1、BRITISH STANDARD AEROSPACE SERIES BS 2A 293:2005 Procurement of self-locking nuts with non-metallic locking elements Metric series Specification ICS 49.030.30 BS 2A 293:2005 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 22 February 2005 BSI
2、 22 February 2005 The following BSI references relate to the work on this British Standard: Committee reference ACE/12 Draft for comment 03/317781 DC ISBN 0 580 45229 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee, ACE
3、/12, Aerospace fasteners and fastening, upon which the following bodies were represented: British Coatings Federation Ltd. Civil Aviation Authority, Airworthiness Energy Institute Ministry of Defence, UK Defence Standardization Society of British Aerospace Companies Amendments issued since publicati
4、on Amd. No. Date CommentsBS 2A 293:2005 BSI 22 February 2005 i Contents Page Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3T e r m s a n d d e f i n i t i o n s 1 4 Requirements and test methods 3 5 Quality Assurance and product qualification testing ap
5、provals 9 6 Packing, packaging and labelling 10 7I n s p e c t i o n 1 0 8 Production acceptance test report 10 Annex A (normative) Axial loads and torque values for thread sizes M8 1.25, M10 1.5 and M12 1.5 17 Bibliography 19 Table 1 Qualification approval testing requirements for self-locking nut
6、samples 11 Table 2 Qualification and production acceptance tests 12 Table 3 Discontinuity depths 12 Table 4 Axial load values 100 % axial load test 13 Table 5 Maximum assembly and wrench torque test values 14 Table 6 Maximum locking torque, minimum breakaway torque, assembly torque (vibration), push
7、 out and torque out values 15 Table 7 Classification of defects 15 Table 8 Sampling data for visual and dimensional characteristics 16 Table 9 Sampling data for mechanical and metallurgical characteristics 16 Table 10 Contaminants 16 Table A.1 Maximum assembly and wrench torque test values for threa
8、d sizes M8 1.25, M10 1.5 and M12 1.5 17 Table A.2 Axial load values for thread sizes M8 1.25, M10 1.5 and M12 1.5 17BS 2A 293:2005 ii BSI 22 February 2005 Foreword This British Standard was prepared by Technical Committee ACE/12. It supersedes BS A 293:1983, which is withdrawn. BS 2A 293 is intended
9、 primarily for use in conjunction with those “A” series British Standard aerospace specifications in which conformity to this standard is a specific requirement. This edition introduces technical changes in line with test methods BS 2A 295:2000 and harmonizes the procurement and testing of the metri
10、c series non-metallic self-locking nuts with the equivalent Unified series nuts contained in BS 3A 125 to 3A . It may also be applied to other aerospace metric threaded fasteners if required by the relevant specification, drawing, contract or order. This standard invokes: a) quality assurance approv
11、al of the manufacturer; and b) product qualification testing approval. Annex A is included in this standard to provide information on the axial loads and torque values for thread sizes M8 1.25, M10 1.5 and M12 1.5. When there is no further requirement for these sizes, Annex A will be deleted by amen
12、dment. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its 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
13、inside front cover, pages i and ii, pages 1 to 19 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 2A 293:2005 BSI 22 February 2005 1 1 Scope This British Standard specifies the requirements for the procurement of self-locking nuts
14、with non-metallic locking elements. This standard invokes product qualification testing requirements and quality assurance approval procedures for manufacture of aerospace standard parts. This standard is intended primarily for use with “A” series British Standard aerospace standards for metric self
15、-locking nuts with non-metallic locking elements. It is also applicable to other aerospace self-locking nuts if required by the relevant drawing, contract or order. NOTE Where the requirements of the nut standard or drawing differ from this standard, they take precedence over the requirements of thi
16、s standard. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the cited edition applies. For undated references, the latest edition of the referenced document (including any amendments) applies. BS 1134, Metho
17、d for the assessment of surface texture. BS 1595-1, Propan-2-ol (isopropyl alcohol) for industrial use Part 1: Specification for propan-2-ol (isopropyl alcohol). BS A 352-2/ISO 5855-2, MJ threads Part 2: Limit dimensions for bolts and nuts. BS 2A 295/ISO 7481, Methods of test for self-locking nuts w
18、ith maximum operating temperature less than or equal to 425 C. BS 3A 125 to 3A ., Specification for stiffnuts (Unified threads) for aircraft. BS EN 9100, Aerospace series Quality management systems Requirements (based on ISO 9001:2000) and Quality systems Model for quality assurance in design, devel
19、opment, production, installation and servicing (based on ISO 9001:1994). 3 Terms and definitions For the purposes of this British Standard the following terms and definitions apply. 3.1 self-locking nut with non-metallic locking element self-contained unit which consists of a nut body surmounted by
20、a non-metallic locking element which imposes friction between itself and the male screw thread upon which it is mounted 3.2 nut body portion of the self-locking nut containing the screw thread 3.3 locking element non-metallic portion of the self-locking nut designed to impose friction between itself
21、 and the male screw thread with which it is engaged NOTE The locking element does not operate by means of a separate movement as a result of installation and does not depend upon pressure on the bearing surface for the locking action. 3.4 maximum locking torque highest torque to overcome the frictio
22、n encountered in any assembly or removal cycle with no axial load on the nut 3.5 minimum breakaway torque torque required to start nut or bolt rotation from a fixed position during any removal cycle with no axial load on the nutBS 2A 293:2005 2 BSI 22 February 2005 3.6 wrench torque minimum torque w
23、hich the driving configuration of the nut has to withstand without any permanent deformation which would interfere with the appropriate wrench and preclude the reuse of the nut 3.7 permanent set test measure of the performance of a nut on a minimum mandrel after having been subjected to a single ass
24、embly and removal cycle on a maximum stud 3.8 reusability test test to measure the torque required to remove a self-locking nut from a standard test bolt after a specified number of assembly and removal cycles 3.9 production lot lot of finished nuts which have the basic part number and diameter, the
25、 individual elements of which have been fabricated by the same process from a single material batch, and which have been heat treated together to the same specified condition and produced as one continuous run 3.10 inspection lot lot of nuts from a single production lot, of the same part number, whi
26、ch completely defines the nut 3.11 Discontinuities 3.11.1 crack rupture in the material which may extend in any direction and which may be intercrystalline or transcrystalline in character 3.11.2 seam longitudinal surface defect in the form of an unwelded open fold in the material 3.11.3 lap surface
27、 defect caused by folding over metal fins or sharp corners and then rolling or forging them into the surface 3.12 random sample sample taken in such a manner that each unit in the inspection lot has the same chance of being the first unit in the random sample; and, after the first unit in the sample
28、 is taken, each of the remaining units in the inspection lot has the same chance of being the second unit in the sample; and so on 3.13 acceptable quality level AQL maximum percentage defective (or maximum number of defects per hundred units) that, for purposes of sampling inspection, can be conside
29、red acceptable as a process average 3.14 limiting quality LQ magnitude of percentage defective, greater than the AQL, which, in accordance with the operating characteristic of the sampling/inspection plan, the purchaser runs a specified risk of accepting NOTE In this standard the LQ corresponds to a
30、 purchasers risk of 10 %.BS 2A 293:2005 BSI 22 February 2005 3 4 Requirements and test methods 4.1 Introduction The technical requirements and test methods given in 4.2, 4.3, 4.4, 4.5 and 4.6 complement the requirements of the self-locking nut standard or drawing, but can supplement the requirements
31、 of the material specification. Table 1 gives the testing for each characteristic of the self-locking nut sample necessary for qualification approval. Table 2 summarizes the testing required for both qualification and production acceptance testing. All tests shall be carried out at ambient temperatu
32、re unless otherwise specified in a particular test method. NOTE 1 A nut is considered to be assembled when a minimum of two full male threads plus the chamfer extend beyond the friction element of the nut. NOTE 2 The removal cycle is considered complete when the friction element is disengaged.BS 2A
33、293:2005 4 BSI 22 February 2005 Subclause Characteristic Technical requirement Inspection and test method Q/A a Sample size 4.2 Materials The nut shall be made from the material specified by the nut standard or drawing. As stated in the material specification. 4.3 Dimensions 4.3.1 General The dimens
34、ions of the finished nut shall comply with the nut standard or drawing. All dimensions shall be controlled by the manufacturers quality system. Q 60 (100 %) A Table 7 and Table 8 4.3.2 Threads The threads shall comply with the requirements specified by the nut standard or drawing. Q 60 (100 %) A Tab
35、le 7 and Table 8 4.3.3 Squareness The bearing surface of the nut shall be square to the axis of the thread within the tolerance specified by the nut standard or drawing. Bearing surface squareness test, 3.2 of BS 2A 295:2000. Q 60 (100 %) A Table 7 and Table 8 4.4 Manufacture 4.4.1 Nut bodies Nut bo
36、dies shall be produced by machining from bar or by a hot or cold forging process. The method of manufacture shall be defined by control documentation to the satisfaction of the appropriate airworthiness authority. 4.4.2 Heat treatment The parts shall be heat treated as necessary, to satisfy the requ
37、irements of this specification. 4.4.3 Surface texture The surface texture shall be as specified by the nut standard or drawing prior to protective treatment. BS 1134 Q 3 A Table 7 and Table 8 4.4.4 Surface protection Surfaces shall be coated as specified by the nut standard or drawing. Relevant coat
38、ing specification. Q3 A Table 7 and Table 8 4.4.5 Lubrication Surfaces shall be coated as specified by the nut standard or drawing. Relevant coating specification. Q3 A Table 7 and Table 8 a Q is the qualification approval test requirement and A is the production acceptance test requirement.BS 2A 29
39、3:2005 BSI 22 February 2005 5 Subclause Characteristic Technical requirement Inspection and test method Q/A a Sample size 4.5 Metallurgical properties 4.5.1 Discontinuities Nuts shall be examined for discontinuities. Nuts having discontinuities exceeding the limitations specified in Table 3 shall be
40、 rejected. Non-corrosion resisting steel nuts shall be magnetically inspected by both longitudinal and circular methods. The combined method is permissible. Q 60 (100 %) A Table 7 and Table 8 Care shall be exercised to avoid confusing cracks with other discontinuities (see 3.11). Cracked parts shall
41、 be rejected. Nuts made from non-magnetic material shall be subjected to a visual examination of magnification 10. Parts showing indications which are considered cause for rejection shall be subjected to metallographic examination at a magnification of 100. A Table 9, column B 4.5.2 Magnetic permeab
42、ility and residual magnetism (applicable to corrosion resisting steel nuts only) The magnetic permeability of corrosion resisting steel nuts shall be as specified in the material specification of the product. Residual magnetism shall not exceed 0.5 gauss. Magnetic field indicator of suitable calibra
43、tion, used in accordance with the manufacturers instructions. Q3 A Table 9, column B NOTE The same test sample may be utilized for more than one test provided that none of the characteristics of the sample are altered during the examination procedure. a Q is the qualification approval test requireme
44、nt and A is the production acceptance test requirement.BS 2A 293:2005 6 BSI 22 February 2005 Subclause Characteristic Technical requirement Inspection and test method Q/A a Sample size 4.6 Product performance 4.6.1 Axial tensile strength Nuts shall withstand the minimum tensile load appropriate to t
45、heir strength classification as defined in the nut standard or drawing, and as specified in Table 4. Nuts shall support the relevant axial tensile strength load without rupture. 3.3 of BS 2A 295:2000. This test shall be carried out at ambient temperature. Q3 A Table 9, column B 4.6.2 Permanent set T
46、he nut shall not exceed the maximum permissible locking torque during assembly onto a maximum mandrel as specified in Table 6. 3.11 of BS 2A 295:2000 Q 3 AN i l During removal from a minimum mandrel the nut shall not exhibit a breakaway torque less than that specified in Table 6. 4.6.3 Accelerated e
47、nvironmental reusability Nuts shall meet the minimum breakaway torque and the maximum locking torque specified in Table 6 after each of four cycles of loaded heat soak. Each cycle shall consist of six hours at minimum operating temperature followed by six hours at maximum operating temperature. 3.10
48、 of BS 2A 295:2000 Q 10 AN i l 4.6.4 Reusability 4.6.4.1 Qualification acceptance Nuts shall be capable of 100 cycles of reuse without exhibiting locking torques outside the range specified in Table 6. 3.9 of BS 2A 295:2000 Q 10 Test shall be carried out on nuts in the “as received” condition. 4.6.4
49、.2 Production acceptance Nuts shall be capable of 30 cycles of reuse without exhibiting locking torques outside the range specified in Table 6. 3.9 of BS 2A 295:2000 A Table 9, column B a Q is the qualification approval test requirement and A is the production acceptance test requirement.BS 2A 293:2005 BSI 22 February 2005 7 Subclause Characteristic Technical requirement Inspection and test method Q/A a Sample size 4.6.5 Contamin
