DESIGN AND ANALYSIS OF SCISSOR JACK FULL REPORT Download-Mechanical Project
A jack is mechanical device used to lift heavy loads or apply great forces. Jacks employ a screw thread or hydraulic cylinder to apply very high linear forces.
A mechanical jack is a device which lifts heavy equipment. The most common form is a car jack, floor jack or garage jack which lifts vehicles so that maintenance can be performed. Car jacks usually use mechanical advantage to allow a human to lift a vehicle by manual force alone. More powerful jacks use hydraulic power to provide more lift over greater distances. Mechanical jacks are usually rated for a maximum lifting capacity.
Scissor jacks are simple mechanisms used to drive large loads short distances.The power screw design of a common scissor jack reduces the amount of force required by the user to drive the mechanism.Most scissor jacks are similar in design, consisting of four main members driven by a power screw. A scissor jack is operated simply by turning a small crank that is inserted into one end of the scissor jack. This crank is usually “Z” shaped. The end fits into a ring hole mounted on the end of the screw, which is the object of force on the scissor jack. When this crank is turned, the screw turns, and this raises the jack. The screw acts like a gear mechanism. It has teeth (the screw thread), which turn and move the two arms, producing work. Just by turning this screw thread, the scissor jack can lift a vehicle that is several thousand pounds. Power screw in a scissor jack is the foundation of whole mechanism of scissor jack.
The most common problem encountered while using scissor jack is the instability of jack while giving jerks to loosen the wheel nut. Also the common jack having small base is unable to provide proper support on uneven surface esp. off-road and no inclination in that jack is tolerable.
The project relates to the designing of simple scissor jack and its analysis along with structural improvements to make such a modified jack that is very stable and can take enough load on uneven surfaces and somewhat inclination is also allowed.
The project also aims at designing and finding stresses, efficiency, expected life of screw. We endeavor to develop a screw jack such that it is cost effective, having a long life and can be handled roughly.
Here we outline the timeline for the completion of various aspects for the project. The schedule is set so that the project is completed in phases. Phase I is market research, Phase II consists of the design process, Phase III entails PRO-e modeling of the design and simulation in ANSYS software, and the final aspect of the project is the presentation and the work that went into it.
The term “scissor jack” describes a wide variety of tools that all follow the same principle: using crossed beams to lift something. They do this by acting on the object they are lifting in a diagonal manner; the lift on the right side lifts the object from its left side and vice versa. This allows the user to store the jack when it is not in use (with the diagonal beams flat) and to expand it when it is needed.
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.
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 small percentage of cars.
• Power screw
• Coupling nut
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