Fagioli was contracted for the transport and installation of a 170t stator as a replacement of an old one. Working in warehouses and in premises with restricted areas, Fagioli is sometimes forced to use a simple but very effective device called “the screw-jacks system”.
This system is composed of an electric motor, a gear speed reducer, the screw (or worm shaft) and a worm gear, all contained in a solid and stable steel frame.
The screw jacks enable Fagioli to move heavy loads slowly, accurately and safely.
The old stator was lifted and skidded onto supports by Fagioli’s client. After the positioning of the screw-jack system inside the premises, the old stator was lifted, a Fagioli eight axle line SPMT was moved underneath and the item was lowered onto it. The old stator was moved outside the warehouse and stored.
The new stator was transported inside and positioned with the same method using the trailers and the screw jacks system.
The heavy duty screw jacks are mechanical linear actuators able to lift up to 800tons, using four units. They are generally used to move the work piece to a comfortable height for assembly or machine operators, but also for loading and offloading it to and from transportation equipment.
The jacking units can be connected by spreader beams or simply to the jacking wings of the vessel to lift or lower.
Each unit comprises an electric motor, a gear speed reducer, the screw (or worm shaft) and a worm gear, all contained in a solid and stable steel frame. The screw jacks enable users to move heavy loads safely; an advantage of the system is its simplicity.
The system is powered by AC motors. The motor type determines the travel speed of the actuator. The motors are three-phase with voltage depending upon the size and lifting capacity of the jacking unit. Its power is such to provide the necessary torque to lift the rated load. A limit switch and a brake are used to stop the motor.
The worm-gear speed reducer is an important part of the linear actuator package. The physics of the mechanical system will not allow high travel speeds. If input to the system is too fast, heat buildup accelerates wear on the machine screw jack. A speed reducer solves this problem. The reducer operates with sliding contact between the worm and the gear. This provides for a smooth transmission of power from the motor to the machine screw jack. Safety factors in a worm-gear set are significantly higher than with other types of power transmission equipment, thereby making the chance of a catastrophic failure remote, even under the most demanding conditions.
The worm-gear set powers a threaded rod or lifting screw, providing lift or force application. Thanks to the small lead of these screws and the inefficiencies of the mechanical system, they are self-locking. This means a load can be lifted and will not back down without power being applied.
The rotating screw is a lifting screw that rotates but does not translate. An external nut or worm gear translates on the screw-extending or retracting depending on the input to the jack. The screw is built in a steel structure on heavy duty conical bearings and is made of carbon steel. The worm gear is made of a brass, so that its internal threads will wear before the threads of the screw shaft.
The screws are regularly inspected for wearing, but for additional safety, a carbon steel nut is added to the mechanism. This nut is at the bottom of the worm gear and is lifted by this; in normal conditions the safety nut does not support any load.
The failure of the threads of the worm gear will cause the load to be transferred to the safety nut or safety disc preventing the load from falling. The safety disc can replace the worm gear to complete the lift and allow replacement of the worm gear after its completion.
Fagioli has also used the screw jack system for heavier jobs. In California, screw jacks were used in the installation of steam generators for a power plant.
Fagioli transported four 327t steam generators from Santander, Spain, to California. The HL sea vessel used sailed through the Panama Canal arriving at the port of Hueneme, the only deep water harbour between Los Angeles and the San Francisco Bay area.
Due to the low draft the generators were transported onto two local ocean-barges using heavy-lift vessel gears. The generators were positioned onto tailored saddles, specially prepared to fit the lifting activity of the screw jack system.
On the first barge, Fagioli positioned the screw jack lifting system. Fagioli, in accordance with the client, positioned the generators on saddles rather than stools due to the violent swells during navigation of the open ocean. After 22 hours the barges arrived at the internal port of the plant. The generators were lifted using the screw jacks and positioned onto two 14 axle SPMTs and unloaded at a ro-ro terminal.
The generator was then transported roughly 1km and stored inside the client’s premises on stools. Once the four generators had been positioned inside the warehouse, SPMTs took the items again one by one. They were then lifted with the screw jack system and positioned onto rollers for installation in the plant.
