Jack is considered to be a device that can lift large loads. Mechanical structures are used not only for cars, but also for many construction works. For example, for the replacement of pipes, construction and repair of bridges. Buying a jack, it is very important to know its device.
Diagram of a pneumatic jack.
Today, screw jacks of mechanical type are considered to be the most common and practical. These designs are distinguished by their high degree of reliability. In addition, they are further subdivided into several subspecies, which makes it possible to choose the most suitable mechanism for themselves.
Working principle of jacks
Diagram of the hydraulic jack.
But before we consider the main types of screw mechanical jacks, their basic characteristics, advantages and disadvantages, let us dwell on the principle of operation of the mechanisms. Indeed, for constructions of the screw type, it is generalizing.
The principle of the screw jack is that in it the rotational movement gradually turns into a translational movement. The worm screw, located on the gearbox inside the housing, transmits torque from the pinion and torque screw. Due to this, the load is lifted to a certain height.
When the cargo reaches the desired height, fixation occurs. The load is fixed manually with a special lever. Depending on the quality of the jack you use and the maximum weight of the load it can withstand, you can hold the load at a fixed height absolutely without displacement.Back to table of contents
Characteristic of jacks like nut-screw and ball screw
The device of the screw jack.
There are two main parameters by which screw mechanisms are distinguished into several other types. This is the movement of the screw and the type of the helical gear. According to the movement of the screw, the jacks can be subdivided into rotating and sliding, and according to the type of transfer - to jacks of the type of ballscrews and devices like the nut-screw. Consider such species in more detail.
So, rotating structures are characterized by the fact that during operation a worm gear is driven, which gradually tightens the nut. This is due to the raising of the platform on which the nut is fixed. Sliding mechanisms operate on the basis of a screw that moves along the body with a nut and a gearbox that rotates it. That is, mutual twisting takes place.
Ball type jacks are based on rolling balls located between the nut and screw. Here the principle of the ball screw drive was originally laid. These are relatively new devices on the market, which are characterized by a longer service life and easier rotation of parts due to the maximum smoothness of the surfaces. Such mechanisms have a high efficiency and cycle of operation. This is largely due to the high speed of the screw jack.
Rack jack scheme.
However, such ball-type devices cost a lot of money and require the presence of a braking device, which will prevent rolling. And this, as a rule, will take additional financial and labor costs.
The jacks of the nut-screw type have such a connection on the thread, where the movement occurs due to sliding and friction at the same time. Threaded screw jack connection is considered a classic option. Mechanisms of this type are much cheaper in price and easier to maintain. In addition, for devices of this type it is much easier to find new parts in case of need to replace old ones.
Such structures are very resistant to rolling, do not require additional braking mechanism. The load capacity of such jacks is quite high. But there are also negative traits: two times lower efficiency than the ball screw jacks. And the duty cycle of such a screw jack is somewhat less.Back to table of contents
Selected features of some jacks
In addition to these types of jacks, today on the market there are also such mechanisms, the device which in some way differs from the described types.
Lifting capacity of the screw jack is calculated by the formula.
There are three types of such devices, each of which has a unique feature.
The first kind is a mechanism with eyes. Its device is characterized by the presence of two lugs, one of which is on the case, and the other - at the end of the screw. By and large, these eyes do not affect the main operation of the mechanism, but can make the operation more convenient in some cases. For example, they are very good to use for arc-type lifts (doors, shutters, etc.).
The second type - backlash jacks, in which there is practically no backlash. And finally, the third type are jacks, completely made of stainless steel. These are the most expensive mechanisms, as they will serve you as long as possible. It is advisable to use them in conditions of constant exposure to moisture and various kinds of chemical reagents.Back to table of contents
The main parameters of the mechanisms
Types of jacks.
So, the main types of screw jacks considered. Of course, this can not be limited. After all, there are also other typologies that open up a wider range of choices. But the above options are the most common.
There are a number of specific parameters by which it is advisable to make a choice of mechanism. These parameters are considered to be common for all types of jacks, but for screw designs they are most important. So, a good jack should have:
- Duty cycle of at least 25%. The higher this figure, the better. When approaching 100%, you can be confident in the almost continuous operation of the mechanism.
- Efficiency is at least 25%. Ideally, it should be close to 95%.
- High accuracy. It should reach tenths of a millimeter. Otherwise, the elevator will not lift the load with high quality, which may lead to a safety violation.
- High payload. In no case should we jack up loads that are even slightly heavier than the permissible load capacity. This may cause damage to the lift and the load and cause injury.
- Good lubrication. This is especially important if the jack is planned to be used outside when it is very cold. High-quality lubricant withstands temperatures from -45 ° C to + 95 ° C. If the temperature does not fit into these limits, or if the lubricant is bad, then the mechanism may stall at any time.
- Greater lift height. This is an important feature. If the figure here is small, then you will not be able to lift the load high.
So, the features of the screw jack device and its main characteristics are fully considered.
As you have already been able to understand from all of the above, you need to take into account absolutely everything when choosing a mechanism, so that the work goes quickly and efficiently.