gearbox.standards.iso6336.pitting

Surface durability (pitting) of cylindrical gears according to ISO 6336-2.

class PittingResult

Bases: object

Result of an ISO 6336-2 contact stress calculation. Stresses are in MPa.

contact_stress_pinion: float

contact stress at the pinion.

Type:

sigma_H1

contact_stress_wheel: float

contact stress at the wheel.

Type:

sigma_H2

permissible_contact_stress_pinion: float

permissible contact stress of the pinion (includes S_Hmin).

Type:

sigma_HP1

permissible_contact_stress_wheel: float

permissible contact stress of the wheel.

Type:

sigma_HP2

safety_factor_pinion: float

S_H1 = sigma_HP1 * S_Hmin / sigma_H1.

safety_factor_wheel: float

S_H2.

zone_factor: float

Z_H.

single_pair_contact_factor_pinion: float

Z_B.

single_pair_contact_factor_wheel: float

Z_D.

elasticity_factor: float

Z_E [sqrt(MPa)].

contact_ratio_factor: float

Z_epsilon.

helix_angle_factor: float

Z_beta.

life_factor_pinion: float

Z_NT of the pinion.

life_factor_wheel: float

Z_NT of the wheel.

lubricant_factor: float

Z_L.

velocity_factor: float

Z_v.

roughness_factor: float

Z_R.

__init__(contact_stress_pinion, contact_stress_wheel, permissible_contact_stress_pinion, permissible_contact_stress_wheel, safety_factor_pinion, safety_factor_wheel, zone_factor, single_pair_contact_factor_pinion, single_pair_contact_factor_wheel, elasticity_factor, contact_ratio_factor, helix_angle_factor, life_factor_pinion, life_factor_wheel, lubricant_factor, velocity_factor, roughness_factor, work_hardening_factor_pinion, work_hardening_factor_wheel, size_factor, dynamic_factor, face_load_factor, transverse_load_factor)

work_hardening_factor_pinion: float

Z_W of the pinion.

work_hardening_factor_wheel: float

Z_W of the wheel.

size_factor: float

Z_X.

dynamic_factor: float

K_v.

face_load_factor: float

K_H_beta.

transverse_load_factor: float

K_H_alpha.

calculate_pitting(transmission, *, static=False)

Compute the contact stress and permissible contact stress of both gears.

Parameters:

• transmission (Transmission) – The gear pair and its operating conditions.

• static (bool) – Evaluate the permissible stress for a static load (N_L below the knee of the S-N curve): Z_NT takes the value of the horizontal branch, Z_L = Z_v = Z_R = 1 (formula 57) and Z_W follows the static formulae (62-64). The design life is then ignored.

Returns:

A PittingResult with the stresses and every intermediate factor.

Return type:

PittingResult

zone_factor(transmission)

Zone factor Z_H.

Return type:

float

single_pair_contact_factors(transmission)

Contact factors (Z_B, Z_D) of pinion and wheel, ISO 6336-2 clause 6.3.

• Spur gears: Z_B = max(M1, 1) and Z_D = max(M2, 1) (formulae 17-18). For an internal wheel z_2 is negative in formula (17) and Z_D = 1.

• Helical gears with eps_beta >= 1: Z_B = Z_D = sqrt(f_ZCa) (19), table 3.

• Helical gears with eps_beta < 1: linear interpolation (20)-(23).

Z_D is only determined for u < 1.5; above that M2 is taken as 1 (as for internal gears, 6.3).

Raises:

ValueError – If eps_alpha <= 1, a case outside the scope of the standard.

Return type:

tuple[float, float]

life_factor(material_type, transmission, speed_rpm, *, static=False)

Life factor Z_NT, ISO 6336-2:2019 table 5 and figure 6 (log-log interpolation).

Steels and pearlitic irons follow curve 2 (no pitting allowed) or, when Transmission.limited_pitting_allowed is set, curve 1. The static value is the horizontal branch of the curve.

Return type:

float

lubricant_factor(transmission)

Lubricant factor Z_L.

Return type:

float

velocity_factor(transmission)

Speed factor Z_v.

Return type:

float

roughness_factor(transmission)

Roughness factor Z_R, based on the lower contact stress limit of the pair.

Return type:

float

work_hardening_factors(transmission)

Work hardening factors (Z_W1, Z_W2) for reference and long life stress.

Z_W takes into account the strengthening of a soft wheel meshing with a harder, smooth pinion and therefore applies to the wheel only (ISO 6336-2, clause 13.3):

• surface-hardened steel pinion with through-hardened steel wheel: formulae (58)-(61);

• through-hardened steel pinion with through-hardened steel wheel: formulae (65)-(68);

• surface-hardened steel pinion with ductile iron wheel: formulae (69)-(71).

For every other combination Z_W = 1.

Return type:

tuple[float, float]

static_work_hardening_factors(transmission)

Work hardening factors (Z_W1, Z_W2) for static stress, ISO 6336-2 clause 13.3.1.4.

Only a surface-hardened pinion against a through-hardened steel wheel gives Z_W > 1: 1.05 - (HB - 130) / 6800 for 130 <= HB <= 470, 1.05 below and 1.0 above. Every other combination uses 1.0 (13.3.2.4 and 13.3.3.4).

Return type:

tuple[float, float]