How Does The Screw Jacks Lifting Screw Operate ?
When a screw jack unit is operated, the rotation of the worm shaft causes the worm gear to rotate. For translating screw jacks the worm gear is threaded to accommodate the lifting screw thread; as the worm gear turns, the friction forces on the screw thread act to turn the screw also. The greater the load on the actuator unit, the greater the tendency of the screw to turn. It is obvious that if the screw turns with the nut (worm gear), it will not raise the load. In those cases where a single unit is used, and where the load cannot be restrained from turning, it is necessary to key the lifting screw. Lifting screw key torque (refer to Design Guide PJLMPTDG-01 section 1.5.1.5.) must be checked as excessively heavy unguided loads could break the key. Rotating screw jacks work in a similar manner except that the lifting screw rotates with the worm gear and the lifting nut translates along the rotating screw.
