The machine has been ordered by Indiana based demolition and recycling contractor Renascent. The company specialises in the demolition and repurposing of building structures and spaces such as campuses, hospitals, stadiums, convention centres and airports. In addition to demolition and recycling, the US firm offers consulting, planning, and budgeting services. 

Key features of the modified carrier 

Renascent specified that the RS 7500-L should be capable of reaching a working height of 52m (including the attachment) operating a Genesis GXT 1550 mobile shear or its equivalent. Since the end user favours Liebherr over other excavator brands, a Frontless Liebherr R9150 was chosen as a base machine. The standard machine was upgraded with a number of new features including an EW-SL undercarriage with a jacking system, a counterweight of 37t, reinforced main body, a tilting cabin with a top window with wind screen wipers and a Liebherr tool linkage. 

Retrofit boom, enhanced undercarriage and integrated ballast pickup system 

The retrofit boom designed by Rusch comes with a sub frame and the two main luffing cylinders and has several functions. The main function is being a carrier for different boom types. The retrofit boom can accommodate a knuckle, telescopic or a ripper boom. The connections to all the booms are the same and are operated hydraulically. The sub frame changes the configuration of the upperstructure/boom/cylinder to enhance stability when working at heights. Thanks to its own lifting device, the sub frame can lift up to 45t, enough to haul up the tracks onto the machine without the use of an external crane. The third function is the lifting of the counterweight with a special rod construction. The Liebherr standard undercarriage is a strong, long and wide structure by itself. It is also equipped with a jacking system for the assembly of the tracks. 

The only thing Rusch had to modify was the width of the machine. In the standard configuration, the machine cannot use the full load/radius diagram over a 360o swing range. A special system designed by Rusch made the machine even more stable over the side than over the front. The ballast pickup system is integrated in the main frame, just behind the engine room. It is operated from the cabin and can pick up to 37t of ballast in one go. A special attachment system makes it possible to pick the ballast up from a lorry even when the ballast is not on a flat surface. The movement of the pickup system is controlled using the retrofit boom.

Four piece knuckle boom 

The knuckle boom comes in four pieces: main boom knuckle, auxiliary boom knuckle, main stick and auxiliary stick. The main boom is connected to the retrofit boom by means of the hydraulically operated cylinders. Once in place, the hydraulic lines are connected to the body hydraulic line manifold via the ball valves. The main boom is mainly used to bring the tool up to the height and must always move to the maximum position at 85o. After that the operator can use the remaining three parts as a ‘triple’ boom. The auxiliary boom is used both for height and radius. The sticks are used for tool connection. The main stick can take a GXT 2550R shear. For this purpose, the auxiliary stick cylinders have to be moved to the connection lugs on top of the main stick. The auxiliary stick will be equipped with a Liebherr tool link and can take a Genesis GXT 1550 to the maximum reach. A lifting lug on the under side of the stick can lift up to 15t over the same range (without the tool attached). With all the modifications implemented, the machine would weigh 300t.  

Advanced safety system 

The safety system measures the overturning moment of the machine (7,500KNm) in real time mode. It involves measuring the angle of each boom part and tool and the calculation of the overturning moment. If the movement of one of the boom parts puts the machine at risk (by increasing the radius) the system gives the operator a warning at 90% of the overturning moment and cuts off the function at 100%. The 87% hydraulic system safety and the 75% tipping safety regulations are incorporated in the system, making the machine extremely safe. For the assembly and raising of the telescopic boom, however, the machine must go to 90% of its tipping safety. In order to achieve this, the system has to be overridden by an authorised person. All configurations and working diagrams are programmed into the computer. The computer detects which boom is installed, if the ballast is mounted, if the tracks are wide etc., to keep the machine safe. Every action is displayed on the monitor in the cabin. All operating movements are logged into a database and can be retrieved by an authorised service engineer. The system has a router for external access. The machine is to be fully assembled and rigorously tested at the Rusch facility in Medemblik, the Netherlands.

www.ruschcranes.com