1、BRITISH STANDARD BS EN 26157-3:1992 ISO 6157-3: 1988 Fasteners Surface discontinuities Part 3: Bolts, screws and studs for special requirements The European Standard EN 26157-3:1991 has the status of a British StandardBSEN26157-3:1992 This British Standard, having been prepared under the directionof
2、 the General Mechanical Engineering Standards Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 1 April 1992 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference GME/9 Draft for comment 85/78855 DC ISBN 0 580
3、 20685 8 Cooperating organizations The European Committee for Standardization (CEN), under whose supervision this European Standard was prepared, comprises the national standards organizations of the following countries. Austria Oesterreichisches Normungsinstitut Belgium Institut belge de normalisat
4、ion Denmark Dansk Standardiseringsraad Finland Suomen Standardisoimisliito, r.y. France Association franaise de normalisation Germany Deutsches Institut fr Normung e.V. Greece Hellenic Organization for Standardization Iceland Technological Institute of Iceland Ireland National Standards Authority of
5、 Ireland Italy Ente Nazionale Italiano di Unificazione Luxembourg Inspection du Travail et des Mines Netherlands Nederlands Normalisatie-instituut Norway Norges Standardiseringsforbund Portugal Instituto Portugus da Qualidade Spain Asociacin Espaola de Normalizacin y Certificacin Sweden Standardiser
6、ingskommissionen i Sverige Switzerland Association suisse de normalisation United Kingdom British Standards Institution Amendments issued since publication Amd. No. Date CommentsBSEN26157-3:1992 BSI 08-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii Foreword 2
7、Text of EN 26157-3 3 National annex NA (informative) Committees responsible Inside back cover National annex NB (informative) Cross-references Inside back coverBSEN26157-3:1992 ii BSI 08-1999 National foreword This British Standard has been prepared under the direction of the General Mechanical Engi
8、neering Standards Policy Committee and is the English language version of EN 26157-3:1991 “Fasteners Surface discontinuities Part 3: Bolts, screws and studs for special requirements”, published by the European Committee for Standardization (CEN). It is identical with ISO 6157-3:1988, published by th
9、e International Organization for Standardization (ISO). EN 26157-3:1991 was produced as a result of international discussion in which the UK took an active part. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for
10、their correct application. 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, theEN title page, pages2 to 16, an inside back cover and a back cover. This standard
11、 has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 26157-3 October 1991 UDC 621.882.2:620.191 Descriptors: Fasteners, bolts, screws, studs, surfa
12、ce defects English version Fasteners Surface discontinuities Part 3: Bolts, screws and studs for special requirements (ISO 6157-3:1988) Elments de fixation Dfauts de surface Partie 3: Boulons, vis et goujons pour applications particulires (ISO 6157-3:1988) Verbindungselemente Oberflchenfehler Teil 3
13、: Schrauben fr besondere Anforderungen (ISO 6157-3:1988) This European Standard was approved by CEN on 1991-10-10. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any
14、alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by t
15、ranslation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxem
16、bourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels CEN 1991 Copyright reserved to all CEN members Ref. N
17、o. EN 26157-3:1991 EEN26157-3:1991 2 BSI 08-1999 Foreword In 1990, ISO 6157-3:1988 was submitted to the CENP.Q.-procedure. Following the positive result of the P.Q., CEN/BT agreed to submit ISO 6157-3:1988 with the following modifications to Formal Vote. In the French version, replace: “boulon” by “
18、vis”, “boulon, vis” by “vis”. In accordance with the Common CEN/CENELEC Rules, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switze
19、rland and United Kingdom. Contents Page Foreword 2 1 Scope and field of application 3 2 References 3 3 Types, causes, appearance and limits ofsurface discontinuities 3 4 Inspection and evaluation procedure 14 Annex Sampling plan for surface discontinuities 15 Table 1 Permissible surface discontinuit
20、ies 13 Table 2 Sample sizes for visual and non-destructive testing 15 Table 3 Secondary sample sizes for destructivetesting 15EN26157-3:1991 BSI 08-1999 3 1 Scope and field of application 1.1 This part of ISO 6157 establishes limits for various types of surface discontinuities on bolts, screws and s
21、tuds for special requirements. It applies to bolts, screws and studs with nominal thread diameters 5 mm and larger; product grades A and B; nominal lenghts l u 10d (or longer if specified); property class 12.9; property classes 8.8, 9.8 and 10.9 when specified in product standards or agreed between
22、supplier and purchaser. 1.2 Where the permissible limits for surface discontinuities indicated in clause 3 occur, the minimum values for the mechanical and functional properties specified in ISO 898-1 should still be met. When fatigue strength requirements are specified, the fatigue strength should
23、not be lower than that obtained on bolts without defects taken from the same lot. NOTE 1The figures in clause 3 are examples only. They apply correspondingly also to other types of bolts, screws and studs. NOTE 2The individual figures show the surface discontinuities exaggerated in some cases for cl
24、arity. 2 References ISO 468, Surface roughness Parameters, their values and general rules for specifying requirements. ISO 898-1, Mechanical properties of fasteners Part 1: Bolts, screws and studs. ISO 2859, Sampling procedures and tables for inspection by attributes. ISO 3269, Fasteners Acceptance
25、inspection. 3 Types, causes, appearance and limits of surface discontinuities 3.1 Cracks A crack is a clean (crystalline) fracture passing through or across the grain boundaries and may possibly follow inclusions of foreign elements. Cracks are normally caused by overstressing the metal during forgi
26、ng or other forming operations, or during heat treatment. Where parts are subjected to significant reheating, cracks usually are discoloured by scale.EN26157-3:1991 4 BSI 08-1999 3.1.1 Quench cracks 3.1.2 Forging cracks Cause Quench cracks may occur during hardening due to excessively high thermal a
27、nd transformation stresses. Quench cracks usually follow an irregular and erratic course on the surface of the fastener. Appearance Limits Quench cracks of any depth, any length, or in any location are not permitted. Cause Forging cracks may occur during the cut-off or forging operations and are loc
28、ated on the top of the head of screws and bolts. Appearance Limits Length, l, of forging cracks: l u d a Depth or width, b, of forging cracks: b u 0,04d NOTEThe limits for forging cracks do not apply to socket head screws (see 3.1.5). a d = nominal thread diameterEN26157-3:1991 BSI 08-1999 5 3.1.3 F
29、orging bursts Cause Forging bursts may occur for example during forging on the flats or corners of the heads of bolts and screws, at the periphery of flanged or circular head products or on the raised periphery of indented head bolts and screws. Appearance Limits Hexagon head screws No forging burst
30、 in the flats of hexagon bolts and screws shall extend into the crown circle on the top of the head surface (chamfer circle) or into the underhead bearing surface. Forging bursts occurring at the intersection of two wrenching flats shall not reduce the width across corners below the specified minimu
31、m. Forging bursts in the raised periphery of indented head bolts and screws shall not exceed a width of 0,06d aor have a depth extending below the indented portion. Circular head screws Flanges of bolts and screws and peripheries of circular head screws may have forging bursts, but they shall not ex
32、ceed the following limits: Width of forging bursts: 0,08d c b(with only one forging burst); 0,04d c(with two or more forging bursts, one of which may extend to 0,08d c ). Depth of forging bursts: 0,04d a a d = nominal thread diameter b d c= head or flange diameterEN26157-3:1991 6 BSI 08-1999 3.1.4 S
33、hear bursts Cause Shear bursts may occur, for example during forging, frequently at the periphery of products having circular or flanged heads, and are located at approximately 45 to the product axis. Shear bursts may also occur on the sides of hexagon head products. Appearance Limits Hexagon head s
34、crews Shear burst limits on the wrenching head are as follows: Width u 0,25 mm + 0,02s a Depth u 0,04d No shear burst in the flats of hexagon bolts and screws shall extend into the crown circle on the top of the head surface (chamfer circle) or into the underhead bearing surface. Shear bursts, occur
35、ring at the intersection of two wrenching flats, shall not reduce the width across corners below the specified minimum. Shear bursts in the raised periphery of indented head bolts and screws shall not exceed a width of 0,06d bor have a depth extending below the indented portion. Circular head screws
36、 Flanges of bolts and screws and peripheries of circular head products may have shear bursts, but shall not exceed the following limits: Width of shear bursts: 0,08d c c(for only one shear burst); 0,04d c(with two or more forging shear bursts, one of which may extend to 0,08d c ). a s = width across
37、 flats b d = nominal thread diameter c d c= head or flange diameterEN26157-3:1991 BSI 08-1999 7 3.1.5 Forging cracks in socket head screws Cause Cracks in the periphery, in the top surface and on the indented portion (hexagon socket) may occur on the inner and outer faces due to cut-off of wire sect
38、ion, shear and compressive stress during forging operations and countersinking of head. AppearanceEN26157-3:1991 8 BSI 08-1999 Appearance 1)d k= head diameter 2)t = key engagement socket depthEN26157-3:1991 BSI 08-1999 9 3.2 Raw material seams and laps A seam or lap is a narrow, generally straight o
39、r smooth curved line discontinuity running longitudinally on the thread, shank or head. Limits Cracks extending from the socket to the outer face and cracks with a traverse indicating a potential to intersect are not permissible. Cracks within 0,3t of the bottom of the socket are not permissible. Cr
40、acks located elsewhere in the socket are permissible, provided that they do not exceed a length of 0,25t and a depth of 0,03d k(0,13 mm max.). One crack in the longitudinal direction with a depth not exceeding 0,03d k(0,13 mm max.) at the head/shank intersection and on the top of the head is permiss
41、ible. Longitudinal cracks with a depth not exceeding 0,06d k(1,6 mm max.) located in the periphery are permissible. Cause Seams and laps are inherent in the raw material from which fasteners are made. Appearance Limits Permissible depth: 0,015d a+ 0,1 mm:0,4 mm max. If laps or seams extend into the
42、head, they shall not exceed the permissible limits for width and depth specified for bursts (see 3.1.3). a d = nominal thread diameterEN26157-3:1991 10 BSI 08-1999 3.3 Voids A void is a shallow pocket or hollow on the surface of a bolt or screw due to non-filling of metal during forging or upsetting
43、. Cause Voids are produced by marks and impressions due to chips (shear burrs) or by rust formation on the raw material. They are not eliminated during forging or upsetting operations. Appearance Limits Depth, h, of voids: hu 0,02d a : 0,25 mm max. Area of all voids: The combined surface area of all
44、 voids on the bearing face shall not exceed 5% of the total area. a d = nominal thread diameterEN26157-3:1991 BSI 08-1999 11 3.4 Folds A fold is a doubling over of metal which occurs at the surface of the fastener during forging. 3.5 Tool marks Tool marks are longitudinal or circumferential grooves
45、of shallow depth. Cause Folds are produced by material displacements due to lack of congruence of forms and volumes of the single forging steps. Appearance Limits Folds at interior corners at or below the bearing surface are not permissible, unless specifically permitted in this part of ISO 6157 or
46、in the product standard. Folds at exterior corners are permissible. Cause Tool marks are produced by the movement of manufacturing tools over the surface of the bolt or screw. Appearance Limits Tool marks produced by machining in the shank, fillet or bearing surface shall not exceed a surface roughn
47、ess of R a= 3,2 4m when tested in accordance with ISO 468.EN26157-3:1991 12 BSI 08-1999 3.6 Laps on the thread A lap is a fold-over of metal in the thread. Laps generally show a pattern of consistency between the same product, that is laps will be identically located and with the same direction of t
48、raverse between all products. 3.7 Damages Damages are indentations of any surface of a bolt or screw. Cause Folds and laps on the thread occur during cold-forming of the thread by rolling. Appearance 1)H 1= depth of thread Limits Laps of any depth or length are not permitted in the following places:
49、 at the root of the thread; at the loaded flank of screw thread below the pitch diameter, even if they start beyond the pitch diameter. The following laps are permissible: laps in the crest of the threads of 0,25 H 1max.; crest of the threads not entirely rolled out, maximum half a turn on one thread; laps below the pitch diameter, if they run on the non-loaded flank towards the major diameter and not deeper than 0,25 H 1and not longer than half a turn on one thread. Cause Damages, for exam
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