Calculating Worm Gear Strength With ANSI

Based on the fixed-end beam calculation. Includes the majority of effects.

Dynamic Load

F d = F t2 K v

where:

	F_t2	Poisson's ratio (material value)
		circumferential force factor
	v₂	gear circumferential speed [ft/min]

Allowable Bending Force

F s = S n b 2 p y ≥ F d

where:

	S_n	limiting bending strength (material value)
	b₂	gear width
	p	gear pitch
	y	form factor (Lewis factor)

Allowable Contact Force

F w = d 2 b 2 K w ≥ F d

where:

	K_w	limiting contact strength (material value)
	b₂	gear width
	d₂	gear pitch diameter

Increase of Temperature Check

Q max ≥ P z

where:

	P_z= P (1 - η + 0.3)	lost power
	Q_max= C A (t_max- t₀) / 33000	heat conducted away in oil
	t_max- t₀= 120° F	allowable temperature drop
	A	gearbox surface, which conducts away the heat, A ≈ 0.3 a^1.7for well ribbed gearbox
	C	transfer of heat factor, C ≈ 0.0356 n₁+ 20 for the gearbox with fan and bottom worm