BS A 302:1992 download free.Self-locking nuts with maximum operating temperature less than or equal to 425 °C — Procurement specification.
1 Scope
BS A 302 specifies the requirements for metric self-locking nuts, with MJ thread, for use in aerospace construction at a maximum temperature less than or equal to 425 °C.
It applies to self-locking nuts as defined above, provided that reference is made to this International Standard in the relevant definition document.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of BS A 302. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. Iso 691:1983, Wrench and socket openings—Met nc series — Tolerances for general use.
ISO 1463:1982, Metallic and oxide coatings — Measurement of coating thickness — Microscopical method.
Iso 2859-1:1989, Sampling procedures for inspection by attributes — Part 1: Sampling plans indexed by acceptable quality level (AQL,) for lot-by-lot inspection.
Iso 3452:1984. Non-destructive testing — Penet rant inspection — General principles.
ISO 3887:1976, Steel, non-alloy and low-alloy — Determination of depth of decarbu rization.
ISO 5855-2:1988, Aerospace — MJ threads — Part 2: Limit dimensions for bolts and nuts. Iso 7403:1983, Fasteners for aerospace construction — Spline drive wrenching configuration — Metric series.
Iso 7481:1984, Aerospace — Fasteners — Self- locking nuts with naxim u tn operating
temperature less than or equal to 425 °C — Test methods.
ISO 8788:1987, Aerospace — Fasteners — Tolerances of form and position for nuts. ISO 9002:1987, Quality systems — Model for quality assurance in production and installation. ISO 9227:1990, Corrosion tests in artificial atmospheres — Salt spray tests.
3 Definitions
For the purposes of BS A 302, the following definitions apply.
3.1
definition document
document specifying all the requirements for nuts, i.e.
— metallurgical;
— geometrical and dimensional:
— functional (strength and temperature classes).
the definition document may be an International Standard. a national standard, an in-house standard or a drawing
3.2
finished nut
nut ready for use, inclusive of any possible treatments andlor surface coatings, as specified in the definition document
3.3
batch
definite quantity of some commodity manufactured or produced under conditions which are presumed to be uniform’
for the purposes of BS A 302, a batch is a quantity of finished nuts, of the same type and same diameter, produced from a material obtained from the same melt, manufactured in the course of the same production cycle, following the same manufacturing route and having undergone all the relevant heat treatments and surface treatments
3.4
crack
rupture in the material which may extend in any direction and which may be intercrystalline or transcrystalline in character
3.5
seam
open surface defect resulting from extension of the metal
3.6
lap
the folding over of unwelded metal that can arise when the material is formed (drawing) or in the finished product (pressing or forging)
3.7
inclusions
non-metallic particles originating from the material manufacturing process. These particles may be isolated or arranged in strings
3.8
critical defect
a defect that, according to judgement and experience, is likely to result in hazardous or unsafe conditions for individuals using, maintaining or depending upon the considered product, or that is likely to prevent performance of the function of a major end item2
3.9
major defect
a defect, other than critical, that is likely to result in
a failure or to reduce materially the usabilit’ of the
considered product for its intended purpose
3.10
minor defect
a defect that is not likely to reduce materially the usability of the considered product for its intended purpose, or that is a departure from established specifications having little bearing on the effective use or operation of this prod uct2
3.11
sampling plan
a plan according to which one or more samples are taken in order to obtain information and possibly to
9)
reach a decision
for the purposes of BS A 302, each sampling plan specifies the number of nuts to be inspected as a function of the size of the batch and the acceptance number (number of defective items acceptable — Ac)3
3.12
simple random sampling
the taking of ii items from a population of N items in such a way that all possible combinations of n items have the same probability of being chosen2
3.13
acceptable quality level (AQL)
a quality level which in a sampling plan corresponds to a specified but relatively high probability of acceptance
it is the maximum percent defective (or the maximum number of defects per hundred units) that, for purposes of sampling inspection, can be considered satisfactory as a process average2
3.14
limiting quality (LQ)
in a sampling plan, a quality level which corresponds to a specified and relatively low probability of acceptance. It is the limiting lot quality characteristic that the consumer is willing to accept with a low probability that a lot of this quality would occur2
in BS A 302, the limiting quality quoted in Table 12 corresponds to a consumer’s risk of 10 %
3.15
self-locking torque
the torque to be applied to the nut or bolt to maintain its movement of rotation in relation to the associated part, the assembly being under no axial load and the nut-locking system being completely engaged with the bolt (two pitches minimum protrusion including the end chamfer)
3.16
seating torque
the tightening torque to be applied to the nut or bolt to introduce or to increase the axial load in the assembly
3.17
unseating torque
the untightening torque to be applied to the nut or bolt to reduce or remove the axial load in the assembly
3.18
breakaway torque
the torque required to start unscrewing the nut or bolt with respect to the associated part, with the nut-locking device stilL fully engaged on the bolt, but after the axial load in the assembly has been removed by unscrewing half a turn followed by a halt in rotational movement
3.19
wrench torque
the tightening and untightening torques which the driving feature of the nut shall withstand. repeatedly, without any permanent deformation which would prevent the appropriate wrench from being used and preclude re-use of the nut
4.3 Production acceptance inspection and test conditions
Production acceptance inspections and tests (requirements, methods, numbers of nuts) are specified in Table 1. They shall be carried out on each batch. Nuts from the batch to be tested shall be selected by simple random sampling.
Each nut may be submitted to several inspections and tests.
The nuts to be subjected to destructive inspections or tests may be those on which non-destructive inspections or tests have been carried out.
If a more stringent inspection is deemed necessary, all or part of the qualification inspections and tests may be performed during the production acceptance inspections and testing. In this case, the number of nuts submitted to these inspections and tests is the same as that submitted for qualification inspections and tests.
Batches declared unacceptable after the production acceptance inspections and tests shall be re-submitted for inspection or testing only after all the defective units have been removed andlor defects have been corrected.
Twice the normal sample size shall be used for re-inspecting or re-testing the attributes causing the initial rejection; the same acceptance level (Ac) shall be used.
Production acceptance inspections and tests are summarized in Table 2.
5 Requirements
The requirements of BS A 302 are given in Table I. They complement the requirements of all other standards or specifications referenced in the definition document of the nut.
NOTE 1 The attention of the users of this international Standard is drawn to the fact that if there is no International Standard specifying the method to be used, a prior agreement is necessary between the user and the manufacturer with respect to the following inspections and tests:
— spectrographic analysis or spectroscopic analysis of the
material (see 5.1.1):
— micrographic inspection of the structure of the
material (see 5.1.2):
— inspection of carburization or decarburization (see 5.1.3):
— niagnetoscopic inspection of surface discontinuities
(see 5.1.4):
— magnetic permeability inspection (see 5.1.6):
— inspection by chemical reagent of the type of surface
coating (see 5.2.2):
— tactile inspection or inspection using a profilometer of the
surface roughness (see 5.3.2).