The grinders have naturally evolved – especially to meet the demands of increased productivity by global bearing manufacturers – to today’s range that embraces machines with table diameters from 1,600mm to 6,000mm having spindles rated at 25kW to 50kW and machines capable of accommodating workpiece heights of 800mm and bearings weighing up to 16,000kg.
One example of the machines’ prowess concerns the success of a RVU 2200/200 model in achieving grinding tolerances of just 1µm. The high-finish demand was because the customer wanted to extend the warranty of its wind turbine bearings from 12 to 24 months in order to reduce the frequency of costly maintenance operations.
Previously turned, the 4,000mm diameter by 500mm high bearings – which weigh 12,000kg and have a hardness value of 58-64 HRC/20 Ni Cr Mo 2 – were subsequently specified as needing the 1µm machining tolerance, obtainable only by grinding.
Of course, such high-precision demands dictate utmost machine rigidity, which the Berthiez machine provides via its: cast iron construction and temperature-controlled spindle and base, plus scraped linear guideways; hydrostatic table with torque motor having a runout of only 2µm; and; dynamic spindle stiffness (electro spindle - optimised specifically for bearing machining).
There is also a choice of large range of water-cooled grinding spindles, according to the type of grinding wheel used and dimensions.
In addition, the machines can also feature integrated probing, part centring and in-process dressing to increase process capability, as well as programming via the Berthigrind software which is customised for each application.
There are also options for hard turning, using a dedicated arm, in all representing the ultimate in single set-up, multi-task machining – while the use of double carriage technology sees two spindles operate simultaneously to reduce grinding time by a claimed 30%.
The Berthiez RVU vertical grinder can be easily integrated in a FMS cell with other Starrag Group machines including Berthiez TVU vertical lathes, and can thus offer an automated solution for machining parts such as bearings.
The success of Berthiez grinders in meeting the demand for 1µm tolerances on wind turbine bearings is mirrored on components of similar material and hardness in other industries: aero engine shaft bearings – machined on a RVU 900/80 – up to 600mm diameter and 50mm high, weighing 10kg; and large roller bearings for mining/cement industries equipment – using a RVU 1350/125 – measuring up to 1,200 mm diameter, 800 mm high and weighing up to 1,000kg.
Starrag UK www.starrag.com
