1、BRITISH STANDARD OBSOLESCENT AUGUST 1988 BS 1768:1963 Incorporating Amendment Nos.1, 2 and 3 Specification for Unified precision hexagon bolts, screws, larger sizes are generally produced by hot forging. Bolts, screws and nuts can also be produced by machining from hexagon bars. Bolts and screws pro
2、duced by cold forging shall, except in the case of bolts and screws bright finished to Grade A (see Table 4, Appendix A) be heat-treated after forging. Bolts, screws and nuts produced by hot forging or by turning from bars, and cold formed nuts shall be heat-treated when this is necessary to give th
3、e requisite mechanical properties specified in Clauses4 and 6 and Appendix A. b. Cold forged bolts and screws. The choice of material used to manufacture bolts and screws by cold forging shall normally be at the discretion of the manufacturer. The finished products shall comply with the requirements
4、 for physical properties as set out in Clause 4 and in Table 4 of Appendix A. If, however, the purchaser wishes to specify the composition of the material to be used, this shall be the subject of agreement with the manufacturer. c. Cold forged nuts and hot forged bolts, screws and nuts. The material
5、 to be used for cold forged nuts or hot forged bolts, screws and nuts depends to a large extent on the size of the product. Unless otherwise stipulated by the purchaser, the choice of material shall therefore be left to the manufacturer provided that the finished products satisfy the requirements fo
6、r mechanical properties set out in Clauses 4 and 6 and in Table 4 and Table 6 of Appendix A, but recommendations on suitable materials are given for guidance in Table 8 and Table 10 of Appendix B. d. Bolts, screws and nuts machined from bars. Table 9and Table 10 of Appendix B give a selection of ste
7、els from BS970 which are among those suitable for particular grades of bolts, screws and nuts. Unless otherwise stipulated by the purchaser, the choice of material shall be left to the manufacturer provided that the finished products satisfy the requirements for mechanical properties set out in Clau
8、ses 4 and 6 and in Table 4 and Table 6 of Appendix A. e. Decarburization. As normally manufactured from wire of ordinary quality, a proportion of threads produced on forged bolts and screws by rolling may have some surface decarburization (principally at crests of threads). For highly stressed bolt
9、applications, the definition and degree of such decarburization shall be negotiated between manufacturer and user. For bolts of strength GradeT and greater, the depth of decarburization, measured from the crest, shall not exceed 33per cent of the height of the threads. Complete freedom from any deca
10、rburization is achieved by shank grinding after heat treatment and before thread rolling; if this is required, it shall be the subject of negotiation between manufacturer and user. f. Rolling laps. When threads are produced by rolling, small laps are commonly present at the crests and are generally
11、of a magnitude which is not detrimental to the performance of the bolt. A lap formed at the crest of the thread perpendicular to the axis of the bolt shall not be considered a cause for rejection if the depth of the lap does not exceed 33per cent of the depth of the thread. Bolts of Grades T, V and X shall be free from laps in the thread flank below the effective diameter. Laps in the flanks above the effective diameter shall not have a depth greater than 33 per cent of the thread depth.
