Scissors lift is one kind of lifting equipment to move the materials to different heights. It is a lift generally used in industries for lifting materials to different heights and floor, lift materials to match the equipment height, lifting cars to different floors in a car show room.
Scissors lift equipment is also used to lift a person to heights to access roof for cleaning and construction industries.
Scissors lift is designed such a way that it is compact in size compared to other lifting equipments, stable during vertical lift with load. Sometimes, scissors lift needs an additional guide support for very high lift height and in applications subject to lateral loads placed on the scissors lift table.
Scissors lift goes inside the ground in case of pit mounted type, hence no structures of scissors lift project outside the ground level and completely free for any other purpose, can be used as a walk way or passing movement of vehicles over the scissors lift table when it is completely in collapsed condition.
Scissors lift are ideal equipment for docking application, for example, loading and unloading materials from a truck or container as they have good stability during load transfer from trucks and containers into the scissors lift.
The basic purpose of a scissors lift is lift materials to different height. It could be about 2000mm height in lifted condition so that it comfortably reaches the height of bed of truck and containers.
It is generally used to load, unload, stuffing and de-stuffing materials into the trucks and containers. In car show rooms, the scissors lift is used for lifting cars to different floors, also used to shift cars to different floors in service work shop.
It saves good amount of cost as storing materials in different floors required minimum and effective use of ground area, especially in metro cites where cost of floor space is very high.
A hydraulic scissors lift requires following technical parameters to work out an appropriate for a specific application:
The various members of a hydraulic scissors lift are the loading platform, hand safety rails, lips, scissors links, base frame, hydraulic cylinders, hydraulic power pack, safety prop-ups, and the electrical control panel.
The loading platform is an important member of a scissors lift, it is a platform on which the load sits, load transferred from a truck or a container. It generally has steel chequered plates with load carrying structure beneath it. This should be designed strong enough to withstand dynamic loads arising out by forklifts, trolleys and while material transfer.
The hand rails are important safety structure which safeguards the user from free fall in the lifted condition of scissors lift.
The lips are bridge structure between a hydraulic scissors lift and trucks. They are foldable type manually or by hydraulic system and sit on the bed of truck or container for easy transfer of trolley or forklifts.
The scissors links are another crucial load carrying members. They need to be designed to withstand bending and torsion loads, arising during lifting and lowering. The interconnection hinge points of links carry maximum load and they need self lubricated journal bearings to ensure frictionless and noiseless operation for many years of usage.
The base frame is bottom most member. Carry the self weight of scissors lift, payload and reaction loads of hydraulic cylinders. This is intermediate member between scissors lift and ground.
The hydraulic cylinders are real muscle in the scissors lift. The important factors to be considered during design stage are less working pressure, sufficient diameter of piston rod to withstand bucking load it encounters during lifting operation. Insufficient diameter of piston may lead to bucking failure on a long run. The hydraulic cylinders could be single or double acting depending upon the requirement and speed requirement of end user. The end mounting should preferably have spherical bearings to accommodate various misalignments during the construction.
The hydraulic power pack of scissors lift may have lift lowering block in the hydraulic circuit for its compact size, energy efficient and easy to attend during service and during malfunctioning. It should have manual override control as an alternative to lower the scissors lift during electrical service interruption. Normally, a 24 volt DC supply voltage is preferred for solenoid coil due its less chattering noise and long life even though it involves additional cost for the manufacturer.
The electrical control panel of hydraulic scissors lift should have motor protection elements, SMPS for have reduced voltage for solenoid coil and control circuit voltage for limit switches.
The reduced voltage of 24VDC saves the life of end user in case of any short circuit situation happens.
Every equipment needs a proper maintenance for its trouble free working and to get long life. Scissors lifts need constant monitoring of any hydraulic oil leakage. Oil leakage can occur in hydraulic cylinders due its failure of seals, in valves due to improper tightening of fittings, loosening of fittings over time.
Hydraulic oil to be replaced as per the manufacturers’ recommendation at a particular interval of time. Top up of hydraulic oil may be needed to compensate loss of quantity of hydraulic oil.
Bearings in moving rollers and in the hinge joints to be checked for its free movement and need to be replaced after its service life.
Structural failures like bending of various load carrying members and weld crack to be observed during preventive maintenance schedule.
Always put prop-ups before a technician enter below the scissors lift as it prevents downward movement and saves the lift of a technician. It should never be compromised as the moving platform may come down due to hose failure or due to oil leakage or structural failures or even a weld failure.
The electrical power should be disconnected before servicing of hydraulic scissors lifts.