scope:

This Japanese Industrial Standard stipulates the method for estimating the strength exhibited by plastic materials against bending fatigue breakage at the dedendum when they are used for cylindrical gears (hereafter referred to as the gears) that constitute a paralleled gear pair. No corresponding International Standard has been established at this point. Evaluation is made by obtaining the allowable bending stress of the gear materials based on results of an operation test of an external gear pair.

It also stipulates the safety evaluation methods using the nominal tangential forces assumed for gears made of plastic materials for which the allowable bending stress has already been obtained based on the evaluation method of this Standard. Safety evaluation is performed by comparing the dedendum bending stress obtained from the nominal tangential force and the allowable dedendum stress obtained from the allowable bending stress of the material. Safety evaluation can be applied to not only external gear pair but also to internal gear pair.

This Standard is applicable to plastic gears and steel gears having the specifications given in a) to l), or to external gear pairs and internal gear pairs consisting only of plastic gears.

Items j) to l) are matters requring special attention.

a) Normal module : ≥ 0.5 mm and ≤ 2.0 mm

b) Reference diameter : ≤ 100 mm

c) Pressure angle : ≥ 14.5° and ≤ 25°

d) Helix angle : ≤ 25°

e) Transverse contact ratio : > 1.0 and < 2.0

f) Facewidth : ≤ 25 mm

g) Gear precision : conforming to the precision class stipulated by JIS B 1702-3

h) Tooth profile : in accordance with the provision in JIS B 1701-1; alternatively, other tooth profile [refer to c) above] than given in the said standard as for normal pressure angle or other dedendum fillet shapes than those created by the basic rack.

i) Others : gear pairs without any contact issues, which consist of gears without natural undercut or sharp tooth tip, and are assembled with a centre distance with no dedendum interference but appropriate backlash, and machined plastic gear pairs apart from the injection-moulded plastic gears mainly covered by this Standard.

j) This Standard can be applied to plastic materials in general, but only when damage mode in the operation test is dedendum fatigue failure.

k) This Standard cannot be applied to cases of extreme friction involving a damage that occurs near the dedendum but may be of a different mode.

l) This Standard can be applied to gears made of fibre-reinforced plastics, except where the strength of the fibre-reinforced plastics, which is dependent on the particular method of fibre reinforcement and the forming process used, is such that a crack can develop in areas other than the dedendum dangerous section (refer to 7.3.2) ^[1].