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1、BRITISH STANDARD BS 6944:1988 Specification for Flash welding of butt joints in ferrous metals (excluding pressure piping applications) UDC 669.15 194.55/.56/.57:621.791.762:620.1 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6944:1988
2、This British Standard, having been prepared under the direction of the Welding Standards Committee, was published under the authority of the Board of BSI and comes into effect on September 1988 BSI 04-1999 The following BSI references relate to the work on this standard: Committee reference WEE/33 D
3、raft for comment 86/77824 DC ISBN 0 580 16660 0 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Welding Standards Committee (WEE/-) to Technical Committee WEE/33, upon which the following bodies were represented: Associated Offices Techn
4、ical Committee British Chain Manufacturers Association British Railways Board British Steel Corporation Electricity Supply Industry in England and Wales Water-tube Boilermakers Association Welding Institute Welding Manufacturers Association (BEAMA Ltd.) Amendments issued since publication Amd. No.Da
5、te of issueComments Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6944:1988 BSI 04-1999i Contents Page Committees responsibleInside front cover Forewordiii 1Scope1 2Definitions1 3Information and requirements to be agreed and to be docum
6、ented1 3.1Information to be supplied by the purchaser1 3.2Requirements to be agreed1 4Welding equipment2 5Material to be welded2 6Process sequence: general2 7Process sequence: preparation3 8Process sequence: welding3 8.1Overhang2 8.2Clamping force3 8.3Alignment3 8.4Initial end squaring3 8.5Pre-heati
7、ng3 8.6Flashing3 8.7Upsetting3 8.8Upset current time3 8.9Unclamping3 9Process sequence: finishing3 9.1Removal of upset metal3 9.2Post weld heat treatments3 10Procedure approval3 10.1 General3 10.2 Monitoring4 10.3 Changes affecting approval4 10.4 Heat treatment and finished condition4 10.5 Sample pr
8、eparation5 10.6 Bend testing5 10.7 Macro-examination5 10.8 Tensile testing6 10.9 Hardness testing6 11Statement of results of procedure approval6 12Production control9 12.1 Visual inspection9 12.2 Mechanical tests9 13Parameter monitoring9 14Non-destructive testing9 15Weld acceptance criteria10 Append
9、ix A Welding equipment11 Appendix B Generalized diagram illustrating monitoring variables11 Appendix C Types of weld features12 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6944:1988 ii BSI 04-1999 Page Figure 1 Typical information to
10、appear on a flash welding procedure record sheet7 Figure 2 Typical information to appear on a flash welding procedure test report sheet8 Figure 3 Generalized diagram illustrating monitoring variables11 Figure 4 Flash welding features (diagrammatic only)13 Publications referred toInside back cover Li
11、censed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6944:1988 BSI 04-1999iii Foreword This British Standard has been prepared under the direction of the Welding Standards Committee and is one of a series of British Standards concerned with the
12、welding of metallic components of regular and irregular cross section. This standard deals with the production of welds made by the flash welding process but excludes the flash welding of steel tubes for pressure applications which is covered in a separate standard (see BS 4204). This standard follo
13、ws the general pattern set by others in the series and is of the “process” type. It embodies the currently accepted practice of initial procedure approval tests followed by periodical production control tests. This standard also details the various parameters specific to the flash welding process th
14、at are required to be determined in establishing the procedure. A list of the typical information to appear on a welding procedure sheet is given together with a typical test record sheet. An appendix gives guidance on typical flash welding imperfections. As the acceptance level of certain requireme
15、nts, e.g. the contour and form of the weld profile, is related to the service conditions of the joint, reference should be made for these details to the appropriate application standard, where such a standard exists. Where such guidance is not given, these aspects should be a matter of agreement bet
16、ween the contracting parties. It has been assumed in the drafting of this British Standard that the execution of its provisions is entrusted to appropriately qualified and experienced people. A British Standard does not purport to include all the necessary provisions of a contract. Users of British
17、Standards are responsible for 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 to iv, pages 1 to 14, an inside back cover and a back cover. T
18、his standard 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. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: she
19、ffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6944:1988 BSI 04-19991 1 Scope This British Standard specifies requirements for the automatic flash welding of ferrous metal sections excluding tubes, pipes and pipe fittings for pressure applications, which
20、are covered in BS 4204. In addition to the definitive requirements, it also requires the items detailed in clause 3 to be documented. For compliance with this standard, both the definitive requirements and the documented items have to be satisfied. NOTEThe titles of the publications referred to in t
21、his standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard the following definitions apply. For other terms the definitions in BS 499-1 apply. 2.1 manufacturer the user of the welding equipment for the purposes of manufacturing welded products 2.2 autom
22、atic flash welding machine a welding machine that has an automatic sequence of events 2.3 inspecting authority the competent independent body or association that, where required, verifies compliance with this standard 2.4 upset current time the time after the commencement of upsetting during which t
23、he current flows 2.5 pre-heating (flash welding) the resistance heating of workpieces to facilitate the onset of flashing by a series of current pulses with a cool time in between each pulse. The pulsing is achieved by moving the workpieces together and apart 3 Information and requirements to be agr
24、eed and to be documented 3.1 Information to be supplied by the purchaser The following information to be supplied by the purchaser shall be fully documented. Both the definitive requirements specified throughout the standard and the documented items shall be satisfied before a claim of compliance wi
25、th the standard can be made and verified. a) Specification of the material to be welded (see clause 5) and of the required welded joint properties. b) Whether procedure approval tests are required and, if so, the necessary details (see clause 10). c) The dimensional tolerances and surface finish of
26、the welded product. d) The number and title of the particular application standard; or where no application standard exists a statement of the quality and mechanical properties required. e) Whether production test specimens are to be retained for examination by the purchaser or his representative. 3
27、.2 Requirements to be agreed The following items to be agreed between the contracting parties, which are specified in the clauses referred to, shall be fully documented. Both the definitive requirements specified throughout the standard and the following documented items shall be satisfied before a
28、claim of compliance with the standard can be made and verified. a) Extent of dressing to remove upset (see 9.1). b) Whether welded joints are to be subjected to any post weld heat treatment or controlled cooling (see 9.2). Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 200
29、6, Uncontrolled Copy, (c) BSI BS 6944:1988 2 BSI 04-1999 c) The type and number of welds required for procedure approval testing (see 10.1). d) Limitations of the applicability of the welding procedure see 10.3 b). e) Whether test specimens are to be subjected to any post weld heat treatment (see 10
30、.4). f) Bend testing: 1) test procedure where this does not comply with BS 709 see 10.6.1 a); 2) test procedure where entire section is used as test specimen see 10.6.1 b); 3) test requirements see 10.6.1 c); 4) variation in acceptable level of defects (see 10.6.2). g) Tensile testing: 1) test requi
31、rements for component testing where no application standard exists see 10.8 a); 2) variation in test specimen shape see 10.8 c). h) Number and type of production control tests (see 12.2.1). i) Whether production control bend test specimens are to be retained for examination (see 12.2.3). j) If param
32、eter monitoring in production testing is required see clause 13 b). k) If non-destructive testing of production welds is required (see clause 14). l) Acceptance criteria for weld imperfections (see clause 15). 4 Welding equipment All welding shall be done on a machine with an automatic flash welding
33、 sequence. NOTE 1Guidance on the choice of welding equipment is given in Appendix A. NOTE 2Where flash welding guards are used, they should be placed at such a distance from the clamped components as to minimize the possibility of particles thrown off during the flashing period richocheting into the
34、 weld. 5 Material to be welded It shall be demonstrated by the procedure approval tests (see clause 10) that the material or combination of materials selected can be satisfactorily flash welded. NOTE 1Certain features of the metallurgical structure such as laminations or non-metallic inclusions, can
35、 be detrimental to weld quality as can the presence of minor alloying elements naturally occurring or deliberately added to aid processing, e.g. to confer free cutting properties. NOTE 2Components to be joined should be of similar shape and cross-sectional area. 6 Process sequence: general The seque
36、nce shall consist of all or selected operations from those listed in clauses 7, 8 and 9 but the order in which the operations are carried out shall be as stated in the welding procedure (see 10.1 and Figure 1) and not necessarily in the sequence given in these clauses. Where specific operations are
37、used these shall be carried out according to the relevant requirements given in clauses 7, 8 and 9. 7 Process sequence: preparation The procedure for component preparation, including the acceptable flatness and other characteristics of the surfaces to be welded, shall be established during the proce
38、dure development. Areas of electrical contact on the component and the machine shall be cleaned, as required, to give a consistent, low resistance interface. 8 Process sequence: welding 8.1 Overhang Where components are of the same nominal size and composition, they shall be positioned in the weldin
39、g machine such that the welding interface is central to the contact dies as assessed by visual or mechanical means. The overhang for a particular application shall be determined and specified in the procedure. NOTEThe two components should be clamped wherever possible so that the overhang of each is
40、 equal. Where the composition or size of the two components is different it may be desirable for them to have different overhangs, either to achieve a heat balance or to permit effective work holding. The initial die opening (sometimes referred to as start gap or clamping distance) is equal to the s
41、um of the overhang of the two components. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 06:14:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6944:1988 BSI 04-19993 8.2 Clamping force Components shall be secured in the welding machine by clamps or a combination of clamps and end-stops. The
42、 clamping force exerted on the components shall not cause deformation or deleterious marking of the components. 8.3 Alignment The ends of the components to be welded shall be aligned such that the tolerances specified for the finished product can be achieved. 8.4 Initial end squaring If initial end
43、squaring is carried out to reduce irregularities on the end of the workpieces by flashing, it shall not overheat the component such as to cause collapse or distortion. NOTEInitial end squaring is sometimes known in flash welding as burnoff. 8.5 Pre-heating During pre-heating, the heating of the comp
44、onent ends shall be uniform when assessed visually. NOTEThere should be no evidence of gross local melting on the ends of the components during pre-heating. 8.6 Flashing Once initiated, flashing shall be continuous. NOTEWhere a monitoring device is used, the record of flashing will assist in assessi
45、ng whether significant breaks have occurred. 8.7 Upsetting Upsetting shall proceed immediately following flashing. Upsetting shall be sufficient to ensure that voids are closed and oxides are expelled from the weld interface. The weld interface shall extend into the upset metal. 8.8 Upset current ti
46、me The upset welding current shall be maintained until after upsetting has commenced. NOTEThe current should not continue for so long that overheating occurs. 8.9 Unclamping The time between completion of welding and unclamping shall be such that cracking is prevented and deformation is minimized. 9
47、 Process sequence: finishing 9.1 Removal of upset metal Removal of the excess upset metal shall not cause mechanical or thermal damage in the parent metals. The surface of the trimmed area shall be free from cracking. The method of trimming shall be stated in the welding procedure record. The design
48、 thickness of the component shall not be reduced as a result of any dressing. NOTEIn general it is not necessary to remove the upset completely but, by agreement between the contracting parties, see 3.2 a) dressing may be continued until the weld is flush with the component surface. 9.2 Post weld he
49、at treatments Any proposed heat treatment or controlled cooling associated with the welding process shall be stated in the welding procedure record and shall be the subject of agreement between the contracting parties see 3.2 b). 10 Procedure approval 10.1 General A procedure shall be established for each machine, for each size of component, and for each material or combination of materials to be used in production. Sufficient additional tests shall be carried out to define acceptable tolerance bands. Licensed Copy: sheffieldun sheffieldun, na, Tue