The majority of worm gears are supplied already mounted in enclosed housings. This provides the equipment builder a speedier and more reliable method of assembling the drive to the machine. The housing provides protection to the drive components and assists in the correct assembly of gears, bearings, and seals. In addition, a reservoir is provided for the lubricant with features such as fins and fans for the rapid dissipation of heat.
Enclosed drives have become so popular that principal manufacturers produce them in large quantities. These mass produced units are made in a series of sizes that are standardized by the center distance of the gear set. They are listed in basic catalogs providing information on the specific design features. Rating tables are included based on the center distance and ratio with recommended factors and guidance in the selection process. Listings are given with recommended service factors for specific applications.
Maintaining an acceptable lubricant temperature in the sump is critical to the life of the components in an enclosed drive. The ratings must, therefore, consider both the mechanical and the thermal rating. The limiting power rating factor for worm gear drives (Fig. 6.6) is thermal capacity.