Single Enveloping Worm Gearing :

The Single Enveloping worm is made as a cylindrical component with the outer diameter the same through the length of the threaded section (Figs. 1 & 3). The teeth on the gear are contoured to partially surround or "envelop" the worm thread (Fig. 2), thus the term "single enveloping" worm gear. Single enveloping worm gear products depend on the mesh of one to two gear teeth to transfer and multiply torque.
Because of the relative simplicity and lower manufacturing costs of single vs. double enveloping worm gears, SE speed reducers provide a highly suitable and economical solution for low and medium horsepower applications.

Double Enveloping Worm Gearing :

Like single enveloping gears, the teeth on the double enveloping gear are contoured to partially surround or "envelop" the worm thread (Fig. 5). The second enveloping condition results from the double enveloping worm being contoured narrower in the middle than at the ends (Figs. 4 & 6), allowing it to partially envelop the gear. Thus the term "double enveloping".
Double enveloping worm gear products depend on the mesh of several gear teeth, up to 1/8 of the gear circumference, to transfer and multiply torque. The additional teeth in contact, two to four times more than in a single enveloping gear set, increases the total contact area in the mesh by a similar amount. In addition, lubrication between the worm and gear is improved due to a more favorable direction of contact lines in the mesh relative to worm rotation. This results in ratings for double enveloping gear sets that are two to four times the ratings for single enveloping gear sets of similar size and are significantly more efficient.

Material:

Clean:

Lubricated:

Phosphor-bronze

0.35

Aluminum-bronze

0.45

Bronze

0.16

Sintered-bronze

0.13

Hard carbon

0.14

0.11-0.14

Graphite

0.1

0.1

Tungsten carbide

0.4-0.6

0.1-0.2

Teflon

0.04

0.04