write four field application of screw jack
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Screw jacks are sometimes misunderstood and overlooked as a method of creating controllable linear motion. Jon Severn provides an overview of these useful mechanical actuators and takes a look at some recent developments in this field.
Screw jacks are an ancient concept but just as relevant today as ever before. For the right type of application a screw jack - or a set of screw jacks - can provide smooth, controllable linear motion by operating a motor, which is usually electrical though it can also be hydraulic or pneumatic. Normally a screw jack is self-locking and cannot be back-driven by the load, although this is not always the case, especially if ball screws are used. The self-locking feature is often seen as an attractive feature when replacing hydraulic and pneumatic actuators and it is necessary to prevent the load from moving once it is in position. Typically screw jacks are available with ratings of a few kilograms up to 100 kN, depending on the manufacturer and model.
'Classic' designs of screw jack have a single mounting face, but most manufacturers today offer designs that are 'cubic' and can be mounted on their other faces (Fig.1). Likewise, manufacturers generally offer two classes of screw jacks: those in which the spindle (screw) moves, and those in which the spindle rotates and a travelling nut moves. Manufacturers of screw jacks are also tending to develop modular designs that enable products to be assembled quickly from standard components so that customers' needs can be met without incurring the expense associated with fully customised unit
Screw jacks are an ancient concept but just as relevant today as ever before. For the right type of application a screw jack - or a set of screw jacks - can provide smooth, controllable linear motion by operating a motor, which is usually electrical though it can also be hydraulic or pneumatic. Normally a screw jack is self-locking and cannot be back-driven by the load, although this is not always the case, especially if ball screws are used. The self-locking feature is often seen as an attractive feature when replacing hydraulic and pneumatic actuators and it is necessary to prevent the load from moving once it is in position. Typically screw jacks are available with ratings of a few kilograms up to 100 kN, depending on the manufacturer and model.
'Classic' designs of screw jack have a single mounting face, but most manufacturers today offer designs that are 'cubic' and can be mounted on their other faces (Fig.1). Likewise, manufacturers generally offer two classes of screw jacks: those in which the spindle (screw) moves, and those in which the spindle rotates and a travelling nut moves. Manufacturers of screw jacks are also tending to develop modular designs that enable products to be assembled quickly from standard components so that customers' needs can be met without incurring the expense associated with fully customised unit
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