SKF’s long-standing partnership with the global steel industry has generated a number of product innovations and improvements. One of those innovative products is the SKF® roller screw jack actuator, which uses an SKF designed roller screw. These low-maintenance linear actuators are commonly used in continous caster applications to position the tundish. Their rugged design enables the unit to operate reliably even in applications where contaminants are abrasive and temperatures are high.

   Unlike hydraulic or pneumatic systems, an SKF roller screw jack actuator does not require a system of sumps, pumps, compressors ot ancillary equipment. These self-contained units can provide an overall efficiency as high as 70%. Efficiency rating depends on the ratio of the worm gear set.

   More than 60 continuous casters in 23 countries are equipped with SKF Roller screw jack actuators. The average life of these screws is over 12 years; the oldest in service has exceeded 22 years.

About the SKF
screw jack actuator
The design of the screw jack actuator is based on the principle of moving a screw vertically by rotating a nut and ring gear assembly in a stationary housing. The nut ring gear assembly, which is driven by a worm gear, is supported by two bearings: a ball bearing and spherical thrust bearing. This configuration distributes compression loads evenly and is ideal for handling heavy loads in one direction.

The gearbox
The rugged welded steel gearbox of an SKF screw jack is designed for maximum performance and reliability. A solid tube extending from the base is used to guide the screw shaft and prevent it from rotating.

   To improve screw jack alignment during installation, the bottom of the gearbox can be supplied with a spherical seat. In addition, a spherical joint can be used between the top of the jack and the tundish frame.

About the roller screw
The design of the roller screw threads and nut permits a planetary motion of the rollers. This unique design feature improves reliability because it eliminates a rolling element recirculation system and the failures associated with it.

Roller screw design
The geometry of the 3 basic elements (screw, rollers and nut) is configured so that the rollers follow a planetary path and cannot move axially. The thread profile of the screw shaft and nut is triangular with an angle of 90°. The thread profile of the roller is also 90° and its flanks are contoured. The number and shape of the contact points maximizes the load-carrying capacity, giving a roller screw approximately three times the capacity of a similarly sized ball screw.