This week we will be reviewing the 5 tonne Potain MC88 tower crane. The set up for this crane was a 50m mast and a 50m jib.
I must forewarn you that this model is the crane I first learnt to operate in and got my licence on, an maybe I am a bit bias but they are great!
Most of these cranes are set up without the cabin for remote operation only and for good reason. Only a lunatic would drive a 5t crane from a cabin, they deflect so much you would be sick in no time.
It has a few shortfalls I must admit: max lift at 50m is about 1 tonne, the hoist is fairly slow, it needs a slower speed for the trolley and it has the worlds worst hook block; it is a kite. Its flat and wide and catches every bit of wind, I don't know what they were thinking going with such a terrible design.
The hetronic remote control is just to big, its about 4 times larger than the standard remote controls used by most of the other tower cranes, expect to bang into things constantly with it.
But faults aside its a good machine for the right job.
The crane is very responsive, much more than the other popular 5t remote out there from Comadil (and wont break down:) They are very durable, most are rentals and they can cope with not being treated properly and keep on going. Also for a small crane it performs quite well in the wind... well except for the hook block.
The Potain MC 88 is a good remote control crane for the very common smaller jobs that are all over Sydney at the moment, which explains the cranes popularity.
I give this crane 4 out of 5.
This week we will be reviewing the 8 tonne Raimondi MRT 144.
The configuration for this crane was a 60m mast with a 65m Jib and a counterweight base (not anchored)
The first thing you will notice operating this crane is how light the controls feel in your hand. Unlike the nice heavy leavers you get with a Jaso or Comansa, these are super light and its hard to feel which gear you are in. If I was running Raimondi first thing is I would get rid of these levers I hated them.
The crane feels light and whilst it is easy enough to operate most of the time, heavier loads towards the end of the jib will throw the crane around. The crane deflects quite a bit, the tower is quite narrow so I guess this is to be expected. It performs poorly in the wind and although the crane is only a year old there is quite a lot of play in the slew brake. Back slew on this thing is hopeless! (makes me mad just thinking about how hopeless it is)
Its max capacity of 8 tonne is in 2 part, this crane does not do 4 part as far as I am aware. Hoist speed is ok but could be faster. Operators with experience on faster hoisting cranes may find it just a bit too slow. The hook block is a great shape, it looks a bit like a liebherr block, it doesn't catch the wind and if you get a bit of a swing it dies down pretty quickly.
The Cabin is actually pretty good overall apart from it having no window tinting except for the door (tint should be mandatory!) and its aircon struggles once it gets to around 30 degrees Celsius.
The cabin is offset quite a fair bit to the side of the jib and along the jib, in fact you can trolley the hook along side the cabin, this makes it very easy to see how the hook is moving when trolleying and catch trolley swing. The cabin has drink and book holders, the seat is ok but doesn't recline so sleeping is out of the question. The way the cabins glass curves down is another big plus, making viewing down pretty easy. The cabin was not big but it wasn't too small, a good enough size.
I'm giving this crane 3 out of 5. If not for the exceptional cabin it would of scored lower. A good crane if you are on a strict budget, if you can afford better... get it.
Tower cranes are seen on almost every major construction site throughout the world. These machines are built to lift heavy loads efficiently and safely. This tower crane is an A frame tower crane, a flat top tower crane does not have pendants or a tower top/a frame, when reading this you should at least know the types of tower cranes so that it will make sense to you.
The jib extends horizontally at various lengths depending on the model and configuration of the crane. A trolley attached to the underside of the jib moves loads in and out from the cranes center axis. Hoist and trolley lines run throughout the jib enabling vertical and horizontal movement of the load. Rotation of the jib is achieved by employing the "slewing" action.
To move a load in and out from the cranes center axis a trolley is employed along the underside of the horizontal jib. Powering the trolley is the trolley drive mounted on the horizontal jib. A cable from the trolley drive runs through the jib and is attached to the trolley. A trolley then controls the loads radial movement and helps stabilize the load.
A hook or hoist is attached to the hook block assembly. Hook block assemblies house a series of sheaves and pulleys that carry the rope. The block provides greater flexibility and facilitates the lifting of a load. The primary function being for the free rotation and positioning of a load. The shape and weight of the hook block can make a big difference in how the hook moves and will effect how much swing the hook will have when moving.
A cranes drives, drums, gears, electronics, and counter-weights are found on the counter-jib platform. Located behind the operator cab, the counter-jib provides a balancing force to the load on the horizontal jib. Drives, drums and electronics are located to the rear of the counter-jib to maximize torque and for ease of maintenance.
Balancing the forces on the crane caused by the load is a primary function of the counterweight. Counterweights are fabricated from concrete and come in modular units. The number of counterweights depends on the expected max load capacity, jib length and tower height.
The hoist unit houses the hoist drum, gear box, gear shift, brake, and supporting components. Typical placement is located behind the counterweights - toward the extreme rear of the counter-jib. Placing all hoist and trolley components in one location makes for efficient servicing of the crane.
A component of the hoist unit that lifts and lowers a load by means of the hoist line. Power to the drum is supplied by the hoist drive. The hoist drum winds the rope or cable in a specific cross-pattern to avoid entanglement of the line.
Tower Top / A-frame
Hammerhead or "high-top" cranes utilize a tower top section for greater torque and stability. Pendant bars are attached from the tower top to the jib and counter-jib that provides further stability. Anemometers and aircraft-warning lamps are placed on the top of the tower.
Pendant bars provide additional stability to the crane. The bars are attached from the tower top to the jib and counter-jib. Flat top tower cranes eliminate the need for pendant bars and a frame by making the crane jib larger and thus stronger.
Trolley and Hoist Lines
Loads are moved up and down by the hoist line and in and out by the trolley line. These lines run throughout the horizontal jib, counter-jib and tower top through a series of pulleys and guides. The trolley line is connected to the trolley unit and the hoist line is connected to the hook block.
The jib, counter-jib, tower top, and slewing assembly collectively make up the slewing unit. This section allows the crane to rotate and perform lifting.
Movements of the crane are controlled from the operator's cabin. Within the cabin sits the operators chair with joystick controls, electronic monitoring devices and communication systems. Many cabins come with climate control to ensure a comfortable work environment. The operator cab is part of the slewing assembly.
The slewing ring drives the rotational movement of the slewing unit (jib, counter-jib, cab, and tower top). Powered by the slewing gear drive the slewing ring is fixed to a ball track and is made up of several hundred precisely machined gear teeth. The slewing ring is capable of enormous torque, yet precise movement.
Top Climbing Unit
How does a crane "grow" taller? The top climbing unit is an essential piece of any tower crane. This specialized section enables tower crane sections to be inserted and connected to the tower. A large hydraulic jack then lifts the Slewing Assembly, Jib, and Counterjib one tower section higher. Another section can then be inserted. The top climbing unit is more common than the bottom climbing unit, this unit adds tower sections to the tower crane, the bottom climbing unit keeps the tower at the same height but raises the whole crane up, repositioning it at a higher point inside the building.
Bottom Climbing Unit
Climbing inside buildings is made possible by the bottom climbing unit. Climbing collars are used with a hydraulic power pack to lift the tower sections upward. The crane leaves Its foundation at the ground, and is completely supported by the structure of the building it is constructing. This leaves the lower levels of a building vacant for finish work, and at times occupancy before the building is completed.
Bolts and Pins
Secure connections are an essential component of any tower crane and those connections are only as secure as the bolts and pins used on the crane. Anchor bolts must be of high tensile strength and pins and other bolts should be routinely re-torqued according to manufacturer specifications. Inspection of these connections are made on a routine schedule. Below on the left you can see where the incorrect holding bolt has been used and on the right how it should look, note how the bolt it is holding has moved and forced the bolt to bend, keep in mind that those bolts hold the tower together. This is what can happen when you do not use a reputable company (don't get black cranes!!!)
A tie-in secures the tower mast to a structure or framework and provides stability when the crane is under load or experiencing wind forces. The number of tie anchors are calculated by taking into account such factors as the type of crane, jib length, height under hook, and maximum out-of-service wind speed.
These are also known as a static base, this base is used so you do not have to excavate and build a concrete in ground base, not as common as an in ground base the down side is they take up more room and require quite a lot of counterweight (eg 70 tonnes for an 8 tonne tower crane with 65m jib) The undercarriage of the crane acts as a base for the tower mast and surrounding lower structure. For a free-standing crane the undercarriage carries ballast weight, stabilizing the crane, while spreading out the load on the ground. Other fixed base cranes use large heavy foundations for stabilizing the crane. The crane tower is connected to foundation anchors embedded in re-enforced concrete.
The knee brace makes up the undercarriage truss, spreading the weight of the crane out to the small corner pad foundations.
Central ballasts provide stability to the tower crane structure. Ballasts are made of concrete and come in modular sections that are stacked above the cross frame.
The cross frame is a square section that connects to the bogies and knee braces as an integral part of the base structure of the crane.
Bogies / Pads
Bogies are used for moving the crane on rails to allow the crane to cover more job site area. Rail mounted cranes use electric driven bogies, so the operator in the top of the crane can control the drive on the rail at the bottom of the crane. Stationary cranes can use corner plates and economical corner pads under the undercarriage.
Foundation anchors are steel posts embedded in re-enforced concrete that are bolted to the tower. These anchors provide a secure connection to prevent the crane from swaying or experiencing structural failure due to overload and wind forces. This is the most common and used instead of the undercarrage
A crane’s tower mast is constructed of a series of tower crane sections. The structure of a section is reinforced by a braced square or truss. Sections are bolted together as the tower crane is erected. Access ladders are incorporated in the interior of the sections to enable workers to move up and down the crane.
Looking at tower cranes, the average person may see little difference between a crane used for low and medium rise and one used for high rise but there are quite a few differences and I will discuss them here.
1. Hoist Speed
The difference in hoist speed is quite significant. A crane used for high rise should have a hoist speed of no less than 1m per second and many go much faster, over 3m per second. While a crane used for low rise, a slower winch speed is an acceptable trade off for using a cheaper crane, the delays of a slow winch speed would be too costly on a high rise job.
2. Larger Mast
High rise cranes use a larger mast, this provides more stability and less deflection, especially at greater heights. Most of the 5t cranes used for low-rise have a max tower height of 50m, in part due to their smaller mast, just one of the reasons making them ineligible to be high rise cranes.
3. Climbing and tied in
Low/medium rise cranes are usually free standing, that is, they are not tied into the building. High rise cranes are very often fitted with a climbing frame. At intervals specified by the engineer the tower crane will be attached "tied in" to the building. Beams are attached to the crane tower and bolted to floors in the building
4. Larger lifting capacity
The combination of a larger crane mast and hoist motors leads to larger lifting capacity in high rise cranes
5. Bigger concrete pad
As there is a larger crane mast and more tower crane sections to support, as well as usually a bigger crane the concrete pad the tower crane will be fixed to are much bigger, requiring more concrete, more reo and more room
6. More expensive
High rise cranes are more expensive than the smaller cranes for obvious reasons. They are built stronger, require more tower sections and hoist rope, a larger base to sit on and require a rigging team each time they need to be raised. A builder needs to take into account that costs increase the higher a building goes.
Also keep in mind a crane used for high rise may be used on low rise, generally this happens when there is heavy lifting required such as building out of concrete panels. A low rise should not be used for high rise construction.
We will discuss an external climbing setup. Both luffing and hammerhead cranes can climb. This process is usually done for high rise construction, where the crane will raise itself up by adding more tower sections as the building is being constructed, and remove tower sections once the crane is no longer needed.
1. Crane lifts additional tower section and suspends it from extendable monorail. Bolts of top tower section are removed
Hydraulic rams lift top section of crane and climbing frame
Additional tower section is drawn into the climbing frame and bolted at top and bottom by the tower crane rigging crew.
To climb down the reverse procedure is followed
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