Scissor lifts are an excellent choice when workers or materials need to be raised above ground level, without the obstructions caused by overhead cranes or machinery that lifts the item from its side (such as forklifts). With a scissor lift, the entire lifting mechanism is contained beneath the lift platform or table, providing lifting capability with a minimal footprint.
A scissor lifts power comes from hydraulic cylinders. This provides abundant force to raise the load on the platform. The "scissors" are crossing struts with hinge pins in the middle and at the ends. These provide stability for the platform. Shafts between the struts keep the two sets of scissors separated at a fixed distance, preventing sideways collapse.
Depending on the lifting height, a single pair of scissors may be used or multiple pairs that are stacked one above the other. Since the lift becomes more unstable the greater the scissors are extended, manufacturers limit the amount of extension that any one pair of scissors can perform. This is most easily controlled by limiting the stroke of the hydraulic cylinder.
Parts of a Scissor Lift
While there are numerous types of scissor lifts, they all have a common design. Many of the same types of parts will be encountered on almost all scissor lifts.
The diagonal arms of the scissors are called struts. They are always in pairs, which cross in the center. A pair of struts will always have a matching pair opposite it, on the other side of the lift.
The rods that separate the struts are called the shafts. These are located at both ends of each strut, forming the "hinge" of the scissors.
The arm pin is the hinge pin that connects the strut to the shaft. This must allow for some rotational movement as the lift raises, while at the same time retaining rigidity to prevent wobble of the platform.
One side of the scissors will be fixed in place, but the other must move as the lift raises. This is accomplished on a track, referred to as the slideway. There are slideways on the base and on the bottom of the platform.
The lifting power of a scissor lift comes from hydraulic cylinders. Extension of the cylinder rod raises the lift. As a safety measure, in the case of power loss, the cylinder will not collapse.
Hydraulic Power Pack
All scissors lifts are hydraulically powered. The hydraulic power pack consists of a motor driven hydraulic pump, which provides the hydraulic fluid to power the hydraulic cylinders. This may be battery powered or require connection to an electrical source.
Scissor lifts which are intended for high reach will often have outrigger legs for added stability. These legs are deployed and pressed into the ground before the lift is raised.
Some lift tables come equipped with bellows to cover the working components of the lift. This is a safety feature, done to prevent the accidental pinching or severing of fingers and toes from getting them trapped between the struts.
Selecting a Scissor Lift
More than anything, scissor lifts are selected based on their intended use. This use will determine the capacity and style of the lift, along with the quality level required and any optional features which might be needed.
Before shopping for a scissor lift, it is important to fully examine and analyze the intended use for it. In this process, a list of minimum specifications should be developed, which will be used in the process of qualifying or eliminating contenders from the selection process. Call one of our sales team at Dexters NZ and we can help you decide which scissor lift is the best option for you.
Some of the characteristics which must be considered include:
Decide whether the scissor lift is going to be used in a fixed location, such as to hold up an assembly on a production line, or if it needs to be mobile, such as for maintenance or construction.
Decide how much weight the lift will need to handle. The limiting factor is usually the size of the hydraulic cylinders. The struts will be designed with a safety factor (to carry more weight than the hydraulics can lift).
Scissors lifts are designed to have the load's center of gravity in the center of the lift; any more than 30 percent offset can cause premature wearing of the lift. This premature wear can be offset by using a lift with a higher weight capacity than the intended load. A lift with a 50 percent greater weight capacity will be able to handle an offset load, without damage.
Figure the maximum height to which a load will need to be lifted. Lifts can be used to raise a load to only a portion of this height, without problem.
Figure out how tall the lift is in its collapsed state. When buying a lift for maintenance, it may need to be able to fit through a doorway. When used as a means of raising workpieces on an assembly line, the folded height must accommodate easy loading of the parts to be worked on.
Most scissors lifts are not designed for a rapid duty cycle, but rather to lift their load less than 20 times per hour.
Specialty Application Scissor Lifts
Although the general design of a scissor lift is consistent, the applications in which the lift is used will often require special features or options. Scissor lifts which meet these various applications are readily available on the market; however, it is important to think of what is needed, before making a selection.
Determining the Quality of a Scissor Lift
Whenever working with a scissor lift, safety is a major concern. This is an important consideration when choosing a scissor lift. The quality of the material and workmanship in the lift will determine its safety. A few key components to review include:
- Bearings: All scissor lifts should have ball-bearing or roller bearing construction, especially lifts with high weight capacities. Sleeve bearings are a sign of a lower quality construction. The bearings should also be fully sealed or have lube points.
- Material thickness: This is one of the first places where manufacturers of low-cost lifts try to save money. Thinner material can reduce service life.
- Hydraulic cylinder seals: The first point of failure on any scissor lift is usually oil leaks at the hydraulic cylinder seals. Lower quality cylinders are likely to leak sooner than high quality ones.
- Motor size: When comparing various lifts, compare the motor size in the hydraulic power pack. A higher horsepower rating will indicate a higher quality lift. This is another place where manufacturers of low cost lifts attempt to save money.
As always, manufacturers of high-quality scissors lifts will have a good reputation. By buying name brand products, you are more assured of a higher quality scissors lift. While a low-cost lift may very well meet your needs, specifying a lift which provides a greater safety margin helps prevent any safety issues.
For more information on our range of Scissor Lift Tables go to our scissor lift tables page or call us on 09 275 5580