Projects (Mechanical)

DESIGN AND FABRICATION OF MOTORIZED SCREW JACK FOR A FOUR WHEELER A PROJECT REPORT Submitted in partial fulfillment for the award of the degree of BACHELOR OF TECHNOLOGY IN MECHANICAL ENGINEERING By Vikas Kumar Rai

Abstract:

With the increasing levels of technology, the efforts being put to produce any kind of work has  been continuously decreasing. The efforts required in achieving the desired output can be effectively and economically be decreased by the implementation of better designs. Power screws are used to convert rotary motion into translatory motion. A screw jack is an example of a power screw in which a small force applied in a horizontal plane is used to raise or lower a large load. The principle on which it works is similar to that of an inclined plane. The mechanical advantage of a screw jack is the ratio of the load applied to the effort applied. The screw jack is operated by turning a lead screw. The height of the jack is adjusted by turning a lead screw and this adjustment can be done either manually or by integrating an electric motor. In this project, an electric motor will be integrated with the screw jack and the electricity needed for the operation will be taken from the battery of the vehicle and thereby the mechanical advantage will be increased.

Power Screw:

A power screw is a mechanical device used for converting rotary motion into linear motion and transmitting power. A power screw is also called translation screw. It uses helical translatory motion of the screw thread in transmitting power rather than clamping the machine components.

2.1 Applications

The main applications of power screws are as follows:

(i) To raise the load, e.g. screw-jack, (ii) To obtain accurate motion in machining operations, e.g. lead-screw of lathe, (iii) To clamp a workpiece, e.g. vice, and (iv) To load a specimen, e.g. universal testing machine. There are three essential parts of a power screw, viz.screw, nut and a part to hold either the screw or the nut in its place. Depending upon the holding arrangement, power screws operate in two different ways. In some cases, the screw rotates in its bearing, while the nut has axial motion. The lead screw of the lathe is an example of this category. In other applications, the nut is kept stationary and the screw moves in axial direction. Screw-jack and machine vice are the examples of this category.

2.2 Advantages

Power screws offer the following advantages: (i) Power screw has large load carrying capacity. (ii) The overall dimensions of the power screw are small, resulting in compact construction. (iii) Power screw is simple to design (iv) The manufacturing of power screw is easy without requiring specialized machinery. Square threads are turned on lathe. Trapezoidal threads are manufactured on thread milling machine. (v) Power screw provides large mechanical advantage. A load of 15 kN can be raised by applying an effort as small as 400 N.Therefore, most of the power screws used in various applications like screw-jacks, clamps, valves and vices are usually manually operated. (vi) Power screws provide precisely controlled and highly accurate linear motion required in machine tool applications. (vii) Power screws give smooth and noiseless service without any maintenance. (viii) There are only a few parts in power screw. This reduces cost and increases reliability.

Screw jack:

A screw jack is a portable device consisting of a screw mechanism used to raise or lower the 

load. The principle on which the screw jack works is similar to that of an inclined plane. There

are mainly two types of jacks-hydraulic and mechanical. A hydraulic jack consists of a cylinder 

and piston mechanism. The movement of the piston rod is used to raise or lower the load. 

Mechanical jacks can be either hand operated or power driven.

Jacks are used frequently in raising cars so that a tire can be changed. A screw jack is commonly 

used with cars but is also used in many other ways, including industrial machinery and even 

airplanes. They can be short, tall, fat, or thin depending on the amount of pressure they will be

under and the space that they need to fit into. The jack is made out of various types of metal, but 

the screw itself is generally made out of lead.

While screw jacks are designed purposely for raising and lowering loads, they are not ideal for 

side loads, although some can withstand side loads depending on the diameter and size of the 

lifting screw. Shock loads should also be avoided or minimized. Some screw jacks are built with 

anti-backlash. The anti-backlash device moderates the axial backlash in the lifting screw and nut 

assembly to a regulated minimum.

A large amount of heat is generated in the screw jack and long lifts can cause serious 

overheating. To retain the efficiency of the screw jack, it must be used under ambient 

temperatures, otherwise lubricants must be applied. There are oil lubricants intended to enhance 

the equipment‟s capabilities. Apart from proper maintenance, to optimize the capability and 

usefulness of a screw jack it is imperative to employ it according to its design and 

manufacturer‟s instruction. Ensure that you follow the speed, load capacity, temperature 

recommendation and other relevant factors for application

3.1 The Screw

The screw has a thread designed to withstand an enormous amount of pressure. This is due to the 

fact that it is generally holding up heavy objects for an extended amount of time. Once up, they 

normally self lock so that they won't fall if the operator lets go, and they hold up well to the wear 

of repeated use. If they are made with a ball nut, they will last longer because there is less 

friction created with this type of jack. However, they will not self lock. This can be dangerous 

and handled carefully.

3.2 Operation

The jack can be raised and lowered with a metal bar that is inserted into the jack. The operator 

turns the bar with his hands in a clockwise direction. This turns the screw inside the jack and 

makes it go up. The screw lifts the small metal cylinder and platform that are above it. As the 

jack goes up, whatever is placed above it will raise as well, once the jack makes contact. The bar 

is turned until the jack is raised to the level needed. To lower the jack the bar is turned in opposite direction. An automatic screw jack has gears inside the jack that are connected to the 

screw. Theses gears are connected by other gears and bars that are turned by a power source to 

raise and lower the jack.

Although a jack is a simple and widely used device, the use of any lifting device is subject to 

certain hazards. In screw-jack applications, the hazards are dropping, tipping or slipping of 

machines or their parts during the operation. These hazards may result in serious accidents. The

main reasons of such accidents are as follows:

(i) The load is improperly secured on the jack

(ii) The screw-jack is over loaded.

(iii) The centre of gravity of the load is off centre with respect to the axis of the jack

(iv) The screw-jack is not placed on hard and level surface.

(v) The screw-jack is used for a purpose, for which it is not designed.

Proper size, strength and stability are the essential requirements for the design of the screw-jack 

from safety considerations.

3.3 Construction of Screw Jack

Screw jack consists of a screw and a nut. The nut is fixed in a cast iron frame and remains 

stationary. The rotation of the nut inside the frame is prevented by pressing a set screw against it. 

The screw is rotated in the nut by means of a handle, which passes through a hole in the head of 

the screw. The head carries a platform, which supports the load and remains stationary while the 

screw is being rotated. A washer is fixed to the other end of the screw inside the frame, which 

prevents the screw to be completely turned out of the nut.

3.4 Function

The basic function of a screw jack is to lift a portion of a vehicle. Typically this is used to change 

a tire although other maintenance is sometimes performed.

3.5 Features

All jacks have safety features to protect the user from accidental injury. Wide bases help to 

stabilize a jack and prevent tilting or sinking into soft soil. Most car jacks also come equipped 

with their own handle or cranking mechanism, but alternately many of these also will accept the 

flat end of a tire tool to jack up a vehicle. When in the extended position, jacks will have a stop 

point that prevents the user from overextending the jack beyond its rated capabilities. When in 

the contracted position, jacks that are provided by the manufacturer will have a storage area 

specially formed or designed for the jack to rest in when not in use.

Construction:

A scissor jack has four main pieces of metal and two base ends. The four metal pieces are all 

connected at the corners with a bolt that allows the corners to swivel. A screw thread runs across 

this assembly and through the corners. As the screw thread is turned, the jack arms travel across 

it and collapse or come together, forming a straight line when closed. Then, moving back the 

other way, they raise and come together. When opened, the four metal arms contract together, 

coming together at the middle, raising the jack. When closed, the arms spread back apart and the 

jack closes or flattens out again.

Design and Lift:

A scissor jack uses a simple theory of gears to get its power. As the screw section is turned, two 

ends of the jack move closer together. Because the gears of the screw are pushing up the arms, 

the amount of force being applied is multiplied. It takes a very small amount of force to turn the 

crank handle, yet that action causes the brace arms to slide across and together. As this happens 

the arms extend upward. The car's gravitational weight is not enough to prevent the jack from 

opening or to stop the screw from turning, since it is not applying force directly to it. If you were 

to put pressure directly on the crank, or lean your weight against the crank, the person would not 

be able to turn it, even though your weight is a small percentage of the cars.

Introduction:

The motorized screw jack has been developed to cater to the needs of small and medium 

automobile garages, which are normally man powered with minimum skilled labor. In most of 

the garages the vehicles are lifted by using screw jack. This needs high man power and skilled 

labour.

In order to avoid all such disadvantages, the motorized jack has been designed in such a way that 

it can be used to lift the vehicle very smoothly without any impact force. The operation is made 

simple so that even unskilled labour can use it with ease.

The d.c motor is coupled with the screw jack by gear arrangement. The screw jack shaft‟s 

rotation depends upon the rotation of D.C motor. This is a simple type of automation project.

This is an era of automation where it is broadly defined as replacement of manual effort by 

mechanical power in all degrees of automation. The operation remains to be an essential part of 

the system although with changing demands on physical input, the degree of mechanization is 

increased.

Need for Automation:

Automation can be achieved through computers, hydraulics, pneumatics, robotics, etc. 

Automation plays an important role in mass production.

For mass production of the product, the machining operations decide the sequence of 

machining. The machines designed for producing a particular product are called transfer 

machines. The components must be moved automatically from the bins to various machines 

sequentially and the final component can be placed separately for packaging. Materials can also 

be repeatedly transferred from the moving conveyors to the work place and vice versa.

Nowadays, almost all the manufacturing processes are being atomized in order to deliver the 

products at a faster rate. The manufacturing operation is being atomized for the following 

reasons:

 To achieve mass production

 To reduce man power

 To increase the efficiency of the plant

 To reduce the work load

 To reduce the production cost

 To reduce the production time 

 To reduce the material handling

 To reduce the fatigue of workers

 To achieve good product quality

 Less Maintenance

CONCLUSION:

Screw Jacks are the ideal product to push, pull, lift, lower and position loads of anything from a 

couple of kilograms to hundreds of tonnes.The need has long existed for an improved portable 

jack for automotive vehicles. It is highly desirable that a jack become available that can be 

operated alternatively from inside the vehicle or from a location of safety off the road on which 

the vehicle is located. Such a jack should desirably be light enough and be compact enough so 

that it can be stored in an automobile trunk, can be lifted up and carried by most adults to its 

position of use, and yet be capable of lifting a wheel of a 4,000-5,000 pound vehicle off the 

ground. Further, it should be stable and easily controllable by a switch so that jacking can be 

done from a position of safety. It should be easily movable either to a position underneath the 

axle of the vehicle or some other reinforced support surface designed to be engaged by a jack.

Thus, the product has been developed considering all the above requirements. This particular 

design of the motorized screw jack will prove to be beneficial in lifting and lowering of loads.

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