Spacepac Industries’ views on the working system of scissor tables
Scissor table
Spacepac Industries have explained how a scissor table works, the safety considerations, limitations and the best value lift tables. Their views are as follows:
Working of scissor table:
The hydraulic lift tables incorporate a scissor mechanism to hold the platform level but allow it to move vertically.
A hydraulic power unit incorporating electric motor and hydraulic pump supply oil to hydraulic cylinders to elevate the platform.
Most lift tables utilise a single acting hydraulic system. This means that the lift table raises by oil supplied to the cylinders under pressure from the pump and descends under its own weight when the down valve is opened, allowing oil to be bled back to tank.
This is sometimes known as a power up gravity down system. It also means that the lift tables are subject to a slow downward drift over time as oil bleeds back to the tank.
Air bag lift tables
The Air bag lift tables provide a safe and clean way to lift without the need for hydraulics. Powered by shop air, they provide a clean alternative to hydraulics but are limited in capacity, accuracy and lift stroke.
Safety
Care must be taken to prevent entrapment of limbs either in the mechanism or under the table’s edge. A safety bar is a good protection whilst skirts are also used. The safety bar stops the downward movement of the table upon contact with any obstruction.
The Lift tables are often used in conjunction with forklift trucks and they can sometimes damage the table leading to operating failure or injury.
Limitations
The Scissor lift tables are active lifting devices and their use may be covered by statutory requirements similar to those applying to lifts and cranes.
According to Spacepac Industries, the hydraulic lift tables are not ideally suited to highly accurate platform placement as may be required in automated processes because of the drift that can occur with oil bleeding back to the tank. Alternative lifting mechanisms include the screw lift tables.
All lift tables must be appropriately specific to use in wash down, corrosive or flammable environments or high cycle applications.
Best value - Spacepac Industries' view
The Lift table prices rise rapidly as extra lift is required because that requires extra sets of scissors, in high cycle applications or where hand pallet truck only access demands a low height profile table.
The stainless steel tables are available but are expensive. An alternative is to use a stainless steel skin for the deck and epoxy plant.
As with most products, lift tables are much cheaper if a standard configuration is used. But very cheap tables may sacrifice safety standards or durability and performance.
8-Sep-2008