BS 235:1987 pdf free download.Specification for Gears for electric traction.
1 Scope
BS 235 specifies requirements for spur and helical gears in accuracy grades 5, 6, 7 and 8 of BS 436-2. for the drive between the electric motors and the axles of vehicles running on rails. It also specifies requirements for the permissible deviations and tolerances of tooth form and dimensions, hardness and the fitting surfaces, keys and keyways of wheels and pinions.
NOTE I Appendix A lists the instructions that should be supplied by the customer to the gear designer. Guidance is given in Appendix B on the materials for the manufacture of gears. Appendix C recommends a method for determining the bedding surface of taper bored pinions. Appendix D gives guidance on the choice of gear tooth accuracy grades.
NOTE 2 The titles of the publications referred to in this standard are listed on the inside back cover.
2 Definitions
For the purposes of BS 235 the definitions given in BS 25 19-1 apply, together with the following.
case depth of a surface hardened gear the depth measured normal to the surface of the gear at which the hardness is 550 HV 1 for carburized and hardened gears and 80 % of surface hardness HV 1 for all other surface hardened gears
3 Gear tooth accuracy grades
Gears for electric traction shall belong to accuracy
grades 5, 6, 7 or 8 of BS 436-2.
4 Symbols
For the purposes of BS 235 the symbols shown in BS 2519-2 apply. For convenience the list of symbols used in BS 235 is as follows:
a Centre distance
b Face width
b1 Face width, pinion Face width, wheel
d Reference circle diameter
d1 Reference diameter, pinion
d9 Reference diameter, wheel
da Tip diameter
d1 Tip diameter, pinion
da9 Tip diameter, wheel
db Base diameter
ha Addendum
KA Application factor
k Number of teeth over which base tangent span is measured
I Length of arc
8 Hardness and case depth of finished,
surface hardened gears
8.1 Hardness tests
Hardness tests, appropriate to the gear being tested, shall be carried out on finished, surface hardened gears in accordance with BS 240, BS 427-1, BS 891-1, BS 6479 or BS 6481.
In cases where it is necessary to convert hardness numbers, such conversions shall be in accordance with BS 860.
8.2 Position and number of hardness tests When measurements on a sufficient number of gears show the relationship between hardness at the chosen position and tooth flank hardness to be consistent, hardness tests shall be carried out on both flanks of two teeth approximately 180° apart or on crests, roots or ends of teeth.
8.3 Carburized and hardened gears The surface hardness of carburized and hardened gears shall be not less than 650 HV 30 (58.0 HRC). Maximum hardness, appropriate to the materials being used, shall be specified on the manufacturer’s drawings.
8.4 Other case hardened gears
The surface hardness of other case hardened gears shall be not less than 550 HV 30 (53.1 HRC). Maximum hardness, appropriate to the material being used and the production process, shall be specified on the manufacturer’s drawings.
8.5 Case depth
8.5.1 General. The effective case depth shall be determined in accordance with BS 6481 for induction hardening and BS 6479 for carburizing.
8.5.2 arburized and hardened gears. The case depth of carburizeci and hardened gears shall comply with Table 6, as appropriate. For checking the case depth each container shall have one “spy piece” when box carburizing, and at least one, but preferably two (towards top and bottom of furnace), when gas carburizing. The “spy piece” shall have a cross section which simulates that of the teeth which it represents, and shall be placed near to, but not on, the teeth of the gear. To verify hardness depth, as specified in Table 6, a traverse shall be made over a section of this “spy piece”.
8.6 Crack detection
After heat treatment all gears shall be inspected for cracks.
NOTE While the magnetic method is generally used
(see BS 6072), the use of other methods. e.g. dye penetrant
(see BS 6443). is not precluded.
9 Gear load capacity
The load capacity of the gears shall be assessed in accordance with BS 436-3.
NOTE It is emphasized that it is the responsibility of the gear designer in collaboration with the customer or his agent, to provide an application factor KA which needs to take into account load increments deriving from condition of the track and any other source, e.g. coupling snatch, high starting-torques.
10 Features of the wheels and pinions
10.1 Fitting surfaces
10.1.1 If tapered, the fitting surface shall have a taper on diameter of either I in 10 or I in 20.
NOTE The latter is usually used for plug-in pinions.
10.1.2 When the pinion is fitted with its corresponding taper gauge there shall be bedding over not less than 90 % of the fitting surface.
NOTE Appendix C gives a recommended method for determining the bedding area of taper bores.
10.1.3 The fitting surface of all taper bores shall have a surface texture not coarser than 0.6 um Rd when measured in accordance with BS 1134-1.
10.1.4 The fitting surface of parallel head gear wheels shall have a surface texture not coarser than 0.8 irn I?. when measured in accordance with
BS 1134-1.
10.1.5 Where oil injection holes and grooves are provided, sharp corners shall be blended out.
10.2 Keys, keyways and shaft ends
10.2.1 General. Keys, keyways and shaft ends shall comply with BS 4235-1 and BS 4506.
10.2.2 Alignment of keyways. The alignment of keyways shall be checked. The tangent of the maximum deviation of the radial plane of symmetry of a keyway, from an axial plane of a bore or shaft, shall not exceed 0.0005 units per unit length.
NOTE 1 The relative positions of keyway and tooth spaces should be such as to reduce the possibility of fracture between root fillet and keyway.
NOTE 2 A suitable means for checking the alignment is a plug gauge with a dummy key.
10.3 Profile grinding of hardened gears
When the teeth of hardened gears are ground, the tooth flanks of the wheels and pinions shall be fully cleaned up over the usable tooth surface.
11 Marking
Each gear wheel and pinion shall be plainly marked with the manufacturer’s identification and serial number.
NOTE Any other information required by the purchaser may also be marked.
Marking shall not result in stress raisers in highly stressed areas.