screw jack , description of screw jack, advantages of screw jack, application of screw jack, industrial and technical application, working principle of screw jack, details of screw jack, 3D cad drawing of screw jack.

1. Screw jack
 What is a screw jack:-
A jackscrew, or screw jack, is a type of jack that is operated by turning
a leadscrew. It is commonly used to lift moderately heavy weights, such
as vehicles. More commonly, it is used as an adjustable support for
heavy loads, such as the foundations of houses or large vehicles.
 Description:-
A screw jack consists of a heavy-duty vertical screw with a load table
mounted on its top, which screws into a threaded hole in a stationary
support frame with a wide base resting on the ground. A rotating collar
on the head of the screw has holes into which the handle, a metal bar,
fits. When the handle is turned clockwise, the screw moves further out
of the base, lifting the load resting on the load table. In order to support
large load forces, the screw usually has either square threads
or buttress threads.
 Advantages
An advantage of jackscrews over some other types of jack is that they
are self-locking, which means when the rotational force on the screw is
removed, it will remain motionless where it was left and will not rotate
backwards, regardless of how much load it is supporting. This makes
them inherently safer than hydraulic jacks, for example, which will
move backwards under load if the force on the hydraulic actuator is
accidentally released.

2.  Applications:-
The large area of sliding contact between the screw threads means
jackscrews have high friction and low efficiency as power transmission
linkages, around 30%–50%. So they are not often used for continuous
transmission of high power, but more often in intermittent positioning
applications.
In heavy-duty applications, such as screw jacks, a square
thread or buttress thread is used, because it has the lowest friction and
wear.
 Industrial and technical applications:-
In technical application such as actuators, an Acme thread is used,
although it has higher friction, because it is easy to manufacture, wear
can be compensated for, it is stronger than a comparably sized square
thread and it makes for smoother engagement.
The ball screw is a more advanced type of leadscrew that uses a
recirculating-ball nut to minimize friction and prolong the life of the
screw threads. The thread profile of such screws is approximately
semicircular (commonly a "gothic arch" profile) to properly mate with
the bearing balls. The disadvantage to this type of screw is that it is not
self-locking. Ball screws are prevalent in powered leadscrew actuators.
Jackscrews are also used extensively in aviation, and are used to raise
and lower horizontal stabilizers. The failure of a jackscrew on
a Yakovlev Yak-42 airliner due to design flaws resulted in the crash
of Aeroflot Flight 8641 in 1982. A similar failure on a McDonnell
Douglas MD-80, resulting from a lack of grease, brought down Alaska
AirlinesFlight 261 in 2000. In 2013, NationalAirlines Flight 102crashed
as a result of a MRAP armoured vehicle breaking loose and breaking
through the rear bulkhead, severing hydraulics lines and most
importantly, destroying the jackscrew, rendering the aircraft
uncontrollable. Investigators found that had the jackscrew not been
destroyed, the 747-400F may have been able to perform a successful
landing at Bagram Airfield.

3.  Screw Jack Working Principle:-
Very common throughout the world, screw jacks are found wherever
there is a need to lift, position, align and hold load. Their high reliability
and synchronization makes screw jacks suitable for a wide variety of
uses that alternative methodsof handlingcannot achieve. This spectrum
of applications reaches across market sectors and includes Steel Works
Equipment, Water Processing, Pharmaceutical, Medical and Laboratory
Equipment, Packaging Equipment, Nuclear and Aerospace and General
Mechanical Handling. Additionally, screw jacks are increasingly finding
uses as alternatives to conventionally pneumaticand hydraulic systems.
A Screw Jack (also known as a Jack Screw, a Worm Screw Jack, a
Machine Screw Jack or a Lead Screw Jack) is a devise used to convert
rotational motion into linear motion. It utilises the property of a screw
thread providing a mechanical advantage i.e. it can be used to amplify
force.

4.  Details of screw jack:-

5.  Assembly of Screw Jack:-