Planetary gear units for big chalk crusher

Edited by the Engineeringtalk editorial team Oct 24, 2001

Reggiana Riduttori UK has supplied one of its Series 2000 planetary gear units for Powertech Industries' new Primary Crushing Plant, capable of processing 2.1 million tons of chalk each year

Newly established Reggiana Riduttori UK of Bradford has specified and supplied one of its latest Series 2000 planetary gear units for Powertech Industries' newly commissioned Primary Crushing Plant, weighing around 35 tonnes and capable of processing 2.1 million tons of chalk each year.

This is a 'big story' in every respect, involving a big standard gearbox and one of the biggest new crushers to be installed in the UK in recent years; it will be operated by one of Britain's biggest plant fleets, Alfred McAlpine Plant, for the country's biggest cement manufacturer, Blue Circle.

Yet, surprisingly, the small size of Reggiana Riduttori's linear reduction gearbox, with a diameter of just over 600mm and weighing little more than 600kg, was considered an asset on this application and will soon be exploited on Powertech's latest generation of twin roll crushers.

RR UK's ability to meet an extremely tight delivery deadline, with a standard gearbox to precise customer specification, was also a deciding factor.

The Powertech range of twin-roll crushing machines, manufactured in Whitwell near Worksop, has a long established reputation in the international mining and quarrying industries, with installations in Europe, North and South America, Australia and the Pacific Rim.

The machines' inherently well-balanced design means no heavy duty foundations are required, while the mechanical principles of counter-rotating twin crushers and high torque/low rolling speeds enable throughputs in excess of 10,000 tph (tonnes per hour) on larger models.

They offer a number of operational, performance and maintenance advantages over traditional high speed impact crushers, most notably the capacity to deliver the specified end-product size, with a minimum of unwanted fines.

The machine specified by Alfred McAlpine Plant is a twin roll crusher with 1000mm centres, which is charged via a feeder by 40 tonne dump trucks operating continuously.

Already installed and commissioned, it is processing chalk at an average rate of 800tph at Blue Circle's Northfleet works, where the raw materials are used to make cement for UK and overseas customers.

One of the main plant criteria was the ability to handle the high moisture content (22%) of Northfleet chalk, which thanks to inbuilt scraper arrangements is a particular feature of Powertech's machines.

With a lead time from order to delivery of only ten weeks, Powertech would have struggled to produce on one of its own heavy duty gearboxes for the Blue Circle application, so was forced to look for an alternative supplier.

The gear unit had to satisfy exacting performance and durability standards and the solution was provided by Reggiana Riduttori UK, which shipped in a standard Series 2000 model from the parent plant in Italy, meeting both the tight timescale and demanding specifications.

The model specified and supplied was an RR8000 two-stage linear planetary gear unit, with a nominal output torque rating of 85,000Nm, capable of transmitting an installed power of 220KW at 1475rpm.

The unit has a splined male output shaft for direct connection to the customer's own final splitter box, for driving the twin rolls.

The input shaft is a male cylindrical type, fitted with a fluid coupling also supplied by RR UK; one of Powertech's performance features is full load start-up, to avoid manual digging and clean-outs, and the fluid coupling provides a suitably soft start and affords a further element of protection in the event of a logjam.

The inherent fit-and-forget reliability, robustness and superior efficiency of Reggiana Riduttori's Series 2000 design makes it ideal for this continuous processing application; whilst its compact dimensions meant the gearbox was easy to install in place of the standard unit and did not add weight to an already heavy machine.

The coaxial planetary configuration has also inspired Powertech to now consider separate drives for the twin shafts and eliminate the final splitter box, the smaller size enabling two boxes to be fitted onto narrow shaft centres.