Contents 1.
ABSTRACT
2.
INTRODU ODUCTION
3.
THEORY
4.
DESIGN
5.
OPE OPERATION PROCE OCESS CH CHART
6.
PRODU ODUCTION PR PROCE OCESS
7.
PLANT LAYOUT
8.
COST OST ESTIMATION
9.
ANNEXURES
10.
BIBLIOGRAP APH HY
Abstract The development of any country mainly depends upon its industrial growth. Now a day’s small scale industries are being encouraged by the Government. By observing the current trend in the industrial growth, it can be understood that our country is developing rapidly in the field of automobiles. Many vechicles such as cars, vans, jeeps, trucks, Lorries, are being manufactured in millions every year. The above mentioned vehicles require some sort of lifting devices for their repairs, replacement of tyres, overhaul etc. for this purpose, generally two types of devices are used namely. 1.
Screw jack
2.
Toggle jack
Screw jack is particularly used as it has following features. 1.
Easy lifting
2.
Rigid
3.
Higher lifting capacity than toggle jack
4.
Good performance
5.
Easy to Handle
6.
Cheap
Intraducation A jackscrew is a type of jack which is operated by turning a leadscrew. In the form of a screw jack it is commonly used to lift heavy weights such as the foundations of houses, or large vehicles. A machine is a contrivance which receives energy in some available form and uses it for doing useful work
.
A lifting machine may be defined as a contrivance to over come a force or load “W” applied at some point by means of another force called effort (P) applied at another point. One of these lifting devices is a screw jack. In screw jack rotary motion of screw is converted in to reciprocating motion of the cup to raise the load.
Now a days road Transport is developing at a faster rate. In road transportation, many vehicles like, cars, Busses, Jeeps, Vans, Trucks, Lorries, Tractors, etc. require screw jacks to lift them for repairing, replacement of tyres, overhauling etc. The screw jack is a Handy, easy non-slipping and efficient performing jack. We propose to manufacture 500 screw jack of various capacities per month, we also intend to utilize the existing machinery and equipment for taking up job work.
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.
Bottle Screw Jack
A bottle type of screw jack is used for lifting loads. It consists of a screw at the top of which the load to be lifted is placed. The load is prevented from rotation by providing a swivel or a thrust bearing. The nut is generally made of gun metal and is press fitted or locked in the cast iron body. The body tapers outwards the bottom to provide better stability on uneven grounds. The load is raised by directly rotating the screw through the head, by means of a tommy bar placed in suitable holes as shown.
The toggle screw jack the screw comprises of right hand and left hand threads as shown. The scew is directly rotated a lever, and the since the screw does not translate, the nuts translate, thus moving the connecting links and the load. For smaller loads a compact design can be achieved by connecting the upper and the lower links by one pin.
Toggle screw jack
Theory Screw jacks are generally used for raising heavy loads through small distances. They are also designed for raising a body vertically and carrying it horizontally occationally. They are used to support odd shaped castings during machining operations. A screw jack essentially consists of a screw spindle at the top of which a cup is provided. The cup supports the load to be lifted. The effort is applied by means of a tommy bar (Handle) inserted in the hole in the head of screw spindle.
The mechanical advantage of a screw jack, the ratio of the force the jack exerts on the load to the input force on the lever, ignoring friction, is
where Fload is the force the jack exerts on the load Finis the rotational force exerted on the handle of the jack r is the length of the jack handle, from the screw axis to where the force is applied l is the lead of the screw. However, most screw jacks have large amounts of friction which increase the input force necessary, so the actual mechanical advantage is often only 30% to 50% of this figure.
Applications A jackscrew's threads must support heavy loads. In the most heavy-duty applications, such as screw jacks, a square thread or buttress thread is used, because it has the lowest friction. In other application such as actuators, an Acme thread is used, although it has higher friction. 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. 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 semicircular to properly mate with the bearing balls. The disadvantage to this type of screw is that it is not self-locking.
Design A 10 tonnes. 25 cm lift “SCREW JACK” is designed assuming the following data. 1. Elastic strength of the screw material (M.S) in tension and compression, Fet or
= 2500 kg/ cm2
2.Elastic strength of the screw material in shear, fes
= 1500 kg/ cm2
3.Elastic strength of nut material (Phosphor bronze) in Tension, fet (nut)
=
1250 kg/ cm2
4.Elastic strength for the material of nut in compression Fec (nut)
=
1150 kg/ cm2
5.Elastic strength for the material of nut in shear
= 1050 kg/ cm2
Fes (nut) 6.
Bearing pressure between the screw and nut Pb
=
180 kg/ cm2
1.DESIG N O F SCREW ;
Let dc
=Core dia.metre of the screw
Since, the screw is under compression Therefore, W = p/ 4 Dc2 X f ec/ F.S (Taking factor of safety = 2) dc2 =10,000 X 4 X 2/ p X 2500 dc2 = 10.18 = 3.19 cm. or
= 3.2 cm. = 32 mm. The nearest core dia. From the tables is 33mm. but a ‘dc’ of
32mm. induced higher stresses than the permissible stresses. Hence a core dia. Of 38mm. = 3.8cm. Square threads are provided on the screw. Pitch of threads, P = 8 mm. (From table) = 0.8 cm. Nominal dia. (or) out side dia. (or) dia. Of spindle
do =d
= 3.8 + 0.8 = 4.6 cm.
