A screw jack, sometimes called a jackscrew, is an adjustable lifting device that works by turning a leadscrew to raise or lower the weight being lifted. These jacks are commonly used to raise moderate or heavy weights. They can also be used to raise the horizontal stabilizers of aircraft and as adjustable supports for heavy loads.
Screw jacks are available in different sizes and spec levels to meet various application needs. The design and construction of a screw jack will determine its torque capacity. Screw jacks must be able to sustain shock loads up to their rated capacity, or they may not function properly. Most screw jacks are capable of sustaining up to 10% overload for dynamic loads, or 30% overload for static loads. Another important factor in determining the right screw jack is the duty cycle. Duty cycle is the percentage of time the screw jack is operational. This number is often found in the product specification page.
Screw jacks can also come with brakes. A self-locking screw jack requires a brake motor that can be released by vibration, an increase in spindle pitch, or the use of rolling screw elements. Self-locking worm gear screw jacks are designed for dynamic use at medium speeds and should include a brake motor.
A screw jack comes in three basic types: the Travelling Screw Type, Travelling Wedge Screw Type, and Travelling Nut Type. The Travelling Screw Type allows for vertical or horizontal movement. This type is ideal for moving objects with irregular sized axes. It also has a fixed load connection, which means the jack's gearbox must be able to receive movement from the screw shaft. A trapezoidal screw, on the other hand, translates linearly up and down, and functions similarly to the wedged type.
Screw jacks are the most common type of jack used in construction and manufacturing applications. They are made of steel, stainless steel, or lead, and are designed for industrial applications. They can also be used on lifting platforms. Some screw jacks are electrically operated. These jacks come with safety bellows and protective tubes.
Generally, worm gear and bevel gear screw jacks have similar applications and are used where speed is required. However, the speed of bevel gear screw jacks can be up to 60% higher. They are also ideal for fast lowering and lifting operations. So, it's a good idea to check the specs and the benefits of each type before you buy one.
Another type of screw jack is the Inch Worm Gear Machine Screw Jack. This type of screw jack incorporates a high-strength bronze worm gear and an alloy steel worm. The rotation of the worm gear causes the linear motion of the lifting screw and the traveling nut. These screw jacks have a capacity of five to 2000kN. The speed of linear motion of the lifting screw depends on the pitch and the rotation ratio of the worm gears.