Why Not Use Worm Gear Unit?
There is one especially glaring reason why one would not select a worm gear over a normal gear: Lubrication.
The movement between the wheel and the worm faces is totally sliding. There is no rolling part to the tooth contact or interaction. This makes them comparatively difficult to lubricate.
The lubricants needed are commonly very great viscosity (ISO 320 and higher) and thus are problematic to filter, and the lubricants needed are usually specialized in what they perform, needing a product to be on-site, particularly for that type of equipment.
