To move heavy objects vertically and horizontally, the crane is often the only solution – and has been since the times of Ancient Greece. Without these machines, the construction of such monumental structures as the Parthenon temple, for example, would have been very different.
This is still true today: cranes are the means of choice not only for lifting heavy loads, but also for setting them down again elsewhere. This ability to move loads in three-dimensional space means that a crane can be required in a wide variety of situations, from the erection of wind turbines to the relocation of industrial machinery or even the transportation of entire ships.
In practice, however, “the crane” is more of an umbrella term for a wide variety of designs. Depending on the requirements, there are many different types available today.
DEFINITION OF TERMS: WHEN IS A CRANE A CRANE?
Between forklift trucks and backhoes, there are many machines that can move loads. But what exactly distinguishes a crane from other types of construction? There are only a few factors, but they are (largely) fixed:
- The load can therefore always be moved in a three-dimensional space. A crane can therefore not only lift and lower, but also always move the load horizontally – regardless of whether it only slews or (additionally) moves it. A machine that can only lift falls into the hoist category.
- A crane can move an extremely wide variety of loads due to its system. For this purpose, most models have a universal lifting system such as a hook. There are sometimes exceptions to this rule if only one type of load needs to be handled at a time. This is the case, for example, with container cranes that only have to move standardized ISO containers and have a harness known as a spreader for this purpose.
- With a few exceptions, all cranes work with a hoist based on ropes and (usually) pulleys. Even if there are rigid or telescopic booms, the actual work is usually carried out using the rope.
As far as the drive and mobility are concerned, however, there is no uniformity. There are therefore cranes that are driven by muscle power or various types of motors, depending on the definition. Depending on their design, cranes can also be mobile, temporary or permanently installed.
The most important main groups of crane types are presented below. In practice, however, there are also crane types that cannot be clearly assigned to a category.
(STATIONARY) JIB AND SLEWING CRANES
These crane systems are completely fixed in one place and can only be moved as part of extensive work – although this is not necessarily intended by the design. It is not possible to move the entire crane laterally (e.g. on rails).
There are different versions, which can be roughly divided into the following types:
- Pillar-mounted slewing jib crane: A fixed jib is attached at right angles to a vertical pillar. The load is either suspended from the jib taper or from a trolley that moves along the jib.
- Derrick crane: This is similar to the pillar-mounted slewing crane, but here the jib can be tilted vertically. The load is only moved radially to the slewing range via this.
- Luffing jib crane: This is the larger and often much more powerful version of a derrick crane. Depending on the variant, the jib also points upwards, can be tilted down to the horizontal plane or tilts downwards, in which case the highest lifting point is in a horizontal position.
- Fixed jib slewing crane: The jib is immobile and has no trolley. This means that the load can only be lifted and lowered and slewed by turning it sideways. Technically, this variant is sometimes closely related to a pillar-mounted slewing crane – see next picture.
Main applications
Stationary jib and slewing cranes exist in a wide range of variants and performance levels. Large derrick cranes, for example, are used in many quarries. Small (often manual) pillar-mounted slewing cranes, on the other hand, are often found in pleasure boat marinas. The large, but otherwise largely immobile slewing cranes used to be a typical sight in many harbors.
Today, they are only used where their immobility is not an issue or is compensated for by other factors – for example as cranes on oil rigs. In many cases, these cranes have now been replaced by more flexible designs, often from the following category:
Bridge and gantry cranes
With a few exceptions, these two closely related crane types are permanently fixed systems that can move freely within a relatively narrow range – typically what is possible within the framework of the corresponding rail system.
Common feature: Both cranes have a transverse bridge that is supported on the sides. A trolley with the hoist can move along the bridge. This construction is responsible for lifting and lowering as well as moving the load along the bridge.
Difference: With an overhead crane, only the bridge moves, which rests at its ends on a fixed, higher support system (e.g. rails along the walls of a factory building). The gantry crane, on the other hand, resembles a door frame or a portal. Here, the lateral support systems are firmly connected to the bridge and move together with it.
Both systems are available in both indoor and outdoor versions.
The semi-gantry crane is also a hybrid form. The gantry luffing slewing crane (see next picture) also combines the gantry crane system with a slewing crane system with jib arm mounted on it. In this form, this crane design is the direct successor to the former stationary slewing cranes.
Main applications
Bridge and gantry cranes can be found in ports as well as in heavy industrial plants, for example. In most cases, the type of load is relatively limited or recurring.
Mobile and truck-mounted cranes
These are (largely) freely mobile cranes. The key features of this category:
- The crane work is always the main task of the system. They are therefore not vehicles that can simultaneously transport a stationary load on a loading area – unlike a loading crane, which only has a supporting function on a transport vehicle.
- Only minor work is required to switch from travel mode to crane mode and back again – such as extending outriggers or a boom. What’s more, the crane can do this all by itself, without any auxiliary machinery. This means that mobile and truck-mounted cranes are always ready for use within a very short time.
- These are almost exclusively jib slewing cranes with a telescopic boom. Very large mobile cranes are often also designed as lattice boom cranes.
Within this group, a distinction is made between self-propelled and externally powered cranes. The latter typically take the form of trailer cranes. Self-propelled mobile cranes are divided into different systems depending on the degree of off-road mobility and the speed that can be achieved.
- The best-known representative is the fast mobile crane.
- The all-terrain or AT crane is technically very similar, but has better off-road capabilities.
- If off-road mobility is much more important than speed on the road, then rough-terrain cranes are the method of choice.
- Crawler cranes are used for particularly challenging situations and especially the heaviest loads and/or lifting heights – for example in wind farms for the erection of wind turbines. Although they are also self-propelled, they can usually only operate off paved roads due to the crawler chassis – often not much faster than walking speed.
- For the sake of completeness, rail-bound railroad cranes and floating cranes (inland waterways and offshore) must also be mentioned in this group.
Main applications
Mobile and truck-mounted cranes are characterized by their great flexibility. Smaller models can be moved very quickly and can be used in a wide variety of locations without a great deal of preparatory work. Their range of applications is therefore very broad.
Large crawler cranes can only be transported disassembled and may require several truckloads for transportation to a new location.
Away from very extensive but permanent locations such as open-cast mines or large construction sites that last for years, these cranes are therefore often used where their performance is only required temporarily, but where it would not be worthwhile setting up cranes that are also mobile but not as mobile.
Tower or slewing tower cranes
These models are the most important helpers on typical building and civil engineering construction sites. To a certain extent, they are also mobile and optimized for easy relocation. However, depending on the system, several days of work and technical equipment are required to make the cranes ready for use.
Typically, the tower crane is a complete lattice boom construction. There are two different boom designs:
- The boom is usually aligned horizontally. The horizontal load movement parallel to the boom is carried out via a trolley, whereby the boom is only moved for slewing.
- With the so-called luffing jib tower crane, on the other hand, the jib can be tilted in a vertical direction, i.e. it can be raised and lowered. This movement replaces the trolley, so the load is always suspended from the tip of the jib. This means that lifting heights greater than the tower can be achieved and the crane can be used in confined spaces.
There are also other types, such as bending beam and telescopic jib tower cranes, but these tend to be used in special cases.
Many modern tower cranes are designed to be self-erecting. This means that no other machines (such as other cranes) are required to set them up and make them ready for use.
From a technical point of view, there is still a big difference in exactly where the pivot bearing for slewing the tower crane is located:
- Top turner: The tower itself is fixed. Only the jib and counter jib with counterweight can be rotated. In some cases, the operator is located in a cabin installed in the slewing area. This places significantly less weight on the slewing bearing. In addition, a smaller slewing range is required on the ground, as the entire system with the counterweight is mounted high up. The disadvantage, however, is the more complex design.
- Bottom slewing jib: The jib and tower can be slewed together. When the crane is slewed, both elements move accordingly. The counterweight must be mounted close to the ground for this. The crane is operated almost exclusively from below, often without a special cabin using remote controls. Technically, these systems are simpler and can be set up more quickly – often within minutes. One disadvantage is the greater overall load on the pivot bearing, because the weight of the tower also rests on it.
Upper turners are often larger and more powerful and are therefore installed where the more complicated assembly and disassembly is not an issue. Conversely, bottom turners are usually designed to be smaller. As a rule, they are driven electrically by nearby power sources.
Main applications
By far the most important terrain for tower cranes is the construction sites of this world. They are usually set up at a central point on the ground. However, in special building construction projects, tower cranes can also be found that “grow” as so-called climbing cranes by inserting intermediate sections or that are installed on the building itself.
Conclusion: A crane for every occasion
Thanks to their performance and a multitude of variants and sub-variants, cranes are one of the world’s most important (and oldest) machines for moving loads that require more than just muscle power. They can be found in a small marina where pleasure boats have to be hoisted into the water, in wind farms, on oil platforms, in container terminals, in industrial plants and on almost every construction site in the world.
Picture credits:
Image 1: Marcus Transport
Image 2: stock.adobe.com © Lukassek
Image 3: stock.adobe.com © Photocreo Bednarek
Image 4: stock.adobe.com © franz massard
Image 5: stock.adobe.com © nicknick_ko
Image 6: stock.adobe.com © nicknick_ko
Image 7: stock.adobe.com © tong2530
Image 8: stock.adobe.com © Brett
Image 9: stock.adobe.com © Dirk
Image 10: stock.adobe.com © Willi
