A little over two years after building one of the world's largest rotor milling machines - an EX Series ‘8EX' model - for a major Chinese compressor manufacturer, Holroyd Precision Ltd is about to ship a second, identical machine to the Zhejiang business.

Just like the 8EX rotor milling machine delivered in late 2013, this latest model from Holroyd Precision will be used to rough mill and ‘finish machine' stainless steel rotors from blanks of up to 850 mm in diameter and 4,500 mm in length.

Manufactured from steel grades such as 1CR13 (UK: 410S21 stainless), rotors produced on the 8EX machine will weigh as much as 8,200 kgs. Applications will include natural gas transportation, Organic Rankine Cycle expansion generators and process industry compressors.

"Our development of the 8EX machine - a new generation in high capacity rotor milling, offering the precise cutting of particularly deep helical profiles - has brought exciting opportunities to organizations looking to machine highly accurate, large diameter compressor rotors," comments Holroyd Sales Manager, Mark Curran.

"As you can imagine," he adds, "we were particularly pleased to receive this significant repeat order from one of our original 8EX customers. Underlining their confidence in our solutions and costing in excess of £1.8 million, the technology will enable them to further increase their capacity to satisfy China's growing energy market."

With models capable of accommodating all screw compressor diameters, Holroyd EX Series CNC rotor milling machines have earned global acclaim for their high speed, high precision, high levels of efficiency and unrivalled build quality.

Delivering reliability and performance, the ‘standard' EX range begins with the 1EX - a machine capable of milling helical components of as little as 150 mm  nd offers stepped increases in capability up to the 8EX, an 850 mm OD rotor miller. A ‘special order' 10EX machine is also available for components exceeding one meter OD. In addition, various bespoke EX models are available. These include a 3EX-R (350 mm OD) model with a specially extended drum rotation for milling compressors for Roots-type (positive displacement lobe pump) superchargers.

Holroyd EX Series milling machines are designed with the ability to maximize the high surface speeds demanded by the very latest cutting technologies. Surface speeds in excess of 200 m/min, for example, are often used when cutting the rotor profile forms in a single pass to leave only the allowance of 0.3 mm stock for the finishing operation. 

EX machines cut a full-depth groove by traversing the cutting tool through the material at the relevant helix angle, whilst at the same time rotating the component in the ‘C' axis. Accurate synchronization between the axes is maintained via CNC, with digital drive technology controlling all axis movements. The cutting head is able to remove so much material in one step because the majority of heat generated is transferred to the swarf chips. These are then removed from inside the machine by means of a conveyor system.

The flexibility of EX Series rotor milling machines means they are equally efficient at producing complex components with helical screw profiles, as they are at producing gear parts such as worm shafts. Indeed, in all manufacturing environments they will improve productivity through a combination of high-speed operation, powerful menu-driven touchscreen CNC programming, quick-change tooling, high power spindles and unbeatable rigidity.

The EX standard range includes 1EX for parts up to 150 mm diameter, 2EX for parts up to 250 mm diameter, 3EX-R for parts up to 350 mm diameter, 5EX for parts up to 550 mm diameter, 6EX for parts up to 650 mm diameter and 8EX for parts up to 850 mm diameter.