Grove’s new flagship all terrain had its debut at the Conexpo show in Las Vegas last month. Rated at 450t and 550 US ton, it is called the GMK 7450 in Europe and most of the world, and the GMK 7550 in North America. This crane is notable for two reasons: firstly, it is the biggest all terrain that Grove has ever built, and secondly it is the first real joint venture product of Grove’s US and German operations.
When Grove took over Germany’s Krupp in 1995 there was reason to suppose that the brightest and best engineers on both sides of the Atlantic would put their heads together to come up with the finest globalised product. In fact it has taken until now for a complete crane to emerge that has been jointly designed by US and German engineers.
While Krupp produced the KMK 8400, the biggest AT in Grove’s range had been the 300t six-axle GMK 6300 (6350 in North America). The GMK 7450 confirms Grove’s growing stature as a serious challenger to Demag and Liebherr in the largest AT and truck crane sizes.
Superstructure
According to Grove, the GMK 7450 has ‘the best load chart for a seven-axle crane’ and the ‘longest on-board boom in the 400t and over class’ i.e. the longest boom that does not have to be specially configured to travel. Five sections make up the main boom that extends from 16m to a maximum tip height of 63m. It has the U-shape Megaform profile and it uses the Twinlock single-cylinder extension and pinning system. If necessary for transport there is a quick removal system for the complete boom assembly.
Attachments available are fixed offset jibs from 12m to 73m, off-settable to 3° and 25°. Luffing jibs from 19m to 73m enable a maximum hook height of 130m to be reached. Ballast required for maximum lifting capacity is 120t of counterweight.
Power comes from a 190kW Mercedes-Benz OM905LA Euromot II superstructure engine.
A new superstructure cab has been designed for this model. It is 500mm wider than normal to give more space and a better working environment. The cab swings away to the rear for stowage during transport and when in operation it can tilt up to 20° to improve visibility on high lifts. The electronic crane operating system (ECOS) has a twin screen graphic display in a ‘new ergonomic display housing’ and an EKS5 load monitoring system that uses CanBus technology.
The carrier
Grove claims that the GMK 7450 is the only all wheel steer crane in this class. The carrier is 15.5m long with the rear outrigger box removed; and 3m wide. First, fourth and fifth axles are driven to give a 14x6x14 drive line configuration as standard. As an option, axle two can be also driven in addition to being steered.
As with all Grove’s GMK product line, the 7450/7550 uses the Grove/Krupp patented all-wheel independent hydropneumatic Megatrak suspension system. Megastrut suspension legs on the first three axles are common to other GMKs but new on the rear four axles is a redesigned unit. These have relocated steering levers at the top of the strut that allow a 30% deeper frame section on the carrier which increases torsional stiffness.
Carrier engine is a 420kW Mercedes-Benz OM502LA to Euromot II/EPA/CARB Tier 2. Maximum travel speed is 89km/h (55mph). The transmission is a fully automatic seven-speed, plus one reverse, Allison HD4076. It also has a two-speed high/low transfer case and inter-axle differential lock for lower travel speeds and better traction on site. Standard fitment are 14.00R25 single tyres, although 16.00R20.5 tyres are an option.
To make the crane more attractive to North American customers the rear outriggers are designed to be detachable. And an auxiliary eighth axle can be pinned to the rear of the carrier instead of the rear outrigger box for different roading requirements. A boom dolly and boom launch trailer are further options. These features typify the whole approach that Grove has taken from the outset in designing this machine.
Global engineering
What is most interesting about this model is that it is the first true collaboration on an entire crane between Grove’s US headquarters and its German subsidiary since the 1995 Krupp acquisition. Grove says that the 7450/7550 has been designed as a ‘global product’, designed with world markets in mind. This is not a unique claim; other manufacturers also ensure from the outset that their models meet the specifications of other continents.
Grove believes, however, that the high level of design collaboration between the German and US technical departments was ‘a major achievement’, resulting in a design and specification which complies with the complex requirements of different markets. For instance, the need to meet different axle-loading requirements (12t per axle on European Union highways; various requirements in different states of North America) meant that it was necessary to design a range of configuration changes which can be easily accommodated in build such as the optional detachable rear axle and outriggers.
As Grove has stepped up integration of its European and US operations, the distinct barrier of Shady Grove building truck cranes and RTs and Wilhelmshaven building ATs has been breaking down. Some GMK 5100 and 5180 AT kits are shipped over from Wilhelmshaven to Shady Grove now for assembly. These kits are not, as one might imagine, a few large sub-assemblies that just need bolting together, they are totally stripped down, comprising thousands of parts, right down to nuts and bolts. Further cross-fertilisation is evident in the US-built 9000E RT that uses a German-style boom.
With manufacturing locations no longer operating so discretely, the design of the GMK 7450/7550 had to allow for manufacture on both sides of the Atlantic, with some parts being sourced on one side or the other. Shady Grove is building the carrier while Wilhelmshaven is building the superstructure, fully built-up boom assemblies, the superstructure cab, electronics and also Megatrak suspension struts. Final assembly can be done in either country.
Minimising the time to market was a major advantage of spreading the engineering design across the European and US resources. A crane this size takes two years to develop, Grove says, and it could have taken twice as long in development if it had been done at just one place rather than using both sets of engineering resources in parallel. At any one time there were 25 engineering staff in Germany and 19 in the USA working on the project.
In its initial stages the 7450/7550 project was led by Wolfgang Schattschneider, VP market development in Wilhelmshaven and then, as it progressed, by Lynn Dietrich, VP product development at Shady Grove. In Germany the engineering was led by Wilhelmshaven engineering manager Gerhard Kaupert and at Shady Grove by project manager Kurt Richter.
The project began with discussions that reviewed existing projects, and many trips and phone calls were made between Germany and the USA before a specification for a European/North American crane was drawn up. Dividing the project into two major sections, broadly speaking the carrier at Shady Grove and the superstructure in Wilhelmshaven, meant that the day-to-day detail design work could be completed independently.
For good communication between the one company in the two countries the 3D CAD system with the same revision number, telephones, Lotus Notes for email, local area networks and other administrative business operating systems used on the project have been linked or common to both places for some time. There is a system to transfer engineering drawings so that they can be viewed in either country in a few hours and video conferencing is available.
All design work was done using metric units and another example of the cultural integration is that there are English speakers at Wilhelmshaven and German speakers at Shady Grove. Translation of technical subjects and procedures had to be talked through carefully, an experience that Grove now has as an asset.
