BS 2M 47:1990 pdf free download.Specification for Retreading of cross ply tyres for aircraft.
BS 2M 47 specifies requirements for the retreading of cross ply aircraft tyres, including carcass rejection criteria and repair limits before processing. It also specifies type approval tests, quality assurance requirements and interchangeability limits to be met by the retreaded tyre after processing. Except where otherwise stated, these requirements apply to both tubed and tubeless tyres.
NOTE 1 The titles of the publications referred to in BS 2M 47 are listed on the inside back cover. NOTE 2 The latest revision of an Aerospace Series standard is indicated by a prefix number. The latest edition of the standard should be used.
2 Definitions
NOTE See Figure 1.
For the purposes of BS 2M 47, the definitions given in BS 3558 apply together with the following.
2.1
batch
a group of tyres of identical size, type and original manufacture that are retreaded in one production run
2.2
buffing
the preparation of the tyre surface before the application of new material
2.3
chine (deflector)
a specially profiled circumferential water-deflecting rib located on one or both side walls of the tyre at a predetermined distance below the tread edge
2.4
mould tread pattern depth
the nominal depth of the groove nearest the centreline of the mould
2.5
R level
the number of times that a carcass has been subjected to a retreading operation (e.g. third retread = R:3)
2.6
retreading
a process of reconditioning a worn tyre by one of the following methods
a) bead-to-bead remoulding. A process in which material is removed as necessary and new material, extending from bead area to head area, is applied.
3.3 Repair limits for tyres operated above 120 miles/h
3.3.1 Tread area. Cuts, cracks or other tread area injuries that are 38 mm in length and 6 mm in
width or less on the first cord body ply and that do not penetrate more than 40 % of the actual tyre cord body plies shall be repaired. Any tread injury
repaired by skiving or rasping shall not have the final repair greater than 50 mm in length.
3.3.2 Tread injuries. Tread injuries shall be
repaired if they penetrate a distance equal to 40 % of actual tyre cord body and if they are 38 mm in
length or less on the first cord body, limited to six per tyre and not less than 60° apart along the tyre circumference. Maximum repairs shall be identified on the tyre.
3.3.3 Sidewall rubber. Surface defects of any degree, weather cracking (ozone cracking), radial and
circumferential cracks, cuts and snags shall be
repaired provided the injuries do not penetrate the cord body fabric plies.
3.3.4 Bead area. Minor injuries to the bead area shall be repaired provided the plies are not
damaged.
3.3.5 Bead seal. The bead seal shall not be affected or intersected by impressions or depressions.
3.3.6 Bead face and bead heel. The bead face and bead heel areas shall be smooth.
3.3.7 Bead toe. The bead toe shall be trimmed so that no edges are exposed above the bead face and so that any bead toe flash remaining does not protrude more than 3 mm from the face contour of the bead. If trimming of the bead toe is necessary, the trimming shall not cut or expose the tyre cord material or more than one layer of chafer material.
3.3.8 Chafer strip. Minor injuries in the chafer strip and slight tyre tool injuries in the general bead area shall be repaired if they do not extend into the plies of the tyre and if there is no sign of separation in the bead area. Loose or blistered chafer strips shall be repaired or replaced.
3.3.9 Inner liner. Inner liner surface damage and defects other than liner splices that are less
than 50 mm in length shall he repaired. A
maximum of 10 of these repairs shall be acceptable with no more than three repairs in any quadrant.
Liner splice damage defects shall be repaired if less than 250 mm in length.
3.3.10 Exposed cord. Exposed cord, either in the
breaker or carcass ply, shall not exceed 1 % of the huffed total tread area on one spot or more than 2 % for the entire tyre. Exposed cord shall not exceed one carcass ply in depth.
5.2.3 Growth allowance. On completion of dynamic testing (see 5.2.2) allow the tyre to cool to ambient temperature. Adjust the pressure to the rated inflation pressure and remeasure the dimensions stated in 5.2.1.1. Calculate the tyre growth, which shall not exceed the allowances given in BS M 45-1 for new tyres.
5.3 Type test report
On completion of each type test the report given in Appendix A shall be forwarded to the approving authority (see foreword).
5.4 Type approval
After type approval has been granted, the individual retreader’s specification shall not be changed without the agreement of the approving authority.
6 R level proof (establishment)
6.1 General
To establish the airworthiness of carcasses used in the manufacture of retreaded tyres, each retread manufacturer shall proceed in accordance with 6.2 to 6.4 and, if applicable. 6.5. This procedure shall be followed for each proposed increase in R level.
6.2 Sample
Select 20 in-service tyres at the highest retread level in use distributed among tyre brands, sizes and operators. If the distribution is biased, it shall be in favour of higher load, high speed tyres.
6.3 Assessment of R level (establishment) Assess the tyre sample in accordance with Table 2 to determine the R level.
6.4 R level proof test
6.4.1 Retreading. Retread the tyre sample in accordance with clause 3.
6.4.2 Proof test. Subject the retreaded sample to the proof test given in Appendix B.
6.5 Retesting
If any tyre fails to comply with the appropriate requirements when tested in accordance with Appendix B. a second sample of 20 tyres, selected and assessed in accordance with 6.2 and 6.3, shall be retested in accordance with 6.4. If any second sample tyre fails to comply with the appropriate requirements, the tyres are below the minimum standards of airworthiness and shall be rejected.
NOTE I A retreader who before publication of this British Standard was retreading aircraft tyres of many sizes to. for example. R7 or higher, may meet the requirements for retreading all tyres up 10 R7 by testing 5 R4 tyres, 10 R6 tyres and 5 R7 tyres. This 20 tyre sample would be distributed among tyre brands, sizes and operators. If later the retreader wanted to qualify for retreading at R9. he would need to test 5 additional R7 tyres and 5 R9 tyres.