Tower Crane's Height and Reach Unfold on Site
Could a machine that stands in one small spot on the jobsite ever come close to replacing a go-anywhere telehandler?
It could, says the Manitowoc Crane Group, if the machine were a self-erecting tower crane. Manitowoc concedes that the telehandler does have certain advantages: It can place material inside structures; it's ready to work the instant it reaches the jobsite; and it's available virtually everywhere. But the other side of that coin, says Manitowoc, is the self-erecting tower's superior lift height and reach, its ability to work in small spaces, its relatively fast deployment, and its jobsite friendliness (it doesn't make ruts, it's exceedingly quiet, and it can place material where a telehandler might not be allowed — such as across fresh concrete.
According to Eric Black, regional business manager for Manitowoc's range of Potain self-erecting tower cranes, the self-erecting tower has long been popular on European jobsites, but it has been slow to catch on in North America. We at Construction Equipment realized that these machines might now be getting a second look from domestic contractors, however, when Jim Yasko, assistant administrator of Local 150's Apprenticeship and Skill Improvement Program (ASIP), told us that the Local had added a Potain Igo 50 to its crane fleet for training International Union of Operating Engineers members.
We asked if we could take a close look at the new addition, and in mid-August visited with Local 150 instructor Glenn Minyard at the ASIP training facility in Plainfield, Ill. Minyard, a long-time crane operator who now specializes in crane training and operator certification for Local 150, spent the morning demonstrating the features and capabilities of the Igo 50. Accompanying us were Manitowoc's Black, Pat Runnion, principal of Runnion Equipment in Lyon, Ill. (the company that supplied the Local's Igo 50) and Leslie Shalabi, vice president of SE10 Creative, a public relations firm representing Manitowoc.
Capabilities and transport
The Igo 50 is the largest and among the newest of the 16 Potain self-erecting tower-crane models. This electrically powered, bottom-slewing crane has a hook height of 76 feet when the jib is horizontal (86 feet with the jib offset 20 degrees) and has a maximum lift radius of 131.17 feet. Maximum lift capacity is 8,818 pounds at a radius of 42.58 feet (or 45.75 feet if the second and third jib sections are folded back). Lift capacity at maximum radius is 2,514 pounds. The Igo 50 has a fully counterweighted working weight of around 103,000 pounds.
The crane requires 480-volt, 60-hertz, 31-amp service, which can be supplied either from temporary power on the job, or from a portable generator. The unit at Local 150 used the latter. The crane utilizes Potain's LVF Optima technology which, says the company, is a variable-frequency system that lowers electrical requirements and "delivers full winch power and ensures the fastest speed possible."
The Igo 50's transport weight is about 52,000 pounds, and its overall transport dimensions are approximately 46 feet in length and 11.8 feet in height. The crane can be towed to the site as either a trailer or a semi-trailer, or it can be transported on a drop-deck trailer.
If the Igo 50 is towed, a transport axle (or two, if weight regulations require) is pinned to a mounting structure on the lower portion of the mast. Then, either a dolly axle or a fifth-wheel attachment is pinned to a mounting structure at the base of the counterweight tray. If the Igo 50 is transported, then an assist crane is required for unloading, unless it is transported with its transport axle in place and conditions allow it to be rolled off the trailer. The approximate 51,000 pounds of concrete counterweight arrive on an assist truck — or two, depending on truck size.
The unfolding story
Once on site, the crane's swing-away outriggers can be deployed on suitable mats and the erecting process can begin. As Minyard explained and demonstrated the assembly process, we were impressed by its seeming simplicity and speed. Inside the crane's right cabinet is a control panel with three rotary switches that program the assembly sequence, and then set working parameters — for example, jib offset, number of jib sections used and parts of line used. Before assembly begins, however, the jib's working attitude — whether horizontal or offset at 8 or 20 degrees — must be selected by adjusting the pendant.
Minyard first turned the left rotary switch to the assembly position, which allows deployment of the mast and first jib section. He initiated this process by clicking the toggle switch on the crane's wireless remote to the right, and then moving the right joystick to its assemble position. This action activates the crane's hydraulic system, and a large hydraulic cylinder, anchored to the mast's bottom section, works through a system of linkage, wire rope and the jib mast to bring these components into position. (The hydraulic pump that powers the assembly process is, in turn, powered by one of the Igo 50's four electric motors, all of which are accessible from ground level.)
As this sequence of the assembly takes place, the crane's base counterweight (made of steel) is sufficient to stabilize the unit, but additional counterweight now must be added before deploying the second and third jib sections. Although Local 150's Igo already was equipped with its full counterweight when we arrived, Minyard demonstrated how the crane's optional derrick, which stows along the mast's upper section, can be used to take on 12 concrete counterweight slabs, each weighing 4,250 pounds.
He first lowered the hoist line and clipped it to another line near the mast base. This line passes through a sheave (which has a brake) near the base of the mast, then is directed upwards, through a second sheave mounted near the base of the upper mast section, and finally across a sheave in the tip of the derrick. Releasing the brake on the lower sheave allows the derrick to lower to its working position, and clicking the rotary switch to its derrick position allows a small hydraulic cylinder to be used for swinging the derrick through an arc of 90 degrees. With this arrangement, the main-hoist line now controls the derrick's hoist line, which can be hooked to the counterweights that arrive on a separate truck.
Actually, the Igo 50 is ready to work in this configuration, with only the first jib section in place. Typically, however, the remaining two sections are deployed for added reach. Hydraulic cylinders (one between the first and second jib sections, another between the second and third sections) deploy the remainder of the jib. Before lifting, though, the operator must use the switches in the cabinet to set the jib sections in use (one, two or three), the jib offset (0, 8 or 20 degrees), and the parts of line used (two or four). A screen below the switches asks the operator to confirm the choices.
The Igo at work
The Igo 50 in action is a quiet machine — just sort of a low purr from its motors. Even with the portable generator running within a few feet of the crane, we could carry on conversation in a normal voice.
Minyard told us that he prefers to use the crane's wireless remote when operating, because it gives him the latitude of staying close to the load when placement is critical. The machine does have a tethered controller which, says Minyard, is probably used only when the operator allows the remote to run low on battery power.
The crane's line speeds range from around 6 feet per minute with four parts of line, to 216 feet per minute with two parts of line. Minyard demonstrated the procedure for switching between two and four parts of line. The switch is relatively simple, because the hook block is made in two sections. He lowered the block (running with four parts of line) to the ground, unpinned the two halves, and then, by using the hoist control, raised the lighter of the two halves (the one without the hook) to dead-end at the trolley.
According to Minyard, the hook and trolley automatically slow when reaching limits of travel, and the crane is equipped with an anti-two-block device. Also, according to Potain, the Igo 50 has a new slewing system that allows "reinforced braking by an opposite movement of the controls (counter-sewing)." A load-moment system allows only hoist-down and trolley-in functions if the system senses an unsafe condition approaching. Also available as operating assists are a wind-sensing system and system that automatically restricts trolley and jib travel into a designated area.
If you're wondering how quickly the crane can be ready to work, we've heard various estimates, but we offer Minyard's opinion:
"If the mats are waiting, I've seen the crane go together in as little as 45 minutes."
