 gives interferences and engage
42、ment lengths. For lengths of engagement of1 1 / 4D, the external thread length and depth of full form threads in tapped holes are set at1 1 / 2 D with a tolerance of plus2 1 / 2pitches minus0. For lengths of engagement of2 1 / 2 D, the length of external thread and depth of full form thread in the t
43、appedhole are set at2 3 / 4D with a tolerance of plus2 1 / 2pitches minus0. 4 Extension of the standard a) Small sizes (under 1 / 4 in). By using the new principles upon which this standard is based, stud sizes may be extended downward. However, adequate data are not yet available to permit setting
44、a standard. American research indicates that on smaller sizes the main reliance for producing adequate breakloose torques should be placed on effective diameter interference and not on increasing the length of engagement. Extension of the standard is being investigated. b) Large sizes (over 1 1 / 2 in). Although there is some current use of interference fits on large size threads, adequate data are not yet available to permit setting a standard or/larger sizes. 1) BS1768, “Unified precision hexagon bolts, screws and nuts (UNC and UNF threads). Normal series”.
