Cranes are designed to handle heavy loads. Lorry-mounted cranes offer one more feature: mobility. As well as having the ability to turn in all directions, they can be driven like regular trucks on highways. These qualities make them highly versatile at construction sites. But do you know what they consist of and how they work?
A lorry-mounted crane is made of two parts: the carrier, also referred to as the lower, and the lifting component, also referred to as the upper.
The lower is the lorry itself. The upper is the part that does the lifting, lowering and swinging. It consists of the base, inner boom, outer boom, telescopic extensions, boom lift cylinders, boom lift pistons, an inner link mechanism and an outer link mechanism.
The base provides support to the upper. The booms are the arms responsible for lifting and lowering the loads. The inner boom and outer boom are like the upper arm and lower arm of your hand. The inner boom sits on top of the base and the outer boom sits on top of the inner boom. The booms are of varying lengths, but they are usually several metres long.
The telescopic extensions allow the booms to be extended for a longer reach. The boom cylinders and pistons are there to swing, lift, lower, extend and contract the booms. The link mechanisms connect the inner and outer booms with each other and the inner boom with the base.
The upper and lower are joined by a turntable, a circular revolving platform that allows the crane to swing and rotate in all directions.
How it Works
The majority of modern cranes are operated by hydraulic systems. The hydraulic system uses an incompressible fluid, such as oil, to transmit force from point to point. As the force is transmitted from one point to another, the force multiplies.
In a simple hydraulic system, a piston pushes on the oil inside a hermetically sealed container, creating a pressure. The oil then pushes up another piston with a much greater force than the force applied by the first piston.
There are two varying types of hydraulic pumps: a gear pump and a variable-displacement pump.
A gear pump has a pair of gears that are inter-meshed and put pressure on the hydraulic liquid. Since the pressure fluctuates with the speed of the engine, the engine has to be run optimally to get high pressure. Most lorry-mounted hydraulic cranes use two-gear pumps.
A variable-displacement pump has a ring of piston cylinders fixed inside a barrel. The cylinders protrude out of the back of the barrel and are attached to an angled swash plate. When the engine spins the barrel at high speed, the swash plate pushes and pulls the cylinders in and out. This causes the oil to be sucked in from the oil tank and pushed into the hydraulic system, creating a high pressure that moves the booms.
Modern hydraulic lorry-mounted cranes have a single engine that powers both the crane and the undercarriage. In older models, there used to be two engines – one for the lower and one for the upper.
If you want to become a crane operator, you have to complete a lorry mounted crane training in Singapore from a government accredited training provider (ATP), pass a test, obtain a certificate, and then get yourself registered as a certified crane operator.